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Oxygen sensitization and incorporation of ternary lead chalcogenide PbSe1-xTex thin films was investigated with two methods: adding oxygen via PbO to the bulk source alloy and post-deposition oxygen annealing. Characterization of the composition, structure, and morphology of these films confirmed that they follow Vegard's law for lattice parameter, and adding PbO to the source alloy did not impact the lattice parameter. However, adding PbO changed the electrical carrier properties observed in Hall effect measurements without forming any new oxide phase. Conversely, post-deposition annealing increased the lattice parameter due to oxygen incorporation into the lattice via interstitials in samples with appropriate grain boundary orientations. Morphological analysis revealed that PbSe0.8Te0.2 films demonstrated (100) texture, while PbSe0.6Te0.4 films demonstrated (111) texture with resulting grain boundary orientations more favorable to oxygen diffusion and incorporation. This varying oxygen incorporation from PbO source and oxygen annealing methods reveals trends that can lead to improved photodetector performance.

We demonstrate thin films of PbSe1−xSx and PbSe1−xTex lead chalcogenide ternary alloys as infrared detectors. The films were deposited on single crystal BaF2 substrates using physical vapor deposition. Detectivity in the wavelength range from 1 μm to 5 μm was measured at −40°C, and all films showed photoresponse signals more than an order of magnitude larger than their noise. The detectivity spectra were used to assess the tunability of the band gap from mixing the lead chalcogenide binaries. The PbSe1−xSx system showed tunability that followed Vegard’s law, while the PbSe1−xTex system showed tunability with a bowing parameter of −0.096 eV. Comparisons to measurements from the literature taken at room temperature suggest that the bowing parameter decreases with decreasing temperature, and the band gap temperature coefficient with respect to composition also shows bowing., ONR (Award N68335- 19-C-0070)

CdTe is considered to be an ideal semiconductor for X-ray and gamma-ray detectors. It is a wide bandgap semiconductor with high absorption coefficient and low electron-hole creation energy. Still, the use of this material is limited by the lack of availability and cost of large area crystals and challenges of coupling CdTe crystals with the read-out electronics. To overcome this problem, we investigated low-temperature growth of CdTe directly on the application-specific integrated circuit (ASIC). CdTe was deposited using modified close-space sublimation; water cooling was utilized to reduce substrate heating. Films, with thickness up to 500 µm, were grown at temperatures as low as 100 °C with the growth rates as high as 80 µm/hour. CdTe films were polycrystalline and highly resistive (9.0 × 107- 2.0 × 108 Ohm*cm). The grain size increased with the substrate temperature while resistivity remained nearly constant. X-ray-generated current was recorded with excitation energies of interest (16.5 KeV - 50 KeV). We are exploring the low-temperature grown CdTe as a potential alternative to expensive single crystals and associated bonding costs which will enable development inexpensive high quality radiation imagers.

Early Precambrian retrogressed eclogites are abundant in the central and northern parts of the Belomorian Province of the Fennoscandian Shield (Gridino + Keret and Salma + Kuru-Vaara study areas, respectively). Older and younger eclogites are recognized and their Archean and Paleoproterozoic ages are argued. Archean eclogites are intensely retrogressed and occur in amphibolite boudins in the tonalite-trondhjemite-granodiorite (TTG) gneiss matrix of the Archean Gridino eclogite-bearing mélange. Less retrogressed Paleoproterozoic eclogites form patches in mafic dikes and some amphibolite boudins, their Paleoproterozoic age is supported by U-Pb/SIMS data on zircons depleted in heavy rare earth elements (REE) with omphacite, garnet, and kyanite inclusions, and Sm-Nd and Lu-Hf mineral isochrons. Archean eclogites contain Archean heavy rare-earth elements (REE)-depleted zircons with garnet and zoisite inclusions and Archean garnets. No omphacite inclusions were found in these zircons, and this fact was considered as evidence against the existence of Archean eclogites. This study reports on the first finding of omphacite (23–25% Jd) inclusions in 2.68 Ga metamorphic zircons from eclogites from the Gridino eclogite-bearing mélange. The zircons are poorly enriched in heavy REE and display a weak negative Eu-anomaly but a poor positive Ce-anomaly typical of eclogitic zircons. Thus, zircons with these decisive features provide evidence for an Archean eclogite-facies metamorphism.

