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Students enter college with widely varying levels of preparation. This is especially visible to faculty and administrators tasked with ensuring student success in core STEM courses and helping underrepresented students succeed. Flexible support strategies are needed. They must be timely and measurable so that limited funds can be optimally allocated. This paper reviews a program that addresses these concerns and is translatable to many higher education settings and disciplines. It is situated in a physics department at a large public research university in an urban city in the southern United States. A group of rotating faculty improved the success rate in an introductory physics course for non-physics majors. A diagnostic exam is used to assess students’ preparation in order to assign some to a peer-led supplementary recitation. An overview of program implementation and results is shared, along with strategies and suggested solutions to further address gaps in success rates in order to provide all students an equitable university experience and chance of success.

Flexible electronics and mechanically bendable devices based on Group III-N semiconductor materials are emerging; however, there are several challenges in manufacturing, such as cost reduction, device stability and flexibility, and device-performance improvement. To overcome these limitations, it is necessary to replace the brittle and expensive semiconductor wafers with single-crystalline flexible templates for a new-bandgap semiconductor platform. The substrates in the new concept of semiconductor materials have a hybrid structure consisting of a single-crystalline III-N thin film on a flexible metal tape substrate which provides a convenient and scalable roll-to-roll deposition process. We present a detailed study of a unique and simple direct epitaxial growth technique for crystallinity transformation to deliver single-crystalline GaN thin film with highly oriented grains along both a-axis and c-axis directions on a flexible and polycrystalline copper tape. A 2-dimensional (2D) graphene having the same atomic configuration as the (0001) basal plane of wurtzite structure is employed as a seed layer which plays a key role in following the III-N epitaxy growth. The DC reactive magnetron sputtering method is then applied to deposit an AlN layer under optimized conditions to achieve preferred-orientation growth. Finally, single-crystalline GaN layers (∼1 μm) are epitaxially grown using metal organic chemical vapor deposition (MOCVD) on the biaxially-textured buffer layer. The flexible single-crystalline GaN film obtained using this method provides a new way for a wide-bandgap semiconductor platform pursuing flexible, high-performance, and versatile device technology.

Although skilled cue utilization is presumed to result primarily from domain-specific experience, individual differences in learning are theorized to play a significant role. Using a single-group correlational design, this study tested whether individuals’ domain-general associative learning capacity was related to performance in a complex real-world decision task presumed to rely heavily on cues: lie detection. A total of 21 participants completed an associative learning task in the form of a Space Invaders-like game. In the game, those who learn the cues are able to respond faster to the appearance of an enemy ship. Participants were also surveyed on their awareness of cues in the game. This was followed by a lie detection task. It was hypothesized that greater associative learning would be associated with greater awareness of cues in the learning task, and subsequently, superior accuracy in the lie detection task. Participants’ associative learning was correlated with their cue awareness ( r pb = .782, p < .001). Further, learning was associated with better performance in the lie detection task ( r = .544, p = .011); however, accuracy was found to be unrelated to the types of cues reportedly used during detection. These findings have implications for our understanding of cue acquisition and expertise development.

Objectives To investigate if an exercise-based injury prevention program (IPP) can modify risk factors for injury in community-level adolescent cricket pace bowlers. Design Cluster-randomised controlled trial. Methods Eight cricket organisations (training two times per week and no previous involvement in a structured IPP) participated in this cluster-randomised trial. Participants were aged 14–17 years, injury free, and not currently performing a rehabilitation/exercise program. Cricket organisations (clusters) were block-randomised by computerised number generation into an intervention group (performed an eight-week IPP at training) or control group (continued their usual cricket activity). Participants were not blinded to group allocation. Strength, endurance, and neuromuscular control were assessed at baseline and follow-up. Treatment effects were estimated using linear mixed models. Results Sixty-five male adolescent pace bowlers (intervention n = 32 and control n = 33) were randomised. There were significant treatment effects favouring the intervention group for shoulder strength (90°/s) 0.05 (95% CI 0.02–0.09) N m/kg, hamstring strength (60°/s) 0.32 (95% CI 0.13–0.50) N m/kg, hip adductor strength dominant 0.40 (95% CI 0.26–0.55) N m/kg and non-dominant 0.33 (95% CI 0.20–0.47) N m/kg, SEBT reach distance dominant 3.80 (95% CI 1.63–6.04) percent of leg length (%LL) and non-dominant 3.60 (95% CI 1.43–5.78) %LL, and back endurance 20.4 (95% CI 4.80–36.0) seconds. No differences were observed for shoulder strength (180°/s) (p = 0.09), hamstring strength (180°/s) (p = 0.07), lumbopelvic stability (p = 0.90), and single leg squat knee valgus angle (dominant p = 0.06, non-dominant p = 0.15). Conclusions Exercise-based IPPs can modify risk factors for injury in community-level adolescent pace bowlers. Future research is needed to confirm if IPPs can also reduce injury risk in this population.

