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Homoepitaxial ZnO growth is demonstrated from conventional RF-sputtering at 400 °C on both Zn and O polar faces of hydrothermally grown ZnO substrates. A minimum yield for the Rutherford backscattering and channeling spectrum, vmin, equal to ~3% and ~12% and a full width at half maximum of the 00.2 diffraction peak rocking curve of (70±10) arc sec and (1400±100) arc sec have been found for samples grown on the Zn and O face, respectively. The structural characteristics of the film deposited on the Zn face are comparable with those of epilayers grown by more complex techniques like molecular beam epitaxy. In contrast, the film simultaneously deposited on the O-face exhibits an inferior crystalline structure ~0.7% strained in the c-direction and a higher atomic number contrast compared with the substrate, as revealed by high angle annular dark field imaging measurements. These differences between the Zn- and O-face films are discussed in detail and associated with the different growth mechanisms prevailing on the two surfaces. [ABSTRACT FROM AUTHOR]

We studied the structural properties, defect formation, and thermal stability of H in hydrothermally grown ZnO single crystals implanted with H- dose ranging from 2.5×1016 to 1×1017 cm-2. H implantation is found to create deformed layers with a uniaxial strain of 0.5-2.4% along the c-axis in ZnO, for the low and high dose, respectively. About 0.2-0.4% of the original implanted H concentration can still be detected in the samples by secondary ion mass spectrometry after annealing at a temperature up to 800 °C. The thermally stable H is tentatively attributed to H related defect complexes involving the substitutional H that are bound to O vacancies and/or the highly mobile interstitial H that are bound to substitutional Li occupying Zn vacancies as the samples are cooled slowly from high temperature annealing. H implantation to a dose of 1×1017 cm-2 and followed by annealing at 800 °C, is found to result in the formation of vacancy clusters that evolved into faceted voids with diameter varying from 2 to 30 nm. The truncations around the voids form more favorably on the O-terminated surface than on the Zn-terminated surface, suggesting that O is a preferred surface polarity for the internal facets of the voids in the presence of H. [ABSTRACT FROM AUTHOR]

Two new electronic transition systems, namely, the [14.0]2[uppercase_phi_synonym]7/2-Χ 2Δ5/2 and the [15.7]2[uppercase_phi_synonym]5/2-Χ 2Δ5/2 transitions were observed and analyzed using laser vaporization/reaction supersonic free jet expansion and high resolution laser induced fluorescence spectroscopy. In addition, the (v, 0) bands with v=6–10 of the [14.6]2Δ5/2-Χ 2Δ5/2 transition were found to be perturbed by the [15.7]2[uppercase_phi_synonym]5/2 state. The interaction between the [14.6]2Δ5/2 and the [15.7]2[uppercase_phi_synonym]5/2 states is evident in the progressive increase in hyperfine width of rotational lines of the [14.6]2Δ5/2-X 2Δ5/2 transition as the vibrational quantum number increases. Deperturbation procedures were successfully applied to analyze the interaction between these two states. All observed spectra show partially resolved hyperfine structure, and the hyperfine width decreases rapidly as J increases suggested that the hyperfine structure conforms to the Hund’s case aβ coupling scheme. Accurate molecular and hyperfine constants for the [14.0]2[uppercase_phi_synonym]7/2, the [14.6]2Δ5/2 and the [15.7]2[uppercase_phi_synonym]5/2 states were obtained and analyzed. [ABSTRACT FROM AUTHOR]

Implantation, annealing, and oxidation processes have been used to form Au nanoparticles with a narrow size and depth distribution in a SiO2 layer. Different approaches have been attempted: in particular, the gettering of Au to fill preformed nanocavities (obtained by H-implantation and annealing) and thus overcome the broad particle size distribution that is normally associated with nanoparticles formed by implantation and annealing. The results suggest that nanocavities cannot be directly formed in SiO2 by H-implantation and a subsequent annealing due partly to the high mobility of H atoms in SiO2. However, cavities formed in Si are useful in obtaining a narrow size and depth distribution of Au precipitates: the Si substrate can then be oxidized to form Au nanoparticles in SiO2. Sequential wet oxidations of Si samples containing Au nanoparticles have revealed several interesting phenomena, namely, segregation of Au particles at a growing oxide interface, Au-enhanced oxidation, dissolution and reprecipitation of Au precipitates during oxidation, and preferential wetting of Au on the oxide layer. In particular, the Au dissolution and reprecipitation processes are Si interstitial mediated. By completely oxidizing the top Si layer, an array of Au precipitates can be confined at a precise depth within a SiO2 layer corresponding to the front interface of a buried oxide layer. The size distribution of the resulting Au precipitates in SiO2 is smallest when Au is first gettered to cavities and vacancies are subsequently introduced into the Si layer prior to oxidation. [ABSTRACT FROM AUTHOR]

