Diamond for Electronic Devices IV

Resume : The Schottky diodes will be the first components commercially available for the diamond technology. However, we have to manage the surface defects which is still too high for large contact, with the current requirement and the rectification behavior. Even though a number of studies have already been performed, some questions are still without answer. One of them is how is the electric field into the stack of diamond layer. From the theory and by doing simulation we know how it should be but experimentally we are able to see only the lateral electric field distribution by performing electron beam induced current (EBIC) and that gives us only a partial view of the problem and not the entire picture The second major problem is the study of the interface and the identification of defects that could lead to a modification of the Schottky barrier. With this study, we propose a new approach combining growth technic and electrical characterization in order to see what is happening underneath the Schottky contact in the depth of the material. The first part was to grow and fabricate the stack for diamond Schottky diode i.e heavily doped p++ layer on top of an HPHT substrate. And after a thick non intentionally doped layer (p-) was grown. Once the sample ready, polishing was performed to remove the lateral overgrowth. Thus, the stack was directly accessible to different electronic probes. We performed EBIC and cathodoluminescence measurements. For instance, For example, with EBIC we observed the electric field directly under the contact for different polarization of the diode. Following this, we combined cathodoluminescence measurements with a specific mapping underneath the contact to correlate the presence of defects and the intensity of EBIC signals which is related to barrier inhomogeneities.

Resume : Diamond is attracting attentions for future semiconductor devices such as high power and low loss devices worked under harsh environmental conditions. High current capability > 3kA/cm2 with long-term stability at high temperature condition > 400degC has been confirmed on SBDs. High radiation hardness of SBDs and MESFETs after 10 MGy of X/gamma-ray has been confirmed as well. Typical maximum electric field strength of the devices are more than 2MV/cm, however, it decreases with increasing the size of the main contact. Estimated density of the defect was in the order of 10,000 /cm2 by Murphy’s analysis and the origin of the defect was not clarified up to now. In this study, diamond SBDs have been fabricated on 0.5 inch wafer by minimal fab system and the yield of the device is analyzed to understand the origin of the defects. Diamond SBDs with pseudo-vertical structure were fabricated on a CVD grown nitrogen doped semi-insulating (001) substrate. p-/p+ Stacked film was deposited by microwave plasma and hot filament CVD techniques. Ohmic and Schottky contacts were fabricated on the same side of the substrate. To suppress the field enhancement at the edge of the main contact, SiO2 field-plate was utilized. The diameter/length of the main contact was varied from 25 to 700 µm. The fabricated SBDs show high on/off ratio when the size of the main contact is less than 220µm, however, the high leakage devices are confirmed with size increased. The estimated density of the defects by Murphy’s analysis is 100 /cm2 which is, at least, two orders of magnitude less than that of crystallographic defect in the substrate. From this analysis, the main reasons of the low yield of diamond devices is the defects during the device processing rather than the crystallographic defects in the film/substrate.

Resume : Nanodiamonds (NDs) are a readily sourced and relatively inexpensive materials. Here, it has been shown that for boron-doped NDs the nano-size of such particles enable them to act as a source of boron dopant when subsequent plasma-CVD diamond growth is carried out on them, without the need for the addition of B-containing species to the plasma-CVD feedstock gases. Here the potential use of B-NDs for the formation of diamond Schottky Diodes through such an approach is explored. Two types of B-NDs are studied; those produced by a top-down process of milling B-doped diamond films and others produced by a bottom-up chemical synthesis approach. In all cases effective diodes were produced with barrier heights of 0.6-0.7eV. Early indications are that the bottom-up grown NDs may offer better breakdown voltages when using this approach, potentially because of their smaller size (~10nm).

Resume : In this talk, I will present the fabrication and characterization of diamond field effect transistors (FETs) with a monocrystalline hexagonal boron nitride (h-BN) as a gate dielectric. A thin crystal of h-BN was obtained by using the Scotch tape exfoliation technique and laminated on hydrogen-terminated (111) diamond surface. A high-quality interface between h-BN and diamond was confirmed by transmission electron microscopy. Excellent insulating properties of h-BN led to high carrier mobilities and low on-resistance of the FETs. The high mobility allowed us to observe quantum oscillations, which provided important information on the hole gas accumulating at the diamond surface. The heterostructure consisting of monocrystalline h-BN and hydrogen-terminated diamond will provide an excellent platform for the study of quantum transport in diamond, as well as the fabrication of high-performance electronic devices. Reference: Y. Sasama et al. APL Materials 6, 111105 (2018).

Resume : Semiconductor nanowires (NWs) represent one of the most important and versatile nanometre-scale structures. In contrast to other classes of 1D nanostructures, such as carbon nanotubes, semiconductor NWs can be rationally and predictably synthesized in single crystal forms with all key parameters controlled, including chemical composition, diameter, length, doping and electronic properties. Diamond can be considered as an ultimate semiconductor with a band-gap of 5.5eV and outstanding electrical properties. We report novel nanoscale electrically addressable diamond nanowire devices. Based on extremely high-quality boron-doped diamond delta-layers, this technology provides an exciting playground for exotic physics and traditional electronic engineering, and many applications in sensor technology. Lateral nanowires are defined in very thin heavily boron doped diamond epi layers. In the results reported here, the delta layer is on the surface of a [100] single crystal diamond. Electrical isolation is possible due to the very low defect and high quality ‘intrinsic’ CVD buffer layer grown on the HPHT substrate before the ∂-layer is grown. The resultant nanowires are some 2nm deep and 10-20nm wide, and show current densities surpassing 300A/mm2. After etching the nanowires the spatial confinement and electrical properties of the wire can be further engineered using electrostatic side and top gating. We report exceptional current densities indicative of ballistic transport and preliminary results from the first ever fabricated diamond-FinFET type devices; an architecture used in the silicon industry for the next generation of processor chips, but obviously without the extreme transport properties shown here. Further, the prospects for the use of these nanowires as sensors for the trace detection of a range important species will be considered.

