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Miniaturized spectrometers are of considerable interest for their portability. Most designs to date employ a photodetector array with distinct spectral responses or require elaborated integration of micro & nano optic modules, typically with a centimeter-scale footprint. Here, we report a design of a micron-sized near-infrared ultra-miniaturized spectrometer based on two-dimensional van der Waals heterostructure (2D-vdWH). By introducing heavy metal atoms with delocalized electronic orbitals between 2D-vdWHs, we greatly enhance the interlayer coupling and realize electrically tunable infrared photoresponse (1.15 to 1.47 μm). Combining the gate-tunable photoresponse and regression algorithm, we achieve spectral reconstruction and spectral imaging in a device with an active footprint < 10 μm. Considering the ultra-small footprint and simple fabrication process, the 2D-vdWHs with designable bandgap energy and enhanced photoresponse offer an attractive solution for on-chip infrared spectroscopy.

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Here we report the evolution of bulk band structure and surface states in rare earth monobismuthides with partially filled f shell. Utilizing synchrotron-based photoemission spectroscopy, we determined the three-dimensional bulk band structure and identified the bulk band inversions near the X points, which, according to the topological theory, could give rise to nontrivial band topology with odd number of gapless topological surface states. Near the surface  point, no clear evidence for predicted gapless topological surface state is observed due to its strong hybridization with the bulk bands. Near the M point, the two surface states, due to projections from two inequivalent bulk band inversions, interact and give rise to two peculiar sets of gapped surface states. The bulk band inversions and corresponding surface states can be tuned substantially by varying rare earth elements, in good agreement with density-functional theory calculations assuming local f electrons. Our study therefore establishes rare earth mono-bismuthides as an interesting class of materials possessing tunable electronic properties and magnetism, providing a promising platform to search for novel properties in potentially correlated topological materials.

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Ultrathin SnS 2 nanosheets are synthesized for the first time by a simple ultrasonic method, and then fabricated onto a SiO 2 /Si substrate to form nanosheet-based phototransistor which exhibits a broad photoresponse from 254 to 980 nm, dependence of photocurrent on optical power and wavelength, fast-response, and long-term stability. Under illumination of 532-nm light with an optical power of 19.3 mW/cm 2 (0.68 nW), the photoswitch current ratio (PCR) is about 8.7, while the photoresponsivity, external quantum efficiency, and detectivity are 0.65 mA/W, 0.15%, and 1.13×10 8 J, respectively. Compared with the reported SnS 2-based photodetectors, the SnS 2nanosheet phototransistor shows an enhanced photosensitive performance.

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