High resolution laser induced fluorescence spectrum of IrB in the spectral region between 545 and 610 nm has been recorded and analyzed. Reacting laser-ablated iridium atoms with 1% B2H6 seeded in argon produced the IrB molecule. This is the first experimental observation of the IrB molecule. Four vibronic transition bands, (v,0) with v=0–3 of an electronic transition system, have been observed. Spectra of all four isotopic molecules, 191Ir10B, 193Ir10B, 191Ir11B, and 193Ir11B, were recorded. Isotopic relationships confirmed the carrier of the spectra and the vibrational quantum number assignment. Preliminary analysis of rotational lines showed that these vibronic bands are with Ω′=2 and Ω″=3. The electronic transition identified is assigned as the [16.5]3Π2-X 3Δ3 system. Partially resolved hyperfine structure which conforms to the Hund’s case aβ coupling scheme has been observed and analyzed. The bond length r0 of the lower X 3Δ3 state of IrB was determined to be 1.7675 Å. [ABSTRACT FROM AUTHOR]

Laser induced fluorescence spectrum of NiBr in the visible region between 604 and 666 nm has been recorded and analyzed. Fourteen bands belonging to three electronic transition systems, namely, [15.1] 2Δ5/2–X 2Π3/2, [15.1] 2Π3/2–X 2Π3/2, and [14.0] 2Δ5/2–X 2Π3/2 have been observed. Spectra of isotopic molecules were also observed and analyzed. Detailed analysis of the recorded spectra indicated that the two electronic states [15.1] 2Π3/2 and [15.1] 2Δ5/2 lie about 1 cm-1 apart from each other and J-dependent perturbation due to spin-uncoupling interaction has been observed. Least squares fitting procedures involving deperturbation matrix elements were used to fit the observed line positions, which yielded accurate molecular constants for the [15.1] 2Π3/2 and [15.1] 2Δ5/2 states. In addition, the (1,0) band of the [15.1] 2Δ5/2–X 2Π3/2 transition shows partially resolved hyperfine structure that was caused by the interaction of unpaired electron with the magnetic moment of the Br nucleus (nuclear spin of I=3/2) in the excited state. The rapid decrease in hyperfine width as J increases suggests that the hyperfine coupling in the excited state conforms to Hund’s case (aβ) coupling scheme. [ABSTRACT FROM AUTHOR]

Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching, annealing studies, and the dependence on impurities. The broad 935 meV photoluminescence band occurs at intrinsic interstitial complexes, the 835 meV band at small vacancy clusters, and the 1062 meV line at a low concentration of vacancy clusters which are possibly formed by aggregation of the 835 meV centers. [ABSTRACT FROM AUTHOR]

The article offers a detailed transmission electron microscopy analysis of defects formed in capped InAs/GaAs quantum dot samples. The three primary types of defects were: V-shaped defects, stacking fault pyramids and single stacking faults. These defects formed under growth conditions that resulted into either very large, indium-enriched, or coalesced islands. All of these defects start at the buried quantum dot layer.

In this work, rapid thermal annealing was performed on InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700 °C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800 °C, in addition to the largely redshifted photoresponse peak of 7.4 μm (compared with the 6.1 μm of the as-grown QDIP), a high energy peak at 5.6 μm (220 meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overall device performance was not affected by low annealing temperature, however, for high annealing temperature, some degradation in device detectivity (but not responsivity) was observed. This is a consequence of increased dark current due to defect formation and increased ground state energy. [ABSTRACT FROM AUTHOR]

The influence of various growth parameters such as coverage, the AsH3 flow (V/III ratio), and growth interrupts on the self-assembled growth of InAs/GaAs quantum dots (QDs) by metal organic chemical vapor deposition is reported. Of the various growth parameters, the AsH3 flow has a particularly strong influence. Higher AsH3 flows during deposition led to a faster nucleation process and larger islands, while the presence of AsH3 after nucleation led to continued island ripening. We suggest that this is the result of increased indium redistribution from the highly strained wetting layer to the islands, and possibly between the islands, at higher AsH3 flows. A large defect density was observed by plan-view transmission electron microscopy, whenever the growth parameters led to larger islands. Using our optimized growth conditions we are able to avoid such defect generation and still achieve a high QD density (3×1010 cm-2). [ABSTRACT FROM AUTHOR]