Despite progress in attractiveness research, we have yet to identify many fitness-relevant cues in the human phenotype or humans’ psychology for responding to them. Here, we test hypotheses about psychological systems that may have evolved to process distinct cues in the female lumbar region. The Fetal Load Hypothesis proposes a male preference for a morphological cue: lumbar curvature. The Lordosis Detection Hypothesis posits context-dependent male attraction to a movement: lordosis behavior. In two studies (Study 1 N: 102, Study 2 N: 231), we presented men with animated female characters that varied in their lumbar curvature and back arching (i.e., lordosis behavior). Irrespective of mating context, men’s attraction increased as lumbar curvature approached the hypothesized optimum. By contrast, men experienced greater attraction to lordosis behavior in short-term than long-term mating contexts. These findings support both the Lordosis Detection and Fetal Load Hypotheses. Discussion focuses on the meaning of human lordosis and the importance of dynamic stimuli in attractiveness research.

Some studies have linked bilingualism with a later onset of dementia, Alzheimer's disease (AD), and mild cognitive impairment (MCI). Not all studies have observed such relationships, however. Differences in study outcomes may be due to methodological limitations and the presence of confounding factors within studies such as immigration status and level of education. We conducted the first systematic review with meta-analysis combining cross-sectional studies to explore if bilingualism might delay symptom onset and diagnosis of dementia, AD, and MCI. Primary outcomes included the age of symptom onset, the age at diagnosis of MCI or dementia, and the risk of developing MCI or dementia. A secondary outcome included the degree of disease severity at dementia diagnosis. There was no difference in the age of MCI diagnosis between monolinguals and bilinguals [mean difference: 3.2; 95% confidence intervals (CI): -3.4, 9.7]. Bilinguals vs. monolinguals reported experiencing AD symptoms 4.7 years (95% CI: 3.3, 6.1) later. Bilinguals vs. monolinguals were diagnosed with dementia 3.3 years (95% CI: 1.7, 4.9) later. Here, 95% prediction intervals showed a large dispersion of effect sizes (-1.9 to 8.5). We investigated this dispersion with a subgroup meta-analysis comparing studies that had recruited participants with dementia to studies that had recruited participants with AD on the age of dementia and AD diagnosis between mono- and bilinguals. Results showed that bilinguals vs. monolinguals were 1.9 years (95% CI: -0.9, 4.7) and 4.2 (95% CI: 2.0, 6.4) older than monolinguals at the time of dementia and AD diagnosis, respectively. The mean difference between the two subgroups was not significant. There was no significant risk reduction (odds ratio: 0.89; 95% CI: 0.68-1.16) in developing dementia among bilinguals vs. monolinguals. Also, there was no significant difference (Hedges' g = 0.05; 95% CI: -0.13, 0.24) in disease severity at dementia diagnosis between bilinguals and monolinguals, despite bilinguals being significantly older. The majority of studies had adjusted for level of education suggesting that education might not have played a role in the observed delay in dementia among bilinguals vs. monolinguals. Although findings indicated that bilingualism was on average related to a delayed onset of dementia, the magnitude of this relationship varied across different settings. This variation may be due to unexplained heterogeneity and different sources of bias in the included studies. Registration: PROSPERO CRD42015019100.

