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The unified defect model has been successful in explaining a wide variety of phenomena as oxygen or a metal is added to the III–V surface. These phenomena cover a range from a small fraction of a monolayer of adatoms to practical III–V structures with very thick overlayers. The tenets of the unified defect model are outlined, and the experimental results leading to its formulation are briefly reviewed. InP levels 0.4 and 0.1 eV and GaAs levels 0.7 and 0.9 eV below the conduction-band minimum (CBM) are associated with either missing column III or V elements. In InP, it has been found possible by a number of workers to ’’switch’’ between the two defect levels by variations in surface processing, temperature, and/or selection of the deposited atom. The need to apply the proper concepts for surface and interface chemistry and metallurgy is recognized, and the danger of using solely bulk concepts is emphasized. The reason for this is examined for certain cases on an atomic level. The need for new fundamental attacks on interface interaction is shown. The importance of semiconductor–oxide chemical stability is also recognized and, drawing on a large body of work from several laboratories, it is suggested that there will be more difficulties with ’’native’’ oxides on GaAs than on InP. It is concluded that ’’scientific engineering’’ of interfaces to give optimum performance should be a goal and test of the fundamental work described here. Specific possibilities are discussed for Schottky barriers on III–V’s.

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Implementation of wearable sweat sensors for continuous measurement of fluid based biomarkers (including electrolytes, metabolites and proteins) is an attractive alternative to common, yet intrusive and invasive, practices such as urine or blood analysis. Recent years have witnessed several key demonstrations of sweat based electrochemical sensing in wearable formats, however, there are still significant challenges and opportunities in this space for clinical acceptance, and thus mass implementation of these devices. For instance, there are inherent challenges in establishing direct correlations between sweat-based and gold-standard plasma-based biomarker concentrations for clinical decision-making. In addition, the wearable sweat monitoring devices themselves may exacerbate these challenges, as they can significantly alter sweat physiology (example, sweat rate and composition). Reported here is the demonstration of a fully integrated, wireless, wearable and flexible sweat sensing device for non-obtrusive and continuous monitoring of electrolytes during moderate to intense exertion as a metric for hydration status. The focus of this work is twofold: 1- design of a conformable fluidics systems to suit conditions of operation for sweat collection (to minimize sensor lag) with rapid removal of sweat from the sensing site (to minimize effects on sweat physiology). 2- integration of Na+ and K+ ion-selective electrodes (ISEs) with flexible microfluidics and low noise small footprint electronics components to enable wireless, wearable sweat monitoring. While this device is specific to electrolyte analysis during intense perspiration, the lessons in microfluidics and overall system design are likely applicable across a broad range of analytes.

Cortisol has long been recognized as the “stress biomarker” in evaluating stress related disorders. Plasma, urine or saliva are the current source for cortisol analysis. The sampling of these biofluids is either invasive or has reliability problems that could lead to inaccurate results. Sweat has drawn increasing attention as a promising source for non-invasive stress analysis. A sensitive HPLC-MS/MS method was developed for the quantitation of cortisol ((11β)-11,17,21-Trihydroxypregn-4-ene-3,20-dione) in human eccrine sweat. At least one unknown isomer that has previously not been reported and could potentially interfere with quantification was separated from cortisol with mixed mode RP HPLC. Detection of cortisol was carried out using atmospheric pressure chemical ionization (APCI) and selected reaction monitoring (SRM) in positive ion mode, using cortisol-9,11,12,12-D4 as internal standard. LOD and LOQ were estimated to be 0.04 ng/ml and 0.1 ng/ml, respectively. Linear range of 0.10 – 25.00 ng/ml was obtained. Intraday precision (2.5% – 9.7%) and accuracy (0.5% – 2.1%), interday precision (12.3% – 18.7%) and accuracy (7.1% – 15.1%) were achieved. This method has been successfully applied to the cortisol analysis of human eccrine sweat samples. This is the first demonstration that HPLC-MS/MS can be used for the sensitive and highly specific determination of cortisol in human eccrine sweat in the presence of at least one isomer that has similar hydrophobicity as cortisol. This study demonstrated that human eccrine sweat could be used as a promising source for non-invasive assessment of stress biomarkers such as cortisol and other steroid hormones.

