Because of the strong quantum confinement effect, few-layer γ-InSe exhibits a layer-dependent band gap, spanning the visible and near infrared regions, and thus recently has been drawing tremendous attention. As a two-dimensional material, the mechanical flexibility provides an additional tuning knob for the electronic structures. Here, for the first time, we engineer the band structures of few-layer and bulk-like InSe by uniaxial tensile strain and observe a salient shift of photoluminescence peaks. The shift rate of the optical gap is approximately 90-100 meV per 1% strain for four- to eight-layer samples, which is much larger than that for the widely studied MoS monolayer. Density functional theory calculations well reproduce the observed layer-dependent band gaps and the strain effect and reveal that the shift rate decreases with the increasing layer number for few-layer InSe. Our study demonstrates that InSe is a very versatile two-dimensional electronic and optoelectronic material, which is suitable for tunable light emitters, photodetectors, and other optoelectronic devices.

Two‐dimensional (2D) materials have attracted increasing attention for their outstanding structural and electrical properties. However, for mass‐production of field effect transistors (FETs) and potential applications in integrated circuits, large‐area and uniform 2D thin films with high mobility, large on‐off ratio, and desired polarity are needed to synthesize firstly. Here, a transfer‐free growth method for platinum diselenide (PtSe2) films has been developed. The PtSe2 films have been synthesized with various thicknesses in centimeter‐sized scale. Typical FET made from a few layer PtSe2 show p‐type unipolar, with a high field‐effect hole mobility of 6.2 cm2 V−1 s−1 and an on‐off ratio of 5 × 103. The versatile semimetal‐unipolar‐ambipolar transition in synthesized PtSe2 films is also firstly observed as the thickness thinning. This work realizes the large‐scale preparation of PtSe2 with prominent electrical properties and provides a new strategy for polarity's modulation.

Electrocatalysts are evolving toward chemically tunable atomic structures, among which the catalyst engineering from a defect perspective represents one of the mainstream technical genres. However, most defects cannot be purified or their numbers gauged, making them too complex to explore the hidden catalytic mechanism. A twin boundary, with well-defined symmetric structure and high electrocatalytic activity, is an elegant one-dimensional model catalyst in pursuing such studies. Here on polished Cu electrodes, we successfully synthesized a series of copper twin boundaries, whose density ranges from 0 to 10 5 cm −1 . The CH 4 turnover frequency on the twin boundary atoms is 3 orders higher than that on the plane atoms, and the local partial current density reaches 1294 mA cm −2 , with an intrinsic Faradaic efficiency of 92%. An intermediate experiment and density functional theory studies confirm the twin boundary's advantage in converting the absorbed CO* into CH 4 .

Monolayer hexagonal boron nitride (h-BN) possesses a wide bandgap of ~6 eV. Trimming down the bandgap is technically attractive, yet poses remarkable challenges in chemistry. One strategy is to topological reform the h-BN’s hexagonal structure, which involves defects or grain boundaries (GBs) engineering in the basal plane. The other way is to invite foreign atoms, such as carbon, to forge bizarre hybrid structures like hetero-junctions or semiconducting h-BNC materials. Here we successfully developed a general chemical method to synthesize these different h-BN derivatives, showcasing how the chemical structure can be manipulated with or without a graphene precursor, and the bandgap be tuned to ~2 eV, only one third of the pristine one’s.

The vibrational and electronic properties of 2-dimensinal (2D) materials can be efficiently tuned by external strain due to their good stretchability. Resonant Raman spectroscopy is a versatile tool to study the physics of phonons, electrons and their interactions simultaneously, which is particularly useful for the investigation of strain effect on 2D materials. Here, for the first time, we report the resonant Raman study of strained few-layer InSe (γ-phase). Under ~ 1% of uniaxial tensile strain, one order of magnitude enhancement of Raman intensity for longitudinal optical (LO) phonon is observed, while other modes exhibit only modest change. Further analysis demonstrates that it arises from the intraband electron-phonon scattering channel for LO phonon in resonance. The large enhancement of Raman intensity provides us a sensitive and novel method to characterize the strain effect and a mapping of the strain distribution in a wrinkled sample is demonstrated. In addition, we observed sizable redshifts of firstorder optical phonon modes. The shift rate exhibits phonon mode dependence, in excellent agreement with density functional perturbation theory (DFPT) calculations.Our study paves the way for sensitive strain quantification in few-layer InSe and its application in flexible electronic and optoelectronic devices. 3 / 41 I. INTRODUCTION Mechanical cleavage of graphene [1] by K. S. Novoselov et al. arouses tremendous research interest in 2D materials. A variety of 2D semimetals and semiconductors have been discovered ever since, such as transition metal dichalcogenides (TMDCs) [2], silicone [3], stanine [4] and black phosphorus [5,6]. Atomically thin indium selenide (γphase) joins the family lately with unique electronic properties [7-9]. Quantum Hall effect was observed in the high quality few-layer InSe electronic devices [9]. Strong quantum confinement in the out-of-plane direction gives rise to layer-dependent bandgap [7], covering a large range of visible and near infrared regions. Few-layer InSe has promised great application potentials in electronics and optoelectronics [10-12]. The mechanical stretchability of 2D materials opens the door for straining, to continuously and reversibly tune their lattice constants and electronic properties [13]. Raman spectroscopy is a crucial diagnostic tool to evaluate the strain effect. Phonon softening and splitting are commonly observed in 2D materials under uniaxial tensile strain, such as graphene [14,15], TMDCs [15,16] and black phosphorus [18,19], indicating the weakening of the bond strength and the symmetry-breaking. The band structure and electronic properties of 2D materials can be engineered efficiently via strain as well. For example, prominent strain-induced shift of the band gap and indirectto-direct bandgap transition were observed in multilayer TMDCs [20]. Owing to the small Young's modulus ( ~ 45 N/m) [21], the bandgap of few-layer InSe can be easily tuned by uniaxial tensile strain with shift rate up to 90-150meV/% [22,23]. Therefore, 5 / 41 II. EXPERI...