Department of physics

Nuclear Reaction Dynamics studies at National Accelerator Facilities:

Nuclear reaction dynamics studies will be continued and new experiments will be planned in the National accelerator facilities of Inter University accelerator centre (IUAC), BARC-TIFR accelerator facility and the variable energy cyclotron centre (VECC) at Calcutta. The upgrading of IUAC accelerator with LINAC booster and the new super conducting cyclotron of variable energy cyclotron centre will provide us some unique projectile target combinations in low and medium energy regime for reaction studies.

For the last three years we are engaged in the Neutron multiplicity, Fission cross sections and evaporation residue cross section measurements for the System ^16,18O+^194,198Pt and ¹⁹F + ^194,196,198 Pt systems. All the measurements were performed using the Pelletron+Linac accelerator facilities of IUAC New Delhi. For ^16,18O+^194,198Pt systems the role of N/Z in the neutron multiplicities is established. For ¹⁹F + ^194,196,198 Pt systems the effect of shell closure in nuclear dissipation is established. The two programmes are complete and Ph.D. students are writing their thesis.

The group will be actively engaged in the fission dynamics studies at IUAC, New Delhi. A neutron array is being established at IUAC in collaboration with Delhi University, Panjab University and Karnataka University and it will come up in next few years. The group has been actively involved in designing this apparatus and proposing experiment the department will be a part of National Neutron Array Collaboration. An experiment using the LINAC beam of IUAC using a 16 neutron detector array was performed to understand the fission dynamics of the heavy nuclei. New experiments are already planned.

New experiments for the measurements of spin distribution of medium mass system and Fusion barrier distribution for heavy nuclei is planned and approved by IUAC , accelerator user Committee. Charged particle spectrum for ³²S+⁴⁵Sc and ²⁸Si+⁴⁵Sc is analyzed. Nuclear Level density for medium mass nuclei in the mass region A=5-80 are extracted from the Alpha particle spectra and systematic study was undertaken. The group has been actively involved in designing and setting up of National Neutron Array at IUAC. An experiment using the LINAC beam of IUAC using a 16 neutron detector array was performed to understand the fission dynamics of the heavy nuclei. Fusion barrier distribution studies through quasi-elastic scattering methods for heavy Nuclei will be performed at IUAC accelerator facilities. The experiments have also been proposed to study the precission and postscission charged particles emission in heavy ion induced reactions at IUAC, New Delhi. Light charged particles spectra will be measured in coincidence with fission fragments and the fission time scales will be extracted using the charged multiplicities. A Project has been sanctioned by IUAC to perform these experiments.

Nuclear physics groups plan to continue with Nuclear Structure, static nuclear electromagnetic moment, Nuclear reaction dynamics studies in the new experiments using National accelerator facilities. The upgrading of IUAC accelerator with LINAC booster and the new super conducting cyclotron of variable energy cyclotron centre will provide us some unique projectile target combinations in low and medium energy regime for reaction studies. New generation gas filled recoil separator (HYRA) at IUAC will give us ample opportunities to study fusion dynamics and gamma ray spectroscopy of heavy system. The group also plans to upgrade PAD facilities involving BaF₂ and LaBr₃ scintillators at IUAC.

The planned new generation gas filled recoil separator (HYRA) at NSC will give us some opportunities to study fusion dynamics of heavy system. Once it comes up fusion experiments will be proposed for this facility.

B4. International Facilities:

Besides using the national accelerator facilities and the activities in house facilities the group is planning to start renew collaboration and active contacts with the international facilities like GSI at Germany, LNL at Italy and Argon National Lab in USA. The group is planning to join in the GSI future accelerator (FAIR) Collaboration. Faculty members will be involved in planning of the experiments and apparatus for this new FAIR Collaboration.

