G.Q. Yu

Preparation and characterization of copper oxide thin films deposited by filtered cathodic vacuum arc

Copper oxide thin films deposited on Si (100) by a filtered cathodic vacuum arc with and without substrate bias have been studied by atomic force microscopy, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results show that the substrate bias significantly affects the surface morphology, crystalline phases and texture. In the film deposited without bias, two phases—cupric oxide (CuO) and cuprous oxide (Cu2O)—coexist as cross-evidenced by XRD, XPS and Raman analyses, whereas CuO is dominant concurrent with CuO (020) texture in the film deposited with bias. The film deposited with bias exhibits a more uniform and clearer surface morphology although both kinds of films are very smooth. Some explanations are given as well.

Room-temperature deposition of amorphous titanium dioxide thin film with high refractive index by a filtered cathodic vacuum arc technique

Amorphous titanium dioxide (TiO2) thin film has been prepared by a filtered cathodic vacuum arc technique at room temperature. It was concluded from the core level of Ti 2p 3/2 (458.3 eV) and O 1s (529.9 eV) and their deviation in binding energy (deltaBE = 71.6 eV) that only one of Ti oxidation states, Ti4+, existed in the film and the film was of ideal stoichiometry. The film possessed high transmittance, which can reach as high as that of a quartz substrate, especially in the visible range, owing to its optical bandgap of 3.2 eV. The high refractive index (2.56 at 550 nm) and low extinction coefficient (approximately 10(-4) at 550 nm) suggested that the film had a high packing density and a low scattering-center concentration. These good optical properties implied the film prepared by this technique was a promising candidate for optical application. Besides, the film was found to transform in the structure from amorphous to anatase crystalline when it was annealed at 300 degrees C, as evidenced by Raman and x-ray diffraction.

Study of the structure and optical properties of nanocrystalline zirconium oxide thin films deposited at low temperatures

Zirconium oxide thin films are deposited at low temperatures (lower than 350?C) using a filtered cathodic vacuum arc. Film structure, surface morphology and optical properties are systematically investigated. The results show the dependence of the properties on substrate temperature. Film structure develops from amorphous to polycrystalline at 150?C. Further increasing the temperature to 230?C leads to the preferred orientation along [?111] and [?221] directions, and at 330?C along only one observed preferred [?111] direction. In addition, crystal size in all the crystallized films is within 15?nm. The increase of substrate temperature results in an increase of surface roughness from room temperature to 230?C, but to a slight decrease at 330?C. The variations in optical properties, such as optical constants and Eg, with substrate temperature are correlated to the changes in film microstructure.

Structural properties and nanoindentation of AlN films by a filtered cathodic vacuum arc at low temperature

Aluminium nitride (AlN) films have been fabricated on Si(100) substrates by an ion-beam-assisted filtered cathodic vacuum arc technique at low temperature. The structural and mechanical properties of the AlN films have been investigated using x-ray photoelectron spectroscopy, by means of an x-ray diffractometer, visible Raman spectroscopy, atomic force microscopy and nanoindentation. The AlN films exhibit a predominant a-axis orientation with hardness as high as 14.5 GPa, which may be suitable for surface acoustic wave devices.

Intrinsic mechanical properties of diamond-like carbon thin films deposited by filtered cathodic vacuum arc

The mechanical properties—Young’s modulus (E) and hardness (H)—of diamond-like carbon (DLC) thin films deposited on p2+ Si (100) by filtered cathodic vacuum arc with different substrate bias voltage have been studied by nanoindentation measurement, where the substrate effect is included. Their intrinsic properties [including E,H, and yield strength (Y)] without the substrate effect are then derived by finite element analysis. The results show that the intrinsic mechanical properties of the DLC thin films are not affected by the film thickness, but significantly affected by change of sp3 bonding fraction caused by varied substrate bias. An empirical relationship among E, Y, and H for DLC thin films has been built, where E, Y, and H are intrinsic properties of DLC thin films. It is also confirmed that, as an empirical rule, the measured H could be used to represent its intrinsic value when the indentation depth is limited to 10% of the film thickness. However, the measured E with the substrate effect does n...

