Zhuowei Wang

Photoluminescence and Raman scattering of silicon nanocrystals prepared by silicon ion implantion into SiO2 films

Photoluminescence (PL) and Raman spectra of silicon nanocrystals prepared by Si ion implantion into SiO2 layers on Si substrate have been measured at room temperature. Their dependence on annealing temperature was investigated in detail. The PL peaks observed in the as-implanted sample originate from the defects in SiO2 layers caused by ion implantation. They actually disappear after thermal annealing at 800 degrees C. The PL peak from silicon nanocrystals was observed when thermal annealing temperatures are higher than 900 degrees C. The PL peak is redshifted to 1.7 eV and the intensity reaches maximum at the thermal annealing temperature of 1100 degrees C. The characterized Raman scattering peak of silicon nanocrystals was observed by using a right angle scattering configuration. The Raman signal related to the silicon nanocrystals appears only in the samples annealed at temperature above 900 degrees C. It further proves the formation of silicon nanocrystals in these samples

Proteomic analysis on the temperature-dependent complexes in Thermoanaerobacter tengcongensis

It is generally accepted that protein complexes play an active role in avoiding the protein degradation of the thermophiles. Thermoanaerobacter tengcongensis was cultured at three different temperatures (55, 75 and 80°C) and the extracts of protein complexes were prepared. Through blue native PAGE, the changes of the relative band volumes in response to different temperatures were semi‐quantitatively compared and six temperature‐dependent bands were obtained. These bands were excised, digested with trypsin and then analyzed with MS for the identification of protein components. With the combination of the proteins identified by LC MS/MS and MALDI TOF/TOF MS, a total of 92 unique proteins were ascertained in these complexes. Besides, some protein components were examined with Western blot, which gave us insights into the survival mechanism of thermophiles. These included (i) the composition of complex at 80°C was significantly different from that at the other two temperatures; (ii) HSPs presented in all temperature‐dependent complexes; (iii) several proteins associated with the functional pathways existed in the same complexes, indicating that the complex structure provided facility for the functional efficiency.

The Temperature Dependent Proteomic Analysis of Thermotoga maritima

Thermotoga maritima (T. maritima) is a typical thermophile, and its proteome response to environmental temperature changes has yet to be explored. This study aims to uncover the temperature-dependent proteins of T. maritima using comparative proteomic approach. T. maritima was cultured under four temperatures, 60°C, 70°C, 80°C and 90°C, and the bacterial proteins were extracted and electrophoresed in two-dimensional mode. After analysis of gel images, a total of 224 spots, either cytoplasm or membrane, were defined as temperature-dependent. Of these spots, 75 unique bacterial proteins were identified using MALDI TOF/TOF MS. As is well known, the chaperone proteins such as heat shock protein 60 and elongation factor Tu, were up-regulated in abundance due to increased temperature. However, several temperature-dependent proteins of T. maritima responded very differently when compared to responses of the thermophile T. tengcongensis. Intriguingly, a number of proteins involved in central carbohydrate metabolism were significantly up-regulated at higher temperature. Their corresponding mRNA levels were elevated accordingly. The increase in abundance of several key enzymes indicates that a number of central carbohydrate metabolism pathways of T. maritima are activated at higher temperatures.

Raman scattering in hexagonal GaN epitaxial layer grown on MgAl2O4 substrate

The room temperature Raman spectra of the hexagonal GaN epilayer grown on [111]- oriented MgAl2O4 substrate were measured in various backscattering and right angle scattering geometries. All of the symmetry-allowed optical phonon modes were observed except the E-2 (low frequency) mode. The quasitransverse and quasilongitudinal modes were also observed in the x(zx)z and x(yy)z configurations, which are the mixed modes of pure transverse and longitudinal modes with A(1) and E-1 symmetry, respectively

Exploring membrane and cytoplasm proteomic responses of Alkalimonas amylolytica N10 to different external pHs with combination strategy of de novo peptide sequencing.

Identification of differentially proteomic responses to external pHs would pave an access for understanding of survival mechanisms of bacteria living at extreme pH environment. We cultured Alkalimonas amylolytica N10 (N10), a novel alkaliphilic bacterium found in Lake Chahannor, in media with three different pHs and extracted the correspondent membrane and cytoplasm proteins for proteomic analysis through 2‐DE. The differential 2‐DE spots corresponding to the altered pHs were delivered to MALDI TOF/TOF MS for protein identification. Since the genomic data of strain N10 was unavailable, we encountered a problem at low rate of protein identification with 18.1%. We employed, therefore, a combined strategy of de novo sequencing to analyze MS/MS signals generated from MALDI TOF/TOF MS. A significantly improved rate of protein identification was thus achieved at over than 70.0%. Furthermore, we extensively investigated the expression of these pH‐dependent N10 genes using Western blot and real‐time PCR. The conclusions drawn from immunoblot and mRNA measurements were mostly in agreement with the proteomic observations. We conducted the bioinformatic analysis to all the pH‐dependent N10 proteins and found that some membrane proteins participated in iron transport were differentially expressed as external pH elevated and most of differential proteins with increased or bell‐shape mode of pH‐dependence were involved in bioenergetic process and metabolism of carbohydrates, fatty acid, amino acids, and nucleotides. Our data thus provide a functional profile of the pH‐responsive proteins in alkaliphiles, leading to elucidation of alkaliphilic‐adaptive mechanism.

