Zishan H. Khan

High-energy ball milling technique for ZnO nanoparticles as antibacterial material

Nanoparticles of zinc oxide (ZnO) are increasingly recognized for their utility in biological applications. In this study, the high-energy ball milling (HEBM) technique was used to produce nanoparticles of ZnO from its microcrystalline powder. Four samples were ball milled for 2, 10, 20, and 50 hours, respectively. The structural and optical modifications induced in the ‘as synthesized’ nanomaterials were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and photoluminescence emission spectra (PL). SEM and TEM results show a gradual decrease in particle size from around 600 to ∼30 nm, with increased milling time. The initial microstructures had random shapes, while the final shape became quite spherical. XRD analysis showed ZnO in a hexagonal structure, broadening in the diffracted peaks and going from larger to smaller particles along with a relaxation in the lattice constant c. The value of c was found to increase from 5.204 to 5.217 Å with a decrease in particle size (600 to ∼30 nm). PL result showed a new band at around 365 nm, whose intensity is found to increase as the particles size decreases. These remarkable structural and optical modifications induced in ZnO nanoparticles might prove useful for various applications. The increase in c value is an important factor for increasing the antibacterial effects of ZnO, suggesting that the HEBM technique is quite suitable for producing these nanoparticles for this purpose.

Effect of Composition on Electrical and Optical Properties of Thin Films of Amorphous GaxSe100−x Nanorods

We report the electrical and optical studies of thin films of a-GaxSe100−x nanorods (x = 3, 6, 9 and 12). Thin films of a-GaxSe100−x nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-GaxSe100−x nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor (σ0) is of the order of 101 Ω−1 cm−1, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases on increasing Ga concentration.

Optical properties of a-Ga20Se80−xSbx thin films

The optical properties of a-Ga20Se80−xSbx thin films (where x = 0, 5, 10, 15, and 20) have been studied. It is found that the optical band gap decreases with increasing Sb component in the a-Ga20Se80 binary alloy. Various optical constants have been calculated for the present system of a-Ga20Se80−xSbx. The value of the refractive index (n) increases with wavelength, while the value of the extinction coefficient decreases with wavelength. The temperature dependence of the DC conductivity has also been studied in amorphous thin films of a-Ga20Se80−xSbx in the temperature range (287–318 K) with a view to see the effect of the metallic component on the a-Ga20Se80 binary alloy. It is observed that the activation energy decreases with the increase of the metallic component in the binary alloy.

Nanorods of LiF:Mg,Cu,P as Detectors for Mixed Field Radiations

Nanocrystalline powder of LiF: Mg,Cu,P phosphor has been synthesized by the chemical coprecipitation technique. Shape and size of these nanomaterials were observed by transmission electron microscope and atomic force microscope. The particles are of rod shapes having diameters from 50 to 80 nm and lengths varying within the range 0.4-0.7 mum. Pellets of these nanorods were irradiated by 48 MeV7Li3+ ions at different fluences in the range 1times1011-1times1014 ions/cm2 (with corresponding doses in the range 0.679-679 kGy) and their thermoluminescence (TL) properties have been studied. The TL glow curves are observed to have prominent peaks at around 588 K along with smaller one at around 410 K. The TL intensity of the former is found to increase with increasing the fluence, while that of the latter decreases. These behaviors are in contrast with those of the peaks induced by 137Cs gamma-rays. This modification in case of irradiation by ion beam has been attributed to the change in population of the luminescent/trapping centers due to the use of highly energetic ions. From these results, it is suggested that the nanorods of LiF:Mg,Cu,P might be used as detectors for mixed fields radiations such as space radiations.

Synthesis and characterization of nanoparticle thin films of a-(PbSe)100−xCdx lead chalcogenides

We report the synthesis of amorphous (PbSe)100−xCdx (x = 5, 10, 15, and 20) nanoparticle thin films using thermal evaporation method under argon gas atmosphere. Thin films with a thickness of 20 nm have been deposited on glass substrates at room temperature under a continuous flow (50 sccm) of argon. X-ray diffraction patterns suggest the amorphous nature of these thin films. From the field emission scanning electron microscopy images, it is observed that these thin films contain quite spherical nanoparticles with an average diameter of approximately 20 nm. Raman spectra of these a-(PbSe)100−xCdx nanoparticles show a wavelength shift in the peak position as compared with earlier reported values on PbSe. This shift in peak position may be due to the addition of Cd in PbSe. The optical properties of these nanoparticles include the studies on photoluminescence and optical constants. On the basis of optical absorption measurements, a direct optical bandgap is observed, and the value of the bandgap decreases with the increase in metal (Cd) contents in PbSe. Both extinction coefficient (k) and refractive index (n) show an increasing trend with the increase in Cd concentration. On the basis of temperature dependence of direct current conductivity, the activation energy and pre-exponential factor of these thin films have been estimated. These calculated values of activation energy and pre-exponential factor suggest that the conduction is due to thermally assisted tunneling of the carriers.

