Surface photovoltage spectroscopy for defect investigation of diamond

Defect related transition energies and charge transfer along grain boundaries were studied in polycrystalline diamond by using a new type of mirrorless double prism monochromator based on fused silica and by introducing modulated transient surface photovoltage spectroscopy. Polycrystalline diamond served as a model system containing small crystallites at the seed and large crystallites at the growth sides. Illumination was performed between 0.4 and 7.3 eV for seed and growth side orientations of the sample which allowed for homogeneous excitation of defect related transitions across the sample and for variation of the penetration depth under fundamental absorption in diamond. Photogenerated electrons were separated towards the seed side independently of the defect related transition for excitation below the range of the bandgap of diamond. Under strong absorption, photogenerated electrons were preferentially separated towards the surface. We found that photogenerated electrons are transferred faster than photogenerated holes along grain boundaries and that photogenerated holes are preferentially trapped at defects in crystallites. The enhancement of electron transfer via grain boundaries also explains the observed preferential electron trapping at surface states of diamon

New insights into non contact reflectance IR mapping of teeth

Teeth are made of highly mineralized tissues that withstand years of daily usage. Their mechanical properties have been studied at all length scales with ageing but manly small areas have been the focus of high sensitivity chemical property quantification. A comprehensive, spatially resolved examination across centimeter sized tooth specimens is needed to expand our comprehension of young versus aged teeth. Specular Reflectance Fourier Transform Infrared Spectroscopy srFTIR is a nondestructive microscopy technique that can be used to characterize the chemical composition of mineralized surfaces. This technique provides spatially resolved chemical absorption information, making it useful to study both organics and mineral in visibly accessible tooth tissues. Highly polished dehydrated cross sectional surfaces of bovine and human teeth were srFTIR imaged, and spectra were processed using a Kramers Kronig Transformation to generate absorbance like chemical maps. Results are comparable with the well established FTIR Transmission and Attenuated Total Reflection ATR methods. Maps of multiple amp; 120584;3 phosphate vibrations, amp; 120584;2 carbonate, and amide I reveal insights into structural and chemical variations across dentine. Young bovine teeth exhibited many chemical and structural similarities to old, partially sclerotic human teeth, affirming their use as proxies in dental research. This work highlights the capability of specular reflection infrared spectroscopy imaging to reveal spatial chemical information and expand our understanding of tooth microstructure and composition variation

Optics for terawatt scale photovoltaics review and perspectives

Photovoltaics, a mature technology, is set to play a vital role in achieving a carbon free energy system. This article examines the pivotal role of optics in advancing photovoltaics. We identify key scientific research areas where the optics community can make significant contributions. We are guided by the central question How can optics facilitate the large scale deployment of photovoltaics necessary for decarbonizing our societies

Importance of Electrostatic Effects for Interpretation of X ray Photoemission Spectra of Self Assembled Monolayers

This paper reviews the relevant work regarding electrostatic effects in X ray photoemission from self assembled monolayers SAMs which are application relevant ultrathin molecular films, coupled over a suitable anchoring group to the substrate. Whereas, in most cases, the standard concept of chemical shift is fully sufficient to describe X ray photoelectron spectra of these systems, consideration of electrostatic effects is frequently necessary for their proper interpretation. Due to the insulator character of the SAM matrix, decoupled electronically from the substrate, the introduction of a dipolar sheet at the SAM substrate interface or within this matrix creates a potential discontinuity shifting the energy levels above the sheet with respect to those below it. This shift is reflected then in the matrix related spectra, resulting in shifts and splitting of the characteristic photoemission peaks. Several representative examples in this context are provided and discussed in detail. These examples and other relevant literature data underline the importance of electrostatic effects in photoemission and suggest that they should be considered on the equal footing as the chemical shift one

Electrostatic and Electronic Effects on Doped Nickel Oxide Nanofilms for Water Oxidation