Vacancy-type defect production in Al- and Si-implanted 4H–SiC has been studied as a function of ion fluence, ion flux, and implantation temperature in the projected ion range region by positron annihilation spectroscopy and Rutherford backscattering techniques. Ion channeling measurements show that the concentration of displaced silicon atoms increases rapidly with increasing ion fluence. In the ion fluence interval of 1013–1014 cm-2 the positron annihilation parameters are roughly constant at a defect level tentatively associated with the divacancy VCVSi. Above the ion fluence of 1014 cm-2 larger vacancy clusters are formed. For implantations as a function of ion flux (cm-2 s-1), ion channeling and positron annihilation measurements behave similarly, i.e., indicating increasing damage in the projected range region with increasing ion flux. However, for samples implanted at different temperatures the positron annihilation parameter S shows a clear minimum at approximately 100 °C, whereas the normalized backscattering yield decrease continuously with increasing implantation temperature. This is explained by the formation of larger vacancy clusters when the implantation temperature is increased. [ABSTRACT FROM AUTHOR]

High-resolution laser-induced fluorescence spectrum of a jet-cooled NiI molecule has been recorded in the near infrared and visible regions. The NiI molecule was produced by reacting laser-ablated nickel atom and methyl iodide (CH[sub 3]I). Three electronic states have been identified that include the X [sup 2]Δ[sub 5/2] and two low-lying [13.9] [sup 2]Π[sub 3/2] and [14.6] [sup 2]Δ[sub 5/2] excited states. Molecular transition bands (v[sup ′],0) of the [13.9] [sup 2]Π[sub 3/2]-X [sup 2]Δ[sub 5/2] system with v[sup ′]=0, 4–9, and the (v[sup ′],0) bands of the [14.6] [sup 2]Δ[sub 5/2]-X [sup 2]Δ[sub 5/2] system with v[sup ′]=0–6 were observed and analyzed. Spectra of isotopic molecules confirmed the assignment of vibrational quantum number of the observed bands. Least squares fit of rotational transition lines yielded accurate molecular constants for the states studied. The bond length r[sub 0] measured for the X [sup 2]Δ[sub 5/2] is 2.3479 Å and the equilibrium bond length, r[sub e], for the [13.9] [sup 2]Π[sub 3/2] and [14.6] [sup 2]Δ[sub 5/2] are, respectively, 2.4834 and 2.5081 Å. With the use of a molecular orbital energy level diagram, we have examined the electronic configurations that give rise to the X [sup 2]Π[sub 3/2] ground state for NiF, NiCl, and NiBr, but the X [sup 2]Δ[sub 5/2] state for NiI. This work represents the first spectroscopic study of the NiI molecule. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article the effect of rapid thermal annealing (RTA) on a 30 stacked InAs/GaAs, molecular beam epitaxially grown quantum dot infrared photodetector (QDIP) device is studied. Temperatures in the range of 600–800 °C for 60 s, typical of atomic interdiffusion methods are used. After rapid thermal annealing the devices exhibited large dark currents and no photoresponse could be measured. Double crystal x-ray diffraction and cross sectional transmission electron microscopy studies indicate that this could be the result of strain relaxation. V-shaped dislocations which extended across many quantum dot (QD) layers formed in the RTA samples. Smaller defect centers were observed throughout the as-grown sample and are also likely a strain relaxation mechanism. This supports the idea that strained structures containing dislocations are more likely to relax via the formation of dislocations and/or the propagation of existing dislocations, instead of creating atomic interdiffusion during RTA. Photoluminescence (PL) studies also found that Si related complexes developed in the Si doped GaAs contact layers with RTA. The PL from these Si related complexes overlaps and dominates the PL from our QD ground state. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

