Ing. Jaroslav Kuliček, Ph.D.

Doped diamond has found a commercial use for achieving durable and reproducible electrical measurements in atomic force microscopy (AFM). Yet so far it has not been used on self-sensing AFM probes due to thermally and mechanically sensitive integrated detection circuits. Herein, conventional microwave plasma chemical vapor deposition (CVD) is employed while taking advantage of thermal conductivity along the silicon AFM cantilever probe for growing high-quality B-doped nanocrystalline diamond film on the probe apex that is selectively seeded by dip coating in nanodiamond solution. By investigating various CVD process parameters, it is shown that the detection circuit remains functional up to 400 °C for 2 h deposition or up to 8 h at 300 °C. Scanning electron microscopy and Raman spectroscopy corroborate quality of the diamond coating and doping. The self-sensing probes are successfully tested in conductive AFM (C-AFM) regime and surface spreading resistance regime, showing linear response in current–voltage spectroscopy and capability of conductivity mapping on metals and semiconductor devices. In the results, prospects for stable C-AFM measurements when conventional optical detection is not suitable, such as on photosensitive materials or in probe-electron microscopy, are opened.

Solvated or hydrated electrons represent smallest possible anion, which can exist. Due to enormous redox activity these electrons, entrapped in solvent cage, have enormous potential in the field of chemical transformation. However, wide utilization of hydrated electrons is significantly restricted by the methods of their creation, which are either highly energy demanding or based on less probable two photons process. In this work, we propose a rationally designed plasmon active nanostructures coated with low work function material for efficient production and utilization of hydrated electrons. In such case, the coupled plasmon active nanostructure can efficiently convert photon energy in the energy of plasmon excited hot electrons. The electrons are subsequently injected in the low work function material (in this case scandium oxide), facilitating their transfer to surrounding electrolyte. Alternatively, the injected electrons can “wait” in the scandium oxide layer for additional plasmon triggering and injecting through two photons process. The creation of hydrated electrons was confirmed by various techniques, including fiber based optical spectroscopy and electronic paramagnetic spectroscopy. The redox potential of hydrated electrons was subsequently demonstrated in nitrogen reduction, where the 28.3 and 38.0 µmol·g−1·h−1 NH3 yield were reached in photo- and photoelectrochemical regimes respectively. Comparison with alternative method and materials, used for NRR performing in “photo-mode” (not based on hydrated electrons utilization) indicate the huge potential of the proposed structure and approach.

Combining diamond and two-dimensional materials is attracting increasing attention for synergic effects that have the best of both worlds. Applications range from electronics and quantum technologies to catalysis, energy conversion, and biosensors. Here, heterostructures based on hydrogenated diamond microcrystalline thin films with attached MoS2 nanosheets are formed by a single-zone annealing at atmospheric pressure. By varying the process parameters, MoS2 sheets are controllably synthesized in a vertical or horizontal orientation with respect to the diamond grain facets, which leads to a pronounced impact on the electronic and optoelectronic properties of the heterostructures. Raman, SEM, AFM, KPFM, and SKP analyses show the influence of the MoS2 orientation and thickness on the work function, surface potential, spatially and spectrally resolved photovoltage, and charge transfer kinetics. The aligned growth of MoS2 nanosheets and their properties are elucidated by molecular mechanics and time-dependent DFT calculations, which explain the mechanism of the assembly and the related optoelectronic effects in a straightforward way. The major switching point occurs precisely at 11 nm of the MoS2 thickness/length. The highest photoresponse of 350 meV and favorable charge transfer are observed for the vertical MoS2 arrangement on diamond, yet without a covalent bond. The results and theoretical model hint at broader implications beyond the MoS2-diamond system.

Nanodiamonds (NDs) are versatile, broadly available nanomaterials with a set of features highly attractive for applications from biology over energy harvesting to quantum technologies. Via synthesis and surface chemistry, NDs can be tuned from the sub-micron to the single-digit size, from conductive to insulating, from hydrophobic to hydrophilic, and from positively to negatively charged surface by simple annealing processes. Such ND diversity makes it difficult to understand and take advantage of their electronic properties. Here we present a systematic correlated study of structural and electronic properties of NDs with different origins and surface terminations. The absolute energy level diagrams are obtained by the combination of optical (UV-vis) and photoelectron (UPS) spectroscopies, Kelvin probe measurements, and energy-resolved electrochemical impedance spectroscopy (ER-EIS). The energy levels and density of states in the bandgap of NDs are correlated with the surface chemistry and structure characterized by FTIR and Raman spectroscopy. We show profound differences in energy band shifts (by up to 3 eV), Fermi level position (from p-type to n-type), electron affinity (from +0.5 eV to -2.2 eV), optical band gap (5.2 eV to 5.5 eV), band gap states (tail or mid-gap), and electrical conductivity depending on the high-pressure, high-temperature and detonation origin of NDs as well as on the effects of NDs' oxidation, hydrogenation, sp(2)/sp(3) carbon phases and surface adsorbates. These data are fundamental for understanding and designing NDs' optoelectrochemical functional mechanisms in diverse application areas.

