Atomic and molecular scale systems and devices

Resume : The endeavour of quantum electronics is driven by one of the most ambitious technological goals of today’s scientists: the realization of an operational quantum computer. People start to address this goal by the new research field of molecular quantum spintronics, which combines the concepts of spintronics, molecular electronics and quantum computing [1]. The building blocks are magnetic molecules, i.e. well-defined spin qubits. Various research groups are currently developing low-temperature scanning tunnelling microscopes to manipulate spins in single molecules, while others are working on molecular devices (such as molecular spin-transistors, spin valves and filters, and carbon-nanotubebased devices) to read and manipulate the spin state and perform basic quantum operations. We will first discuss this - still largely unexplored - field and then summarize our first results [2-5]. Finally, we will discuss the new challenges of the field and the requirements to achieve them. [1] L. Bogani, W. Wernsdorfer, Nature Mater., 2008, 7, 179. [2] M. Urdampilleta, S. Klyatskaya, M.-P. Cleuziou, M. Ruben, W. Wernsdorfer, Nature Mater., 2011, 10, 502. [3] A. Candini, S. Klyatskaya, M. Ruben, W. Wernsdorfer and M. Affronte, Nano Lett., 2011, 11, 2634. [4] S. Thiele, F. Balestro, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Science, 2014, 344, 1135; Nature, 2012, 488, 357. [5] M. Ganzhorn, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Nature Nanotechnol., 2013, 8, 165; Nature Comm., 2016.

Resume : Manipulating a single 3/2 nuclear-spin embedded in a molecular magnet spin-transistor is of great interest to explore fundamental law of quantum physics. Since we showed the coherent manipulation of a single nuclear spin using electric fields only [1], we are now able to coherently manipulate the four nuclear spin states by performing on the 3 different transitions: - Rabi oscillations with frequency range from one to ten MHz, - Ramsey fringes leading to coherence time T2* of the order of 0.3 ms, - Spin-echo exhibiting coherence time T2 of the order of 0.7 ms. These measurements enlighten the strong potential of using single molecular magnet as building blocks for quantum computing as the figure of merit is of the order of 3000. More than a model system to explore quantum properties, it was shown that a 4-level system can be used to implement the Grover’s research algorithm [2]. The idea of this quantum algorithm is to use the quantum parallelism to get a square root speed up of the research of an element in a database. In a recent experiment we pointed our ability to implement this algorithm : creating a 3 or 4 quantum states Hadamard gate, then, applying an unitary evolution to find out one of this quantum state. [1] Thiele et al.Science 344, 1135 (2014) [2] Leuenberger et al. PRL 89, 207601

Resume : Magnetic molecules have recently attracted considerable interest in view of their potential to design of (quantum) spintronic devices as there are spin valves,[1,2] spin transistors[3,4] and spin resonators[5] by a combination of bottom-up self-assembly and top-down lithography techniques. We report herein on the self-assembly of iron (II) spin transition (ST) compounds with gold-nanoparticles to percolated networks. These hybrid materials were contacted by additional gold electrodes and the transport through has been measured in trench devices. The observed reversible minimum in the temperature dependence of the resistivity of the device reveals the fingerprint of the S=0 --> S=2 spin transition.[6] This presence of ST in the hybrid material was additionally confirmed by Raman and SQUID experiments and also by blind measurements of the transport in networks formed from non-switching compounds.[7] [1] S. Kyatskaya et. al. J. Am. Chem. Soc. 131, 15143-15151 (2009) [2] M. Urdampilleta et al. Nature Mater. 10, 502-506 (2011) [3] R. Vincent et al. Nature 488, 357-360 (2012) [4] S. Thiele et al. Science 344, 1135-38 (2014). [5] M. Ganzhorn et al. Nature Nano. 8, 165–169 (2013) [6] E. J. Devid et. al. ACS Nano 9, 4496–507 (2015). [7] E. J. Devid et. al. Beilstein J. Nano. 5, 1664–74 (2014).

