Tuning electronic properties of epitaxial multilayer-graphene/4H–SiC(0001) by Joule heating decomposition in hydrogen

Abstract(#br)On the semi-insulating 4H–SiC (0001) surface, hydrogenated multilayers graphene (MLG) were epitaxially prepared by the method of Joule heating decomposition in the hydrogen atmosphere. The structural and chemical characteristics of multilayers graphene have been elaborately analyzed by the X-ray photoelectron and Raman spectroscopies, showing the level of hydrogenation being promoted with the increase of hydrogen pressure. Then, diodes with MLG/4H–SiC contact were fabricated and studied, proving that the Schottky barrier height (SBH) of MLG/4H–SiC junction was enhanced by the hydrogenation. By studying the typical current-voltage characteristics, the SBH was observed to be heightened from 0.84 eV to 1.0 eV along with the hydrogen pressure increasing from 10 −2 mbar to 10 2 mbar. Finally, graphene-semiconductor-graphene photodetectors were fabricated, showing peak responsivity as high as~ 0.9 A/W and external quantum efficiency of 345%, under the 324 nm illumination and biased at 3V

Case studies of electrical characterisation of graphene by terahertz time-domain spectroscopy

Graphene metrology needs to keep up with the fast pace of developments in graphene growth and transfer. Terahertz time-domain spectroscopy (THz-TDS) is a non-contact, fast, and non-destructive characterization technique for mapping the electrical properties of graphene. Here we show several case studies of graphene characterization on a range of different substrates that highlight the versatility of THz-TDS measurements and its relevance for process optimization in graphene production scenarios

A Honeycomb BeN₂ Sheet with a Desirable Direct Band Gap and High Carrier Mobility

Using global particle-swarm optimization method, we report, for the first time, a BeN₂ sheet (h-BeN₂) with a graphene-like honeycomb lattice but displaying a direct band gap. Symmetry group analysis indicates that the dipole transition is allowed between the conduction band minimum and the valence band maximum. Although the direct band gap of 2.23 eV is close to that (2.14 eV) of MoS₂ sheet, the h-BeN₂ sheet has additional advantages: the direct band gap feature of the h-BeN₂ sheet is quite insensitive to the layer stacking pattern and layer number, in contrast to the well-known direct-to-indirect band gap transition observed in TMDs and h-BN sheets. When rolled up, all the resulting h-BeN₂ nanotubes have direct band gaps independent of chirality and diameter. Furthermore, the intrinsic acoustic-phonon-limited carrier mobility of the h-BeN₂ sheet can reach ∼10⁵ cm² V^–1 s^–1 for electron and ∼10⁴ cm² V^–1 s^–1 for hole, which are higher than that of MoS₂ and black phosphorus

Dynamics of disordered Tavis-Cummings and Holstein-Tavis-Cummings models

By employing the time-dependent variational principle and the versatile multi-D2 Davydov trial states, in combination with the Green's function method, we study the dynamics of the Tavis-Cummings model and the Holstein-Tavis-Cummings model in the presence of diagonal disorder and cavity-qubit coupling disorder. For the Tavis-Cummings model, time evolution of the photon population, the optical absorption spectra, and the hetero-entanglement between the qubits and the cavity mode are calculated by using the Green's function method to corroborate numerically exact results of Davydov's Ansätze. For the Holstein-Tavis-Cummings model, only the latter is utilized to simulate effects of disorder on the photon population dynamics and the absorption spectra. We have demonstrated that the complementary employment of analytical and numerical methods permits uncovering a fairly comprehensive picture of a variety of complex behaviors in disordered multidimensional polaritonic cavity quantum electrodynamics systems.Ministry of Education (MOE)Submitted/Accepted versionThe authors acknowledge the support from the Singapore Ministry of Education Academic Research Fund (Grant Nos. RG190/18 and 2020-T1-002-075). K. Sun acknowledges the Natural Science Foundation of Zhejiang Province (Grant No. LY18A040005) for partial support. M.F.G. acknowledges Hangzhou Dianzi University for startup funding

Identifying the Ground State Geometry of a MoN₂ Sheet through a Global Structure Search and Its Tunable p‑Electron Half-Metallicity

MoN₂ and MoS₂ sheets are representatives of two-dimensional transition metal dinitrides and dichalcogenides, respectively. Their similarity in atomic ratios misled people to make an incorrect assumption in previous studies that the former adopts the geometry of the latter. However, compared with S, N is smaller and has fewer valence electrons, and N is more effective in mediating magnetic couplings; therefore, a different geometry and different properties can be expected for the MoN₂ sheet. Here using a global structure search, for the first time we have identified the ground state geometry of this sheet named Tetra-MoN₂ that is much more stable than the H phase proposed previously. Different from the metallic nature of H-MoN₂, Tetra-MoN₂ is a semiconductor having an indirect band gap of 1.41 eV with a flexible strain tunability. In particular, Tetra-MoN₂ can exhibit rich half-metallic behaviors mediated by the polarized p electron of N and induced by low-concentration hole doping and small strains that are readily achievable experimentally

Critical Role of Hepatic Cyp450s in the Testis-Specific Toxicity of (5R)-5-Hydroxytriptolide in C57BL/6 Mice

Low solubility, tissue accumulation, and toxicity are chief obstacles to developing triptolide derivatives, so a better understanding of the pharmacokinetics and toxicity of triptolide derivatives will help with these limitations. To address this, we studied pharmacokinetics and toxicity of (5R)-5-hydroxytriptolide (LLDT-8), a novel triptolide derivative immunosuppressant in a conditional knockout (KO) mouse model with liver-specific deletion of CYP450 reductase. Compared to wild type (WT) mice, after LLDT-8 treatment, KO mice suffered severe testicular toxicity (decreased testicular weight, spermatocytes apoptosis) unlike WT mice. Moreover, KO mice had greater LLDT-8 exposure as confirmed with elevated AUC and Cmax, increased drug half-life, and greater tissue distribution. γ-H2AX, a marker of meiosis process, its localization and protein level in testis showed a distinct meiosis block induced by LLDT-8. RNA polymerase II (Pol II), an essential factor for RNA storage and synapsis in spermatogenesis, decreased in testes of KO mice after LLDT-8 treatment. Germ-cell line based assays confirmed that LLDT-8 selectively inhibited Pol II in spermatocyte-like cells. Importantly, the analysis of androgen receptor (AR) related genes showed that LLDT-8 did not change AR-related signaling in testes. Thus, hepatic CYP450s were responsible for in vivo metabolism and clearance of LLDT-8 and aggravated testicular injury may be due to increased LLDT-8 exposure in testis and subsequent Pol II reduction