Resume : Fabrication of diamond power devices as prototypes can be based on structures with stacked layers consisting of buried epitaxial layers or buried wells. To fabricate buried n-doped wells for example, the technology involves several steps such as realization of V-shape structures via catalytic etching with nickel along defined crystalline directions of the diamond layer and subsequent growth of n-doped layer via phosphorous doping. In this paper we report first on experimental results of phosphorous doping at different growth conditions to pave the way for finding optimum growth conditions leading to high phosphorous incorporation, suppression of nitrogen incorporation and low growth rates required for fabricating thin, high quality n-type layers. Then we go on with catalytic etching on intrinsic (100) diamond via nickel. Catalytic etching on (100) diamond layers results in V-shapes with atomically smooth (111)-oriented sidewalls and (100)-oriented bottoms, whereas the crystalline orientation of the sidewalls is optimal for the growth of n-type doped layers since in these layers the incorporation efficiency of phosphorous is higher enabling realization of highly doped n-type layers in (100) diamond. Experimental results indicate for example that the relationship between the orientation of the nickel mask and the crystal orientation of the diamond layer is important. Smooth (111) etched surfaces are achieved by depositing the nickel mask with edges parallel to the <110> direction of the diamond layer. The fabricated V-shape structures are subsequently overgrown with n-type layers. CL measurements on these grown n-type wells reveal different degree of phosphorous incorporation for different crystal orientation of the facets.

Resume : There is considerable interest in the fabrication and electronic properties of graphene and related 2D materials, such as hexagonal boron nitride (hBN), for low-dimensional materials engineering. [1] Previously, catalytic conversion of diamond substrates into large-domain high-quality graphene was shown, via transition-metal-induced growth of sp2 bonded carbon from sp3 bonded surface atoms. [2] Modern advancements in sintering of polycrystalline cubic boron nitride have made possible comparative methodology for mediated growth of low-dimensional hBN regions. In-situ deposition and annealing cycles were performed, and through use of real-time photoelectron-based methods, the proliferation of BN through a metallic overlayer was observed with temperature dependence. Boron and nitrogen K-edge spectra of the near-edge X-ray absorption fine structure (NEXAFS) allowed for clear determination of hexagonal phase, due to the emergent π-π* transition state not present in the cubic phase. [3] The results indicate that controllable growth of single and multi-layer hBN is feasible, given precise control over substrate temperature, polish and pre-treatment. This technique may provide a new alternative source of high-quality low-dimensional hBN for graphene-based electronic devices with wide band gap substrates. [1] C. R. Dean et al., Nat. Nanotechnol., 5, 10, 722, (2010). [2] S. P. Cooil et al., Appl. Phys.Lett., 107, 18, (2015). [3] D. A. Evans et al., Appl. Phys. Lett., 89, 161107 (2006).

Resume : Controlled synthesis of nanodiamond particles has recently seen an increased interest due to breakthroughs in quantum sensing and entanglement, biolabeling, and nanoscale sensing[1]. While nanodiamonds are typically fabricated in large amounts by two main techniques: (1) detonation synthesis and (2) by crushing larger microsized crystals[2], neither of these methods allow for a high degree of manipulation of their properties. High quality nanodiamonds grown by chemical vapour deposition are thus highly favoured for precise control over crystal morphology, size, and dopants. Since nucleation and early stages of growth play an important role in the properties of the particles[3], it is mandatory to reach equilibrium within the plasma conditions as quickly as possible so that nucleation happens at equivalent parameters. Here we propose a methane pulsing scheme to quickly increase methane concentration, allowing it to reach steady-state concentration within seconds instead of minutes depending on pressure, chamber volume, target concentration, and attainable flows. Pulses are designed by numerical simulations and compared to experiments performed by optical emission spectroscopy for accuracy. The influence of the pulsing schemes on diamond growth is studied by growing on vertically aligned substrates, allowing to rapidly explore the effect on a broad parameter space, since temperature, plasma density and hydrogen density vary continuously along the vertical axis[1]. The developed technique allows us to prepare ND with nearly perfect crystalline shape of size < 100 nm and various type of colour centres as characterised spectrally. We also present data on coherence time in NV nanodiamonds and compare with HPHT nanocrystals. References: 1. Tzeng, Y., Zhang, J., et al. (2017). Vertical-Substrate MPCVD Epitaxial Nanodiamond Growth. Nano Letters, 17 (3), pp. 1489-1495. 2. Alkahtani, M., Alghannam, F., Jiang, L., et al. (2018). Fluorescent nanodiamonds: past, present, and future. Nanophotonics, 7(8), pp. 1423-1453. 3. Domonkos, M., Ižák, T., et al. (2018), Diamond nucleation and growth on horizontally and vertically aligned Si substrates at low pressure in a linear antenna microwave plasma system. Diamond and Related Materials, 82, pp. 41-49.

