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RISS 인기검색어
- 검색키워드
- 저자 : Aljawfi, Rezq Naji (검색결과 4 건)
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Aljawfi, Rezq Naji,Kumari, Kavita,Vij, Ankush,Hashim, Mohd.,Chae, K. H.,Alvi, P. A.,Kumar, Shalendra Springer-Verlag 2018 Journal of materials science Materials in electron Vol.29 No.7
<P>In this study, Ti0.95Mn0.05O2-delta nanostructured thin films were fabricated by pulsed laser deposition technique followed by rapid thermal annealing (RTA) in pure O-2 and N-2 atmospheres. The RTA process induced a substantial change in the surfaces morphology and local atomic structure around Ti4+ cation that have been studied by means of atomic force microscopy, Raman scattering and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Raman spectra of the films were resembled to that of TiO2 rutile phase, and the change in the width of E-g (434 cm(-1)) Raman active modes has been attributed to oxygen non-stoichiometry. NEXAFS spectra were carried out in synchrotron facility at Ti/Mn L (3,2) edges and O-K edge. The ligand-field splitting, estimated from the energy difference between t(2g) and e(g) features in O K-edge spectra were similar to 2.81 eV for pristine and annealed film, which is a characteristic of the TiO2 rutile structure, and the asymmetry of t(2g) and e(g) bands at the O-K edge has been ascribed to oxygen vacancy (Vo(2+)). The annealing of film in O-2 gas optimized the surface structure and healed the Vo(2+) bridging, while the RTA in N-2 gas introduced Vo and reduced the valence state of Ti4+ (TiO2) into Ti3+ (Ti2O3) that have been probed by comparing the NEXAFS spectra of N-2 annealed film with the reference spectra of Ti2O3. Experimental and atomic multiplet calculations revealed that the Mn ions exist in 2+ valence state.</P>
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Aljawfi, Rezq Naji,Vij, Ankush,Chae, K.H,Dalela, S.,Alvi, P.A.,AL-Maghrabi, M.A.,Kumar, Shalendra Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.445 No.-
<P><B>Abstract</B></P> <P>In this report, nanostructure thin films of Ti<SUB>0.97</SUB> Mn<SUB>0.03</SUB> O<SUB>2−δ</SUB> were deposited on Si (001) substrate by pulsed laser deposition (PLD) technique, followed by rapid thermal annealing (RTA) in different ambient gases; O<SUB>2</SUB>, N<SUB>2</SUB> and Ar. The RTA treatment dramatically affected the surface defects, local environment, electronic structure and magnetic properties of the films, where, annealing of the film in O<SUB>2</SUB> gas recovered the dislocated atoms of oxygen vacancy (Vo) at the surfaces and induced a diamagnetic phase, whereas the annealing of film in N<SUB>2</SUB> gas introduced Vo, reduced the valence state of Ti<SUP>4+</SUP> (TiO<SUB>2</SUB>) into Ti<SUP>3+</SUP> (Ti<SUB>2</SUB>O<SUB>3</SUB>) and induced ferromagnetic (FM) signal. Therefore, the change in the local atomic defects of Vo at the surface texture is likely to be responsible for the magnetic response. The presence of oxygen vacancy has been traced by means of Raman scattering and near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. The NEXAFS spectra were carried out in synchrotron facility at Ti/Mn <I>L</I> <SUB>3,2</SUB> and O-<I>K</I> edges. The spectral feature at Ti <I>L</I> <SUB>3,2</SUB> edges revealed the rutile phase of TiO<SUB>2</SUB>. The asymmetry of <I>t</I> <SUB>2</SUB> <I> <SUB>g</SUB> </I> and <I>e<SUB>g</SUB> </I> bands at the O-<I>K</I> edge confirmed the formation of Vo and reflected the modification in the O co-ordination around Ti<SUP>4+</SUP>cations. The Mn <I>L</I> <SUB>3,2</SUB> edges revealed the incorporation of Mn ions in the TiO<SUB>2</SUB> network with Mn<SUP>2+</SUP> and Mn<SUP>3+</SUP> mixed valence states. This different valance states (Mn<SUP>2+</SUP> and Mn<SUP>3+</SUP>) is the basis for the ferromagnetism induced by Stoner spin-splitting of the local density of defects state at Fermi level (E<SUB>F</SUB>). The change in the magnetic moment of the films after RTA process is related to the change in the local density of defects band. Crystal field and charge transfer parameters were extracted roughly by using atomic multiplet calculations (theory).