Role of hydrogen in hydrogen-induced layer exfoliation of germanium

The role of hydrogen in the exfoliation of Ge is studied using cross-sectional transmission electron microscopy, atomic force microscopy, and multiple-internal transmission mode Fourier-transform infrared absorption spectroscopy and compared with the mechanism in silicon. A qualitative model for the physical and chemical action of hydrogen in the exfoliation of these materials is presented, in which H-implantation creates damage states that store hydrogen and create nucleation sites for the formation of micro-cracks. These micro-cracks are chemically stabilized by hydrogen passivation, and upon annealing serve as collection points for molecular hydrogen. Upon further heating, the molecular hydrogen trapped in these cracks exerts pressure on the internal surfaces causing the cracks to extend and coalesce. When this process occurs in the presence of a handle substrate that provides rigidity to the thin film, the coalescence of these cracks leads to cooperative thin film exfoliation. In addition to clarifying the mechanism of H-induced exfoliation of single-crystal thin Ge films, the vibrational study helps to identify the states of hydrogen in heavily damaged Ge. Such information has practical importance for the optimization of H-induced layer transfer as a technological tool for materials integration with these materials systems

Spectroscopic studies of the mechanism for hydrogen-induced exfoliation of InP

The motion and bonding configurations of hydrogen in InP are studied after proton implantation and subsequent annealing, using Fourier transform infrared (FTIR) spectroscopy. It is demonstrated that, as implanted, hydrogen is distributed predominantly in isolated pointlike configurations with a smaller concentration of extended defects with uncompensated dangling bonds. During annealing, the bonded hydrogen is released from point defects and is recaptured at the peak of the distribution by free internal surfaces in di-hydride configurations. At higher temperatures, immediately preceding exfoliation, rearrangement processes lead to the formation of hydrogen clusters and molecules. Reported results demonstrate that the exfoliation dynamics of hydrogen in InP and Si are markedly different, due to the higher mobility of hydrogen in InP and different implant-defect characteristics, leading to fundamental differences in the chemical mechanism for exfoliation

From reflective learning to reflective practice: assessing transfer

A key attribute of reflective practice is its capacity for on-going purposeful learning in relation to changing and demanding professional work. The teaching of reflective learning techniques in management education is intended to promote deep-level learning and the application of critical thinking to oneself, personal experience and the work environment. However, we lack empirical evidence that the teaching of reflective learning leads to enhanced reflective practice in professional work. This study provides an examination of reflection in work post formal education. It reports on interviews with 18 Human Resource professionals. Reflection does not get ‘left behind’ on completion of formal teaching but there is not an even or simple process of transfer to a work context. Likewise, there was not a slavish adherence to reflective techniques but rather some evidence that students were able to translate their learning into something meaningful for their practice. © 2016 Society for Research into Higher Educatio

Striving to Practice What We Preach: Academics reflecting on teaching reflective practice

That reflection is part of the HRD academics’ continuing professional development is a powerful rhetoric. But to what extent are we guilty of hypocrisy? Inspired by the title and theme of the conference ‘HRD: Reflecting upon the Past, Shaping the Future’ this paper seeks to make a critically reflective statement on our own practice as HRD academics teaching and researching reflective practice. Researching ‘practising what we preach’, in the context of reflective practice, raises difficult questions but offers the potential for valuable insight into the HRD academics’ professional practice

Design approaches and materials processes for ultrahigh efficiency lattice mismatched multi-junction solar cells

In this study, we report synthesis of large area (>2cm^2), crack-free GaAs and GaInP double heterostructures grown in a multi-junction solar cell-like structure by MOCVD. Initial solar cell data are also reported for GaInP top cells. These samples were grown on Ge/Si templates fabricated using wafer bonding and ion implantation induced layer transfer techniques. The double heterostructures exhibit radiative emission with uniform intensity and wavelength in regions not containing interfacial bubble defects. The minority carrier lifetime of ~1ns was estimated from photoluminescence decay measurements in both double heterostructures. We also report on the structural characteristics of heterostructures, determined via atomic force microscopy and transmission electron microscopy, and correlate these characteristics to the spatial variation of the minority carrier lifetime

p-n junction heterostructure device physics model of a four junction solar cell

We present results from a p-n junction device physics model for GaInP/GaAs/GaInAsP/GaInAs four junction solar cells. The model employs subcells whose thicknesses have an upper bound of 5μm and lower bound of 200nm, which is just above the fully depleted case for the assumed doping of N_A = 1 x 10^(18) cm^(-3) and N_D = 1 x 10^(17) cm^(-3). The physical characteristics of the cell model include: free carrier absorption, temperature and doping effects on carrier mobility, as well as recombination via Shockley-Read-Hall recombination from a single midgap trap level and surface recombination. Upper bounds on cell efficiency set by detailed balance calculations can be approached by letting the parameters approach ideal conditions. However whereas detailed balance calculations always benefit from added subcells, the current matching requirements for series connected p-n multi-junctions indicate a minimum necessary performance from an added subcell to yield a net increase in overall device efficiency. For the four junction cell considered here, optimizing the subcell thickness is an important part of optimizing the efficiency. Series resistance limitations for concentrator applications can be systematically explored for a given set of subcells. The current matching limitation imposed by series connection reduces efficiency relative to independently-connected cells. The overall trend indicates an approximately 5% drop in efficiency for series connected cells relative to identical independently connected cells. The series-connected devices exhibit a high sensitivity to spectral changes and individual subcell performance. If any single subcell within the series-connected device is degraded relative to its optimal design, the entire device is severely hindered. This model allows complex heterostructure solar cell structures to be evaluated by providing device physics-based predictions of performance limitations

Reflective practice: is there transfer from classroom to workplace?

Does HE based teaching of reflective practice transfer into management practice in the workplace? This paper reports on research addressing this question. Initially the research is set in context. Extensive theorising, conceptual debate and discussion on a problematic curriculum have not been matched with empirical data about reflection as part of managing. Interviews with eighteen HR professionals provide the data upon which initial findings are drawn. Management practice is influenced by their professional programme and, in the main, reflection is an important element of perceived change. For some transfer appears restricted to instrumental practice. For others, however, a more complex picture emerges; one where glimpses of criticality are evident but where the link to the formal teaching of reflection is less straightforward. This, together with factors influencing the reflective landscape observed, warrant further analysis as a precursor to consideration of curriculum implication