B5. X-ray Fluorescence Laboratory:

Photon-atom interaction and subsequent processes near the electron binding energies and applications:

The laboratory is equipped with X-ray tube based intense photon source, ²⁴¹Am and ⁵⁵Fe radioisotope based photon sources and Low energy Ge detector, Si(Li) detector and recently procured Peltier-cooled detector. Peltier cooled X-ray fluorescence (XRF) spectrometer (AMPTEK Make, USA) consisting of 0.5 m Silicon Drift Detector (25 mm², 500 mm Be window), Digital pulse processor and MCA. The Peltier cooled EDXRF spectrometer has been installed. The spectrometer shows FWHM 130 eV at 5.89 keV Mn K X-rays. The data acquisition and analysis software has been loaded on PC/Laptop, which makes it capable for in-vivo field measurements. Geometrical set ups has been designed for use with (i) Mn K x-rays from the ⁵⁵Fe source and (ii) the K x-rays of various elements, viz., Se, Mo, Zr, Rh, Ag, Sn, and Gd elements excited by the 59.5 keV gamma ray from the ²⁴¹Am point source (100 mCi) (secondary excitation mode). The geometrical set up has been designed and fabricated using workshop facility available Department of Physics. The spectrometer can be used efficiently in the photon energy range up to 30 keV. The following measurements are being performed/planned using the detector set up: (a) Characterization of the Peltier cooled detector – Measurements of resolution as a function of energy, escape peaks and its theoretical modeling. (b) In-vivo field measurements for articles lying in the Museum are being planned. (c) Angular distribution of the L₃ subshell x-ray emission and the scattering cross-section measurements are being planned using this detector and secondary exciter source. Because of the small size, measurements at large angles approaching 180^o are possible and the solid angle corrections will be minimized. (b) The procurement of Microfocus XRF spectrometer is under process.

The following are the current investigations taken by the group:

1. 
   Study of Influence of resonant Raman scattering in the elemental analysis using X-ray emission based techniques. Contribution of near-edge processes (RRS and XAFS) to attenuation of the characteristic X-rays in various elements for the photon energies (E_in) in the region of respective K-shell/L_i subshell (i = 1, 2, 3) ionization threshold (B_K/B_Li). The observed alteration from the theoretical values is attributed to the X-ray Absorption Fine Structure (XAFS) for negative B_K/Li - E_in values, and the K-shell/Li subshell resonant Raman scattering (RRS) process for positive B_K/Li-E_in values. Systematic of the K-shell/L_i subshell RRS contribution to attenuation of the X-rays are discussed in terms of the respective oscillator density and fraction of electrons available in the K-shell/Li subshell Lorentzian profile of the attenuation element below E_in. Possible matrix effects in the energy dispersive x ray spectrometry due to RRS are also explored.
   

(b) Differential cross sections for Elastic scattering of 59.54-keV γ-rays in elements with 22 ≤ Z ≤ 92 at momentum transfer 0.4 ≤ x ≤ 4.7 Å⁻¹ . The measured differential scattering cross sections are compared with those based on the form-factor (FF) formalism and state-of-the-art S-matrix calculations to differentiate between their relative efficacies and to check angular-dependence of the anomalous scattering factors (ASF) incorporated as correction to the modified form-factor (MF).

(c) Alignment of the L₃ subshell (J = 3/2) vacancy states produced following photoionization in the L_i (i = 1–3) subshells of ₇₉Au, ₈₃Bi, ₉₀Th, and ₉₂U have been investigated through angular distribution of the subsequently emitted L₃ subshell x rays. The measurements were also performed for these elements to investigate the effects of external magnetic field (0.60 T) on the L₃ subshell x-ray emission.

(d) The EDXRF set up has been used in the following applications

(i) Heavy metal uptake studies by biomass of immobilized microorganisms

(ii) Heavy metal induced physiological alterations in Salvinia natans

(iii) Elemental analysis of ground water from different regions of Punjab state (India) using EDXRF technique and the sources of water contamination - Multielemental analysis of the ground water samples from different locations at the boundary between Hoshiarpur and Nawanshahr districts, and Bathinda district of Punjab state (India) was performed. These regions are known to be contaminated by selenium and uranium, respectively. The water samples were analysed using the Energy-dispersive X-ray fluorescence (EDXRF) technique. The water samples from surroundings of the coal-fired thermal power plant in the city and the industrial waste water draining into Sutlej river were also analyzed to investigate the possible sources of water contamination in Bathinda. Agrochemical processes in the water-logged agricultural areas with calcareous soils and use of phosphate fertilizers are favoured sources deterioration of ground water quality in Bathinda district.