Resume : Spins in molecular materials are a promising resource for the realization of devices, with possible applications from nano-spintronics to quantum computing. The key challenge is how to address and exploit them in scalable devices architectures. We present our approach that is to use graphene as a suitable template for embed and read out molecular spins in electronic circuits. In this emerging field, few basic results have already been demonstrated, including the realization of hybrid graphene - magnetic molecules nanodevices where the electrical current is sensitive to the molecules magnetization reversal, with sensitivity down to the single molecule level [1]. Here we will report our most recent advances, exploring two main directions. Firstly, we develop graphene based electrodes which we employ to contact molecular units. By engineering the gap between the graphene electrodes in the nanometer range, we demonstrate charge transport through individual magnetic molecules, in a single-molecule transistor geometry. Alternatively, we used the graphene electrodes to contact atomically precise graphene nanoribbons, which represent the ultimate miniaturization of graphene devices with controllable edge properties and functionalities. The resulting all-graphene based devices show great potentialities for optoelectronic applications, including ultra-sensitive photo-detection in the UV-Vis range. References [1] A. Candini et al. Nano Letters 11, 2634-2639 (2011)

Resume : Graphene nanoribbons (GNRs) are few atoms wide nanostructures of graphene and attract particular attention due to the physical phenomena that result from their geometrical confinement. We have shown that in our chemically synthesized GNRs the edge structure is perfect on the atomic level [1]. They are synthesized on gold surfaces employing chemical vapor deposition [2]. Using specially tailored precursor molecules it is possible to obtain a variety of different GNRs. By evaluating their electric field dependence in standard FET devices, we determine the conductivity and mobility of chevron edged structures with 9 carbon atoms across the ribbon (N=9). At room temperature the resistivity of such devices lies in the regime of approximately 1 GOhm and the mobility is with 10^-4 cm²/Vs typical for conducting thin films of polymers. We compare their properties with armchair edged ribbons with N=9 to test the influence of the edge structure. Secondly, armchair ribbons with N=7 and N=9 are studied to test for the influence of the ribbon width. By modifying the precursors hetero-atomic doping with nitrogen and co-doping with nitrogen and sulfur is obtained for which a reduction of the charge carrier mobility is observed. Here, possible mid-gap states can be identified by performing temperature dependent measurements [3]. [1] A. Narita et al., Nature Chem. 6, 126 (2014). [2] Z. Chen et al., (under Revision 2016). [3] N. Richter et al., (manuscript in preparation 2016).

Resume : Rapid progress has been made in studies of carrier transport in single molecular junctions. It has been demonstrated that the electronic coupling between the molecule and the electrode governs the current-voltage (I-V) characteristics of the junction. The studies have implied that the configuration of the molecule on the metal electrodes causes the fluctuation of electrical conductance values. We have installed a mechanically controllable break junction (MCBJ) device in a loe-temperature cryostat, which enables us to trace the I-V characteristics of the molecular junctions as a function of the gap spacing between electrodes with the resolution of 0.01 nm. It was found that the reproducible I-V characteristics were mostly observed for the junctions with the molecule elongated just before losing the contact. In the present work, we have investigated the I-V characteristics of molecules having a permanent dipole moment. The low-temperature MCBJ measurements revealed that the molecules showed clear rectification behaviors. The rectification ratio became larger with an increase of the molecular length by the sequential stacking of the dipole unit from a monomer to a trimer. The first-principles transport calculations indicated that the electric field between the electrodes during the I-V measurements induces the deformation of the highest occupied molecular orbital, which causes the asymmetric electronic coupling between the molecule and the electrode. The guiding principle for preparation of molecular rectifiers will be given.

Resume : In contrast to the zero-bandgap graphene, structurally confined nanographenes, namely graphene nanoribbons (GNRs) and nanographene molecules, possess open bandgaps, which render them highly interesting for the nanoelectronic and optoelectronic applications. The properties of the nanographenes are critically defined by their structures such as the width, length, and the edge configuration, and thus the precise structural control is essential to reproducibly achieve desired optical and electronic properties. Nevertheless, the required precision cannot be obtained with the predominant “top-down” fabrication methods, such as “cutting” of graphene sheets and “unzipping” of carbon nanotubes. To this end, we employ “bottom-up” approaches for the synthesis of structurally defined GNRs and nanographene molecules, which can be performed “in solution” by the synthetic chemistry as well as “on surface” using metal substrates. The GNRs are characterized by a combination of different spectroscopic and microscopic methods. By changing the monomer design, GNRs can be synthesized with varying widths and edge structures, allowing for the tuning of their bandgaps. Narrow (~1 nm) and dispersible GNRs with the optical bandgap of ~1.9 eV could be obtained with the length over 600 nm, which enabled fabrication of transistor devices with films as well as isolated strands of GNRs. Moreover, lateral extension of the GNR to the width of ~2 nm lowered optical bandgap down to ~1.2 eV. Such narrow GNRs with strong absorption in the visible to near-infrared region also displayed interesting photophysical properties such as exciton-exciton annihilation and stimulated emission, marking their potential for applications in optoelectronic and photonic devices. Moreover, we have recently achieved unprecedented nanographene molecules with unique structures, such as hexa-peri-hexabenzocoronene with four extra K-regions and large nanographene disk with an internal cavity, showing modulated properties, which further enriches the chemistry of nanographenes as well as paves the way toward their applications in (opto)electronic devices.

