Subsequent Flash Research Articles

Formation of InAs quantum dots in silicon by sequential ion implantation and flash lamp annealing

InAs quantum dots (QDs) were successfully formed in single-crystalline Si by sequential ion implantation and subsequent milliseconds range flash lamp annealing (FLA). Samples were characterized by μ-Raman spectroscopy, Rutherford Backscattering Spectrometry (RBS) high-resolution transmission electron microscopy (HRTEM) and low temperature photoluminescence (PL). The Raman spectrum shows two peaks at 215 and 235 cm−1 corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs phonon modes, respectively. The PL band at around 1.3 μm originates from the InAs QDs with an average diameter 7.5±0.5 nm and corresponds to the increased band gap energy due to the strong quantum confinement size effect. The FLA of 20 ms is sufficient for InAs QDs formation. It also prevents the out-diffusion of implanted elements. Moreover, the silicon layer amorphized during ion implantation is recrystallized by solid-phase epitaxial regrowth during FLA.

Heavily Ga-doped germanium layers produced by ion implantation and flash lamp annealing: Structure and electrical activation

Heavily p-type doped Ge layers were fabricated by 100 keV Ga implantation and subsequent flash lamp annealing for 3 ms in the temperature range between 700 and 900 °C. For comparison, some samples were annealed in a rapid thermal processor for 60 s. Ga fluences of 2×1015, 6×1015, and 2×1016 cm−2 were chosen in order to achieve Ga peak concentrations ranging from values slightly below the equilibrium solid solubility limit of 4.9×1020 cm−3 up to 3.5×1021 cm−3 which corresponds to a maximum Ga content of about 8 at. %. The structure of the doped layer and the Ga distribution were investigated by Rutherford backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy, and secondary ion mass spectrometry. Temperature dependent Hall effect measurements were carried out in order to determine the electrical properties of the Ga-doped Ge layers. It is shown that by flash lamp annealing Ga diffusion into the bulk can be completely avoided and the Ga loss by outdiffusion from the surface is reduced. The lowest sheet resistance of 36 Ω/sq. was achieved for the medium Ga concentration annealed at 900 °C. The best Ga activation values are 73%, 60%, and 24% for the three Ga fluences under investigation. The Ga activation is correlated with the layer regrowth. Incomplete epitaxial regrowth as observed in some samples leads to lower activation.

Semi-automated protein crystal mounting device for the sulfur single-wavelength anomalous diffraction method

Use of longer-wavelength X-rays has advantages for the detection of small anomalous signals from light atoms, such as sulfur, in protein molecules. However, the accuracy of the measured diffraction data decreases at longer wavelengths because of the greater X-ray absorption. The capillary-top mounting method (formerly the loopless mounting method) makes it possible to eliminate frozen solution around the protein crystal and reduces systematic errors in the evaluation of small anomalous differences. However, use of this method requires custom-made tools and a large amount of skill. Here, the development of a device that can freeze the protein crystal semi-automatically using the capillary-top mounting method is described. This device can pick up the protein crystal from the crystallization drop using a micro-manipulator, and further procedures, such as withdrawal of the solution around the crystal by suction and subsequent flash freezing of the protein crystal, are carried out automatically. This device makes it easy for structural biologists to use the capillary-top mounting method for sulfur single-wavelength anomalous diffraction phasing using longer-wavelength X-rays.

Small and Reproducible Isotope Effects during Methylation with Trimethylsulfonium Hydroxide (TMSH): A Convenient Derivatization Method for Isotope Analysis of Negatively Charged Molecules

Negatively charged analytes must be derivatized prior to gas chromatography-isotope ratio mass spectrometry (GC-IRMS), with stringent control of isotope fractionation. Current methods require offline sample preparation. This study tests for the first time trimethylsulfonium hydroxide (TMSH) as online methylation agent prior to isotope analysis, addressing the herbicides bentazone and MCPA. Fully automated derivatization was achieved in a temperature-programmable GC injector, where reactants were injected into a packed liner, solvents were removed by split flow, and subsequent flash heating triggered the derivatization, thereby transferring derivatives onto the chromatographic column. Stoichiometric addition of TMSH resulted in complete conversion giving accurate and reproducible nitrogen isotope values of bentazone. In contrast, reproducible carbon isotope analysis required TMSH in > or = 250-fold excess. Contrary to expectations, delta(13)C values became more negative at smaller TMSH excess. This indicates that elevated methyl group concentrations in the pore space of the injection liner facilitated close-to-equilibrium rather than kinetic isotope fractionation resulting in reproducible derivatization conditions. delta(13)C results under these conditions compared favorably with liquid chromatography-IRMS: low standard deviations (0.3 per thousand for GC-IRMS, 0.1 per thousand for LC-IRMS) and a comparable offset of 1 per thousand compared to elemental analyzer-IRMS demonstrate that both methods represent expedient ways for online isotope analysis of anionic target compounds.

