Savita Roy

Extremely non-equilibrium synthesis of luminescent zinc oxide nanoparticles through energetic ion condensation in a dense plasma focus device

Luminescent ZnO nanoparticles have been synthesized on silicon and quartz substrates under extremely non-equilibrium conditions of energetic ion condensation during the post-focus phase in a dense plasma focus (DPF) device. Ar+, O+, Zn+ and ZnO+ ions are generated as a result of interaction of hot and dense argon plasma focus with the surfaces of ZnO pellets placed at the anode. It is found that the sizes, structural and photoluminescence (PL) properties of the ZnO nanoparticles appear to be quite different on Si(1 0 0) and quartz substrates. The results of x-ray diffractometry and atomic force microscopy show that the ZnO nanoparticles are crystalline and range in size from 5-7 nm on Si(1 0 0) substrates to 10-38 nm on quartz substrates. Room-temperature PL studies reveal strong peaks related to excitonic bands and defects for the ZnO nanoparticles deposited on Si (1 0 0), whereas the excitonic bands are not excited in the quartz substrate case. Raman studies indicate the presence of E2 (high) mode for ZnO nanoparticles deposited on Si(1 0 0).

Effect of laser irradiation on structural, electrical, and optical properties of p-mercury cadmium telluride

Single crystals of p‐Hc1−xCdxTe (x=0.16) were grown by the Bridgeman technique. The bulk single crystals were irradiated with laser pulse of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53 μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the Van der Pauw technique in the temperature range 77–300 K for both as‐grown and laser‐irradiated samples. Also the x‐ray diffraction pattern and transmission measurements of the samples were taken at room temperature. Electrical studies shows that the p‐mercury cadmium telluride after the laser irradiation becomes n type and optical results show that the free‐carrier concentration after laser irradiation increases sharply so that there is negligibly small transmission. The x‐ray studies show that single crystal p‐type samples after laser irradiation undergo structural changes as well, introducing ...

Dense Plasma Focus-Based Nanofabrication of III–V Semiconductors: Unique Features and Recent Advances

The hot and dense plasma formed in modified dense plasma focus (DPF) device has been used worldwide for the nanofabrication of several materials. In this paper, we summarize the fabrication of III-V semiconductor nanostructures using the high fluence material ions produced by hot, dense and extremely non-equilibrium plasma generated in a modified DPF device. In addition, we present the recent results on the fabrication of porous nano-gallium arsenide (GaAs). The details of morphological, structural and optical properties of the fabricated nano-GaAs are provided. The effect of rapid thermal annealing on the above properties of porous nano-GaAs is studied. The study reveals that it is possible to tailor the size of pores with annealing temperature. The optical properties of these porous nano-GaAs also confirm the possibility to tailor the pore sizes upon annealing. Possible applications of the fabricated and subsequently annealed porous nano-GaAs in transmission-type photo-cathodes and visible optoelectronic devices are discussed. These results suggest that the modified DPF is an effective tool for nanofabrication of continuous and porous III-V semiconductor nanomaterials. Further opportunities for using the modified DPF device for the fabrication of novel nanostructures are discussed as well.

Effect of laser annealing on electrical and optical properties of n‐mercury cadmium telluride

Single crystals of n‐Hg1−xCdxTe (x=0.18) were grown by the Bridgman technique. The bulk single crystals were irradiated with laser pulses of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53‐μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the van der Pauw technique in the temperature range 77–300 K, for both as‐grown and laser‐irradiated samples. Also, transmission measurements of the samples were taken at room temperature. Both electrical and optical studies showed that laser irradiation introduces additional defects in mercury cadmium telluride (MCT), and its quality deteriorates instead of improving as observed in many other semiconductor materials. We found that laser irradiation increases free‐carrier concentration and decreases the band gap of MCT.

