3μm GaInNAs/GasAs Quantum Well Resonant Cavity Enhanced Photodetector

A 1.3μm GaInNAs resonant cavity enhanced (RCE) photodetector (PD) has been grown by molecular beam epitaxy (MBE) monolithically on (100) GaAs substrate using a home-made ion-removed dc-plasma cell as nitrogen source. A transfer matrix method was used to optimize the device structure. The absorption region is composed of three GaInNAs quantum wells separated by GaAs layers. Devices were isolated by etching 130μm-diameter mesas and filling polyamide into grooves. The maximal quantum efficiency of the device is about 12% at 1.293μm. Full width at half maximum (FWHM) is 5.8nm and 3dB bandwidth is 304MHz. Dark current is 2 * 10~(-11) A at zero bias voltage. Further improvement of the performance of the RCE PD can be obtained by optimizing of the structure design and MBE growth conditions.

SiGe/Si quantum well resonant-cavity-enhanced photodetector

Resonant-cavity-enhanced photodetectors have been demonstrated to be able to improve the bandwidth-efficiency product. We report a novel SiGe/Si multiple quantum-well resonant-cavity-enhanced photodetector fabricated on a separation-by-implanted-oxygen wafer operating near 1300nm. The buried oxide layer in SIMOX is used as a bottom mirror to form a vertical cavity with silicon dioxide/silicon Bragg reflector deposited on the top surface. The quantum efficiency at the wavelength of 1300nm is measured with 3.5% at a reverse bias of 15V, which is enhanced by 10 folds compared with a conventional photodetector with the same absorption structures.

Long-wavelength SiGe/Si MQW resonant-cavity-enhanced photodiodes (RCE-PD)

Si1-xGex/Si optoelectronic devices are promising for the monolithic integration with silicon-based microelectronics. SiGe/Si MQW RCE-PD (Resonant-Cavity-Enhanced photodiodes) with different structures were investigated in this work. Design and fabrication of top- and bottom-incident RCE-PD, such as growth of SiGe MQW (Multiple Quantum Wells) on Si and SOI (Si on insulator) wafers, bonding between SiGe epitaxial wafer and SOR (Surface Optical Reflector) consisting Of SiO2/Si DBR (Distributed Bragg Reflector) films on Si, and performances of RCE-PD, were presented. The responsivity of 44mA/W at 1.314 mum and the FWHM of 6nm were obtained at bias of 10V. The highest external quantum efficiency measured in the investigation is 4.2%.

Si-based resonant-cavity-enhanced photodetector

Resonant-cavity-enhanced (RCE) photodetectors have been demonstrated to be able to improve the bandwidth-efficiency product. We report one top-illumination and one bottom-illumination SiGe/Si multiple quantum-well (MQW) RCE photodetectors fabricated on a separation-by-implanted-oxygen (SIMOX) wafer operating near 1300nm, The buried oxide layer in SIMOX is used as a mirror to form a vertical cavity with the silicon dioxide/silicon Bragg reflector deposited on the top surface. A peak responsivity with a reverse bias of 5V is measured 10.2mA/W at 1285nm, and a full-width at half maximum of 25nm for the top-illumination RCE photodetector, and 19mA/W at 1305nm, and a full-width at half maximum of 14nm for the bottom-illumination one. The external quantum efficiency of the bottom-illumination RCE photodetector is up to 2.9% at 1305nm with a reverse bias of 25V. The responsivity of the bottom-illumination RCE photodetector is improved by two-fold compared with that of the top-illumination one.

Electrochemical deposition of silver in room-temperature ionic liquids and its surface-enhanced Raman scattering effect

The use of room-temperature ionic liquids (RTILs) as media for electrochemical application is very attractive. In this work, the electrochemical deposition of silver was investigated at a glassy carbon electrode in hydrophobic 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) and hydrophilic 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) RTILs and in KNO3 aqueous solution by cyclic voltammetric and potentiostatic transient techniques. The voltammograms showed the presence of reduction and oxidation peaks associated with the deposition and dissolution of silver from AgBF4 in both BMIMPF6 and BMIMBF4, resembling the redox behavior of AgNO3 in KNO3 aqueous solution. A crossover loop was observed in all the cyclic voltammograms of these electrochemical systems, indicating a nucleation process. From the analysis of the experimental current transients, it was shown that the electrochemical deposition process of silver in these media was characteristic of 3D nucleation with diffusion-controlled hemispherical growth, and the silver nucleation closely followed the response predicted for progressive nucleation in BMIMPF6 and instantaneous nucleation in KNO3 aqueous solution, respectively.

