Current trends in optical and X-ray metrology of advanced materials for nanoscale devices V

Resume : Spectroscopic Ellipsometry in the VIS-UV spectral range is a standard optical technique to determine the complex refractive index n(ω) or the dielectric function ε(ω) of materials, thin layers, surfaces or complex layer stacks. A unique ellipsometry setup operating with synchrotron radiation in the visible to vacuum-UV spectral range has been developed by ISAS and is operated in collaboration with the Physikalisch-Technische Bundesanstalt (PTB) at the Metrology Light Source (MLS) in Berlin. The synchrotron ellipsometer is completely in Ultra-High-Vacuum, consisting of a Θ/2Θ-goniometer, a sample stage with He-cooling and resistive heating, polarizers, and directly connected to the beamline without any windows. The synchrotron ellipsometer thus allows precise operation in a very broad spectral range between 2eV and 40eV, with high spectral resolution and small spot size. The setup and possible extensions will be discussed. In recent years, mostly binary and ternary III-nitride and metal-oxide wide wide band gap semiconductors have been studied, in collaboration with external groups. Main interest is the basic understanding of optical properties, like excitonic absorption at the fundamental band edge, interband transitions at higher energies and shallow core level excitations, respectively. Exemplarily, results of ZnO/MgZnO and GaN/AlGaN will be presented and discussed in detail.

Resume : The spinel zinc gallate (ZnGa2O4), with a band gap of 4.4–4.7 eV, is of technological interest for the development of persistent luminescence materials, i.e. materials that are able to glow in the dark for long time (up to several hours) after the end of the excitation, and multicolor emitting phosphors. The possibility to tune ZnGa2O4 photo- and cathodo-luminescence properties by doping with transition metal or rare-earth ions has stimulated further interest on this material for optics. With some transition metals doping, specific optical properties, for example green emission in ZnGa2O4: Mn2+ and red emission in ZnGa2O4:Cr3+, can be obtained. Indeed, ZnGa2O4 : Cr3+, having emissions centered at 700 nm, is also interesting as rechargeable and LED-activated near-infrared system, and as background-free luminescent nanoprobe for developing more sensitive biosensors and recently extensively studied for in vivo bioimaging and security applications. The optical properties of ZnGa2O4 depend strongly on the composition (ZnO-rich and Ga2O3-rich composition) and structure, i.e. defects and oxygen deficiency, therefore non-destructive techniques that offer opportunities for establishing the interplay among optical, structural and compositional properties are demanded. In this contribution, we discuss ZnGa2O4 thin films, also activated with Cr3+, focusing on the impact of the composition and structure on the optical functionality. The materials are depicted using a combination of spectroscopic ellipsometry (SE) Raman spectroscopy, atomic force microscopy (AFM), and X-ray diffraction (XRD).

Resume : Macro imaging spectroscopic ellipsometers have been developed for high speed mapping of large area thin layer coated substrates. Non-contact and non-destructive characterization techniques based on spectroscopic ellipsometry are widely used by the photovoltaic and semiconductor industry for process or quality control in production. In many cases, thin layer properties must be mapped by an „in-line” or „in-situ” method avoiding mistakes resulting from layer inhomogeneities. Scanning, single-spot collimated beam ellipsometry methods provide high accuracy but suffer from long mapping times as the polarization state of the reflected beam must be detected. Expanded beam ellipsometry was developed to measure rapidly the polarization state changes after reflection from bigger surfaces. Our instruments use non-collimated illumination with a special light source and an optical arrangement allowing multiple angles of incidence. New prototypes have been prepared for spectroscopic measurements that provide a line image of spectroscopic ellipsometry data with a lateral resolution of ~10 mm over the range of 350-1000 nm. Ellipsometric information of large areas can be collected a couple of 10 times faster compared to scanning methods. Prototypes have been built for structures with nominal widths of 300-450-600-900 mm (SiO2, ZnO/Mo, ion-implanted semiconductors) on rigid substrates. Thin layers (ZnO/a-Si:H/Ag) on plastic foil substrates were also investigated in roll to roll operation. Measurements and results of different structures are presented. We can demonstrate spectroscopic ellipsometry mapping measurements over 1800 points in ~1 min traverse of a 300-450 mm diameter Si-wafer (demonstration in clean room environment) or 600x1200 mm solar panel.

Resume : Fabrication of nanostructures by lithography requires new tools to characterize their shape, size and organization. In fact, the continuous minimization of the nanostructure sizes pushes the conventional techniques, such as scanning electron microscopy (SEM) or atomic force microscopy (AFM), to their limits. Scatterometry methods offer an attractive approach but require an optical model to calculate the response of the system. (GI)-SAXS ((Grazing Incidence)-small angle X-ray scattering) is a characterization technique considered promising for dimensional control by the ITRS roadmap. Actually, several analytical models and experimental approaches have been developed, during the last years around the CD-SAXS technique. In this talk will be presented the CD-SAXS capabilities through several examples (line gratings with different periodicity, line width, profile and lateral roughness). Measurements were performed both on a Rigaku smartlab diffractometer equipped with a Cu rotating anode (8.05 keV) and on beamlines BM02 and BM32 at ESRF at an incident energy of 17 keV. Thanks to reverse Monte Carlo simulations, the line periodicity and line width were extracted and revealed to be in good agreement with the one obtained by CD-SEM and CD-AFM. Sidewall angle was extracted and compared to cross sectional SEM images. Stitching effect was also detected and its period was determined. Amplitude and periodicity of the lateral uni-frequency roughness was also deduced.

Resume : Ideal sapphire crystals can be used as backscattering monochromator for synchrotron radiation. We report on the characterization of high quality crystals suitable for meV resolution X-ray optics above 30 keV.[1] Using backscattering rocking curve imaging with a relative lattice spacing resolution of 5e-8 reveals very diverse quality maps for sapphire crystals. Small nearly ideal areas with an edge length of 0.2–0.5 mm are observed in the best crystals. We will illustrate the use of such a crystal for phonon spectroscopy by means of backscattering nuclear inelastic scattering.[2] [1] Jafari, A., et al. (2017). "Rocking curve imaging of high quality sapphire crystals in backscattering geometry." Journal of Applied Physics 121(4). [2] Sergueev, I., et al. (2011). "Milli-electronvolt monochromatization of hard X-rays with a sapphire backscattering monochromator." Journal of Synchrotron Radiation 18: 802-810.

Resume : X-ray diffraction and X-ray imaging have been viewed for a century as essentially two distinct techniques using the same type of radiation. The recent evolution of optics leading to highly focused beams, as well as the brilliance of available synchrotron sources show a rapid development of the potential of imaging techniques under Bragg diffraction conditions. This allows to image strain and orientation of the crystal lattice with scanning, full-field, or coherent reconstruction techniques. These techniques benefited greatly from the rebuilding of beamline ID01 during Phase I of the ESRF upgrade and offer spatial resolution down to 10 nm at unrivalled strain resolution. Examples in this talk show the value of these new techniques for the imaging of devices and novel semiconductor structures and substrates. A particularly interesting feature is their capacity to follow processes at operando conditions. Being mainly limited by the source brilliance, these newly available imaging tools will substantially benefit from the foreseen source upgrade of the ESRF planned to be operational from 2020 on. These enhancements will strengthen the ESRF's position as a global leader in the exploitation of hard X-rays for science

Resume : The GaN-based devices cover a broad area of applications, including high-power and high-frequency electronics, photodetectors, or light emitting diodes, but the presence of structural defects determines generally negative effects on both optical and electrical properties. Although these drawbacks are well known, the individual contribution of each type of threading dislocations (TDs), edge, screw or mixed, is not completely understood. X-ray diffraction methods are, first of all, non-destructive ones, and, in addition, allow completing the information and finding a correlation between dislocation types or presence of annihilation or generation sources in materials. In this paper, we calculated the density of TDs analyzing the tails of the experimental X-ray rocking curves profiles of three samples of GaN epitaxial films on sapphire substrate with different thicknesses, 300, 1000 and 5000 nm, respectively. Then we have proposed a new, simplified method to obtain the correlation parameter between TDs and we proved its validity comparison with Wilkens standard parameter. The results indicate that the dislocation density decreases with GaN thickness, concomitant with the positional decorrelation of TDs, which can be determined by the annihilation mechanisms of TDs inside the epilayer evidenced through the depth profiling of the investigated samples.

Resume : This original work aimed at quantifying the time-dependent indirect corrosion of high alumina refractories by Al2O3-CaO-SiO2 secondary steelmaking slag. The corrosion kinetics was determined by time-resolved X-ray diffraction at high temperature combined with Rietveld quantification. The tests were performed on a Thermo Scientific ARL EQUINOX 3000 diffractometer equipped with a dedicated furnace (Anton Paar HTK16) allowing for very fast heating. Alumina powder was mixed with crushed slag and put on a custom-designed heating strip. The mixture alumina/slag was heated up to 1600°C in less than 5 minutes to prevent solid/solid reaction before the slag melts. A full 2θ pattern was recorded every 5 s by means of a Curved Position Sensitive detector (CPS120). Rietveld refinement was carried out and crystallized phases were quantified. The liquid phase content was evaluated from stoichiometric balance. The results show that the indirect corrosion process is very fast and involves both solid-state diffusion of calcium cations through the successive aluminate layers and dissolution of the outer layer at the interface with slag providing slag exists. The effect of silica in slag was also addressed. Combining a dedicated furnace with the CPS 120 detector makes it possible to catch very fast reaction kinetics.

