Indian Journal of Pure and Applied Physics

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 ISSN: 0019-5596

CODEN: IJOPAU 44 (2) 81-204

VOLUME  44

NUMBER 2

FEBRUARY 2006

 

[This special issue is based on the papers presented at the National Symposium on Science, Technology & Applications of Nanomaterials held at Applied Physics Department, Faculty of Technology and Engineering, The Maharaja Sayajirao University of Baroda, Vadodara 390 001 during March 21-22, 2005]

 

 

 

CONTENTS


Editorial

 

83

  Arun Pratap

 

 

 

Invited Papers

 

 

Low frequency phonons in nanoparticles

87

    Prafulla K Jha

 

 

 

Hyperfine splitting and quantum beats in CdSe quantum dots

93

        Pratima Sen* & Pranay K Sen 

 


Many particle aspects of a quantum wire

98

        A C Sharma

 

 

 

Integrating nano and microparticles

107

       Shriwas Ashtaputre*, Aparna Deshpande, Moussa Ali Ahmed, Sonali Marathe,   Suchita Kalele, J Chimanpure, J Urban, S W Gosavi & S K Kulkarni

 

 

 

Visit to the fascinating world of nano-ceramic powders via solution-combustion

113

        A K Tyagi*, S V Chavan & R D Purohit
 
 
 

Transmission electron microscopy of nanomaterials

119

        S Neogy, R T Savalia, R Tewari, D Srivastava & G K Dey

 

 

 

Measurement of structural and optical band gaps of Cd1-xZnxS (x = 4 and 6) nanomaterials

125

        T P Sharma, Dinesh Patidar, N S Saxena & Kananbala Sharma

 

 

 

Room temperature magnetism in Ge based bulk dilute magnetic semiconductors

129

        D R S Somayajulu, Narendra Patel, Mukesh Chawda, Mitesh Sarkar & K C Sebastian

 

 

 

Nanocomposites for structural applications

135

        L M Manocha, Jignesh Valand, Nikesh Patel, Ashish Warrier & S Manocha

 

 

 

Contributory Papers

 

 

Two band model for a semiconductor quantum dot

143

        Rohit Makwana & A C Sharma

 

Mechanical, elastic and anharmonic properties of Zn1-xCrxTe(0≤x≤1)diluted magnetic semiconductor

148

        Satyam Shinde*, Ankur Pandya & Prafulla K Jha

 

 

 

Effect of temperature on nonlinear optical properties of InGaAs/GaAs single quantum dot

152

        M K Bafna, P Sen & P K Sen

 

 

 

Crystallite size estimation of elemental and composite silver nano-powders using XRD principles

157

        Bharati R Rehani*, P B Joshi, Kirit N Lad & Arun Pratap

 

 

 

Low frequency vibrational modes of nano-metric spherical viruses

162

        Mina Talati* & Prafulla K Jha

 

 

 

Study of elastic properties of fine particle copper-zinc ferrites through infrared spectroscopy

165

        K B Modi, U N Trivedi, P U Sharma, V K Lakhani, M C Chhantbar & H H Joshi

 

 

 

Superparamagnetic behaviour of nano-particles of Ni-Cu ferrite

169

        S N Dolia*, Subhash Chander, M P Sharma & Sudhish Kumar

 

 

 

Growth of single walled carbon nanotubes over Co-MCM-41 mesoporous molecular sieves

173

        Thirunavukkarasu Somanathan* , Arumugam Pandurangan, Dayalan Subashini &Dakshinamoorthy Sathiyamoorthy

 

 

 

Disproportionation of 1,2,4-trimethylbenzene over bifunctional bimetallic catalysts

177

        A Geetha Bhavani*, D Karthikeyan, N Lingappan & A Sreenivasa Rao

 

 

 

Acoustic wave amplification in ion-implanted piezoelectric semiconductor

183

        S Ghosh* & Pragati Khare

 

 

 

Electro - kinetic wave spectrum in group-IV semiconductors: Effect of streaming carriers

188

        S Ghosh* & Preeti Thakur

 

 

 

Optical band gap studies on Zn-Te pellets

192

        R Sharma*, N S Saxena, S Kumar & T P Sharma

 

 

 

I-V measurements on chalcogenide glass thin films

196

        Vibhav K Saraswat*, Vimal Kishore, N S Saxena & T P Sharma

 

 

 

________

*The corresponding author has been indicated by (*) mark in case of papers with more than one author.

