Stability and electronic properties of "4-8"-type ZnSnN2_2 thin films free of spontaneous polarization for optoelectronic devices

Ternary nitride ZnSnN$_2$ is a promising photovoltaic absorber material. In this work, using first-principles calculations, we investigate the stability and electronic properties of "4-8"-type ZnSnN$_2$ thin films. We find that below a certain thickness "4-8"-type thin films have lower total energy than polar films. For 4-layer ZnSnN$_2$ thin film, the Pna2$_1$/Pmc2$_1$ $\rightarrow$ 4-8 transition can spontaneously occur at finite temperatures. All "4-8"-type thin films studied are semiconducting and free of spontaneous polarization, the bandgaps of which can be tuned by the thickness of films, ranging from 1.4 eV to 1.8 eV. Furthermore, these films show light electron effective masses, and octet-rule-preserving disorder has insignificant effects on the electronic properties. Our results provide new insights into the structure of ZnSnN$_2$ in the thin film form and guidance for the experimental investigation

Nuclear modification factor in intermediate-energy heavy-ion collisions

The transverse momentum dependent nuclear modification factors (NMF), namely $R_{CP}$, is investigated for protons produced in Au + Au at 1$A$ GeV within the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. It is found that the radial collective motion during the expansion stage affects the NMF at low transverse momentum a lot. By fitting the transverse mass spectra of protons with the distribution function from the Blast-Wave model, the magnitude of radial flow can be extracted. After removing the contribution from radial flow, the $R_{CP}$ can be regarded as a thermal one and is found to keep unitary at transverse momentum lower than 0.6 GeV/c and enhance at higher transverse momentum, which can be attributed to Cronin effect.Comment: 8 pages, 5 figures; aceepted by Physics Letters

Excitation Energy as a Basic Variable to Control Nuclear Disassembly

Thermodynamical features of Xe system is investigated as functions of temperature and freeze-out density in the frame of lattice gas model. The calculation shows different temperature dependence of physical observables at different freeze-out density. In this case, the critical temperature when the phase transition takes place depends on the freeze-out density. However, a unique critical excitation energy reveals regardless of freeze-out density when the excitation energy is used as a variable insteading of temperature. Moreover, the different behavior of other physical observables with temperature due to different $\rho_f$ vanishes when excitation energy replaces temperature. It indicates that the excitation energy can be seen as a more basic quantity to control nuclear disassembly.Comment: 3 pages, 2 figures, Revte