Physica E-low-dimensional Systems & Nanostructures最新文献

In recent years, the role of four-phonon (4ph) scattering in thermal transport properties has been gradually revealed. However, the underlying scattering mechanisms of the bulk β-Ga₂O₃ and monolayer Ga₂O₃ remain unclear. Hence, we evaluate the effect of 4ph scattering on the thermal transport properties of the bulk β-Ga₂O₃ and monolayer Ga₂O₃ by utilizing first-principles calculations. It has been observed that the Young's modulus and lattice thermal conductivity (κ) of the bulk β-Ga₂O₃ are anisotropic, while the values of the monolayer Ga₂O₃ are isotropic. The κ of the bulk β-Ga₂O₃ along the three directions ([100], [010], and [001]) and monolayer Ga₂O₃ after adding 4ph scattering are decreased by 9.23%, 11.52%, 13.89%, and 29.24% at 300 K, respectively. Moreover, the effect of four-phonon scattering is more pronounced at the high temperature. Afterwards, based on the phonon behaviors, we can prove that the addition of 4ph scattering can increase the phonon scattering rate, decrease the phonon mean free path, and increase the phase space, which results in lower thermal conductivity. The findings can contribute to a better understanding of high-order phonon scattering mechanisms of the Ga₂O₃ materials.

The unique one-dimensional chain structure of violet phosphorus provides an ideal platform for the study of second-order nonlinear optical properties. This also offers more possibilities for the further development of novel two-dimensional layered nanomaterials in the frequency domain. The research suggest that the highest occupied molecular orbital of monolayer phosphorene is characterized by a small effective mass and high hole mobility, while the lowest unoccupied molecular orbital exhibits opposite properties. This may be attributed to increased lattice scattering or electron-electron interactions in the conduction band. Monolayer violet phosphorus exhibits strong absorption capabilities in the near-ultraviolet light range, which can be utilized in UV spectroscopy technology for detecting harmful substances in water and air. Besides, its second harmonic generation response is also very strong within the visible light spectrum, and this response significantly varies with changes in angle. This provides theoretical guidance for optimizing the different stacking directions and heterojunction structures of violet phosphorus, more importantly, the sensitivity and directional selectivity of sensors can be improved. The work not only deepens the understanding of the electro-optical performance of violet phosphorus materials but also lays a theoretical foundation and guidance for the design and application of devices based on violet phosphorus.

We study the effects of a transverse magnetic field and bias voltage on the electronic properties of buckled tetragonal Germanene in the context of Hubbard model with ferromagnetic ordering. In particular, the behavior of density of states and temperature dependence of specific heat, thermoelectric properties and magnetic susceptibility have been investigated. Mean field approximation has been employed in order to obtain the effects of local coulomb interaction on the band structure of the system. Our results show the band gap in the density of states decreases with increase of bias voltage. Also the low temperature dependence of specific heat of tetragonal Germanene is found to be exponentially increasing behavior with temperature for all magnetic field and local coulomb interaction strength values. Seebeck coefficient shows an increasing behavior in terms of temperature with positive sign for all values of interaction strength. However Seebeck coefficient gets both positive and negative signs due to variation of transverse magnetic field strength in the absence of coulomb interaction and bias voltage.

Recently, synthesis and experimental research of fractalized materials has evolved in a paradigmatic crossroad with topological states of matter. Here, we present a theoretical investigation of the helical edge transport in Sierpiński carpets (SCs), combining the Bernevig–Hughes–Zhang model with the Landauer transport framework. By starting from a pristine two-dimensional topological insulator, the results reveal vanishing and reentrant resonant transport modes enabled for increased SC fractal generation. We observe that fractal with superior hierarchy inherits characteristics due to self-similarity and present conductance patterns resembling a miniband transport picture with fractal fingerprints. Real-space mapping of emerging resonant and antiresonant states provides an unprecedented view of helical-edge currents encoded in these intricate geometries and their multiple edges, underscoring the significance and consistency of our findings.

We investigate the transport properties in silicene-based ferromagnet/antiferromagnet/ferromagnet/p-wave superconductor junctions within the Blonder–Tinkham–Klapwijk formalism by solving the Dirac–Bogoliubov-de Gennes equation. The results show that the conductance and the shot noise strongly depend on the p-wave superconducting pair potentials and the magnetic configurations of the ferromagnetic regions. The simultaneous diminution of the conductance and enhancement of the shot noise can be achieved with the increase of the antiferromagnetic exchange field strength. The conductance and the shot noise can be effectively modulated by the external electric field and the ferromagnetic exchange field strength, and the corresponding switch effects are also achieved. The tunneling magnetoresistance (TMR) outside the subgap energy interval is always larger than the one obtained in the subgap energy interval. When the antiferromagnetic exchange field strength is large enough, a larger TMR can be obtained by tuning the external electric field.

The dice lattice bears a similar honeycomb lattice structure to graphene but with a non-dispersive flat band intersecting the Dirac bands at the band center. In this work, we investigate Nernst effect of the dice lattice in a strong magnetic field, focusing on the role of the flat band. By using the Chebyshev polynomial Green’s function method, we show that no Nernst effect ($S_{xy}=0$) is around the Dirac point in the clean limit contrary to the graphene case because of the existence of a zero Hall conductivity platform. However, an unconventional negative $S_{xy}$ of the double-peak structure emerges instead when the flat band is broadened by disorder and temperature. In addition, when a mass term of Dirac electrons is introduced in the system to open an energy gap, a negative single peak of $S_{xy}$ appears at the Dirac point and this is due to the derivative quantum Hall effect of non-Dirac electrons in the flat band appearing in the energy gap.

