Institute of High Pressure Physics

We analyze the thermal and electrical characteristics of the metasurface composed of a coplanar interdigital array of the graphene microribbons (GMRs) connected by nanobridges (NBs). These nanobridges could be implemented using graphene nanoribbons (GNRs) or black-arsenic-phosphorus (b-AsP) nanostructures. When a bias voltage applied between neighboring GMRs, it induces electron and hole two-dimensional systems within the GMRs, leading to thermionic currents that flow through the connecting NB resulting in the self-heating effect. This self-heating effect increases the thermionic currents, creating an effective positive feedback loop between the carrier effective temperature and the injected currents, and the bias voltage. This mechanism may lead to thermal breakdown enabling threshold behavior of current–voltage characteristics and yielding an S-shaped response. The devices based on the GMR/GNR and GMR/AsP metasurface structures can serve as fast voltage-controlled current switches, sensors, thermal terahertz and infrared sources, and among other applications.

Pseudomorphic growth of a UV-C laser diode heterostructure is demonstrated on a bulk AlN substrate by MBE. While stimulated emission is not observed under current injection, spontaneous emission at 265 nm is observed. Current densities up to 800 A/cm2, >5 orders on/off ratio at ±5 V, and a low differential on-resistance of 2.6 mΩ cm2 at the highest current density are achieved. The heterostructure has a high refractive index waveguide core surrounded by n- and p-cladding layers for mode confinement at 270 nm to facilitate edge emission and collection of photons. Edge-collection electroluminescence of the devices is achieved by cleaving the fabricated devices along the m-plane of the wurtzite crystal. Electrical injection results in the emission of high-energy 4.7 eV photons that are collected from the cleaved edge of the heterostructure, corresponding to the optical bandgap of the AlGaN active region. The contribution of power dissipation across the n- and p-regions of the diode is discussed. The n-contact resistance to n-AlGaN is identified as the largest contributor to the series resistance of these devices. Reduction of these resistances will allow these heterostructures to achieve lasing in the future.

Bone grafting in equine medicine offers a promising contribution to treating orthopaedic developmental diseases and chondral, osteochondral and segmental bone defects. Among grafts, synthetic bone substitutes-alloplastics-show favourable biological properties addressing numerous limitations presented by autografts, xenografts and allografts. To compile and disseminate clinical data and research findings from existing publications on the use of alloplastics in horses. Systematic review. Following Preferred Reporting Items for Systematic Reviews and Meta-analysis 2020 guidelines, literature searches were conducted in PUBMED, Scopus and Web of Knowledge. The inclusion criteria covered case reports and research articles on the use of alloplastics in the horses. The selected research articles were grouped considering clinical and experimental studies. A risk of bias assessment was performed for the research articles. Use of synthetic bone substitutes in horses has been described in 17 publications to date, grouped as 5 case reports and 12 research articles. The latter were subdivided by main study issue-as involved subchondral cystic lesion, aneurysmal bone cyst and chondral, osteochondral or segmental bone defects. The four treatment models were distinguished and described. The lack of clinical and alloplastics data in some records. Clinical evaluation in some studies was inconsistent or incomplete. A risk of bias particularly arises from missing data, outcome measurement and the reported results. In equine medicine, hydroxyapatite, calcium phosphate and β-tricalcium phosphate were the leading alloplastics applied. When applied alone, they demonstrated osteoconductive and osteoinductive properties, while the addition of biologically active additives-especially autologous bone marrow-enhanced these biological properties toward osteogenic and chondrogenic effects. Treatment outcomes were generally favourable, although segmental bone defect treatment requires considering the limitations associated with weight-bearing effects. These findings suggest alloplastics in horses may be particularly beneficial for treating certain bone diseases.