Resume : The negatively charged Nitrogen Vacancy (NV-) centre in diamond has been shown to possess desirable properties for use in quantum technologies [1]. In applications based on the NV centre, where the centres are located close to the diamond surface, it has been shown that spin states localised on the diamond surface disrupt the sub surface NV- centres [2]. Control of the surface spin states can be achieved by in vacuum surface processing steps that are monitored in-situ using a combination of surface science methods such as electron spectroscopy and optical methods. The oxygen terminated surface has shown promise as an ideal candidate for near-surface nitrogen vacancies, so an understanding of this surface is crucial. Using a CVD grown B-doped (001) diamond, we have monitored the electronic and optical properties of oxygen terminated surfaces produced by acid etching and plasma treatments over a series of temperature ramps up to 1300K. In this range, physical and chemical changes in the bulk diamond to reveal distinct regimes of oxygen desorption and their influence on the surface band bending, near-surface defects and surface conductivity. [1] X. Song, et al., Generation of nitrogen-vacancy color center in nanodiamonds by high temperature annealing, Appl. Phys. Let., 102, 133109, (2013) [2] S. Sangtawesin, B. L. Dwyer, N. P. D. leon, et al., Origins of diamond surface noise probed by correlating single spin measurements with surface spectroscopy, arXiv:1811.00144v1

Resume : Supercapacitor (SC) is an electrochemical device which stores electrical energy by means of an electrical double layer capacitor (EDLC) or a pseudocapacitor (PC). The SC performance is evaluated by its capacitance, power and energy densities, as well as the capacitance stability. Battery-like SCs are the mostly investigated these days. These SCs feature not only high energy density, but also high power density. The SC performance is known to be mainly determined by the used capacitor electrodes and the electrolytes. Boron-doped diamond is one of the best electrodes, resulting from its high stability in different media and under harsh conditions as well as its wide electrochemical potential window. Diamond, one sp3 carbon material, brings rich and stable C-C surface chemistry as well. In this presentation, the employment of doped diamond, diamond networks, diamond composites (carbon fiber coated diamond, TiC/diamond) as the capacitor electrodes for the construction of such high performance EDLCs will be shown. The fabrication of high-performance of PCs using electrochemically deposited MnO2 and soluble redox electrolytes will be also summarized. Estimation of the power and energy densities of these SCs by use of the assembled two-electrode symmetrical devices will be shown in detail. These high-performance battery-like and industry-orientated supercapacitors are therefore useful and promising for future power devices.

Resume : Sensing explosives in aqueous solutions is important for the determination due to environmental pollution of soil and water especially in places where munitions were previously produced, loaded and stored. However, most of the commonly used detection techniques require very expensive and complicated instruments which are often not portable and not sensitive enough to detect trace amounts of explosives. The presence of nitro groups in nitroaromatic compounds with redox properties makes electrochemical methods ideal for its electrochemical sensing. In this study, we propose electrochemical detection of nitro-explosives using boron-enhanced carbon nanowalls (BCNW) and surface-functionalized boron-doped diamond. The electrodes were synthesized using the microwave plasma enhanced chemical vapor deposition system. (thin films were grown on (100)-oriented silicon substrates). We present 2,4,6-trinitrotoluene and 2,4,6-trinitroanisole detection in the water at different pH and extreme complex system which is landfill leachates. The measurements were conducted using two electrochemical techniques: cyclic voltammetry and differential pulse voltammetry. Three well-defined nitro-group reduction peaks were observed. According to the best of our knowledge electrochemical detection of nitroaromatic compounds on BCNW has not been reported. Acknowledgment The authors gratefully acknowledge financial support from the Polish National Science Centre under Grant No. 2016/21/B/ST7/01430, 2016/22/E/ST7/00102, 2014/14/M/ST5/00715 and National Centre for Science and Development Grant Techmatstrateg No. 347324 2015/16/T/ST7/00469. This work was partially supported by the Science for Peace Programme of NATO (Grant No. G5147). The DS funds of the Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged.

Resume : Traditionally, optical methods are used for the high sensitivity detection of analytes, which require samples to be extracted and transported to a laboratory for analysis [1]. Electrochemical detection is an alternative method that facilitates in situ measurements. Boron doped diamond (BDD) has been gaining interest as an electrode for the trace detection of analytes because in addition to the low background and capacitive currents associated with the material it has the widest solvent window of any known electrode [2]. The hardness and chemically inert nature of diamond also enables BDD electrodes to be used in environments where other electrodes could be damaged. The ability to detect trace concentrations of mercury in situ is imperative because contamination with this highly toxic heavy metal poses a severe threat to human health, as it tends to form complexes with biological ligands, leading to an accumulation in the food chain [3]. To date the literature indicates that concentrations of mercury detected electrochemically can be down to levels of around 0.42 nM using a glassy carbon electrode modified with 36 nm diameter gold nanoparticles (AuNPs) [4]. The AuNPs act catalytically during the pre-concentration step of the square wave anodic stripping voltammetry (SWASV) measurements, improving the sensitivity of the electrode. This work compares polished and unpolished BDD electrodes decorated with AuNPs for use as robust mercury sensors in aquatic environments. The influence of altering the dispersion of AuNPs on the electrode surface sensitivity for electrochemical measurements was explored. This was achieved through the novel approach of using a TEM grid as a shadow mask during the gold deposition to produce a grid with 28 m square patches of AuNPs separated by 23 m gaps. The size of the catalytically active AuNPs on the electrode surface was shown to have a smaller effect on the sensitivity for mercury detection than the surface preparation of the BDD. The lowest limits of detection were achieved with the polished BDD electrodes, which both detected mercury at a concentration of 1 pM, six orders of magnitude greater sensitivity than the lowest detection limit of 5 M achieved with an unpolished BDD electrode. The performance of the polished BDD electrodes is excellent when compared to recent reports of alternative electrode materials for this purpose which are in the M-nM range [5,6]. References [1] F. Arduini, J. Q. Calvo, G. Palleschi, D. Moscone, A. Amine Trends Anal. Chemistry 29 (2010) 1295 [2] J. V. Macpherson Physical Chemistry Chemical Physics 17 (2015) 2935 [3] G. Aragay, J. Pons, A. Merkoçi Chemical Reviews 111 (2011) 3433 [4] T. Hezard, K. Fajerwerg, D. Evrard, V. Collíere, P. Behra, P. Gros Journal of Electroanalytical Chemistry 664 (2012) 46 [5] E. Eksin, A. Erdem, T. Fafal, B. Kivçak Electroanalysis 31 (2019) [6] H. L. Nguyen, H. H. Cao, D. T. Nguyen, V. A. Nguyen Electroanalysis 29 (2016) 595