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ti<SUB>0.93</SUB>Mn<SUB>0.03</SUB>O<SUB>2</SUB> thin films were deposited on Si substrate (001) by PLD technique. </LI> <LI> The films have been treated via rapid thermal annealing (RTA) in Ar, N<SUB>2</SUB> and O<SUB>2</SUB>. </LI> <LI> A significant modification is induced by RTA in different ambient gas. </LI> <LI> RTA in O<SUB>2</SUB> decreases the oxygen vacancy (Vo) and optimizes the crystal structure. </LI> <LI> N<SUB>2</SUB> induces the Vo and reduces the valance state of TiO<SUB>2</SUB> (Ti<SUP>4+</SUP>) to be Ti<SUB>2</SUB>O<SUB>3</SUB> (Ti<SUP>3+</SUP>). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Sharma, Mayuri,Naji Aljawfi, Rezq,Kumari, Kavita,Chae, K.H.,Dalela, S.,Gautam, S.,Alvi, P.A.,Kumar, Shalendra Elsevier 2019 Journal of electron spectroscopy and related pheno Vol.232 No.-
<P><B>Abstract</B></P> <P>We have investigated the ferromagnetic behavior, electronic states and local geometrical structure of Ni (2 and 10 at %) doped SnO<SUB>2</SUB> thin films. The films were successfully fabricated with the help of pulsed laser deposition (PLD) technique on Si (100) substrate under ultrahigh vacuum (UHV) condition. X-ray diffraction (XRD) results revealed the single phase character of SnO<SUB>2</SUB> rutile lattice structure with P4<SUB>2</SUB>/mnm space group. The inclusion of Ni ions into SnO<SUB>2</SUB> matrix induced oxygen vacancy (Vo), enhanced the distortion in octahedral local symmetry and reduced the oxidation state of the host Sn<SUP>4+</SUP> (SnO<SUB>2</SUB>) to Sn<SUP>3+</SUP> (Sn<SUB>2</SUB>O<SUB>3</SUB>), these details have been estimated by Raman scattering, Near edge X-ray absorption fine structure (NEXAFS) spectra at Ni L<SUB>3,2</SUB> and O K edges. Further quantitative details on the local geometrical structure around Ni ions were obtained via fitting the experimental Fourier transforms EXAFS spectra |X(R)| with FEFF6 code. The magnetization measurements performed at room temperature (RT) infers that Ni doped SnO<SUB>2</SUB> films displayed ferromagnetic (FM) signal, and there was no significant difference in the saturation moments even with increase in the Ni content. Hence, the similarity in the observed magnetic behavior of the films seems relevant to the same crystal growth condition (UHV) and might not be limited directly to the Ni dopant concentrations. The FM signal and the role of surface defects have been discussed in the light of spin-split impurity band percolation mechanism.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ni doped SnO<SUB>2</SUB> thin films were deposited on Si substrate (001) by PLD technique. </LI> <LI> NEXAFS at Ni L<SUB>3,2</SUB> edges confirmed that the Ni ions exist in high spin divalent ground state. </LI> <LI> The UHV assisted growth condition created a favorable condition for oxygen non-stoichiometry. </LI> <LI> A significant modification have be observed in the surface morphology. </LI> <LI> Magnetic behavior seems to be more relevant to the formation of VO<SUP>2+</SUP> at the surfaces. </LI> </UL> </P>
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