Seed-mediated synthesis of branched gold nanoparticles with the assistance of citrate and their surface-enhanced Raman scattering properties

We report an easy synthesis of highly branched gold particles through a seed-mediated growth approach in the presence of citrate. The addition of citrate in the growth solution is found to be crucial for the formation of these branched gold particles. Their size can be varied from 47 to 185 nm. The length of the thumb-like branch is estimated to be between about 5 and 20 nm, and changes slightly as the particle size increases. Owing to these obtuse and short branches, their surface plasmon resonance displays a marked red-shift with respect to the normal spherical particles. These branched gold particles exhibit stronger SERS activity than the non-branched ones, which is most likely related to these unique branching features.

Controlled nucleation and growth of surface-confined gold nanoparticles on a (3-aminopropyl)trimethoxysilane-modified class slide: A strategy for SPR substrates

The thickness of the gold film and its morphology, including the surface roughness, are very important for getting a good, reproducible response in the SPR technique. Here, we report a novel alternative approach for preparing SPR-active substrates that is completely solution-based. Our strategy is based on self-assembly of the gold colloid monolayer on a (3-aminopropyl)trimethoxysilane-modified glass slide, followed by electroless gold plating. Using this method, the thickness of films can be easily controlled at the nanometer scale by setting the plating time in the same conditions. Surface roughness and morphology of gold films can be modified by both tuning the size of gold nanoparticles and agitation during the plating. Surface evolution of the Au film was followed in real time by UV-vis spectroscopy and in situ SPRS. To assess the surface roughness and electrochemical stability of the Au films, atomic force microscopy and cyclic voltammetry were used. In addition, the stability of the gold adhesion is demonstrated by three methods. The as-prepared Au films on substrates are reproducible and stable, which allows them to be used as electrodes for electrochemical experiments and as platforms for studying SAMs.

Enhanced crystallization and phase transformation of amorphous silicon nitride under high pressure

The crystallization and phase transformation of amorphous Si3N4 ceramics under high pressure (1.0-5.0 GPa) between 800 and 1700 degreesC were investigated. A greatly enhanced crystallization and alpha-beta transformation of the amorphous Si3N4 ceramics were evident under the high pressure, as characterized by that, at 5.0 GPa, the amorphous Si3N4, began to crystallize at a temperature as low as 1000 degreesC (to transform to alpha modification). The subsequent alpha-beta transformation occurred completed between 1350 and 1420 degreesC after only 20 min of pressing at 5.0 GPa. In contrast, under 0.1 MPa N-2, the identical amorphous materials were stable up to 1400 degreesC without detectable crystallization, and only a small amount of a phase was detected at 1500 degreesC. The crystallization temperature and the alpha-beta transformation temperatures are reduced by 200-350 degreesC compared to that at normal pressure. The enhanced phase transformations of the amorphous Si3N4, were discussed on the basis of thermodynamic and kinetic consideration of the effects of pressure on nucleation and growth.

Evaluation of Altered Kras Codon Bias and NOS Inhibition During Lung Tumorigenesis

The small GTPases HRAS, NRAS and KRAS are mutated in approximately one-third of all human cancers, rendering the proteins constitutively active and oncogenic. Lung cancer is the leading cause of cancer deaths worldwide, and more than 20% of human lung cancers harbor mutations in RAS, with 98% of those occurring in the KRAS isoform. While there have been many advances in the understanding of KRAS–driven lung tumorigenesis, it remains a therapeutic challenge. To further this understanding and assess novel approaches for treatment, I have investigated two aspects of Kras–driven tumorigenesis in the lung:

(I) Despite nearly identical protein sequences, the three RAS proto-oncogenes exhibit divergent codon usage. Of the three isoforms, KRAS contains the most rare codons resulting in lower levels of KRAS protein expression relative to HRAS and NRAS. To determine the consequences of rare codon bias during de novo tumorigenesis, we created a knock-in Krasex3op mouse in which synonymous mutations in exon 3 converted codons from rare to common. These mice had reduced tumor burden and fewer oncogenic mutations in the Krasex3op allele following carcinogen exposure. The reduction in tumorigenesis appeared to be a product of rare codons affecting both the oncogenic and non–oncogenic alleles. Converting rare codons to common codons yielded a more potent oncogenic allele that promoted growth arrest and enhanced tumor suppression by the non-oncogenic allele. Thus, rare codons play an integral role in Kras tumorigenesis.