Resume : Modern ultrafast science can famously trace its roots back to high-speed photography and snapshot images of a racehorse in full stride [1]. The concept of recording an image that corresponds to a particular time window endures, even though studying many of the most interesting phenomena of today demands an experimental technique with not only far better temporal resolution, but also sub-wavelength, or even nanoscale, spatial resolution. Terahertz microscopy based on sharp metal tips can achieve femtosecond, subcycle time resolution and, simultaneously, spatial resolution down to the atomic scale, a combination not currently possible with any other experimental approach. Here, we demonstrate two methods for recording femtosecond nanoscale snapshot images with ultrafast terahertz microscopy: scattering-type scanning near-field optical microscopy (s-SNOM) and lightwave-driven terahertz scanning tunneling microscopy (THz-STM). We employ near-infrared-pump / multi-THz-probe s-SNOM to study polaritons in black phosphorus heterostructures. Specifically, we activate a transient interface polariton mode, launch propagating polariton waves, and resolve femtosecond snapshot images of the resulting polariton interference fringes within the 5 picosecond lifetime of the mode. These measurements reveal that the transient polariton mode has a hybrid plasmon-phonon character that makes it both switchable and minimally damped [2]. To explore even smaller length scales, we build on the concept of THz-STM [3], introducing state-selective tunneling in the regime of a single rectified electron per THz pulse [4]. We further unite THz-STM with cutting-edge single-molecule STM imaging [5], resolving ultrafast snapshot images of the electron density within a single orbital of a single pentacene molecule [4]. Finally, we use femtosecond orbital imaging to resolve the ultrafast vibrations of the pentacene molecular frame in the time domain through a THz-driven quantum pump-probe experiment [4]. [1] J. S. Baskin and A. H. Zewail, J. Chem. Educ. 78, 737 (2001). [2] M. A. Huber, F. Mooshammer, M. Plankl, L. Viti, F. Sandner, L. Z. Kastner, T. Frank, J. Fabian, M. S. Vitiello, T. L. Cocker, and R. Huber, Nature Nanotech. 12, 207 (2017). [3] T. L. Cocker, V. Jelic, M. Gupta, S. J. Molesky, J. A. J. Burgess, G. De Los Reyes, L. V. Titova, Y. Y. Tsui, M. R. Freeman, and F. A. Hegmann, Nature Photon. 7, 620 (2013). [4] T. L. Cocker, D. Peller, P. Yu, J .Repp, and R. Huber, Nature 539, 263 (2016). [5] J. Repp, G. Meyer, S. M. Stojković, A. Gourdon, and C. Joachim, Phys. Rev. Lett. 94, 026803 (2005).

Resume : The potential of microscopy-based spectroscopic techniques for characterization of local optical properties is illustrated in films containing self-assembled SiGe/Si in-plane nanowires (NWs) grown by molecular beam epitaxy on a Si(001) substrate. The diffraction-limited spatial resolution of the techniques is of the order of ∼1 μm and in this case it allows to investigate individual NWs. In the Raman study [1], Raman scattering intensity differences for different polarizations of the incident laser with respect to the nanostructure axis can be related to anisotropic absorption in the NWs whereas the intrinsic Raman efficiency is much less affected by the nanostructuration. The absorption anisotropy can be visualized by imaging ellipsometry which allows spatial resolution of contributions to the dielectric function within the films, coming f. i., from composition variations and, interestingly, from the strong in-plane anisotropy of the optical response of the NWs [2]. In fact, spatial resolution is found to be essential to discern different contributions that in principle are contained in an average ellipsometry spectrum. In the studied case, the large contribution arising from NWs oriented along the plane of incidence was absent in the average ellipsometry measurements. The origin of the observed anisotropy is ascribed to the presence of waveguide-like leaky resonant modes in the NWs. [1] M. I. Alonso et al., J. Phys. Chem. C 119 (2015) 22154. [2] M. I. Alonso et al., Appl. Surf. Sci. 421B (2017) 547.

Resume : We present a new in-house designed and built terahertz (THz) frequency-domain spectroscopic ellipsometer with a new far infrared (FIR) extension at the Terahertz Materials Analysis Center at Linköping University. The variable angles of incident instrument is based on the rotating analyzer ellipsometer principle, employs a backward wave oscillator THz source which provides highly coherent THz radiation and a FIR Fourier transform infrared spectrometer. The instrument uses a Golay cell and two bolometer detectors and covers the spectral range of 0.1–20 THz (3.3–650 cm-1 or 0.4–80 meV). The instrument is designed to incorporate a superconducting 8 T magnet and allows for standard and generalized ellipsometry at in both reflection and transmission configuration. The system can be equipped with different add-ons, enabling optical Hall effect experiments, cavity-enhanced measurements and environmental control. Methods to suppress standing waves are discussed and presented together with the experimental results employing different system add-ons. Examples include accurate determination of the THz optical constants of isotropic and anisotropic single crystals, the determination of free charge carrier properties of group-III nitride high mobility transistor structures, in-situ measurements of ambient effects on free charge carrier properties in epitaxial graphene and free charge carrier properties and dielectric response in PEDOT:TOS.

Resume : Time-resolved fluorescence imaging (TR-FLIM) is presented as a new optical contactless characterization method for optoelectronic devices. Its application leads to time-resolved photoluminescence (PL) maps having a micrometric spatial resolution and a temporal resolution of 500 ps. It notably relies on a wide-field illumination of the sample, which can be beneficial in many ways. On the one hand, on high mobility devices such as III-V solar cells, local recombination sites have a global influence and their study yields precious information about the lateral diffusion of charge carriers. Thanks to a model including diffusion and recombinations of minority carriers applied to a single TR-FLIM acquisition, we could determine key transport properties for the considered device, including bulk lifetime, charge carrier effective diffusion length, and injection-dependent contact recombination velocity. On the other hand, on various devices based on perovskite materials, slow motion and long carrier lifetime are highlighted and quantified. In-depth diffusion has to be considered to precisely model TRPL data. Here again, the combined study of spatial and temporal evolution of the PL leads to a complete characterization method for diffusion and recombination of charge carriers. Eventually, TR-FLIM appears as a versatile method, perfectly suited to the development of innovative optoelectronic devices.

Resume : Hard X-ray photoelectron spectroscopy (HAXPES) uses X-rays in the 2-10 keV range to excite photoelectrons, which are used to non-destructively study the chemical environment and electronic structure of materials. It is particularly useful as it can be applied to bulk materials and heterostructures which are not accessible by common soft XPS, which is very surface sensitive. The bulk sensitivity of HAXPES means that realistic samples can be investigated without the need of prior surface preparation. To date, HAXPES systems were predominantly located at synchrotrons due to low photoionization cross sections necessitating high X-ray intensities, limiting their availability to users and applications. This work presents a new laboratory-based instrument capable of delivering monochromated hard X-rays with an energy of 9.25 keV and a focused 30x45 μm2 X-ray spot, giving excellent energy resolution of <0.5 eV. The instrument behaviour and capability is showcased by experimental results from reference as well as technologically relevant systems, including TiO2 bulk samples and multilayer structures used in transistors. Measurements including shallow and deep core levels, Auger lines, and valence bands will be presented, including comparison of VB data with theoretical density of states calculations. Ultimately, this spectrometer presents an alternative to synchrotron-based endstations and will help to expand the number and range of HAXPES experiments performed in the future.

Resume : Being a fast and non-destructive method, one of the most important feature of optical metrology is its capability for real-time characterization. There have been many works published on real time ellipsometry during the past decades, demonstrating measurements in special vacuum chambers and flow-cells to understand deposition and adsorption processes, behavior of films and surfaces during annealing and high temperature treatment. In spite of those efforts, there are still numerous possibilities and ways to improve the measurement configuration, to extend the range of angles of incidence and wavelength, to realize faster measurement, using smaller spots, and to improve the sensitivity by special surface coatings, such as plasmonic or Bragg multi-layers. The aim of this contribution is to present recent [B. Kalas et al., Appl. Surf. Sci. 421 (2017) 585; E. Agocs et al., Appl. Surf. Sci. 421 (2017) 289] and current developments of our group in heat- and flow-cell design, including wavelength and angle of incidence extension in flow-cells, multiple angle of incidence heat cells, cells for combined measurements, special cells in mid-infrared ellipsometry, in context of the tools known from the literature.

Resume : The Pair Distribution Function (PDF) obtained by Fourier transform of total scattering data represents the probability of finding two atoms separated by a distance r in a sample and provides information about the local structure whatever the crystallization state of the materail. PDF analysis is now applied to a wide range of "pseudocrystalline" materials, such as nanoparticles or samples in which the local and average structure are different and at least partial disorder exists. The PDF being intrinsically multi-scale, it can be studied as function of the distance range, evidencing the specificities of the local structure. It is also a unique tool for quantitative analysis of amorphous and crystalline phase’s mixtures. Among many applications for inorganic compounds, we will focus on examples of local structure studies of electrode materials and catalysts [1] and the identification of carbon blacks from archeological origin [2]. For molecular compounds, the investigation by PDF analysis of the amorphization/recrystallization of trehalose and lactose will be presented [3]. 1. R. Chattot, et al, Nano Lett., 2017, 17(4), 2447, M. Diaz-Lopez et al., 2018, submitted 2. S. Cersoy et al. J. Appl. Cryst., 2016, 49, 585 3. P. Bordet et al., Cryst. Growth Des., 2016, 16(8), 4547

Resume : The pair distribution function (PDF) technique exploits the total, i.e. the Bragg and diffuse, X-ray scattering of crystallographically challenging materials to derive their structure - with nanoparticles being the biggest showcase in recent years. 1 The strong increase in flux at high X-ray energies combined with novel detector technologies (CdTe) at synchrotron radiation facilities allows in-operando studies of chemical reactions and nanoparticle formation on a time scale of seconds. 2 Moreover, the signal-to-noise ratio enables us to probe weak scattering contrasts as in the case of solvation shells around colloidally dispersed nanoparticles. 3 Yet and shown here, such borderline cases require data analysis strategies to treat radially varying intensities on the detectors beyond e.g. common radial integration procedures. Transferring the synchrotron know-how to lab PDF instruments necessitates rethinking about the relevance of monochromatization and suitable detector technology. The design of a novel PDF diffractometer will be presented herein which allows monochromatic data collection with outstanding resolution and reasonable exposure time of few hours. References [1] S. J. L. Billinge, M. G. Kanatzidis, Chem. Commun. 2004, 7, 749 [2] M. Zobel, et al. CrystEngComm 2016, 18, 2163 [3] M. Zobel, R. B. Neder, S. A. J. Kimber, Science 2015, 347, 6219, 292

Resume : Microelectronic devices are continuously reducing in size and the mechanical and electronic properties of these devices are dependent on its internal phases and microstructure of the materials. Therefore, it is important to extract the information regarding microstructure, phases, texture and strain in these materials. XRD is one of the non-destructive tool to extract these informations. We rely on measuring a full 3D Reciprocal Space Maps which gives a complete overview of the reciprocal space in a large range of Bragg angles in order to detect and characterize the nature and texture of all phases present in a polycrystalline film. For this reason, we use pole figures, which is a representation of the diffracted intensity of a sample as a function of the azimuthal angles at a given 2θ position of the detector. With the help of synchrotron sources and 2D detectors, larger volume of the reciprocal space can be explored by means of a series of pole figures in a feasible amount of time. We have developed a new toolbox in-house at the French CRG BM02 beamline at ESRF using Python and parallel computing in order to rapidly analyze and treat the multidimensional data in an automatic way. With the help of this toolbox, we can generate pole figures in-situ during the experiment at the synchrotron. Consequently, the texture and possible phase sequences can be calculated rapidly. This tool will be presented with some examples including Ni(Pt)Si, Ni-InGaAs-InP solid state reactions etc.

