Convolutional neural network-based spectrum reconstruction solver for channeled spectropolarimeter.

Channeled spectropolarimetry is a snapshot technique for measuring the spectra of Stokes parameters of light by demodulating the measured spectrum. As an indispensable part of the channeled spectropolarimeter, the spectrometer module is far from being perfect to reflect the real modulation spectrum, which further reduces the polarimetric reconstruction accuracy of the channeled spectropolarimeter. Since the modulation spectrum is composed of many continuous narrow-band spectra with high frequency, it is a challenging work to reconstruct it effectively by existing methods. To alleviate this issue, a convolutional neural network (CNN)-based spectral reconstruction solver is proposed for channeled spectropolarimeter. The key idea of the proposed method is to first preprocess the measured spectra using existing traditional methods, so that the preprocessed spectra contain more spectral features of the real spectra, and then these spectral features are employed to train a CNN to learn a map from the preprocessed spectra to the real spectra, so as to further improve the reconstruction quality of the preprocessed spectra. A series of simulation experiments and real experiments were carried out to verify the effect of the proposed method. In simulation experiments, we investigated the spectral reconstruction accuracy and robustness of the proposed method on three synthetic datasets and evaluate the effect of the proposed method on the demodulation results obtained by the Fourier reconstruction method. In real experiments, system matrices are constructed by using measured spectra and reconstructed spectra respectively, and the spectra of Stokes parameters of incident light are estimated by the linear operator method. Several other advanced demodulation methods are also used to demodulate the measured spectrum in both simulation and real experiments. The results show that compared with other methods, the accuracy of the demodulation results can be much more improved by employing the CNN-based solver to reconstruct the measured spectrum.

Tuning electronic structure of monolayer InP3 in contact with graphene or Ni: effect of a buffer layer and intrinsic In and P-vacancy.

Monolayer indium triphosphide (m-InP3), predicted theoretically to be a new 2D semiconducting material, exhibits a promising opportunity for applications in electronic and optoelectronic devices [N. H. Miao, et al., J. Am. Chem. Soc., 2017, 139, 11125-11131]. For these applications, excellent contact performance between m-InP3 and the electrodes is vital. In this work, by first-principles calculations, the electronic structures of m-InP3 in contact with graphene (G) and Ni are investigated and the contact characters are further tuned by inserting a buffer layer, e.g., a G or BN monolayer (m-BN) along with the introduction of intrinsic P- and In-vacancy defects. For m-InP3 in contact with G, inserting an m-BN can alter the contact character from an n-type to a p-type Schottky contact. This is consistent with the prediction of the Schottky-Mott rule, indicating that Fermi level pinning is removed in the interface. However, for the contact with Ni, if an m-BN or G is inserted into the interface, an n-type Ohmic contact is obtained, rather than the p-type Schottky one based on the Schottky-Mott rule. We attribute this inconsistency to the effect of electron transfer from m-BN or G to Ni, which leads to a decreased work function for Ni. Additionally, introducing In- and P-vacancy defects can reduce the Schottky barrier in the interfaces between m-InP3 and G or Ni. Moreover, if m-BN is inserted into these defect-containing interfaces, an n-type Ohmic contact could be achieved and dominate the contact character. Our results offer deeper insights into factors such as the Fermi level pinning on the band alignment of the interfaces between m-InP3 and G or Ni, and how the contact characters are improved by inserting a buffer layer along with the introduction of In- and P-vacancy defects.

Spatial and thickness dependence of coupling interaction of surface states and influence on transport and optical properties of few-layer Bi2Se3.

Coupling interaction between the bottom and top surface electronic states and the influence on transport and optical properties of Bi2Se3 thin films with 1-8 quintuple layers (QLs) have been investigated by first principles calculations. Obvious spatial and thickness dependences of coupling interaction are found by analyzing hybridization of two surface states. In the thin film with a certain thickness, from the outer to inner atomic layers, the coupling interaction exhibits an increasing trend. On the other hand, as thickness increases, the coupling interaction shows a disproportionate decrease trend. Moreover, the system with 3 QLs exhibits stronger interaction than that with 2 QLs. The presence of coupling interaction would suppress destructive interference of surface states and enhance resistance in various degrees. In view of the inversely proportional relation to transport channel width, the resistance of thin films should show disproportionate thickness dependence. This prediction is qualitatively consistent with the transport measurements at low temperature. Furthermore, the optical properties also exhibit obvious thickness dependence. Especially as the thickness increases, the coupling interaction results in red and blue shifts of the multiple-peak structures in low and high energy regions of imaginary dielectric function, respectively. The red shift trend is in agreement with the recent experimental observation and the blue shift is firstly predicted by the present calculation. The present results give a concrete understanding of transport and optical properties in devices based on Bi2Se3 thin films with few QLs.

Ultrathin (Bi1-xSbx)2Se3 Field Effect Transistor with Large ON/OFF Ratio.

Ultrathin three-dimensional topological insulator films are promising for use in field effect devices. (Bi1-xSbx)2Se3 ultrathin films were fabricated on SrTiO3 substrate, where large resistance changes of ∼25 000% could be achieved using the back gate voltage. We suggest that the large ON/OFF ratio was caused by the combined effect of Sb-doping and the reduction of film thickness down to the ultrathin regime. The crossover of different quantum transport under an electric field may form the basis for topological insulators (TI)-based spin transistors with large ON/OFF ratios in the future.

[Structure analysis on growth solid-liquid boundary layer of BSO crystal at real time].

The micro Raman spectra of solid-liquid boundary layer, the melts and crystal side, were measured at real time, concerning BSO crystal grown with zone-melting method. The structure characters in boundary layer, melts and crystal were analyzed. The process, of which the growth unit structure changed while they transited from melts through boundary layer to crystal lattice, was analyzed. The results show that, there exists Bi3O4 and [SiO4] bonding structure in the melts of BSO crystal. While in the solid-liquid boundary layer, the Bi3O4 molecular units converge into [BiO7] octahedron monomer of polymer in form, the monomer or the polymer converge with the [SiO4] structure units, then all these converged structure enter into crystal lattice sites.

[High temperature Raman spectra and structure character study of BSO crystal].

The structure character of BSO crystal at room temperature was generalized. The main Raman shifts of lattice vibration at room temperature were interpreted. The Raman spectra of BSO crystal were measured in a temperature range from 293 K to 1123 K with high temperature Raman spectroscopy and time-resolved detection techniques. Temperature-dependence character of the Raman spectra of the crystal was investigated. The vibration mode of the longest bond Bi-O(1) in crystal shifts from 542 cm(-1) to 512 cm(-1) with the temperature increasing from room temperature to 1123 K. It can be attributed to the fact that oxygen atoms are electrostatic bond to Bi atoms. The intensity of 88 cm(-1) modes, which belongs to combination mode of bending and stretching in Bi3O4 unit, changes not so noticeably as other modes, and even the 58 cm(-1) mode of Bi atoms motions in crystal lattice decreases rapidly when the temperature is higher than 873 K, which indicates that the framework structure of the crystal is broken down at high temperature, while the Bi3O4 unit still exists.

[Raman spectra study of tellurium dioxide (TeO2) crystal].

The room temperature and high temperature Raman spectra of solid/melt growth boundary layers of TeO2 grown from melt were measured by high-temperature laser-micro-Raman spectrum. By analyzing, vibrational modes of the room temperature Raman spectra peaks of TeO2 crystal from band 200-800 cm-1 were confirmed, the expansion and frequency shift of each peak of the high temperature Raman spectra were interpreted and the possible structure group of the melt was proposed. So, certain foundation for studying the growth theory of functional crystal materials was provided.