Showing papers by "Xiang Qi published in 2023"
TL;DR: In this paper , a trilayer MoS2 with the twisted angle of 12° by optimized vapor deposition rather than the conventional mechanical stacking method was successfully fabricated, and the twist-related properties of homogeneous bilayer 2DMs have been rarely reported.
Abstract: Two-dimensional materials (2DMs) that are stacked vertically with a certain twist angle provide new degrees of freedom for designing novel physical properties. Twist-related properties of homogeneous bilayer and heterogeneous bilayer 2DMs, such as excitons and phonons, have been described in many pioneering works. However, twist-related properties of homogeneous trilayer 2DMs have been rarely reported. In this work, trilayer MoS2 with the twisted angle of 12° by optimized vapor deposition rather than the conventional mechanical stacking method was successfully fabricated. The inversion symmetry of trilayer MoS2 is changed by twist. Phonons and excitons produced by twist have an enormous influence on the interlayer interaction of trilayer MoS2, making trilayer MoS2 appear to have exotic optical properties. Compared with monolayer MoS2, the phonon vibration and photoluminescence intensity of trilayer MoS2 with one-interlayer-twisted are significantly improved, and the second harmonic generation response in the non-twist region of trilayer MoS2 is ∼3 times that of monolayer MoS2. In addition, interlayer coupling, inversion symmetry, and exciton behavior of the twist region show regional differences. This work provides a new way for designing twist and exploring the influence of twist on the structures of 2DMs with few layers.
1 citations
TL;DR: In this article , the authors applied scanning tunneling microscopy to investigate the influence of the defects on the lattice structure and electronic properties of Bi4I4 crystals, which revealed a bandgap around 0.1 eV at the terrace of the (001) surface of the crystal.
Abstract: The defects play a crucial role in the determination of the crystal structure and electronic properties of the matter, evoking tremendous interest in the manipulation of defects and exploration of underlying mechanisms. In this work, we applied scanning tunneling microscopy to investigate the influence of the defects on the lattice structure and electronic properties of Bi4I4 crystals. A lattice phase separation in the nanoscale is identified in the vicinity of hollow defects, which is absent in the sample without defects. The scanning tunneling spectroscopy reveals a bandgap around 0.1 eV at the terrace of (001) surface of Bi4I4, which is consistent with the angle-resolved photoemission spectroscopy results and first-principles calculations. The hollow defects modulate the local density of the state, leading to the edge state residing in the gap region. This edge state is regarded as responsible for the varied resistivity in different Bi4I4 samples in previous reports as their densities of the hollow defects are diverse. Our results shed light on the argument over the lattice phase of Bi4I4 at low temperatures as well as the factors determining the electronic properties.
1 citations
TL;DR: In this article , the photoactive Cu2O film has been prepared by electrochemical deposition for effective and selective detection of glucose, which can provide in-depth understanding on electric assist-redox and glucose catalytic processes.
Abstract: Developing enzyme-free glucose sensors that rely on transitional metal oxides has become a tendency to satisfy the growing demands of glucose monitor. In this work, the photoactive Cu2O film has been prepared by electrochemical deposition for effective and selective detection of glucose. Characterizations including XRD, Raman spectrum, UV–vis reflectance spectrum, and electrochemical testing were performed. We found that the as-prepared Cu2O films were self-composed of p-n Cu2O homojunction structure with enhanced photocurrent response for PEC-type glucose sensing. Further investigation on p-n Cu2O indicates that the intrinsic charge recombination has been retarded, which paves the way to construct photoelectrochemical-type (PEC-type) glucose sensors. Benefitted from the properties of p-n Cu2O homojunction, high sensitive PEC-type glucose detection has been achieved at the dual-range of 1 μM to 10 μM and 20 μM to 11 mM. We attribute to our investigations can provide in-depth understanding on electric assist-redox and glucose catalytic processes for the detection of glucose, that may guide the fabrication of glucose sensors with high sensitivity and selectivity.
TL;DR: In this article , the phase and shape of as-prepared MoTe2 are determined by the coupling effect in the growth temperature and the lattice strain between 2H and 1T′ MoTe 2.
