Helium bubble nucleation at low-angle twist boundaries in gold has been investigated. It is found that the helium bubbles preferentially nucleate at screw dislocation nodal points and result in helium bubble superlattice formation, which is completely isomorphic with the screw dislocation network along the twist-grain boundary. Molecular statics calculations reveal that defect formation/solution energies along the screw dislocations, especially at the nodal points, are lower than their bulk counterparts. It is believed that this driving force is responsible for the helium bubble superlattice formation. Our study suggests that grain boundary engineering via adjustable twist angles in parallel boundaries to form tunable 3D bubble superlattices could afford a very promising approach for design of radiation tolerant materials.

One of the open issues in organic electronics is the long-term stability of devices based on organic materials, as oxidation is believed to be a major reason for early device failure. The focus of our research is to investigate the effects of low energy ion implantation (N and Ne) in the reduction and control of the degradation of pentacene organic thin film transistors (OTFTs) due to the exposure to atmosphere (i.e. oxygen and water). Despite the strong molecular structure modifications induced by ion implantation, we have observed that a controlled damage depth distribution preserves the functionality of the device. The electrical properties of the pentacene layer and of the OTFT have been investigated by means of current–voltage and photocurrent spectroscopy analyses. We have characterized the structural modification induced by ion implantation and we have monitored the effectiveness of this process in stabilizing the device carrier mobility and threshold voltage over a long time (over 2000 h). In particular, we have assessed by depth resolved X-ray photoemission spectroscopy analyses that, by selectively implanting with ions that can react with the hydrocarbon matrix (e.g. N+), it is possible to locally modify the charge distribution within the organic layer.

In contradiction to conventional damage annealing, thermally annealed H-implanted Si exhibits an increase in damage or reverse annealing behavior, whose mechanism has remained elusive. In this work, we conclusively elucidate that the reverse annealing effect is due to the nucleation and growth of hydrogen-induced platelets. Platelets are responsible for an increase in the height and width of the channeling damage peak following increased isochronal anneals. This work is supported by the Department of Energy, Office of Basic Energy Science.

ABSTRACT We have quantitatively studied by transmission electron microscopy the growth kinetics of platelets formed during the continuous hydrogenation of a Si substrate/SiGe/Si heterostructure. We have evidenced and explained the massive transfer of hydrogen from a population of platelets initially generated in the upper Si layer by plasma hydrogenation towards a population of larger platelets located in the SiGe layer. We demonstrate that this type of process can be used not only to precisely localize the micro-cracks, then the fracture line at a given depth but also to “clean” the top layer from pre-existing defects. The work at LANL was supported by the Department of Energy, Office of Basic Energy Science.

The influence of dynamic and thermal annealing on hydrogen platelet formation in silicon have been studied. For cryogenic and room temperature implantations, where dynamic annealing is suppressed, hydrogen platelets form upon subsequent thermal annealing on primarily (100) planes. However, under high temperature implantation (dynamic annealing), a high density hydrogen platelet network consisting of both (111) platelets and (100) platelets is observed. Our findings demonstrate that hydrogen implantation under dynamic annealing conditions leads to a modification of the implantation-induced stress, which eventually guide the nucleation and growth of hydrogen-induced platelets.

We have studied the mechanisms underlying strained layer relaxation by means of point defect interaction. During high temperature (300 °C) proton irradiation, vacancies generated in the vicinity of SiGe layer migrate and accumulate within the compressively strained SiGe layer. The accumulating vacancies are stabilized by hydrogen, which diffuses from the implanted region, thus allowing the nucleation and growth of hydrogen-vacancy (V-H) complexes. The formation of V-H complexes is accompanied by gradual strain relief in SiGe layer. Since the diffusion of both vacancies and hydrogen is limited by the irradiation temperature, strain relaxation of the SiGe layer is not realized during room temperature (20 °C) proton irradiation. The study supports the idea that the compressive stress in the SiGe layer induces the indiffusion of vacancies and H, and reveals the important role of point defects in the strain relaxation of the strained SiGe layer.