 

 


Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 87-92  


Low frequency phonons in nanoparticles

Prafulla K Jha

Department of Physics, Faculty of Science, The MS University of Baroda, Vadodara 390 002

Email: prafullaj@yahoo.com

Received 25 May 2005;  accepted 20 December 2005

The consequence of the phonon confinement on the phonon spectra particularly the low frequency spectra in nanocrystal quantum dots has been investigated. Due to the phonon confinement effect, there appears spheroidal and quadrupolar modes of nanoparticles in the low frequency spectra. The frequency of these modes increases with the decrease of the size of the nanocrystal quantum dot (nanoparticle). The effect of surrounding medium on the phonon spectra of the nanoparticles, which is observed as the broadening of the phonon line shape due to the acoustic mismatch at the surface of the nanoparticles has also been discussed. The effect of density of the surrounding medium on the phonon modes has been discussed and the results on the damping constant and quality factor have been studied.

Keywords: Phonons, Acoustic, Nanoparticles, Raman spectra, Damping

IPC Code: B82B

 

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 93-97


Hyperfine splitting and quantum beats in CdSe quantum dots

Pratima Sen & Pranay K Sen

Department of Applied Physics, S G S Institute of Technology & Science, 23, Park Road, Indore 452 003

Email : pratima_sen@hotmail.com

Received 25 May 2005; revised 26 October 2005;accepted 14 December 2005

The occurrence of quantum beat phenomena in CdSe quantum dots (QD) has been explained on the basis of hyperfine splitting of the excitons. The spin degeneracy of the conduction electrons is lifted by the magnetic field arising due to hole spin. The interaction of the coherent linearly polarized light with a quantum dot has been described by a V-type transition in which the two excited states are formed by the spin-split energies of the conduction band electrons while ground state is the hole state. The output radiation corresponding to each of the transitions will have polarization states characteristic of the -state of the electrons in the conduction band. Accordingly, in a time resolved measurement at a specific analyzer axis, the interference and consequent beating of the signal is expected to occur. The spin states of the excitons in a quantum dot have been analyzed using Dirac’s relativistic wave equation. The results are found to be in good agreement with the reported experimental observations.

Keywords: Hyperfine splitting, Quantum beats, Quantum dots

IPC Code: B82B1/00

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 98-106

Many particle aspects of a quantum wire

A C Sharma

Physics Department, Faculty of Science, The M S University of Baroda, Vadodara 390 002

Received 25 May 2005; revised 24 November 2005; accepted 8 December 2005

The electronic systems in one dimension have features quite distinct from those in higher dimensions. The one-dimensional Fermi surface consists of two discrete points, while in higher dimensions it is continuous. The low-energy particle-hole pairs’ spectrum, which arises from momentum and energy conservations for wave vector between zero and twice of Fermi wave vector does not exist in one dimension. In higher dimensions, this region of missing states is filled in. The Fourier transform of one-dimensional Coulomb potential diverges. This led to wide spread belief that one-dimensional interacting electronic systems should exhibit non-Fermi liquid (known as Luttinger liquid) behaviour.  However, there is still no unambiguous evidence both for the real existence or non-existence of Luttinger liquid behaviour in a realistic quantum wire. This talk briefly reviews key aspects of Fermi liquid approach and Tomonaga-Luttinger liquid approach for a one-dimensional system. In this paper, structure factor, pair distribution function and electron-electron scattering, which exhibit similarity between two approaches in low energy and momentum regime, is reviewed.

Keywords: Quantum wire, Fermi surface, Coulomb potential

IPC Code: B82B1/00

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 107-112

Integrating nano and microparticles

Shriwas Ashtaputre, Aparna Deshpande, Moussa Ali Ahmed, Sonali Marathe,
Suchita Kalele, J Chimanpure,+, J Urban*, S W Gosavi & S K Kulkarni

. DST Unit on Nanoscience, Department of Physics, University of Pune, Pune 411 007

*Fritz – Haber Institute, Faradayweg 4-6, 14195, Berlin, Germany

+Vidya Pratishthan’s ASC College,Vidyanagri, Baramati

Received 25 May 2005; accepted 7 December 2005

A variety of nanomaterials have been developed in last few years with interesting physico-chemical properties. Most of the attempts so far have been to gain understanding of this new class of materials and look for potential applications. This has lead to the formulation of some scaling laws to explain, reasonably well, the properties of nanomaterials. It is realized, however, that the nanomaterials are often too difficult to handle due to their chemical, thermal etc instabilities as well as smallness. There is now a growing interest to integrate nanoparticles with microparticles to get advantages of both the nano and micro world of materials.The synthesis and characterization of ZnO, CdSe, TiO2 and SiO2 nano to micro particles and about core-shell particles have been studied.