Lead salt detectors consisting of PbSe-PbS alloys offer detection capability in the 3-5 µm midinfrared wavelength range and exhibit responsivity at near-room temperature conditions. In this paper, we present the growth of PbSe0.6S0.4 layers by physical vapor deposition and evaluate their properties and performance as a function of the deposition temperatures (50°C and 200°C). Specifically, the influences of deposition temperature on the microstructure of PbSe0.6S0.4 and its subsequent detectivity is evaluated. The high temperature growth at 200°C results in films with the near-columnar fiber-like microstructure; low temperature growth at 50°C results in films with the fine equiaxed grains. Importantly, reduction of the growth temperature leads to a better photoresponse (up to two orders of magnitude) following the O2 sensitization of the PbSe0.6S0.4 films. We attribute this improvement to the more effective oxidation process due to a large increase in the density of the grain boundaries as a result of a smaller grain size.

The number of multi-robot systems deployed in field applications has risen dramatically over the years. Nevertheless, supervising and operating multiple robots simultaneously is a difficult task for a single operator to execute. In this article we propose a novel approach for utilizing automated advising agents in assisting an operator to better manage a team of multiple robots in complex environments. We introduce an advice provision methodology and exemplify its implementation using automated advising agents in two real-world human–multi-robot team collaboration tasks: the Search And Rescue (SAR) and the warehouse operation tasks. Our intelligent advising agents were evaluated through extensive field trials, with over 150 human operators using both simulated and physical mobile robots, and showed a significant improvement in the team's performance.

This paper considers a new, complex problem of UAV/UGV collaborative efforts to search and capture attackers under uncertainty. The goal of the defenders (UAV/UGV team) is to stop all attackers as quickly as possible, before they arrive at their selected goal. The uncertainty considered is twofold: the defenders do not know the attackers' location and destination, and there is also uncertainty in the defenders' sensing. We suggest a real-time algorithmic framework for the defenders, combining entropy and stochastic-temporal belief, that aims at optimizing the probability of a quick and successful capture of all of the attackers. We have empirically evaluated the algorithmic framework, and have shown its efficiency and significant performance improvement compared to other solutions.

The new results of the isotope UPb dating of zircons from zoisitites, which are the isofacies accessories of the eclogites in the Gridino eclogitebearing melange of the Belomorian mobile belt, Fennoscandian Shield, are reported. They can be used to modify the geodynamic evolution model of the Archean Belomorian subductioncollision system. Isotope and geochemical analyses of zircons were performed using the laser ablation method at the Beijing University laboratory, China. The isotope ages obtained vary from 3.0 to 1.9 Ga, but six groups/generations with the ages 3.0, 2.9, 2.82, 2.75, 2.72 and 1.96 Ga have been revealed. Morphological and geochemical data on zircons and their mineral inclusions were analyzed to assess the conditions of formation of each of the six groups and show that the early zircons, dated at 3000, 2900 and 2820 Ma, were trapped by gabbro anorthosites from granitoid enclosing rock upon intrusion; zircons dated at 2745 Ma seem to be associated with the formation of gabbroanorthosites, dated at 2720 Ma, and are consistent with the time of formation of an early zoisite association under eclogitefacies conditions, dated at 2680 Ma, which is the time of retrograde alterations at high pressures (10–14 Kbar). Zircon rims, dated at 1960 Ma and indicating the LaplandKola orogeny, have also been revealed. To interpret the data obtained, it should be admitted that the Gridino eclogitebearing melange began to form at 2720 Ma upon the transition from classical subduction to continental subduction, and at 2680 Ma its structure became more complex upon continental collision and eclogitefacies metamorphic events took place.

Area coverage is an important task for mobile robots, mainly due to its applicability in many domains, such as search and rescue. In this paper we study the problem of multi-robot coverage, in which the robots must obey a strong communication restriction: they should maintain connectivity between teammates throughout the coverage. We formally describe the Multi-Robot Connected Tree Coverage problem, and an algorithm for covering perfect N-ary trees while adhering to the communication requirement. The algorithm is analyzed theoretically, providing guarantees for coverage time by the notion of speedup factor. We enhance the theoretically-proven solution with a dripping heuristic algorithm, and show in extensive simulations that it significantly decreases the coverage time. The algorithm is then adjusted to general (not necessarily perfect) N-ary trees and additional experiments prove its efficiency. Furthermore, we show the use of our solution in a simulated officebuilding scenario. Finally, we deploy our algorithm on real robots in a real office building setting, showing efficient coverage time in practice.