Resume : Graphene has attracted increasing interests since its discovery in 2004 owning to the potential application in electronics. Cutting infinite graphene into nano-sized structures, such as graphene nanoribbons and nanographene molecules, can open the band gap and bring new properties as a result of quantum confinement effect. This also opens an opportunity to alter specific properties by edge structure engineering, such as optical and electronic properties in the zigzag edges. In recent years, the bottom up synthesis method using small molecule have proved to be effective in controlling the edge structure with atomically precision. Here, we demonstrated the application of this strategy toward the synthesis of novel nanographene molecule with a combination of armchair and zigzag edges. First, intermediate 2 was prepared using a reported method by our group. After treatment with excess amount of 2-mesitylmagnesium bromide and BF3•OEt2, compound 1 was obtained as a blue solid. Compared with cove-edged precursor, filling the cove region with two sp2 hybridized carbons caused obvious bathochromic shift, thus leading to a narrowed HOMO-LUMO band gap. High stability in air and strong fluorescence emission make it potential applicable as OLED or Laser materials.

Resume : Atomically precise graphene nanoribbons (GNRs) are excellent candidates to further stretch the upcoming scaling limit of integrated circuits technology. GNRs exhibit a sizeable bandgap, which is inversely proportional to their width, and are thus excellent candidates to overcome some of the major limitations of their parent material graphene. A bottom-up approach based on surface-assisted covalent coupling of molecular precursors1 allows for the synthesis of ultra-narrow GNRs with defined edge topologies and uniform width2. Production is, however, just the starting point of a GNR technology - in order to evaluate and exploit their properties GNRs must be transferred to semiconducting or insulating substrates. Here, we focus on 9-atom wide armchair GNRs (9-AGNR) grown under high to ultrahigh vacuum conditions on 200 nm Au(111)/mica substrates. The GNRs were transferred from the Au growth surface to SiO2/Si using a membrane-free method that avoids residual contamination. Raman spectra indicated no significant degradation of GNR quality and revealed a homogeneous GNR distribution on the target surface. Detailed characterization including multi-wavelength Raman spectroscopy and GNR stability under ambient conditions will be discussed. The overall GNR film morphology was characterized by optical and atomic force microcopy, which showed transferred films with very few tears and wrinkles. Finally, we report the fabrication of GNR field-effect transistors using 9-AGNRs (predicted band gap of 2.1eV) that show on-off ratios in the range of 10^2 to 10^5 and on-currents up to 100 nA3 1J.Cai et al. Nature 466 (2010) 470 2L.Talirz et al. Adv. Mater.(2016) DOI:10.1002/adma.201505738 3J.P. Llinas et al. http://arxiv.org/abs/1605.06730

Resume : Graphene nanoribbons (GNRs), quasi-one-dimensional narrow strips of graphene, have shown great promise for use as advanced semiconductors in electronics. Compared with the lack of structural control in GNRs fabricated by “top-down” approaches, atomically precise GNRs can be “bottom-up” synthesized by surface-assisted assembly of molecular building blocks under ultrahigh vacuum (UHV) conditions. Such “bottom-up” synthesized ultranarrow (~1-2 nm) GNRs have demonstrated large bandgaps of ~1 to 2 eV with visible to near-infrared absorption, rendering them highly interesting for a broad range of applications in next-generation transistors, as well as optoelectronic and photonic devices. However, a large-scale synthesis of uniformly narrow GNRs at low cost and their transfer to insulating substrates remain significant challenges, and the device applications of the “bottom-up” synthesized GNRs are still elusive. Moreover, structural characterizations of GNRs have been limited to microscopic and spectroscopic methods, hindering the direct elucidation of the exact chemical composition, especially for heteroatom-doped GNRs. To further exploring the structural information of GNRs and make them applicable for real device applications, we demonstrate an efficient CVD process for inexpensive and high-throughput growth of structurally defined GNRs over large areas under ambient-pressure conditions. The CVD-grown GNRs exhibit similar structures and properties with those synthesized under UHV conditions, as supported by Raman spectroscopy, high-resolution electron energy loss spectroscopy, and STM characterizations. Homogenous GNR films over areas of centimetres have been successfully transferred to non-conducting wafers and exhibited a large current on/off ratio of up to 6,000 in field-effect transistor devices, which is significantly larger than values reported so far for other GNR thin film transistors. Moreover, by using graphene electrodes, the contact resistance can be drastically reduced while preserving the high current on/off ratio. This “bottom-up” CVD method further allows the growth of N-doped GNRs as well as their heterojunctions, demonstrating the versatility and scalability of this process, which provides access to a broad class of GNRs with engineered structures and properties based on molecular-scale design. These results pave the way toward the scalable and controllable growth of GNRs, and provide practical solutions to the current challenges in graphene-based nanoelectronic, optoelectronic and photonic devices.

