We present a comprehensive study of the band alignments of two-dimensional (2D) semiconducting materials and highlight the possibilities of forming momentum-matched type I, II, and III heterostructures, an enticing possibility being atomic heterostructures where the constituent monolayers have band edges at the zone center, i.e., $\mathrm{\ensuremath{\Gamma}}$ valley. Our study, which includes the group IV and III-V compound monolayer materials, group V elemental monolayer materials, transition-metal dichalcogenides, and transition-metal trichalcogenides, reveals that almost half of these materials have conduction and/or valence band edges residing at the zone center. Using first-principles density functional calculations, we present the type of the heterostructure for 903 different possible combinations of these 2D materials which establishes a periodic table of heterostructures.

/pdf/band-alignment-of-two-dimensional-semiconductors-for-12tbs8yhp0.pdf

Band alignment of two-dimensional semiconductors for designing heterostructures with momentum space matching

A new two-dimensional (2D) layered material, namely, titanium trisulfide (TiS3) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS3 monolayer is a direct-gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in-plane electron mobility of the 2D TiS3 is highly anisotropic, amounting to about 10 000 cm2 V−1 s−1 in the b direction, which is higher than that of the MoS2 monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS3 possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS3. Both dynamical and thermal stability of the TiS3 monolayer is examined by phonon-spectrum calculation and Born–Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS3 monolayer a promising 2D atomic-layer material for applications in future nanoelectronics.

/pdf/titanium-trisulfide-monolayer-theoretical-prediction-of-a-53pxyjt5ve.pdf

Titanium Trisulfide Monolayer: Theoretical Prediction of a New Direct‐Gap Semiconductor with High and Anisotropic Carrier Mobility

Here, we isolate thin TiS3 ribbons, a layered direct band gap semiconductor (1.1 eV, well suited for detection all across the visible spectrum), thus far almost unexplored. We fabricate field effect transistors and study their electrical characteristics and optoelectronic properties. The measured FET characteristics show mobilities up to 2.6 cm^2/Vs and ON/OFF ratios up to 10^4. Under illumination, the TiS3 NR-FETs present an ultrahigh photoresponse of 2910 A/W and fast rise/fall times of ~4 ms. In addition, we measure cutoff frequencies (f3dB) up to 1000 Hz. The strong combination of ultrahigh sensitivity all along the visible spectrum and fast time response of TiS3 nanoribbon transistors put them among the best nanoscale photodetectors to date.

Ultrahigh Photoresponse of Few‐Layer TiS3 Nanoribbon Transistors

Control over the morphology of TiS3 is demonstrated by synthesizing 1D nanoribbons and 2D nanosheets. The nanosheets can be exfoliated down to a single layer. Through extensive characterization of the two morphologies, differences in the electronic properties are found and attributed to a higher density of sulphur vacancies in nanosheets, which, according to density functional theory calculations, leads to an n-type doping.

TiS3 Transistors with Tailored Morphology and Electrical Properties

Magnetic-field-induced microwave absorption in sintered high-Tc copper oxide superconductors is found to be proportional to the surface area of samples and not to their volume, establishing that absorption takes place near the sample surface. The surface resistance and reactance increase with magnetic field as a result of energy loss through fluxons driven by superconducting currents. When the magnetic field is modulated, absorptive and dispersive signals arise from modulation of the complex surface impedance through processes induced by the changing magnetic fields.

https://iopscience.iop.org/article/10.1209/0295-5075/5/5/015/pdf

Microwave Magneto-Surface Impedance of High-Tc Superconductors

ESR in new high temperature superconductors

Electrical transport measurements in TiS3

The authors report ESR measurements on YBa2Cu3O7-y(0<y<1), the 123 phase and related phases of the Y-Ba-Cu oxide system-Y2BaCuO5 (the green phase), Y2Cu2O5 (the blue phase) and BaCuO2 (the dark phase)-over a temperature range between 5 and 300 K. The ESR observed in the different phases are due to Cu ions. The temperature behaviour of the linewidths, Delta H, of the green and blue phases is in accordance with the magnetic phase transition. In the dark phase they observe a very large variation of the linewidth with temperature, d( Delta H)/dT=25 G K-1. The intensity of the 123 spectra varied by more than two orders of magnitude for different samples, indicating that its origin is due to impurity phases. Its lineshape, down to 80 K, resembles that of the green phase. On further cooling (below 60 K) the linewidth passes through a maximum at Tm, where Tm depends on y. Its signal intensity, as determined from the peak-to-peak intensity and linewidth, shows an exponential decrease with temperature. The authors show that the LT ESR line in the 123 samples originates from the interplay of the green and the dark impurity phases, and they present evidence of coupling between spins of these inclusions which is mediated by the conduction electrons of the 123 matrix. They also offer a qualitative explanation for the increase of the signal intensity of the LT line, and speculate about the rapid linear temperature dependence of the linewidth of the dark-phase ESR line.

B. Fisher

Papers

ESR in new high temperature superconductors

Electrical transport measurements in TiS3

Comparison of the ESR spectra in ceramic YBa2Cu3O7-y (1>y>0) and related phases

The thermoelectric power of TaS3

The resistivity of Y1Ba2Cu3O7 between 80 K and 1240 K