Azher M. Siddiqui

Synthesis, Electrical Conductivity, and Dielectric Behavior of Polyaniline/V2O5 Composites

Conducting polymer composites of polyaniline/vanadium pentaoxide PANI/V2O5 (with different initial weight percentage of V2O5) has been synthesized by in situ polymerization method. DC conductivity of compressed pellets has been analyzed in the temperature range 300–550 K and was found to increase with V2O5 doping. This increase in conductivity is mainly due to band conduction. It has also been observed that the dielectric constant and dielectric loss increase with the level of doping of V2O5 but remain independent of the frequency (50 KHz–1 MHz). X-ray diffraction pattern shows some order of crystallinity of composites due to interaction of polyaniline with V2O5. UV-visible spectroscopy shows an increase in the optical band gap with doping.

Development of a large area two-dimensional position sensitive ΔE−E detector telescope for material analysis

A large area two-dimensional position sensitive detector telescope has been designed and fabricated at NSC, New Delhi for performing ERDA based material characterization experiments. This gas ionization detector is working well with position resolution better than 2 mm and good z-separation in both high and low mass regions. Large solid angle is a pre-request to minimize the possible unwanted radiation damage during the measurement. The consequent kinematic broadening has been corrected by recording the position information. Two-dimensional position sensitivity has also been obtained. Possibility of controlled modification is shown in this work.

Ion beam characterization and engineering of strain in semiconductor multi-layers

Abstract The objective of this work is to measure and engineer the strain in III–V compound semiconductor multi-layers using ion beams, which leads to spatial band-gap tuning for the integration of optoelectronics devices. Strained layer superlattices have been of unique interest due to their ability to tune the band gap, which depends on the strain at the interface. Therefore the strain measurements at the interface are of great interest. A large area two-dimensional positions sensitive Δ E − E detector telescope and a fully automated high energy channeling facility have been developed at NSC, New Delhi. An overview of the series of ERDA, RBS, Channeling, HRXRD and ion beam mixing experiments performed in this direction will be discussed in this paper.

Synthesis and Structural Analysis of Al‐doped Qandilite (Mg2TiO4)

We report here, the synthesis and characterization of Aluminum (Al) doped Mg2TiO4. Magnesium ortho titanates spinel {with composition Mg2TiO4; tetrahedral site A = Mg and octahedral site B = Mg, Ti (equal amounts)} for general formula AB2O4 has been synthesized by solid‐state reaction technique. The formations of titanates, the successive sintering process and the corresponding microstructure evolution, phase purity and crystal structure have been investigated using X‐ray powder diffraction and scanning electron microscopy. X‐ray diffraction confirms that the sample is single phase and the lattice parameter 842.00 pm for cubic (x = 0) Mg2TiO4 and a = b = 836.00 pm, c = 842.00 pm for x = 0.4 in tetragonal structure. Scanning electron microscope (SEM) images confirms that the samples Mg2TiO4, (x = 0) have a cubic and as we increase the dopant concentration (x = 0.2 and x = 0.4), we observe a change in the phase from cubic to tetragonal.

Ion beam studies in strained layer superlattices

Abstract The potential device application of semiconductor heterostructures and strained layer superlattices has been highlighted. Metal organic chemical vapour deposition grown In 0.53 Ga 0.47 As/InP lattice-matched structure has been irradiated by 130 MeV Ag 13+ and studied by RBS/Channelling using 3.5 MeV He 2+ ions. Ion irradiation seems to have induced a finite tensile strain in the InGaAs layer, indicating thereby that ion beam mixing occurs at this energy. Other complementary techniques like high resolution XRD and STM are needed to conclude the structural modifications in the sample.