Resume : Epitaxial growth of small organic semiconducting molecules on 2D materials allows efficient control of electronic properties of organic films by a suitable substrate choice. For example, a previously observed lying-down configuration of pentacene molecules on graphene is expected to promote light harvesting in solar cells or switching speed in vertical FETs. To get insight into the mechanism of such lying-down phase formation, we performed real-time grazing incidence small- and wide-angle X-ray scattering (GISAXS/GIWAXS) experiments at synchrotron beamlines supported by ex-situ atomic force microscopy and polarized confocal Raman microscopy The GISAXS reveals nucleation and growth of islands on a seed monolayer (ML) that exhibit elongated shapes due to a growth saturation in one direction along the substrate at 1-3 ML thickness depending on the substrate temperature while the GIWAXS shows a perpendicular growth saturation of the islands after 10 MLs. A narrow angular spread of the pentacene 001 diffraction spot suggests a locked alignment of the pentacene crystalline islands with the six-fold symmetry of the underlying graphene crystal lattice. In particular, the c* axis of pentacene reciprocal lattice is parallel to the [210] direction of graphene crystal lattice, being thus inclined by 18° with respect to the graphene (001) plane. This corresponds to a final 11° inclination of the pentacene molecules with respect to the graphene surface driven by the energy minimization.

Resume : Understanding the mechanism of charge collection and its relation to elemental composition and structural variations at the nanoscale is of critical importance for developing efficient solar cell materials. This is true for silicon solar cells but it is much more critical for polycrystalline thin-film absorber layers such as CIGS, CdTe and hybrid organic-inorganic perovskites (PSC), which are deposited by methods much faster than epitaxial growth. A tool capable of correlating composition and properties on a nano- pixel-to-pixel basis could help point to the origins of performance losses, metastabilitites as well as degradation pathways. Correlative X-ray Microscopy (XRM) with a resolution down to the nanoscale offers a method to fill this gap. In this contribution, we will present results from a modified in-situ stage used for studying the electrical performance (current and voltage) and elemental distribution in CIGS, CdTe and PSC solar cells with high sensitivity, voxel sizes <40nm and under various operating conditions (light, bias, temperature). Using this tool, we can map the electrical performance of cells under operation with unprecedented nanoscale lateral resolution. Further upgrades to the tool allow to collect information under growth and/or processing conditions enabling access to kinetics and transport information, which is crucial to understand degradation mechanisms and even more important to engineer the next generation absorbers.

Resume : In the past five years, solution-processed organometallic perovskite based solar cells have emerged as a promising thin-film photovoltaic technology.(1) Presently, the intended optoelectronic applications of this class of 3D materials are in the realm of conventional semiconductors. The presentation will review recent optical spectroscopy and diffraction results on monocrystals of halide perovskites, colloidal nanocrystals or thin-films.(2) Related 2D multilayered phases, composed of perovskites multilayers sandwiched between two layers of large organic cations,(3) have recently demonstrated improved solar cells photostability under standard illumination as well as humidity resistance over 2000 hours, leading to a conversion efficiency of 12.5 %.(4) In this case, intrinsic quantum and dielectric carrier confinements are afforded by the organic inner barriers, which lead to a stable Wannier exciton at room temperature. However, solar cells or LED device efficiencies are related to internal exciton dissociation through edge states in layered 2D Ruddlesden-Popper perovskites, as shown from the investigation of both thin films and small exfoliated single crystals.(4) References 1 W. Nie et al, Nature Comm. 2016 ; W. Nie et al, Adv. Mat. 2017 ; H. Tsai et al, Adv. Ener. Mat. 2017 2 H.H. Fang et al, Nature Comm. 2017; K. Appavoo et al, Phys. Rev. B 2017 ; Q. Shen et al, Appl. Phys. Lett. 2017 ; M. Fu et al, Nanoletters 2017 3 C. Stoumpos et al, Chem 2017; C. M. M. Soe et al, Adv. Ener. Mat.; C. M. M. Soe et al, J. Am. Chem. Soc. 2017 ; L. Mao et al, J. Am. Chem. Soc. 2017 ; M. Smith et al, Chem. Sci. 2017 4 H. Tsai et al, Nature 2016; H. Tsai et al, Adv. Mat. 2017; J. C. Blancon et al, Science 2017

Resume : Organic -conjugated small molecules are a matter of a wide interest in the field of materials chemistry, in multi-layered OLEDs, as active matrix for organic thin-film transistors, or as donor materials in organic photovoltaic devices and as hole-transporting emitters (HTMs) in electroluminescent devices. Moreover, they exhibit key advantages such as easy synthesis and purification, well-defined and finely-tuned electrical and optical properties, suitability to different types of device fabrication i.e. solution processable and thermal evaporation techniques, high reproducibility of molecular performance in devices, a good electron-donating ability and reasonably high ambient stability. In our study, we focused on the investigation of a new family of organic conjugated materials, based on the dibenzofulvene core, characterized by a molecular structure of easy synthesis and functionalization, and possessing hole-transporting properties suitable for photovoltaic and electronic applications. We have synthetized a new family of molecules with a symmetric structure containing two dibenzofulvene moieties connected by a thiophene or bithiophene ring, and functional groups in different positions of the conjugated skeleton. We first achieved insights into structure-properties relationship to extrapolate a general pathway to select the best performance tuning the optical properties of the HTM layers. The correlation between the optical properties (optical constants and interband transitions) and structural parameters (coniugation, planarity, order degree, interchain interactions and crystallinity) are investigated by spectroscopic ellipsometry corroborated by Raman spectroscopy and atomic force microscopy.

Resume : Interdiffusion over length scales of 10-100 nm is often observed at polycrystalline semiconductor heterointerfaces, even when grown at room temperature. This results in graded interfaces with possible band gap changes of the two semiconductors in the region of interdiffusion. Standard band alignment measurement methods based solely on photoemission spectroscopy (PES) were originally intended for monocrystalline semiconductors with sharp interfaces and do not take this effect into account. For this purpose, we complement the standard PES measurement with a spectroscopic ellipsometry measurement. The goal of the ellipsometry measurement is to determine possible band gap changes from bulk to the near-interface region. Then, the combination of PES and ellipsometry could be used to determine the band alignment and interface band diagram of, in principle, any semiconductor heterointerface where chemical processes during interface growth modify the electronic properties of the two separated surfaces. This method is demonstrated on the Cu2ZnSnS4/CdS interface for photovoltaics. Interdiffusion-driven band gap changes on both sides of the interface (up to 0.3 eV) are revealed by ellipsometry. Adding those corrected band gaps to the valence band offsets measured by PES improves accuracy in the determination of the conduction band offset, which is a key quantity for any electron-transporting heterojunction. The limitations of the proposed measurement method will also be discussed.

Resume : GaP, quasi-lattice matched to Si, allows growth of low defect density III-V/Si pseudo-substrates [1]. However, Antiphase boundaries (APB) likely appear and must be avoided. Different GaP/Si nanolayers were studied at ID01/ESRF with an 8 keV coherent X-ray beam of the order of 100x300nm2 at sample position. A 140nm thick GaP/Si has been studied. TEM imaging showed a weak density of emerging APB (less than 3/micrometer APB at the sample surface) and partial plastic relaxation. Bragg ptychography has been attempted using the (002)GaP weak reflection showing peak splitting, that could be attributed to a heterogeneous APB domain configuration. Two-dimensional quick mapping (kmap) [2] over (004) and the (002) has been also performed using weak (Bragg maximum +-0.5° on rocking angle) and strong scattering conditions. Weak conditions exhibit contrast lines oriented along both [110] and [-110] crystallographic directions, clearly related to regions of high tilt, surrounding misfit dislocations [2]. Strong scattering conditions reveal a very different contrast that could be attributed to weak lattice tilts surrounding crystal defects.

Resume : Conjugated polymers as well as their blends are attracting worldwide attention due to their potential for use as the active layer in advanced optoelectronic applications and their cost-effective and low thermal processing traits. They are semicrystalline, possessing amorphous regions and crystalline regions of varying orientations and volume fractions, so they are capable of exhibiting a range of morphologies that influence carrier transport. A fundamental understanding of the connection between optical properties, morphology and carrier transport processes is important to achieve effective control of quantum efficiencies in organic light emitting diodes (OLEDs). This work deals with the determination of complex dielectric function and refractive indexes of the MDMO-PPV and MEH-PPV conjugated polymer films and F8: F8BT blended films that are used as emitting layers to fabricate OLEDs. The assessment implemented by spectroscopic ellipsometry as a highly sensitive and non-invasive method to obtain fundamental information about polymer films. The obtained ellipsometric data were evaluated according to the modified Tauc–Lorentz (TL) model, in which the energy-depended broadening of the TL oscillators is introduced. The correlation of the optical properties with the materials' composition and physical phase can be the basis for the implementation of ellipsometry as an in-situ and real time characterization and control tool for OLED devices manufacture.