Keywords: Microparticles, Nanoparticles

IPC Code: B82B

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 113-118

Visit to the fascinating world of nano-ceramic powders via solution-combustion

A K Tyagi*, S V Chavan & R D Purohit

Applied Chemistry Division, Powder Metallurgy Division

Bhabha Atomic Research Centre, Mumbai 400 085

Received 25 May 2005; accepted 21 December 2005

Soft-chemical routes play an important role in preparation of nano-materials. In particular, the combustion synthesis has emerged as a promising solution-chemistry route for synthesizing a variety of oxide ceramics in the nano-crystalline form. In this review article, the potential of this technique for preparation of a few oxide ceramics viz. yttria, barium polytitanates, barium and strontium thorate, strontium cerates powders has been presented. The role of process parameters in controlling the powder characteristics has also been established. These powders were characterized in terms of X-ray diffraction, surface area analysis, electron microscopy and sinterability. This process was shown to be a simple and cost effective, which results in the phase pure, nano-crystalline powders having high surface area and better sinterability. These combustion-synthesized sinter-active powders achieved near the theoretical density, while retaining the fine grain microstructure.

Keywords: Combustion, Nanocrystalline, Ceramics

IPC Code: B82B 1/00

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 119-124


Transmission electron microscopy of nanomaterials

 

S Neogy, R T Savalia, R Tewari, D Srivastava & G K Dey

Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085

Received 25 May 2005; accepted 5 December 2005

Transmission electron microscope (TEM) has emerged as a very powerful tool for probing the structure of metals and alloys because of its capability to provide morphological information, crystallographic details, and chemical composition of phases distributed on a very fine scale in a given microstructure. Convergent beam electron diffraction, nano or micro beam diffraction and selected area diffraction techniques have been used to obtain crystallographic information whereas structural information is obtained by high-resolution electron microscopy (HREM). With its multifaceted capabilities such as nano-beam diffraction, composition analysis and imaging abilities at angstrom level, TEM has emerged as an instrument for complete characterization of nano scale microstructure of materials. The use of TEM in the study of various types of nanomaterials is described in this paper.

Keywords: Transmission electron microscope, Nanomaterials, High resolution electron microscopy, Microstructural characterization

IPC Code: GO1N

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 125-128

 
Measurement of structural and optical band gaps of Cd1-xZnxS (x = 4 and 6) nanomaterials

T P Sharma, Dinesh Patidar, N S Saxena & Kananbala Sharma

Department of Physics, University of Rajasthan, Jaipur 302 004

E-mail: n_s_saxena@rediffmail.com, dinupatidar@yahoo.co.in

Received 25 May 2005; revised 4 August 2005; accepted 20 December 2005

The sulphides of cadmium and zinc are widely used materials due to their suitable energy band gaps. Their energy band gap depends on the particle size. The materials have been prepared using a simple solution of CdCl2 and ZnCl2 mixed in proper ratio without use of thiophenol. Precipitate of CdZnS is obtained by passing H2S, liberated from heated thiourea through this solution. It is confirmed by X-ray diffraction (XRD) and optical band gap estimation that materials prepared are nano-materials. The optical band gap of these materials has been determined in order to establish a relationship between energy band gap of bulk and nanomaterial. It has been noticed that optical band increases with the increase of Zn concentration in CdZnS.

Keywords: Nanoparticle, Absorption spectra, Chemical method, Energy band gap, Grain size

IPC Code: B82B

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 129-134

   

Room temperature magnetism in Ge based bulk dilute magnetic semiconductors

 

D R S Somayajulu, Narendra Patel, Mukesh Chawda, Mitesh Sarkar & K C Sebastian

Department of Physics, Faculty of Science, The M S Universtiy of Baroda, Vadodara 390 002

Received 5 May 2005; revised 9 November 2005; accepted 5 December 2005

Mössbauer spectroscopy was used to study the hyperfine interactions in the Bulk Fe0.008Ge0.992 system. The room temperature magnetism observed in the V and VI group donor impurity (As, Sb, Bi and Te) doped FeGe system is reviewed. Magneto-resistance and Hall effect measurements on these systems are discussed. The formation of Donor-Acceptor Pairs (DAP’s) and carrier mediation seems to be the cause for this room temperature magnetic interactions in the Ge based bulk dilute magnetic semiconductors.