Resume : Bis(phtalocyaninato) lanthanide double-decker complexes (LnPc2, Pc=phtalocyanine) are among the most promising candidates for the implementation of molecular quantum technologies. In their neutral form, LnPc2 complexes show an additional radical spin ½ delocalized onto the Pc molecules, which influences the low temperature magnetic properties and plays an important role when the molecule is coupled to a spintronic device or deposited on a magnetic surface. Although neutral LnPc2 have been widely investigated with different experimental techniques, a clear understanding of the radical-lanthanide interaction in different double-decker complexes is still lacking. This motivated us to carry out a systematic study by means of Electron Paramagnetic Resonance (EPR) spectroscopy on the LnPc2 series, where Ln=Tb, Dy, Ho and Er. EPR spectra taken at different frequencies in the range 9-400 GHz show that the radical transition is influenced by the presence of different Ln ions. In particular, respect to a single doublet transition with g=2.01 measured in the analogous YPc2 compound, powder samples of LnPc2 show multiple resonances with different g-factors. We discuss these results on the basis of theoretical models comprising the Ln-radical exchange interaction.

Resume : For decades, the smallest known systems showing slow relaxation behavior have been polynuclear [1] and mononuclear [2] metal-organic complexes, so-called single-molecule magnets (SMM). Beyond SMM, the ultimate limit of magnet size shrinkage is an isolated magnetic atom on a nonmagnetic substrate. However, since the report of giant magnetic anisotropy in individual magnetic atoms on surfaces [3], the observation of magnetic remanence in single adatoms has remained an elusive goal, since the coupling- i.e. energy and angular momentum exchange, of the magnetic moment to the environment occurred on a timescale in the pico- to microsecond range, i.e. much faster compared to magnetization loop measurements. The key to stabilize the single magnetic moment of an adatom is therefore to develop a viable route for minimizing the coupling with the surrounding electronic/crystalline environment. We have recently achieved this goal for Ho atoms adsorbed on thin MgO(100) films on Ag(100), for which we measured a magnetic lifetime of 1500 s at 10 K and an open hysteresis loop with a coercive field of 3.7 T [4]. Magnetic remanence is observed up to 30 K, a temperature higher than typical SMM. The extraordinary magnetic bistability of the Ho/MgO system is attributed to the effect of (i) the mixing of odd Jz states in the ground state of Ho due to the C4v symmetry of ligand field of MgO(100), which protects the magnetization from the reversal by quantum tunneling as well as by first-order electron scattering at zero and finite fields; (ii) the weak coupling to the electronic and (iii) vibrational degrees of freedom of the substrate ensured by the insulating and stiff MgO film. [1] R. Sessoli, et al., Nature 365, 141 (1993). [2] N. Ishikawa, et al., Angewandte Chemie International Edition 44, 2931 (2005). [3] P. Gambardella, et al. Science 300, 1130 (2003). [4] F. Donati, et al. Science 352, 318 (2016).

Resume : We present a combined theoretical density-functional and experimental study of the electronic and magnetic properties of Terbium double deckers (TbPc2) adsorbed on Ni(111) substrates [1,2]. The calculations have been carried out by state-of-the-art density-functional theory methods, as implemented in the Quantum Espresso simulation packages. The neutral TbPc2 molecule in the gas phase is characterized, in addition to the Tb magnetic moment, by having a spin radical S=1/2 delocalized on the Pc organic planes. We have focussed on the role of the radical in mediating the magnetic coupling between the Tb magnetic moment and the Ni magnetization, considering in particular the case where a graphene layer is interposed between the molecules and the substrate. If, on one hand, graphene acts as an electronic decoupling layer, preserving the integrity of the magnetic properties of the molecule, on the other hand it allows an efficient transfer across it of the spin information leading to a measurable molecule-surface exchange coupling, as demonstrated by XMCD experiments. We observe that the spin radical is only partially suppressed on the graphene decorated Ni(111) substrate, and we explicitly consider its existence in a spin-model Hamiltonian, which is able to fit the magnetization curves extracted by the XMCD experiments. When the molecule is deposited directly on the highly-interacting Ni(111) surface, the spin radical is fully quenched and the lower Pc planes becomes spin-polarized only in virtue of a magnetic proximity mechanism. We also investigated the role of the Tb d-orbitals in allowing the localized f electronic spins to communicate with the external world. Overall, the magnetic interaction between the Tb spin and the Ni magnetization becomes possible in virtue of a Tb(f)-Tb(d)-spin polarized Pc-graphene-Ni relay-like exchange mechanism, which is able to sustain the spin communication over a distance of around 7 Angstrom. [1] Scientific Report, 2016, 6, 21740. [2] S. Marocchi et al., to be submitted, 2016.

