rishat Mamat

Asymmetric dark matter and the scalar-tensor model

The relic abundance of asymmetric dark matter particles in the scalar-tensor model is analyzed in this paper. We extend the numerical and analytical calculations of the relic density of the asymmetric dark matter in the standard cosmological scenario to the nonstandard cosmological scenario. We focus on the scalar-tensor model. Hubble expansion rate is changed in the nonstandard cosmological scenario. This leaves its imprint on the relic density of dark matter particles. In this paper we investigate to what extent the asymmetric dark matter particle’s relic density is changed in the scalar-tensor model. We use the observed present day dark matter abundance to find the constraints on the parameter space in this model.

Multifunctional BBF monolayer with high mechanical flexibility and strong SHG response

Multi-functional two-dimensional (2D) materials are being researched due to their attractive properties and novel applications in nano-electronic, nano-optoelectronic, topological insulator, and energy-storage devices. In the present contribution, with the aid of first-principles calculations, the mechanical and nonlinear optical properties of a newly designed Be2BO3F2 (BBF) monolayer were investigated. Our results illustrate that the BBF monolayer possesses unexpectedly higher flexibility than the typical and well-known flexible optoelectronic material MoS2 in terms of Youngs modulus. Moreover, the BBF monolayer also exhibits a strong second harmonic generation (SHG) response of 5.65 × 104 pm2 V−1 which is 2.5 times that of a MoS2 monolayer. The honeycomb structure of the BBF monolayer appears to have a good mechanical stability, as revealed by the positive phonon modes and elastic constants. The highlighted electronic structure and properties, such as the large band gap (7.95 eV) and the large SHG response, make the BBF monolayer suitable for potential applications in flexible deep ultra-violet (DUV) nonlinear optical devices. We believe that the present research will provide useful guidance for the design of a new generation of nano-electronic devices.

The Effects of Multiple Scattering on Performance of Ballistic Channel Strained-Si Diodes

We have investigated the effects of multiple scattering on electron velocity, current and energy in the drain regions of the Strained-Si diodes. The covered cases in this study are ballistic channel Si-diodes with strained channel or drain, and with strained channel and drain, respectively. For a selected Ge content, the simulation results show that the velocity of electrons in the drain regions of strained channel and drain is lower than that of strained drain at the lower bias voltages (Vd 0.5V), the velocity in the drain regions of strained channel and drain regions is lower than that of strained drain regions. Meanwhile, the velocity of electrons in the drain regions of ballistic channel diodes with strained channel and drain reduces due to optical phonon scattering, when bias voltage increases.

The effects of drain scatterings on the electron transport properties of strained-Si diodes with ballistic and non-ballistic channels*

The effects of multiple scattering on the electron transport properties in drain regions are numerically investigated for the cases of strained-Si diodes with or without scattering in the channel. The performance of non-ballistic (with scattering) channel Si-diodes is compared with that of ballistic (without scattering) channel Si-diodes, using the strain and scattering model. Our results show that the values of the electron velocity and the current in the strain model are higher than the respective values in the unstrained model, and the values of the velocity and the current in the ballistic channel model are higher than the respective values in the non-ballistic channel model. In the strain and scattering models, the effect of each carrier scattering mechanism on the performance of the Si-diodes is analyzed in the drain region. For the ballistic channel model, our results show that inter-valley optical phonon scattering improves device performance, whereas intra-valley acoustic phonon scattering degrades device performance. For the strain model, our results imply that the larger energy splitting of the strained Si could suppress the inter-valley phonon scattering rate. In conclusion, for the drain region, investigation of the strained-Si and scattering mechanisms are necessary, in order to improve the performance of nanoscale ballistic regime devices.