Effect of annealing on the electrical properties of polycrystalline intermetallic compound HgTe

Polycrystalline HgTe samples have been prepared by taking Hg and Te in stochiometeric compositions. The effect of annealing in mercury has also been studied. The effect of temperature on the electronic conduction mechanism and grain‐boundary states has been observed through the measurement of Hall coefficient RH resistivity (ρ) and Hall mobility μH=(RH/ρ) on the polycrystalline HgTe in the temperature range ∼77–350 K. It is found that in electronic conduction in the low‐temperature range, the conduction is dominated by the thermionic emission of electrons over the grain boundaries. At a critical temperature Tc where the barrier height Φb and, hence the width of the space‐charge region near the grain boundaries tends to zero, a crossover from the barrier limited to the mobility limited resistivity occurs. RH is found to be thermally activated over the temperature range where the conduction mechanism is governed by the grain‐boundary barrier. The experimental results are explained on the basis of a grain‐bo...

Fabrication of Gold Nanostructures and Studies of Their Morphological and Surface Plasmonic Properties

We report fabrication of gold nanostructures on glass and indium tin oxide (ITO)-coated glass substrates using high fluence and highly energetic gold ions generated by hot, dense, and strongly non-equilibrium plasma. Nanodots and nanorods are observed in scanning electron microscopy (SEM) of nanostructures grown on glass substrate with single and double shots of gold ions which is in conformity with the transmission electron microscopy image. SEM images for single and double shots of gold ions on ITO-coated glass substrate show only nanodots. The mean diameter of nanodots obtained on both glass and ITO-coated glass is found to increase with increase in the number of gold ions shot from one to two. The gold nanostructures exhibit red shift in surface plasmon resonance with increased interaction which is in agreement with other reported work.

Deposition of aluminium nanoparticles using dense plasma focus device

Plasma route to nanofabrication has drawn much attention recently. The dense plasma focus (DPF) device is used for depositing aluminium nanoparticles on n-type Si (111) wafer. The plasma chamber is filled with argon gas and evacuated at a pressure of 80 Pa. The substrate is placed at distances 4.0 cm, 5.0 cm and 6.0 cm from the top of the central anode. The aluminium is deposited on Si wafer at room temperature with two focused DPF shots. The deposits on the substrate are examined for their morphological properties using atomic force microscopy (AFM). The AFM images have shown the formation of aluminium nanoparticles. From the AFM images, it is found that the size of aluminium nanoparticles increases with increase in distance between the top of anode and the substrate for same number of DPF shots.

Anomalous Hall effect in polycrystalline HgTe

We report the anomalous Hall effect and nonuniformities introduced by aging in the bulk polycrystalline HgTe, which was grown in a predetermined profile, and measurements were taken in the temperature range of 82–350 K. It is found that anomalous behavior is caused by domain formation which is due to acceptor states and this domain formation effect gets diminished by annealing the sample in a mercury atmosphere.

Formation of iron nanoparticles on quartz substrate using dense plasma focus device

Fabrication of nanoparticles and nanostructured materials is at the heart of modern nanoscience. In the present work, we are reporting the fabrication of Iron nanoparticles making use of high temperature, high density, and extremely non equilibrium pulsed plasma produced in 3.3 KJ Mather type Dense Plasma Focus (DPF) device. The Iron nanoparticles were deposited on quartz substrate at a distance of 5 cm above the ion source. The Iron nanoparticles are characterized structurally using X-ray diffractometer and topographically using Atomic force microscopy (AFM). The magnetic property was investigated using Magnetic Force Microscopy (MFM). It is found that these nanoparticles have a dimension in the range of 20-60 nm size and are magnetic in nature.

Deposition and surface characterization of nanoparticles of zinc oxide using dense plasma focus device in nitrogen atmosphere

Nanoparticles of zinc oxide from zinc oxide pellets in the nitrogen plasma atmosphere are deposited on n and p type silicon substrates using Dense Plasma Focus device. The hot and dense nitrogen plasma formed during the focus phase ionizes the ZnO pellet, which then move upward in a fountain like shape and gets deposited on substrates which are placed above the top of the anode. Structural and surface properties of the deposited ZnO are investigated using X-ray diffraction and Atomic force microscope (AFM). X-ray spectra shows the diffraction plane (002) of ZnO nanoparticles deposited on Si with few shots in nitrogen atmosphere. AFM investigations revealed that there are nanoparticles of size between 15-80 nm on n-Si and p-Si substrates. The deposition on n-type Si is better than the p-type Si can be seen from AFM images, this may be due to different orientation of silicon.