Resume : Sensors with a sufficiently robust nature are in increasing demand for environmental monitoring under extreme conditions. The properties of diamond make it an ideal platform for the formation of such sensors, but conventional strategies often lead to devices with insufficient sensitivity and/or discrimination between the species of interest and others in the environment. Vibrational spectroscopies, and in particular Raman spectroscopy, offer the discrimination between differing organic species that is required, but conventional Raman is insufficiently sensitive to be of use. The sensitivity of Raman can, however, be greatly enhanced when plasmonic structure are present at the sensing surface, leading to the technique known as Surface Enhanced Raman Spectroscopy, or SERS. This presentation addresses a novel means by which the desirable properties of diamond as an exposed sensing surface can be combined with the advantageous plasmonic properties of metallic nanoparticles. Here, MWPECVD of thin diamond films over gold nanoparticles is reported and the SERS activity of these composite layers studied. It is shown that an effective sensor for the detection of the molecule Benzo[a]pyrene – an EC accredited monitor species for oil derived pollution – can be realised in this way. Acknowledgement: BAE Systems for the award of a CASE PhD studentship for MR.

Resume : Nowadays, flexible sensing devices play a crucial role in electronics. Boron doped diamond has been highlighted as a potential material in the flexible device, owing to its properties such as high mechanical durability, low electrical resistivity, and good thermal conductivity. Here, we propose to apply free-standing boron doped diamond nanosheets transferred to the various polymer substrates as a hybrid material designed for flexible devices. The free-standing boron doped diamond nanosheets were fabricated in MW PA CVD system at mirror-polished tantalum substrates [1]. BDDs were doped using diborane (B2H6) as a dopant precursor. Mechanically isolated diamond nanosheets were transferred to the various polymer substrates (PDMS, Kapton and PLA). The conductivity of the hybrid diamond-polymer was determined using the four-point method, while the Hall mobility studies were performed using the Van der Pauw geometry. The electronic properties has been investigated versus applied strain up to 10%. The morphology of diamond nanosheets was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), while the molecular composition of films was studied by means of Raman spectroscopy. Diamond structures were electrochemically tested using redox probes and impedance spectra studies. Moreover, model protein adsorption (e.g. FBS, BSA and amino acids) was utilized to reveal the efficiency and repeatability of biosensing properties of electrodes exposed to strain. Acknowledgments The authors gratefully acknowledge financial support from the Polish National Science Centre (NCN) under Grant No. 2016/21/B/ST7/01430, 2016/22/E/ST7/00102 and National Centre for Science and Development Grant Techmatstrateg No. 347324. The funds of the Gdańsk University of Technology and the DS funds of the Faculty of Electronics, Telecommunications, and Informatics are also acknowledged. References 1. R. Bogdanowicz, et al., Advanced Functional Materials. (2018): p. 1805242.

Resume : The stopping power of a material upon interaction with an energetic ion is the key measure of how far that ion will travel. The implications of accurate particle range calculations are tremendous, affecting every single application in which particle radiation is used ? from nuclear power to medicine. In addition to this, understanding the precise range of neutron products in diamond and boron carbide is crucial for designing the most efficient solid state neutron detectors. A model is presented which attempts to overcome current weaknesses in the physical understanding of ? as well as the mathematical methods used to interpret ? the stopping power at low energies. This is a considerable challenge, however the use of a fundamentally new machine learning methodology has been shown to hold great promise in this field. A random forest regression algorithm has been trained using over 34,000 experimental measurements, representing the stopping power values for 522 ion-target combinations across the energy range 10(?3) to 10(2) MeV, and ion and target atomic masses (A(ion) and A(target) 1 to ? 240. The ultimate aim of the algorithm being the ability to predict the stopping value for any energy, ion and target combination, having seen no pre-existing experimental data. Evaluation is performed using four error metrics (R2, RMSE, MAE and MAPE) to provide the best understanding of model performance when tested against strict cross-validation criteria. The resulting model is shown to have minimal bias when evaluating its internal per- formance, and the errors evaluated on the external ?blind? predictivity of the model concurrently show low levels of overfitting and variance ? despite a noisy and unbal- anced dataset. Examination of the error distributions suggests better predictions are made for A(Ion) < 50 and A(Target) > 4, which make up nearly 30,000 of the training observations. Hydrogen and helium targets suffer the greatest errors, particularly for heavy ions with large stopping powers, and possibly pointing to more complex non-linear physical relationships in this regime. The extraordinary power of the model is observed when comparing the predicted stopping power as a function of energy against existing experimental data points. Not only do the predicted curves correspond closely to those of the true values, but the model is able to generalise across target elements, compounds, mixtures, alloys and polymers; in solid, liquid and gaseous states; for a wide range of ion masses. Although difficult to evaluate fully due to a difference in methods and evaluation benchmarks, the regressive error of the model (2.1%) could be considered nearly half that of the leading interpolant method, SRIM (4.0%); and the fully blind predictions of the model not far behind (6.6%). The investigation presented in this paper clearly shows how the benefits of machine learning methods and big data analysis may begin to provide new and more accurate approaches to decades-old problems in physics.

