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   Indian Journal of Pure and Applied Physics

 

Special Issue on Thermophysical Properties

 

ISSN: 0019-5596

 

CODEN:IJOPAU  41(6) 413-504(2003) 

VOLUME 41

 NUMBER 6

  JUNE  2003

                                                                                                                                         

The papers published in this issue are from the symposium

held in University of Rajasthan, Jaipur

on 19 September 2002 to 21 September 2002

 

CONTENTS

Nature of heat conduction in manganese perovskites at cryogenic temperatures

T K Dey

417

Microwave processing of electronic ceramics – State of art and emerging trends

D C Dube

423

Temperature dependence of dynamical correlation in liquid lithium

Minal H Patel*, B Y Thakore, P N Gajjar & A R Jani

428

Field instrumentation for thermal conductivity measurement

A K Singh* & N S Reddy

433

Theoretical study of heat capacity of inert liquids

P Dashora*, U Parnami & P Karnawat

438

Magneto-transport studies in yttrium doped lanthanum manganites between 10-300K

M Battabyal*, A Ray & T K Dey

443

Thermal conduction and diffusion through glass-banana fiber polyester composites

Rajni Agarwal*, N S Saxena, K B Sharma, S Thomas & Laly A Pothan

448

Role of alloying elements during high temperature oxidation of bulk amorphous alloy Zr65 Du17.5 Ni10Al7.5 in air

A Dhawan* & S K Sharma

453

Crystallization kinetics of NixTi100-x (x=35,40) glasses before and after high energy heavy ion irradiation

Rohit Jain*, N S Saxena, Deepika Bhandari & S K Sharma

457

Bandgap determination of chemically doped polyaniline materials from reflectance measurements

G P Joshi*, N S Saxena, T P Sharma, V Dixit & S C K Misra

462

Pressure dependence of thermal conductivity and thermal diffusivity of Se-Te In chalcogenide glasses

Kedar Singh* & N S Saxena

466

Crystallization kinetics of pineapple leaf fiber reinforced phenol formaldehyde composites

R Mangal*, N S Saxena, G P Joshi, G P Singh, M S Sreekala & S Thomas

470

Electrical and optical properties of Ag-(p) CdTe-ITO structure

G Wary* & A Rahman

474

Theoretical study of self-diffusion of liquid alkali elements

P Dashora*, P Karnawat & U Parnami

479

Study of hygroscopic properties of some plant fibres under thermal condition

D Saikia & M N Bora

484

Magnetic behaviour of (Fe0.90 MnxCo0.1-x) 2P

S K Jain*, Subhash Chander, S N Dolia, Anjali Krishnamurthy & Bipin K Srivastava

488

Dependence of electrical conductivity on selenium and sulphur doping in a-Si:H

S K Sharma*, J Baveja & R M Mehra

491

Photoconductivity spectra of porous silicon as a function of preparation parameters

Kiran Sehrawat* & R M Mehra

495

Photoluminescence studies on pre- and post-irradiated ruby

D M Bhardwaj*, D C Jain, K V R Rao, Ravi Kumar & K Asokan

498

 

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

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 417-422

 

 

Nature of heat conduction in manganese perovskites
at cryogenic temperatures

T K Dey

Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur, (WB) 721 302

 

Received 3 February 2003; accepted 5 May 2003

 

 

Colossal magneto-resistance (CMR) manganites are important for the unusually large effect, an external magnetic field has on their ability to transport electricity and heat. A sensitivity of this magnitude is not observed in any bulk metallic systems where, mostly, at low temperatures, magneto-resistance arises from a field-dependent electronic mean free path. CMR in the perovskite manganites involves electron-phonon interaction in addition to double exchange mechanisms. Further, because of variable interplays among charge, spin and lattice, these compounds exhibit complex transport behavior. The electrical transport mechanism in the paramagnetic phase for mixed-valence manganites is attractive but, still controversial. The presence of small polarons in the paramagnetic phase and a cross-over from itinerant large polarons to localized small polarons has been put forward to account for the metal-insulator transition associated with the ferromagnetic to paramagnetic transition in manganites. While electronic transport has received considerable attention, very few studies are reported in the literatures on thermal conductivity of manganites. Heat conduction in these systems is dominated by phonons over that of the charge carriers. However, presence of double exchange interaction, Jahn-Teller effect, the strong electron–phonon interaction and local lattice distortions makes the interpretation of thermal conductivity of manganites complicated and interesting. In the present report, recent data of the authors on the electrical resistivity and thermal conductivity on La0.67Ca0.33MnO3, La0.67Sr0.33MnO3 and La0,67Ca0.16Sr0.16MnO3 between 300 and 10K. Electrical conductivity data for T> TMI confirms small polaronic transport, while analysis of the thermal conductivity data indicates a small (~5-18%) contribution from phonon-spin wave near TMI. Strengths of the various phonon scattering mechanisms at low temperatures (<100 K) are evaluated and discussed.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 423-427