4H-SiC wafers of orientations (0001) and (1120) were implanted with 60 keV Al[sup -] in different major axial, planar, and low symmetry (“random”) directions to ascertain the degree of channeling and to determine the optimum tilt conditions for ion implantation. Significant channeling was observed for all axial directions with the [1120] channel exhibiting the deepest channeling with a maximum penetration depth 45 times greater than the projected range of the random implants. Significant channeling was observed for the {1120} and especially the {0001} planar channels while the implants in the {1010} planar channels did not differ from the corresponding random implants. To minimize channeling in (0001) crystals, our results show that beam alignment normal to the surface is advisable for off-axis (0001) wafers with the miscut toward <1120>, while tilting of the wafer is necessary when the miscut is toward <1010>. For the (1120) material, channeling can be minimized by a tilt of >=10° toward the [0001] direction. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An experimental method of studying shifts between concentration-versus-depth profiles of vacancyand interstitial-type defects in ion-implanted silicon is demonstrated. The concept is based on deep level transient spectroscopy measurements utilizing the filling pulse variation technique. The vacancy profile, represented by the vacancy-oxygen center, and the interstitial profile, represented by the interstitial carbon-substitutional carbon pair, are obtained at the same sample temperature by varying the duration of the filling pulse. The effect of the capture in the Debye tail has been extensively studied and taken into account. Thus, the two profiles can be recorded with a high relative depth resolution. Using low doses, point defects have been introduced in lightly doped float zone n-type silicon by implantation with 6.8 MeV boron ions and 680 keV and 1.3 MeV protons at room temperature. The effect of the angle of ion incidence has also been investigated. For all implantation conditions the peak of the interstitial profile is displaced towards larger depths compared to that of the vacancy profile. The amplitude of this displacement increases as the width of the initial point defect distribution increases. This behavior is explained by a simple model where the preferential forward momentum of recoiling silicon atoms and the highly efficient direct recombination of primary point defects are taken into account. [ABSTRACT FROM AUTHOR]

In this work, different dielectric caps were deposited on the GaAs/AlGaAs quantum well (QW) structures followed by rapid thermal annealing to generate different degrees of interdiffusion. Deposition of a layer of Ga[sub x]O[sub y] on top of these dielectric caps resulted in significant suppression of interdiffusion. In these samples, it was found that although the deposition of Ga[sub x]O[sub y] and subsequent annealing caused additional injection of Ga into the SiO[sub 2] layer, Ga atoms were still able to outdiffuse from the GaAs QW structure during annealing, to generate excess Ga vacancies. The suppression of interdiffusion with the presence of Ga vacancies was explained by the thermal stress effect which suppressed Ga vacancy diffusion during annealing. It suggests that Ga[sub x]O[sub y] may therefore be used as a mask material in conjunction with other dielectric capping layers in order to control and selectively achieve impurity-free vacancy disordering. [ABSTRACT FROM AUTHOR]

The (0,0) band of the B ²Σ[sup +]-X²Σ[sup +] transition of LaS near 726 nm has been studied at high resolution using laser vaporization/reaction supersonic free jet expansion and laser induced fluorescence spectroscopy. Spectra taken at a resolution of about 50 MHz show resolved hyperfine structure which is caused principally by the unpaired 6sσ- electron in the ground state interacting with large magnetic moment of the [sub 57][sup 139]La nucleus with nuclear spin I=7/2. The X²Σ[sup +] state of LaS is in good Hund's case (b[sub βs]) coupling, however, the upper state, B ²Σ[sup +], is close to case (b[sub βJ]) coupling. A total of 1850 rotational-hyperfine transition lines have been assigned and measured. Accurate rotational, spin and hyperfine parameters for the B ²Σ[sup +] and X²Σ[sup +] states have been obtained, which give information about the electron distribution in the molecule. [ABSTRACT FROM AUTHOR]

Four electronic states of NiBr have been studied using the technique of laser vaporization/reaction with supersonic cooling and laser induced fluorescence (LIF) spectroscopy. NiBr molecules were produced by reacting laser ablated nickel atoms and ethyl bromide (C[sub 2]H[sub 5]Br). High resolution LIF spectrum between 724 and 810 nm was recorded, which consists of the (2,0), (1,0), and (0,0) bands of the [13.2] ²Π[sub 3/2-]-X²Π[sub 3/2] system and the [13.2] ²Π[sub 3/2]--A ²Δ[sub 5/2] system, and also the (v,0) with v = 0-4 bands of the [12.6] 2Σ[sup +]-X²Π[sub 3/2] system. Spectra of four isotopic molecules: [sup 58]Ni[sup 79]Br, [sup 58]Ni[sup 81]Br, [sup 60]Ni[sup 79]Br, and [sup 60]Ni[sup 81]Br were observed and analyzed. Least squares fit of rotationally resolved transition lines yielded accurate molecular constants for the X²Π[sub 3/2], A ²Δ[sub 5/2], [12.6] 2Σ[sup +], and [13.2] ²Π[sub 3/2] electronic states of NiBr. The bond length, r[sub 0], measured for the X²Π[sub 3/2] and A ²Δ[sub 5/2] states is 2.19628 and 2.16445 Å, respectively. A molecular orbital diagram has been constructed to explain the four observed electronic states. This work represents the first high-resolution spectroscopic study of NiBr. [ABSTRACT FROM AUTHOR]