(iv) Elemental analysis of some ceria-based synthesized catalyst particles is preformed to know the composition of the mixed oxides of some metals with gold. The possibility of the reversible transition from CeO₂ to Ce₂O₃ makes cerium oxide one of the promising materials. Mixed oxide catalytic particlas were synthesized by the research group of Dept. of applied Chemistry, ISM, Dhanbad.

(v) EDXRF set up has been used to study of uptake of selenium in different portions of chick pea plant i.e. seeds leaves stem and roots is performed. The research group at Department of Botany, Panjab University, has undertaken these investigations. The experiment was designed for application as phytoremidation.

(vi) Thickness determination of CNT (carbon nanotube) films deposited on Si/Glass substrate using the EDXRF set-up involving Mo anode x-ray tube with suitable absorber to reduce the bremsstrahlung and LEGe detector.

(vii) Qualitative and quantitative analysis of Eu³⁺ and Sm³⁺ ions doped ZnS nanocrystals synthesized at Nano-material research laboratory, Chitkara University, Punjab for the photo-catalytic degradation of environmental organic pollutants.

(viii) The analysis of the targets used for nuclear and material science experiments by the students from IUAC, New Delhi.
X-ray production using Heavy ions :

The group has also measured the Li-subshell X-ray production cross-sections for ₇₈Pt, ₇₉Au, ₈₂Pb, ₈₃Bi, ₉₀Th, and ₉₂U elements ionized by (i) ¹⁹F ions in the energy range 76 - 114 MeV, and (b) ²⁸Si ions in the energy range 84 - 140 MeV. The measurements have been performed at 15 UD Pelletron accelerator at IUAC, New Delhi. Measured cross sections reproduced by Ionisation cross-sections based on the ECUSAR theory and recently recommended set of the Li subshell fluorescence and Coster-Kronig yields after accounting for the effect of multiple ionisation.

We are using the accelerator at National Centre for Compositional Characterization of Materials (CCCM), BARC Hydrabad for trace elements analysis and atomic physics. We have performed the experiment on Aerosole, soil and water samples and analysis is in progress. We have also proposed the experiment there to measure the L-subshell ionization cross -sections. We are planning to do the experiment in Feb-March to measure the cross-sections on La-57, Sm-62, Dy-66 and Yb-70 with O-16 and F-19 beams with energies 0.5-1.5 MeV/amu.

B6. Hyperfine Interaction Studies:

The research group has been engaged in the measurement of Hyperfine Interactions i.e. measurement of nuclear electromagnetic moments of the excited states and electric and magnetic hyperfine fields in the magnetic and non-magnetic systems, using PAC (off-line) and PAD (In Beam) techniques. The present facilities include a PAC set up involving multi-BaF₂ Scintillators, a Closed Cycle Helium Refrigerator (10K-300K) and Argon Arc Furnace. In the PAC experiments, the activity of the sample cannot be increased beyond a certain level set by the signal-to-noise requirements, the only way to reduce the data collection time, especially for shorter lived radioactive samples, is to increase the efficiency of the spectrometer. The proposed PAC spectrometer with 6 conical LaBr₃ detectors and NIM based data acquisition system will be resulting in 30 coincidence spectra simultaneously, with optimised detector-sample geometries covering about 60% of the 4 solid angle and the system having excellent time resolution to resolve the fast interaction frequencies encountered in many experiments. Solid state physics with radioactive isotopes is a prospering and growing field. The established nuclear techniques based upon hyperfine techniques (like PAC, PAD, NMR, NQR, Mössbauer spectroscopy etc have clearly proven the enormous potential of using radioactive probe atoms to characterize defects and impurities in solids. To exploit radioactive probe atoms even more efficiently, implantation energies up to some MeV would be highly desirable. Numerous radioactive species have been employed in the past to attack problems involved with defects or impurities in metals, semiconductors and superconductors.