Drones can assist in mitigating traffic accidents by deterring reckless drivers, leveraging their flexible mobility. In the real-world, drones are fundamentally limited by their battery/fuel capacity and have to be replenished during long operations. In this article, we propose a novel approach where police cruisers act as mobile replenishment providers in addition to their traffic enforcement duties. We propose a binary integer linear program for determining the optimal rendezvous cruiser-drone enforcement policy, which guarantees that all drones are replenished on time and minimizes the likelihood of accidents. In an extensive empirical evaluation, we first show that human drivers are expected to react to traffic enforcement drones similar to how they react to police cruisers, using a first-of-its-kind human study in realistic simulated driving. Then, we show that our proposed approach significantly outperforms the common practice of constructing stationary replenishment installations using both synthetic and real-world road networks. Finally, we propose and evaluate a novel optimization speedup method for mitigating the increased runtime of our proposed approach.

We have used spectroscopic ellipsometry to determine the complex dielectric function of a series of ternary BexZn1−xTe thin films grown by molecular beam epitaxy. The II–VI semiconductor alloys were grown on InP substrates that had an InGaAs buffer layer. After the growth, X-ray diffraction experiments were performed in order to determine the alloy concentration. A standard inversion technique was used to obtain the dielectric functions from the measured ellipsometric spectra, obtained between 2000 nm (5000 cm−1) and 40,000 nm (250 cm−1). By modelling the dielectric function as a collection of oscillators, representing longitudinal and transverse optical phonons of the BexZn1−xTe lattice, we were able to recover the phonon spectra for this alloy system. It is argued that the additional phonon modes that are obtained from ellipsometry are best understood from the recently-proposed percolation model.

We synthesized ZnO films via oxidative annealing of ZnSe/GaAs heterostructures and investigated their structural and optical properties. Films were polycrystalline, c -axis oriented and exhibited superior optical properties. In addition, we detected nanometer-size As clusters into the ZnO film and a Ga x O y layer at the ZnO/GaAs interface. Formation of an interfacial layer can prevent use of this technique for p-type doping and complicates identification of the origin of p-type response in the annealed ZnO/GaAs heterostructures.

Ba0.6Sr0.4TiO3 films were deposited by pulsed laser deposition on orthorhombic REScO3(1 1 0) (RE=Dy, Gd) single-crystal substrates. Films were investigated for their growth mode, crystalline quality, and strain states. Substrates were treated prior to growth to produce atomically flat surfaces having wide terraces (≈200 nm) and clear unit-cell-high steps. Atomic force microscopy and reflection high-energy electron diffraction indicated that the films grew epitaxially in a two-dimensional (2D) layer-by-layer mode. X-ray diffraction showed that all films (200 nm thick and less) were coherently/orthorhombically strained to the substrate according to the epitaxial relationship: (0 0 1)film∥(1 1 0)substrate; [1 0 0]film∥[0 0 1]substrate (and [0 1 0]film∥[1 1¯ 0]substrate). (0 0 2) rocking curves were 17 and 20 arcsec wide for films grown on RE=Dy and Gd, respectively.These films have rocking curve widths and dislocation densities that are several orders of magnitude lower than a film grown on SrTiO3 (0 0 1).

We have studied the microstructure of TiO2 films, grown by reactive molecular beam epitaxy (MBE) on LaAlO3 (LAO) and SrTiO3 (STO) substrates, using a combination of transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS). TiO2 films grew epitaxially in the anatase polymorph and exhibited the crystallographic orientation relation of (001)(010)TiO2||(001)(010)substrate. High-resolution TEM and EELS studies indicated the presence of a cubic TiOx phase at the TiO2/STO interface. Interfacial TiOx phases were eliminated and a sharp TiO2/STO interface was achieved by growing the TiO2 film on a heteroepitaxial STO buffer layer.