Keywords: Mössbauer spectroscopy, Magnetic semiconductors, Hyperfine interactions, Hall effect

IPC Code: B82B3/00

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 135-142

  

Nanocomposites for structural applications

L M Manocha*, Jignesh Valand, Nikesh Patel, Ashish Warrier & S Manocha

Department of Materials Science, Sardar Patel University, Vallabh Vidyanagar 388 120, Gujarat

*Email: manocha52@rediffmail.com

Received 25 May 2005; accepted 7 December 2005

Nanocomposites comprise multiphase materials such as metals, polymers inorganic ceramics where at least one constituent phase has one dimension less than 100 nm. Different types of nanosize reinforcements, e.g. fiber, nanoclays, nanospheres, nanopowder etc amorphous or crystalline have been described along with fabrication processes and characteristics properties of different types of nanocomposites for structural applications.

Keywords: Nanocomposites, Nano-reinforcements, Polymers

IPC Code:  B82B

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 143-147

  

Two band model for a semiconductor quantum dot

 

Rohit Makwana & A C Sharma

Physics Department, Faculty of Science, The M S University of Baroda, Vadodara 390 002

Received 25 May 2005; accepted 7 December 2005

Two band model for a semiconductor quantum dot has been developed. Energy eigenvalues and the wavefunctions have been calculated for the dot of radius, a. Our calculation shows that energy eigenvalues which become discrete due to the quantum confinement depends on a. The band gap between two bands has been found a-dependent and it increases on decreasing the size of the dot. The calculated wavefunctions and energy eigenvalues are aimed to use for computing the size dependent static dielectric constant of the quantum dot. The computed wavefunctions and energy eigenvalues and preliminary calculations of dielectric constant are presented in this paper.

Keywords: Quantum dot, Energy eigenvalues, Wavefunctions, Band gap, Dielectric constant

IPC Code: H01L, B82B

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 148-151

 

 Mechanical, elastic and anharmonic properties of Zn1-xCrxTe(0≤x≤1) diluted magnetic semiconductor

Satyam Shinde, Ankur Pandya & Prafulla K Jha

Department of Physics, Faculty of Science, The M S University of Baroda, Vadodara 390 002

Received 25 May 2005; revised 5 October 2005; accepted 7 December 2005

The mechanical, elastic and anharmonic properties of II –VI diluted magnetic semiconductor Zn1-xCrxTe (0≤x≤1) have been reported by using a phenomenological model based on the charge transfer effects due to the deformation of the electronic shell of overlapping ions. The obtained results on the elastic properties agree reasonably well with the available experimental data. The Debye temperature, third order elastic constants and the pressure derivatives of second order elastic constants have also been reported. The decrease in Debye temperature with the increase in Cr concentration suggests that the lattice gets soften with the increase of Cr concentration.

Keywords: Magnetic semiconductor, Charge transfer, Elastic constants

IPC Code: H01L

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 152-156

 

  Effect of temperature on non-linear optical properties of InGaAs/GaAs single quantum dot

M K Bafna, P Sen & P K Sen

Department of Applied Physics, S G S Institute of Technology & Science, 23, Park Road, Indore 452 003

Email: pratima_sen@hotmail.com

Received 25 May 2005; revised 23 November 2005; accepted 5 December 2005

Based upon the semi-classical density matrix approach, a detailed theoretical investigation has been made to analyze the effect of temperature on non-linear optical properties of InGaAs/GaAs single quantum dot (QD). The temperature effects have been incorporated via temperature dependent (i) dephasing mechanism, (ii) band gap energy and (iii) population density. The semiconductor QD has been chosen to be small enough such that the confinement effect dominates over the Coulombic contribution. Detailed numerical estimates of the non-linear refraction and absorption properties have been made. Redshifts of the non-linear refraction and absorption peaks as well as reduction in the induced polarization are found to occur with increasing temperature. The present analysis further reveals that the non-linear gain reduces at higher temperature.