Objectives Undesirable bowling kinematics can increase the risk of low back injury. This study investigated if an exercise-based injury prevention program (IPP) could modify bowling kinematics in community-level adolescent pace bowlers. Design Cluster-randomised controlled trial. Methods Pace bowlers from eight cricket organisations were cluster-randomised into an intervention or control group. At baseline and follow-up sessions biomechanical bowling data were collected. Between sessions, the intervention group completed an eight-week IPP while the control continued their normal cricket activity. Treatment effects (95% CI) were estimated with linear mixed models. Results There were significant treatment effects favouring the intervention group for shoulder counter-rotation (−3.8°; −7.2° to −0.3°) and lateral trunk flexion relative to the pelvis (−2.2°; −4.0° to −0.5°). Shoulder counter-rotation also increased in the control group by 2.2° (Cohen’s d = 0.22). There were no effects of the intervention on: lateral trunk flexion at front foot contact (FFC) (1.2°; −2.5° to 4.8°), lateral trunk flexion at ball release (BR) (−0.5°; −3.0° to 2.0°), pelvis rotation at FFC (0.9°; −4.0° to 2.2°), pelvis rotation at BR (−1.1°; −5.7° to 3.6°), front hip angle at FFC (1.6°; −3.6° to 6.7°), front hip angle at BR (−1.6°; −5.0° to 1.9°), front knee angle at FFC (−1.1°; −4.5° to 2.3°), front knee angle at BR (1.7°; −5.6° to 9.1°), or ball velocity (1.1 km h−1; −7.5 km h−1 to 9.7 km h−1). Conclusions The IPP maintained shoulder counter-rotation and lateral trunk flexion relative to the pelvis in the intervention group and this could attenuate injury risk. No treatment effects were observed for lower-limb kinematics.

The timing of exercise relative to meal consumption has recently been identified as potentially moderating the effectiveness of exercise on glycemic responses in type 2 diabetes mellitus (T2DM). The aim of this study was to systematically review the literature related to exercise timing, relative to meal consumption, and glycemic control in individuals with T2DM.Systematic searches in PubMed, EMBASE, CINAHL, Cochrane Library, and ClinicalTrials.gov Registry databases were performed to identify articles published in English from inception to October 2017. Two authors independently extracted data and evaluated the quality of studies using the Cochrane Collaboration Data Collection Form and the Cochrane Collaboration Risk of Bias Assessment Tool, respectively. A qualitative synthesis was performed on the included studies, and results summarized in tables.Nineteen randomized controlled trials with a total of 346 participants were included. Improvements in glycemia (glucose concentrations and glucose area under the curve) and insulin area under the curve appeared more consistent when exercise was performed during the postmeal period as compared with the premeal period; however, this observation was largely based on indirect comparisons between studies.There is some evidence from randomized controlled trials that exercise performed 30 min after meal consumption may convey greater improvements in glycemic control for individuals with T2DM. However, there are only two studies that have directly assessed the role of exercise timing on glycemic management, and adopted methodologies are heterogeneous. Future low-risk trials in this field are warranted.

Chemotherapy can cause serious neurotoxic side effects, such as painful peripheral neuropathies and disabling cognitive impairments. Four experiments examined whether Ibudilast, a clinically approved neuroimmune therapy, would reduce tactile allodynia and memory impairments caused by oxaliplatin in laboratory rats. Rats received an intraperitoneal injection of oxaliplatin (6mg/kg i.p.) or vehicle and were assessed for tactile allodynia 3 or 5days after injection, memory impairments in the novel object and novel location recognition tests 10-12days after injection, and fear conditioning 14days after injection. Ibudilast (7.5mg/kg) or vehicle was administered prior to oxaliplatin (Experiments 1 and 3) or prior to behavioural testing (Experiments 2 and 4). Ibudilast treatment prior to oxaliplatin prevented the development of tactile allodynia and memory impairments. Ibudilast treatment prior to behavioural testing reduced oxaliplatin-induced tactile allodynia, memory impairments, and impaired renewal of fear conditioning. These results suggest that Ibudilast could be an effective treatment against oxaliplatin-induced neuropathies and cognitive impairments.