Resume : III/V-on-Si integration is a generic element for many opto-electronic applications such as high-performance photovoltaics and solar water splitting. A well-ordered hetero-interface is highly desirable - however, the formation of a polar-on-nonpolar interface is not yet fully understood. It appears instructive to describe and to control each of the three steps on the atomic scale (i) Si surface formation, (ii) III/V nucleation, and (iii) III/V layer growth individually, which largely benefits from optical in situ spectroscopy combined with complementary surface science techniques as well as density functional theory (DFT). We will highlight how such a scientific approach supports specific metal-organic vapor phase epitaxy (MOVPE) preparation of virtual GaP/Si (100) substrates. In such a complex vapor phase environment both kinetic and energetic driving forces have to be considered to describe the hetero-interface formation appropriately. At elevated temperature the formation depends on numerous aspects, such as preferred binding sites, atom mobility, step height, and density, as well as process routes. Si-P bonds at the interface imply a kinetically limited interface structure that is ‘frozen’ during further processing. Controlled modification of the Si surface with arsenic prior to GaP nucleation enables inversion of the GaP sublattice orientation both on Si(111) and Si(100).

Resume : Novel concepts in photovoltaics encompass new design principles of the device (e.g. multijunction, hot carrier cells, etc.) and the implementation of new absorber materials. These emerging material systems call for a distinct approach to determine the basic properties integral to optoelectronic operation. At the example of the new class of hybrid organic-inorganic perovskite absorbers and quantum dot solar cells we will illustrate the need to establish reliable measurement protocols to assess the fundamental structural, optical and electronic properties of the new materials. Therein, synchrotron based methods such as X-ray absorption and photoemission spectroscopy play a key role to link the microscopic materials parameters to device functionality. Here, we examine the use of these methods to tailor the layer layout and composition for the optimization of next generation solar cells.[1] In another instance, QD solar cells have been proposed to work either as intermediate band (IB) solar cells or hot carrier (HC) solar cells. We characterized quantitatively the device operation and evidence the emergence of a HC population. Absolute calibrated photoluminescence spectroscopy shows that the triggering mechanism happens when the QD ensemble gets half-filled behaving as a metal-like IB. At the same time, sequential two-photon absorption is demonstrated both optically and electrically. [1] R.L.Z. Hoye, P. Schulz, et al. Chem. Mater. 2017, 29, 1964

Resume : Though many materials are now used as the starting material for photovoltaic devices, the most popular material remains crystalline or semicrystalline silicon. As a result, accurate values of the complex refractive index are essential for silicon solar cell modelling as well as many diagnostic experiments. Of course, the complex refractive index is a strong function of wavelength, but it also is a strong function of temperature, morphology and doping. Over the last several decades, the complex refractive index of silicon has been accurately measured by many groups using different spectroscopic ellipsometry techniques, yielding very similar results. However, ellipsometry measurements of the absorption coefficient are quite inaccurate for wavelengths longer that ~700 nm, requiring reliance on the old technique of optical transmission. A new formulation of the absorption coefficient will be presented, which fits new optical transmission measurements from 700 to 1170 nm. This new formulation is based on the older work of MacFarlane, et. al. (Phys. Rev. 111, 1245 (1958).) and models the absorption coefficient to an accuracy of ~2% over 4 orders of magnitude. In addition, the ellipsometry results from the different groups will be compared, which will show that the agreement is good within the errors of the measurements, even though the spectroscopic ellipsometry techniques are quite different.

Resume : X-ray beam induced current (XBIC) can be used as a local excitation of nanodevices with high spatial resolution[1,2]. We employed the nanofocused X-ray beam with a diameter of 50 nm to generate X-ray beam induced current (XBIC) within single p-i-n doped nanowire solar cells. The beam was scanned over the nanowire at different X-ray photon fluxes and applied biases. The XBIC signal attributed by photogenerated charge carriers was mostly collected from the nominally intrinsic segment. The XBIC peak decayed exponentially toward the p- and n-segments, with a characteristic decay length that varies between 50 and 750 nm depending on the flux and the applied bias. The XBIC signal was saturated at reverse bias indicating the highest charge collection probability or the maximum internal quantum efficiency (IQE). On the other hand, at forward bias, the XBIC peak was reduced in both amplitude and width suggesting that the IQE is lower. Finite-element modeling using COMSOL showed excellent quantitative agreement with the measurements. Nano-XBIC can be used for investigations of a wide range of nanodevices, such as electronics and batteries. References [1] Jesper Wallentin, Markus Osterhoff, Robin N. Wilke, Karl-Magnus Persson, Lars-Erik Wernersson, Michael Sprung, and Tim Salditt, Nano Letters 14 (12), 7071 (2014). [2] Andreas Johannes, Damien Salomon, Gema Martinez-Criado, Markus Glaser, Alois Lugstein, and Carsten Ronning, Science Advances 3 (12) (2017).

Resume : In this work, the development of dilute nitride (Ga1-xInxAs1-yNy) n-i-p-i structure which is novel concept in solar cell (SC) design is investigated. An n-i-p-i solar cell structure is formed by growing series of horizontal n-type and p-type layers. The device also has vertical doped layers throughout the device which are used to selectively contact the n and p-type horizontal layers. When the structure is illuminated, electron hole pairs are generated throughout the horizontal layers. If the horizontal layers’ thicknesses are comparable with the photogenerated minority carrier diffusion lengths, the minority carriers diffuse to the n and p-type side respectfully before they can recombine. Once spatially separated the carriers have a much longer life time, drift or diffuse to their corresponding selective electrode. In this study, metal electrodes were used instead of implanted vertical selective doped contacts. A V-groove etching process is characterized and used to expose the multiple n-type and p-type layers for electrical connection made by different metal grid-finger electrodes. Experimentally, the enhancement in the open circuit voltage has been observed. Drift diffusion conductivity is used to model the performance of GaInNAs nipi solar cells. GaInNAs nipi solar cells with 1 eV is a standalone device that is incorporated into a tandem solar cell as the 3rd junction. Prototype of GaInNAs n-i-p-i and GaInP/GaAs/GaInNAs n-i-p-i structures were grown by molecular beam epitaxy (MBE). Currently, V-groove etching process of GaInNAs and designing fabrication method of 3 Junction (3J) solar cell structure is being studied. *This work is supported by the TUBITAK with project no: 115F419

Resume : Van der Waals (vdW) crystals are known for long time but for recent years they have garnered significant interest because of unique mechanical and optical properties of samples obtained by exfoliation of bulk material to a single layer. Currently, it is well established that the electronic band structure of many vdW crystals strongly varies with the number of layers and exhibits indirect-to-direct band gap transition with the size reduction to a single layer. In this work the electronic band structure of vdW crystals and samples composed of a few layers of these crystals is explored by modulated reflectance (MR) and photoacoustic (PA) spectroscopy. It is shown that the indirect band gap can be determined by PA technique while the direct band gap can be probed by MR spectroscopy which is not sensitive to indirect optical transitions. By measuring PA and MR spectra for a given compound and comparing them with each other it is easy to conclude about the band gap character in the investigated compound and the energy difference between indirect and direct band gap. In this work such measurements, comparisons, and analyses have been performed and chemical trends in variation of indirect and direct band gap with the change in atom sizes have been discussed for proper sets of vdW crystals. Moreover it is shown that the change in the electronic band structure which is related to reduction of the number of vdW layers can be very well explored by these techniques.

Resume : Tip enhanced Raman scattering (TERS) has come a long way since original publication in 2000. During first 10 years after the discovery single point TERS measurements and TERS imaging have been demonstrated on as diverse materials as self assembled monolayers, biological molecules, fullerenes, carbon nanotubes, graphene and stressed silicon. Single molecule sensitivity of TERS and sub-molecular spatial resolution has been demonstrated in 2012-2013 clearly showing huge potential of TERS as a nanoscale chemical characterization technique. Despite all this progress TERS has not yet become a widely accepted analytical tool. There are several reasons for that: until very recently, most of the TERS data were generated on home-built systems which lacked sophistication and the ease of use required for a broad use instrumentation; efficient TERS probes were not commercially available and their efficiency was rather inconsistent. The situation changed dramatically with the advent of new generation of highly automated TERS instrumentation, dedicated TERS imaging modes and new commercially available highly reproducible probes for the STM, tuning fork and AFM feedback control. Thanks to these innovations, hyperspectral TERS imaging with routine spatial resolution of 10 nm has become an everyday experience, that could be demonstrated even in out-of lab environment. As an illustration of this progress, recent advances in TERS imaging of novel 2D materials and upcoming developments of this exciting technique will be discussed.

Resume : Surface-enhanced Raman scattering (SERS) is a powerful method for high-sensitive molecular sensing. We utilized oil-in-water emulsion to self-assemble silver nanoparticles into two-dimensional (2D) array [1]. The 2D silver nanoparticle array was removed onto a glass substrate, which was used as a SERS active substrate, giving the enhancement factor of ~105. para-Aminothiophenol (p-ATP) was measured on the substrate at the different excitation laser intensities [2]. It was observed the SERS spectrum of p-ATP changed according to the excitation laser intensities. The results indicated that p-ATP was chemically transformed into dimercaptoazobenzene (DMAB) during the SERS measurements. Furthermore, we performed SERS measurement of p-ATP on silver nanoparticle array coated with thin SiO2 layer. No Raman signals of DMAB was observed even the sufficient intensity of the excitation laser was irradiated, indicating that the chemical transformation was induced by hot electron emission from the silver nanoparticle surface [3]. SERS measurements of the other molecules will be also discussed if time permits.