 

 

Microwave processing of electronic ceramics  – State of art
and emerging trends

D. C. Dubetc "D. C. Dube"

Department of Physics, Indian Institute of Technology, New Delhi 11 0016tc

"Department of Physics, Indian Institute of Technology, New Delhi 11 0016"

 

Received 3 February 2003, accepted 5 May 2003tc "Received 3 February 2003, accepted 5 May 2003"

 

 

Microwave processing is emerging as a noble technique for the processing of   advanced ceramics. A large variety of materials have been successfully microwave processed. The materials thus processed demonstrate greater phase homogeneity, higher density and better microstructure as compared to conventionally prepared materials. The process is fast and energy efficient. Recent advancements and achievements in the microwave processing are discussed along with the future challenges and opportunities.

 

  

   

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 428-432

 

 

Temperature dependence of dynamical correlation in liquid lithium

Minal H. Patel, B  Y  Thakore, P  N  Gajjar & A  R  Jani

Department of Physics, Sardar Patel University, Vallabh Vidyanagar 388 120, Gujarat, INDIA

 

Received 3 February 2003, accepted 7 May 2003

 

 

The temperature dependence of dynamical variables, the velocity correlation function (VACF), the power spectrum (PS) and the mean square displacement (MSD) of liquid lithium at T = 470 K, 725 K, 843 K and 1000 K are studied by static harmonic-well approximation.  The effective interatomic potential for liquid lithium is computed using our recently proposed model potential with the dielectric function of Sarkar et al.  It is observed that for the higher temperature, the VACF furnishes very short memory than at melting temperature.  The increase in the temperature decays the VACF slowly and also decreases the back scattering of atoms.  The increase in the temperature increases the flatness of the shoulder of the power spectrum.  The result of the MSD concludes that the presence of the vibrating component in the atomic motion decreases with increasing T.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 433-437

 

 

Field instrumentation for thermal conductivity measurementtc "Field instrumentation for thermal conductivity measurement"

A K Singh & N S Reddytc "A K Singh & N S Reddy"

Institute of Armament Technology, Girinagar, Pune 411 025, Maharashtra

 

Received 3 February 2003; revised 25 April 2003; accepted 30 April 2003

 

 

The paper deals with the development of instrumentation for automated thermal conductivity measurement. Sensor used is transient thermal probe, which is based on line heat theory. The thermal probe is interfaced with PC by using a data acquisition module with, application software written in C/C++. The developed instrumentation has been tested by measuring thermal conductivity of standard materials like glycerol, distilled water, etc., for different sampling periods, number of samples and probe heater currents. The instrumentation has been used for measurement of thermal conductivity of propellants and other materials in laboratory, as well as, in field.tc "The paper deals with the development of instrumentation for automated thermal conductivity measurement. Sensor used is transient thermal probe, which is based on line heat theory. The thermal probe is interfaced with PC by using a data acquisition module with, application software written in C/C++. The developed instrumentation has been tested by measuring thermal conductivity of standard materials like glycerol, distilled water, etc., for different sampling periods, number of samples and probe heater currents. The instrumentation has been used for measurement of thermal conductivity of propellants and other materials in laboratory, as well as, in field."