We report measurements of room-temperature mean free paths of long-lived THz acoustic phonons in wurtzite GaN. Longitudinal phonon wave packets are excited and probed by femtosecond laser pulses in two InGaN-GaN multiple quantum well structures separated by a GaN layer. By measuring the temperature dependence of the phonon attenuation in the range 80--300 K we isolate the intrinsic phonon mean free path at 300 K which is found to be 5.3 and 3.5 \ensuremath{\mu}m at 1.06 and 1.43 THz, respectively. The measurements are found to be in good agreement with ab initio calculations which show that the main channel of the acoustic phonon decay is a three-phonon scattering process involving the acoustic phonon and two high-frequency optical phonons. Our results indicate that the contribution of low-THz acoustic phonons to thermal transport in GaN is relatively smaller than in Si; thus finite size effects are expected to be less important in GaN.

Adolescent cricket pace bowlers are prone to non-contact shoulder, low back and lower-limb injuries. Exercise-based injury prevention programmes (IPPs) are effective for reducing non-contact injuries in athletes; however, a specific programme for adolescent pace bowlers has not been published. This paper therefore seeks to provide a rationale for the development of an exercise-based IPP specific for adolescent pace bowlers. It also outlines design principles and provides an example exercise programme that can be implemented at the community level. In addition, the paper addresses other injury prevention techniques concerned with the prescription of appropriate bowling loads and the modification of poor bowling biomechanics. Performing an exercise-based IPP before cricket training could reduce injury rates in adolescent pace bowlers. Eccentric strengthening exercises can be employed to target injuries to the posterior shoulder muscles, hip adductors and hamstring muscles. The risk of low back, knee and ankle injury could also be reduced with the inclusion of dynamic neuromuscular control exercises and trunk extensor endurance exercises. Other prevention strategies that need to be considered include the modification of poor bowling biomechanics, such as shoulder counter-rotation and lateral trunk flexion. Coaches and players should also aim to quantify bowling load accurately and coaches should use this information to prescribe appropriate individualised bowling loads. Specifically, players would benefit from avoiding both long periods of low load and acute periods when load is excessively high. Future evidence is needed to determine the effectiveness of the example programme outlined in this paper. It would also be beneficial to investigate whether the modification of bowling biomechanics is achievable at the non-elite level and if bowling load can be accurately measured and manipulated within a community-level population.

Pretesting and early intervention measures to identify and remediate at-risk students were implemented in algebra-based introductory physics to help improve student success rates. Pretesting via a math and problem-solving diagnostic exam administered at the beginning of the course was employed to identify at-risk students based on their scores. At-risk students were encouraged to utilize an online math tutorial to increase their chances of passing the course. The tutorial covers the same math topics covered by the diagnostic exam. Results from 643 students enrolled in the course showed that the 61 at-risk students who successfully completed the math tutorial increased their odds of passing the course by roughly 4 times those of the at-risk students who did not. This intervention is easily implemented, short term, and can be administered concurrently with the course. Based on these results, the Department of Physics has implemented the math tutorials in all sections of the introductory algebra as well as the calculus-based physics courses.

Adolescent cricket pace bowlers are prone to injury. Recognising the risk factors for non-contact injury in this population will aid future injury prevention strategies. To identify the risk factors for non-contact injury in adolescent cricket pace bowlers. We systematically searched PubMed, Cochrane Library, PEDro, SPORTDiscus, Embase, and the South African Journal of Sports Medicine to identify all experimental and observational studies reporting risk factors for non-contact injuries in pace bowlers (aged 12–19 years). The search syntax included terms relevant to cricket bowling, injury, and known risk factors for injury. The Newcastle-Ottawa Quality Assessment Scale and a modified Newcastle-Ottawa Quality Assessment Scale were used to assess the risk of bias in the cohort and cross-sectional studies, respectively. Sixteen studies (five cross-sectional studies, 11 cohort studies) comprising 687 participants (96% male, 75% playing cricket in Australia) met the selection criteria and were included for qualitative synthesis. Three cross-sectional studies were rated as high risk of bias and two as very high risk of bias. For the cohort studies, three were rated as low risk of bias, and eight as high risk of bias. Injury was associated with bowling biomechanics (excessive lateral trunk flexion and pelvis/hip kinematics), reduced trunk endurance, poor lumbo-pelvic-hip movement control, and early signs of lumbar bone stress. Conflicting results were found by studies examining the mixed technique, bowling workload and quadratus lumborum asymmetry. The current systematic review identified a number bowling biomechanics and various neuromuscular deficiencies as risk factors for non-contact injury in adolescent pace bowlers. These factors may provide a useful target for future interventional research aiming to prevent injury in this population. Future studies should utilise prospective cohort designs, and ensure that participants are injury-free at baseline, confounding factors are well controlled and attrition rates are reported. This systematic review was registered a priori (PROSPERO, CRD42016043956).