The paper presents a systematic investigation of point defects in a series of high-quality GaN crystals grown through halide vapor phase epitaxy (HVPE) and ammonothermal synthesis (AM). The GaN crystals were characterized using positron annihilation spectroscopy (PAS), along with measurements of photoluminescence (PL) and ab-initio modelling of various point defect configurations and calculations of positron lifetimes. The concentration of impurities in each GaN crystal was determined using secondary ion mass spectrometry. Our study revealed that the concentration of gallium vacancies (V Ga ) in GaN crystals is influenced by the levels of hydrogen and oxygen impurities. Most HVPE GaN crystals exhibit low concentrations of hydrogen and oxygen, with no defects detectable by PAS. Only one HVPE crystal showed an enhanced concentration of oxygen, which is associated with V Ga , forming negatively charged V Ga +O N complexes, where one nitrogen nearest neighbour of the vacancy is substituted by oxygen. In contrast, AM GaN crystals contain at least two orders of magnitude higher concentrations of hydrogen and oxygen impurities. This results in a high concentration (≥ 10 18 cm⁻³) of V Ga complexes with H and/or O. The configuration of these complexes is determined by the ratio of hydrogen to oxygen concentration within the crystal. The undoped n-type AM GaN crystal contains V Ga +2H+O N complexes, while the manganese-doped semi-insulating AM crystal contains V Ga +3H complexes, both complexes being in neutral charge state. The PL results provide evidence that the V Ga +2H+O N and V Ga +3H complexes are the source of the green emission bands at 2.34 eV and 2.37 eV, respectively, in AM crystals.

Abstract Ammonia hydrates are important components in planetary interiors, among which ammonia hemihydrate (AHH) exhibits remarkable stability under high pressure. In this study, we report for the first time the elastic properties of the recently discovered quasi-bcc ammonia hemihydrate (AHH- q bcc) at high pressures, using externally heated diamond anvil cells combined with Raman spectroscopy and Brillouin scattering. We synthesized single crystals of AHH- q bcc in the DAC. Subsequently, we measured its full elastic tensor up to 17.6 GPa at room temperature via Brillouin scattering. The results show that the elastic constants increase linearly with increasing pressure. Based on the obtained elastic constants, we calculated the bulk modulus, shear modulus, Poisson's ratio, and velocity anisotropy. The results reveal significant anisotropy in wave velocities and Poisson's ratio on the (110) crystallographic plane of AHH- q bcc. Compared to ice VII, AHH- q bcc has a lower bulk modulus and shear modulus, yet exhibits higher compressional wave velocity and similar shear wave velocity. Our findings provide important constraints for understanding the internal structure and seismic velocity profiles of icy planets.

Corrigendum: ‘Excitons and trions in WSSe monolayers’ (2023 2D Mater. 10 015018), Olkowska-Pucko, Katarzyna, Blundo, Elena, Zawadzka, Natalia, Cianci, Salvatore, Vaclavkova, Diana, Kapuściński, Piotr, Jana, Dipankar, Pettinari, Giorgio, Felici, Marco, Nogajewski, Karol, Bartos, Miroslav, Watanabe, Kenji, Taniguchi, Takashi, Faugeras, Clement, Potemski, Marek, Babiński, Adam, Polimeni, Antonio, Molas, Maciej Roman

Three Machine Learning algorithms, namely Random Forest, Neural Networks and Extreme Gradient Boosting, were applied to recognize the shape and surface structure of diamond nanoparticles from powder diffraction data. The algorithms were trained to recognize three types of shapes: 1D - rods, 2D - plates and 3D superspheres and, in the case of plate-like shapes, two types of (111) surfaces, with either one or three dangling bonds per surface atom. The classifiers’ training was based on structure functions S(Q) of the nanograin models obtained by Molecular Dynamics simulations. The software tools for models building, diffraction data calculations, and the procedure of grain shape and surface classification are given. It is shown that both Random Forest, Neural Networks and Extreme Gradient Boosting classifiers recognize the shape and surface structure of nanodiamonds with a low number of misclassifications. The derived classifiers were applied to a series of experimental diffraction patterns of diamond nanoparticles with sizes from 1.2 to 3.3 nm. It is shown that ML classification algorithms reproduce very well the results obtained for those samples by real space diffraction data analysis, namely Pair Distribution Function. ML studies prove that the dominating shape of adamantane-synthesized nanodiamonds is a plate terminated by (111) surfaces with 3 dangling bonds of carbon atoms

