Despite belonging to a well-studied family of transition metal trihalides, VI_3 has received significant attention only recently. As a hard ferromagnetic van der Waals compound with a large coercivity, it attracted much attention because of its potential use in atomically thin spintronic and optoelectronic devices. However, practical exploration of VI_3 is challenging due to its instability under ambient conditions. Here, we present a comprehensive set of optical, x-ray diffraction, magnetization, and ellipsometric measurements of VI3 and demonstrate that, similarly to the related van der Waals ferromagnet CrI_3, the degradation process is accelerated by the presence of moisture. The VI_3 surface was covered by selected media commonly used in physical measurements to test its stability and lower the degradation rate three times or higher, providing practical information for experimentalists interested. The decomposition study at ambient conditions shows that the VI_3 single crystal can be used for most of the bulk, magnetization, and optical measurements without any noticeable change of physical properties, as the significant degradation appears first after ~ 2 hours of exposition as illustrated, e.g., by the evolution of the ferromagnetic T_1 and T_2 transitions. The ellipsometric measurement demonstrates that even the surface remains optically stable for at least 5 minutes.
Wavelength-Dependent Photoluminescence Mapping of Depth-Dependent Degradation Under Thermal Stress in Phenethylammonium Tetrafluoroborate Treated Perovskite Solar Cells
Enhanced EV market penetration requires durability of the battery with high energy throughput. For long-term cycle stability of silicon-graphite anode capable of high energy density, the reversible redox reactions are crucial. Here, we unveil intriguing electrochemical phenomena such as crosstalk of lithium ion ($Li^{+}$) between silicon and graphite, $Li^{+}$ accumulation in silicon, and capacity depression of graphite under high pressure, which engender the irreversible redox reactions. Active material properties, i.e. the size of silicon and the hardness of graphite, silicon-graphite anode,…
We find significant differences between degradation and healing at the surface or in the bulk for each of the different APbBr3 single crystals (A=CH3NH3+, methylammonium (MA); HC(NH2)2+, formamidinium (FA); and cesium, Cs+). Using 1- and 2-photon microscopy and photobleaching we conclude that kinetics dominate the surface, and thermodynamics the bulk stability. Fluorescence-lifetime imaging microscopy, as well as results from several other methods, relate the (damaged) state of the halide perovskite (HaP) after photobleaching to its modified optical and electronic properties. The A cation type…
In this study, a complete study of the effect of hydrothermal reaction temperatures on the synthesis and physical properties of V2O5 using the green facile mild hydrothermal method has been performed with six different temperatures 100 °C to 200 °C, in the step of 20 °C. . The XRD pattern confirm the stable orthorhombic crystal structure of the synthesized samples at all reaction temperatures. The SEM and TEM images demonstrate the particle-like morphology, and these characterizations affirmed that the particles size became larger with the increase of reaction temperatures. The FTIR analysis i…
We report electrical measurements showing the degradation processes of LaMnO$_{3-y}$ (LaMnO) in LaMnO/normal metal interface in both point contact and planar-type junctions. Immediately after the preparation of the interface, the degradation process was followed by measuring the evolution of the junction resistance versus time. This process is characterized by the appearance of a second maximum in the resistance vs. temperature (R-T) dependence at temperatures lower than the Curie temperature T$_c$, at which the metal-insulator transition occurs in the bulk. These effects are explained in term…
Micro-alloying was performed using additions of Co and Fe to monolithic Pd40Ni40P20 bulk metallic glass to study selectively the influence on the plastic behavior in uniaxial compression and three-point bending tests. The corresponding Poisson's ratios were determined by ultrasonic measurements. The microstructure of the individual bulk metallic glasses was characterized by electron microscopy, X-ray diffraction and calorimetry. A plastic strain of 13% was found for the Co addition (1 at.%), whereas the Fe addition (0.6 at.%) led to immediate failure after reaching the elastic limit. Surprisin…
The ongoing search for high voltage positive electrode materials for Mg batteries has been primarily hampered by poor Mg mobility in bulk oxide frameworks. Motivated by the presence of Mo$_3$ clusters that can facilitate charge redistribution and the presence of Mg in a non-preferred (tetrahedral) coordination environment, we have investigated the Mg (de)intercalation behavior in layered-Mg$_2$Mo$_3$O$_8$, a potential positive electrode. While no electrochemical activity is observed, chemical demagnesiation of Mg$_2$Mo$_3$O$_8$ is successful but leads to amorphization. Subsequent first-princip…