A systematic study is presented on the effects of process parameters of S-gun configured DC magnetron sputtered ZrN thin films on c-plane Al2O3 substrates. Using a quartz crystal microbalance the deposition rate of ZrN is investigated as a function of Ar and N2 flow rates, target power, chamber pressure and gas injection position in the chamber. Selected growth conditions for ZrN show the interrelation of growth parameters on film orientation and crystallinity. (111) oriented ZrN thin films exhibit X-ray diffraction rocking curve FWHM as low as 0.36°. Additionally, (111) oriented ternary ZrxTi1−xN thin films (0≤x≤1) are also deposited on c-plane Al2O3 substrates. High resolution X-ray diffraction characterization shows that ZrxTi1−xN (x=0, 0.64, 0.80, 0.93, 1) layers exhibit rocking curve FWHM values of 0.0045–0.006° for the (111) reflection, indicating highly crystalline thin films. Atomic force microscopy characterizations show ZrxTi1−xN thin films with a surface roughness between 1.2 nm and 2.9 nm.

Presentations of a to-be-conditioned stimulus (CS) on its own impairs subsequent learning when that CS is paired with an unconditioned stimulus (US). Evidence for this latent inhibition (LI) effect in humans is said to require a “masking task” that diverts attention from the CS during preexposure. We present three experiments that demonstrate LI in humans without masking. Subjects performed a computerised task, making speeded responses to an imperative cue (the US) presented within a continuous stream of stimuli. During preexposure, a to-be-CS was presented 20 times among other stimuli, but excluding the US. Instructions ensured subjects actively monitored all stimuli at this time. This was immediately followed by the training phase, which included the US, the preexposed CS, and a novel CS. Both CSs were reliably followed by the US, but these associations were incidental to the instructed task. Nonetheless, some subjects learned the CS-US associations, responding faster when the US followed a CS than when it was unsignalled. All three experiments also found evidence for LI, in that subjects learned the novel CS-US association sooner than the preexposed CS-US association. We conclude that humans can show LI even when actively attending to the CS during preexposure.

Adolescent fast bowlers are prone to sustaining lumbar injuries. Numerous components have been identified as contributing factors; however, there is limited empirical evidence outlining how the muscles of the lumbopelvic region, which play a vital role in stabilising the spine, function during the bowling action and the influence of such activation on injuries in the fast bowler.Surface electromyography was utilised to measure the function of the lumbar erector spinae, lumbar multifidus, gluteus medius and gluteus maximus muscles bilaterally during the fast bowling action in a group of 35 cricket fast bowlers aged 12-16 years.Two prominent periods of activation occurred in each of the muscles examined. The period of greatest mean activation in the erector spinae and multifidus occurred near back foot contact (BFC) and within the post-ball-release (BR) phase. The period of greatest mean activation for the gluteus medius and gluteus maximus occurred during phases of ipsilateral foot contact.The greatest periods of muscle activation in the paraspinal and gluteal muscles occurred at times where vertical forces were high such as BFC, and in the phases near BR where substantial shear forces are present.The posterior muscles within the lumbopelvic region appear to play a prominent role during the bowling action, specifically when compressive and shear forces are high. Further research is required to substantiate these findings and establish the role of the lumbopelvic muscles in the aetiology of lumbar injury in the cricket fast bowler.

We use femtosecond laser pulses to generate coherent longitudinal acoustic phonons at frequencies of 1–1.4 THz and study their propagation in GaN-based structures at room temperature. Two InGaN-GaN multiple-quantum-well (MQW) structures separated by a 2.3 μm-thick GaN spacer are used to simultaneously generate phonon wave packets with a central frequency determined by the period of the MQW and detect them after passing through the spacer. The measurements provide lower bounds for phonon lifetimes in GaN, which are still significantly lower than those from first principles predictions. The material Q-factor at 1 THz is found to be at least as high as 900. The measurements also demonstrate a partial specular reflection from the free surface of GaN at 1.4 THz. This work shows the potential of laser-based methods for THz range phonon spectroscopy and the promise for extending the viable frequency range of GaN-based acousto-electronic devices.