Resume : The eventual incorporation of 2D materials into electronic devices will require an intimate understanding of their electronic structure, including how the structure is affected by the material's local environment. This is especially true of silicene, which at present can only be produced on a narrow range of supporting substrates. Synchrotron-based X-ray spectroscopy is an excellent tool for answering such questions. Modern synchrotron facilities provide extremely high flux that is tuneable across a wide range of energies, and X-ray emission and absorption spectroscopy (XES and XAS) provide complementary, direct probes of the material’s all-important valence and conduction states. XES and XAS are also element-specific, so they are able to differentiate between states that belong to the 2D material and those of the substrate. Finally, the results of X-ray spectroscopy measurements can be calculated through first-principles density functional theory (DFT), allowing for a direct comparison between models and experiment. We have used these experimental and theoretical techniques to study a number of epitaxial silicene structures on Ag(111), including pristine and oxidized monolayers and pristine thin multilayers. This presentation will discuss the results of these studies specifically, as well as the challenges and opportunities in characterizing 2D materials through XES, XAS and DFT generally.

Resume : The study of development and manufacturing techonology of the TCOs (Transparent Conducting Oxides) thin film material has been rapidly increasing. ITO(Sn-doped In2O3) thin films are widely used among TCOs because they have a wide bandgap, exhibit high transmittance in a visible light region, and exhibit high electrical conductivity. However, in order to manufacture ITO thin film, a high temperature deposition process of over 300? is required. In addition, there is a problem of insufficient supply of In as a raw material, toxicity, resistance increase due to thin film damage by sputtering impact. IZO(Indium Zinc Oxide) thin films can be deposited at low temperatures and are known to have a transmittance of over 90% in a visible region and a low resistivity without additional heat treatment. Therefore, it can be used for various organic substrate used in flexible display and it is a material which can produce high efficiency organic light emitting device. In addition, plasma stability is excellent during the sputtering process, it is attracting attention as TCOs material that can replace ITO. In this study, IZO thin film, which is a Transparent Conducting Oxide material that can replace ITO, was deposited using R.F magnetron sputter. The structural and electrical characteristics of the IZO thin film are described in terms of the substrate temperature and the flow rate of hydrogen and oxygen, which are atmospheric gases. X-ray diffraction and FE-SEM were used to analyze the structural characteristics of IZO thin films. In addition, AFM was used for the surface analysis of IZO thin films. The optical characteristics and the thickness of the thin films were measured by Ultraviolet Spectrophotometer and a-step, respectively. Finally, electrical properties such as sheet resistance, resistivity, carrier concentration, and hole mobility were measured using Hall Effect Measurement (HMS-3000) and electrical characteristics were further analyzed by XPS.

Resume : It is well known, that the planar X-ray waveguide-resonator (PXWR) functioned on base of the waveguide-resonance mechanism and forms the nanosize width radiation beams [1]. But its emergent beams are characterized by some spatial (angular) divergence, which leads to loss its nanosize feature on small distance from PXWR outline (3-5 cm). So, the fundamental task of PXWR modification was it emergent beam angular divergence decreasing. The experimental search of the task solution led to elaboration of the composite planar X-ray waveguide-resonator (CPXWR), which reduces the beam angular divergence at preservation of its integral intensity [2]. The CPXWR consists of two simplest design PXWR, which are installed the one after another and characterized by mutual alignment. The size gap between PXWRs must be smaller the critical distance (Lg). In that case the emergent beam angular divergence will be smaller as the input capture angle magnitude. The divergence reduction effect is connected with the radiation flux partial angular tunneling in the gap between PXWRs. On base of this effect we elaborated the CPXWR function model taking into account the Liouvile theorem and found the beam parameter, which underwent change of its value in results of the divergence reduction. [1] V.K. Egorov, E.V. Egorov. Physics of X-ray waveguide // Proc. of SPIE. V4502 (2001) P. 148-172. [2] V.K. Egorov, E.V. Egorov. Composite X-ray waveguide-resonator // Proc. of MRS. V716 (2002) P. 189-195.

Resume : The two last decades witnessed huge improvements in the performance of commercial X-ray diffractometers devoted to the analysis of thin films and epitaxial heterostructures, which opened the way to studies that were previously restricted to synchrotron facilities, like, for instance, in-situ experiments or the study of ultra-thin films while keeping a monochromatic and well collimated beam. A direct consequence of this increase in performances is that the amount of data that the users have to deal with also increased significantly, and all manufacturers provide dedicated programs to read and handle the data generated with their equipment. However, these programs are often very expensive and, more importantly, their sources are not available so that there is no way for the users to know how their data have been manipulated. This situation led us to develop a free and open-source software, called DxTools (Data eXtraction Tools), that allows to process large XRD data files as those obtained when recording reciprocal space maps, temperature-dependent scans, spatially-resolved measurements, time-resolved measurements, sin²ψ measurements and pole figures. For the moment, DxTools is compatible with data formats from Bruker, but it can be extended to any other format. The program is written in Python and runs both in Windows and Linux environments, and it can be downloaded from https://aboulle.github.io/DxTools/. Detailed application examples will be given at the conference.

Resume : Organic-inorganic hybrid perovskites are semiconductors with highly interesting and tunable properties and are subject of intense research for several applications, mainly in photovoltaics but also as light emitters. Knowledge of the optical properties is both of fundamental and practical interest for these applications, for example, for designing and optimizing the harvesting and out-coupling of light in devices. In the generic perovskite formula ABX3, the cations A and B are organic and metallic, respectively, and X is the halide anion. In this work, we study the tunability of the optical properties in mixed A-site cation methylammonium (MA) / formamidinium (FA) lead iodide hybrid solid solutions FAxMA1−xPbI3 from room-temperature spectroscopic ellipsometry (SE) and photoluminescence measurements in single crystal samples. The composition dependence of the interband optical transitions in the VIS-UV range is obtained from fitting critical point lineshapes to the numerically built second derivatives of the dielectric functions. The results are discussed in relationship to the structural phase behaviour and relative comparison to the electronic structures of the parent compounds.

Resume : Usually, the room temperature epitaxial growth of oxide films on c-cut sapphire substrates is observed on atomically stepped (001) sapphire substrates, the (001) terraces being obtained via a high thermal annealing (> 1000°C) [1]. In the present work, the room temperature (T) epitaxial growth of pure or doped iron oxide films on c-cut sapphire substrates was obtained without any high T annealing pre-treatment before the growth. AFM measurements of these c-cut sapphire substrates do not show the presence of straight atomic steps and atomically flat terraces, and a surface roughness lower than 1 nm was evidenced. Room T pulsed-laser ablation of a Fe3O4 or Zn:Fe3O4 target leads to the formation of the wüstite (FeO or Zn:FeO) and/or spinel (Fe3O4 or Zn:Fe3O4) phases on the c-cut substrate, depending upon the oxygen pressure during the room T growth. The (111) oriented wüstite and/or spinel films were grown, and pole figure measurements were used to determine the precise epitaxial relationships between film and substrate. These relationships correspond to a 30° rotation of the hexagons of the (111) wüstite and/or spinel with respect to the surface (001) Al2O3 plane. TEM analyses were carried out to characterize the wüstite and spinel phases in the films, and their orientations with the substrate. The epitaxial relationships were interpreted in the frame of the domain matching epitaxy approach. The mechanisms of the room T epitaxial growth of oxide films on such c-cut sapphire substrates will be presented and discussed. [1] – R; Yamauchi et al, Scientific Reports 5 (2015) 14385.

Resume : In recent years, methods of ion implantation, lazer treatment and micro wave radiation have been widely used in order to receive nano-sized stuructures in various depths of semiconductors for the last years. These structures have great prospects in the development of new micro, nano-, and opto-electrics. In particular, CdTe- based heterostructure can be used as effective irradiation detectors in a wide frequency range, using the low- energy (Е0=0,5-2 кэВ) ion bombardment method on the surface of the CdTe/Mo(111) films nano-sized Cd phases, including the solar one. Cd, Te, ВаСdTe, and their effects on the morphology and electronic properties of the film surface were studied. In order to obtain nano-sized phase and nano-layers in near surfaces CdTe, implantation of Ba ions have been occuried with energies of Е0≥10 кeV. Dependence of surface concentration of Cd, Te and Ва atoms from dose of ions for CdTe (111) implanted Ва Е0=15 кeV. From this figure with increasing ions dose till D=1015 sm-2 the concentration of Cd will increase to 10-15 аtm.%, in interval D=1015 -1016 sm-2 will decrease till 8-10 аtm.%, and then in D≥5∙1016 sm-2 not change. In this case surface concentration Te first under D(7-8)·1014 sm-2 gets through minimum ( 40 at.%), but then under D1016 sm-2 through maximum ( 85-90 at.%). As from D=1016 sm-2 atoms Ba appears on surfaces and under D1017 sm-2 the concentration СВа forms 5-6 at.%. Under D1017 sm-2 surface concentrations Te, Cd and Ba accordingly are fixed at a rate of 82-84 at.%, -10-12 at.%, 6-8 at.% .Further increase D does not bring about observable change the composition of surfaces. The Surface layer CdTe beginning from d1015 will completely vary. Thereby, for the first time studied change the composition, structures and electronic characteristic of surfaces and subsurface layers of the CdTe at implantations ion Ba with E0 >10 кeV. It is shown that ion-implanted layers have very complex in-depth-changing composition and semiconductor have the narrow band characteristic. The width of the forbidden band, which changes within 0,3-1,2 eV. After heating under T=1000 K CdTe, implanted with dose of the saturation in the subsurface layer, the composition of the type Cd0,5Ва0,5Те is formed and a three-layer system CdTe/Cd0,5Ва0,5Те/CdTe is shaped. The depth of forming three-component composition and their width depend on energy of ions: under E0 =15 кeV dm=9-10 nm, d=7-8 nm, under E0=30 кeV dm=16-18 nm, d=9-10 nm.