Abstract: Molybdenum ditelluride (MoTe2) has a stable semiconducting hexagonal (2H) phase and a metastable metallic distorted octahedral (1T′) phase at the same time, which attracts much attention due to its attractive properties. However, the mechanism of phase and shape evolution in the preparation of MoTe2 is still unclear, which limits the controllable preparation and the wider device application of MoTe2. Here, we prepare few-layer MoTe2 with controllable phase and shape by using MoO3 and Te powders as precursors. With this method, triangle and hexagon 2H MoTe2 can be prepared, and long-strip and irregular 1T′ MoTe2 can be obtained. The phase and shape of as-prepared MoTe2 are determined by the coupling effect in the growth temperature and the lattice strain between 2H and 1T′ MoTe2. Low growth temperature combined with low Te concentration could induce small growth strain potential, leading to the growth of triangle and hexagon 2H MoTe2. While high growth temperature combined with high Te concentration could induce large strain potential, which is conducive to the preparation of long-strip and irregular 1T′ MoTe2. This study deeply investigates the evolution mechanism of phase and shape in MoTe2 growth, which has important guiding significance for the controllable preparation of phase and shape of other two-dimensional materials.
TL;DR: In this paper , the authors synthesized α-In2Se3 nanosheets with rare in-plane ferroelectric stripe domains at room temperature on mica substrates using a reverse flow chemical vapor deposition (RFCVD) method and optimized growth parameters.
Abstract: The two-dimensional (2D) layered semiconductor α-In2Se3 has aroused great interest in atomic-scale ferroelectric transistors, artificial synapses, and nonvolatile memory devices due to its distinguished 2D ferroelectric properties. We have synthesized α-In2Se3 nanosheets with rare in-plane ferroelectric stripe domains at room temperature on mica substrates using a reverse flow chemical vapor deposition (RFCVD) method and optimized growth parameters. This stripe domain contrast is found to be strongly correlated to the stacking of layers, and the interrelated out-of-plane (OOP) and in-plane (IP) polarization can be manipulated by mapping the artificial domain structure. The acquisition of amplitude and phase hysteresis loops confirms the OOP polarization ferroelectric property. The emergence of striped domains enriches the variety of the ferroelectric structure types and novel properties of 2D In2Se3. This work paves a new way for the controllable growth of van der Waals ferroelectrics and facilitates the development of novel ferroelectric memory device applications.
TL;DR: In this article , a review of 2DMOs applied in liquid metals is presented, where the surface oxidation process and in situ electrical replacement reaction process of liquid metals are introduced in detail.
Abstract: With the continuous exploration of low-dimensional nanomaterials, two dimensional metal oxides (2DMOs) has been received great interest. However, their further development is limited by the high cost in the preparation process and the unstable states caused by the polarization of surface chemical bonds. Recently, obtaining mental oxides via liquid metals have been considered a surprising method for obtaining 2DMOs. Therefore, how to scientifically choose different preparation methods to obtain 2DMOs applying in different application scenarios is an ongoing process worth discussing. This review will provide some new opportunities for the rational design of 2DMOs based on liquid metals. Firstly, the surface oxidation process and in situ electrical replacement reaction process of liquid metals are introduced in detail, which provides theoretical basis for realizing functional 2DMOs. Secondly, by simple sticking method, gas injection method and ultrasonic method, 2DMOs can be obtained from liquid metal, the characteristics of each method are introduced in detail. Then, this review provides some prospective new ideas for 2DMOs in other energy-related applications such as photodegradation, CO2 reduction and battery applications. Finally, the present challenges and future development prospects of 2DMOs applied in liquid metals are presented.
TL;DR: In this paper , a bifunctional electrocatalyst (BF ECS), FeCo2S4 nanowire (FCS NWs/Ni)/nickel (Ni) foam, with superior HER/OER activity and stability was designed and fabricated using a hydrothermal method.
Abstract: The development of effective, feasible, stable, and inexpensive electrocatalysts has been a great challenge in the field of overall water splitting (WS). Herein, a bifunctional electrocatalyst (BF ECS), FeCo2S4 nanowire (FCS NWs/Ni)/nickel (Ni) foam, with superior HER/OER activity and stability was designed and fabricated using a hydrothermal method. In addition, this efficient method can be used for the synthesis of other bimetallic MCo2S4 sulfides (M = Cu, Zn, Mn, etc.). Electrochemical experiments showed the as-synthesized FCS NWs/Ni exhibited overpotentials of 350.5, 203.7, 115.97, and 62.6 mV (0.05, 0.1, 0.2, and 1 M KOH) at the current density of −10 mA cm−2 for HER, including small overpotentials of 1.51, 1.36, 1.24, and 1.11 V (10 mA cm−2) in a 0.05, 0.1, 0.2, and 1 M KOH solution for OER. The FCS NWs/Ni has a splendid electrocatalytic performance which is related to the synergistic effect of cobalt, iron, and sulfur. Specifically, it has excellent electrical conductivity, a higher specific capacity, and a rich redox state of iron, cobalt, and sulfur elements. The results demonstrate a promising method for the design and fabrication of metal BF ECS for overall water splitting.
