Dr. A.N.Mallika - Academia.edu (original) (raw)

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Papers by Dr. A.N.Mallika

In this paper, a simple and cheap method to prepare porous ZnO by using zinc nitrate, ethanol and... more In this paper, a simple and cheap method to prepare porous ZnO by using zinc nitrate, ethanol and triethanolamine (TEA) is reported. The as-prepared sample consisted of nano and micro pores. The sample was calcined at 300 ℃, 400 ℃ and 500 ℃ with different heating rates. At 500 ℃, the nano pores disappeared but the sample maintained its micro porosity. Field emission scanning electron microscopy (FE-SEM) pictures confirmed that the size and growth of ZnO nanoparticles depended on the heating conditions. The infrared (IR) absorption peak of Zn-O stretching vibration positioned at 457 cm 1 was split into two peaks centered at 518 cm 1 and 682 cm 1 with the change of morphology. These results confirmed that Fourier transform infrared (FT-IR) spectrum was sensitive to variations in particle size, shape and morphology. The photoluminescence (PL) spectrum of porous ZnO contained five emission peaks at 397 nm, 437 nm, 466 nm, 492 nm and 527 nm. Emission intensity enhanced monotonously with increase of temperature and the change was rapid between temperatures of 300 ℃ and 500 ℃. This was due to the elimination of organic species and improvement in the crystallanity of the sample at 500 ℃.

Journal of Alloys and Compounds, 2008

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Journal of Materials Science: Materials in Electronics, 2016

Materials Science in Semiconductor Processing, 2014

The effect of annealing temperature on photoluminescence (PL) of ZnO-SiO 2 nanocomposite was inve... more The effect of annealing temperature on photoluminescence (PL) of ZnO-SiO 2 nanocomposite was investigated. The ZnO-SiO 2 nanocomposite was annealed at different temperatures from 600 1C to 1000 1C with a step of 100 1C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5 nm are capped with amorphous SiO 2 matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800 1C and dumbbell morphology above 800 1C. The absorption spectrum of ZnO-SiO 2 nanocomposite suffers a blue-shift from 369 nm to 365 nm with increase of temperature from 800 1C to 1000 1C. The PL spectrum of ZnO-SiO 2 nanocomposite exhibited an UV emission positioned at 396 nm. The UV emission intensity increased as the temperature increased from 600 1C to 700 1C and then decreased for samples annealed at and above 800 1 C. The XRD results showed that formation of willemite phase starts at 800 1C and pure willemite phase formed at 1000 1C. The decrease of the intensity of 396 nm emission peak at 900 1C and 1000 1C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into SiO 2 at these temperatures. At 1000 1C, an emission peak at 388 nm is observed in addition to UV emission of ZnO at 396 nm and is believed to be originated from the willemite.

Materials Letters, 2013

In this study, the effects of annealing temperature on photoluminescence (PL) of ZnO nanoparticle... more In this study, the effects of annealing temperature on photoluminescence (PL) of ZnO nanoparticles were studied. ZnO was annealed at various temperatures between 600 and 900 1C. The X-ray diffraction (XRD) results demonstrated that grain size increased with increase of annealing temperature. As the annealing temperature increased from 600 to 800 1C, the intensities of both UV peak and that of green luminescence (GL) enhanced monotonously but reduced at 900 1C. The enhancement in the UV peak intensity is attributed to the decrease of grain boundaries and surface states; whereas, the remarkable improvement in the GL is assigned to the out-diffusion of oxygen from the sample up to 800 1C. It supports that GL is induced by the singly ionized oxygen vacancies. These oxygen vacancies are saturated due to the finiteness of the defects at 800 1C. So, it is speculated that the deterioration of GL intensity at 900 1C is due to the evaporation of Zn which is predominant at temperatures higher than 850 1C.

Physics of Semiconductor Devices, 2014

This paper reports on the structural and optical properties of Al with different doping concentra... more This paper reports on the structural and optical properties of Al with different doping concentrations on ZnO nanoparticles prepared through Sol–Gel method. The XRD results revealed the wurtzite structure of ZnO without any secondary phase related to Al. The absorption spectrum of the sample exhibited an absorption in UV region and the Photoluminescence properties of Al doped ZnO were studied.

Ceramics International, 2014

This paper reports on the structural and optical properties of Al doped ZnO nanoparticles prepare... more This paper reports on the structural and optical properties of Al doped ZnO nanoparticles prepared through solgel method. Different atomic ratio percents of Al were doped into ZnO ranging from 1 at.% to 6 at.%. X-ray diffraction (XRD) results showed that ZnO crystallized into hexagonal wurtzite structure. The average crystallite size of ZnO nanoparticles decreased with increasing Al concentration. A compressive strain induced in ZnO upon Al doping was calculated using W-H plot analysis. The morphology of the samples is studied by using Field Emission Scanning Electron Microscope (FE-SEM). The Tauc relationship has been employed for calculating the band gap energy of Al doped ZnO samples based on UV-Vis data of the samples. The band gap increased monotonously as the Al concentration was increased from 1 at.% to 6 at.%. In addition to this, the photoluminescence (PL) properties of Al doped ZnO were studied.

International Conference on Advanced Nanomaterials & Emerging Engineering Technologies, 2013

ABSTRACT This paper reports on the structural and optical properties of Mg doped ZnO nanoparticle... more ABSTRACT This paper reports on the structural and optical properties of Mg doped ZnO nanoparticles through sol-gel method using polyvinyl alcohol as chelating agent. For studying the effect of Mg doping on particle size and morphology, the prepared samples were characterized by using X-ray diffractometer, and Field Emission Scanning Electron Microscope (FE-SEM). The optical properties of the samples were investigated by UV-Vis spectroscopy (UV-Vis), and Fourier Transform Infrared Spectroscopy (FTIR). The particles size was evaluated using Scherrer's formula from XRD patterns. It was observed from XRD studies that the particles size decreased with increasing Mg concentrations. It is observed from FE-SEM microstructure that the grain size of the samples decreased with increasing Mg doping. The samples exhibited a blue shift in absorption in UV spectra indicating good optical properties.