Resume : Substrates for surface-enhanced Raman spectroscopy (SERS) are typically fabricated with complex (micro/nano)structures of noble metals to obtain high surface-area plasmonic surfaces, which are capable to enhance this effect and, therefore, the detection of chemical species at very low concentrations. These substrates are frequently high-priced and because their high reactivity, they often have a limited shelf life. Development of new SERS substrates that minimize these issues but preserving a good analytical performance is a constant concern. In this work, the electrogeneration of particular silver nanoscale features on screen-printed electrodes was carried out to obtain SERS-active surfaces. The effect of several factors such as the electrolyte, electrochemical parameters and the presence of structure-directing agents was evaluated. Scanning electron microscopy was used for the characterization of the electrogenerated nanofeatures. The experimental conditions used during the electrogeneration have a significant effect on the density, shape and size of the silver particles generated on the electrode surface, so these properties could be tuned by selecting the appropriate parameters leading to surfaces with specific functionalization. Simultaneously to the silver electrogeneration, the in situ SERS detection of some species was performed to evaluate the enhancement produced by the different nanoscale silver features at different stages of their formation.

Resume : The crystal phase Bi2GeO5 has ferroelectric properties with spontaneous polarization value comparable to BaTiO3 ceramic. This phase is metastable, so it can be hardly synthesized by standard crystal growth methods, but can be crystallized by heat treatment of bismuth-germanium oxide glasses. A variation of the initial oxides ratio and the heat treatment conditions may lead to crystallization of either a single phase or several phases’ mixture. The secondary phases deteriorate the ferroelectric properties of ceramics so it’s necessary to control the phase purity. In the present research a single-phase Bi2GeO5 glass-ceramic has been successfully synthesized in the Bi2O3:GeO2 glasses with 40:60 and 45:55 molar ratio by several methods and under different crystallization conditions (temperature range 430-520ºC, duration 4-87 h). The structure and morphology of induced crystal phases as well as the influence of heat treatment conditions on crystallization result have been investigated by XRD, Raman spectroscopy and SEM. The 45Bi2O3:55GeO2 glass after crystallization at 460ºC during 87 h contains nano-sized Bi2GeO5 crystallites (15-30 nm). The optimal initial glass composition and crystallization conditions to produce a single Bi2GeO5 crystal phase has been found. This research was financially supported by the Ministry of Education and Science of the Russian Federation by SA 17.1.18.0026.01 (10.4702.2017/BC).

Resume : Nanoparticles composed of two different metals or two different structural phases (e.g. liquid/solid) show novel electronic, optical, catalytic or photocatalytic properties from monometallic nanoparticles. Those multiphase nanoparticles could show not only the combination of the properties related to the presence of two individual metals/phases, but also new properties due to a synergy between the two phases. The structure of bimetallic nanoparticles can be oriented in random alloy, alloy with an intermetallic compound, cluster-in-cluster or core–shell structures and is strictly dependent on the relative strengths of metal-metal bond, surface energies of bulk elements, relative atomic sizes, preparation method and conditions, etc In this contribution, we demonstrate a combination of spectroscopic ellipsometry and phase imaging scanning microscopy and as a non destructive way to detect the coexistence of buried crystallographic phases or liquid-phases in plasmonic multiphase nanoparticles supported on a variety of substrates, and simultaneous detect their optical plasmonic response. In this way, we are able to establish a direct correlation between the complex multi-phase structure of a nanoparticle and its plasmonic response. The data are interpreted and validated by a combination of high-resolution of cross-sectional transmission electron microscopy (TEM), high resolution HAADF-STEM (high angle annular dark field scanning transmission electron microscopy) imaging. We acknowledge the contribution of the H2020 European programme under the project TWINFUSYON (GA692034).

Resume : New opportunities for energy harvesting, plasmonics, biomimetic catalysis, chemosensing, biosensing, immunosensing and cellular recognition are offered by novel hybrid heterojunctions combining, semiconductors, graphene, plasmonic metals and porphyrines. In those hybrids, graphene activates interfacial charge transfer, metal nanoparticles, in turn, activate the plasmonic electromagnetic coupling of light, and the porphyrines act as redox-mediators in view of their various properties, such as reversibility, regeneration at low potential, and generation of stable redox states. In order to design these platforms to take advantage of applications exploiting interfacial charge transfer, we need to better understand the surface and interfacial electronic phenomena in graphenebased hybrids. In this contribution, we present extensive optical characterisation using spectroscopic ellipsometry, magneto-optical spectroscopy, magneto-Raman and kelvin probe atomic force microscopy to describe charge transfer and interface phenomena in graphene coupled to various plasmonic metals that extend far beyond gold, further functionalization with porphyrins, highlighting aspects of the interfacial charge transfer controlling activation of recognition processes to enzymes and proteins. Experimental pectroscopic data will be corroborated by simulations by FEM and RWCA (rigorous wave coupled analysis). We aknowledge the contribution of the H2020 European programme under the project TWINFUSYON (GA692034)

Resume : Zinc oxide arouses great interest in semiconductor optical components in the UV spectral domain. Understanding band gap narrowing is of crucial importance for tunable devices. Despite numerous publication on optical band gap measurements in semiconductor material, measuring the value of the band gap –and not only the optical band gap may be difficult. We propose here a study on the different parameters that could influence the optical band gap of ZnO. We use a theoretical approach based on the calculation of the absorption coefficient that were early developed by Versteegh et al[1], and completed by Nakamura et al[2] for its temperature dependence. We compared theoretically the position of the band gap of the material and the position of the optical band gap using the so-called Tauc’s plot. This approach allows to separate the different physical phenomena that’s are responsible for the shift of the optical gap with carrier concentration. The band gap renormalization and the Burstein –Moss shift are evaluated for all carrier densities in a wide range from 10+16 to 10+20 cm-3. We conclude on the need to exercise prudence in experimental measurements using the Tauc’s model for the evaluation of the optical band gap of the material. [1] M.A.M. Versteegh, T. Kuis, H.T.C. Stoof, J.I. Dijkhuis, Phys. Rev. B 84 (2011). [2] T. Nakamura, K. Firdaus, S. Adachi, Phys Rev B 86 (2012) 205103.

Resume : The discovery of superconductivity in LaO1-xFxFeAs, has triggered large interest and soon after several iron-based layered pnictides/chalcogenides are found to be superconducting. This work provides a study of the effect of direct elemental substitution to the active layer on nanoscale structural disorder and physical properties in layered Iron-based Superconductors (FeSCs). In this work, we have studied Mn and Co substitution to the Fe site (active layer) on LaFeAsO (1111 type) and BaFe2As2 (122 type) systems respectively and Te substitution to the Se site (active layer) on FeSe system by means of local structure and physical properties. In La(Fe1-xMnx)AsO study we have performed extended x-ray absorption fine structure (EXAFS) measurements on Fe K- and As K- Edges and magnetic M versus T measurements on several samples. The results reveal that the FeAs-layer thickness, measured by the As height (hAs) from the Fe-Fe plane, is correlated with the Néel temperature estimated from magnetic M vs T Measurement. For the study of Ba(Fe1-xCox)2As2 superconductor, we have carried out temperature dependent extended x-ray absorption fine structure (EXAFS) measurements across the superconducting transition temperature (Tc). Polarized EXAFS measurements at the Fe K-edge on optimally doped (x=0.06) single crystal have permitted to determine atomic displacements across the superconducting transition temperature (Tc). The Fe-As bondlengths hardly show any change with temperature, however, the Fe-Fe sublattice reveals a sharp anomaly across Tc, similar to the one known for cuprates and A15-type superconductors, consistent with the important role of Fe-Fe fluctuations in the superconductivity of Ba(Fe1-xCox)2As2 materials. In FeSe1-xTex study, we have carried out extended x-ray absorption fine structure (EXAFS) measurements by a combined analysis of Se K, Te L1 and Fe K-edges. The results show that iron–chalcogen (Fe–Se and Fe–Te) distances in ternary FeSe1-xTex are similar to those measured for binary FeSe and FeTe. The local Fe–Se/Te distances determined by different absorption edges fit well in the characteristic Z-plot of random alloys, providing unambiguous support to the inhomogeneous nanoscale structure of the ternary FeSe1-xTex system [1]. References 1. M. Y. Hacisalihoglu, Ph.D. Thesis, “Investigation of Effect of Elemental Substitution in Layered Iron-Based and Related Superconductors on Nanoscale Structural Disorder” Karadeniz Technical University, July 2017, Trabzon, Turkey

Resume : We used ellipsometry to characterize zirconium surfaces in forms of tubes and plates for nuclear applications [Z. Hózer, Cs. Győri, L. Matus, M. Horváth, Ductile-to-brittle transition of oxidized Zircaloy-4 and E110 claddings, Journal of Nuclear Materials 373, 415–423 (2008)]. We have shown earlier that ellipsometry can be used even on the surface of tubes with a diameter of approx. 9 mm, when applying proper focusing. We also determined reference refractive indices for both zirconium and zirconium oxide, and demonstrated the capability of ellipsometry for the determination of surface oxide applying different oxidation parameters [P. Petrik, A. Sulyok, T. Novotny, E. Perez-Feró, B. Kalas, E. Agocs, T. Lohner, D. Lehninger, L. Khomenkova, R. Nagy, J. Heitmann, M. Menyhard, Z. Hózer, Optical properties of Zr and ZrO2, Appl. Surf. Sci. 421 (2017) 744–747]. In the present work, we use the technique determined in the previous work for the characterization of processed zirconium surfaces. We use both ultra violet-visible-near infrared (191-1690 nm) and mid-infrared (1.7-30 micron) ellipsometry to study the surface properties. We also developed a heat cell that allows multiple angle of incidence ellipsometry measurement at elevated temperatures up to 600 °C. We use this setup to in situ characterize the temporal behavior of hydrogenated and oxidized zirconium surfaces.