TL;DR: In this article , a novel heterobilayer Janus structure is designed by replacing the chalcogenide atomic layers in the original bilayer MoS2, which exhibits a direct band-gap semiconductor and a typical type-II band alignment with longer carrier lifetime.
Abstract: Inspired by potential application prospects of spintronics and valleytronics, a novel heterobilayer Janus structure is designed by replacing the chalcogenide atomic layers in the original bilayer MoS2. Based on first-principles calculations, it is found that the SMoS/SeMoS structure exhibits a direct band-gap semiconductor and a typical type-II band alignment with longer carrier lifetime. The transition metal (TM) atom represented by V/Cr/Mn can be stably adsorbed on the heterobilayer Janus SMoS/SeMoS sheet and effectively introduce magnetic moments (m). The calculation results demonstrate that the most stable adsorption site of the TM atom is CX(A), and the TM (V/Cr/Mn) adatom modified SMoS/SeMoS system is converted into metal (V-) or half-metal (Cr/Mn-), respectively. Under the coupling of different indirect exchange interactions, the structure exhibits stable intrinsic anti-ferromagnetic interactions for V-SMoS/SeMoS and ferromagnetic ground state for Cr/Mn-SMoS/SeMoS, respectively, and the magnetic transition temperature (T c) reaches a high temperature or even room temperature. Moreover, the robust out-of-plane magnetocrystalline anisotropy energy ensures stable long-range magnetic order. Specifically, the combination of spin injection and strong spin–orbit coupling interaction effectively breaks the time-reversal symmetry, which leads to valley polarization of the system. Based on this, the biaxial strain can effectively regulate the electronic structure, magnetic properties and valley polarization of TM-SMoS/SeMoS nanosheets with double breaking of spatial-inversion and time-reversal symmetry.
05 Jun 2023
TL;DR: In this paper , the structural, electronic and optical properties of MoSSe, PbS (111) and MoSSE/PbS(111) have been studied by the first-principles calculations, and the effect of VS on electronic properties has been analyzed.
Abstract: The structural, electronic and optical properties of MoSSe, PbS (111) and MoSSe/PbS (111) have been studied by the first-principles calculations, and the effect of VS on electronic and optical properties of MoSSe/PbS (111). When PbS (111) is stacked on MoSSe, an internal electric field and ohmic contact are formed at interlayer, and exhibited metal property. Compared with MoSSe and PbS (111) monolayer, MoSSe/PbS (111) heterostructure has higher absorption coefficients. Further analysis shows that this can be attributed to the orbital hybridization between the heterostructure layers. When VS is introduced, spin splitting occurs, making the spin-down channel below the Fermi level and inducing half-metallicity. What’s more, Vs MoSSe/PbS (111) still performances better optical absorption coefficient. Based on these findings, the heterogeneous structures and defects not only affect the electronic properties, but also can be used as an effective method to regulate the electrical and optical properties, providing useful theoretical guidance for further experimental studies.
TL;DR: In this article , a biomimetic self-powered photoelectrochemical-type flexible photodetector using liquid-stripped Cr2Ge2Te6 nanosheets as the photoanode was constructed.
Abstract: Two-dimensional (2D) semiconductor materials have been extensively studied as excellent candidates for future optoelectronic devices. Cr2Ge2Te6, as a two-dimensional semiconductor material, has attracted extensive interest in the field of photodetectors due to its excellent light absorption properties and suitable band gap. Inspired by biological photosynthesis, this study constructed a high-performance biomimetic self-powered photoelectrochemical-type flexible photodetector using liquid-stripped Cr2Ge2Te6 nanosheets as the photoanode. The device exhibits obvious self-powered photoresponse behavior and excellent photoresponse performance with a responsivity of 54.4 μA/W. Furthermore, the addition of nicotinamide adenine dinucleotide phosphate (NADPH) effectively consumes the photo-excited holes on the Cr2Ge2Te6 nanosheets to inhibit the recombination of photogenerated electron–hole pairs, and the cyclic regeneration of NADPH is realized by adding adenosine triphosphate. In addition, the flexible photodetector also exhibits excellent stability and durability, and it still maintains good photoresponse characteristics after 1000 times of bending and folding. Our work fully confirms that it is an effective means to improve the photoresponse performance of 2D materials by simulating biological photosynthesis, and it also provides theoretical and experimental guidance for the research and development of high-performance biomimetic devices.