An ideal water splitting electrocatalyst is inexpensive, abundant, highly active, stable, selective, and durable. The anodic oxygen evolution reaction OER is the main bottleneck for H2 production with a complex and not fully resolved mechanism, slow kinetics, and high overpotential. Nickel oxide based catalysts NiOx are highly active and cheaper than precious metal catalysts. However, rigorous catalyst tests and DFT calculations are still needed to rationally optimize NiOx catalysts. In this work, we combine plasma enhanced atomic layer deposition PE ALD and density functional theory DFT to address the role of dopants in promoting NiOx OER activity. Ultrathin films of NiOx doped with Zn2 , Al3 , and Sn4 presented improved intrinsic activity, stability, and durability for the OER. The results show a low to high catalytic performance of ZnNiOx lt; NiOx lt; AlNiOx lt; SnNiOx, which we attribute to an increase in the concentration of valence band VB holes combined with conduction band CB electron conductivity, characterized by electrochemical impedance spectroscopy EIS . The influence of doping on the electronic structure and catalytic activity was investigated using advanced characterization techniques and density functional theory DFT calculations PEB0 pob TZVP . DFT complements the experimental results, showing that the dopant charge states and orbital hybridization enhance the OER by improving the charge carrier concentration and mobility, thus allowing optimal binding energies and charge dynamics and delocalization. Our findings demonstrate the potential of PE ALD doped nanofilms NiOx and DFT to rationally design and develop catalysts for sustainable energy application

Fragile spin liquid in three dimensions

Motivated by the recent appearance of the trillium lattice in the search for materials hosting spin liquids, we study the ground state of the classical Heisenberg model on its line graph, the trilline lattice.We find that this network realizes the recently proposed notion of a fragile spin liquid in three dimensions. Additionally, we analyze the Ising case and argue for a possible Z2 quantum spin liquid phase in the corresponding quantum dimer model. Like the well known U 1 spin liquids, the classical phase hosts moment fractionalization evidenced by the diluted lattice, but unlike those, it exhibits exponential decay in both spin correlations and interactions between fractionalized moments. This provides an instance of a purely short range correlated classical Heisenberg spin liquid in three dimension

Synthesis, structural characterization, and investigation of anti glioblastoma activity of copper complexes supported by bis pyrazol 1 yl acetate ligands functionalized with memantine

The new ligand bis 1H pyrazol 1 yl acetyl 3,5 dimethyladamantane 1 amide LMem was synthesized by conjugating the drug memantine with the bifunctional species bis pyrazol 1 yl acetic acid and used as supporting ligand of copper II and copper I complexes 1 7. In the synthesis of the CuI complexes, the lipophilic triphenylphosphine PPh3 and hydrophilic 1,3,5 triaza 7 phosphaadamantane PTA were selected as co ligands, in order to stabilize copper in 1 oxidation state and to confer different solubility properties to the corresponding metal complexes. The electronic and molecular structures of CuI and CuII coordination compounds were investigated by high resolution Synchrotron Radiation induced X ray Photoelectron Spectroscopy SR XPS , Near Edge X ray Absorption Fine Structure NEXAFS spectroscopy. The local structure around the copper ion sites was studied combining Density Functional Theory DFT modelling and X ray Absorption Fine Structure XAFS spectroscopy, in both X ray Absorption Near Edge Spectroscopy XANES and Extended X ray Absorption Fine Structures EXAFS regions. X ray diffraction XRD studies were carried out on suitable crystals to describe the molecular structure and the intermolecular contacts of the LMem ligand. Among all Cu complexes tested, compounds 4 and 5 exhibited potent antiproliferative and cytotoxic effects in U87, T98, and U251 glioma cell lines. These effects were associated with increased reactive oxygen species ROS production and mitochondrial dysfunction, as evidenced by mitochondrial depolarization and altered intracellular distribution. Furthermore, the cytotoxic activity of these compounds was shown to be Cu dependent, as it was effectively inhibited by the Cu chelator tetrathiomolybdate, confirming the essential role of copper in their mechanism of actio

Exploring Electronic States and Ultrafast Electron Dynamics in AlInP Window Layers The Role of Surface Reconstruction