Resume : Phenomena that are connected to quantum mechanics, such as magnetism, transport, and the effect of impurity atoms and disorder, and their relation to material design and energy needs are important for almost every branch of the industry. Density functional theory (DFT) was successful at making accurate predictions for many materials,in particular compounds which have a metallic behaviour. DFT combines high accuracy and moderate computational cost, but the computational effort of performing calculations with conventional DFT approaches is still non negligible and scales with the cube of the number of atoms. A recent optimised implementation of DFT was however shown to scale linearly with the number of atoms (ONETEP), and opened the route to large scale DFT calculations for molecules and nano-structures. Nonetheless, one bottleneck of DFT and ONETEP, is that it fails at describing well some of the compounds where strong correlations are present, in particular because the computational scheme has to capture boththe band-like character of the uncorrelated part of the compound and the Mott-like features emerging from the local strongly correlated centres. A recent progress has been made in this direction by the dynamical mean-field theory (DMFT), that allows to describe the two limits (metal and insulator) in a remarkable precise way when combined with DFT. The ONETEP+DMFT implementation and strategies to overcome the main bottlenecks of this type of calculations will be discussed, and its applications illustrated by a few case of studies, such as the role of quantum entanglement in Myoglobin and heme systems. References : PRL 108, 256402 ‘ 12 PRL 110, 106402 ' 13 PNAS 111, 5790 '14

Resume : Creation of a new generation of solar cells involves coating the Graphene on the free surface of transition metals. Therefore, the research of the multilayer relaxation Fe surface induced by coating of Graphene is interesting. Such a task was solved by us using molecular dynamics method. Relaxation of the top five atomic layers of Fe has been simulated, taking into account the crystallographic surface orientation (001), (011), (111) before and after the Graphene coating. The conjugation angle of the Fe and Graphene crystal lattice has been also varied. Calculations of system energy and stresses have been performed for two temperatures: 300K and 400K. There was analyzed the change of interplanar distances along a normal to the surface compared to the undisturbed state (volume) depending on the packing density of different Fe verges. There was a comparison of the obtained results with literature data for pure Fe and confirmed the oscillating nature of the multilayer relaxation in particular. We have established the regularities of Graphene influence on the structural parameters of the Fe surface and discussed the conditions of practical application of the Fe/Graphene system in the solar energy.

Resume : The use of graphene in electronic devices requires the presence of an energy gap. One viable strategy to achieve this goal is the reduction of the lateral size of the graphene layers down to graphene nanoribbons (GNRs) with nm-sized width. However, as long as the GNRs are obtained by conventional top-down approaches, the resulting structure is not controllable. High-quality GNRs are grown in ultra high vacuum on metallic surfaces, whereas a non-conducting substrate is mandatory for applications in electronics. Alternatively, GNRs can be synthesized in liquid-phase. Given their huge mass, they cannot be evaporated and the deposition is usually performed by drop casting. Electrospray deposition (ESD) is an alternative technique that allows to softly land large and heavy molecules from liquid suspension. In this work Electrospray deposition (ESD) in ambient conditions has been used to deposit graphene nanoribbons (GNRs) dispersed in liquid phase on different types of substrates, including ones suitable for electrical transport. The deposition process was controlled and optimized by using Raman spectroscopy, Scanning Probe Microscopy and Scanning Electron Microscopy. When deposited on graphitic electrodes, GNRs were used as semi-conducting channel in three terminal devices showing gate tunability of the electrical current. These results suggest that ESD technique can be used as an effective tool to deposit chemically synthesized GNRs onto substrates of interest for technological applications.