The first implementation of fitting X-ray Bragg diffraction profiles from strained multilayer crystals at a remote web-based X-ray software server is presented. The algorithms and the software solutions involved in the process are described. The suggested technology can be applied to a wide range of scientific research and has the potential to promote remote collaborations across scientific communities.

We report the analysis of lateral composition modulation in (InAs)m/(GaSb)m superlattices by x-ray diffraction. Vertical and lateral satellite peaks for a 140 period structure were observed. The lateral modulation wavelength, average superlattice composition, and vertical superlattice wavelength were determined. The lateral modulation was observed only along one in-plane direction resulting in quantum wire-like structures along the [110] direction. The unconventional structure of the lateral composition modulation, in which the stacking of the layers leads to a doubling of the vertical superlattice period, is discussed.

We present quantitative characterization of atomic ordering in semiconductor alloy films by x-ray diffractometry. In particular, we show that the order parameter of CuPt-B ordered GaInP2 films can be determined without measuring the fundamental reflections or examining structural details of the ordered domains. Our method is based on the fact that the ordering peak is modulated by statistical displacements of atom planes, which is a function of the degree of ordering. Therefore, by comparing two or more ordering peaks in an x-ray spectrum, the order parameter of an ordered film can be extracted solely for those regions that are, in fact, ordered. The method can straightforwardly be extended to other ordered alloys.

High-quality strain-relaxed SiGe templates with a low threading dislocation density and smooth surface are critical for device performance. In this work, SiGe films on low temperature Si buffer layers were grown by solid-source molecular beam epitaxy and characterized by atomic force microscope, double-axis x-ray diffraction, photoluminescence spectroscopy, and Raman spectroscopy. Effects of the growth temperature and the thickness of the low temperature Si buffer were studied. It was demonstrated that when using proper growth conditions for the low temperature Si buffer the Si buffer became tensily strained and gave rise to the compliant effect. The lattice mismatch between the SiGe and the Si buffer layer was reduced. A 500 nm Si0.7Ge0.3 film with a low threading dislocation density as well as smooth surface was obtained by this method.

We applied high resolution x-ray diffraction techniques to determine the three dimensional domain shape in nominally lattice-matched, CuPtB ordered, InxGa1−xP epitaxial layers deposited on GaAs by metal organic vapor phase epitaxy. A technique of reciprocal space mapping is described which provides three-dimensional information on the shape and size of the ordered domains. The domain shape is obtained by reciprocal space mapping along orthogonal crystallographic directions. Applying this technique shows that, at large miscut angles, the domains are oriented close to the growth direction, and are elongated by differing extents along the [110] and [\(\bar 110\)].

Shear strain is present in Hg0.68Cd0.32Te epitaxial layers grown by molecular beam epitaxy on (211)-oriented Cd1−yZnyTe substrates. Differences in the substrate zinc composition led to lattice mismatch between the epitaxial layer and the substrate. The shear strain induced by the mismatch was measured using reciprocal space maps in the symmetric (422) and asymmetric (511) and (333) reflections. In addition, strain relaxation through the formation of misfit dislocations was confirmed using double crystal x-ray topography. Both the shear strain and the misfit dislocation density increased with increasing mismatch between the epitaxial layer and the substrate. Lattice-matched layers were free of misfit dislocations and exhibited triple axis diffraction rocking curve widths of approximately 6 arcsec. The combination of a thick epitaxial layer, a low index substrate, and the potential for lattice mismatch indicates that both shear strains and misfit dislocations must be considered in the structural analysis of HgCdTe/CdZnTe heterostructures.

X-ray diffraction is shown to provide a direct, quantitative, structural measurement of the degree of spontaneous ordering in GaInP. In this paper we combine x-ray diffraction and excitation photoluminescence analyses of CuPt-ordered GaInP, and comparing the results to theoretical predictions for the dependence of the band structure on order parameter, determine the values of the band-gap reduction and crystal-field splitting parameters for the perfectly ordered alloy.