Keywords: Semiconductor quantum dot, Temperature dependent non-linear absorption, Exciton, Biexciton, Third-order susceptibility.

IPC Code: B82B 3/00

 

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 157-161

 

Crystallite size estimation of elemental and composite silver
nano-powders using XRD principles

Bharati R Rehani1, P B Joshi1, Kirit N Lad2 & Arun Pratap2

1Department of Metallurgical Engineering
Faculty of Technology & Engineering, The M S University of Baroda,Vadodara 390 001

2Applied Physics Department, Faculty of Technology & Engineering, The M S University of Baroda,Vadodara  390 001
E-mail: apratapmsu@yahoo.com

Received 25 May 2005; revised 8 November 2005; accepted 8 December 2005

Studies on nanocrystalline materials require an accurate determination of crystallite size as well as the microstrains induced in the material. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are the two well-known techniques for this purpose. Based on XRD principles, numerous approaches such as use of Scherrer equation, integral breath analysis, single-line approximation, Hall-Williamson method, etc have been developed for estimation of crystallite size. Present work deals with a systematic application of Hall-Williamson method for crystallite size estimation of high-energy milled elemental silver and silver-metal oxide (AgMeO) type composite powders and its comparison with Scherrer equation that does not take into account the peak broadening due to strain. The effect of second phase particles on the crystallite size of silver matrix in AgMeO composite is also investigated.

Keywords: Crystal size, X-ray diffraction, Transmission electron microscopy

IPC Code: G01N

 

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 162-164

 

 Low frequency vibrational modes of nano-metric spherical viruses

Mina Talati & Prafulla K Jha

Department of Physics, Faculty of Science, The M S University of Baroda, Vadodara 390 002

Received 25 May 2005; accepted 12 December 2005

The low frequency dynamics has been investigated by using an elastic body approximation for a spherical virus with free surface. The frequencies for spheroidal mode are obtained in terms of their eigen values. The effect of aqueous surrounding medium is also observed by incorporating the acoustic impedance factor. The damping time, frequency and quality factor are evaluated for a virus-medium system.

Keywords: Acoustic vibrations, Phonons, Protein, Nano-metric spherical viruses

IPC Code: B82B1/00

 

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 165-168

 

 Study of elastic properties of fine particle copper-zinc ferrites

through infrared spectroscopy

 

K B Modi, U N Trivedi, P U Sharma, V K Lakhani, M C Chhantbar & H H Joshi

Department of Physics, Saurashtra University, Rajkot 360 005

Received 25 May 2005; accepted 1 December 2005

The elastic moduli for fine particle ZnxCu1-xFe2O4 (x = 0.2, 0.4, 0.6 and 0.8) spinel ferrite system synthesized by wet-chemical technique have been determined through infrared spectroscopy and X-ray diffraction pattern analysis. The force constants for tetrahedral and octahedral sites determined through IR spectral analysis, lattice constant, X-ray density values through XRD pattern analysis; have been used to calculate elastic constants like bulk modulus, Young’s modulus, rigidity modulus, Poisson’s ratio and Debye temperature corrected to zero porosity. The elastic moduli values for all the compositions are found larger as compared to conventional ceramically prepared compositions. The results have been explained on the basis of elastic energy and grain size reduction effect of fine particle. The observed variation of elastic constants with zinc substitution have been interpreted in the light of strength of interatomic bonding.

Keywords: Infrared spectroscopy, Elastic constants, Fine particles, Interatomic bonding

IPC Code: G01N21/00

  

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 169-172

 

  

Superparamagnetic behaviour of nano-particles of Ni-Cu ferrite

S N Dolia1, Subhash Chander2, M P Sharma1 & Sudhish Kumar3

1Department of Physics, University of Rajasthan, Jaipur 302 004

2 Department of Physics, S S Jain Subhodh P G College, Jaipur 302 004

3Department of Physics, M L Sukhadia University, Udaipur 313 002

Received 25 May 2005; revised 21 September 2005: accepted 7 December 2005

The nano-particles of Ni0.8Cu0.2Fe2O4 with a log-normal size distribution of the median diameter of 9 nm and standard deviation of 0.60 have been synthesized by the chemical co-precipitation method followed by annealing at 500°C. The cubic spinel structure in single phase has been confirmed by X-ray diffraction. Reduction in saturation magnetization has been explained on the basis that the magnetic moments in the surface layers, outside the core are in a state of frozen disorder. The dc magnetization is measured which show that the nano-particle sample is super-paramagnetic above the blocking temperature of 250 K. Secondly, the departure of fc curve from the zfc curve is suggestive of temporal relaxation.