Resume : The high carrier mobility of graphene offers the possibility to build high-performance graphene-based electronic, photonic and optoelectronic devices. Graphene layers can be efficiently employed as a transparent electrode and to contact other low-dimensional materials, such as molecule or carbon based nano-structure. Starting from a pristine graphene flake a thin gap can be opened via electro-burning procedure or via EBL patterning and RIE of oxygen plasma, according to the dimension of the gap to achieve: RIE technique allow to realize a gap of around 100 nm, while a controlled electro-burning allow to realize gaps of few nanometres. To use the exceptional optical and electrical performance of graphene in applications the presence of a bandgap is fundamental. Lateral confinement of graphene in almost monodimensional(few nanometres) structure produce a band gap, due to quantum confinement and edge effects. Although various techniques allow the realization of Graphene nano-ribbons(GNR) like top-down approaches(unzipping of carbon nano-tubes or via electron beam lithography of graphene flakes), the only way to have precisely defined in size and shape GNRs is a bottom-up grown. Here we used GNRs grown from chemical synthesized monomers by chemical vapour deposition method. Large area of GNR are grown on a 200 nm of Au(111) epitaxially grown on mica substrate. As grown the GNR/Au?mica compound is put in hydrofluoric acid for etching away the mica; after washing with ultra-pure water the Au film was etched away by gold etchant; finally the GNR film is transfer on a pre-patterned graphene-based contacts. To avoid the broken of the thin film when transferring large area of GNR films, spin-coated PMMA thin film was used as a mechanical support before etching with HF. The PMMA was washed away by hot acetone in the last step. The devices realized as described are electrically characterized at room temperature in vacuum condition in a LakeShore probe-station. Annealing up to 400 K could be performed during the electric characterization. Here we present the realization and characterization of a field-effect transistor(FET) device, totally made of graphene, in which we combine the electrical of graphene with the band-gap of the GNRs. The conductive channel consists in a layer of chemically precise GNRs attached to multilayer graphene working as electrical contacts. GNRs are grown from chemically synthesized monomers by a chemical vapour deposition (CVD) method and are transferred on the prefabricated graphene electrodes. The devices show a current on/off ratio as high as 104 and photoresponsivity of 6 × 105 A/W in the visible-UV range. The light sensitivity is orders of magnitude higher than the ones reported for pristine graphene sheets[3] and other photo-transistors based on two dimensional materials. Our results show the potentialities of all-graphene devices for the development of novel applications in nano-optoelectronics and sensing.

Resume : A tandem demethylation-aryl borylation strategy was developed to synthesize OBO-doped tetrabenzo[a,f,j,o]perylenes (namely “bistetracenes”) and tetrabenzo[bc,ef,kl,no]coronenes (namely “peritetracenes”). The OBO-doped bistetracene analogues exhibited excellent stability and strong fluorescence, in contrast to the unstable all-carbon bistetracene. Single-crystal X-ray analysis for OBO-doped bistetracene revealed a twisted double [5]helicene structure, indicating that this synthesis is applicable to new heterohelicenes. Importantly, cyclodehydrogenation of the bistetracene analogues successfully produced the unprecedented heteroatom-doped peritetracenes, which opened up a new avenue to periacene-type nanographenes with stable zigzag edges.

Resume : Molecular spin systems are promising candidates for the implementation of future quantum devices. In fact, they can be synthesized in large ensembles of identical systems, and their physical properties can be tailored at the chemical level. In recent years, most attention has been devoted to the ensembles of s=1/2 spins, coherently coupled with one mode of the quantized electromagnetic field and in the low-excitation regime [1-3]. Molecular spin clusters provide a variety of spin systems, with larger spin lengths and diverse level schemes. Here we provide a theoretical investigation of these cases, in the regime where the photon number is at least comparable to that of the spins in the ensemble. In particular, we consider the case of multiple ensemble of s=1/2 spins and of ensemble of spins s>1/2, characterized by different level schemes and coherently coupled with one mode of the field. When the number excitations is much larger than that of the spins, the energy spectrum can be approximated by treating the field classically. On the other hand, the presence in the system ground state of spin-photon and spin-spin entanglement provides evidence of clear quantum-mechanical features in such supposed “classical limit”. References: [1] M. Jenkins, T. Hümmer, M. J. Martínez-Pérez, J. García_Ripoli, D. Zueco, and F. Luis, New J. Phys. 15(9), 095007 (2013). [2] A. Ghirri, C. Bonizzoni, D. Gerace, S. Sanna, A. Cassinese, and M. Affronte. App. Phys. Lett. 106(16), 184101 (2015). [3] A. Ghirri, C. Bonizzoni, F. Troiani, N. Buccheri, L. Beverina, A. Cassinese, and M. Affronte, arXiv:1605.02879.