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 438-442

 

 

A theoretical study of heat capacity of inert liquids

P. Dashora1, U. Parnami2 and P. Karnawat1

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

2 Government P G College, Sambharlake (Rajasthan)

 

Received 3 February 2003; accepted 1 May 2003

 

 

A statistical theory for heat capacity of atomic liquids is presented in this paper. Both the characteristic features of the liquid phase viz. the short-range spatial order and significant temporal disorder have been incorporated in the development of the theory. A relation has been deduced for specific heat at constant volume CV in terms of topological-short-range-order parameter, x. Calculated values of CV for neon, argon, krypton and xenon over temperature region Tm - 0.9 Tc are in good agreement with the experimental values. The maximum deviation is less than 5 %. Interestingly, it is found that for these inert liquids, some of the equilibrium and transport properties, viz. average coordination number, surface tension, self-diffusion, viscosity and thermal conductivity, studied by the authors earlier, trends of CVr = CV / CVm versus Tr = T / Tm also correspond quite closely.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 443-447

 

 

Magneto-transport studies in yttrium doped
lanthanum manganites between 10-300K

M Battabyal, A Ray & T K Deytc "M Battabyal, A Ray & T K Dey"

Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur, 721 302

 

Received 3 February 2003; revised 6 May 2003; accepted 13 May 2003

 

 

The hole doped manganite systems A1-xA’xMnO3 (where A represents lanthanides and A’s are divalent cations) with x  0.45 exhibit the electronic transport behavior that results from the complex interplay among charge carriers, spin and lattice. The system shows a metal-insulator transition and the transition temperature (TMI) is strongly dependent on various factors, viz, dopant, thermal history, oxygen content grain size etc. Large magneto-resistance observed near TMI in these perovskites is another interesting feature that has enormous implications in device and sensor technology. In the present paper, we report our results on the temperature dependence of the electrical resistivity on a set of samples of the type La0.6Y0.07Ca0.33MnO3 , prepared by a new pyrophoric technique. Our analysis confirms adiabatic small polaron hopping for T>TMI, while,  in the metallic region (T<TMI), electron-electron and  electron-magnon scattering play the dominant role in defining the influence of annealing time on the electrical resistivity of  fine grained polycrystalline La0.6Y0.07Ca0.33MnO3 pellets.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 448-452

 

 

Thermal conduction and diffusion through glass-banana fiber  
polyester composites

Rajni Agarwal1, N. S. Saxena2, K. B. Sharma2, S. Thomas3 & Laly A Pothan4

1Department of Physics, Government College, Dausa-303303

2Department of physics, University of Rajasthan,  Jaipur 302004, India

3School of Chemical Sciences, M.G. University, Kottayam 686560, Kerala, India

4Department of Chemistry, Bishop Moore College, Mavelikara 690110, Kerala, India

 

Received 3 February 2003; accepted 6 May 2003

 

 

The analysis of variation in thermal conductivity and thermal diffusivity of Banana fiber reinforced polyester composites caused by the addition of glass fiber have been presented in this paper. The composite shows an increase in thermal conductivity in comparison to matrix. However, the thermal conductivity of the composites with increased percentage of glass fiber, decreases in comparison to composite of pure banana fiber. It is minimum when glass fiber fraction is 11% in the composite. The decrease in thermal conductivity values with increasing percentage of glass fiber from 3% to 11 % in the composite is due to fiber/ matrix de-bonding, fiber pull out and matrix fracture. Increase in thermal conductivity at 15% of glass fiber can be attributed to a change in the energy dissipation mechanism. Y. Agari model is used to evaluate the thermal conductivities of the fibers in the hybrid composite.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 453-456

 

 

Role of alloying elements during high temperature oxidation of bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 in air

A Dhawan & S K Sharma

Department of Physics, Malaviya National Institute of Technology, Jaipur 302 017

 

Received 3 February 2003; accepted 9 May 2003

 

 

Oxidation of the bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 (also known as Inoue alloy) in air has been studied at 573 and 603 K using X-ray photoelectron spectroscopy (XPS). The oxide film at these temperatures mainly consists of the oxides of Zr (as ZrO2) and Al (as Al2O3) in addition to small amounts of Cu (as CuO) while no significant signal due to Ni on the top surface could be detected. The results of high temperature oxidation are in contrast with those at room temperature oxidation (native oxidation) as neither Cu nor Ni is present in the oxide film formed at room temperature. The role of the various alloying elements during oxidation at high temperatures (573  and 603 K) and at room temperature in air has been  discussed in the paper.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 457-461