The interfacial roughness morphology of sputtered Fe/Au multilayers was derived by combining the results from X-ray specular and non-specular (diffuse) scattering. From the non-specular intensity collected by a two-dimensional image plate we determined the in-plane height–height correlation function 〈 H i ( R ) H i (0)〉 and the growth correlation length as a function of feature size. From these parameters we determined both the static and dynamic roughness exponents α and z , which agree with the Kardar–Parisi–Zhang (KPZ) model of surface growth. The height difference function derived from the diffuse scattering is compared with several model functions that incorporate the asymptotic behavior of 〈 H ( R ) 2 〉 for the cases of R →0 and R →∞. We show that only one particular function is appropriate. The evolution of the interfacial slope is determined from the roughness exponents, and it is shown that it decreases as a function of time. This asymptotic smoothing is analyzed using the noiseless and stochastic KPZ equations. The noiseless KPZ equation predicts that the growth front is composed of paraboloids, which increase in lateral size and coalesce. This result is supported by an Atomic-force Microscopy measurement of the surface of one of the Fe/Au Multilayers.

Growth of epitaxial GaAs thin film on flexible, inexpensive substrates can open up the possibility of fabricating affordable and high efficiency III-V photovoltaics which may lead to a complete transformation of the PV market. Here we report the successful hetero-epitaxial growth of GaAs thin film by metal organic chemical vapor deposition on single-crystallinelike Ge thin film on flexible metal foils. GaAs epilayers showed (00l) orientation with zinc blende structure and good optoelectronic quality with minimal thermoelastic/lattice mismatch strain. High doping density due to Ge diffusion from the substrate was observed in the GaAs film with a Hall mobility of 285 cm2/V-s. XPS depth profiles showed significant diffusion of Ge in GaAs thin film.

Lateral structure is investigated in two antimonide superlattices using x-ray diffraction. We report periodic lateral modulation in AlSb/AlAs digital superlattices, while no lateral modulation is observed in similar InAs/Al(In)Sb digital superlattices. By fitting the diffraction data with dynamical diffraction theory we are able to determine the strain in each layer and at the interfaces. The findings are consistent with recent predictions of the critical thickness for three-dimensional growth.

Relaxed SiGe attracted much interest due to the applications for strained Si/SiGe high electron mobility transistor, metal-oxide-semiconductor field-effect transistor, heterojunction bipolar transistor, and other devices. High-quality relaxed SiGe templates, especially those with a low threading dislocation density and smooth surface, are critical for device performance. In this work, SiGe films on low-temperature Si buffer layers were grown by solid-source molecular-beam epitaxy and characterized by atomic force microscope, double-axis x-ray diffraction, and photoluminescence spectroscopy. It was demonstrated that, with the proper growth temperature and Si buffer thickness, the low-temperature Si buffer became tensily strained and reduced the lattice mismatch between the SiGe and the Si buffer layer. This performance is similar to that of the compliant substrate: a thin substrate that shares the mismatch strain in heteroepitaxy. Due to the smaller mismatch, misfit dislocation and threading dislocation de...

Nominally lattice-matched GaInAs layers grown by metal organic vapor phase epitaxy on InP substrates have been studied using high-resolution x-ray diffraction (HRXRD) to determine the growth conditions under which ordering is introduced. HRXRD provides an independent means to quantify the order parameter of semiconductor heterostructures as well as the ordering on different {111} planes, i.e., double variant ordering. This independent means to determine ordering provides for a better understanding of the effects of ordering on the electronic and optical properties. Double variant ordering was observed for epitaxial layers grown on exact (001) InP substrates, with an order parameter of about 0.1 in both variants. For substrates that were miscut by 6 degrees, single variant ordering was detected. In these cases, an order parameter as high as 0.66 was measured for certain growth conditions. The layers grown on vicinal substrates are all of high crystalline quality, those on (001) substrates exhibit some mosaic spread.