Keywords: Nano-particles, Spinel ferrite, Magnetism, Super-paramagnetic behaviour

IPC Code: B82B

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 173-176

   

Growth of single walled carbon nanotubes over Co-MCM-41
mesoporous molecular sieves

Thirunavukkarasu Somanathan1, Arumugam Pandurangan1, Dayalan Subashini1 & Dakshinamoorthy Sathiyamoorthy2

1Department of Chemistry, Anna University, Chennai 600 025

2 Materials Processing Division, Bhabha Atomic Research Centre, Mumbai 400 085

*E-mail address: pandurangan_a@yahoo.com

Received 25 May 2005; revised 18 August 2005; accepted 18 November 2005

Highly ordered cobalt substituted MCM-41 mesoporous molecular sieves was synthesized by direct incorporation of cobalt into the MCM-41 framework through hydrothermal method. The calcined Co-MCM-41 was characterised by physico-chemical technique. The above-characterised material was tested for the application as catalytic template synthesizing single walled carbon nanotubes (SWCNTs) using acetylene as a carbon precursor by chemical vapour deposition (CVD) method in the temperature range 700-900 ºC. The well graphitised CNTs in the pores of Co-MCM-41 was observed and confirmed by SEM and TEM. The good thermal stability and high productivity observed in this study suggest that the mesoporous molecular sieves could be a promising catalytic template for synthesizing carbon nanotubes.

Keywords: Single walled carbon nanotubes, Co-MCM-41, Chemical vapour deposition, Carbon nanotubes

IPC Code: B82B3/00

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 177-182

  

Disproportionation of 1,2,4-trimethylbenzene over bifunctional bimetallic catalysts

A Geetha Bhavani, D Karthikeyan, N Lingappan & A Sreenivasa Rao

Department of Chemistry, Anna University, Chennai 600 025

E-mail: gitabhavani_19@yahoo.co.in

Received 25 May 2005;revised 27 October 2005;accepted 29 November 2005

Zeolite-β and mordenite have been impregnated with 0.1 wt.% Pt and varying (0, 0.1, 0.3, 0.5 wt.%) amounts of Ni and reduced at 475 ºC. The line broadening XRD analysis indicates that the increasing Ni addition decreases the crystallinity of zeolites. The TEM analysis indicates that the average metal particle size increases with increasing Ni addition. The states of Ni and Pt have been analyzed by ESCA. The acidity measurements by pyridine adsorbed FTIR spectroscopy show the occupation of some of the acid sites by the added Ni species. Disproportionation of 1,2,4-trimethylbenzene was carried out in the temperature range 250-400 ºC and found that Ni addition up to 0.3 wt.% over 0.1 wt.% Pt/H-β and 0.1 wt.% over 0.1 wt.% Pt/H-MOR enhances the 1,2,4-trimetylbenzene conversion and disproportionation selectivity of the catalysts. Further, Ni addition above the threshold value leads to fall in activity and disproportionation selectivity drastically. Zeolite-β based Ni-Pt catalysts always show higher activity and selectivity than mordenite based catalysts.

Keywords: Disproportionation, 1,2,4-trimetylbenzene, Nickel, Platinum, Zeolite-β, Mordenite

IPC Code: B82B3/00

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 183-187

  

Acoustic wave amplification in ion-implanted piezoelectric semiconductor

 

S Ghosh* & Pragati Khare

School of Studies in Physics, Vikram University, Ujjain 456 010

Received 25 May 2005; accepted 22 November 2005

An analytical study on excitation of acoustic waves and novel properties introduced by considering that the implanted ions in a group III-V crystal agglomerate to form nanoclusters (NCs) and some of them acquire negative charge in compensated piezoelectric semiconductor plasma has been presented. By using multi-fluid analysis and Maxwell’s equations, a compact dispersion relation for the acoustic wave in a piezoelectric semiconductor has been derived. It is found that the presence of charged NCs not only modifies the wave spectrum but also alters the amplification characteristics even though NCs, on account of their heavy masses, are assumed to be stationary in the background.