B7. Nuclear Physics (Theory) Group:

Theoretical nuclear physics group at Chandigarh is involved in studying the nuclear dynamics at low, intermediate and relativistic energies. The research topics undertaken are (a) Cluster radioactivity, (b) Fusion, (c) Multifragmentation (d) Nuclear flow and its disappearances, and (e) Particle production at intermediate energies. At low energy, the concern is on the problems of fusion and fission processes whereas at intermediate energies, the work is on the problems of multifragmentation, collective flow and its disappearance, differential flow, elliptic flow, and their connection with nuclear equation of state, rapidity and stopping of nuclear matter and thermalization reached in a reaction. Efforts will be made to compare our theoretical predictions with experimental data. A dynamical cluster decay model is advanced for the formation and decay of hot and rotating compound nuclear formed in light heavy ion reactions. Calculations are made for various compound systems. Studies are being done to include deformations and orientations degree of freedom to generalize proximity nuclear potential and the Coulomb potential. Possible new reactions for synthesis of new and super-heavy elements are pursued.

During 2008-2012 period, we studied various phenomena at low and intermediate energies. Some of these are fusion using proximity potentials for both symmetry and asymmetric reactions. At intermediate energies the process of multuifragmentaton, collective flow and nuclear stopping were investigated. We also studied the entropy production using SACA and MST models.

Fusion-fission dynamics of low energy heavy-ion reactions:

Knowing that Wong formula is a simplification of the dynamical cluster-decay (DCM) of Gupta et al., we have analyzed the Wong model for angular momentum and barrier modification effects in capture cross-sections σ_capture, fusion-evaporation cross-sections σ_evr known for fusion hindrance phenomenon in coupled-channels calculations at sub-barrier energies, and fusion-fission cross-sections σ_ff using the proximity potential due to Blocki et al. with effects of multipole deformations (β₂ -β₄) and orientations (both co-planer and non-coplaner) included, and the one derived from Skyrme forces based semi-classical energy density formalism in extended Thomas Fermi (ETF) method. One of the interesting result is that the ℓ-dependence in Wong via ℓ-summation is found enough to explain the σ_capture for all the reactions studied, but in the case of σ_evr, a further modification of barriers is required for below barrier energies, affected in terms of either the barrier ''lowering" or barrier ''narrowing" via the curvature constant or choosing different Skyrme forces. Furthermore, the DCM is shown to contain the "barrier lowering" property as its inbuilt characteristic.

The role of deformations and orientations of nuclei is investigated in detail for the exotic cluster radioactive decay using the preformed cluster model (PCM) of Gupta and Malik. An interesting result of this study is that, except for ¹⁴C decays where higher multipole deformations up to β₄are found essential, the β₂ alone is found good enough to fit all other experimental data on cluster-decay half-lives. More recently, this study is extended to the use of relativistic mean field densities in the double folding procedure for constructing the cluster-daughter potential with M3Y nucleon-nucleon interaction containing exchange effects. Interestingly, the RMF-densities based nuclear potential supports the concept of preformation for both the α- and heavier cluster decays. As a by product of this study, the phenomenological M3Y type of effective interaction is shown to be derivable from the RMF theory itself, whose optical potential is shown to describe the exotic cluster radioactive decay process nicely.

Further studies are on fusion-fission dynamics of the compound nucleus Z=117, the nuclear structure effects in Z=117 nucleus, nuclear sub-structure of cluster effects in ^112-122Ba nuclei using the RMF theory, the problem of establishing the magic shells in superheavy mass region by using the reaction data in DCM, entrance channel effects in some reactions, and nuclear reaction cross-sections of exotic nuclei in the Glauber model for the RMF densities.

Some of the recent works are reviewed in the following two Reviews: Lecture Notes in Physics 818, “Clusters in Nuclei”, 1 (2010) 223-264, and International Review of Physics (I.RE.PHY.) 5 (2011) 74-87.