 

 

Crystallization kinetics of NixTi100-x (x=35,40) glasses before and
after high energy heavy ion irradiation

                        Rohit Jain1,N S Saxena1,Deepika Bhandari1 & S K Sharma2

1Condensed Matter Physics Laboratory, Department of Physics, University of Rajasthan, Jaipur 302 004

2Department of Physics,MNIT Jaipur

 

Received 3 February 2003; accepted 8 May 2003

 

 

   Non-isothermal crystallization process in amorphous alloys Ni35Ti65 and Ni40Ti60 before and after high-energy heavy ion irradiation with 150 MeV Ni+11 ions have been investgated using differential scanning calorimetry (DSC). The alloys have been irradiated with fluences varying between 1×1011 and 1×1013 ions/ cm-2. DSC traces have been analyzed in terms of activation energy for crystallization, Avrami exponent dimensionality of growth by using four different models viz. Kissinger equation [J Res NBS, 57 (1956) 217], Ozawa equation [Bull Chem Soc Jpn, 35 (1956) 881], Matusita equation  [J Mater Sci, 19 (1986) 291] and Gao and Wang equation [J Non-Cryst Solids, 87 (1980) 129]. No effect of heavy ion irradiation of above mentioned energy, on the crystallization kinetics has been found.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 462-465

 

 

Bandgap determination of chemically doped polyaniline materials from reflectance measurements

G P Joshi1, N S Saxena1, T P Sharma1, V Dixit2 & S C K Misra2

1Condensed Matter Physics Laboratory, Department of Physics, University of Rajasthan, 5-6, Vigyan Bhawan, Jaipur 302 004

2National Physical Laboratory, Dr K S Krishnan Road, New Delhi 110 012

 

Received 3 February 2003; revised 1 April 2003; accepted 29 April 2003

 

 

Spectroscopic techniques are very useful for characterizing semiconducting and conducting materials. The optical properties (specially reflection spectra) of polyaniline mix with metal Mn and Fe with different composition in bulk form were studied. The reflection spectra of these materials are recorded by a Hitachi spectro-photometer model (330), at room temperature, in the wavelength range 300-600 nm. From the analysis of reflection spectra, polyaniline mix with metal Mn and Fe have been found to have energy bandgap which decreases with increase of concentration of iron. An effort has also been made to study the structure formation using XRD techniques.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 466-469

 

 

Pressure dependence of thermal conductivity and
thermal diffusivity of Se-Te -In chalcogenide glasses

Kedar Singh & N S Saxena

Condensed Matter Physics Laboratory, Department of Physics, University of Rajasthan, Jaipur 302 004

 

Received 3 February 2003; revised 7 April 2003; accepted 25 April 2003

 

 

Measurements of effective  thermal  conductivity  (le)  and  effective thermal diffusivity (ce) of twin pellets of Se80Te20-XInX (x= 2, 4, 6 and 10) chalcogenide glasses, prepared under pressure (load) of 5, 7 and 9 tons, have been made at room temperature, using transient plane source (TPS) technique. The results indicate that, both the values of le and ce increase with the increase of In concentration. Besides, le and ce also depend upon the load at which the pellets have been formed. The composition and pressure (load) dependent behaviour of le and ce is explained in terms of the ion-covalent type of bond which In makes with Se as it is incorporated in the Se-Te glasses.

 

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 470-473

 

 

Crystallization kinetics of pineapple leaf fiber reinforced
phenol formaldehyde composites

R Mangal1, N S Saxena2, G P Joshi2, G P Singh1, M S Sreekala3 & S Thomas4

1Department of Physics, Dunger College, Bikaner 334 001

2Condensed Matter Physics Laboratory, Department of Physics, University of Rajasthan, Jaipur 302 004

3Rubber Institute of India, Kottayam, Kerala 686 009

4School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala 686 560

 

Received 3 February 2003; revised 8 April 2003; accepted 14 April 2003

 

 

Kinetics of crystallization in pineapple leaf fiber reinforced phenol formaldehyde (PF) composites has been studied employing Differential Scanning Calorimetry (DSC). Kinetic parameters such as activation energy in crystallization as well as in glass transition region have been investigated at different percentage of fiber (typically at 15, 20, 30, 40 and 50% by weight) and at different heating rate (typically at 5, 10, 15, 20 K/min). The obtained data has been analyzed in terms of modified Kissinger equation and also using Matusita’s equation to determine the activation energy. The results from one model are compared with the value obtained from the other equation. It is found that, activation energy depends upon the fiber percentage whereas it shows a weak dependence on heating rate.

