Vishakha Kaushik

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

Structural and photoluminescence properties of tin oxide and tin oxide: C core–shell and alloy nanoparticles synthesised using gas phase technique

In the present study, we report a controlled growth of tin oxide and tin oxide: carbon nanoparticles by an integrated method comprising of the gas phase agglomeration, electrical mobility based size selection, and in–flight sintering steps. The effect of in-flight sintering temperature and variation in growth environment (N2, H2 and O2) during nanoparticle formation, morphology and composition has been investigated by carrying out High Resolution Transmission Electron microscopy and X-Ray diffraction studies. The results highlight the novelty of the present technique to grow alloy and core-shell nanoparticles in which the stoichiometery (x) of SnOx and the mode of incorporation of carbon into the tin oxide lattice (alloy or core-shell structure), along with well-defined size can be controlled independently. Detailed Photoluminescence (PL) studies of well sintered monocrystalline SnO, SnOx and SnO2 nanoparticles along with SnOx:C and SnO2:C alloy and C@SnO core-shell nanoparticle has been carried out. The ...

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.

On the nature of AFM tip metal-MoS2 contact; effect of single layer character and tip force

In the present study, the nature of metal-MoS2 contacts has been investigated using conductive atomic force microscopy. The point I-V characteristics have been acquired as a function of loading force (53 nN–252 nN) for an interface formed between the atomic force microscopy (AFM) tip (Pt and Co coated) and MoS2 domains (single and multilayer). The metal-MoS2 junctions for both Co and Pt tips exhibit a rectifying nature with higher forward current for the Co tip as compared to the Pt tip for both single and multilayer samples. An interesting behavior of decreasing junction current and rectification ratio with increasing tip loading force is observed in the case of single layer MoS2. In comparison, negligible or very small change in the forward junction current is observed in the case of multilayer samples. The single layer MoS2 undergoes charge polarization in the presence of uniaxial strain exerted in the form of AFM tip loading force, resulting in current in a direction opposite to the forward current du...

Field emission properties of vertically grown Carbon Nanotubes, Nanoflakes and mechanically exfoliated Highly Oriented Pyrolitic Graphite: A comparison

Field emission properties of vertically grown Carbon Nanotubes (CNTs), Nanoflakes (CNFs), and mechanically exfoliated Highly Oriented Pyrolitic Graphite (ex-HOPG) has been investigated using digital Field Emission Microscopy (FEM), Current-Voltage (I-V), and Current-time (I-t) measurements. Prior to the field emission experiments, surface morphology of the samples was studied by using Scanning Electron Microscopy (SEM), Scanning Tunneling Microscopy (STM)/ Spectroscopy (STS), and Atomic Force Microscopy (AFM). The number of emitting spots in FEM images was found to be: nHOPG>nCNT>nCNT in contrast to NCNT> NCNF> NHOPG sequence observed for the potential emitters. The turn-on voltage for 10μA field emission current for CNT, CNF, and ex-HOPG was 400V, 1200V, 1300V respectively. The plot of ln(I/V2) versus 1/V beyond the turn-on voltage was linear for CNF and ex-HOPG but was markedly nonlinear at low voltage for CNT. The I-t characteristics for all the samples exhibited random noise with intermittent spikes for CNT and ex-HOPG. The spikes were totally absent in CNF data. The spectral density of CNT,CNF and HOPG exhibited P(f)=A(Iα/fξ) behaviour with the exponent α=1.6, 1.3, 2 and ξ=1.7, 1.8, 1.8 respectively.The magnitude of current fluctuation for CNT, CNF, and HOPG was 24%, 5%, 28% respectively.