The following innovations and new observations are made:

A complete dynamical theory of heavy ion reactions, based on microscopic Skyrme energy density formalism (SEDF), using the semiclassical extended Thomas Fermi (ETF) method, is developed which includes temperature of the compound system and deformations to all higher multi-pole orders and orientations of both coplanar and non-coplanar nuclei. The model developed help us to calculate the fusion cross-sections, barrier modification effects at sub-barrier energies with in one parameter description, the neck length parameter, with nuclear structure effects included, missing in its simplified version, the Wong model. The new results obtained are given as the following observations:

1. Use of a simplified version of DCM, the Wong formula, in SEDF of semiclassical ETF method.

2. Barrier modification effects assessed by using the ℓ-summed extended Wong model for both the “pocket formula” and Skyrme forces based proximity potential derived from ETF method.

3. The role of deformations and orientations in spontaneous exotic cluster decays using PCM.

4. Role of Skyrme forces in capture reactions, for which the Wong model is most suited.

5. Role of co-planar and non-coplanar degrees of freedom in dominantly quasi-fission, equivalently capture, evaporation residue and fusion-fission reactions.

6. Use of RMF densities in cluster decay studies, including the deformation effects.

(C) Condensed Matter Group

C1. Experimental Condensed Matter

Solid state Physics is one of the thrust areas recognised by UGC under CAS. The experimental activities of this group involve materials which are important from applications point of view as well as those that lead to an understanding of basic properties of matter and materials. On-going work involves identification of materials suitable for opto-electronic devices, fabrication and characterisation of semi-conducting thin films and preparation and characterisation of carbon Nanotubes.

During the last decade, this group has made significant contributions in training graduate and post-graduate students as well as research personnel. They have picked up the latest techniques being used by academics, research organisations and industry. At any given point in time there are about 18 Ph.D. scholars, 3-4 M.Sc. students, 2-3 M. Tech. (Nano-science and nano-technology) students and 2-3 M.Phil. students working in these laboratories.

Carbon nanomaterials such as C₆₀ and carbon nanotubes (CNTs) are deposited as thin films on various substrates, irradiated with swift heavy ions at IUAC, Delhi, and characterized by various means. We have also set up an arc discharge unit which can produce C₆₀ as well as CNTs, and has been used mainly as a training equipment for M. Sc. and M.Tech (NSNT) project students. This apparatus is also a part of regular lab. Course for M. Tech. (NSNT). Magnetic properties of nanoparticles of Ni are being studied in collaboration with materials science group at Central Scientific Instrumentation Organisation, Chandigarh, a CSIR lab.

Ion Beams on Materials

The importance of studying the properties of carbon nanotubes (CNTs) under various extreme conditions is underlined by the fact that numerous usages have been envisaged. Some of these conditions are purported to be created by a passing ion beam through the material. We irradiate films of CNTs with swift heavy ions of widely varying energies to simulate these, and find the surprising result that instead of being damaged at the outset, the CNTs are healed (annealed) to better crystallinity when there is a low dose of incident ions.

The following is the summary of the work done during the recent past:

(a) Optical constants of thermally deposited In₅₀Se₅₀ and Ag₁₀(In₅₀Se₅₀)₉₀ thin films:
Thin films of chemical composition In₅₀Se₅₀ and Ag₁₀(In₅₀ Se₅₀)₉₀ are prepared by thermal evaporation technique. The optical properties of these thin films are determined by a method, based only on the transmission spectra at normal incidence, measured over the 400-1000 nm spectral range. The optical absorption edge is described using the indirect transition model proposed by Tauc and the optical band gap (E_g) is calculated from the absorption coefficient (α) by Tauc’s extrapolation procedure. It is observed that the value of refractive index (n) and α decrease and the value of Eg increases after the incorporation of Ag.

