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Non-equilibrium photocarriers in multilayer WSe₂injected by femtosecond laser pulses exhibit extraordinary nonlinear dynamics in the presence of intense THz fields. The THz absorption in optically excited WSe₂rises rapidly in the low THz field regime and gradually ramps up at high intensities. The strong THz pulses drive the photocarriers into sidebands of higher mobility and release trapped charge carriers, which consequently enhance the transient conductivity of WSe₂. The spectrally analyzed conductivity reveals distinctive features, indicating that the photocarriers undergo resonant interactions such as carrier-photon scattering. 

Abstract The ongoing reduction in transistor sizes drives advancements in information technology. However, as transistors shrink to the nanometer scale, surface and edge states begin to constrain their performance. 2D semiconductors like transition metal dichalcogenides (TMDs) have dangling‐bond‐free surfaces, hence achieving minimal surface states. Nonetheless, edge state disorder still limits the performance of width‐scaled 2D transistors. This work demonstrates a facile edge passivation method to enhance the electrical properties of monolayer WSe₂nanoribbons, by combining scanning transmission electron microscopy, optical spectroscopy, and field‐effect transistor (FET) transport measurements. Monolayer WSe₂nanoribbons are passivated with amorphous WO_xSe_yat the edges, which is achieved using nanolithography and a controlled remote O₂plasma process. The same nanoribbons, with and without edge passivation are sequentially fabricated and measured. The passivated‐edge nanoribbon FETs exhibit 10 ± 6 times higher field‐effect mobility than the open‐edge nanoribbon FETs, which are characterized with dangling bonds at the edges. WO_xSe_yedge passivation minimizes edge disorder and enhances the material quality of WSe₂nanoribbons. Owing to its simplicity and effectiveness, oxidation‐based edge passivation could become a turnkey manufacturing solution for TMD nanoribbons in beyond‐silicon electronics and optoelectronics. 

Abstract Source/Drain extension doping is crucial for minimizing the series resistance of the ungated channel and reducing the contact resistance of field‐effect transistors (FETs) in complementary metal–oxide–semiconductor (CMOS) technology. 2D semiconductors, such as MoS₂and WSe₂, are promising channel materials for beyond‐silicon CMOS. A key challenge is to achieve extension doping for 2D monolayer FETs without damaging the atomically thin material. This work demonstrates extension doping with low‐resistance contacts for monolayer WSe₂p‐FETs. Self‐limiting oxidation transforms a bilayer WSe₂into a hetero‐bilayer of a high‐work‐function WO_xSe_yon a monolayer WSe₂. Then, damage‐free nanolithography defines an undoped nano‐channel, preserving the high on‐current of WO_xSe_y‐doped FETs while significantly improving their on/off ratio. The insertion of an amorphous WO_xSe_yinterlayer under the contacts achieves record‐low contact resistances for monolayer WSe₂over a hole density range of 10¹²to 10¹³cm⁻²(1.2 ± 0.3 kΩ µm at 10¹³cm⁻²). The WO_xSe_y‐doped extension exhibits a sheet resistance as low as 10 ± 1 kΩ □⁻¹. Monolayer WSe₂p‐FETs with sub‐50 nm channel lengths reach a maximum drain current of 154 µA µm⁻¹with an on/off ratio of 10⁷–10⁸. These results define strategies for nanometer‐scale selective‐area doping in 2D FETs and other 2D architectures. 

Abstract Universal platforms for biomolecular analysis using label‐free sensing modalities can address important diagnostic challenges. Electrical field effect‐sensors are an important class of devices that can enable point‐of‐care sensing by probing the charge in the biological entities. Use of crumpled graphene for this application is especially promising. It is previously reported that the limit of detection (LoD) on electrical field effect‐based sensors using DNA molecules on the crumpled graphene FET (field‐effect transistor) platform. Here, the crumpled graphene FET‐based biosensing of important biomarkers including small molecules and proteins is reported. The performance of devices is systematically evaluated and optimized by studying the effect of the crumpling ratio on electrical double layer (EDL) formation and bandgap opening on the graphene. It is also shown that a small and electroneutral molecule dopamine can be captured by an aptamer and its conformation change induced electrical signal changes. Three kinds of proteins were captured with specific antibodies including interleukin‐6 (IL‐6) and two viral proteins. All tested biomarkers are detectable with the highest sensitivity reported on the electrical platform. Significantly, two COVID‐19 related proteins, nucleocapsid (N‐) and spike (S‐) proteins antigens are successfully detected with extremely low LoDs. This electrical antigen tests can contribute to the challenge of rapid, point‐of‐care diagnostics.