Resume : Graphene is considered an appealing material for the replacement of the traditionally used metal electrodes in single-molecule devices, as its covalent bond structure assures a high mechanical stability even above room temperature and its planar geometry (with a thickness comparable to the molecular size) allows for the anchoring of diverse molecules, which strongly couple to the graphene electrodes via carbon bonds and/or pi-pi stacking. Here, we shall present the realization and functional characterization of three-terminal molecular devices in which a single-molecule magnet (the bis(phthalocyanine) terbium (III), TbPc2) is embedded between two nanometer-spaced electrodes made of few-layer graphene grown on the C-face of SiC. Nanogaps in graphene are opened via a feedback-controlled electroburning (EB) procedure, whose fast response avoids the abrupt breaking of the graphene junction and allows for a high-yield precise control on its final molecular-sized structure. Our devices work as molecular spin transistors allowing to detect the Tb3+ electronic spin flip during the sweeping of an external magnetic field. Moreover, the magnetic exchange coupling between the current passing through the molecular system in the Coulomb blockade regime and the Tb3+ electronic spin can be characterized. Our results suggest that the use of graphene is a promising and viable route for contacting single molecules and realizing complex electronic architectures at the molecular scale.

Resume : In the field of nanotechnology, characterization of thin films, nanostructures, interfaces and critical dimensions (CD) are very important in order to see morphology and topology of grown materials. Usually, different techniques are used i.e. transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD) to analyze the surface. All these techniques could be used to see the morphological study but in order to observe surface topology with critical dimensions high quality 3D atomic force microscope (AFM) imaging is desirable. Carbon nanotubes (CNT) are suitable candidate for 3D AFM probes due to their exceptional strength, elastic modulus and high level of aspect ratio. Unfortunately, due to strong sp2 hybridization of CNT's the bond breaking or attachment of any host molecule is quite crucial. However, another major issue includes homogeneous dispersion of highly agglomerated CNTs and their attachment. A lot of work is being done to deal with the said attachment and dispersion problems. In the field of microscopy, atomic force microscopy (AFM) is a handy tool to observe the 2D surface topology of grown surfaces. The quality of the images is dependent on the applied force and aspect ratio of the cantilevers and tuning fork based sensor. Combination of multiwall carbon nanotubes with silicon cantilever were previously used to address these issues. Furthermore, it was impossible to get high resolution images of undercut side wall structures by using flared tips. By using this approach to attach CNTs on tungsten probes, high quality imaging and surface investigation of deep and trench structures was possible. In current work we focused on the fabrication of nanoneedle shaped long probes for 3D topography. Firstly, these probes were fabricated by electrochemical etching process and secondly, MWCNTs were attached by using dielectrophoresis method. Although, these probes are cost effective and having high Q value but its scanning speed was comparatively slow than normally used silicon cantilevers. For comparison, we did surface scanning of readable compact disk (CD-R) at ambient condition with tungsten tip and MWCNT attached tungsten probe.The topographic images confirm that the quality of our fabricated CNTs based probe was good compared with the bare tungsten tip. However, MWCNT attached tungsten probe quality factor was little decrease from 6600 to 6000 but still it is comparatively too high with commercially used cantilever's. Degradation of quality factor could be due to mass attachment with tip. To overcome most challenging issue Through Silicon Via (TSV), we believe that our fabricated MWCNT based AFM probes could be an efficient tool to get high quality topography.

Resume : In recent years hybrid graphene – hexagonal boron nitride (hBN) materials with highly defined patterns have been produced. Although graphene and hBN are very similar materials from the structural point of view, with a lattice mismatch of only 2%, the electronic properties are quite different: while graphene is zero-overlap semimetal with very high electrical conductivity, hBN is a wide band gap semiconductor. Based on these properties, graphene-hBN binary composites are ideal candidates for tunable electronic materials. Here we investigate the influence of the halogen passivation on the electronic and mechanical properties of zig-zag graphene nanoribbons with embedded hBN domains by ab initio density functional theory (DFT) calculations. Passivating halogen atoms of different electronegativity, present at the extremities of zig-zag terminated nanoribbons, introduce different antiferromagnetic spin couplings between the two edges. Molecular dynamics (MD) calculations performed in the framework of DFT reveal the mechanical properties of the nanoribbons, which depend on the specific shape of the graphene-hBN domains and also on the mass of the halogen atoms. In particular, the stiffness of the nanoribbon may be gradually changed by adjusting the ratio between graphene and hBN domains, which has consequences in the phonon spectrum and further in the thermal transport. Using MD simulations we make a statistical analysis of the nanoribbon buckling and establish the low noise conditions for the charge and spin transport. Our analysis is focused on attaining highly electrically conductive elements based on halogenated graphene-hBN nanostructures, with low thermal conductance and low noise suitable for thermoelectric applications.

