The properties of multilayer exfoliated MoTe₂ field-effect transistors (FETs) on SiO₂ were investigated for channel thicknesses from 6 to 44 monolayers (MLs). All transistors showed p-type conductivity at zero back-gate bias. For channel thicknesses of 8 ML or less, the transistors exhibited ambipolar characteristics. ON/OFF current ratio was greatest, 1 $\times$ 10⁵, for the transistor with the thinnest channel, 6 ML. Devices showed a clear photoresponse to wavelengths between 510 and 1080 nm at room temperature. Temperature-dependent current-voltage measurements were performed on a FET with 30 layers of MoTe₂. When the channel is turned-on and p-type, the temperature dependence is barrier-limited by the Au/Ti/MoTe₂ contact with a hole activation energy of 0.13 eV. A long channel transistor model with Schottky barrier contacts is shown to be consistent with the common-source characteristics.

We report on the fabrication and characterization of synthesized multiwall MoS₂ nanotube (NT) and nanoribbon (NR) field-effect transistors (FETs). The MoS₂ NTs and NRs were grown by chemical transport, using iodine as a transport agent. Raman spectroscopy confirms the material as unambiguously MoS₂ in NT, NR, and flake forms. Transmission electron microscopy was used to observe cross sections of the devices after electrical measurements and these were used in the interpretation of the electrical measurements, allowing the estimation of the current density. The NT and NR FETs demonstrate n-type behavior, with ON/OFF current ratios exceeding 10³, and with current densities of 1.02 μA/μm and 0.79 μA/μm at V_DS = 0.3 V and V_BG = 1 V, respectively. Photocurrent measurements conducted on a MoS₂ NT FET revealed short-circuit photocurrent of tens of nanoamps under an excitation optical power of 78 $\mu$ W and 488 nm wavelength, which corresponds to a responsivity of 460 $\mu$ A/W. A long channel transistor model was used to model the common-source characteristics of MoS₂ NT and NR FETs and was shown to be consistent with the measured data.

We report the realization of top-gated graphene nanoribbon field effect transistors (GNRFETs) of ∼10 nm width on large-area epitaxial graphene exhibiting the opening of a band gap of ∼0.14 eV. Contrary to prior observations of disordered transport and severe edge-roughness effects of graphene nanoribbons (GNRs), the experimental results presented here clearly show that the transport mechanism in carefully fabricated GNRFETs is conventional band-transport at room temperature and inter-band tunneling at low temperature. The entire space of temperature, size, and geometry dependent transport properties and electrostatics of the GNRFETs are explained by a conventional thermionic emission and tunneling current model. Our combined experimental and modeling work proves that carefully fabricated narrow GNRs behave as conventional semiconductors and remain potential candidates for electronic switching devices.

High-aspect ratio β-Ga₂O₃ nanorods consisting of prism-like crystals were formed using gallium oxyhydroxide and ammonia hydroxide via a hydrothermal synthesis followed by the subsequent calcination process. The formation of high-aspect ratio β-Ga₂O₃ nanorods was attributed to the oriented attachment mechanism that was present during the hydrothermal synthesis. A field-effect transistor was fabricated using the high-aspect ratio β-Ga₂O₃ nanorod, and it exhibited the typical charge transfer properties of an n-type semiconductor. This facile approach to forming high-aspect ratio nanorods without any surfactants or additives can broaden the science of β-Ga₂O₃ and expedite the integration of one-dimensional β-Ga₂O₃ into future electronics, sensors, and optoelectronics.

Tin (Sn)-doped beta phase gallium oxide (β-Ga₂O₃) nanostructures at different Sn concentrations (0 to 7.3 at%) are synthesized using a facile hydrothermal method. The Sn-doped β-Ga₂O₃ nanostructures are characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and absorbance spectroscopy. In addition, their photocatalytic activity is evaluated by observing methylene blue degradation under ultraviolet light (254 nm) irradiation. The photocatalytic activity of the Sn-doped (0.7 at%) β-Ga₂O₃ nanostructures is significantly enhanced compared to that of intrinsic β-Ga₂O₃ nanostructures due to the elevated charge separation. Excessive Sn concentrations (exceeding 2.2 at%) above the solid solubility limit of the Sn in β-Ga₂O₃ nanostructures lead to SnO₂ and SnO precipitation. The presence of SnO₂ and SnO degrades the photocatalytic efficiency in the β-Ga₂O₃ nanostructures. The results suggest new opportunities for the synthesis of highly effective β-Ga₂O₃-based photocatalysts for applications in environmental remediation, disinfection, and selective organic transformations.

We demonstrate a novel method using electric field cycling to induce a phase transition in Hf _x Zr _1−x O ₂ to reach the morphotropic phase boundary of tetragonal and orthorhombic phase. Conventional methods used to induce the phase transition, such as high temperature annealing, cannot be used with the DRAM cell capacitor fabrication process because it associates with grain enlargement, increased leakage current, and a narrow process margin due to the metastability of the morphotropic phase boundary. To achieve an morphotropic phase boundary in Hf _x Zr _1−x O ₂ without high temperature annealing and without increasing leakage current, we propose a two-step process, using low temperature annealing to form the tetragonal phase and electric field cycling to achieve the morphotropic phase boundary of tetragonal and orthorhombic phase in Hf _x Zr _1−x O ₂ film. This approach enabled us to achieve both low voltage with high dielectric k value, and low leakage current, meeting the requirements for the next-generation DRAM cell capacitor dielectric materials.