Secondary defects induced by ion implantation in silicon after annealing have been previously shown to vary with the implantation and annealing conditions. However, in the low dose implants, well below the amorphization dose, the defects have been predominantly characterized to be interstitial in nature. In this article, we study the effect of implant temperature on secondary defects created by 1 MeV Sn implantation to a dose of 3x10[sup 13] cm-2 after subsequent annealing. We report a variation in the defect microstructure with implant temperature showing preferential formation of small interstitial loops for -191 °C and only rod-like defects for similar implants carried out at 300 °C. We conclude that these microstructures are a result of the dense cascades created by heavy Sn ions, creating local amorphous pockets in the implant damage region at the lowest implant temperatures. The variation of the microstructure with implant temperature is interpreted in terms of the effect of dynamic annealing over the defects formed in silicon. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies extended defects created in silicon by ion implantation to doses below the amorphization threshold. Implant species; Effect of the mass of implanted ion on the type of defect; Implantation process.

Studies the precipitation kinetics of Fe contamination at Si-Sio2 interfaces during dry oxidation at 900 degrees Celcius. Experimental procedure used; Definition of the surface and bulk Fe contamination; Results of the study.

Ion implantation of Zn substituting elements in ZnO has been shown to result in a dramatic Li depletion of several microns in hydrothermally grown ZnO. This has been ascribed to a burst of mobile Zn interstials. In this study, we seek to understand the reason behind this interstitial mediated transient enhanced diffusion in Li-containing ZnO samples after Zn implantation. ZnO wafers were implanted with Zn to two doses, 5×1015 cm-2 and 1×1017 cm-2. Secondary ion mass spectrometry was carried out to profile the Li depletion depth for different annealing temperatures between 600 and 800 °C. The 800 °C annealing had the most significant Li depletion of close to 60 μm. Transmission electron microscopy (TEM) was carried out in selected samples to identify the reason behind the Li depletion. In particular, TEM investigations of samples annealed at 750 °C show significant Zn precipitation just below the depth of the projected range of the implanted ions. We propose that the Zn precipitation is indicative of Zn supersaturation. Both the Li depletion and Zn precipitation are competing synchronous processes aimed at reducing the excess Zn interstitials. [ABSTRACT FROM AUTHOR]

Thermally equilibrated nano-cavities are formed in ZnO by H implantation and subsequent high temperature annealing to determine the relative surface formation energies and step energies of ZnO from reverse Wulff construction and related analysis. H adsorption, vicinal surfaces, and surface polarity are found to play an important role in determining the final thermal equilibrium shape of the nano-cavities. Under H coverage, the O-terminated surface shows a significantly lower surface formation energy than the Zn-terminated surface. [ABSTRACT FROM AUTHOR]

Photoluminescence measurements have been used to investigate the optically active defect centers formed by silicon implantation and a subsequent anneal at 275, 400, or 525 °C. The presence of boron in p-type silicon is found to produce deleterious effects on the luminescence of the interstitial-related W- and X-centers as well as a lower energy broad luminescence band. This effect has not been previously reported but it is consistent with the suppression of interstitial-related {311} extended defect formation in the presence of high boron concentrations at higher annealing temperatures. The results presented in this letter provide insight into the role of boron in the initial stages of interstitial cluster formation. [ABSTRACT FROM AUTHOR]

High-purity and low-doped n-type epitaxial layers of 4H-SiC have been implanted with N and C ions by using energies in the MeV range and doses from 2×108 to 1×109 cm-2. Postimplant annealing was performed at 1100 °C prior to sample analysis by deep-level transient spectroscopy (DLTS). A drastic and irreversible instability of the prominent EH7 deep-level defect occurs during the first DLTS temperature scan because of the electric field applied during the measurements. Depending on the implanted species, EH7 can decrease (N implants) as well as increase (C implants) in strength and the effect is attributed to charge-state controlled annealing and formation processes of EH7. The origin of EH7 is discussed and the experimental data support a model invoking interstitial C atoms. [ABSTRACT FROM AUTHOR]