Keywords: Acoustic wave amplification, Piezoelectic semiconductor, Doping, Nanoclusters, Amplification

IPC Code: H01L, B82B

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 188-191

   

Electro-kinetic wave spectrum in group-IV semiconductors:
Effect of streaming carriers

S Ghosh & Preeti Thakur

School of Studies in Physics, Vikram University, Ujjain  456 010 (MP), India

*E-mail: drsanjayghosh@rediffmail.com

Received 25 May 2005; revised 2 September 2005; accepted 19 October 2005

The implanted ions in a group-IV semiconductor agglomerate to form nano-clusters (NCs) and some of them acquire negative charge which change the balance between electron-hole densities in an otherwise compensated semiconductor. An analytical study has been made on wave spectrum of electro-kinetic (EK) waves propagating through such medium. Using multi-fluid analysis and Maxwell’s equations, a linear dispersion relation for the EK wave in such medium has been derived. This dispersion relation is used to study slow electro-kinetic wave phenomena and resultant instabilities numerically. The drift velocities of electrons and holes are found to be responsible for converting two aperiodic modes into periodic ones. They are also found helpful in reducing the absorption of all the four possible EK modes. It is found that choosing the proper values of applied electric field and wave number one may optimize the amplification coefficients of propagating modes.

Keywords: Electrostatic waves, Electrostatic oscillations, Plasma effects, Doping, Ion-implantation, Colloids (NCs)

IPC Code: B82B

 

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 192-195

Optical band gap studies on Zn-Te pellets

R Sharma1, N S Saxena1, S Kumar2 & T P Sharma1

1Semiconductor and Polymer Science Laboratory, Department of Physics, 5-6 Vigyan Bhawan, University of Rajasthan Jaipur 302 004

2Department of Physics, C.C.S. University,  Meerut

E-mail: n_s_saxena@rediffmail.com;  r_4_rakeshsharma@rediffmail.com

Received 25 May 2005; accepted 15 December 2005

Spectroscopic techniques are very useful for characterizing semiconducting and conducting materials. The optical properties (specially reflection spectra) of ZnxTe100-x (x=5, 10, 30 and 50) material in pellet form were studied. Polycrystalline semiconducting material has been prepared by Melt quenching method by taking pure Zn and pure Se in appropriate atomic weight ratio. The polycrystalline nature of  Zn5Te95 was confirmed by  XRD studies. In order to compare the studies on so prepared polycrystalline material and commercially obtained  pure Zn50Te50 material,  investigations were carried out on both types of samples. From the analysis of reflection spectra, energy band gaps of ZnxTe100-x material have been determined, which were found to increase from 1.67 to 2.31 eV. It is observed that the optical band gap of laboratory prepared Zn50Te50 material is in excellent agreement with that of commercially obtained pure Zn50Te50 material. 

Keywords: Polycrystalline semiconducting material, Reflection spectra, Spectrophotometer, Energy band gap

IPC Code: G01J

Indian Journal of Pure & Applied Physics

Vol. 44, February 2006, pp. 196-200

 

I-V measurements of chalcogenide glass thin films

Vibhav K Saraswat, Vimal Kishore, N S Saxena & T P Sharma

Semiconductor & Polymer Science Laboratory, 5-6, Vigyan Bhawan, University of Rajasthan, Jaipur 302 004

Email: n_s_saxena@rediffmail.com, vibhu_saraswat@sify.com

Received 25 May 2005; revised 16 November 2005; accepted 5 December 2005

Measurements of I-V characteristics of Se85-xTe15Sbx (where x = 2, 4, 6, 8 and 10) glassy thin films have been carried out at ambient conditions. These measurements have been taken using Keithley Electrometer/High Resistance Meter 6517A in its force voltage measure current (FVMI) mode. Measurements show that the film containing 4 at. wt. % of Sb allows the maximum current to pass through itself as compared to other counterparts of this series. The composition dependence of resistance has been explained on the basis of bond formation between Se and Sb at different compositions and hence Se81Te15Sb4 composition could be termed as “critical composition” in the series under test as it is also strongly supported by dc electrical conductivity, thermal conductivity and thermal diffusivity measurements of these materials in bulk. Besides, the linear relationship between ln (I) and V1/2 confirm the conduction mechanism as to be Poole-Frenkel type.

Keywords: Chalcogenide glasses, Thin film, I-V characteristics, Se-Sb bonds, dc conductivity

IPC Code: G01R