Solely light-induced water splitting represents a promisingavenuefor a carbon-free energy future, based on reliable energy sources.Such processes can be performed using coupled semiconductor materials(the so-called direct Z-scheme design) that facilitate spatial separationof (photo)excited electrons and holes, prevent their recombination,and allow water-splitting half-reactions proceeding at each correspondingsemiconductor side. In this work, we proposed and prepared a specificstructure, based on WO3g-x /CdWO4/CdS coupled semiconductors, created by annealing of a commonWO(3)/CdS direct Z-scheme. WO3-x /CdWO4/CdS flakes were further combined with a plasmon-activegrating for the creation of the so-called artificial leaf design,making possible complete utilization of the sunlight spectrum. Theproposed structure enables water splitting with high production ofstoichiometric amounts of oxygen and hydrogen without undesirablecatalyst photodegradation. Several control experiments confirm thecreation of electrons and holes participating in the water splittinghalf-reaction in a spatially selective manner.

Diamond nanoparticles so-called nanodiamonds (NDs) have recently experienced raising scientific interest due to interesting optical and electronic properties, nontoxicity, biocompatibility, and large surface area. Another significant feature of NDs is the versatility of the surface chemistry, where various functional groups can be attached. This provides an excellent platform for adjusting NDs properties and functions for many applications including in photovoltaic devices. Herein, high-pressure high-temperature (HPHT) NDs are tested as charge extraction material in organic solar cells using various surface chemistries: as-received (HPHT ND-ar), oxidized (HPHT ND-O), and hydrogenated (HPHT ND-O-H) NDs. Despite the high work function values (approximate to 5.3 eV) of HPHT ND-ar and HPHT ND-O, which make these materials normally suitable for hole extraction, devices made with them failed. In contrast, the work function decreases upon hydrogenation (approximate to 4.5 eV) of the beforehand oxidized NDs, making them interesting for electron extraction. By employing such HPHT ND-O-H for electron extraction layers, PBDB-T:ITIC-based devices reach 77%, while PM6:Y6-based devices reach even 85% of the performance when process on standard ZnO electron transport layers. Improvement of the film-forming qualities of this new electron extraction material is expected to further improve the performance.

Plasma provides specific adjustment of solid-state surface properties offering an alternative to high temperature treatment. Herein, hydrogen plasma treatment of monocrystalline (0001) ZnO surface is studied in an inductively coupled plasma reactor with reduced capacitively coupled plasma mode. The crucial role of electrical grounding of the sample holder for plasma etching and related changes in the morphology, optical, and electrical properties of surfaces exposed to electron and ion bombardment are explained. The effects on the chemical composition of the surface are analyzed by X-ray photoelectron spectroscopy (XPS), optical properties by photoluminescence spectroscopy, topography, roughness, and surface measurements by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). All methods show altered ZnO surface properties before and after plasma treatment strongly depending on the electrical potential of the holder.

Organic-based photovoltaic devices emerged as a complementary technology to silicon solar cells with specific advantages in terms of cost, ease of deployment, semi-transparency, and performance under low and diffuse light conditions. In this work, thin-film boron-doped diamond (B:NCD) electrodes are employed for their useful op-tical, electronic, and chemical properties, as well as stability and environmental safety. A set of oligothiophene perylene diimide (nT-PDI) donor-acceptor chromophores is designed and synthesized in order to investigate the influence of the oligothiophene spacer length when the nT-PDI molecule is attached to a B:NCD electrode. The chromophores are anchored to the diamond surface via diazonium grafting followed by Sonogashira cross -coupling. X-ray photoelectron spectroscopy shows that the surface coverage decreases with increasing oligo-thiophene length. Density functional theory (DFT/TDDFT) calculations reveal the upright nT-PDI orientation and the most efficient photogenerated charge separation and injection to diamond for elongated oligothiophene chains (8T-PDI). Yet, the maximum photovoltage is obtained for an intermediate oligothiophene length (3T-PDI), providing an optimum between decreasing transport efficiency and increasing efficiency of charge separation and reduced recombination with increasing oligothiophene length. Holes transferred from nT-PDI to diamond persist there even after the illumination is switched off. Such features may be beneficial for application in solar cells.

