K. Samanta

Structural and optical properties of nanocrystalline Zn1−xMnxO

The multi phonon Raman scattering in Mn doped (1%–10%) ZnO was observed at room temperature using 514.5nm Ar+ laser. The additional optical modes at 327, 332, 482, 532, and 680cm−1 in Zn1−xMnxO targets were identified as the second order Raman modes in the disordered lattice and the precipitation of the secondary phase ZnMn2O4. The crystalline grain sizes of 1%, 3%, 5%, and 10% Mn doped ZnO samples were calculated by phonon confinement model as 31.8, 18.3, 15.9, and 14.1nm, respectively. The optical band gap was found to be increased (3.27–3.41eV) due to the Mn doping.

Optical properties of Zn1−xCoxO thin films grown on Al2O3 (0001) substrates

Thin films of Zn1−xCoxO (x=1–15%) were grown on an Al2O3 (0001) substrate by pulsed laser deposition and characterized by investigating their photoluminescence (PL) and other optical properties. The films were highly (0001) oriented without any impurity phases as observed in x-ray diffraction. The optical transmittance spectra showed that the band edge of Zn1−xCoxO was decreased with increase of Co concentration along with a subbandgap absorption in the range of 1.8to2.2eV. The near band-edge PL spectrum of ZnO thin films at 77K showed a strong peak of donor bound exciton at 3.307eV along with the free excitons. However, the PL spectra for free excitons of the Zn1−xCoxO films at 77K did not show any significant redshift due to Co incorporation.

Raman scattering studies of p-type Sb-doped ZnO thin films

Antimony doped p-type ZnO films were grown on Al2O3 (0001) substrate by pulsed laser deposition. The structural properties of Zn1−xSbxO (3% and 5%) thin films were investigated by Raman scattering studies. The softening of local lattice due to the formation of (SbZn−2VZn) acceptor complexes was detected as the shift in E2high mode toward lower frequency side in ZnSbO thin films. Additional optical modes observed at 277, 333, 483, and 534 cm−1 are due to the breaking of translational symmetry in w-ZnO by Sb doping. The Zn–Sb related local vibrational mode was detected around 237 cm−1 in 5% Sb doped ZnO thin film. Room temperature Hall measurements exhibited low resistivity of 0.017 Ω cm, high hole concentration of 6.25×1018 cm−3, and mobility of 57.44 cm2/V s in the 5% Sb-doped ZnO thin film.Antimony doped p-type ZnO films were grown on Al2O3 (0001) substrate by pulsed laser deposition. The structural properties of Zn1−xSbxO (3% and 5%) thin films were investigated by Raman scattering studies. The softening of local lattice due to the formation of (SbZn−2VZn) acceptor complexes was detected as the shift in E2high mode toward lower frequency side in ZnSbO thin films. Additional optical modes observed at 277, 333, 483, and 534 cm−1 are due to the breaking of translational symmetry in w-ZnO by Sb doping. The Zn–Sb related local vibrational mode was detected around 237 cm−1 in 5% Sb doped ZnO thin film. Room temperature Hall measurements exhibited low resistivity of 0.017 Ω cm, high hole concentration of 6.25×1018 cm−3, and mobility of 57.44 cm2/V s in the 5% Sb-doped ZnO thin film.

Structural and magnetic properties of (In1−xFex)2O3 (0.0⩽x⩽0.25) system: Prepared by gel combustion method

(In1-xFex)2O3 polycrystalline samples with x = (0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of X raydiffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy (HRTEM) imaging, and indexing of the selected-area electron diffraction (SAED) patterns, X-ray Absorption Spectroscopy (XAS) and Raman Spectroscopy. DC Magnetization studies as a function of temperature and field indicatethat they are ferromagnetic with Curie temperature (TC) well above room temperature.

Microstructural and ferromagnetic properties of Zn1−xCuxO thin films

Room temperature ferromagnetism is observed in Zn1−xCuxO (x=0.01, 0.03, and 0.05) thin films grown on Al2O3 substrates by pulsed laser deposition technique. Raman scattering and high resolution transmission electron microscopy analyses confirm the substitution of Cu up to 3% in ZnO host lattice, and the films are nearly single crystalline. Optical transmission and photoluminescence (PL) analyses provide evidence of sp-d exchange interaction in Zn1−xCuxO thin films; the p-d exchange interaction may explain the observed room temperature ferromagnetism in Zn1−xCuxO thin films. Room temperature PL shows the green emission (∼2.60 eV) in Cu doped ZnO samples.

Self-Assembled ZnO Nanostructure for Field-Emission Devices

Zinc oxide (ZnO) nanorods on Au patterned Si substrates were fabricated using vapor transport method. The XRD pattern showed the ZnO nanorods were highly c-axis oriented similar to ZnO thin films. The photoluminescence spectrum at 77 K of ZnO nanorods was consisting of the fundamental near band edge emission of ZnO in the UV region along with a broad defect induced emission around green band. The field emission properties of the nanorods showed a current density of 1mA/cm2 at an applied field of 10V/m, which is comparable to other reported values of ZnO nanorods. The patterned gold island formed by self-assembly of polystyrene ball on Si substrate acted as a catalyst in the growth of nanorods as well as stable ohmic contact for field emission.

Structural and optical properties of Zn 1−x Co x O and ZnCo 2 O 4 thin films

Thin films of Co substituted ZnO and ZnCo 2 O 4 were deposited on c-axis (0001) oriented Al 2 O 3 substrates using pulsed laser deposition. The XRD results showed all the films were highly (002) oriented with a less intense peak of (311) for ZnCo 2 O 4 thin film. Micro-Raman spectra of ceramic targets showed the modes related to wurtzite ZnO and spinel ZnCo 2 O 4 structures. In thin films of Zn 1−x Co x O no modes corresponding to ZnCo 2 O 4 were detected. The intensity of E 1 (LO) and multiphonon peak at 584 and 540 cm −1 respectively, increased with increase in Co substitution. The optical absorption of the films showed that the band gap decreased with increase of Co concentrations at room temperature along with the sub-bandgap absorptions due to d-d transitions of Co 2+ . Similar sub-bandgap d-d transition was also observed in the absorption spectra ZnCo2O4 thin films. The highest saturated magnetization (0.2μ B /Co) was obtained for 5%Co substituted ZnO.