The photoluminescence intensity from ion-implanted silicon can be quenched by the radiation damage implicit in the implantation. Annealing is then required before the intensity of the luminescence from a defect center is approximately proportional to the concentration of that center. Data from positron annihilation and photoluminescence experiments establish that severe quenching of the luminescence occurs when the mean separation of the small vacancy clusters is less than ∼30 atomic spacings, and the authors map out where, in the annealing and implantation phase space, the luminescence intensity is expected to be approximately proportional to the concentration of the optical centers. [ABSTRACT FROM AUTHOR]

The dopant dependence of photoluminescence (PL) from interstitial-related centers formed by ion implantation and a subsequent anneal in the range 175-525 °C is presented. The evolution of these centers is strongly effected by interstitial-dopant clustering even in the low temperature regime. There is a significant decrease in the W line (1018.2 meV) PL intensity with increasing B concentration. However, an enhancement is also observed in a narrow fabrication window in samples implanted with either P or Ga. The anneal temperature at which the W line intensity is optimized is sensitive to the dopant concentration and type. Furthermore, dopants which are implanted but not activated prior to low temperature thermal processing are found to have a more detrimental effect on the resulting PL. Splitting of the X line (1039.8 meV) arising from implantation damage induced strain is also observed. [ABSTRACT FROM AUTHOR]

The deformation mechanisms of crystalline (100) Ge were studied using nanoindentation, cross sectional transmission electron microscopy (XTEM) and Raman microspectroscopy. For a wide range of indentation conditions using both spherical and pointed indenters, multiple discontinuities were found in the force–displacement curves on loading, but no discontinuities were found on unloading. Raman microspectroscopy, measured from samples which had plastically deformed on loading, showed a spectrum shift from that in pristine Ge, suggesting only residual strain. No evidence (such as extra Raman bands) was found to suggest that any pressure-induced phase transformations had occurred, despite the fact that the material had undergone severe plastic deformation. Selected area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Moreover, XTEM showed that, at low loads, plastic deformation occurs by twinning and dislocation motion. This indicates that the hardness of Ge measured by indentation is not primarily dominated by phase transformation, rather by the nucleation and propagation of twin bands and/or dislocations. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence (CL) monochromatic imaging. CL imaging of indents which exhibit plastic deformation (based on indentation data) shows an observable “footprint” of deformation-produced defects that result in a strong reduction in the intensity of CL emission. Multiple discontinuities are observed during loading when the maximum load is above the elastic-plastic threshold, and such a behavior can be correlated with multiple slip bands revealed by XTEM. No evidence of pressure-induced phase transformations is found from within the mechanically damaged regions using selected-area diffraction patterns. The main deformation mechanism appears to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes on further loading. XTEM reveals no cracking or delamination in any of the samples studied for loads of up to 250 mN. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An experimental concept of studying shifts between concentration-versus-depth profiles of vacancy and interstitial-type defects in ion-implanted silicon is demonstrated. This concept is based on deep level transient spectroscopy measurements where the filling pulse width is varied. The vacancy profile, represented by the vacancy-oxygen center, and the interstitial profile, represented by the substitutional carbon-interstitial carbon pair, are obtained at the same sample temperature and can be recorded with a high relative depth resolution. For 6 MeV [sup 11]B ions, the peak of the interstitial profile is displaced by ∼0.5 μm towards larger depths compared to that of the vacancy profile, which is primarily attributed to the preferential forward momentum of recoiling Si atoms. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The mechanical deformation by spherical indentation of both crystalline InP and GaAs was characterized using cross-sectional transmission electron microscopy (XTEM) and atomic force microscopy. All load-unload curves show a discontinuity (or "pop in") during loading. Slip bands oriented along {111} planes are visible in XTEM micrographs from residual indentations in both materials and no evidence of any phase transformations was found. Higher load indentations (35 mN for InP and 50 mN for GaAs) also revealed subsurface cracking. In contrast no cracking was found beneath a 25 mN InP indent although the hardness and modulus data are almost identical to those of the cracked sample. The subsurface cracks are thought to be nucleated by high stress concentrations caused by dislocation pileup. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The results reported in this letter indicate that the spatial separation of the vacancy and interstitial excesses which result from ion bombardment gives rise to stable voids upon annealing at 850 °C even for implants where the projected ion range is only of the order of a few thousand Ångstrom. Such voids have been observed directly by transmission electron microscopy. Furthermore, in cases where both voids and interstitial-based defects are present at different depths, it is found that Au has a strong preference for decorating void surfaces and hence Au can, indeed, be used as a selective detector of open volume defects in Si. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The selectivity of interstitial-based extended defects (loops) and nanocavities for the gettering of Cu and Fe in Si has been studied. Controlled amounts of Cu and Fe were introduced by ion implantation into wafers containing pre-existing nanocavities and/or dislocations. Results show that Cu has a strong preference for gettering to open volume defects, even when high concentrations of interstitial-based loops are present in close proximity. However, the gettering of Fe in samples containing both vacancy- and interstitial-type defects is more complex, with Fe accumulation at all regions in the sample which contain defects, whether they are vacancy- or interstitial-like in character. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Preamorphous damage in p-type Si implanted with MeV Si ions and annealed at elevated temperature is characterized using deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). P-type Si was implanted with 4 MeV Si at doses from 1×10[sup 13] to 1×10[sup 14] cm[sup -2] and annealed at 800 °C for 15 min. For doses below this critical dose, a sharp peak is observed in the DLTS spectrum, corresponding to the signature of point defects. Above the critical dose, a broad DLTS peak is obtained, indicating the presence of extended defects. This behavior is found to be consistent with TEM analyses where extended defects are only observed for doses above the critical dose. This suggests a critical dose at which point defects from implantation act as nucleating sites for extended defect formation. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the gettering of ion implanted gold (AU) to defects in silicon Si) using Rutherford backscattering and transmission electron microscopy. Occurrence of annealing into dislocations by the damage from a Si implant; Evolution of the damage introduced by a hydrogen implant; Role of the diffusion of a supersaturated solid solution of Au in the process.