Resume : Our technological preference for perfection can only lead us so far: as traditional transistor-based electronics rapidly approach the atomic scale, small amounts of disorder begin to have outsized negative effects. Surprisingly, a promising pathway out of this conundrum may emerge from embracing the quantum nature of atomic-scale defects to construct 'quantum machines’ that enable new information processing and sensing technologies. Recently, individual defects in diamond [1], silicon carbide [2-4], and other wide-gap semiconductors [5] have attracted interest as they possess electronic and nuclear spin states that can be employed as solid-state quantum bits. These systems provide a built-in optical interface in the visible and telecom bands, retain their coherence over millisecond timescales, and can be polarized, manipulated, and read out using a combination of light and microwaves [1-4]. Here, we focus on recent progress in quantum-optical techniques for qubit control compatible with an all-photonic quantum network. Utilizing a nitrogen-vacancy center lambda system, we achieve robust qubit rotations based on the quantum geometric, or Berry, phase [6] and accelerate the preparation and transfer of coherent superposition states via ‘shortcuts to adiabaticity’ [7]. These results advance defect-based qubits as platforms for novel science and scalable photonic implementations of spintronic technologies. [1] D.D. Awschalom, L.C. Bassett, A.S. Dzurak, E.L. Hu and J.R. Petta, Science 339, 1174 (2013). [2] W. F. Koehl, B. B. Buckley, F. J. Heremans, G. Calusine, and D. D. Awschalom, Nature 479, 84 (2011). [3] D. J. Christle, A. L. Falk, P. Andrich, P. V. Klimov, J. Hassan, N. T. Son, E. Janzén, T. Ohshima, and D. D. Awschalom, Nature Materials 14, 160 (2015). [4] P. V. Klimov, A. L. Falk, D. J. Christle, V. V. Dobrovitski, and D. D. Awschalom, Science Advances 1, e1501015 (2015). [5] J. R. Weber, W. F. Koehl, J. B. Varley, A. Janotti, B. B. Buckley, C. G. Van de Walle, and D. D. Awschalom, Proc. Natl. Acad. Sci. 107, 8513 (2010). [6] C. G. Yale, F. J. Heremans, B. B. Zhou, A. Auer, G. Burkard, and D. D. Awschalom, Nature Photonics 10, 184 (2016). [7] B. B. Zhou, A. Baksic, H. Ribeiro, C. G. Yale, F. J. Heremans, P. C. Jerger, A. Auer, G. Burkard, A. A. Clerk, and D. D. Awschalom. arXiv:1607.06503 (2016).

Resume : Spin of donors or double donors in silicon are the heart of several schemes for qubits. In the last decade there has been a revival of the pioneering continuous wave electron paramagnetic resonance (CW-EPR) investigations, started in the late 50s, of these class of impurities in silicon taking advantage of pulse-EPR techniques. In addition the availability of isotopically purified silicon-28 allowed a detailed investigation of the main relaxation mechanisms and of the coherence time when super-hyperfine interactions are mostly eliminated and spin diffusion processes suppressed. We will review the main results related to the pulse-EPR investigation of conventional donors (P, As) [1, 2], other group V impurities (Bi and N) [3, 4] and double donors (S, Se) [5, 6] focusing on spin-lattice and spin-spin relaxation processes in bulk silicon. In any silicon based, CMOS compatible, nano-electronic device a major role is played by the Si/SiO2 interface and by the well-known defects, the Pb center family, there localized. Due to sensitivity issues the investigation of the spin dynamics of these centers has not been reported so far. Taking advantage of silicon nanowires fabrication and surface/interface preparation and modification we have been able to investigate the spin relaxation mechanisms of the Pb-centers and also their interaction with the donor spin dynamics [7]. These results will be reported and discussed. 1. M. Fanciulli, P. Höfer, and A. Ponti, Physica B 340-342, 895 (2003) 2. A. Ferretti, M. Fanciulli, A. Ponti, and A. Schweiger, Phys. Rev. B 72, 235201 (2005) 3. M. Belli, M. Fanciulli, N. V. Abrosimov , Phys. Rev. B 83, 235204 (2011) 4. M. Belli, M. Fanciulli, D. Batani, Phys. Rev. B 89, 115207 (2014) 5. S. Paleari, M. Belli, M. Fanciulli, Yu. A. Astrov, ICDS 2013 6. R. Lo Nardo, et al. Phys. Rev. B 92, 165201 (2015) 7. M. Fanciulli, APS March Meeting, Baltimore, USA (2016)

Resume : QuantERA

Resume : CEA Leti

Resume : STMicro