TiO"2 films were grown using a reactive molecular beam epitaxy system equipped with high-temperature effusion cells as sources for Ti and an ozone distillation system as a source for O. The growth mode, characterized in-situ by reflection high-energy electron diffraction (RHEED), as well as the phase assemblage, structural quality, and surface morphology, characterized ex-situ by X-ray diffraction and atomic force microscopy (AFM), depended on the choice of substrate, growth temperature, and ozone flux. Films deposited on (100) surfaces of SrTiO"3, (La"0"."2"7Sr"0"."7"3)(Al"0"."6"5Ta"0"."3"5)O"3, and LaAlO"3 grew as (001)-oriented anatase. Both RHEED and AFM indicated that smoother surfaces were observed for those grown at higher ozone fluxes. Moreover, while RHEED patterns indicated that anatase films grown at higher temperatures were smoother, AFM images showed presence of large inclusions in these films.

GaN films are grown on [0 0 1] GaAs substrates by plasma-assisted molecular beam epitaxy using a three-step process that consists of a substrate nitridation, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. X-ray diffraction and transmission electron microscopy indicate that this method promotes prismatic growth of c-oriented α-GaN. Photoluminescence studies show that the emission from cubic β-GaN inclusions dominates the spectrum.

We use the Hanle effect to study spin relaxation in self-assembled CdSe quantum dots embedded in a Be 0.03 Zn 0.97 Se matrix. We measure a short transverse spin lifetime in the sub nanosecond range (0.31–0.35 ns) at 4.2 K. We propose that strong phonon and/or impurity scattering, due to unintentional contamination, limit the spin coherence time in CdSe / Be 0.03 Zn 0.97 Se QDs.

We propose a simplified version of our 1-bond 2-mode percolation model initially developed for the q ∼ 0 phonon properties of the stiff Be-VI bond in (Zn,Be)-chalcogenides, which open the class of random mixed crystals with contrast in the bond stiffness. The simplified version applies to the ‘usual’ alloys, i.e. made of soft-like bonds only. It is derived from detailed comparison of the Raman responses from the stiff Be-Te bond and the soft Zn-Te one in the pioneer (Zn,Be)Te system. The simplified version is eventually tested on (Ga,In)As whose 1-bond 2-mode behavior in the Ga-As range of the Raman spectra remains a much debated issue. Further, we lay the foundations for a comprehensive re-examination of the puzzling phonon behavior' of the similar (Ga,In)P alloy, by analogy with (Ga,In)As. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We propose a simplified version of the one-bond two-mode percolation model originally developed for the long wave phonons related to the stiff Be–VI bond in (Zn, Be) chalcogenides, which open the class of random mixed crystals with contrast in the bond stiffness. This is deduced from the comparison between the Raman responses from the stiff Be–VI bond and the soft Zn–VI one in these systems. The simplified version is tested on (Ga, In)As, made of soft-like bonds only and taken here as a representative challenging system. This results in a successful reinterpretation of the puzzling multi-phonon behaviour in the Raman/infrared spectra of this alloy, that has been a subject of debate. The discussion is supported by contour modelling of the TO and LO Raman lineshapes by applying the Hon and Faust treatment to a version of the modified-random-element-isodisplacement model generalized to multi-oscillators. Also, the assignment of the long wave phonons in (Ga, In)As is supported by atomistic calculations of the bond length distributions of the minority bond species in large (Ga, In)As supercells corresponding to alloy compositions close to the In–As (In ~0.19) and Ga–As (In ~0.81) bond percolation thresholds. The configurations are analysed to distinguish between isolated and connected bonds, not in the usual terms of next nearest neighbours.

We propose a ‘one bond→two modes’ model for the long wavelength optical phonons in random zinc-blende A x B 1− x C ternary alloys, based on the percolation site theory. Our model takes into account the ‘fractal→normal’ object transition, which goes with the ‘dispersion→continuum’ topology transition at the percolation thresholds of the A–C and B–C bonds. We first introduce the basics of our model in the case of Zn 1− x Be x (Se,Te) mixed crystals, whose parent binaries display a high contrast in the bond stiffness, which enhances the percolation effects. We then focus our study on standard systems, which display a much weaker contrast in the bond stiffness. The multi-phonon behavior of GaInAs alloys is re-examined in the light of the percolation model, with much success.