Ion channeling, high resolution x-ray diffraction and Raman spectroscopy in strained quantum wells

InGaAs strained epitaxial layers on GaAs are of considerable interest in semiconductor devices. An important feature is the critical thickness of the epitaxial layer beyond which relaxation occurs, affecting the device performance. With this in view, a series of such structures have been grown by organometallic vapor phase epitaxy and characterized by ion channeling, high resolution x-ray diffraction and Raman spectroscopy. The results of these three techniques are compared for the samples in this study which are fully strained, nominally and by experimental measurements. Beam steering effect that occurs at low energy channeling is also addressed.

Effects of Si5+ Ion Irradiation on Poly(3-methyl thiophene) Films

Poly(3-methyl thiophene) has been synthesized by the chemical oxidation polymerization method using FeCl3. The powder has been dissolved in CHCl3 and thin films of thickness 2 µm are prepared on glass and Si substrates. The polymerization has been confirmed by FTIR spectrum. The films are irradiated by 60 MeV Si5+ ions at different fluences and modifications in optical, electrical and structural properties are studied. FTIR spectra show methyl group evolution after irradiation. The optical band gap decreases after irradiation and dc conductivity increases four orders of magnitude after irradiation at the highest fluence. The conduction mechanism has been found mainly by band conduction.

Studies on structural, optical and cluster size of poly(m-toluidine)–polyvinyl chloride blends

Poly(m-toluidine) (PmT), a derivative of polyaniline, has been prepared by chemical oxidation polymerization method. The synthesized PmT powder is blended with plasticized polyvinyl chloride (PVC) to achieve 20 μm thick self-supported films. These films were irradiated with 60 MeV Si5+ ions at three different fluences whose S e (electronic energy loss) value is found to be 1.988×103 KeV/μ m, an order of magnitude larger than 60 MeV C5+ (2.958×102 KeV/μ m). Fourier transform infrared (FTIR), X-ray diffraction (XRD) and ultraviolet-visible (UV) absorption studies of pre- and post-irradiated films of PmT–PVC blends were carried out to study the heavy ion irradiation effects on these polymer blends. An overall change in the structure of the polymer blend has been observed from FTIR studies. UV-visible spectra show a decrease in the optical band gap (E g) and an increase in cluster size with increasing fluence. An effort is made to compare these results with our earlier studies. We found that the variation in S e plays an important role in the structural and optical properties of PmT–PVC blends.

60-MeV C5+ ion irradiation effects on conducting poly (o-toluidine)–poly vinyl chloride blend films

Abstract Poly (o-toluidine) was synthesized from a derivative of aniline (o-toluidine) monomer by chemical oxidative polymerization method. After polymerization, the polymer prepared was blended with poly vinyl chloride and irradiated by 60-MeV C5+ ions at five different fluences of 1×1011, 3.3×1011, 1×1012, 3.3×1012 and 1×1013 ions/cm2. The swift heavy ion irradiation effects on crystallinity and DC conductivity were studied. X-ray diffraction study showed variations in crystallinity of the blend films upon irradiation. The crystallinity, DC conductivity and activation energy were found to vary discontinuously with fluence. The DC conductivity and activation energy were obeying Meyer–Neldel rule.

Ion beam induced modification of lattice strains in In0.1Ga0.9As/GaAs system

Abstract The effects of 150 MeV Ag ion irradiation on the molecular beam epitaxially grown In0.1Ga0.9As/GaAs samples have been studied using high resolution X-ray diffraction (HRXRD). Our earlier experiments suggest that the compressive strain will decrease due to ion beam mixing effects in an initially strained system. Similarly a tensile strain will be induced in an initially lattice matched system. These studies are being performed to explore the possibility of spatial bandgap tuning for the integration of optoelectronics circuits. Here we present a systematic study to understand the effects of ion fluence and the initial strain/layer thickness on the modification of strain. Strain measurements are performed using HRXRD by determining the angular shift in the layer peak position with respect to that of the substrate peak. Substrate peak broadens with ion fluence due to the implantation effects at the end of the ion range (∼13 μm). However, the thin InGaAs layer and the substrate region near to this layer will not be affected. It is shown that the Swift Heavy Ion induced mixing can alter the lattice strain at room temperature without loss of the quality of the structure.