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Chinese Physics B 2016年第5期25卷 380-387页

作者： Ahmed S Jbara zu.kafli othaman M A Saeed Center for Sustainable Nanomaterials Universiti Teknologi Malaysia Physics Department Science College Al-Muthanna University Department of Physics Faculty of Science Universiti Teknologi Malaysia

Based on the Schr ¨odinger equation for envelope function in the effective mass approximation, linear and nonlinear optical absorption coefficients in a multi-subband lens quantum dot are investigated. The effects of quantum dot size on the interband and intraband transitions energy are also analyzed. The finite element method is used to calculate the eigenvalues and eigenfunctions. Strain and In-mole-fraction effects are also studied, and the results reveal that with the decrease of the In-mole fraction, the amplitudes of linear and nonlinear absorption coefficients increase. The present computed results show that the absorption coefficients of transitions between the first excited states are stronger than those of the ground states. In addition, it has been found that the quantum dot size affects the amplitudes and peak positions of linear and nonlinear absorption coefficients while the incident optical intensity strongly affects the nonlinear absorption coefficients.

关键词： linear and nonlinear optical absorption coefficients lens quantum dot finite element method

Growth of Ge/Si(100) Nanostructures by Radio-Frequency Magnetron Sputtering: the Role of Annealing Temperature

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Chinese Physics Letters 2012年第4期29卷 225-228页

作者： ALIREZA Samavati S.K.Ghoshal Z.othaman Ibn Sina Institute for Fundamental Science Studies Universiti Teknologi Malaysia81310 SkudaiJohor BaharuMalaysia Advanced Optical Material Research Group Department of PhysicsFaculty of ScienceUniversiti Teknologi Malaysia81310 UTM SkudaiJohorMalaysia

Surface morphologies of Ge islands deposited on Si(100) substrates are characterized and their optical properties *** are prepared by rf magnetron sputtering in a high-vacuum chamber and are annealed at 600℃,700℃ and 800℃ for 2 min at nitrogen ambient *** force microscopy,field emission scanning electron microscopy,visible photoluminescence (PL) and energy dispersive x-ray spectroscopy are *** results for the annealing temperature-dependent sample morphology and the optical properties are *** density,size and roughness are found to be strongly influenced by the annealing temperature.A red shift of ~0.29 eV in the PL peak is observed with increasing annealing temperature.

关键词： temperature annealing roughness

Morphology and Optical Properties of Self-Assembled In_(0.5)Ga_(0.5)As Quantum Dots with Different Spacer Layer Thickness

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Tsinghua Science and Technology 2010年第5期15卷 534-539页

作者： Didik Aryanto Abd. Khamim Ismail zu.kafli othaman Quantum Structure Research Group Physics Department Faculty of Science Universiti Teknologi Malaysia Ibnu Sina Institute for Fundamental Science Studies Universiti Teknologi Malaysia Physics Department Faculty of Mathematics and Science Education IKIP PGRI Semarang Semarang 50125 Indonesia

Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer and In0.5Ga0.5As QDs were trimethylgallium（TMGa）,trimethylindium（TMIn）,and arsine（AsH3）.The morphology and optical properties of the self-assembled In0.5Ga0.5As QDs were investigated and characterized using atomic force microscopy（AFM） and photoluminescence（PL）.The AFM images revealed that the sizes of the dots on the topmost were not uniformly *** average size of the dots fluctuated as the GaAs spacer layer thickness increased.A room temperature PL measurement was used to establish the quality and quantity of the stacked *** PL peak position remained at 1148 nm for all samples of QDs;however,the PL intensity increased as spacer layer thickness *** structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the *** PL measurement coherently reflected the AFM characterization,in which the strong PL spectra were caused by the uniformity and high density of the *** surface morphology,structure,and optical properties of the stacked QDs are attributed to seed-layer（first layer） formation of dots and spacer layer structures.

关键词： quantum dots(QDs) spacer layer atomic force microscopy(AFM) photoluminescence(PL)

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

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Chinese Physics B 2015年第2期24卷 459-466页

作者： Alireza Samavati Z.othaman S.K.Ghoshal M.K.Mustafa Ibn Sina Institute for Fundamental Science Studies Universiti Teknologi Malaysia Advanced Optical Material Research Group Department of PhysicsFaculty of ScienceUniversiti Teknologi Malaysia Faculty of Science Technology and Human Development Universiti Tun Hussein Onn Malaysia

The influences of thermal annealing on the structural and optical features of radio frequency（rf） magnetron sputtered self-assembled Ge quantum dots（QDs） on Si（100） are *** oriented structures of Ge along the（220） and（111） directions together with peak shift and reduced strain（4.9%to 2.7%） due to post-annealing at 650 ℃ are discerned from x-ray differaction（XRD） *** force microscopy（AFM） images for both pre-annealed and post-annealed（650 ℃） samples reveal pyramidal-shaped QDs（density - 0.26×10^11 cm^-2） and dome-shape morphologies with relatively high density - 0.92×10^11 cm^-2,*** shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain *** annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal *** observed red-shift - 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing,and is related to the effect of quantum ***,the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge *** spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk *** experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes.A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is *** growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.

