In spite of recent significant research into various two-dimensional (2D) materials after the emergence of graphene, the development of a new 2D material that provides both high mobility and an appropriate energy band gap (which are crucial for various device applications) remains elusive. In this report, we demonstrate that the carrier transport behaviour of 2D Ti2CTx, which belongs to the family of 2D transition metal carbides and nitrides, can be tuned by modifying the surface group Tx (-OH, -F, and -O). Our results show that 2D Ti2C(OH)xFy and Ti2COx films can be obtained via simple chemical treatment, thermal annealing, and mechanical exfoliation processes. For the first time, we study the carrier transport properties of 2D Ti2CTx field effect transistors (FETs), obtaining the high field effect carrier mobilities of 10(4) cm(2) V(-1) s(-1) at room temperature. The temperature dependent resistivity of the Ti2COx film exhibits semiconductor like Arrhenius behaviour at zero gate voltage, from which we estimate the energy gap of 80 meV. One interesting feature of the FETs based on transition metal carbides is that the field effect mobility at room temperature is less sensitive to the measured transport gaps, which may arise from the dominant charge transport of activated carriers over the narrow energy gaps of the transition metal carbides. Our results open up the possibility that new 2D materials with high mobilities and appropriate band gaps can be achieved, and broaden the range of electronic device applications of Ti2CTx films.

We report the preparation of thickness-controlled few-layer black phosphorus (BP) films through the modulated plasma treatment of BP flakes. Not only does the plasma treatment control the thickness of the BP film, it also removes the chemical degradation of the exposed oxidized BP surface, which results in enhanced field-effect transistor (FET) performance. Our fabricated BP FETs were passivated with poly(methyl methacrylate) (PMMA) immediately after the plasma etching process. With these techniques, a high field-effect mobility was achieved, 1150 cm(2)/(V s), with an Ion/Ioff ratio of ∼10(5) at room temperature. Furthermore, a fabricated FET with plasma-treated few-layer BP that was passivated with PMMA was found to retain its I-V characteristics and thus to exhibit excellent environmental stability over several weeks.

1wileyonlinelibrary.com mobility. In TMD-based FETs, Schottky junction contacts are formed between the source/drain electrode and the channel, so the barrier heights at the junction interfaces have important roles in the polarity and performance of such devices. [8,9] Therefore, appropriate electrode materials are required for TMD-based devices. As a gapless semi-metal material, [10] graphene is an important material for 2D electrodes owing to its high conductivity and transparency. A vertically stacked grapheneMoS 2 FET was first reported by Duan et al., [11] and found to exhibit a high current density and a high on-off ratio when graphene was used as a tunable source electrode. Since this study, graphene electrodes have been more extensively tested, [12,13] and found to exhibit better electrical performance than other metal electrodes. Flexible and transparent MoS 2 FETs, in which graphene serves as a gate electrode and boron nitride acts as the dielectric layer, have also been demonstrated by Lee et al., [12] which enables the integration of FETs with 2D electronic components. Although the work function of graphene can be tuned with an electric field, which modulates the Schottky barrier height, [14] graphene's cone band structure means that this barrier height does not vary significantly under large gate voltages because the Fermi level of graphene is far from the Dirac point and exists in the region with a high density of states. [12] The relatively low work function of graphene (≈4.6 eV) and its small tuning range [12,14] mean that it has been primarily utilized in n-channel FET electrodes.Recently, newly emerging MXene 2D materials have attracted much attention. In general, MXenes are obtained by selectively etching A from a MAX phase, where M is an early transition metal, A is mostly a group IIIA or IVA element, and X is C or N. [15] During the etching process, the A atoms, which act as glue between the M n+1 X n layers (n = 1, 2, or 3), are removed and replaced by surface groups. The remaining M n+1 X n layers with surface groups are labeled an MXene because of their graphene-like 2D nature. Mxenes are now widely studied in lithium battery applications because of their high capacities and good conductivity. [16] MXenes are also potential candidates for 2D FET electrodes. Naguib et al. [17] showed that MXene materials have low-sheet resistivities that are comparable to that of multilayer graphene. Halim et al. [18] claimed that Ti 3 C 2 films synthesized via deposition and subsequent etching steps can achieve 90% transmission of light

AlxGa1−xN (0≤x≤0.50) ultraviolet photoconductors with a minimum cutoff wavelength shorter than 260 nm have been fabricated and characterized. The AlGaN active layers were grown on (00⋅1) sapphire substrates by metalorganic chemical vapor deposition (MOCVD). The spectral responsivity of the GaN detector at 360 nm is about 1 A/W biased at 8 V at room temperature. The carrier lifetime derived from the voltage-dependent responsivity is 0.13–0.36 ms.