For n- and p-doped III–V compounds, Fermi-level pinning and accompanying phenomena of the (110) cleavage surface have been studied carefully using photoemission at hν≲300 eV (so that core as well as valence band levels could be studied). Both the clean surfaces and the changes produced, as metals or oxygen are added to those surfaces in submonolayer quantities, have been examined. It is found that, in general, the Fermi level stabilizes after a small fraction of a monolayer of either metal or oxygen atoms have been placed on the surface. Most strikingly, Fermi-level pinning produced on a given semiconductor by metals and oxygen are similar. However, there is a strong difference in these pinning positions depending on the semiconductor: The pinning position is near (1) the conduction band maximum (CBM) for InP, (2) midgap for GaAs, and (3) the valence band maximum (VBM) for GaSb. The similarity in the pinning position on a given semiconductor produced by both metals and oxygen suggests that the states responsible for the pinning resulted from interaction between the adatoms and the semiconductor. Support for formation of defect levels in the semiconductor at or near the surface is found in the appearance of semiconductor atoms in the metal and in disorder in the valence band with a few percent of oxygen. Based on the available information on Fermi energy pinning, a model is developed for each semiconductor with two different electronic levels which are produced by removal of anions or cations from their normal positions in the surface region of the semiconductors. The pinning levels have the following locations, with respect to the VBM: GaAs, 0.75 and 0.5 eV; InP, 0.9 and 1.2 eV (all levels + 0.1 eV). The first energy given is assocaited with a missing anion and the second with a missing cation. For GaSb, only an acceptor due to a missing Sb has been located at 0.1 eV. Our work is found to correlate well with that on practical Schottky barriers. A detailed comparison is made with interface state positions and densities found by others on practical MIS structures, and it is suggested that the large density of these states on III–V’s as compared to Si is due to extrinsic interface states created by stoichiometric deficits of the III–V semiconductor. For GaAs, the dominant state is found at 0.7 eV and is associated with an As deficit. For InP, the major interface level is about 0.1 eV below the CBM. These positions are in good agreement with the existing data obtained from a wide variety of samples.

Some cancer survivors report positive subjective changes they describe as “life transforming.” We used a grounded theory approach to identify the content, underlying process, and identifying characteristics of self-defined “life-transforming” changes (LTCs) reported by 9 cancer survivors. To actualize their hopes for improvement, participants used a self-guided process centered on pragmatic action: researching options, gaining experience, and frankly evaluating results. Many participants discovered unanticipated personal abilities and resources, and those became highly useful in coping with other challenges apart from cancer. This made the increased personal abilities and resources “life transforming” rather than being substantially limited to reducing cancer-related problems. The action-oriented features and processes of LTCs seemed to be more fully described by experiential learning theory than by posttraumatic growth and coping. Supportive intervention to facilitate positive change processes could decrease suffering and enhance positive psychosocial and spiritual outcomes for cancer survivors.

The early stages of the formation of the Au-Si interface have been studied with photoelectron spectroscopy of the valence-band and core levels. In this study, the Si sample was prepared by cleavage in ultrahigh vacuum and Au was deposited in a controlled manner at room temperature, By slowly increasing the Au coverage on the surface, the silicon surface states were depleted rapidly (by a factor of 2 at an Au coverage of 0.2 monolayers) without any observable change ()0.1 eV) in the Fermi-level pinning position. Furthermore, at low coverages, the binding energies of the Au core levels and the Sd peaks in the valence band were similar to those of atomic Au; however, the width of the structure indicated that the Au is strongly interacting with Si. Measurement of the strength of the Au core levels gives evidence for penetration of a fraction of Au into Si. Thus, at low coverages, the Au is probably dispersed in and on the Si, causing the removal of the surface states and production of new states in the band gap. As the Au coverage is increased, the Au 4f and Si 2p core levels shift in such a way as to suggest the formation of an alloy with variable composition at the Au-Si interface. At the highest Au coverages {above 15 monolayers), a small amount (less than 1 monolayer) of Si was observed on the surface of the deposited Au overlayer. Thermal annealing of a thin Au (50 monolayers of Au) on Si at 500'C resulted in an increased Si concentration at the surface with the photoelectron spectra resembling those at low coverages (about 1.5 monolayers), thus indicating a high diffusion coefficient of Si through the Au layer. When less than 1 monolayer of 02 was adsorbed onto the cleaved Si surface prior to the deposition of Au, the intermixing of Au and Si was significantly reduced,