Systematic characterization of a novel gal operon in Thermoanaerobacter tengcongensis

On the basis of the Thermoanaerobacter tengcongensis genome, a novel type of gal operon was deduced. The gene expression and biochemical properties of this operon were further characterized. RT-PCR analysis of the intergenic regions suggested that the transcription of the gal operon was continuous. With gene cloning and enzyme activity assays, TTE1929, TTE1928 and TTE1927 were identified to be GalT, GalK and GalE, respectively. Results elicited from polarimetry assays revealed that TTE1925, a hypothetical protein, was a novel mutarotase, termed MR-Tt. TTE1926 was identified as a regulator that could bind to two operators in the operon promoter. The transcriptional start sites were mapped, and this suggested that there are two promoters in this operon. Expression of the gal genes was significantly induced by galactose, whereas only MR-Tt expression was detected in glucose-cultured T. tengcongensis at both the mRNA and the protein level. In addition, the abundance of gal proteins was examined at different temperatures. At temperatures ranging from 60 to 80 degrees C, the level of MR-Tt protein was relatively stable, but that of the other gal proteins was dramatically decreased. The operator-binding complexes were isolated and identified by electrophoretic mobility shift assay-liquid chromatography (EMSA-LC) MS-MS, which suggested that several regulatory proteins, such as GalR and a sensory histidine kinase, participate in the regulation of the gal operon.

Pressure Behavior of Deep Centers in ZnSxTe1—x Alloys

We have measured photoluminescence of ZnSxTe1-x alloys (x > 0.7) at 300 K and under hydrostatic pressure up to 7 GPa. The spectra contain only a broad emission band under excitation of the 406.7 nm line. Its pressure coefficients are 47, 62 and 45 meV/GPa for x = 0.98, 0.92 and 0.79 samples, which are about 26%, 7% and 38% smaller than that of the band gap in the corresponding alloys. The Stokes shifts between emission and absorption of the bands were calculated by fitting the pressure dependence of the emission intensity, being 0.29, 0.48 and 0.13 eV for the three samples, respectively. The small pressure coefficient and large Stokes shift indicate that the emission band observed in our samples may correspond to the Te isoelectronic center in the ZnSxTe1-x alloy.

Pressure behaviour of photoluminescence from InAs submonolayer in GaAs matrix

We have investigated the dependence on hydrostatic pressure of the photoluminescence of an InAs submonolayer embedded in a GaAs matrix at 15 K and for pressure up to 8 GPa. Strong InAs-related emissions are observed in all three samples at ambient pressure. The temperature dependence of the emission intensity for these peaks can be well characterized by the thermal activation of excitons from the InAs layer to the GaAs matrix. With increasing pressure, the InAs-related peaks shift to higher energies. The pressure coefficients of these peaks are very close to that of the free exciton in bulk GaAs. Some weak peaks observed at pressures above 4.2 GPa are attributed to indirect transitions involving X states in the InAs layer. These results are similar to the pressure behaviour observed in the InAs/GaAs monolayer structures. A group of new lines has been observed in the spectra when pressure is increased beyond 2.5 GPa, which is attributed to the N isoelectronic traps in the GaAs matrix.

Near-resonance Raman scattering of longitudinal optical phonon modes and interface modes in GaAs/AlAs superlattices

The near-resonance Raman scattering of GaAs/AlAs superlattices is investigated at room temperature. Owing to the resonance enhancement of Frohlich interaction, the scattering intensity of even LO confined modes with A1 symmetry becomes much stronger than that of odd modes with B2 symmetry. The even modes were observed in the polarized spectra, while the odd modes appear in the depolarized spectra as in the off-resonance case. The second-order Raman spectra show that the polarized spectra are composed of the overtone and combinations of even modes, while the depolarized spectra are composed of the combinations of one odd mode and one even mode. The results agree well with the selection rules predicted by the microscopic theory of Raman scattering in superlattices, developed recently by Huang and co-workers. In addition, the interface modes and the combinations of interface modes and confined modes are also observed in the two configurations.

Self-ordering of quasi-quantum wire in InAlAs/AlGaAs multilayer nanostructure and its optical anisotropy

Self-ordering of quasi-quantum wires in multilayer InAlAs/AlGaAs nanostructures grown by molecular beam epitaxy is identified. The chain-like structures along the [1 (1) over bar 0] Of direction formed by coalescence of quantum dots were observed. The photoluminescence of the nanostructures is partially polarized along the [1 (1) over bar 0] direction. The polarization ratio depends on the wavelength and the maximum polarization is on the lower energy side. The maximum polarization increases from 0.32 at 10 K to 0.53 at 100 K, and the energy position of maximum polarization moves near to PL peak with increasing temperature. They are all related to the existence of isolated islands and quasi-quantum wires in our sample. This result provides a novel approach to produce narrow quantum wires