Ohmic contacts play a crucial role in realizing high-performance electronic devices based on two-dimensional materials. The contact between semimetals and semiconductors can mitigate the formation of metal-induced gap states (MIGS), thereby reducing the SBH, enhancing the efficiency of high charge injection, and facilitating the establishment of ohmic contacts. This study involves a systematic exploration of the contact characteristics between the two-dimensional semimetal TiS₂ and semiconductor MX₂ (M = Mo, W, Cr, Zr, Hf; X = S, Se, Te) through first-principles calculations. It is found that the TiS₂/MoSe₂ and TiS₂/WSe₂ heterojunction achieve ohmic contact. Investigations into their transport properties reveal that significant currents can be observed at relatively low voltages, indicating excellent transport performance of these heterojunctions. The TiS₂/CrSe₂ and TiS₂/HfSe₂ contact heterojunctions also show low Schottky barrier height (SBH), with the barrier height being adjustable under strain. The SBH of TiS₂/CrSe₂ and TiS₂/HfSe₂ heterojunctions are very close to zero under stresses of 4 % and −4%, respectively. This also implies that our research can offer valuable guidance for the development of adjustable Schottky nano-devices and high-performance optoelectronic devices.

We investigate the effect of solvent, i.e., ethanol and deionized (DI) water, on the structural, optical, and dielectric characteristics of SnO₂ nanostructures, synthesized via the hydrothermal method. Utilizing X-ray diffraction (XRD), we find the rutile phase for both nanostructures with average crystallite sizes of 12.53 nm and 6.62 nm for the samples synthesized using ethanol and DI water as solvents, respectively. The energy-dispersive X-ray spectroscopy (EDX) confirms the presence of Sn and O elements in both samples. Scanning electron microscopy (SEM) reveals that the samples prepared using ethanol and DI water exhibit nanorods and nanoflowers structures, respectively. The calculated band gap for SnO₂ based on ethanol and DI water solvents is found to be 3.54 eV and 3.45 eV, respectively. The SnO₂ nanostructure prepared by ethanol solvent demonstrates a higher dielectric constant which is attributed to higher defect density and more grain boundaries in it than in the sample synthesized using DI water. At low frequencies, the high tanδ values in the case of both nanostructures are explained based on space-charge polarization (SPC). The SnO₂ prepared by DI water exhibits higher tangent loss than the one synthesized using ethanol because of its significant surface area. The significant amount of conducting grains in the SnO₂ nanostructure while using ethanol solvent makes it a better conductive. Furthermore, the dielectric constant increases with increasing temperature which suggests considerable changes in the polarization behavior, while the tangent loss and conductivity demonstrate dependency on the temperature, indicating the promise of the nanostructures for electrical applications.

In this study, we propose an innovative type-II ZnSe/InSSe heterojunction for efficient photocatalytic water-splitting. This heterojunction exhibits a direct band gap of 1.9 eV and staggered band alignment, which efficiently separates photogenerated carriers, facilitating overall water-splitting. The built-in electric field drives electrons to accumulate in the InSSe layer and holes accumulate in the ZnSe layer, thereby suppressing recombination and enhancing photocatalytic efficiency. The solar-to-hydrogen efficiency reaches 8.92 %. Furthermore, the electronic and optical properties of ZnSe/InSSe heterojunction can be modified by biaxial strain, with tensile strain significantly improving visible light absorption and overall efficiency. Under tensile strain, the band gap decreases, enhancing the light absorption capability in the visible range, which further boosts the photocatalytic performance. Our findings demonstrate the ZnSe/InSSe heterojunction as a promising candidate for high-efficiency photocatalytic hydrogen production, offering valuable insights for future photocatalyst development. This research provides a potential pathway to optimize semiconductor heterojunctions for sustainable energy applications through strain engineering.

Determining suitable anode materials is crucial in the advancement of lithium-ion and sodium-ion battery technologies. We propose that the two-dimensional (2D) material Cu₂N holds promise as a viable anode candidate. The Cu₂N monolayer exhibits a stable checkerboard lattice crystal structure, ensuring structural integrity. Its excellent metallic electronic structure facilitates efficient conductivity during battery operation. We have observed that Li/Na ions can chemically bond to Cu₂N substrates via specific charge exchange mechanisms. Moreover, the Cu₂N monolayer demonstrates favorable wettability and compatibility with common electrolytes used in lithium-ion and sodium-ion batteries, including solvent molecules and metal salts. Our findings indicate that the Li/Na storage capacity of the Cu₂N monolayer reaches approximately 760/760 mAh/g, surpassing that of graphite anodes significantly. Notably, the Li/Na diffusion barrier on the Cu₂N monolayer is merely 5/13 meV, lower than that of most other 2D anode materials. Our results underscore the potential of the Cu₂N monolayer as an outstanding electrode material, offering high storage capacity, rapid charge/discharge rates, and favorable wettability with electrolytes.