Resume : In recent years, diamond detectors have been widely developed. Wide band gap (5.5 eV) and high resistivity (up to 1014 Ω∙cm) together with high transport parameters of non-equilibrium current carrier give possibility for such detectors to be used up to a temperature – 300 °C with no serious change in their characteristics. The paper presents the results of HPHT single-crystal diamond substrates IIa type characterization for particle detectors. The used diamond substrates [(100), with size 4 × 4 mm and with thickness 0.5 mm] were produced by company “New Diamond Technology”. The diamond substrates were investigated by X-ray diffraction, Fourier transform infrared spectroscopy and by atomic force microscopy. It has been shown that substrates have significant crystalline perfection. No crystallites inclusions with a different orientation were detected. At rocking curves measuring, no physical broadening was detected. The dislocation density in the current substrates is at a level below of the method sensitivity < 103 cm-2. The nitrogen and boron concentrations in the substrates were estimated at 10 and 50 ppb, correspondently. To create a test detector, contacts (3.5 × 3.5 mm2) based on Pt (thickness – 150 Å) were applied to both substrate sides. Deposition was made through a metal mask using ion-plasma sputtering. At a next step, the charge transport properties were investigated by alpha spectrometry method. For this, the dependence of the charge collection efficiency versus bias voltage under irradiation with α-particles (5.499 МeV) from 238Pu and different polarities of the bias voltage on the detector was measured. The obtained results were correlated with the deep centers parameters investigation by the DLTS method.

Resume : The single-crystalline Chemical Vapor Deposition (scCVD) diamond device is considered as a prospective candidate for future particle detector due to its excellent electronics, mechanical and thermal properties. However, a comprehensive model that can characterize the intrinsic diamond detector is not available. Hence, we develop a model which is applied in Technology Computer Aided Design (TCAD) simulation program. The validation of the model is conducted by evaluation of an intrinsic diamond detector. The substrate for detector is ElementSix diamond with a thickness of 500 μm. The detector shows an excellent Charge Collection Efficiency (CCE) ≈ 97.5% at room temperature with energy resolution 0.7%. Application of diamond in general electronics application is quite new. Therefore, the related references still do not agree about some essential characteristics of the diamond device. The characteristics that become the main focus of our investigation are the mobility of carriers and effective charge density of the bulk. Those two properties are crucial to define the distribution of electric field, drift velocity of charge-carriers and CCE. In this work, fitting the results of the numerical calculation to experimental data allow us to extract the main parameters of diamond. We present a model that apply double-Schottky contacts model with an effective carrier concentration of 1010 /cm3 and carrier mobility of 2559 cm2/V.s (2205 cm2/V.s) of holes (electrons) to reproduce experimental data of the diamond detector. With the model, we also conduct simulation to design a diamond detector that may generate charge amplification effect. Compared to silicon detector, diamond detector generates lower signal amplitude due to its wide energy gap. In order to produce amplification effect, the detector should generate high electric field. Short needle structures with diameter of 4 µm on a bulk diamond can improve more than 60% of electric field. Based on our simulation under few hundreds Volt of bias voltage, this diamond can produce electric field that exceed threshold value of 0.3 kV/cm. Therefore, this structure may help to realize a new thick substrate intrinsic diamond detector with carrier multiplication effect.

Resume : Attempts to synthesize wafer-scale single-crystal diamond have recently resulted in the successful demonstration of a disc with a diameter of ~ 3.5 inch and a total weight of 155 carat created by heteroepitaxial nucleation and growth on Ir/YSZ/Si(001) [1]. Parallel activities on (111)-oriented substrates have revealed that similar improvements in structural quality can be obtained by growth of thick samples for this crystal direction, too [2]. In order to assess the future potential of the obtained homoepitaxial diamond for electronic applications detailed studies of its carrier transport properties are needed. In this presentation, the variation of carrier lifetime and trapping with dislocation density will be investigated in few millimeters thick homoepitaxial diamond layers cut in the growth direction. For carrier lifetime investigation two photon excited (350 nm) electron-hole pair recombination was probed using either delayed 1064 nm probe or time resolved exciton photoluminescence. Drastic decrease of dislocation density in growth direction from 1010 to 107 cm-2 correlated well with increasing differential transmission lifetime and exciton decay time by two orders of magnitude (0.2-10 ns). Moreover, the impact of dislocation on the ambipolar diffusivity was investigated by light induced transient technique to provide excitation and dislocation density dependent values of the diffusion length. [1] M. Schreck, S. Gsell, R. Brescia, M. Fischer, Sci. Rep. 7, 44462 (2017). [2] B.-C. Gallheber, M. Fischer, M. Mayr, J. Straub, and M. Schreck, J. Appl. Phys. 123, 225302 (2018).

