ABSTRACT
We demonstrate that charge-density-wave devices with quasi-two-dimensional 1T-TaS2 channels show remarkable immunity to bombardment with 1.8 MeV protons to a fluence of at least 1014 H+cm-2. The current-voltage characteristics of these devices do not change as a result of proton irradiation, in striking contrast to most conventional semiconductor devices or other two-dimensional devices. Only negligible changes are found in the low-frequency noise spectra. The radiation immunity of these "all-metallic" charge-density-wave devices is attributed to the quasi-2D nature of the electron transport in the nanoscale-thickness channel, high concentration of charge carriers in the utilized charge-density-wave phases, and two-dimensional device design. Such devices, capable of operating over a wide temperature range, can constitute a crucial segment of future electronics for space, particle accelerator and other radiation environments.
ABSTRACT
It is widely believed that high-kinetic-energy (>1 keV) recoils in crystalline Si result in the formation of amorphous regions, whereas low-kinetic-energy recoils lead directly to isolated point defects. Here we study the response of a Si crystal using dynamical density-functional calculations and show that recoils of much less than 1 keV result in highly disordered regions that persist for hundreds of femtoseconds. Therefore, beam-induced defect formation is controlled by recrystallization processes during dynamic annealing even following low-energy ion implantation.
ABSTRACT
Given that H(2)O dissolves minimally in quartz, the mechanism for the ubiquitous dissolution of H(2)O in silica glasses has been a long-standing puzzle. We report first-principles calculations in prototype silica glass networks and identify the ring topologies that allow the exothermic dissolution of H(2)O as geminate Si-O-H groups. The topological constraints of these reactions explain both the observed saturation of Si-O-H concentrations and the observed increase in the average Si-Si distance. In addition, calculations of H(2)O and Si-O-H dissociation account for the observed response to radiation by wet thermally grown SiO(2).
ABSTRACT
Oxygen vacancies in SiO2 have long been regarded as bistable, forming a Si-Si dimer when neutral and a puckered configuration when positively charged. We report first-principles calculations of O vacancies in amorphous SiO2 supercells that unveil significantly more complex behavior. We find that the vast majority of O vacancies do not pucker after capture of a hole, but are shallow traps. The remaining vacancies exhibit two distinct types of puckering. Upon capturing an electron, one type forms a metastable dipole, while the other collapses to a dimer. A statistical distribution of O vacancies is obtained, and the implications for charge transport and trapping in SiO2 are discussed.
ABSTRACT
Hydrogen is known to passivate Si dangling bonds at the Si-SiO(2) interface, but the subsequent arrival of H(+) at the interface causes depassivation of Si-H bonds. Here we report first-principles density functional calculations, showing that, contrary to conventional assumptions, depassivation is not a two-step process, namely, neutralization of H(+) by a Si electron and subsequent formation of an H(2) molecule. Instead, we establish that H(+) is the only stable charge state at the interface and that H(+) reacts directly with Si-H, forming an H(2) molecule and a positively charged dangling bond (P(b) center). As a result, H-induced interface-trap formation does not depend on the availability of Si electrons.