Millisecond flash lamp annealing of shallow implanted layers in Ge

Shallow n+ layers in Ge are formed by phosphorus implantation and subsequent millisecond flash lamp annealing. Present investigations are focused on the dependence of P redistribution, diffusion and electrical activation on heat input into the sample and flash duration. In contrast to conventional annealing procedures an activation up to 6.5×1019 cm−3 is achieved without any dopant redistribution and noticeable diffusion. Present results suggest that independently of pretreatment the maximum activation should be obtained at a flash energy that corresponds to the onset of P diffusion. The deactivation of P is explained qualitatively by mass action analysis which takes into account the formation of phosphorus-vacancy clusters.

Examination of the Low-Temperature Region in a Downdraft Gasifier for the Pyrolysis Product Analysis of Biomass Air Gasification

Treatment of biomass in nitrogen and air at 240−340 °C was conducted in order to examine the low-temperature region in a downdraft gasifier by analyzing the treated precursors and product distribution. Gas-treated precursors were then pyrolyzed in flash mode at 764 °C for further analysis. Overall, the tar yield decreased from approximately 50 wt % to less than 20 wt % upon oxidation of the sample at a very low heating rate to 260−300 °C in air. Moreover, tar evolution was almost completely suppressed during the subsequent flash pyrolysis. This indicates that the structure of the treated precursors was gradually changed to suppress tar release through cross-linking reactions and partial oxidation. From elemental analysis of the precursors treated with air, it was also estimated that dehydration and partial oxidation proceeded simultaneously. The results indicate that the release of tar products such as dimers can be partially suppressed by air treatment at low temperature.

Luminescence flashes induced by microwave radiation in undoped GaAs quantum wells

Bright flashes of exciton emission are observed in photoexcited, undoped GaAs/AlGaAs quantum wells under pulsed microwave (36 GHz) irradiation. The flash intensity is in the range of 10--100 times the steady-state photoluminescence intensity with a decay time of $(1--10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }\text{s}$ (depending on the applied microwave power and photoexcitation). These observations indicate a reservoir of long-lived carriers that is formed at low temperature due to localization of photogenerated electrons and holes at spatially separated shallow traps. Microwave-heated electrons activate the localized carriers into free states by means of avalanche impact ionization. This gives rise to rapid exciton formation with subsequent luminescence flash. A detailed model based on the coupled rate equations for free electrons, excitons and localized electrons (holes) is presented.

Controlled localised melting in silicon by high dose germanium implantation and flash lamp annealing

High intensity light pulse irradiation of monocrystalline silicon wafers is usually accompanied by inhomogeneous surface melting. The aim of the present work is to induce homogeneous buried melting in silicon by germanium implantation and subsequent flash lamp annealing. For this purpose high dose, high energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp irradiation at high energy densities leads to local melting of the germanium rich buried layer, whereby the thickness of the molten layer depends on the irradiation energy density. During the cooling down epitaxial crystallization takes place resulting in a largely defect-free layer. The combination of buried melting and dopant segregation has the potential to produce unusually buried doping profiles or to create strained silicon structures.

Buried melting in germanium implanted silicon by millisecond flash lamp annealing

Flash lamp annealing in the millisecond range has been used to induce buried melting in silicon. For this purpose high dose high-energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp treatment at high energy densities leads to local melting of the germanium rich layer. The thickness of the molten layer has been found to depend on the irradiation energy density. During the cool-down period, epitaxial crystallization takes place resulting in a largely defect-free layer.