The principal obstacle to long-time operation of silicon detectors at the highest energies in the next generation of experiments arises from bulk displacement damage which causes significant degradation of their macroscopic properties. The analysis of the behaviour of silicon detectors after irradiation conduces to a good or reasonable agreement between theoretical calculations and experimental data for the time evolution of the leakage current and effective carrier concentration after lepton and gamma irradiation and large discrepancies after hadron irradiation and this in conditions where a …
We report on thermal transport properties of wurtzite GaN in the presence of dislocations, by using molecular dynamics simulations. A variety of isolated dislocations in a nanowire configuration were analyzed and found to reduce considerably the thermal conductivity while impacting its temperature dependence in a different manner. We demonstrate that isolated screw dislocations reduce the thermal conductivity by a factor of two, while the influence of edge dislocations is less pronounced. The relative reduction of thermal conductivity is correlated with the strain energy of each of the five st…
The electrical evaluation of the crystallinity of hexagonal boron nitride (h-BN) is still limited to the measurement of dielectric breakdown strength, in spite of its importance as the substrate for 2-dimensional van der Waals heterostructure devices. In this study, physical phenomena for degradation and failure in exfoliated single-crystal h-BN films were investigated using the constant-voltage stress test. At low electrical fields, the current gradually reduced and saturated with time, while the current increased at electrical fields higher than ~8 MV/cm and finally resulted in the catastrop…
We present a quantitative investigation of the impact of tip radius as well as sample type and thickness on the lateral resolution in piezoresponse force microscopy (PFM) investigating bulk single crystals. The observed linear dependence of the width of the domain wall on the tip radius as well as the independence of the lateral resolution on the specific crystal-type are validated by a simple theoretical model. Using a Ti-Pt-coated tip with a nominal radius of 15 nm the so far highest lateral resolution in bulk crystals of only 17 nm was obtained.
Nickel-based layered oxides offer an attractive platform for the development of energy-dense cobalt-free cathodes for lithium-ion batteries but suffer from degradation via oxygen gas release during electrochemical cycling. While such degradation has previously been characterized phenomenologically with experiments, an atomic-scale understanding of the reactions that take place at the cathode surface has been lacking. Here, we develop a first-principles methodology for the prediction of the surface reconstructions of intercalation electrode particles as a function of the temperature and state o…
An important challenge in the field of topological materials is to carefully disentangle the electronic transport contribution of the topological surface states from that of the bulk. For Bi$_2$Te$_3$ topological insulator samples, bulk single crystals and thin films exposed to air during fabrication processes are known to be bulk conducting, with the chemical potential in the bulk conduction band. For Bi$_2$Te$_3$ thin films grown by molecular beam epitaxy, we combine structural characterization (transmission electron microscopy), chemical surface analysis as function of time (x-ray photoelec…
We present phonon dispersions, element-resolved vibrational density of states (VDOS) and corresponding thermodynamic properties obtained by a combination of density functional theory (DFT) and nuclear resonant inelastic X-ray scattering (NRIXS) across the metamagnetic transition of B2 FeRh in the bulk material and thin epitaxial films. We see distinct differences in the VDOS of the antiferromagnetic (AF) and ferromagnetic (FM) phase which provide a microscopic proof of strong spin-phonon coupling in FeRh. The FM VDOS exhibits a particular sensitivity to the slight tetragonal distortions presen…
Bi2Se3 is a topological insulator with metallic surface states residing in a large bulk bandgap. It is believed that Bi2Se3 gets additional n-type doping after exposure to atmosphere, thereby reducing the relative contribution of surface states in total conductivity. In this letter, transport measurements on Bi2Se3 nanoribbons provide additional evidence of such environmental doping process. Systematic surface composition analyses by X-ray photoelectron spectroscopy reveal fast formation and continuous growth of native oxide on Bi2Se3 under ambient conditions. In addition to n-type doping at t…
