A. K. Shukla

Silicon nanowires prepared by metal induced etching (MIE): good field emitters

Micro-Raman scattering and electron field emission characteristics of silicon nanowires (SiNWs) synthesized by metal assisted chemical etching (MACE) are investigated. Scanning electron microscopy images reveal the growth of well aligned vertical SiNWs. Raman shift and size relation from bond-polarizability model has been used to calculate exact confinement sizes in SiNWs. The Si optical phonon peak for SiNWs showed a downshift and an asymmetric broadening with decreasing diameter of the SiNWs due to quantum connement of optical phonons. The field emission characteristics of these SiNWs are studied based by carrying out currentvoltage measurements followed by a theoretical analysis using FowlerNordheim equation. The electron field emission increased with decreasing diameter of SiNWs. Field emission from these SiNWs exhibits signicant enhancement in turn-on eld and total emission current with decreasing nanowire size. The reported results in the current study indicate that MACE is a simple technique to prepare well-aligned SiNWs with potentials for applications in field emission devices. ‡ Electronic mail: vivek@unitus.it ar X iv :1 40 5. 71 93 v1 [ co nd -m at .m es -h al l] 2 8 M ay 2 01 4 Micro-Raman and FE studies of SINWs... 2

Study of Porous Silicon Prepared Using Metal-Induced Etching (MIE): a Comparison with Laser-Induced Etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.

De Novo Assembly of Bitter Gourd Transcriptomes: Gene Expression and Sequence Variations in Gynoecious and Monoecious Lines

Bitter gourd (Momordica charantia L.) is a nutritious vegetable crop of Asian origin, used as a medicinal herb in Indian and Chinese traditional medicine. Molecular breeding in bitter gourd is in its infancy, due to limited molecular resources, particularly on functional markers for traits such as gynoecy. We performed de novo transcriptome sequencing of bitter gourd using Illumina next-generation sequencer, from root, flower buds, stem and leaf samples of gynoecious line (Gy323) and a monoecious line (DRAR1). A total of 65,540 transcripts for Gy323 and 61,490 for DRAR1 were obtained. Comparisons revealed SNP and SSR variations between these lines and, identification of gene classes. Based on available transcripts we identified 80 WRKY transcription factors, several reported in responses to biotic and abiotic stresses; 56 ARF genes which play a pivotal role in auxin-regulated gene expression and development. The data presented will be useful in both functions studies and breeding programs in bitter gourd.

Raman study of phase transformation from diamond structure to wurtzite structure in the silicon nanowires

Hexagonal silicon has emerged as an exciting material due to its novel vibrational and electronic properties. Synthesis of the wurtzite silicon nanowires (w-SiNWs) is studied here using metal assisted chemical etching (MACE) technique. Stress induced in the SiNWs during wet chemical etching is attributed to formation of the w-SiNWs. Presence of the w-SiNWs is revealed by first-order and second-order Raman spectra. The effect of variation of deposition time of silver (catalyst) is explicitly studied for growth of w-SiNWs. The deposition time enhances the density of SiNWs in an island of vertically aligned SiNWs. Absorption coefficient studies of the w-SiNWs are also conducted using UV–vis spectroscopy as a function of deposition time. Increase in the absorption coefficient in SiNWs is noticed with increasing deposition time. The prominent quantum confinement along with stress and porosity is shown to be mainly responsible for the transformation from diamond structure to wurtzite structure in the silicon nanowires.

Au-nanoparticles-decorated MWCNTs demonstrating enhanced fluorescence and Raman spectroscopy

The gas sensing characteristics of ZnO nanowires (NWs) coated with different thickness of CuO film have been investigated. ZnO NWs were grown on Si/SiO2 by hydrothermal method and CuO films were deposited by thermal evaporation. It has been found that ZnO NWs exhibit characteristic n-type behavior upto a CuO thickness of 50 nm; whereas at higher thickness the samples show p-type behavior (typical of CuO). At a CuO thickness of 10 nm the sensitivity towards H2S was 500% more as compared to pure ZnO NWs films. In addition, the operating temperature was reduced to 200°C.

Modification in surface morphology and enhanced field emission properties of pristine carbon nanotubes by introducing nitrogen gas

Bamboo shaped multiwalled carbon nanotubes (MWCNTs) were grown using iron (Fe) catalyst over aluminum (Al) film by microwave plasma enhanced chemical vapour deposition. The effect of nitrogen plasma in the modification of the microstructure has been investigated. Field emission from pristine MWCNTs and bamboo shaped MWCNTs has been investigated. The turn-on field for bamboo shaped MWCNTs was (1.17 V/μm) which is smaller as compared to pristine MWCNTs (1.42 V/um) and thus shows better emission properties.

Thermal Effects on Electron-Phonon Interactions in Silicon Nanostructures

Raman spectroscopy of silicon nanostructures, recorded using an excitation laser power density of 1.0 kW/cm2 , was employed here to reveal the dominance of thermal effects at temperatures higher than room temperature. The room temperature Raman spectrum showed only phonon confinement and Fano effects. Raman spectra recorded at higher temperatures showed an increase in FWHM and a decrease in asymmetry ratio with respect to its room temperature counterpart. Experimental Raman scattering data were analyzed successfully using theoretical Raman line-shapes generated by incorporating the temperature dependence of a phonon dispersion relation. The experimental and theoretical temperature dependent Raman spectra are in good agreement. Although quantum confinement and Fano effects persist, heating effects start dominating at temperatures higher than room temperature.

GENETIC DIVERSITY AMONG FOUR MOMORDICA SPECIES USING RAPD, SSR AND ISSR MARKERS.

* Anjali Shukla 1,2 , D. P. Sinha 1,3 , D. R. Bhardwaj 1 , Abaidya Nath Singh 4 , Pankaj Kumar 4 and Major Singh 1 . 1. Divisionof CropImprovement,IndianInstituteofVegetableResearch,PostBox01,Jakhini (Shahanshahpur), Varanasi,UttarPradesh221 305,India. 2. Department of Biotechnology, Microtek College of Management and Technology, Varanasi. 3. NationalInstituteofVirology,C/oRGICDCampus,NearNimhans,Bangaluru,Karnataka-560 029,India. 4. Department of Botany, UdaiPratap Autonomous College, Varanasi. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History