Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGrowth kinetics and atomistic mechanisms of native oxidation of ZrS$_x$Se$_{2-x}$ and MoS$_2$ crystals
163
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A thorough understanding of native oxides is essential for designing semiconductor devices. Here we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrS$_x$Se$_{2-x}$ alloys and MoS$_2$. ZrS$_x$Se$_{2-x}$ alloys oxidize rapidly, and the oxidation rate increases with Se content. Oxidation of basal surfaces is initiated by favorable O$_2$ adsorption and proceeds by a mechanism of Zr-O bond switching, that collapses the van der Waals gaps, and is facilitated by progressive redox transitions of the chalcogen. The rate-limiting process is the formation and out-diffusion of SO$_2$. In contrast, MoS$_2$ basal surfaces are stable due to unfavorable oxygen adsorption. Our results provide insight and quantitative guidance for designing and processing semiconductor devices based on ZrS$_x$Se$_{2-x}$ and MoS$_2$, and identify the atomistic-scale mechanisms of bonding and phase transformations in layered materials with competing anions.
rate research
Read More
After our first discovery of superconductivity (SC) with $T_C$=3.7 K in TlNi$_2$Se$_2$, we grew successfully a series of TlNi$_2$Se$_{2-x}$S$_x$ (0.0 $leq$ x $leq$2.0) single crystals. The measurements of resistivity, susceptibility and specific heat were carried out. We found that SC with $T_C$=2.3 K also emerges in TlNi$_2$S$_2$ crystal, which appears to involve heavy electrons with an effective mass $m^*$=13$sim$25 $m_b$, as inferred from the normal state electronic specific heat and the upper critical field, $H_{C2}(T)$. It was found that the $T_C$ and superconducting volume fraction in TlNi$_2$Se$_{2-x}$S$_x$ crystals changes with the disorder degree induced by the partial substitution of S for Se, which is characterized by the residual resistivity ratio (textit{RRR}). The effect of the disorder on SC may provide some information for understanding the mechanism of SC in this new Ni-chalcogenide system.
By using solid-state reactions, we successfully synthesize new oxyselenides CsV$_2$Se$_{2-x}$O (x = 0, 0.5). These compounds containing V$_2$O planar layers with a square lattice crystallize in the CeCr$_2$Si$_2$C structure with the space group of $P4/mmm$. Another new compound V$_2$Se$_2$O which crystallizes in space group $I4/mmm$ is fabricated by topochemical deintercalation of cesium from CsV$_2$Se$_2$O powder with iodine in tetrahydrofuran(THF). Resistivity measurements show a semiconducting behavior for CsV$_2$Se$_2$O, while a metallic behavior for CsV$_2$Se$_{1.5}$O, and an insulating feature for V$_2$Se$_2$O. A charge- or spin-density wave-like anomaly has been observed at 168 K for CsV$_2$Se$_2$O and 150 K for CsV$_2$Se$_{1.5}$O, respectively. And these anomalies are also confirmed by the magnetic susceptibility measurements. The resistivity in V$_2$Se$_2$O exhibits an anomalous log(1/$T$) temperature dependence, which is similar to the case in parent phase or very underdoped cuprates indicating the involvement of strong correlation. Magnetic susceptibility measurements show that the magnetic moment per V-site in V$_2$Se$_2$O is much larger than that of CsV$_2$Se$_{2-x}$O, which again suggests the correlation induced localization effect in the former.
We have systematically studied the magnetic properties of chromium chalcogene compounds FeCr$_2$Se$_{4-x}$Te$_x$. The FeCr2Se4 undergoes antiferromagnetic ordering below 222 K. Substitution of tellurium lowers the antiferromagnetic ordering temperature and leads to short range ferromagnetic cluster behavior towards the tellurium end. Change over from antiferromagnetic to ferrimagnetic like behavior is also reflected in the corresponding transformation from semiconducting to metallic transport behavior. There is a large variation in the Curie-Weiss temperature, effective magnetic moment and ordering temperature (TN / TC) with Te substitution. The electronic band structure calculations suggest antiferromagnetic and ferrimagnetic ground state for the FeCr2Se4 and FeCr2Te4 respectively.
The compression of SH$_2$ and its subsequent decomposition to SH$_3$, presumably in a cubic Im$overline{3}$m structure, has lead to the discovery of conventional superconductivity with the highest measured and confirmed $T_c$ to date, 203 K at 160 GPa. Recent theoretical studies suggest that a mixture of S with other elements of the chalcogen group could improve the superconducting temperature. Here, we present a detailed analysis of the thermodynamic properties of S and Se mixtures in the bcc lattice with Im$overline{3}$m symmetry using a cluster expansion technique to explore the phase diagram of S$_x$Se$_{1-x}$H$_{3}$. In contrast to earlier reports, we find that S$_{0.5}$Se$_{0.5}$H$_3$ is not stable in the pressure range between 150-200 GPa. However, phases at compositions S$_{0.2}$Se$_{0.8}$H$_3$, S$_{0.overline{3}}$Se$_{0.overline{6}}$H$_3$, and S$_{0.6}$Se$_{0.4}$H$_3$ are stable at 200 GPa, while additional phases at S$_{0.25}$Se$_{0.75}$H$_3$ and S$_{0.75}$Se$_{0.25}$H$_3$ are accessible at lower pressures. Electron-phonon calculations show that the values of $T_c$ are consistently lower for all ternary phases, indicating that mixtures of S and Se with H might not be a viable route towards compounds with improved superconducting properties.
We present a study on the growth and characterization of high-quality single-layer MoS$_2$ with a single orientation, i.e. without the presence of mirror domains. This single orientation of the MoS$_2$ layer is established by means of x-ray photoelectron diffraction. The high quality is evidenced by combining scanning tunneling microscopy with x-ray photoelectron spectroscopy measurements. Spin- and angle-resolved photoemission experiments performed on the sample revealed complete spin-polarization of the valence band states near the K and -K points of the Brillouin zone. These findings open up the possibility to exploit the spin and valley degrees of freedom for encoding and processing information in devices that are based on epitaxially grown materials.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
