B. N. Singh

Field emission studies on well adhered pulsed laser deposited LaB6 on W tip

Lanthanum hexaboride films have been deposited on a tungsten tip by pulsed laser deposition technique. The field emission studies have been performed in the conventional field emission geometry. The Fowler-Nordheim plot obtained from the current-voltage characteristic is found to be linear in accordance with the quantum mechanical tunneling phenomenon. A current density of 1.2×104A∕cm2 is drawn from the deposited tip. The field enhancement factor is calculated to be 5537cm−1, indicating that the field emission is from nanoscale protrusions present on emitter surface. The emission current-time plots show the very good stability of the emitter.

STUDIES ON UV PHOTOLUMINESCENCE FROM PULSED LASER DEPOSITED ENSEMBLES OF CAPPED SILICON NANOPARTICLES

Multilayer ensembles of alumina capped, widely dispersed silicon nanoparticles (Si-nps) with mean diameter in the range of about 1–4 nm were grown using pulsed laser deposition. With photo-excitation at ~3.82 eV, photoluminescence (PL) was found to emanate from these Si-nps mainly in the UV spectral region centered at about 3.37 eV due to the Γ25–Γ15 transitions. It was found that while the bandgap measured from photoabsorption spectra showed blueshift with decreasing mean size of the Si-nps, spectral position of the PL peaks remained almost insensitive to variation in the mean size. The PL peak at about 3.37 eV was observed to vanish at temperatures higher than 70 K and another one at about 3.31 eV attributed to the TO phonon replica disappeared above 100 K. In general FWHM of both these PL peaks was found to increase monotonically from about 6 to 19 meV and the peak positions were found to undergo redshift with increase in the sample temperature from 10 to 100 K. These observations could be explained by applying Bose statistics for a 6 meV confined phonon mode broadening of the Si-nps and using the Varshni equation, respectively. Si-nps grown in oxygen ambient at 600°C showed significant enhancement in the PL intensity with increasing pressure. These findings elicit that light emission from Si-nps is either due to the nanoparticles of about 1 nm and smaller size primarily driven by the quantum confinement or due to an interface state pumped by these Si-nps.

Field Emission from Nanocrystalline LaB6 Prepared by Laser Ablation

Dattatray J. Late, Mahendra A. More, Dilip S. Joag * Centerfor Advanced Studies in Material Science and Condensed Matter Physics, Department ofPhysics, University ofPune, Pune 411007, India Pankaj Misra, B. N. Singh and Lalit M. Kukreja Thin Film Laboratory, Raja Ramanna CentreforAdvance Technology, Indore 452013, India Corresponding Author E-mail: hod@physics.unipune.ernet.in ; Phone: 91-020-25692678; Fax: 91-020-25691684