X-ray scattering and transmission electron microscopy (TEM) have been used to study short-range order in Al1−xlnxAs thin films grown by molecular beam epitaxy. Two samples grown on (001) InP at temperatures of 370°C and 400°C are characterized. The first exhibits simultaneous triple-period-A and CuPt-A short-range order with a rather short correlation range of about 2.4 nm normal to the (111) planes. Within these (individual) planes the concentration, however, is uniform over a considerably greater distance – about 6 to 9 nm – leading to a highly anisotropic scattering. This observation of triple-period short-range ordering in a sample that exhibits 2×1 surface reconstruction during growth is unexpected. We also report on the first observation of the coexistence of triple-period-A and CuPt-B short-range order. The diffuse scattering exhibits significant intensity anomalies that we attribute to atomic displacements associated with the short-range order. The second sample exhibits CuPt-B short-range ordering with scattering that is significantly streaked, suggestive of lamellar-shaped ordered domains. This sample also exhibits intensity anomalies that must be associated with atomic displacements. The first sample contains a high density of twin lamellae, while both samples contain high densities of stacking faults leading to additional narrow streaking along symmetry-allowed 〈111〉 directions. These growth faults most likely arise from the relatively low growth temperatures.

The growth by sputtering of a series of thin films of Fe/Au on MgO(001) substrates was analyzed using Bragg and diffuse X-ray scattering. The Fe (bcc) layer grows rotated by 45° with respect to the MgO – Au(fcc) (001) epitaxial orientation, resulting in an almost perfect match between the two metallic structures. By collecting the X-ray diffuse scattering under grazing incidence using a 2-dimensional image plate detector, we mapped the reciprocal space of these films. We characterized the correlated interface roughness starting with a buffer of Fe in which only three interfaces are present. The propagation of the roughness was subsequently characterized for Fe/Au multilayers with 40 and 100 bilayers. We observe an enlargement of the surface features as a function of time, evidenced by the longer lateral cutoff length measured for thicker films.

The Wake Shield Facility (WSF) created to characterize and utilize the ultra‐vacuum of space has corroborated the formation of a wake region behind an orbiting vehicle. In its maiden flight on the remote manipulator arm of STS‐60 in February, 1994, the WSF generated the highest vacuum ever measured in low earth orbit space. In addition, details of wake formation and flow field characterization have been obtained with the added benefit of the characterization of the contaminating effects of the Orbiter on the low earth vacuum environment.

We report the results of a detailed x-ray diffraction analysis of two AlxIn1−xAsySb1−y∕GaSb multilayer samples grown by molecular beam epitaxy on GaSb (100). The kinematical scattering theory was used to fit the x-ray diffraction intensity profiles to determine the lattice spacing, composition, and strain of the multilayers, allowing for interdiffusion between the layers and variation in the multilayer wavelength. It has been determined that the quaternary alloy composition varies throughout the layer and that there is an interfacial quaternary layer that differs in composition from that of the bulk AlxIn1−xAsySb1−y layer. A rationale for this graded composition and interfacial layer will be discussed based on the growth dynamics for this system.

Lateral compositional modulation in a (InAs)C13 (GaSb)13 superlattice grown by molecular beam epitaxy for infrared detector applications has been investigated using high-resolution X-ray diffraction. X-ray diffraction reciprocal space maps exhibit distinct lateral satellite peaks about the vertical superlattice peaks; however, the pattern is tilted with respect to the (001) direction. This tilt is directly related to the stacking of the layers as revealed by cross-sectional scanning tunnelling microscopy (XSTM) images. XSTM shows the morphology of the structure to consist of InAs- and GaSb-rich regions with a modulation wavelength of ∼1200 A and a lateral composition wavelength of 554± 3AA. The modulation only occurs along one in-plane direction, resulting in InAs ‘nanowires’ along the [110] direction, which are several microns long. The possible causes of the lateral composition modulation and its impact on device performance are discussed.

We have performed an investigation into the synthesis of Al2O3/Si heterostructures grown by gas source molecular beam epitaxy. The study has been motivated by the potential of the aluminum oxide as a barrier material for silicon, enabling Si based tunneling resonant diodes, as well as the possibility for a coherent silicon on insulator material with low dislocation density. The films have been grown on Si(111) orientation, in a gas source molecular beam epitaxy chamber equipped with silane, nitrous oxide gas sources, and solid state aluminum cell. The growth temperature was varied between 700 and 900 °C. A silicon thin film has been grown above 950 °C with the source material obtained from cracking of silane gas at the growth surface. The samples were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, Auger electron spectroscopy, and scanning electron microscopy. The films growth rate has been found to be very sensitive to the growth tempera...

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