(II) Lung cancer patients exhale higher levels of NO and iNOS-/- mice are resistant to chemically induced lung tumorigenesis. I hypothesize that NO promotes Kras–driven lung adenocarcinoma, and NOS inhibition may decrease Kras–driven lung tumorigenesis. To test this hypothesis, I assessed efficacy of the NOS inhibitor L–NAME in a genetically engineered mouse model of Kras-driven lung adenocarcinoma. Adenoviral Cre recombinase was delivered into the lungs intranasally, resulting in expression of oncogenic KrasG12D and dominant-negative Trp53R172H in lung epithelial cells. L–NAME treatment was provided in the water and continued until survival endpoints. In this model, L–NAME treatment decreased tumor growth and prolonged survival. These data establish a potential clinical role for NOS inhibition in lung cancer treatment.

Spatial attentional bias as a marker of genetic risk, symptom severity, and stimulant response in ADHD

Attention-deficit hyperactivity disorder (ADHD) is a heritable childhood onset disorder that is marked by variability at multiple levels including clinical presentation, cognitive profile, and response to stimulant medications. It has been suggested that this variability may reflect etiological differences, particularly, at the level of underlying genetics. This study examined whether an attentional phenotype-spatial attentional bias could serve as a marker of symptom severity, genetic risk, and stimulant response in ADHD. A total of 96 children and adolescents with ADHD were assessed on the Landmark Task, which is a sensitive measure of spatial attentional bias. All children were genotyped for polymorphisms (30 untranslated (UTR) and intron 8 variable number of tandem repeats (VNTRs)) of the dopamine transporter gene (DAT1). Spatial attentional bias correlated with ADHD symptom levels and varied according to DAT1 genotype. Children who were homozygous for the 10-repeat allele of the DAT1 30-UTR VNTR displayed a rightward attentional bias and had higher symptom levels compared to those with the low-risk genotype. A total of 26 of these children who were medication naive performed the Landmark Task at baseline and then again after 6 weeks of stimulant medication. Left-sided inattention (rightward bias) at baseline was associated with an enhanced response to stimulants at 6 weeks. Moreover, changes in spatial bias with stimulant medications, varied as a function of DAT1 genotype. This study suggests an attentional phenotype that relates to symptom severity and genetic risk for ADHD, and may have utility in predicting stimulant response in ADHD.

Frequency spectroscopy of irreversible electrochemical nucleation kinetics on the nanoscale

An approach is developed for probing the thermodynamics and kinetics of irreversible electrochemical reactions on solid surfaces based on local frequency-voltage spectroscopy. For a model Li-ion conductor surface, two regimes for bias-controlled behavior are demonstrated and ascribed to the difference in the critical nucleus size. The electrostatic and electrochemical phenomena at the tip-surface junction are analyzed. These studies suggest an experimental pathway for exploring local electrochemical activity in solids.

Sequential injection of domain walls into ferroelectrics at different bias voltages: Paving the way for “domain wall memristors”

Simple meso-scale capacitor structures have been made by incorporating thin (300 nm) single crystal lamellae of KTiOPO4 (KTP) between two coplanar Pt electrodes. The influence that either patterned protrusions in the electrodes or focused ion beam milled holes in the KTP have on the nucleation of reverse domains during switching was mapped using piezoresponse force microscopy imaging. The objective was to assess whether or not variations in the magnitude of field enhancement at localised “hot-spots,” caused by such patterning, could be used to both control the exact locations and bias voltages at which nucleation events occurred. It was found that both the patterning of electrodes and the milling of various hole geometries into the KTP could allow controlled sequential injection of domain wall pairs at different bias voltages; this capability could have implications for the design and operation of domain wall electronic devices, such as memristors, in the future.

