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Undoped SnO2−x thin films with amorphous phase were prepared at room temperature by radio frequency magnetron sputtering, and the changes in electrical, optical and structural properties were investigated upon annealing in atmosphere. The amorphous SnO2−x film had the minimum resistivity of 1.5 × 10− 3 Ω cm and the highest Hall mobility of 22 cm2/V s, which were comparable to those observed in polycrystalline doped SnO2 films. Examination of the temperature dependent Hall mobility revealed the grain boundary scattering as the dominant scattering mechanism for the crystallized SnO2−x films. Analysis made by using four coefficients instrument showed that undoped SnO2−x films had the characteristics of degenerate semiconductor with non-parabolic band structure, and that ionized impurity scattering with free electron screening was dominant mobility limiting mechanism in amorphous SnO2−x films.

In this study, indium–zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In 2 O 3 –12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In 2 O 3 -oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10 − 4 Ω cm, and the highest mobility value amounting to 47 cm 2 /V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.

Nano-composite films, consisting of GaAs quantum dots embedded in SiO2 glass matrix, were fabricated and analyzed in terms of their structural, chemical, and optical properties. In order to fabricate uniformly dispersed GaAs quantum dots in the SiO2 matrix, composite films consisting of alternate layers of GaAs and SiO2 were deposited in the manner of a superlattice by radio frequency magnetron sputter deposition. In order to control the size of GaAs quantum dots the thickness of GaAs in individual layers was varied at a fixed GaAs total volume fraction. Transmission electron microscopy and X-ray photoelectron spectroscopy analyses revealed that GaAs quantum dots were in crystalline phase and in the form of a Ga–As compound. From optical absorbance measurements, absorption edges at visible wavelength band were determined and compared among composite films of varying GaAs nominal thickness. The amount of blue shift of the absorption edge increased with decreasing GaAs nominal thickness, i.e. quantum dots size. Band gaps of the composite films determined from Tauc plots and photoluminescence measurements exhibited a linear decrease with increasing GaAs nominal thickness. Large values of third-order non-linear optical susceptibility χ(3) (∼ 7.6 × 10− 14 m2/V2 at 488 nm), which were believed to originate due to the state filling effect, were observed.

Amorphous Zn–Sn–O (ZTO) thin films with relative Zn contents (= [at.% Zn]/([at.% Zn] + [at.% Sn])) of 0, 0.08 and 0.27 were fabricated by co-sputtering of SnO2 and ZnO targets at room temperature. Changes in structural, electrical and optical properties together with electron transport properties were examined upon post-annealing treatment in the temperature range from 200 to 600 °C in vacuum and in air. Characterization by XRD showed that an amorphous ZTO thin film crystallized at higher temperatures with increasing Zn content. Crystallized ZTO films with a relative Zn content of 0.27 might not contain a single SnO2 phase which is observed in the films of the other compositions. Amorphous ZTO films showed decreasing electrical resistivities with increasing annealing temperature, having a minimum value of 1 × 10− 3 Ω cm. Upon crystallization, the resistivities increased drastically, which was attributed to poor crystallinity of the crystallized films. All the ZTO films were found to be degenerate semiconductors with non-parabolic conduction bands having effective masses varying from 0.15 to 0.3 in the carrier concentration range of 6 × 1018 to 2 × 1020 cm− 3. As for a ZTO film with a relative Zn content of 0.27, the degree of non-parabolicity was much lower compared with films of the other compositions, leading to a relatively stable mobility over a wide range of carrier concentration.

Au/SiO2 nanocomposite films in which Au nanoparticles were embedded in SiO2 matrix were fabricated via alternating sputtering of SiO2 and Au layers. In particular, we kept the nominal thickness of the Au layers below the threshold for the continuous layer formation whereas that of SiO2 layers was sufficient to form continuous layers. Transmission electron microscopy (TEM) images revealed that the Au nanoparticles were spherical in shape and that their average size was linearly proportional to the nominal thickness of Au layers. To account for the absorption variation of the composite films, including the absorption peak around 530 nm due to the surface plasmon resonance (SPR), we used Maxwell–Garnett effective medium theory (EMT) together with the modified Drude model. As it turned out, the combination of the modified Maxwell–Garnett effective medium theory and the aforementioned modification of the Drude model, which took the size of Au nanoparticles into consideration, were sufficient to model the variable–angle spectroscopic ellipsometry spectra. The values of the fitting parameters, such as film thickness, volume fraction of Au, and the diameter of Au nanoparticles, extracted from the modeling procedure were in good agreement with the results of TEM and spectrophotometer measurements.

A study was made to examine the electromagnetic interference (EMI) shielding effect of multilayered thin films in which indium–zinc oxide (IZO) thin films and Ag or Ag alloy thin films were deposited alternately at room temperature using a RF magnetron sputtering. The optical, electrical and morphological properties of the constituent layers were analyzed using an ultraviolet-visible photospectrometer, a 4-point probe and an atomic force microscopy (AFM), respectively. The EMI shielding effect of the multilayered thin films was also measured using a coaxial transmission line method. A detailed analysis showed that the control of the film morphologies, i.e., the surface roughnesses of the constituent metal layers was essential to an accurate estimate of the electrical and optical properties of multilayered coatings. It was shown that properly designed IZO/Ag alloy multilayered thin films could yield a visible transmission of more than 70%, a sheet resistance of less than 1 Ω/sq., together with an EMI shielding effect larger than 45 dB in the range from 30 to 1000 MHz.

Volmer–Weber type island growth mode was adopted to form nano-sized metal particles embedded in a dielectric matrix by the alternate deposition of metal and dielectric layers. Particle size and volume fraction were controlled by changing the nominal thickness of the metal layer and its ratio to that of dielectric layer, respectively. For comparison, the Au cluster formation was investigated in detail in both co-sputtered and alternatively sputtered films. Plan-view and cross-sectional transmission electron microscopy experiments combined with the optical absorption near the surface plasmon band show that well-defined Au metal spheres can be obtained by alternating sputtering, while closely spaced small particles, some connected and losing their sphericity even in the small volume fraction, are formed in the co-sputtered films. Their size was controlled by the volume fraction. The optical constants of the alternatively sputtered composite films were determined from spectroscopic ellipsometry measurements through the Maxwell–Garnett effective medium model fitting, considering the size dependent mean free path limitation of the free electrons. There was good agreement between simulated and measured optical spectra for the as-grown films.

Composite films of Au and dielectric material (TiO2 and/or mixed ZnS–SiO2) with a wide range of Au fractions were fabricated through a co-sputtering method utilizing a multi-target sputtering system. The optical absorption spectra of these composite films demonstrated an absorption peak due to surface plasmon resonance of embedded Au nanoclusters. It was found that, depending on the dielectric matrix, Au concentration, and post-deposition annealing, the wavelength of the surface plasmon resonance of nanoclusters shifted by 130 nm: from 550 to 680 nm. The third-order non-linear susceptibility χ(3) of these composite films, which also originates from field enhancement due to the surface plasmon resonance, demonstrated a corresponding variation.