Resume : To provide a post-accident monitoring system which can survive after the severe accident of nuclear reactor, we developed a high temperature and radiation hard diamond sensor and transistors. Stable operation of the diamond FET at 300 degC and higher and radiation resistance performance of >3 MGy were both achieved. The stable operation of FET was confirmed up to 500 °C, which is the measurement upper limit of the measurement apparatus. As for the detector, the combination of MIM and pin type achieved the 7 orders of dynamic range which is required for the containment atmospheric monitoring system (CAMS). At present, prototype development of diamond CAMS including the development on monolithic IC component technology for diamond ICs are started utilizing successful research activities on diamond detectors and transistors. Radiation hard CAMS with diamond detector and IC will appear in the near future.

Resume : The study of diamond crystallization in various systems at high pressures and high temperatures is of great interest in connection with the study of mechanisms of nucleation and crystal growth and the possibility of obtaining diamond single crystals with different properties. The experiments on diamond crystallization in Fe-Co-C were carried out at high pressure and high temperature in large volume cubic high pressure apparatus CS-VII. A cubic container with dimensions of 58x58x58 mm was used. The Mg additives used in the experiments were 5 wt.% and 10 wt.%. The growing process was carried out by the temperature gradient method under pressure of 6.0-6.5 GPa and a temperature of 1420-1500 °C. It was established that adding of 10 wt. % Mg leads to the capture of boron impurities by grown crystal. Boron content in grown crystals increases up to 1.4•1016 cm-3. Increasing of magnesium content in the growth system based on Fe-Co from 5 to 10 wt. % leads to a change in the degree of diamond single crystals faces development; for crystals obtained with a large magnesium content, the tetragon-trioctahedron faces {311} are wedged out. Increasing of magnesium content in the growth system stabilizes the growth of the octahedron and the cube faces, slowing their growth and contributing to their area development.

Resume : In this paper, we propose a new approach to enhance the electrical and optical performances of thin diamond-like carbon (DLC) transparent electrode films using metallic nanoparticles (Au, Ag and Ti). The proposed approach can offer the benefits of improved optical behavior and reduced resistance values. Our study shows that the proposed design provides the possibility for modulating the conductivity and the optical absorbance in the DLC films, which leads to an improved performance of the transparent electrode. This concept suggests achieving the dual role of an appropriate transparency behavior and enhanced resistivity values. Furthermore, a new hybrid approach based on metaheuristic optimization and numerical simulation is proposed to estimate the better compromise between the transparency behavior and resistivity value of the amended transparent electrode film. Therefore, the optimized transparent electrode film using metallic nanoparticles paradigm pinpoints a new path toward high-performance transparent conducting electrodes for photovoltaic and sensing applications.

Resume : In connection with the development of industrial technology for the production of diamond single crystals with a controlled defect-impurity composition, the study of mechanical properties is an urgent scientific task. For this purpose an indentation model was developed, in which not only the sample, but also the indenter are deformed elastically-plastically. On the basis of this model, a method for determining the yield strength of the sample and indenter has been developed, in which the theoretical equation of the indentation model are supplemented by equation that use the experimental values of the effective indentation angle in the sample and the measured Meyer hardness values. The model generalizes the well-known Johnson model and was applied to determine the diamond hardness with a diamond indenter and description of the characteristics of diamond deformation at a temperature of 900 °C. On the basis of the proposed model, an approximate estimate of the average deformations in the field of the contact between sample and indent was carried out and a comparison was made with the mechanical properties of natural diamonds. The obtained results indicate that the values of microhardness of diamonds grown by the temperature gradient method, as well as the mechanism of their deformation, do not differ significantly from the properties and mechanisms of plastic deformation of natural diamonds.

Resume : The first-principle studies with the use of density functional theory and slater half-occupation technique (DFT-half) were performed to evaluate the electronic properties of modified boron-doped diamond (BDD) surfaces. BDD surfaces were modified by carboxyl linkers to archive biofunctional surfaces effective towards covalent protein grafting. The 4-aminobenzoic, 4-azidobenzoic acids and glutaraldehyde were particularly studied. Calculations of density of states (DoS), work functions values, electron transmission pathways and I/V curves of BDD surfaces were conducted using software package QuantumATK 2019.03 from Synopsys. The general gradient approximation exchange-correlation (GGA) was used for the description of energy functions. The optimized norm-conserving, Vanderbilt pseudopotential basis set was applied. The results showed that carboxyl modified BDD surfaces exhibit lower electron density (DoS) on the plane passing thanks to the linkers applied in this work. The BDD donates electrons to linkers, resulting in cross-sectional tunnelling of charge. The corresponding electron pathways revealed a high probability of intermolecular charge transfers, which has demonstrated efficient diffusion to the electrode, due to the high in-plane surface charge transfer. Analysis of structure versus bias potential in the range from -1.0 to 1.0 V revealed that the charge transport is not symmetrical. Moreover, I-V curves revealed nonlinear diode-like behaviour followed by a typical electron saturation region attributed to the limited charge velocity. Acknowledgement: The authors gratefully acknowledge financial support from National Centre for Science and Development Techmatstrateg No. 347324.