关键词： Ge QDs sputtering surface morphology optical properties

Spectral features and antibacterial properties of Cu-doped ZnO nanoparticles prepared by sol-gel method

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Chinese Physics B 2016年第7期25卷 459-465页

作者： Alireza Samavati A F Ismail Hadi Nur Z othaman M K Mustafa Centre for Sustainable Nanomaterials Ibnu Sina Institute for Scientific and Industrial ResearchUniversiti Teknologi Malaysia Advanced Membrane Technology Research Centre (AMTEC) Universiti Teknologi Malaysia Faculty of Science Technology and Human Development Universiti Tun Hussein Onn Malaysia

Zn（1-x）Cux O（x=0.00, 0.01, 0.03, and 0.05） nanoparticles are synthesized via the sol-gel technique using gelatin and nitrate precursors. The impact of copper concentration on the structural, optical, and antibacterial properties of these nanoparticles is demonstrated. Powder x-ray diffraction investigations have illustrated the organized Cu doping into ZnO nanoparticles up to Cu concentration of 5%（x = 0.05）. However, the peak corresponding to CuO for x= 0.01 is not distinguishable. The images of field emission scanning electron microscopy demonstrate the existence of a nearly spherical shape with a size in the range of 30–52 nm. Doping Cu creates the Cu–O–Zn on the surface and results in a decrease in the crystallite size. Photoluminescence and absorption spectra display that doping Cu causes an increment in the energy band gap. The antibacterial activities of the nanoparticles are examined against Escherichia coli（Gram negative bacteria）cultures using optical density at 600 nm and a comparison of the size of inhibition zone diameter. It is found that both pure and doped ZnO nanoparticles indicate appropriate antibacterial activity which rises with Cu doping.

关键词： Cu-doped ZnO nanoparticles photoluminescence antibacterial E.coli

Germanium nanoislands grown by radio frequency magnetron sputtering: Annealing time dependent surface morphology and photoluminescence

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Chinese Physics B 2013年第9期22卷 600-604页

作者： Alireza Samavati Z.othaman S.K.Ghoshal R.J.Amjad Ibn Sina Institute for Fundamental Science Studies Universiti Teknologi Malaysia Advanced Optical Material Research Group Department of PhysicsFaculty of ScienceUniversiti Teknologi Malaysia

Structural and optical properties of ～ 20 nm Ge nanoislands grown on Si（100） by radio frequency （rI） magnetron sputtering under varying annealing conditions are reported. Rapid thermal annealing at a temperature of 600 ℃ for 30 s, 90 s, and 120 s are performed to examine the influence of annealing time on the surface morphology and photoluminescence properties. X-ray diffraction spectra reveal prominent Ge and GeO2 peaks highly sensitive to the annealing time. Atomic force microscope micrographs of the as-grown sample show pyramidal nanoislands with relatively high-density （～ 10^11 cm^-2）. The nanoislands become dome-shaped upon annealing through a coarsening process mediated by Oswald ripening. The room temperature photoluminescence peaks for both as-grown （～ 3.29 eV） and annealed （～ 3.19 eV） samples consist of high intensity and broad emission, attributed to the effect of quantum confinement. The red shift （～ 0.10 eV） of the emission peak is attributed to the change in the size of the Ge nanoislands caused by annealing. Our easy fabrication method may contribute to the development of Ge nanostructure-based optoelectronics.

关键词： germanium nanoislands radio frequency magnetron sputtering photoluminescence surface mor-phology

Effects of Mg substitution on the structural and magnetic properties of Co0.5Ni（0.5-x）MgxFe2O4 nanoparticle ferrites

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Chinese Physics B 2016年第4期25卷 358-364页

作者： R M Rosnan Z othaman R Hussin Ali A Ati Alireza Samavati Shadab Dabagh samad Zare Centre for Sustainable Nanomaterials Ibnu Sina Institute for Scientific and Industrial Research Universiti Teknologi Malaysia 81310 Skudai Johor Bahru Malaysia

In this study, nanocrystalline Co-Ni-Mg ferrite powders with composition Coo.5Nio.5-xMgxFe2O4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co-Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction （XRD） analysis, Fourier transform infrared spectroscopy （FTIR）, field emission scanning electron microscopy （FESEM）, and vibrating sample magnetometry （VSM）. The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of - 32 nm to - 36 nm. The lat- tice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2- substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from - 57.35 emu/g to - 61.49 emu/g and - 603.26 Oe to 684.11 Oe （l Oe = 79.5775 A.m-l）, respectively. The higher values of magnetization Ms and Mr suggest that the opti- mum composition is Co0.5Ni0.4Mg0.1Fe204 that can be applied to high-density recording media and microwave devices.