AlInP 001 is widely utilized as a window layer in optoelectronic devices, including world record III V multi junction solar cells and photoelectrochemical PEC cells. The chemical and electronic properties of AlInP 001 depend on its surface reconstruction, which impacts its interaction with electrolytes in PEC applications and passivation layers. This study investigates AlInP 001 surface reconstructions using density functional theory and experimental methods. Phosphorus rich P rich and indium rich In rich AlInP surfaces are prepared with in situ monitoring of the process by reflection anisotropy RA spectroscopy and confirmed by low energy electron diffraction and photoemission spectroscopy. The experimental RA spectra closely match the theoretical predictions obtained by solving the Bethe Salpeter equation. It is shown that missing hydrogen on P rich surfaces and formation of In In 1D atomic chains on In rich surfaces introduce mid gap surface states that pin the Fermi level and induce band bending. Time resolved two photon photoemission measurements reveal ultrafast near surface electron dynamics for both P rich and In rich surfaces, demonstrating photoexcited electrons reaching the surface conduction band minimum and relaxing to mid gap surface states on about hundreds of fs. This work provides the most extensive AlInP surface analysis to date, allowing for more targeted surface and interface engineering, which is crucial for the optimization and design of III V heterostructure

Sb2S3 solar cells with TiO2 electron transporting layers synthesized by ALD and USP methods

Electronic characteristics were investigated for solar cells SCs based on FTO TiO2 Sb2S3 P3HT Au structure, employing TiO2 electron transport layers ETLs fabricated by two different methods ultrasonic spray pyrolysis USP and atomic layer deposition ALD . Regardless of the deposition method, both ALD and USP TiO2 exhibit the anatase crystal structure. The calculated crystallite sizes, derived from the 101 reflection of TiO2 layers using the Scherrer equation, show minimal variance between the two methods, with values 25 nm for USP and 30 nm for ALD TiO2, respectively. Optical band gaps Eg were found to be 3.31 eV and 3.35 eV for USP and ALD methods, respectively. Exploring the thickness series of ALD TiO2, ranging from 100 to 1000 cycles approximately 5 75 nm , solar cell performance was evaluated, with the highest power conversion efficiency PCE of 3.3 achieved using ALD TiO2 of 400 cycles approximately 30 nm thick . Notably, SCs featuring USP TiO2 ETL layers, with a thickness of approximately 35 40 nm, outperform their ALD TiO2 counterparts, improving PCE by 15 , recording 4.0 versus 3.3 , respectively. This superiority in PCE is attributed to the more favorable conduction band minimum CBM position of USP TiO2 relative to the Fermi level, as revealed in the band diagram. Specifically, a lower CBM spike at the USP TiO2 Sb2S3 interface indicates reduced recombination rates compared to those at the ALD TiO2 Sb2S3 interface. This study offers valuable insights into enhancing SC performance by optimizing deposition methods and synthesis parameters of ETL layer

R for Reactive Revealing Rhodium, Ruthenium, and Rhenium s Rare Oxides through X ray Absorption Spectroscopy

Discovering compounds that present transition metals with high oxidation states or reactive oxygen species, such as the oxygen centered radical, is of great scientific interest, as they have key applications as oxidizing agents, catalysts, or reaction intermediates. Due to the high reactivity of such chemical entities, experimental investigations of their electronic structures are limited. The study of small systems as models can be used to understand their properties and expand the applicability of related materials. This work aims to investigate highly oxidized transition metals, bringing a new perspective towards their electronic structure and properties. For that, X ray absorption spectroscopy, at the oxygen K and metal M3 or N3 edges of [MOn] molecular ions M transition metal, n integer , is used to identify the spectroscopic signatures of oxygen ligands and assign the oxidation state of the metal. The highly oxidized [MOn] gas phase species are produced by argon sputtering of a metal target in the presence of oxygen. The X ray absorption spectroscopy, performed in ion yield mode, is used here as a tool to directly probe the electronic ground state structure of the investigated samples, that are analysed in stable conditions in their lowest energy states. The highest oxidation state of rhodium is here presented for the first time in the trioxidorhodium VII cation, for which the rhodium M3 edge shows the chemical shift corresponding to its high oxidation state, while the oxygen K edge shows the spectral signature of oxo ligands. Further, the oxygen centered radical tetroxidoruthenium VIII cation and diradical tetroxidorhenium VII cation are here investigated by X ray absorption spectroscopy for the first time, where the oxygen centered singly occupied molecular orbitals are identified by a low energy transition at the oxygen K edge, which is suppressed upon hydrogenation. Computational studies corroborate the experimental observations, that will hopefully contribute to the scientific knowledge of these species and their oxidative propertie