   

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 474-478

 

 

Electrical and optical properties of Ag-(p)CdTe-ITO structure

G Wary1 & A Rahman2

1Department of Physics, Cotton College, Guwahati 781 001

2Department of Physics, Gauhati University, Guwahati 781 014

 

Received 3 February 2003; accepted 9 May 2003

 

 

Ag-(p)CdTe-ITO heterojunctions were prepared by thermal evaporation under pressure 10-5 torr. The p-type CdTe films, with acceptor concentration (3.85-5.20) ´1017/cm3, were obtained by mixing 4.9% Sb with CdTe powder. The junctions exhibited rectifying I-V characteristics. Saturation current density was calculated for dark and illuminated junctions and found to be (5.5-9.12)´10-5 A/cm2 and (1.37-7.50)´10-6A/cm2, respectively. The ideality factor of a typical junction was found to be 4.75 in dark and 2.18 under illumination, at room temperature (296K). Also ideality factor was found to decrease with increase in temperature. The value of A*, the effective Richardson constant of a typical junction was found to be 81 Acm-2 K–2 and the value of barrier height was found to be 0.65 eV in dark which increased to 0.74 under illumination. The barrier height did not show significant change with the variation of temperature in the range 299-338K. The structure exhibited photovoltaic effect characterized by high series resistance. The maximum power output under 759 lux of illumination was found to be 2´10-4mW.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 479-483

 

 

Theoretical study of self-diffusion of liquid alkali elements

P Dashora*, P Karnawat* & U Parnami†

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

†Govt. PG College, Sambhar Lake, Rajasthan

 

Received 3 February 2003; accepted 5 May 2003

 

A new approach to study the variation of the self-diffusion coefficient through the temperature dependence of the topological-short-range-order (TSRO) existing in the liquid phase has been presented. A relation has been obtained for the temperature dependence of the coefficient of self-diffusion (D). Present study indicates that, both the decrease in TSRO as well as the increase in thermal energy govern the trend of self-diffusion coefficient with temperature. Calculated values of the self-diffusion coefficient for alkali elements (Li, Na, K, Rb) are in good agreement with the available experimental data, over a wide range of temperatures (Tm-Tb) i.e. from melting to normal boiling temperature, the maximum deviation is 6.9%. It is found that, the trends of reduced self-diffusion coefficient Dr=D/Dm versus reduced temperature Tr=T/Tm correspond quite closely, for all alkali elements except lithium, the maximum deviation from common trend being ~6%.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 484-487

 

 

Study of hygroscopic properties of some plant fibres
under thermal condition

D Saikia* & M N Bora†

*Department of Physics, Duliajan College, Duliajan, Assam 786 602

†Department of Physics, Gauhati University, Guwahati, Assam 781 014

 

Received 3 February 2003; accepted 1 May 2003

 

 

The hygroscopic properties such as hygroscopicity, water yielding capacity, capillarity etc of cellulosic plant fibres such as sisal, bowstring hemp (dagger), pineapple, lady’s finger and betel-nut annealed from 310 to 430 K have been investigated. The hygroscopicity of the plant fibres at constant relative humidity decreases with an increase in annealing temperature from 310 to 430 K. The bleached and mercerized samples are more hygroscopic than native samples. The rate of sorption of water content at constant relative humidity increases on pre-heating. The water-yielding capacity as well as capillary action at constant relative humidity decreases with increase in annealing temperature.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 488-490

 

 

Magnetic behaviour of (Fe0.90MnxCo0.1-x)2P

S K Jain, Subhash Chander, S N Dolia, Anjali Krishnamurthy & Bipin K Srivastava

Department of Physics, University of Rajasthan, Jaipur 302 004

 