(b) Light, Annealing and Plasma induced changes on the electrical properties of a- GaSe Thin films

Thin films of GaSe have been deposited at room temperature on glass substrate by physical vapor deposition technique. These films are irradiated with light for 6 hrs at room temperature using heat filtered white light by using tungsten lamp (1035 lux), annealed at 523K for 1 hr and irradiated with argon- plasma (p~0.2 mbar, I=20mA) for 1 hr. Dark conductivity measurements were made on as-deposited and irradiated GaSe thin films in the temperature range 100-370 K in order to identify the conduction mechanism and the effect of different treatments on its electrical properties. The obtained results revealed two distinct regions. The mechanisms of such regions were analyzed. At high temperatures dc conductivity (σ_d) obeys the law: ln σ  1/T, indicating conduction in extended states, and at low temperatures, obeys the law ln σ  T^-1/4, indicating variable range hopping in localized states near the Fermi level. The density of localized states N(E_F) and various other Mott’s parameters like degree of disorder (T_o), hopping distance (R) and hopping energy (W) near the Fermi level is calculated before and after different treatments using dc conductivity measurements at low temperatures. Steady state photoconductivity measurements were done in the temperature range 303-373 K by using heat filtered white light.

(c) Effect of In concentration on the electrical properties of InSe alloy:
In_xSe_1-x (x = 0.4, 0.5, 0.6) thin films are deposited at room temperature on glass substrates by thermal evaporation technique. The X-Ray diffraction analysis showed that both the as-deposited films In₂Se₃ and InSe (x = 0.4 and 0.5) are amorphous in nature while the as-deposited films of In₃Se₂ are polycrystalline. Scanning electron microscopy (SEM) photographs of these samples have been taken. The dc measurements are made on the In_xSe_1-x films at all concentrations, in the temperature range 100-400 K. The obtained results revealed three distinct regions. Temperature dependence of conductivity are analyzed by three mechanisms, extended state conductivity, conduction in band tail and conduction in localized sites. It is clear from the results, that at high temperatures conductivity mechanism obeys the law ln σ  1/T and at low temperatures: ln σ  T^-1/4, indicating variable range hopping energy in the localized states near the Fermi level N (E_f). The incorporation of In atoms in Se matrix leads to an increase in the electrical conductivity and decrease in the thermal activation energy. The change in the above parameters has been discussed in terms of the phase transition which is taking place in In_xSe_1-x thin films.

(d) Effect of Bi Addition on the Physical Parameters of a-GeSe Glassy Alloy:
Physical parameters like mean bond energy (), average heat of atomization and average coordination number () have been calculated. Cohesive energy (CE) is also calculated by using chemical bond approach (CBA) method and electronegtivity is calculated by using Sanderson principle. The glass transition temperature (T_g) has been calculated and it increases as the Bi concentration increases. The results have been explained on the basis of some structural changes which occur after the addition of Bi into the system.

5. 
   Effect of proton irradiations on amorphous InSe thin film:
   

Optical parameters have been studied after proton irradiation (fluence: 1 × 10¹⁵ and 1 × 10¹⁴ ions/cm²)of a-In₅₀Se₅₀ thin films at room temperature in vacuum (~10⁻⁶ Torr) at 3 MeV proton energy from Chandigarh Cyclotron. The beam was focused using a circular collimator so that an area of ~0.75 cm² on the films received a uniform ion dose. Changes in the optical parameters like refractive index (n), absorption coefficient (α), optical gap (E_g^opt), extinction coefficient (k), real and imaginary dielectric constants (ε₁ and ε₂) are observed in a-In₅₀Se₅₀ thin films prepared by thermal evaporation technique under vacuum. Transmission measurements have been done before and after proton irradiation. The mechanism of optical absorption follows the rule of indirect allowed transition model proposed by Tauc and the optical band gap (E_g^opt) is calculated by Tauc’s extrapolation. It is found that after the proton irradiation, the refractive index, absorption coefficient and optical gap decreases for the fluence 1 × 10¹⁴ ions/cm² and for higher fluence the value of these parameters increase. These results will be explained on the basis of some structural changes occurring after proton irradiations.