Analysis of thunderstorm and lightning activity associated with sprites observed during the EuroSprite campaigns: Two case studies

During the summers of 2003 to 2006 sprites were observed over thunderstorms in France by cameras on mountain tops in Southern France. The observations were part of a larger coordinated effort, the EuroSprite campaigns, with data collected simultaneously from other sources including the French radar network for precipitation structure, Meteosat with images of cloud top temperature and the Météorage network for detection of cloud-to-ground (CG) flash activity. In this paper two storms are analyzed, each producing 27 sprite events. Both storms were identified as Mesoscale Convective Systems (MCS) with a trailing stratiform configuration (ST) and reaching a maximum cloud area of ~ 120,000 km 2. Most of the sprites were produced while the stratiform area was clearly developed and during periods of substantial increase of rainfall in regions with radar reflectivity between 30 and 40 dBZ. The sprite-producing periods followed a maximum in the CG lightning activity and were characterized by a low CG flash rate with a high proportion of + CG flashes, typically around 50%. All sprites were associated with + CGs except one which was observed after a − CG as detected by the Météorage network. This − CG was estimated to have − 800 C km charge moment change. The peak current of sprite-producing + CG (SP + CG) flashes was twice the average value of + CGs and close to 60 kA with little variation between the periods of sprite activity. The SP + CG flashes were further characterized by short time intervals before a subsequent CG flash (median value < 0.5 s) and with clusters of several CG flashes which suggest that SP + CG flashes often are part of multi-CG flash processes. One case of a lightning process associated with a sprite consisted of 7 CG flashes.

P implantation into preamorphized germanium and subsequent annealing: Solid phase epitaxial regrowth, P diffusion, and activation

Phosphorus implantation (30 keV, 3×1015 cm−2) into preamorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. During annealing a significant P diffusion in amorphous Ge is not observed. However, the fast solid phase epitaxial regrowth causes a rapid redistribution of P. After completion of the regrowth and at temperatures above 500 °C, a concentration-dependent diffusion of P in crystalline Ge takes place and leads to considerable loss of P toward the surface. An appreciable influence of implantation defects on the diffusion coefficient of P is not detected. For 60 s rapid thermal annealing at 600 °C and for 20 ms flash lamp annealing at 900 °C, the junction depth and the sheet resistance vary between 140 and 200 nm and between 50 and 100 Ω, respectively, and the maximum electrical activation of P is about 3–7×1019 cm−3.

Near‐Infrared Dyes and Fluorophores Based on Diketopyrrolopyrroles

Our research activities over the last few decades have concerned correlations between molecular structure and fluorescence. 2] A central theme of the research has been the synthesis and spectroscopic investigations of near-infrared (NIR) dyes to get insights into what degree the obtainable fluorescence quantum yields are restricted by the S0$S1 energy gap. Our results on the condensation of 1,4phthalazinediones with heteroarylacetonitriles in POCl3 prompted us to carry out the reaction with diketopyrrolopyrroles (DPPs) 1. Herein we report the results of the investigations. To date, attempts to activate the carbonyl group of DPPs with POCl3, and to subsequently convert the intermediates with nucleophiles, only led to monosubstitution or to ring opening. 10] The reaction of 1 and 2 in refluxing toluene with an excess of POCl3 according to Scheme 1 afforded disubstituted NIR dyes 3. The progress of the reaction was controlled by recording absorption spectra and stopping the heating as soon as the DPP was used up and/or products absorbing at short wavelengths appeared. Purification was carried out by digesting the product in acetone and subsequent flash chromatography (silica gel/CHCl3 or CH2Cl2). The NIR dyes 3a–3h (the structures and spectroscopic data of 3b–3h can be found in the Supporting Information) were synthesized according to this procedure (Scheme 1) from the reaction of 1 and 2. The course of the reactions was the same in all cases and side-products with strong absorptions below 350 nm were observed. These side-products are most likely compounds formed by the opening of the DPPs pentalene ring system. Prerequisite for the reactions is a certain solubility of the DPPs. This is a feature of all of the DPPs used here with the exception of the 4-methoxy derivative 1b. Remarkably, the 4(N-methyl-N-octyl amino) derivative 1e has a much better solubility than all the other DPPs used. Only in the case of the reaction of 1e with 2a were we able to isolate the 1:1 condensation product (13% yield). The heteroarylacetonitriles 2a and 2b substituted with a tert-butyl group were used to improve the solubility of the condensation products 3. In general, satisfying yields were obtained only if the solubility of both condensation partners was improved by having longer alkyl groups (Table 1). From these observations we draw the following conclusion concerning the reaction pathway: DPP reacts with POCl3 to form a monophosphorylated intermediate, which reacts with the Scheme 1. Reagents and conditions: a) absolute toluene/POCl3, reflux; b) 1,2-dichlorobenzene/BF3·Et2O, reflux, diisopropylethylamine; c) xylene/chlorodiphenylborane, reflux; DPPs 1: R=4-octyloxy (1a), R=4-methoxy (1b), R=4-butyloxy (1c), R=4-(hex-5-enyloxy) (1d), R=4-(N-methyl-N-octylamino) (1e); heteroarylacetonitriles 2 : 2-(6tert-butylquinolin-2-yl)acetonitrile (2a), 2-(6-tert-butylbenzothiazol-2yl)acetonitrile (2b), 2-(quinoxalin-2-yl)acetonitrile (2c), 2-(6-methylpyridin-2-yl)acetonitrile (2d). A: aromatic ring.

