The physics of the heat conduction and viscous dissipation in rarefied gases is analyzed and discussed. A heat transfer model valid for arbitrary Knudsen numbers, defined as the ratio of the molecular mean free path to the characteristic length of channels, is derived by treating the heat transfer behavior in the slip and transition regimes as an intermediate function of continuum heat transfer model and free molecular heat transfer model. Comparison studies reveal that this model not only shows good agreement with the numerical results based on the direct simulation Monte Carlo method, but also has some unique features that can overcome the deficiencies existing in the previous models. Therefore, this model is capable to study the heat transport phenomena in very dilute gas Couette flows through micro/nanochannels more accurately.

The authors present the surface plasmon effects of Au nanoparticles on the photoluminescence properties of ZnCdO/ZnO coaxial multiquantum-well nanowires fabricated using chemical vapor deposition and pulse laser deposition methods. The spontaneous emission rate from ZnCdO quantum wells was increased by surface plasmon coupling by 1.29 times. The strong plasmon coupling between ZnO barriers and Au nanoparticles provides an extra fast decay channel for excitons generated in ZnO barrier layer and leads to exciton redistribution in ZnCdO/ZnO coaxial quantum wells, which promotes radiative recombination in ZnO barriers but reduces the number of excitons relaxing into the ZnCdO quantum wells.

Effective Ohmic contact between metals and their conductive channels is a crucial step in developing high-performance Ga₂O₃-based transistors. Distinct from bulk materials, excess thermal energy of the annealing process can destroy the low-dimensional material itself. Given the thermal budget concern, a feasible and moderate solution (i.e., Ar-containing plasma treatment) is proposed to achieve effective Ohmic junctions with (100) β-Ga₂O₃ nanosheets. The impact of four kinds of plasma treatments (i.e., gas mixtures SF₆/Ar, SF₆/O₂/Ar, SF₆/O₂, and Ar) on (100) β-Ga₂O₃ crystals is comparatively studied by X-ray photoemission spectroscopy for the first time. With the optimal plasma pre-treatment (i.e., Ar plasma, 100 W, 60 s), the resulting β-Ga₂O₃ nanosheet field-effect transistors (FETs) show effective Ohmic contact (i.e., contact resistance R_C of 104 Ω·mm) without any post-annealing, which leads to competitive device performance such as a high current on/off ratio (>10⁷), a low subthreshold swing (SS, 249 mV/dec), and acceptable field-effect mobility (${\mu }_{\mathrm{e}\mathrm{f}\mathrm{f}}$, ~21.73 cm² V⁻¹ s⁻¹). By using heavily doped β-Ga₂O₃ crystals (N_e, ~10²⁰ cm⁻³) for Ar plasma treatments, the contact resistance R_C can be further decreased to 5.2 Ω·mm. This work opens up new opportunities to enhance the Ohmic contact performance of low-dimensional Ga₂O₃-based transistors and can further benefit other oxide-based nanodevices.

Understanding the low-temperature stability and degradation mechanism of Ga $_{\text{2}}$ O $_{\text{3}}$ -based transistors is important for their harsh-environment applications. This study examines the ultralow-temperature-dependent (i.e., 50–150 K) behavior of the $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ nanosheet field-effect transistor (FET). The $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ nanosheet with a thickness of 170 nm was peeled off from the single crystal and held on the substrate via van der Waals (vdWs) integration. At room temperature (i.e., 300 K), the vdW-integrated $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ transistor exhibits well-behaved performance, such as low subthreshold slope ( SS , 120.1 mV/dec), large $I_{\text{ON}}$ / $I_{\text{OFF}}$ ratio ( $\sim$ 1.28 $\times $ 10 $^{\text{8}})$ , and small OFF-state current ( $<$ 100 fA). At temperatures ranging from 150 down to 50 K, the electrical parameters were measured and analyzed. The conductive channel still maintains high quality without evident interfacial defects even at 50 K, whereas the mobility decreases considerably. Greater degradation occurs in the contacts between the electrodes and $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ compared to the channel layer. The degradation in the device performance of the $\beta $ -Ga $_{\text{2}}$ O $_{\text{3}}$ nanosheet transistor is associated with severely degraded electrical contact at extremely low temperatures. Nevertheless, optimized Ohmic electrodes (i.e., higher carrier density of $\sim$ 10 $^{\text{18}}$ cm $^{-\text{3}}$ and annealed at 420 $^{\circ}$ C) can effectively relieve the low-temperature effects on the contacts. Different from the high-temperature operation, the contact deterioration induced by low-temperature is reversible. The contact performance can recover to the original state after low-temperature experiments. The obtained results have significance in developing robust Ga $_{\text{2}}$ O $_{\text{3}}$ -based electronic devices and circuits for extreme-environment applications.