Resume : Brain Computer Interface (BCI) offers a way to restore neuronal dysfunction due to degenerative diseases or accidents. Thus it becomes possible to restore vision with retinal implant, or to offer a way for tetraplegic to control a robot by thinking with electrodes implanted in the cortex. Main limitation of these systems is their stability. After several weeks of implantation, some modification can appear such as swelling of the passivation polymers thus inducing current leakage, or degradation of the electrode material. Moreover neuronal prostheses are poorly accepted by tissues and a glial reaction may appear at the vicinity of the implant. Hence for future generation of implants it will be crucial to limit glial reactions and fabricate a full hermetic implant. Several research teams proposed to protect the metallic tracks by encapsulating in multilayers of in-organic materials like AL203 or TiO2 obtained by ALD. But in case of pin holes or adhesion problems between each layer, metallic parts will not be fully protected. To overcome these issues we propose to fabricate a full hermetic diamond implant. To assess this new concept, on ERC NEURODIAM we develop full diamond strip and test on ageing set-up and validate technology to achieve soft full diamond implant. This work is supported by European Research Council (ERC NEURODIAM). www.NEURODIAM.eu

Resume : In the future, closed-loop, implantable neuromodulation devices will not only be able to treat conditions using neural stimulation but will assess the efficacy of treatment via electrical recording and biosensing. Such devices must be based on stable neural/electrode interfaces. Carbon fiber microelectrodes have been used extensively for neural recording and neurochemical sensing. They do not, however, possess suitable electrochemical properties for neural stimulation. Conductive diamond has an established pedigree of biocompatibility, electrochemical stability and high resistance to fouling. Diamond has also been successfully employed for neural stimulation, recording and biochemical sensing. The hardness of diamond, however, is not a good match for brain tissue and is likely to cause tissue damage. Here we report on a hybrid diamond/carbon fibre electrode by incorporating microscale films of diamond on 7 µm diameter carbon fibers. This hyrbrid electrode combines the electrochemical benefits of diamond with the mechanical compliance and small size of carbon fibers. We have grown nitrogen-included ultrananocrystalline diamond on the tip of carbon fibers by microwave plasma assisted chemical vapour deposition. After a covalent pre-seeding method to protect the carbon fiber during growth of the diamond, film growth progressed in stages exhibiting a mixture of nanodiamond films and graphitic carbon nanowalls. The specific capacitance of the resulting hybrid electrodes exhibited a 238 fold capacitance increase rendering them safe for neural stimulation despite being small in diameter. Furthermore, we demonstrate that the electrodes retains excellent single-neurons recording properties, in vivo, and the capability to perform high sensitivity electrochemical dopamine detection. With these hybrid electrodes the three principle functions of a neuromodulatory implant ( stimulation, recording and chemical detection) are possible in the same anatomical location and at the level of a single neuron. Such electrodes are needed as components of the next generation of miniaturized, smart, closed-loop implants.

Resume : The surface chemistry of diamond plays a crucial role for the electronic properties of the material, i.e. the electron affinity of the surface[1] or the control of charge states of lattice defects[2]. The establishment of electron withdrawing or donating surface groups influences the charge state of lattice defects close to the surface. Additionally, the band structure of the material is strongly depending on the surface termination. Therefore, the homogeneous and stable surface functionalization with suitable atoms or groups is key for the fabrication of diamond based devices for e.g. photocatalytic or quantum applications. Here we report on the efficient surface termination of diamond using a wet-chemical fluorination method as well as the treatment with ozone at low temperatures. These treatments lead to highly functionalised surfaces that enable the stabilisation of negative charge states of lattice defects as well as the control of the electron affinity of the surface. Characterisation using e.g. solid-state NMR techniques and Boehm titration have been used to analyse the functionalised materials qualitatively and quantitatively. This research has received funding from the European Union’s Horizon 2020 Programme (Grant Agreement no. 665085, DIACAT, www.diacat.eu) and Deutsche Forschungsgemeinschaft under grant KR3316/6-2. References [1] D. Zhu, J. A. Bandy, S. Li, R. J. Hamers, Surf. Sci. 650, 295 (2016) [2] S. Cui, E. L. Hu, Appl. Phys. Lett. 103, 051603 (2013)

Resume : Diamond is an excellent material for advanced electronics and sensors operating under extreme conditions. However, its surface contains many defects that should be removed to increase its performance. Three diamond samples, synthesized using heteroepitaxial growth method on sapphire substrate, were used for this experiment. In order to remove the defects on the surface, Chemical Mechanical Polishing (CMP) treatment was applied to the samples following to conventional mechanical polishing with diamond abrasives. After the treatment, the secondary electrons (SE) signals and in situ SEM-cathodoluminescence (SEM-CL) data has been detected and collected in only one scan of the electron beam and corelated to highlight both the material quality and the sample history. X-ray reflectivity measurements were performed to obtain the mass density and average surface roughness of the surface region while grazing incidence and high-resolution X-ray diffraction measurements were used to assess the modifications of the structure by the CMP process. X-ray photoelectron spectroscopy investigations were used to check if the CMP process introduces contaminants of the diamond surface. The results showed that both the surface morphology and defects size and density were significantly reduced by the CMP process, while the surface remained the same, without new chemical elements or contaminants.