In the framework of a continuum theory, it is shown that the direct flexoelectric response of a finite sample essentially depends on the surface polarization energy, even in the thermodynamic limit where the body size tends to infinity. It is found that a modification of the surface energy can lead to a change of the polarization response by a factor of two. The origin of the effect is an electric field produced by surface dipoles induced by the strain gradient. The unexpected sensitivity of the polarization response to the surface energy in the thermodynamic limit is conditioned by the fact t…
The incorporation of noble metal nanoparticles, displaying localized surface plasmon resonance, in the active area of donor-acceptor bulk-heterojunction organic photovoltaic devices is an industrially compatible light trapping strategy, able to guarantee better absorption of the incident photons and give an efficiency improvement between 12% and 38%. In the present work, we investigate the effect of Au and Ag nanoparticles blended with P3HT: PCBM on the P3HT crystallization dynamics by synchrotron grazing incidence X-ray diffraction. We conclude that the presence of (1) 80nm Au, (2) mix of 5nm…
The topologically nontrivial and chemically functional distorted octahedral (T') transition metal dichalcogenides (TMDCs) are a type of layered semimetal that has attracted significant recent attention. However, the properties of monolayer (1L) T'-TMDC, a fundamental unit of the system, is still largely unknown due to rapid sample degradation in air. Here we report that well-protected 1L CVD T'-MoTe2 exhibits sharp and robust intrinsic Raman bands, with intensities about one order of magnitude stronger than those from bulk T'-MoTe2. The high-quality samples enabled us to reveal the set of all …
Radiative efficiency of highly luminescent bulk InP wafers severely degrades upon heat treatment involved in epitaxial growth of quaternary layers and fabrication of photodiodes on the surface. This unfortunate property impedes the use of bulk InP as scintillator material. On the other hand, it is known that thin epitaxial InP layers, grown by molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD), do not exhibit any degradation. These layers, however, are too thin to be useful in scintillators. The capability of hydride vapor phase epitaxy (HVPE) process to grow thick…
The observation of helical surface states in Bi-based three-dimensional topological insulators has been a challenge since their theoretical prediction. The main issue raises when the Fermi level shifts deep into the bulk conduction band due to the unintentional doping. This results in a metallic conduction of the bulk which dominates the transport measurements and hinders the probing of the surface states in these experiments. In this study, we investigate various strategies to reduce the residual doping in Bi-based topological insulators. Flakes of Bi$_2$Se$_3$ and Bi$_{1.5}$Sb$_{0.5}$Te$_{1.…
Our recent modelling works and corresponding numerical simulations realized to describe the UO2 oxidation processes confirm the theory showing that an applied mechanical strain can strongly affect the local oxygen diffusion in a stressed solid. This result allows us to assume that stress field, previously applied at the surface of a metallic sample on several microns, will delay the degradation during its oxidation. Considering this hypothesis, we implemented a FEM simulation code developed in our laboratory to numerically investigate some different stress fields applied on a sample sub-surfac…
The effect of water exposure on MgB2 is studied by submerging an 800 nm thick MgB2 film into deionized water at room temperature for 1 hour, 4 hours, 10 hours, and 15 hours, and by analyzing the resulting material using scanning electron microscopy and resistance vs. temperature measurements. It is clearly observed that Tconset of these films (obtained by an ex-situ reaction of a e-beam evaporated boron layer) remains unchanged throughout this process, indicating that at least a portion of the sample retains its original bulk-like properties. The data is consistent with an interpretation in wh…
The design of catalysts with desired chemical and thermal properties is viewed as a grand challenge for scientists and engineers. For operation at high temperatures, stability against structural transformations is a key requirement. Although doping has been found to impede degradation, the lack of atomistic understanding of the pertinent mechanism has hindered optimization. For example, porous gamma-Al2O3, a widely used catalyst and catalytic support, transforms to non-porous alpha-Al2O3 at ~1,100C. Doping with La raises the transformation temperature to ~1,250C, but it has not been possible t…