关键词： co-precipitation magnetic materials spinel ferrite magnetic properties

Structural and Optical Behavior of Germanium Quantum Dots

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Chinese Physics Letters 2012年第11期29卷 202-206页

作者： ALIREZA Samavati Z.othaman S.K.Ghoshal M.R.Dousti R.J.Amjad Ibn Sina Institute for Fundamental Science Studies Universiti Teknologi Malaysia81310 SkudaiJohorMalaysia Advanced Optical Material Research Group Department of PhysicsFaculty of ScienceUniversiti Teknologi Malaysia81310 UTM SkudaiJohorMalaysia

Controlled growth,synthesis,and characterization of a high density and large-scale Ge nanostructure by an easy fabrication method are key issues for optoelectronic *** quantum dots(QDs)having a density of~1011 cm^(-2) and a size as small as~8 nm are grown by radio frequency magnetron sputtering on Si(100)substrates under different heat *** annealing temperature dependent structural and optical properties are measured using AFM,XRD,FESEM,EDX,photoluminescence(PL)and Raman *** effect of annealing is found to coarsen the Ge QDs from pyramidal to dome-shaped structures as they grow larger and transform the nanoislands into relatively stable and steady state ***,the annealing allows the intermixing of Si into the Ge QDs and thereby reduces the strain energy that enhances the formation of larger *** room temperature PL spectra exhibits two strong peaks at~2.87 eV and~3.21 eV attributed to the interaction between Ge,GeO_(x) and the possibility of the presence of QDs core-shell *** reports so far exist on the red shift~0.05 eV of the strongest PL peak that results from the effect of quantum ***,the Raman spectra for the pre-annealed QDs that consist of three peaks at around~305.25 cm^(-1),409.19 cm^(-1) and 515.25 cm^(-1) are attributed to Ge-Ge,Ge-Si,and Si-Si vibration modes,*** Ge-Ge optical phonon frequency shift(~3.27 cm^(-1))associated with the annealed samples is assigned to the variation of shape,size distribution,and Ge composition in different *** variation in the annealing dependent surface roughness and the number density is found to be in the range of~0.83 to~2.24 nm and~4.41 to~2.14×10^(11)cm^(-2),respectively.

关键词： spectroscopy annealing annealed

Optical behavior of self-assembled high-density Ge nanoislands embedded in SiO_2

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Chinese Optics Letters 2013年第11期11卷 91-95页

作者： Alireza Samavati zu.kafli othaman Sib Krishna Ghoshal Samad Zare Ibn Sina Institute for Fundamental Science Studies Universiti Teknologi Malaysia Advanced Optical Material Research Group Department of PhysicsFaculty of ScienceUniversiti Teknologi Malaysia

The radio frequency magnetron sputtering method is used to prepare well-dispersed pyramidal-shaped Ge nanoislands embedded in amorphous SiO2 sublayers of various thicknesses. The estimated size and number density of Ge nanoislands in SiO2 sublayer thicknesses beyond 30 nm are approximately 15 nm and 1011 cm-2, respectively. Atomic force microscopy （AFM） reveals root mean square （RMS） roughness sensitivity as the SiO2 sublayer thickness varies from 30 to 40 nm. The formation of nanoislands with high aspect ratios is attributed to the higher rate of surface reactions between Ge adatoms and nucleated Ge islands than reactions associated with SiO2 and Ge. The Ge nanoisland polyorientation on SiO2 （50-nm thickness） is revealed by X-ray diffraction （XRD） patterns. Photoluminescence （PL） peaks of 2.9 and 1.65 eV observed at room temperature （RT） are attributed to the radiative recombination of electrons and holes from the Ge nanoislands/SiO2 and Si02/Si interfaces, respectively. The mean island sizes are determined by fitting the experimental Raman profile to two models, namely, the phonon confinement model and the size distribution combined with phonon confinement model. The latter model yields the best fit to the experimental data. We confirm that SiO2 matrix thickness variations play a significant role in the formation of Ge nanoislands mediated via the minimization of interfacial and strain energies. OCIS codes： 250.5230, 170.5660.

关键词： Ge SiO high