5. 
   On the calorimetric study of chalcogenide Se₈₅Te₁₅ glass:
   

The calorimetric parameters of Se₈₅Te₁₅ glass has been investigated using differential scanning calorimetry (DSC) in non-isothermal conditions at different heating rates of 5, 10, 15, and 20 ⁰Cmin^-1. Double crystallization behaviour is observed at all heating rates. The glass transition temperature (T_g) is found to increase with increase in heating rate (α). The activation energy for glass transition (E_g) and for the both crystallization phases is determined using different empirical approaches for different heating rates. The kinetic parameters are calculated using methods recently developed for non-isothermal conditions. The calculated value of kinetic exponent n indicates one dimensional growth with surface nucleation for first crystallization peak and two (two- and three-dimensional growth) mechanisms are working simultaneously for second crystallization peak. The average value of crystallization reaction order, n is (1.28±0.03) and (3.4±0.5) for the first and second crystallization stages respectively. The average value of E_g, E_c1 and E_c2 are (67.02±1.5) kcalmol^-1, (37.93±2.1) kcalmol^-1 and (57.11±7.5) kcalmol^-1 respectively. Thermal stability and glass forming tendency have also been studied for different heating rates.

5. 
   Crystallization study of Sn additive Se-Te chalcogenide alloys:
   

Calorimetric study of Se_85–xTe₁₅Sn_x (x = 0, 2, 4 and 6) glassy alloys have been performed using Differential Scanning Calorimetry (DSC) under non-isothermal conditions at four different heating rates (5, 10, 15 and 20°C/min). The glass transition temperature and peak crystallization temperature are found to increase with increasing heating rate. It is remarkable to note that a second glass transition region is associated with second crystallization peak for Sn additive Se-Te investigated samples. Three approaches have been employed to study the glass transition region. The kinetic analysis for the first crystallization peak has been taken by three different methods. The glass transition activation energy, the activation energy of crystallization and Avrami exponent (n) are found to be composition dependent. The crystallization ability is found to increase with increasing Sn content. From the experimental data, the temperature difference (T_p – T_g) is found to maximum for Se₈₃Te₁₅Sn₂ alloy, which indicates that this alloy is thermally more stable in the composition range under investigation.

5. 
   Glass transition and crystallization study of chalcogenide Se₇₀Te₁₅In₁₅ glass
   

Differential scanning calorimetry (DSC) data at different heating rates (5, 10, 15 and 20°Cmin^–1) of Se₇₀Te₁₅In₁₅ chalcogenide glass is reported and discussed. The crystallization mechanism is explained in terms of recent analyses developed for use under non-isothermal conditions. The value of Avrami exponent (n) indicates that the glassy Se₇₀Te₁₅In₁₅ alloy has three dimensional growths. The average values of the activation energy for glass transition, E_g, and crystallization process, E_c, are (154.16 ± 4.1) kJmol^–1 and (98.81 ± 18.1) kJmol^–1, respectively. The ease of glass formation has also been studied. The reduced glass transition temperature (T_rg), Hruby’ parameter (K_gl) and fragility index (F_i) indicate that the prepared glass is obtained from a strong glass forming liquid.

5. 
   On the crystallization kinetics of In additive Se-Te chalcogenide glasses
   

The calorimetric parameters of glassy Se_85–xTe₁₅In_x (x = 0, 2, 6 and 10) alloys have been investigated using Differential Scanning Calorimetry (DSC) in non-isothermal conditions at different heating rates of 5, 10, 15 and 20ºC/min. It is observed that in these glasses, the glass transition temperature, the onset crystallization temperature and the peak temperature of crystallization are found to be dependent on the composition and heating rates. The glass transition activation energy and crystallization activation energy have been determined using different empirical approaches. The kinetic analysis of the crystallization peak has been performed using Matusita’s model. The values of Avrami exponent (n) and activation energy of crystallization (E_c) are evaluated. The validity of Matusita’s model is ascertained by comparison with the results obtained by Kissinger model and Augis and Banett method as well as their approximations. The activation energy of crystallization is determined by analyzing the data using the isoconversional methods. The present study shows that the activation energy of crystallization varies with the degree of conversion and hence with temperature. Thermal stability and glass forming tendency have also been studied for different heating rates.