Examines gettering of copper (Cu) to the cavities in silicon (Si) formed by hydrogen (H) implantation and annealing. Redistribution of Cu with increasing temperature; Effects of H+Cu annealing on temperature; Dissolution of implanted Cu in Si wafer.

Presents a response to the comments concerning the separation of vacancy and interstitial depth profiles in ion-implanted silicon. Representation of vacancy-oxygen center and the substitutional carbon; Role of silicon ions in separating the initial distribution of vacancies; Annihilation between overlapping distributions of vacancies and self-interstitial.

GaAs/AlxGa1-xAs core-shell nanowires were grown by metal organic chemical vapor deposition with optimized AlxGa1-xAs shell and twin-free Au-catalyzed GaAs cores. Time-resolved photoluminescence measurements were carried out on single nanowires at room temperature, revealing minority carrier lifetimes of 1.02 ± 0.43 ns, comparable to self-assisted nanowires grown by molecular beam epitaxy. The long minority carrier lifetimes are mainly attributed to improvement of the GaAs/AlxGa1-xAs interface quality. The upper limit of surface recombination velocity of the structure is calculated to be 1300 cm/s with the AlxGa1-xAs shell grown at 750 °C, which is comparable with planar double heterostructures. [ABSTRACT FROM AUTHOR]

N-type ZnO samples have been implanted with MeV Zn+ ions at room temperature to doses between 1×108 and 2×1010cm-2, and the defect evolution has been studied by capacitance-voltage and deep level transient spectroscopy measurements. The results show a dose dependent compensation by acceptor-like defects along the implantation depth profile, and at least four ion-induced deep-level defects arise, where two levels with energy positions of 1.06 and 1.2 eV below the conduction band increase linearly with ion dose and are attributed to intrinsic defects. Moreover, a re-distribution of defects as a function of depth is observed already at temperatures below 400 K. [ABSTRACT FROM AUTHOR]

