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Two-dimensional (2D) semiconductors are promising candidates for next-generation flexible electronics, but their performance is often limited by low electron mobility and substantial Schottky barriers (SBs) at metal contacts. Here, we demonstrate that PdSe2/WSe2 nanosheet-based van der Waals heterostructures outperform PdSe2 or WSe2 nanosheets alone as channel materials for n-type field-effect transistors. Here, the WSe2 nanosheet serves as a buffer layer, mitigating Fermi-level pinning and reducing SBs between Ti metal and PdSe2 nanosheets. These heterostructures achieve two-terminal effective mobility exceeding 200 cm2 V–1 s–1 at room temperature and nearing 680 cm2 V–1 s–1 at 77 K. Additionally, the increased bandgap in thinner PdSe2 nanosheets enables high on/off ratios (∼107) in PdSe2/WSe2. These results underscore the potential of PdSe2/WSe2 nanosheet-based heterostructures and the importance of interfacial engineering in advancing 2D electronic devices. 

Modern society, revolutionized by the Internet of Things (IoTs), is witnessing exponential growth in the number of connected devices and the volume of data being generated and shared, raising significant concerns about safeguarding classified information against various cyber threats. Here, we introduce a lightweight, robust hardware security primitive based on the electromagnetic physical unclonable function (PUF) for cryptographic identification and authentication of wireless devices. Unlike traditional digital-based PUFs, the proposed electromagnetic PUF keys are generated using graphene-based harmonic transponders, of which the inherent variations in electronic properties of ambipolar graphene field-effect transistors (GFETs) result in highly stochastic, mixed modulations of radio frequency (RF) signals (i.e., unique electromagnetic fingerprints). Our experimental results demonstrate that this electromagnetic PUF exhibits excellent PUF performance metrics in terms of randomness, uniqueness, reliability, and resistance to machine learning-based modeling attacks. Moreover, the PUF keys can be reconfigured by altering the RF excitation frequency or through the electrostatic gating effect, further strengthening the security and resilience against modeling attacks. The proposed electromagnetic PUF may be well-suited for a variety of wireless authentication, encryption, and anticounterfeiting applications, and supports cryptographic key generation. 

We propose zero-bias, wavelength-scalable, and polarization-selective mid-infrared photodetectors based on metal–insulator–metal (MIM) metasurfaces. Specifically, these photodetectors leverage the second-order quantum conductivity sourced from photon-assisted tunneling and strong electric field localization in the MIM nanojunction to achieve efficient optical rectification. We show that by tailoring metasurface geometry, the incident infrared radiation can be efficiently coupled into the MIM heterojunction, with certain wavelength and polarization selectivity, and the optical rectification effect can be achieved with a photoresponsivity as high as tens of mA/W. Such results may pave a promising route toward the next-generation mid-infrared photodetection and energy harvesting. 

We report the fabrication of hexagonal-boron-nitride (hBN) encapsulated multi-terminal WSe_2 Hall bars with 2D/2D low-temperature Ohmic contacts as a platform for investigating the two-dimensional (2D) metal-insulator transition. We demonstrate that the WSe_2 devices exhibit Ohmic behavior down to 0.25 K and at low enough excitation voltages to avoid current-heating effects. Additionally, the high-quality hBN-encapsulated WSe_2 devices in ideal Hall-bar geometry enable us to accurately determine the carrier density. Measurements of the temperature (T) and density (n_s) dependence of the conductivity \sigma(T,n_s) demonstrate scaling behavior consistent with a metal-insulator quantum phase transition driven by electron-electron interactions, but where disorder-induced local magnetic moments are also present. Our findings pave the way for further studies of the fundamental quantum mechanical properties of 2D transition metal dichalcogenides using the same contact engineering. 

We report a reversible photo-induced doping effect in two-dimensional (2D) tungsten diselenide (WSe 2 ) field effect transistors on hexagonal boron nitride (h-BN) substrates under low-intensity visible light illumination (∼10 nW μm −2 ). Our experimental results have shown that this reversible doping process is mainly attributed to two types of defects in h-BN substrates. Moreover, the photo-doped WSe 2 transistors can be stable for more than one week in a dark environment and maintain the high on/off ratio (10 8 ) and carrier mobility, since there are no additional impurities involved during the photo-induced doping process to increase the columbic scattering in the conducting channel. These fundamental studies not only provide an accessible strategy to control the charge doping level and then to achieve a writing/erasing process in 2D transistors, but also shed light on the defect states and interfaces in 2D materials. 

We investigate electronic and optoelectronic properties of few-layer palladium diselenide (PdSe 2 ) phototransistors through spatially-resolved photocurrent measurements. A strong photocurrent resonance peak is observed at 1060 nm (1.17 eV), likely attributed to indirect optical transitions in few-layer PdSe 2 . More interestingly, when the thickness of PdSe 2 flakes increases, more and more photocurrent resonance peaks appear in the near-infrared region, suggesting strong interlayer interactions in few-layer PdSe 2 help open up more optical transitions between the conduction and valence bands of PdSe 2 . Moreover, gate-dependent measurements indicate that remarkable photocurrent responses at the junctions between PdSe 2 and metal electrodes primarily result from the photovoltaic effect when a PdSe 2 phototransistor is in the off-state and are partially attributed to the photothermoelectric effect when the device turns on. We also demonstrate PdSe 2 devices with a Seebeck coefficient as high as 74 μV K −1 at room temperature, which is comparable with recent theoretical predications. Additionally, we find that the rise and decay time constants of PdSe 2 phototransistors are ∼156 μs and ∼163 μs, respectively, which are more than three orders of magnitude faster than previous PdSe 2 work and two orders of magnitude over other noble metal dichalcogenide phototransistors, offering new avenues for engineering future optoelectronics.