Optical and electrical properties of glassy Ga10Te90−xSbx alloys

Abstract The optical band gap and optical constant for Ga10Te90−xSbx (where x=5, 10, 20 and 30) thin films have been studied as a function of photon energy in the wave length region (720–1200 nm). It was found that the optical band gap and refractive index decrease on incorporation of antimony in Ga10Te90−x alloy. The dc conductivity of Ga10Te90−xSbx thin films is also reported for the temperature range 308–368 K. The temperature dependence of the conductivity is very low and increases on adding antimony in Ga10Te90−xSbx system.

Electrical transport properties of thin film of a-Se87Te13 nanorods

We have studied the electrical transport properties of thin film of a-S87Te13 nanorods. Initially, the glassy alloy of S87Te13 is prepared by melt-quenching technique. The amorphous nature of this alloy is verified by using X-ray diffraction technique. The nanorods of a-S87Te13 are synthesised on a glass substrate under an ambient gas (Ar) atmosphere using physical vapour condensation system. The morphology and microstructure of these nanorods are studied using scanning electron microscopy and transmission electron microscopy. The temperature dependence of dc conductivity for these nanorods is also studied over a temperature range of 500–100 K. On the basis of the temperature dependence of dc conductivity, the conduction mechanism in these nanorods is investigated. The results reveal that the thermally activated process is responsible for the transport of carriers in the temperature range 500–300 K. While the conduction takes place via variable range hopping (VRH) for temperature region 300–100 K. It is therefore, suggested that three-dimensional Motts variable range hopping (3D VRH) is the conduction mechanism responsible for the transport of charge carriers in the temperature region 300–100 K. Various Motts parameters such as density of states, degree of disorder, hopping distance and hopping energy are estimated on the basis of best fitting to our experimental data for Motts 3D VRH model.

Electrical and thermal properties of a-(Se70Te30)100−x(Se98Bi2)x (0⩽x⩽20) alloys

Abstract In electrical properties, the dc conductivity and photoconductivity measurements have been made in vacuum evaporated thin films of a-(Se 70 Te 30 ) 100− x (Se 98 Bi 2 ) x system, in the temperature range (308–355 K). It has been observed that dc conductivity and activation energy depend on the Bi concentration. Photocurrent dependence on incident radiation has also been observed which follow the power law ( I ph ∝ F γ ). Transient photocurrent exhibits the non-exponential decay time. All these parameters show that the recombination within the localized states is predominant. In crystallization kinetics, the heating rate dependence of glass transition and crystallization temperatures is studied to calculate the activation energy for thermal relaxation and activation energy for crystallization. The composition dependence of the activation energy for thermal relaxation and activation energy for crystallization is discussed in terms of the structure of Se–Te–Bi glassy system.

Introduction to Nanomaterials

The applications of nanomaterials have been enormous, which not only encompasses a single discipline but it stretches across the whole spectrum of science right from agricultural science to space technology. New approaches to synthesize nanomaterials in order to design new devices and processes are being developed and the techniques of fabrication of nanomaterials involve analyzing and controlling the matter at atomic scales. This fascinating research field has started a new era of integration of basic research and advanced technology at the atomic scale which has a potential to bring the technological innovations at highest level. The rudimentary capabilities of nanomaterials today are envisioned to evolve in our overlapping generations of nanotechnology products: passive nanostructures, active nanostructures, systems of nanosystems, and molecular nanosystems. This chapter presents the basic introduction to nanomaterials and their popular applications.

Optical band gap and optical constants in a-GaxTe100-x thin films

Abstract The optical band gap and optical constants for a-Ga x Te 100− x thin films have been measured as a function of photon energy. The optical band gap is found to increase with the increase in Ga content in the a-Ga x Te 100− x system. The spectral dependence of optical constants shows that the refractive index ( n ) decreases while the extinction coefficient ( k ) increases with photon energy.