Heavily Al-doped 4H–SiC structures have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in an Ar atmosphere in a rf-heated furnace between 1500 °C and 2000 °C for 0.5 to 3 h. Secondary ion mass spectrometry has been utilized to obtain Al concentration versus depth as well as lateral distributions (ion images). Transmission electron microscopy (TEM) has been employed to study the crystallinity and determine phase composition after heat treatment. A solubility limit of ∼2×10[sup 20] Al/cm[sup 3] (1900 °C) is extracted. Three-dimensional ion images show that the Al distribution does not remain homogeneous in layers heat treated at 1700 °C or above when the Al concentration exceeds 2×10[sup 20] cm[sup -3]. Al-containing precipitates are identified by energy-filtered TEM. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Spherical indentation of crystalline silicon has been studied using cross-sectional transmission electron microscopy (XTEM). Indentation loads were chosen below and above the yield point for silicon to investigate the modes of plastic deformation. Slip planes are visible in the XTEM micrographs in both indentation loads studied. A thin layer of polycrystalline material has been identified (indexed as Si-XII from diffraction patterns) on the low-load indentation. The higher-load indentation revealed a large region of amorphous silicon. The sequence of structural deformation by indentation in silicon has been observed with the initial deformation mechanism being slip until phase transformations can take place. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cavities, formed in Si by hydrogen implantation and subsequent annealing, can provide strong sinks for metal interstitials and are ideal gettering sites for metal impurities. This letter reports the effect of cavities on the transient enhanced diffusion (TED) of boron. Boron implantation was carried out into wafers containing pre-formed cavities and TED of boron was suppressed during subsequent annealing. In some cases, the boron was introduced into an amorphous layer and the presence of cavities was also observed to reduce the amount of the transient enhanced diffusion occurring. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The efficient gettering to hydrogen-induced cavities in Si has been successfully demonstrated for low concentrations of Cu, unintentionally introduced during wafer processing. Secondary ion mass spectrometry showed up to 5×10[sup 12] cm[sup -2]Cu could be introduced into a silicon wafer and trapped at cavities. Neutron activation analysis indicated that, in samples with cavities, the Cu within the bulk was below the detection limit (around 4×10[sup 11] cm[sup -2]), while Cu was detected throughout the bulk of samples without cavities. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The gettering of implanted Pt and Ag to hydrogen-induced cavities in Si has been compared for doses from 1×10[sup 13] to 1×10[sup 15] cm[sup -2]. After annealing at 850 °C for 1 h, almost 100% of both implanted metals were relocated to the cavity band for doses less than 1×10[sup 14] cm[sup -2]. At higher doses, large differences were observed in the gettering behaviour of Pt and Ag, where the amount of Pt was saturated at close to a monolayer coverage of cavity walls, whereas the Ag accumulation at cavities continually increased with dose. Cross-sectional transmission electron microscopy revealed strong differences in the ability of Pt and Ag to form a bulk phase at the cavities. The results indicate that stable silicide formation at the near-surface and trapping of Ag to implantation damage are the main processes which limit gettering at the higher doses. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

"Representational Momentum" (RM) is a mislocalization of the endpoint of a moving target in the direction of motion. In vision, RM has been shown to increase with target velocity. In audition, however, the effect of target velocity is unclear. Using a perceptual paradigm with moving broadband noise targets in Virtual Auditory Space resulted in a linear increase in RM from 0.9° to 2.3° for an increase in target velocity from 25°/s to 100°/s. Accounting for the effect of eye position also reduced variance. These results suggest that RM may be the result of similar underlying mechanisms in both modalities.

Free-field source localization experiments with 30 source locations, symmetrically distributed in azimuth, elevation, and front-back location, were performed with periodic tones having different phase relationships among their components. Although the amplitude spectra were the same for these different kinds of stimuli, the tones with certain phase relationships were successfully localized while the tones with other phases led to large elevation errors and front-back reversals, normally growing with stimulus level. The results show that it is not enough to have a smooth, broadband, long-term signal spectrum for successful sagittal-plane localization. Instead, temporal factors are important. A model calculation investigates the idea that the tonotopic details that mediate localization need to be simultaneously, or almost simultaneously, accessible in the auditory system in order to achieve normal elevation perception. A qualitative model based on lateral inhibition seems capable in principle of accounting for both the phase effects and level effects.

High resolution laser induced fluorescence spectrum of IrB in the spectral region between 545 and 610 nm has been recorded and analyzed. Reacting laser-ablated iridium atoms with 1% B(2)H(6) seeded in argon produced the IrB molecule. This is the first experimental observation of the IrB molecule. Four vibronic transition bands, (v,0) with v=0-3 of an electronic transition system, have been observed. Spectra of all four isotopic molecules, (191)Ir(10)B, (193)Ir(10)B, (191)Ir(11)B, and (193)Ir(11)B, were recorded. Isotopic relationships confirmed the carrier of the spectra and the vibrational quantum number assignment. Preliminary analysis of rotational lines showed that these vibronic bands are with Omega' = 2 and Omega" = 3. The electronic transition identified is assigned as the [16.5](3)Pi(2)-X(3)Delta(3) system. Partially resolved hyperfine structure which conforms to the Hund's case a(beta) coupling scheme has been observed and analyzed. The bond length r(0) of the lower X(3)Delta(3) state of IrB was determined to be 1.7675 A.