OPTICAL PROPERTIES OF FILTERED CATHODIC VACUUM ARC-DEPOSITED ZIRCONIUM OXIDE THIN FILMS

Zirconium oxide thin films were grown on n-Si(100) and quartz substrates by using an off-plane filtered cathodic vacuum arc without external heating. A Zr cathode was used to obtain the plasma and the deposition rate was varied from 75 to 35 nm min−1 corresponding to various oxygen flow rates. Optical properties of as-deposited films are presented as a function of oxygen flow rate and shown to depend greatly on it. The transmittance and optical band gap (Eg) increase with the oxygen flow rate whereas optical constants decrease. Film optical homogeneity is considerably enhanced and good homogeneity is exhibited for the films deposited at oxygen flow rate above 50 sccm. Structural homogeneity remains throughout the film depth even though the respective film structure changes with the different oxygen flow rates. Bulk-like stoichiometric amorphous zirconium oxide film exhibits high Eg (5.0 eV), high transmittance and good optical constants (high refractive index of 2.16 at 550 nm and low extinction coefficient of at 550 nm) with homogeneous structure.

Band-gap expansion, core-level shift, and dielectric suppression of porous silicon passivated by plasma fluorination

The effect of plasma fluorination on the band gap, 2p core-level energy, and the dielectric behavior of porous silicon (PS) prepared under constant conditions has been examined using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, photoluminescence, and reflection. It has been found that with increasing extent of fluorination, the band gap expands, and the 2p level and the dielectric constant drop down substantially compared with those of the as-grown PS, being quite similar to the effect of particle size reduction. These findings could be interpreted as the fluorination-induced crystal field enhancement and the valence charge repopulation of silicon. The surface fluorination may provide an effective method for tuning the optical and dielectric properties of nanometric silicon.

Distinguishing the effect of surface passivation from the effect of size on the photonic and electronic behavior of porous silicon

CF4 plasma-passivation enhanced size dependence of the blueshift in photoemission and photoabsorption, E2p-level shift, and band-gap expansion of porous silicon has been measured and analyzed numerically based on the recent “bond order-length-strength” correlation [C. Q. Sun, Phys. Rev. B 69, 045105 (2004)]. Matching predictions to the measurements conducted before and after fluorination reveals that fluorination further enhances both the crystal binding intensity that determines the band gap and core level shift and the electron-phonon coupling that contributes to the energies of photoemission and photoabsorption. This approach enables us to discriminate the effect of surface-bond contraction from the effect of surface-bond nature alteration on the unusual behavior of photons, phonons, and electrons in nanosolid Si.

Nitrogen-ion-energy dependent optical and structural properties of AlN films obtained using a filtered cathodic vacuum arc

We report on the successful fabrication of transparent and uniform aluminium nitride (AlN) III–V semiconductor films using an ion-beam assisted filtered cathodic vacuum arc technique at room temperature. A nitrogen-ion beam with energy varying from 200 to 650 eV has been employed to assist the deposition of AlN films. Effects of the nitrogen-ion-beam energy on optical and structural properties of AlN films have been investigated using an optical spectrophotometer, visible Raman spectroscopy, x-ray diffraction, atomic force microscopy and nanomechanical test instruments. The optical and structural properties of the AlN films depend significantly on the nitrogen-ion-beam energy. The AlN films deposited under ion energies below 300 eV are all amorphous and enhanced polycrystalline AlN films are obtained for energies above 400 eV.

Studies of copper vacuum arc plasma through an off-plane double-bend filtering duct

A novel off-plane double-bend (OPDB) magnetic filter, designed to remove unwanted macroparticles effectively from the plasma beam of a cathodic vacuum arc, was used in our filtered vacuum arc system to deposit copper thin film as an interconnect material for deep submicron IC applications. A filter with high plasma transmission efficiency is essential for a high deposition rate, which is key to the commercialisation of the technology. Hence, an investigation has been carried out to study the copper arc plasma under varying magnetic field and duct bias. The ion throughput was determined by measuring the ion saturation output current using a copper disc probe. To study further the copper ion motion in the OPDB filter, a modified drift model was applied, which took into account radial electric fields generated by the potential difference between the duct wall and torus centre. Relatively good agreement between the experimental and simulation results were obtained.