Motor-Sensory Recalibration Leads to an Illusory Reversal of Action and Sensation

To judge causality, organisms must determine the temporal order of their actions and sensations. However, this judgment may be confounded by changing delays in sensory pathways, suggesting the need for dynamic temporal recalibration. To test for such a mechanism, we artificially injected a fixed delay between participants' actions (keypresses) and subsequent sensations (flashes). After participants adapted to this delay, flashes at unexpectedly short delays after the keypress were often perceived as occurring before the keypress, demonstrating a recalibration of motor-sensory temporal order judgments. When participants experienced illusory reversals, fMRI BOLD signals increased in anterior cingulate cortex/medial frontal cortex (ACC/MFC), a brain region previously implicated in conflict monitoring. This illusion-specific activation suggests that the brain maintains not only a recalibrated representation of timing, but also a less-plastic representation against which to compare it.

Generation of aligned γ precipitates in Cu-Zn-Al single crystals

Several thermal treatments are known from literature to generate different distributions of γ phase precipitates in Cu-Zn-Al alloys with martensitic transformation temperatures below room temperature. Some of these treatments are composed of a first quench followed by a flash heating to 670K for different times up to hundreds of seconds. The same type of treatments have been used in a Cu - 12.7Zn - 17.7Al alloy (% at, e/a = 1.48) with a nominal Ms of 320 K, in order to study the influence of the precipitates on the martensite stabilization. In step-quenched specimens, the martensite stabilization by quenching was small and the precipitates obtained after the flash heating were homogeneously distributed, like in the alloys with low transformation temperatures. However, the specimens directly quenched to martensite exhibited a strong stabilization degree. After the subsequent flash heating, the distributions of precipitates clearly showed particular alignments along the boundaries of the martensite plates existing before the flash heating, as well as along the basal plane of certain martensite plates. In the present work the characteristics and mechanisms of formation of these particular distributions of precipitates will be discussed.

A device for the high-pressure oxygenation of protein crystals

A system has been developed for subjecting protein crystals to hyperbaric pressures of oxygen gas in order to promote enzymatic reaction. Crystals of an oxygenase or oxidase enzyme are grown anaerobically by hanging drop vapor diffusion, under crystallization conditions modified to eliminate combustible materials such as plastic coverslips and grease. The crystalline enzyme:substrate complex can then be exposed to oxygen gas at pressures up to 60 bar using a custom-built device or “bomb.” In this way, reaction is initiated synchronously throughout the crystal and subsequent flash freezing allows the trapping of enzyme:product complexes in high occupancy. These complexes can then be structurally characterized by conventional monochromatic X-ray crystallography. The bomb is furnished from naval brass and lubricated with Fomblin RT15 perfluorinated polyether grease in order to ensure compatibility with the highly oxidizing environment.

Radiation from Collision‐dominated Relativistic Pair Fireballs

It is generally accepted that gamma-ray bursts (GRBs) are initiated by a relativistic pair fireball, converting its internal energy into kinetic energy of a relativistically moving plasmoid and subsequently into radiation. Here, we investigate the early stages of this evolution, after the pair fireball has become optically thin to gamma-gamma pair production. We show that for a short period of time, ~ 0.1 - a few seconds after the initial explosion, the pair plasmoid evolution might be dominated by collisional processes prior to the formation of a collisionless shock. We simulate these processes during the early pair plasmoid evolution and calculate the expected radiative signatures. We show that the radiation from the collision-dominated pair plasmoid phase results in a short (~ a few ms) flash of thermal soft X-ray emission, followed by a transition phase of < 1 s during which the fireball turns Thomson thin, but its radiation remains dominated by thermal Comptonization, peaking at around E_pk ~ 100 MeV - a few GeV. While the very early thermal emission could be associated with the quasi-thermal radiation signatures found in the very early phases of several bright BATSE GRBs, the predicted subsequent flash of high-energy emission should be easily detectable with the GLAST satellite.