We discuss the annealing-dependence of exchange bias in Ga1-xMnxAs epilayers that are overgrown with Mn. Although pure Mn is a known antiferromagnet, we find that the as-grown Mn overlayer does not produce any exchange coupling with Ga1-xMnxAs. Rather, our studies indicate that annealing in air is essential for creating the standard signatures of an exchange bias (a clear shift in the magnetization hysteresis loop and an increased coercive field). We use x-ray photoelectron spectroscopy to characterize the compositional depth profile of both as-grown and rapid thermal annealed samples. These studies demonstrate that the cleanest exchange bias arises when the Mn overlayer is completely converted into MnO., To be published in Journal of Superconductivity, Proceedings of 3rd International Conference on Physics & Applications of Spin-dependent Phenomena in Semiconductors

We use the Hanle effect to study spin relaxation in ZnxCd1−xSe epilayers grown on lattice-matched InP substrates. We study three samples with a fixed composition (x = 0.4) and with varying levels of n-doping, as well as an undoped sample with x = 0.5. Our measurements show that the spin relaxation time changes non-monotonically as a function of carrier density, with a maximum transverse spin lifetime of ~10.5 ns at low temperatures for a sample doped near the metal–insulator transition.

BexZn1−xTe thin films were grown on InP substrates by molecular beam epitaxy (MBE). Optical properties of the epilayers were studied using reflectance and photoluminescence (PL) measurements. An increase in the full width at half maximum of the emission line with the increase in BeTe content was observed and explained by the disorder-induced broadening. The temperature dependence of the band gap energy was determined from reflectance spectra and fitted by semiempirical equation taking into account average phonon energy and electron–phonon interaction. A reduction of the temperature variation of the band gap with the increase in BeTe content was observed. We propose that this effect is due to the decrease of the lattice contribution caused by the lattice hardening properties of BeTe.

Relaxed In y Ga 1− y As epilayers grown on (0 0 1) GaAs are known to exhibit a cross-hatched surface with ridges running along the [1 1 0] and [1 1 0] directions. We find that Ga 1− x Mn x As epilayers grown on such buffer layers can have as-grown Curie temperatures ( T C ) that are higher than the as-grown 110 K value typical of Ga 1− x Mn x As/GaAs heterostructures. Further, low-temperature annealing leads to only modest additional increases in T C , contrasting with the behavior in Ga 1− x Mn x As/GaAs where T C typically increases significantly upon annealing. Our observations suggest that the initial concentration of Mn interstitials in as-grown Ga 1− x Mn x As /In y Ga 1− y As heterostructures is smaller than that in as-grown Ga 1− x Mn x As/GaAs heterostructures. We propose that strain-dependent diffusion may drive Mn interstitials from the bulk of the growing crystal to more benign locations on the ridged surface, providing a possible route towards defect-engineering in these materials.

We report photoluminescence and reflectivity measurements of Mg x Zn y Cd 1-x-y Se epitaxial layers (0 0.3), we observe an anomalous temperature dependence of both the emission energy and line broadening. This behavior is assigned to the emission from localized states. Different mechanisms of carrier localization are discussed and exciton localization on statistical CdSe clusters is proposed to be the most likely one.

The optical constants e(E) of direct band gap Be x Zn 1 - x Te have been measured at 300 K using spectral ellipsometry (0.73-6.45 eV). The e(E) spectra displayed distinct structures associated with critical points at E 0 , E 0 +Δ 0 , E 1 , E 1 +Δ 1 , e 1 +Δ 1 and E 2 . The experimental data over the entire measured spectral range has been fit using the Holden-Munoz model dielectric function, which is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at E 0 , E 0 +Δ 0 and the E 1 , E 1 +Δ 1 , doublet. In addition to evaluate the energies of these various band-to-band critical points, information about the binding energy (R 1 ) of the two-dimensional exciton related to the E 1 , E 1 +Δ 1 critical points was obtained. The value of R 1 was in good agreement with effective mass theory. The ability to evaluate R, has important ramifications for first-principles band-structure calculations that include exciton effects at E 0 , E 1 , and E 2 .