Various single-stranded DNA (ssDNA) chains were attached to nanostructured gold and silver surfaces highly active in surface-enhanced Raman scattering (SERS) spectroscopy. The DNA was attached to the metal surface using alkanethiol linkers with 6 or 3 carbon atoms in the chain, and then the metal surface was sealed with HS-(CH2)n-OH alkanethiols having the same number of carbon atoms in the chain as one of the linkers. The immobilized ssDNA was then hybridized with complementary ssDNA, which induced significant changes in the conformation of the chains of chemisorbed ω-substituted alkanethiols. For the first time, it has been investigated how the length of the alkanethiol chain through which the capture ssDNA is attached to the metal surface affects the DNA hybridization-induced changes in the measured SERS spectra. We found that the differences between the SERS spectra of the DNA layers recorded before and after hybridization were much larger when thiols with 6 carbon atoms in the chain were used as linking and sealing compounds than when compounds with 3 carbon atoms in the chains were used. This means that, in SERS DNA sensors based on the rearrangement of linking layers, using C6 linkers should make it easier than C3 linkers to observe the rearrangement based on SERS measurements. The properties of the monolayers formed from the compounds used to seal the metal surfaces with immobilized DNA chains (6-mercaptohexanol and 3-mercaptopropanol) were also analyzed. It was found that monolayers on silver generally form faster, but are less stable, than those formed on gold.

Modulating metal oxide-based gas sensors with light is emerging as an alternative to enhance their sensitivity and selectivity. Plasmonic gas sensors based on excitation of the localized surface plasmon resonance (LSPR) in noble metals have recently shown promising properties. The classic approach of incorporating LSPR in sensors is to measure changes in the optical properties of the plasmonic material that depend on the surrounding local environment, i.e., an optical sensor device. The less common approach is to utilize chemiresistive sensors that consist of a gas-sensitive material (like graphene) decorated with plasmonic nanoparticles and employ solely electrical measurements for sensing data acquisition. This work demonstrates a chemiresistive gas sensor graphene/silicon Schottky junction decorated with palladium nanoparticles (PdNPs) that exhibit LSPR in the UV light range. We demonstrate a method of recording responses of plasmonic gas sensors based only on their DC characteristic measurements, which is simplified compared to optical and spectroscopic methods. Supported by the DC characteristics recorded under different UV wavelengths (255 nm, 275 nm, 355 nm), we show that the highest sensitivity to NO2 and NH3 is obtained for plasmonic resonant wavelength excitation of the PdNPs occurring at about 275 nm. The LSPR-modulated sensor response is nearly 14 times greater for NO2 gas compared to NH3 and exhibits a sensitivity toward NO2 gas with an ultralow detection limit of 4 ppb, thus showing that both the selectivity and sensitivity of plasmonic chemiresistive gas sensors can be significantly enhanced by LSPR-tuned light modulation.

• F-doped SmFeAsO (Sm1111) bulks are prepared by Spark Plasma Sintering (SPS) process. • The sample density and critical current density of Sm1111 are enhanced by SPS. • These bulks are compared by the Sm1111 bulks prepared by high pressure technique at 500 MPa. We optimize the superconducting properties of Sm-based oxypnictide (Sm1111: SmFeAsO 0.80 F 0.20 ) by using the Spark Plasma Sintering (SPS) technique under various synthesis conditions, including heating temperatures ranging from 600 to 1000 °C for durations of 5 to 30 min at the applied pressure of 45 MPa. All prepared bulks are characterized by structural and microstructural analysis as well as transport and magnetic measurements to conclude our findings. SmFeAsO 0.80 F 0.20 bulks are also prepared using the conventional synthesis process at ambient pressure (CSP) and the high gas pressure and high temperature (HP-HTS) methods at 500 MPa, which exhibit a superconducting transition temperature ( T c ) of 53–54 K. Interestingly, the SPS process of SmFeAsO 0.80 F 0.20 increases the sample densities up to 97–98 % and confirms the optimized synthesis conditions of 900 °C for 5–10 min; however, the increased sintering temperature or duration reduces T c due to the possible evaporation of lighter elements, particularly fluorine. Furthermore, the SPS technique is unable to reduce the observed impurity phases for the Sm1111, which is similar to the CSP and HP-HTS processes. A slight increment in the J c by the SPS process is observed due to the enhancement of sample density. A comparative analysis of Sm1111 superconductors prepared by SPS is performed with CSP and HP-HTS processes, suggesting that an increased sample density is ineffective on the superconducting properties in the presence of the impurity phases. This finding can be beneficial for the fundamental and applied research of iron-based superconductor (FBS)