Resume : One of the most relevant topics in environmental areas is freshwater stocks and pollution. The goal of this work is the development of a device for detecting various water pollution molecules (metals and nitrogen oxide ions). Various types of sensor surfaces are investigated including dielectrics, nanostructures or genetically modified bacterial flagellar filaments (FF) that have specific binding sites for specific molecules. The adsorption of the target molecules can induce a change in the conductance in a circuit between the electrodes used for different voltammetry and amperometry approaches. We prepared sensing layers by various approaches from FF immobilization to spin coating and growing of nanostructures. The wild type FFs were covalently attached to the gold surface using dithiobis(succinimidyl propionate) (DSP) as linking agent. We used various surface nanostructures that can facilitate the adsorption of the proteins as well, such as titanate nanotubes, TiO2 nanoparticles and ZnO nanorods. The experiments were carried out on gold-coated glass substrates and on the golden surface of the electrode on the chips that are going to be applied in the sensor device. The coverage of the FF layers was investigated in situ by plasmon enhanced spectroscopic ellipsometry (SE), as well as ex situ by AFM, SEM and SE. (Support from the M-ERA.NET-WaterSafe/Nr. 39/2016, OTKA NN117849, OTKA NN117847, OTKA K115852 projects is greatly acknowledged.)

Resume : In recent years, the terahertz (THz) electromagnetic spectrum (100 GHz – 10 THz) has become of interest for space, security, science and medicine. The THz radiation can penetrate non-metallic materials and reveal their unique spectral fingerprint in interaction with THz domain. At present, most of the THz-TDS systems use mirrors and other optical components for control of the THz radiation beam. In this work we present a new method for control the THz beam using plasma as an on/off switch of the THz ray. In our experiment we used a mercury vapor - discharge tube. The discharge tube contain argon gas at 3-4 Torr pressure with vapors of the mercury. The plasma from tube had a 20mm length and about a 2 mm diameter. To investigate the attenuation of the THz radiation by the plasma we used the Pulsed Terrahertz Time-Domain Spectrometer - THz IRS2000 Pro (Aispec ). The spectral domain of the spectrometer is 100GHz-5 THz and the diameter of the THz beam is about 3mm. The preliminary studies showed that the plasma has attenuated 70% from THz beam and the switch on/off plasma has not changed the THz phase radiation.

Resume : We used spectroscopic ellipsometry in the Kretschmann-Raether configuration to measure flagellar filaments as a special model material for nanorods being adsorbed at the gold-water interface. Ellipsometry has a sub-nanometer resolution in the direction perpendicular to the surface, and a sensitivity of better than 10^-5 for the refractive index, especially in the applied high-sensitivity plasmonic configuration. This method is very sensitive at the proximity of the surface, but the sensitivity drops exponentially with the distance from the interface. Among all the pros and cons however, the major drawback of this approach is the lack of lateral resolution on the nanometer scale. Therefore, our question was, how far can we go in understanding and reconstructing the evolving time-dependent structure of filamental nanorods, using the above configuration together with special optical and numerical models. In the numerical model we can define constraints, such as the distance between the rods, the allowed angles and the movements during adsorption in contrast to our previous, purely analytical model [P. Kozma, D. Kozma, A. Nemeth, H. Jankovics, S. Kurunczi, R. Horvath, F. Vonderviszt, M. Fried, P. Petrik, In-depth characterization and computational 3D reconstruction of flagellar filament protein layer structure based on in situ spectroscopic ellipsometry measurements, Appl. Surf. Sci]. The numerical model can be used to calculate the volume fraction of rods in sublayers parallel to the sample surface as a function of distance from the surface, which can readily be compared to quantities determined by ellipsometry. This can be used to understand the process and to test different assumptions of the adsorption.

Resume : High periodicity 2D multilayers, often referred to as nanolaminates or superlattices, represent an exciting new method for tuning the optical and electrical properties of materials. In many cases the estimation and fitting of the dielectric function of an inhomogeneous medium is performed via theoretical Effective Medium Approximation models. However, the basis of these generic models on the assumption that the inhomogeneity is evenly distributed and disperse means they are often not well suited for the treatment of high periodicity (1-10nm) multilayers. A simpler approach in the case of high periodicity multilayers is to replace the multiple dielectric functions of the individual layers with a singular function which describes the overall interaction of the superstructure with incident light. This method is valid as long as all the individual layer thicknesses (d) are significantly lower than the incident light wavelength (λ) (λ>>d). We shall explicitly confirm the validity of this approach for a set of InGaZnO4 based nanolaminates with differing dielectric spacer layers. To do so we shall address three essential criteria: (1) That constructing a singular dielectric function for the nanolaminate produces an equivalent result to considering the discrete dielectric function and thickness of each individual layer. (2) That the nanolaminates discussed in this work fulfil the λ>>d condition and the threshold thicknesses at which this condition is broken. (3) We will explicitly discuss the thickness range at which the λ>>d condition breaks down and conventional transfer matrix multilayer calculations can be applied.

Resume : The present work deals with an advanced optical material based on silicate glasses doped with semiconductor nanoparticles those provide their optical features of both practical and scientific interest. The glasses with lead chalcogenide nanoparticles have been fabricated by the secondary heat treatment of the molten and cooled batch mixtures of oxides and chalcogens. They are featured by the absorption and photoluminescence in the near IR range controlled by the nanoparticle size (2-10 nm) and are of interest for perspective application in design of selective filters, spectral converters, non-linear optical elements, etc. In this communication we consider experimental data on monitoring the structural features of a series of PbS- and PbSe-doped glasses by means of optical spectroscopy, wide-angle X-ray diffraction (WXRD) and small-angle neutron scattering (SANS). Optical absorption and photoluminescence demonstrates regular variations of excitonic absorption and emission due to the quantum confined energy levels in the nanoparticles. WXRD detects the nanocrystalline forms for both PbS and PbSe stabilized within the glass matrix and estimates particle size well correlates with the data of the optical measurements. SANS was recorded in the range of scattering factors Q of 0.005-0.5 1/Ǻ. For the lowest Q (QR<<1, R the radius of particles) the conventional Gunier analysis reveals that the particle size depends on heat treatment steps and fits the values of 4-8 nm. The full Q range analysis evidences formation of more complicated structures promoted by late heat treatment steps in the form of fractal aggregates consisted from overlapping spheres.

Resume : Recently, we demonstrated multiple angle ellipsometry in a Kretschmann-Raether cell, searching for optimum configurations with plasmonic gold films of different thicknesses. We have also shown that compared to standard surface plasmon resonance configurations, the phase determination capability of ellipsometry reduces the measurement error significantly [B. Kalas, J. Nador, E. Agocs, A. Saftics, S. Kurunczi, M. Fried, P. Petrik, Protein adsorption monitored by plasmon-enhanced semi-cylindrical Kretschmann ellipsometry, Appl. Surf. Sci. 421 (2017) 585–592]. In this work, we show two directions of development for the existing Kretschmann-Raether setup. The first one is the extension of the wavelength range toward the ultra violet region (down to approximately 190 nm, the limit of the instrument) by replacing the hemicylinder, the focusing and the glass slide with the plasmonic layer. This extended wavelength range includes that around 280 nm with a protein absorption feature, leading to an enhanced sensitivity and selectivity. The second direction is the modification of the plasmon layer using nanostructures or multi-layers. The aim is to increase the intensity of the electric field at the solid liquid interface at certain controlled wavelengths, depending on the investigated material and the used angle of incidence. We demonstrate the improved cell capabilities using in situ adsorption measurements of special proteins, including flagellar filaments.

Resume : Terahertz cavity-enhanced optical Hall effect (OHE) measurements are employed to study free charge carrier properties in epitaxial graphene (EG) grown on semi-insulating 4H-SiC(0001) substrates. As-grown monolayer (ML), quasi-free-standing ML and bilayer (BL) samples are investigated. An optical model based analysis of OHE data reveals a strong in-plane anisotropy of the free charge carrier mobility for the quasi-free-standing BL samples, which also have the highest mobility and mean free path parameters compared with the rest of the samples. The as-grown ML and quasi-free-standing ML samples show only weak or no anisotropy within the sensitivity of the OHE measurements. Combining the OHE results with surface morphology investigations, we were able to correlate the directions of the high and low mobility axes, with the orientation of the steps formed on the SiC substrate, where the higher mobility axis is oriented along the step edges. LEEM and micro-LEED measurements reveal a homogeneous distribution in number of EG layers at the terrace and step edge regions, and an uniform intercalation process for the quasi-free-standing BL graphene samples. We attribute the scattering of free charge carriers from step edges to variation of surface potential due to detachment of graphene from the SiC. Furthermore, we show that the higher mean free path parameters, resulting in more carriers scattered from the step edges, can affect the observed anisotropy in free charge carrier mobility

Resume : The popular use of hydrostatic pressure in optical studies of materials is due to the fact that variations of the lattice constant by a few percent has a large impact on the electronic band structure and thus on the optical properties. The development of the gasketed diamond anvil cell into a tool for optical measurements at hydrostatic pressures well above 10 GPa has opened new possibilities for studying the physics and chemistry of materials under pressure. For instance, tetrahedrally coordinated semiconductors like the group-IV materials Si, Ge and diamond, as well as all III-V and II-VI compounds, exhibit a clear systematics regarding the pressure dependence of the fundamental band gaps [1], which had led to a fairly complete picture of the electronic band structure of semiconductors and their nanostructures. In this talk, I will show the power of combining optical spectroscopy and high pressure techniques to unravel the nature of the different electronic states involved in optical emission processes using as examples the cases of InGaAs/GaP quantum dots (QDs) [2,3] and amorphous Si nanoparticles (NPs) embedded in a silica matrix [4]. Both material systems are promising candidates to attain monolithic integration of efficient light emitters on Si substrates. The optical high-pressure experiments were complemented by tight-binding and ab-initio density-functional calculations, which have taken into account the precise QD and NP morphology, respectively

Resume : We present an overview of the nanoelectronic devices based on the 2D materials enabling new device architectures, fabrication and characterization. Hundreds of atomically thin materials termed as 2D materials are known today. Among them, graphene monolayers are the most studied, followed by the transitional-metal-dichalcogenides (TMDs).The graphene electronics is the single area of 2D electronics developed at the wafer scale while the other 2D materials are researched even now using small area flakes. We will focus here on graphene ballistic devices at room temperature encompassing diodes, transistors, photodetectors and even quantum gates fabricated at the wafer scale. TMDs allow the fabrication of transistors with gate length of 1nm and photodetectors with unprecedented high responsivities. We will finally present the new devices based on few-atom-thick HfO2-based ferroelectrics such as miniaturized antennas arrays at high-frequencies, which are CMOS compatible.