Received 3 February 2003; accepted 30 April 2003

 

 

(Fe0.90MnxCo0.1-x)2P with x=0.03, 0.05 and 0.07 (hereafter referred to as FMC37, FMC55 and FMC73, respectively) crystallize in Fe2P like hexagonal symmetry. DC magnetization measurements have been made on these alloy systems in external fields up to 8.5 kOe and in the temperature range 85-400K. The alloys are ferromagnetic with Tc~325K for FMC37, ~250K for FMC55 and ~220K for FMC73. While FMC37 shows a clear paramagnetic to ferromagnetic transition, in FMC55 and FMC73, the transition anomaly is field-dependent and gets suppressed by rather low fields. In these two systems, FM order keeps evolving with cooling below these Curie points and at still lower temperatures negative exchange gains in strength, giving rise to disordered magnetic state, which shows long time magnetic relaxation. Below 85K, there could be another modification in magnetic states of the two systems with positive exchange interaction regaining in strength.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 491-494

 

 

Dependence of electrical conductivity on selenium
and sulphur doping in a-Si:H

S K Sharma, J Baveja & R M Mehra

Department of Electronic Science, University of Delhi South Campus, New Delhi 110 021

 

Received 3 February 2003; accepted 1 May 2003

 

 

Se- and S-doped a-Si:H films were prepared by the decomposition of H2Se and H2S with SiH4 gas mixtures by plasma enhanced chemical vapour deposition (PECVD) in a ratio of H2Se/SiH4=1.0´10-4 to 1.0´10-1 and H2S/SiH4=6.8´10-7 to 1.0´10-4. The dielectric constant of Se- and S-doped a-Si:H films vary with doping concentration and can be tailored by changing the gas ratio. The dc dark and photoconductivity showed a maximum at H2Se/SiH4 = 10-3 and a-Si,S:H at H2S/SiH4 = 1.0´10-4 and the activation energy is lower at these doping levels. The room temperature dark and photoconductivity in Se and S-doped a-S:H films have been found to increase as the gas ratios increase for H2Se/SiH4= 10-3 and H2S/SiH4= 10-4, after this range in Se-doped, the dark and photoconductivity decrease to the alloy range.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 495-497

 

 

Photoconductivity spectra of porous silicon as a function of
preparation parameters

Kiran Sehrawat & R M Mehra

Department of Electronic Science, University of Delhi, South Campus, New Delhi110 021

 

Received 3 February 2003; accepted 7 May 2003

 

 

Photoconductivity (PC) which is controlled by non-radiative recombination could provide important information for the understanding of the transport and microscopic origin of photoluminescence (PL) and electro-luminescence (EL) of porous silicon (PS). With this, it may be possible to address the instability encountered in PS optoelectronic devices. An attempt has been made to investigate the transport properties of porous silicon by undertaking a systematic study of the influence of the anodisation parameters on photoconductivity spectra of PS, prepared by wet electrochemical anodisation of p-type c-Si. The PC peak was observed to blueshift with increasing current density/anodisation time and decreasing HF concentration, due to a decrease in crystallite size that was confirmed by SEM observations. The results have been explained as a consequence of bandgap widening, according to the quantum confinement model.

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 41, June 2003, pp. 498-500

 

 

Photoluminescence studies on pre- and post- irradiated ruby

D M Bhardwaj1, D C Jain1, K V R Rao1, Ravi Kumar2 & K Asokan2

1Department of Physics, University of Rajasthan, Jaipur

2Nuclear Science Centre, Arun Asaf Ali Marg, New Delhi

 

Received 3 February 2003; accepted 9 May 2003

 

 

Results of photoluminescence (PL) measurements on the Fe3+ ion irradiated ruby samples at different fluence have been presented. Absence of R1 and R2 lines in spectra at 4.2 K compared to that at room temperature in pristine ruby and appearance of a band centered around 1.6 eV have been discussed in terms of coexistence of Cr3+ and Cr4+. The variation in intensity of this band at 4.2 K with fluence rate is discussed in terms of depopulation of 2E state and lattice deformation. Appearance of a band at 0.95 eV at fluence rate 10 12 ions/cm2 is also reported. This band has been found absent in all other cases.