Understanding and controlling the optical and electrical properties of the solar cells, from the absorber layer to the complete devices, is one of the key elements for engineering high-efficiency devices. Such an understanding, especially the correlation between device performance and optical-structural-morphological properties of film stack, is still lacking in the field of cadmium selenide/telluride alloy-based solar cells. Here, we report confocal Raman and photoluminescence microscopy study results obtained through exciting both film and glass sides of cadmium selenide and cadmium telluride bilayer device stacks treated with cadmium chloride. We show that the device stack, especially the glass side, losses significant charge carries to the recombination arising from uniformity issues related to material composition, energetics, and defects. Furthermore, there is a high energy tail emission peak originating from CdTe, and CdSe can suppress it significantly under CdCl-2 treatment.

Properties and functions of various ZnO materials are intensively investigated in biological systems for diagnostics, therapy, health risks assessment as well as bactericidal and decontamination purposes. Herein, the interface between ZnO and biological environment is studied by characterizing adsorption of bovine serum albumin (BSA) and fetal bovine serum (FBS) using atomic force microscopy with CF4-treated tips. Similar molecular morphologies (thickness around 2 nm) yet different binding forces to ZnO (10–25 nN) are observed. These observations are corroborated by atomic scale simulations of BSA on (0001) ZnO surface using force-field method and showing rearrangements of Zn surface atoms. Such binding may have an impact also on other properties of ZnO–BSA complex.

MXenes have drawn considerable attention in the past decade, thanks to their attractive properties such as metallic conductivity and surface hydrophilicity. While MXenes form highly stable dispersions in water, it can act as a limitation for certain applications such as photoactive layer in photovoltaic devices. In this work, delaminated MXenes of aqueous solution type Ti3C2 were prepared first, and then we have used a solvent-exchange technique to prepare suspensions of MXenes in three polar aprotic solvents namely, DMSO, DMF and NMP. Upon spin-coating under the same conditions, each solvent variation yields a different thin film morphology – in terms of particle size and surface coverage, as evidenced from AFM investigations. While the MXenes in DMSO yielded large aggregated particles with µm-sized islands in the film, MXenes in DMF and NMP were found to form films with well-dispersed MXene sheets in the size range 250 nm-50 nm and 80 nm-10 nm, respectively. This study also provides additional insights into the microstructure and opto-electronic properties of the MXene thin films using correlative Raman microscopy and photoluminescence spectroscopy. The information provided by this study on the variation in the properties depending on the solvent used to process and spin-cast the films are important for evaluating MXenes in thin film device applications.

Zinc oxide nanoparticles have been synthesized using non-thermal atmospheric pressure plasma (ZnO-NTP). We investigated the behavior of these ligand-free as a colloid suspension using different solvents, from deionized water to physiological saline and microbial culture broth. We found that the zeta potential of ZnO-NTP became more negative after exposure to microbial culture broth relative to water, which suggests increased colloid stability. Photoluminescence spectra of ZnO-NTP were similar regardless of liquid type, yet optical and fluorescent images of samples showed different agglomeration behavior depending on liquid type. Scanning electron microscopy images revealed large agglomerates of ZnO-NTP interacting with the surface of bacteria cells, ranging in size from 200 nm up to 2 µm. We also studied effect of sub-lethal concentrations of ZnO-NTP on bacteria under illumination. There was no significant difference in viable bacteria concentration after 24h exposure to 10 µg/mL ZnO-NTP relative to untreated control irrespective of sample illumination.

Perovskites are one of the most intensively studied photovoltaic materials nowadays. Microscopic studies can provide useful information about material roughness, conductivity, structure, mechanical and opto-electronic properties as well as about kinetic effects from short to long time scale for understanding and improving the photovoltaic performance. Here, time-resolved photovoltage was measured by Kelvin probe in the dark and under white light illumination. Morphology was characterized by optical and atomic force microscopy. We identify the impact of charge transporting layers (CTLs) on structural and opto-electronic properties of MAPbI3 perovskite with different ratio of MAI and PbI2.