ZnO nanoparticles (NPs) were extracted from a commercial paste in both colloidal and precipitate forms. The Zetasizer analysis performed on the colloid showed ZnO NPs ranging from ∼30 nm to ∼100 nm. Thin films of ZnO were deposited on glass substrates by spin-coating technique from a mixture of the extracted colloid and precipitate. The scanning electron microscope (SEM) images showed uniformly arranged, mesoporous, and nanostructured ZnO particles of different shapes, with an estimated film thickness of 0.67 μm. Analysis by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analysis (XRD) confirmed the presence of ZnO in the films, with no impurities or remnants of other materials. The XRD analysis showed a polycrystalline nature of the films and identified a pure phase formation of the hexagonal wurtzite structure. The average crystallite size calculated from the diffraction peaks is ∼43.25 nm. The calculated crystal tensile strain is 1.954 × 10−3, which increases the crystal volume by 0.728% compared with the crystal volume of standard ZnO. The calculated crystal parameters are a = b = 3.258 Å and c = 5.217 Å. The calculated dislocation density (d) and bond length Zn–O (L) are 5.35 × 10−4 nm−2 and 2.695 Å, respectively. Ultraviolet-visible absorption spectra showed an optical band gap of ∼3.80 eV.
An aluminum-germanium eutectic bonding technology has been used to uniformly bond two silicon wafers for MEMS packaging at temperatures as low as 450 o C, well below the aluminum-silicon eutectic temperature (577 o C). A device silicon wafer has been put in contact with a cap wafer where an aluminum film covered by a germanium film has been thermally evaporated. The annealing has been performed in a vacuum furnace under uniaxial pressure variable from 1.8 up to 30 kbar. The samples have been analyzed with various analytical techniques. 4 He + MeV Rutherford Backscattering Spectrometry (RBS) has been used to measure the thicknesses of the deposited films and to follow the aluminum-germanium intermixing, Scanning Acoustic Microscope (SAM) to control the uniformity of the bonding, Scanning Electron Microscope (SEM) associated with electron induced X-ray fluorescence to analyze composition, morphology and elements distribution in the film between the two bonded wafers. The temperatures for the annealing were selected above and below the Ge-Al the eutectic temperature. At temperatures below the eutectic no-bonding has been obtained for any applied pressure. Above the eutectic bonding occurs. The formation of a liquid film is mandatory to obtain a reproducible and robust bonding. The pressure is necessary to improve the contacts between the two wafers; its role in the metallurgy of the bonding needs to be explored.
ZnO thin films were deposited on ITO/glass substrates by pulsed laser deposition (PLD) using two different kinds of targets. One of the targets was made of pure ZnO powder and the other one consisted of a mixture of ZnO powder with cyanoacrylate glue. The structural and morphological properties of the films obtained using both targets were compared, in order to determine which one produces samples with properties more suitable for their use as buffer and antireflective layer in CdTe-based solar cells, also different heterostructures were deposited to study the optical properties of the obtained thin films and their utility in the applications mentioned before. The films deposited with the mixture powder target were polycrystalline with preferential orientations in the planes (100) and (101) with a high transmittance in the range of 70-90% in the 540-850 nm wavelength region and showed a high resistivity of ∼1.30×10 2 cm −1 , such properties are considered to be appropriate for thin films that are wanted to be used as a buffer and antireflective layer in CdTe solar cells.
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