Alternative oxidation by isopenicillin N synthase observed by X-ray diffraction

Background: Isopenicillin N synthase (IPNS) catalyses formation of bicyclic isopenicillin N, precursor to all penicillin and cephalosporin antibiotics, from the linear tripeptide δ-( L-α-aminoadipoyl)- L-cysteinyl- D-valine. IPNS is a non-haem iron(II)-dependent enzyme which utilises the full oxidising potential of molecular oxygen in catalysing the bicyclisation reaction. The reaction mechanism is believed to involve initial formation of the β-lactam ring (via a thioaldehyde intermediate) to give an iron(IV)-oxo species, which then mediates closure of the 5-membered thiazolidine ring. Results: Here we report experiments employing time-resolved crystallography to observe turnover of an isosteric substrate analogue designed to intercept the catalytic pathway at an early stage. Reaction in the crystalline enzyme–substrate complex was initiated by the application of high-pressure oxygen, and subsequent flash freezing allowed an oxygenated product to be trapped, bound at the iron centre. A mechanism for formation of the observed thiocarboxylate product is proposed. Conclusions: In the absence of its natural reaction partner (the N–H proton of the L-cysteinyl- D-valine amide bond), the proposed hydroperoxide intermediate appears to attack the putative thioaldehyde species directly. These results shed light on the events preceding β-lactam closure in the IPNS reaction cycle, and enhance our understanding of the mechanism for reaction of the enzyme with its natural substrate.

Involuntary orienting to sound improves visual perception.

To perceive real-world objects and events, we need to integrate several stimulus features belonging to different sensory modalities. Although the neural mechanisms and behavioural consequences of intersensory integration have been extensively studied, the processes that enable us to pay attention to multimodal objects are still poorly understood. An important question is whether a stimulus in one sensory modality automatically attracts attention to spatially coincident stimuli that appear subsequently in other modalities, thereby enhancing their perceptual salience. The occurrence of an irrelevant sound does facilitate motor responses to a subsequent light appearing nearby. However, because participants in previous studies made speeded responses rather than psychophysical judgements, it remains unclear whether involuntary auditory attention actually affects the perceptibility of visual stimuli as opposed to postperceptual decision and response processes. Here we provide psychophysical evidence that a sudden sound improves the detectability of a subsequent flash appearing at the same location. These data show that the involuntary orienting of attention to sound enhances early perceptual processing of visual stimuli.

Tamoxifen-Induced Hot Flashes

Hot flashes are the most prominent side effect of tamoxifen, the most frequently prescribed antitumor agent in the world. Little detailed information is available to predict who will develop hot flashes on tamoxifen, to describe the natural history of these hot flashes, and/or to predict who will request therapy for such a side effect. This current trial was developed to address these items. Women who were about to begin adjuvant tamoxifen for locally treated breast cancer were approached for this trial. Before initiating tamoxifen, patients completed a short questionnaire designed to inquire about potential prognostic factors. Upon starting tamoxifen, women were asked to complete a hot flash diary daily for 3 months, and then daily for 1 week of each of the subsequent 9 months. Fifty patients, aged 51-83 years, provided data for this report. Approximately half of the women reported that they did not have any substantial hot flashes while the other half reported hot flashes of variable intensity. On average, these hot flashes gradually increased over 3 months and then plateaued. Baseline factors that appeared to predict for subsequent hot flash problems included a prior history of moderate to severe hot flashes with menopause and a history of prior estrogen therapy use. Overall, 16% of the women reported the desire for therapy for their hot flashes. Thirty-seven and one-half percent of the women (6/16) had a history of both prior estrogen use and moderate to severe hot flashes with menopause as compared to none (0/14) of the women without either of these factors. The data from this study can be utilized to better identify and educate women as to their probability of developing hot flashes after starting tamoxifen, to describe the average time frame for these hot flashes, and to predict the likelihood of whether resultant hot flashes will be substantial enough to have a woman request therapy for them.

状態方程式による完全陰解多成分系モデルの開発

A fully implicit compositional model is developed following the Coats approach. Although the fully implicit formulation guarantees a high degree of computational stability, it aggravates the computational efficiency due to the large number of independent variables. To relax this deficiency, a phase-stability analysis routine is included in the model. Adopting the Gibbs free energy as a stability criterion, we can estimate the number of phase present, prior to the flash calculation. If a single phase is detected, the subsequent flash computation routine can be detoured.The developed model is verified against an established model, an adaptive implicit compositional simulator, GEM. The computationa efficiencies with and without the stability analysis are evaluated to confirm the improvement in the iterative flash calculations. When there exists only one phase, the number of iterations is largely reduced by virtue of the stability analysis. In addition, even in two-phase situations. the flash computation is efficiently performed, because the stability analysis yields proper guesses. It is revealed that the stability analysis improves the computational efficiency regardless of the number of phases.