Resume : Diamond is a semiconductor material that not only has physical properties superior to other materials, but also can withstand harsh environments such as high temperature and high radiation. We have studied diamond MESFET for the application of pre-amplifier of radiation detectors worked in nuclear reactors. However, the diamond MESFETs fabricated so far are small MESFETs with a gate width of 0.62 mm, and drain current of 0.1 mA. Therefore, in order to obtain high drain current and transconductance with low threshold voltage, we fabricated diamond MESFETs with long gate width. A boron-doped diamond layer was grown by plasma CVD method on 4 mm square high temperature high pressure (001) Ib diamond substrates as a drift layer of MESFET. Lateral diamond MESFETs with different gate width were fabricated on the drift layer. By optimizing the device process, diamond MESFETs with 30 mm gate width have been realized. From the electrical characteristics of these diamond MESFETs, by increasing the gate width from 0.62 mm to 30 mm, the maximum drain current increased from 0.28 mA to 26 mA. The transconductance also increased from 9.8 uS to 1.2 mS. Thus, the maximum drain current and transconductance of the 30 mm gate width MESFET were nearly 100 times as large as those of the conventional small MESFET. In addition, at 300 ° C , the drain current increased to 0.5 A at the source-drain voltage of -22.5 V.

Resume : The electronic properties were investigated of D2/CH4/B2H6 of thin diamond film, synthesized by Microwave Plasma-Assisted Chemical Vapour Deposition (MWPACVD). The influence of doping level on electronic properties was studied using by Hall mobility measurements, laser-induced breakdown spectroscopy (LIBS) Raman spectra, spectroscopic ellipsometry, and X-Ray Photoelectron Spectroscopy (XPS). Moreover, and the brief electrochemical study was carry on. For the plasma containing deuterium, an increased dissociation of B2H6 and intense boron-radicals production was confirmed. In consequence, a higher doping level of diamond films was observed by LIBS. Deuterium modifies the mechanism of boron incorporation into thin films leading to increased boron concentration. Lower concentrations of sp2 phases and CH defects have been noticed in the films deposited in the plasma with deuterium than with hydrogen addition. The increase in the carrier concentration and the decrease in the Hall mobility for the BDD samples grown in deuterium was registered. BDDD electrode exhibits extraordinary peak-to-peak separation values (ΔE) in both [Ru(NH3)6]2+/3+ and ferricyanide/ferrocyanide redox system. The ΔE value obtained for 10 mV s-1 Ru(NH3)62+/3+ is almost 59 mV, which is expected for Nernstian one-electron reaction. The separation between the oxidation and reduction peak potentials increases with rising scan rate from 59.4 eV to 84.4 eV for Ru(NH3)62+/3+ and from 63.0 eV to 78.4 eV for Fe(CN)63-/4- redox system. This work was supported by the Polish National Science Centre under the Grants Nos. 2017/01/X/ST7/02045 and The National Centre for Research and Development Techmatstrateg, 347324/12/NCBR/2017. The DS funds of Faculty of Electronics, Telecommunications.

Resume : Low defect smooth substrates are essential to achieve high quality diamond epitaxial growth and high perfor- mance devices. The optimisation of Ar/O2/CF4 Reactive Ion Etching plasma treatment for diamond substrate smoothing and its effectiveness to remove sub-surface polishing damage is characterised. An O2/CF4 RIE process and the effect of different process parameters (ICP and platen power, pressure) were initially exam- ined. This process however still produced a detrimental effect to surface roughness, with etch pits across the surface of the sample. The addition of Argon to the process achieved near-zero surface pit density and reduced roughness by 20 to 44% after 6 and 10 μm etching. Iterative HRXRD measurements provided a non- destructive tool to examine the effectiveness of polishing damage removal, in this case reduced after removal of 6 μm of material from the surface of the diamond substrate with the smoothing treatment.

Resume : We investigated the electronic transport properties of diamond-on-graphene heterojunctions. The mechanical transfer of the free-standing diamond nanosheets onto graphene is grown by CVD on a Si/SiO2 substrate allowed us to fabricate heterostructure devices [1]. We measured the current-voltage characteristics of the devices versus temperature, finding behavior consistent with thermally activated transport over a barrier of 20 meV. At elevated temperatures, we observed a barristor-type behavior of our lowly doped diamond-on-graphene device, which showed an optimal functionality around 100C. Upon reaching 300C the barristor behavior diminished, most likely due to thermally excited charge carriers reducing the effects of a Schottky barrier. Low-temperature measurements of our sample exhibit an unusual transition from variable range hopping transport (~230K to 16K) to another type of transport (~16K to 10K) before reaching the quantum tunneling limit (10K). Varying the doping level of boron in diamond films leads to variations in device behavior. Our latest results will be discussed. [1]. Bogdanowicz, Robert, et al. "Growth and Isolation of Large Area Boron‐Doped Nanocrystalline Diamond Sheets: A Route toward Diamond‐on‐Graphene Heterojunction." Advanced Functional Materials 29.3 (2019): 1805242. Acknowledgments The authors gratefully acknowledge financial support from the Polish National Science Centre under Grant No. 2016/21/B/ST7/01430, 2016/22/E/ST7/00102 and National Centre for Science and Development Grant Techmatstrateg No. 347324. This work was partially supported by the Science for Peace Programme of NATO (Grant No. G5147). The DS funds of the Faculty of Electronics, Telecommunications, and Informatics of the Gdansk University of Technology are also acknowledged.