Resume : Characterization with visible photons of semiconductor nanostructures and 2D materials is mostly non-invasive and needs no special sample preparation. Here, we studied hybrid GaN-based nanorods (NRs) - graphene heterostructures using a combination of optical methods including micro-Raman, steady-state micro-photoluminescence (PL), and time-correlated single photon counting (TCSPC). The GaN NRs were either (1) grown by MOVPE on graphene/silicon and graphene/sapphire substrates or (2) etched by RIE in a GaN-based layer stack and covered by graphene. In the first case, the GaN NRs grew almost relaxed with only a mild tensile strain (0.067%) at their bases, while the graphene itself was efficiently doped with nitrogen (11 atom %) accompanied by negligible defect generation. These materials characteristics support high crystal quality and vertical conduction of GaN NRs on graphene acting as both growth substrate and bottom contact. In the second case, the nanostructuring of the initially compressively strained (-0.2%) layer stack led to virtually strain-free GaN NRs and to an increase of 80% in the PL emission after proper surface treatments. Such features indicate the reduction in the number of surface pathways for non-radiative recombination confirmed also by the increase in the carrier lifetime by TCSPC, with graphene as suspended top contact. Our metrology approach can be extended to new hybrid systems to integrate technologically relevant semiconductors in nanoscale devices.

Resume : Atomically thin two dimensional layered transition metal dichalcogenides and their heterostructures are highly promising for optoelectronic devices owing to their suitable band gap and high mobility of charge carriers. However, the design of heterostructures with two dimensional materials having proper interfacial contacts with other material for device applications, have been a challenging task. Here, we report a new defect passivated colloidal synthetic route for the formation of MoSe2–Cu2S vertical nanoheterostructure. Structural and optical properties of the material confirms the formation of vertical heterostrucure with well define interfaces. These MoSe2–Cu2S heterostructures have been used to fabricate the photodetector with superior photo response characteristics. The fabricated photodetector exhibit a broadband spectral photo response over the visible to near infrared range with a peak responsivity of 180 mA/W at −2 V and a high photo-to-dark current ratio of ∼10^3. The highest detectivity of the device is estimated to be ~ 1.6 × 10^12 Jones at an applied voltage of -2V. The superior device performance of MoSe2-Cu2S is due to the combined effect of passivation of defects, trapping of light, widening of the absorption window and interfacial charge transfer. This study would pave the way to design new heterostructure materials as well as its potential applications in next generation photonic devices.

Resume : Lithium ion batteries (LIBs) with drastically enhanced power densities will enable excellent acceleration and better fuel saving in cars of the automotive industry. Those batteries are thus promising candidates to power next-generation vehicles. A breakthrough involving dielectric polarization to assist ultrahigh rate capability of the LIBs was recently proposed. It is related with the use in the batteries of dielectric nanoparticles having large dielectric constant as an artificial solid electrolyte interfaces (SEIs). The dielectric interfaces were synthesized via a simple sol–gel and metal organic decomposition (MOD) route. In fact, high rate capability was drastically improved by incorporating barium titanate (BaTiO3) based ferroelectrics. In-situ analysis, e.g., electrochemical impedance spectroscopy and X-ray absorption fine structure (XAFS) were performed. Drastic enhancement of the high rate capability was attributed to polarization driven smooth charge transfer at dielectrics-active materials-electrolyte triple phase junction.

Resume : Despite the Ångstrom spatial resolution achieved by electron microscopes and scanning probe microscopes, optically “seeing” nanoscale objects in the ambient is a limitless demand of human because of its high chemical sensitivity, which has led to the development of near-field optics, and recently, super-resolution optics. On one hand, scientists are still trying to improve the spatial resolution of each technique. On the other hand, it is equally important to develop spectroscopic methods to distinguish different chemical species. While optical spectroscopy method provides various chemical information, the spatial resolution has been very poor due to diffraction limit of light as compared to electron microscopy, SEM and TEM or scanning probe microscopy, AFM, and STM. However, since its inception in the year 2000 [1], tip-enhanced Raman spectroscopy (TERS) has been recognized as one of the promising spectroscopic techniques in nanoscale due to the plasmonic properties of tip-enhancement, which work for both photon confinement and enhancement [2]. From the scientific point of view, lots of efforts have been paid for the improvement of spatial resolution and sensitivity. One of the promising approaches is utilizing nonlinear response of material such as the narrowband coherent anti-Stokes Raman scattering (CARS) [3] and broadband CARS [4]. The other approach recently on trend is the hot spot engineering of gap-mode plasmon based on scanning tunnelling microscopy (STM) based TERS, which achieved up to ~1 nm spatial resolution in ambient [5]. In this presentation, we report an extremely high spatial resolution down to 1.7 nm in tip-enhanced Raman spectroscopy, which is currently the highest spatial resolution that has been achieved in Raman spectroscopy in ambient [6]. While developing the optical microscope with high spatial resolution, a natural question subsequently arises as to how short excitation is possible with such an extremely high spatial resolution since one of the virtues of optical excitations is its high temporal resolution that is not attainable by any other techniques. We demonstrate a generation of extreme spatio-temporally confined nano-light source exhibiting 10 fs in time [7]. The mechanism is based on degenerated four-wave mixing (FWM) at a sharp metallic tip. We will discuss the potential applications of tip-enhanced Raman and nonlinear Raman spectroscopy and microscopy based on our extreme spatial and temporal resolution. References [1] N. Hayazawa, Y. Inouye, Z. Sekkat, S. Kawata, Opt. Commun. 183 (2000), 333–336. [2] N. Hayazawa, T. Yano, and S. Kawata, J. Raman Spectrosc. 43, 1177 (2012). [3] T. Ichimura, N. Hayazawa, M. Hashimoto, Y. Inouye, S. Kawata, Phys. Rev. Lett. 92 (2004), 220801. [4] K. Furusawa, N. Hayazawa, S. Kawata, J. Raman Spectrosc. 41 (2010), 840-847. [5] C. Chen, N. Hayazawa, S. Kawata, Nat. Commun. 5 (2014), 3312. [6] https://en.wikipedia.org/wiki/Tip-enhanced_Raman_spectroscopy [7] K. Furusawa, N. Hayazawa, T. Okamoto, T. Tanaka, and S. Kawata, Opt. Exp. 19, 25328 (2011).

Resume : We have studied the influence of boron incorporation up to 4.3% on the photoluminescence (PL) properties of BGaN alloys. All the PL spectra of BGaN materials were dominated by the yellow luminescence (YL) band, suggesting a deterioration of the material optical quality with introduction of boron. The YL band was found to systematically red shift with increasing boron incorporation. As a consequence, the colour of the YL band changes from yellow to amber with increasing boron uptake. An estimate of the band offsets of the BGaN/GaN heterojunction was obtained. 7-MeV electron irradiation followed by rapid thermal annealing reduces the intensity of the YL (amber) band, especially its low energies side.

Resume : Static (SLS) and dynamic (DLS) light scattering are powerful and widely employed optical characterization techniques used to characterize the dynamics and structure of soft matter systems. Accurate characterization using SLS and DLS methods mandates the measurement and analysis of singly scattered light. In turbid samples, the suppression of multiple scattering is therefore required to obtain meaningful results. One powerful technique for achieving this, known as 3D modulated cross-correlation, uses two temporally separated light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. The performance of this 3D technology can be further enhanced through means of optical path length reduction. The ability to modify the position of the sample cell by means of a sample goniometer enables the reduction of multiple scattering, thus enhancing the cross-correlated signal. In this presentation, we will give an overview of the 3D technology and the path length reduction technique, using a suspension of nanoparticles. The performances will be evaluated through a Static Light Scattering study of these suspensions. We will show how the modulated 3D cross-correlation technology associated with the use of a sample goniometer enables us to fully suppress multiple scattering even in very turbid suspensions, while keeping a high signal. Hence, measurements of the structure factor of highly concentrated suspensions are possible.

Resume : Surface structure has been studied for decades using techniques such as Low Energy Electron Difraction (LEED) and Scanning Tunnelling Microscopy, (STM). However, these methods can only be applied to highly ordered, extremely flat surfaces. There is as yet no method for surface structural analysis applicable to a wide range of sample types such as nanoparticles, powders, and rough surfaces. X-ray photoelectron spectroscopy (XPS) is a widely used analysis tool that can measure the composition and chemical environment of a surface. As a technique that probes filled electronic states, XPS spectra consist of peaks corresponding to core electrons, and at lower binding energy, the valence electrons. The shape of valence band spectra is a result of the electronic density of states, and hence contains structural information. A method of quantitative structural analysis using valence band X-ray photoelectron spectra is presented and applied to the analysis of powders and nanoparticles, such as TiO 2 anatase-rutile mixtures. The valence band spectra of pure TiO 2 polymorphs were measured, and these spectral shapes used to fit valence band spectra from mixed phase samples. Given the surface sensitive nature of the technique, this yields a surface phase fraction. Mixed phase samples were prepared from high and low surface area anatase and rutile powders. In the samples studied here, the surface phase fraction of anatase was found to be linearly correlated with photocatalytic activity of the mixed phase samples, even for samples with very different anatase and rutile surface areas. We apply this method to monitor the anatase-rutile phase transition, and to create a spatial surface phase map with micron resolution. This highly versatile method has the potential to be extended to any sample that can be placed into a vacuum, enabling surface structural information to be extracted from a much wider range of samples, incuding nanoparticles and non crystalline materials.