(j) Effect of irradiation on the optical properties of a-GaSe thin films:

The effect of laser irradiation (λ= 532 nm), argon plasma treatment (p~0.2 mbar, I=20mA), effect of proton irradiation (1×10¹⁴ ions/cm²) and effect of annealing (T = 523K) have been studied on the optical properties of GaSe semi-conducting material. Thin films of GaSe are deposited by physical vapor deposition technique. Optical measurements have been taken at room temperature and the different parameters like refractive index (n), absorption coefficient (α), optical gap (E_g^opt), extinction coefficient (k), real and imaginary dielectric constants (ε₁ and ε₂), before and after these treatments have been calculated. The mechanism of optical absorption follows the rule of indirect allowed transition and the optical band gap (E_g^opt) is calculated by Tauc’s extrapolation.

(k) Optical nonlinearity in chalcogenide glasses:

Chalcogenide glasses have large values of non-linearity at 1.55 μm, several orders of magnitude larger than the value for conventional silica glass. Recently, third-order optical nonlinearity of chalcogenide glasses has attracted a considerable attention. According to the semi empirical Miller’s rule, third order optical nonlinear susceptibility (χ⁽³⁾) can be enhanced with the increase of the refractive index (n). As metal ions play an important role in augmenting the value of ‘n’, the addition of metal ions may rise the value ‘n’ and is expected to improve the value χ⁽³⁾ comparing with the host material. Thin films of Ge₂₀Se₈₀ and Ag₁₀Ge_0.18Se_0.72 have been prepared using thermal evaporation technique. Photo-diffusion of Ag metal has also been done on Ge₂₀Se₈₀ thin films. Refractive index (n) has been measured using the transmission data. Third order optical nonlinear susceptibility (χ⁽³⁾) have been calculated using the Miller’s formula for all three samples. It has been observed from the results that the addition of Ag into the Ge₂₀Se₈₀ system enhances the value of ‘n’ and χ⁽³⁾. Increase in these values is more in case of the photo-diffused film. A careful analysis of these results also suggests that the contribution to polarizability from the lone electron pairs is not predominant factor influencing the non-linear properties of Ag metal alloyed Ge₂₀Se₈₀ glasses. Additional factors such as glass structure or density, the presence of unpaired electrons and the presence of defect states must be taken into account.

(l) Non-Ideal p-n junction Diode of Sb_xSe_1-x (x = 0.4, 0.5, 0.6, 0.7) Thin Films:

We have made diodes consisting of the same alloy i.e. Sb_xSe_1-x (x = 0.4, 0.5, 0.6 and 0.7), but change the concentration of Sb metal from 40% to 70% atomic weight percentage. It is observed from the Hall measurements that the nature of charge carriers have changed from p- to n-type at x = 0.6 for Sb_xSe_1-x. We have measured I-V characteristics of four p-n junction diodes i.e. p-Sb₂Se₃ / n-Sb₃Se₂, p-Sb₂Se₃ / n-Sb₇Se₃, p-SbSe / n-Sb₃Se₂ , p-SbSe / n-Sb₇Se₃. We have calculated the parameters as built -in voltage (V_bi), forward resistance (R_f), ideal factor (n), saturation current (I_o), breakdown current (I_Bd) and breakdown voltage (V_Bd).

(m) Photodarkening Effect in a-(GaSe)₉₀Ag₁₀ Thin Films:

The present paper reports the laser induced changes on the optical properties of a-(GaSe)₉₀Ag₁₀ thin films prepared by thermal evaporation technique. Thin film samples, on glass substrate, were exposed to laser light of wavelength λ = 532 nm for different exposure times, t_E (t_E = 0 s, 500 s, 1000 s and 3000 s). Optical parameters like absorption coefficient and optical energy gap of as- deposited thin film and their laser induced changes were studied at three different times of exposure. The value of absorption coefficient of these thin film increases on exposing the film to laser irradiation. The optical absorption edge shift to lower photon energy i.e. the photo darkening (PD) effect occurs. The results have been explained on the basis of structural changes that are occurring after the laser irradiation.