Effect of Non-Hydrostatic Stress on Kinetics and Interfacial Roughness during Solid Phase Epitaxial Growth in Si

We report preliminary in-situ time-resolved measurements of the effect of uniaxial stress on solid phase epitaxial growth in pure Si (001) for the case of stress applied parallel to the amorphous-crystal interface. The growth rate is reduced by the application of uniaxial compression, in agreement with previous results. Additionally, the velocity continues to decrease with time. This is consistent with interfacial roughening during growth under stress, and is supported by both reflectivity measurements and cross-sectional TEM observations. We present a new kinetically-driven interfacial roughening mechanism which is consistent with our observations.Engineering and Applied Science

Strain-Stabilized Solid Phase Epitaxy of Si–Ge on Si.

We compare solid phase epitaxial growth of amorphous Si–Ge alloys created by Ge ion implantation into Si with and without the imposition of 0.5 GPa of externally applied biaxial tensile stress. External loading stabilizes the growth front against roughening, resulting in a doubling of the maximum reported Ge concentration for stable growth to 14 at. %. The externally applied stress appears to superpose with the intrinsic compositional stress and indicates a threshold of approximately 0.6 GPa for interface breakdown. This principle is expected to be applicable to expanding the composition range for stable growth of other semiconductor alloy combinations by other growth techniques.Engineering and Applied Science

Kinetically Driven Growth Instability in Stressed Solids

We report a new stress-induced kinetically driven morphological instability for driven systems. The effect of stress on the interfacial mobility couples to stress variations along a perturbed planar growth front. Comparison of theory and experiment for solid phase epitaxy at a corrugated Si(001) interface, with no free parameters, indicates that the new mechanism is required to account for the observed growth of the corrugation amplitude. This mechanism operates in conjunction with known diffusional and elastic strain energy-driven instabilities in determining morphological evolution.Engineering and Applied Science

IMECE2005-80090 TOWARDS HIGH TEMPERATURE ACTUATION USING GRAPHITE INTERCALATION COMPOUNDS

ABSTRACT Electrochemically formed graphite intercalation compounds (GICs) have many intrinsic properties well-suited for compact actuation in applications at high temperatures. GICs using ionic liquids are of interest because of their good thermal stability at elevated temperatures, high ionic conductivity, and low volatility. In this study we observed the potential and strain behavior of highly oriented pyrolytic graphite and 1-ethyl-3-methylimidazolium hexafluorophosphate subjected to a light compressive load and constant current. In situ measurements of the anode during intercalation showed a reversible strain of 2.5% to 4.5% from 100ºC up to 250ºC

Stability of Solid State Reaction Fronts

We analyze the stability of a planar solid-solid interface at which a chemical reaction occurs. Examples include oxidation, nitridation, or silicide formation. Using a continuum model, including a general formula for the stress-dependence of the reaction rate, we show that stress effects can render a planar interface dynamically unstable with respect to perturbations of intermediate wavelength

Spin relaxation in (110) and (001) InAs/GaSb superlattices

We report an enhancement of the electron spin relaxation time (T1) in a (110) InAs/GaSb superlattice by more than an order of magnitude (25 times) relative to the corresponding (001) structure. The spin dynamics were measured using polarization sensitive pump probe techniques and a mid-infrared, subpicosecond PPLN OPO. Longer T1 times in (110) superlattices are attributed to the suppression of the native interface asymmetry and bulk inversion asymmetry contributions to the precessional D'yakonov Perel spin relaxation process. Calculations using a nonperturbative 14-band nanostructure model give good agreement with experiment and indicate that possible structural inversion asymmetry contributions to T1 associated with compositional mixing at the superlattice interfaces may limit the observed spin lifetime in (110) superlattices. Our findings have implications for potential spintronics applications using InAs/GaSb heterostructures.Comment: 4 pages, 2 figure

Territorialising movement: the politics of land occupation in Bangladesh

This paper considers the politics of land occupation in Bangladesh. Contentious politics have been conceptualised as 'societies in movement' by Raul Zibechi, defined through their attempts to disperse power through the reconfiguration of social relations between peasants, the state and capital. Drawing on the author's ethnographic engagement with peasant farmer movements in Bangladesh since 2002, the paper analyses the differential powers generated in, by and through the production of relations and connections involved in land occupations. This requires a consideration of both relational and structural understandings of contentious politics. Organisational structures and dynamics, as well as the 'resourcefulness' of social movements (e.g. their capacities to deploy material resources, skills and knowledges), enable land occupation since these are crucial in creating and maintaining the socio-material relations necessary for political activity to be prosecuted. Drawing together these insights, the paper conceptualises land occupation as a process of 'territorialising movement' articulated through three interwoven spatial practices: strategic occupation, reconfiguration of social relations and territorialisation of translocal solidarities