Perceptions of intergroup bias : the roles of social projection and meta-stereotypes

Underlying intergroup perceptions include processes of social projection (perceiving personal traitslbeliefs in others, see Krueger 1998) and meta-stereotyping (thinking about other groups' perceptions of one's own group, see Vorauer et aI., 1998). Two studies were conducted to investigate social projection and meta-stereotypes in the domain of White-Black racial relations. Study 1, a correlational study, examined the social projection of prejudice and 'prejudiced' meta-stereotypes among Whites. Results revealed that (a) Whites socially projected their intergroup attitudes onto other Whites (and Blacks) [i.e., Whites higher in prejudice against Blacks believed a large percentage of Whites (Blacks) are prejudiced against Blacks (Whites), whereas Whites low in prejudice believed a smaller percentage of Whites (Blacks) are prejudiced]; (b) Whites held the meta:..stereotype that their group (Whites) is viewed by Blacks to be prejudiced; and (c) prejudiced meta-stereotypes may be formed through the social projection of intergroup attitudes (result of path-model tests). Further, several correlates of social projection and meta-stereotypes were identified, including the finding that feeling negatively stereotyped by an outgroup predicted outgroup avoidance through heightened intergroup anxiety. Study 2 replicated and extended these findings, investigating the social projection of ingroup favouritism and meta- and other-stereotypes about ingroup favouritism. These processes were examined experimentally using an anticipated intergroup contact paradigm. The goal was to understand the experimental conditions under which people would display the strongest social projection of intergroup attitudes, and when experimentally induced meta-stereotypes (vs. other-stereotypes; beliefs about the group 11 preferences of one's outgroup) would be most damaging to intergroup contact. White participants were randomly assigned to one of six conditions and received (alleged) feedback from a previously completed computer-based test. Depending on condition, this information suggested that: (a) the participant favoured Whites over Blacks; (b) previous White participants favoured Whites over Blacks; (c) the participant's Black partner favoured Blacks over Whites; (d) previous Black participants favoured Blacks over Whites; (e) the participant's Black partner viewed the participant to favour Whites over Blacks; or (£) Black participants previously participating viewed Whites to favour Whites over Blacks. In a defensive reaction, Whites exhibited enhanced social projection of personal intergroup attitudes onto their ingroup under experimental manipulations characterized by self-concept threat (i.e., when the computer revealed that the participant favoured the ingroup or was viewed to favour the ingroup). Manipulated meta- and otherstereotype information that introduced intergroup contact threat, on the other hand, each exerted a strong negative impact on intergroup contact expectations (e.g., anxiety). Personal meta-stereotype manipulations (i.e., when the participant was informed that her/ his partner thinks s/he favours the ingroup) exerted an especially negative impact on intergroup behaviour, evidenced by increased avoidance of the upcoming interracial interaction. In contrast, personal self-stereotype manipulations (i.e., computer revealed that one favoured the ingroup) ironically improved upcoming intergroup contact expectations and intentions, likely due to an attempt to reduce the discomfort of holding negative intergroup attitudes. Implications and directions for future research are considered.

Exchange bias effect in partially oxidized amorphous Fe–Ni–B based metallic glass nanostructures

The magnetic properties of amorphous Fe–Ni–B based metallic glass nanostructures were investigated. The nanostructures underwent a spin-glass transition at temperatures below 100 K and revealed an irreversible temperature following the linear de Almeida–Thouless dependence. When the nanostructures were cooled below 25 K in a magnetic field, they exhibited an exchange bias effect with enhanced coercivity. The observed onset of exchange bias is associated with the coexistence of the spin-glass phase along with the appearance of another spin-glass phase formed by oxidation of the structurally disordered surface layer, displaying a distinct training effect and cooling field dependence. The latter showed a maximum in exchange bias field and coercivity, which is probably due to competing multiple equivalent spin configurations at the boundary between the two spin-glass phases

A demonstration of attentional bias, using a novel dual task paradigm, towards clinically salient material in recovering alcohol abuse patients?

Background. This study examined whether alcohol abuse patients are characterized either by enhanced schematic processing of alcohol related cues or by an attentional bias towards the processing of alcohol cues. Method. Abstinent alcohol abusers (N = 25) and non-clinical control participants (N = 24) performed a dual task paradigm in which they had to make an odd/even decision to a centrally presented number while performing a peripherally presented lexical decision task. Stimuli on the lexical decision task comprised alcohol words, neutral words and non-words. In addition, participants completed an incidental recall task for the words presented in the lexical decision task. Results. It was found that, in the presence of alcohol related words, the performance of patients on the odd/even decision task was poorer than in the presence of other stimului. In addition, patients displayed slower lexical decision times for alcohol related words. Both groups displayed better recall for alcohol words than for other stimuli. Conclusions. These results are interpreted as supporting neither model of drug cravings. Rather, it is proposed that, in the presence of alcohol stimuli, alcohol abuse patients display a breakdown in the ability to focus attention.