Materials Science Forum Vols. 654-656

Abstract: A series of Ti/TiN multilayer films was deposited on Si substrates by DC reactive magnetron sputtering process. The influence of sputtering current density and substrate temperature on cycle membrane structure and its electrical properties was investigated in this study. The results show that: when the current density is 0.4A, the sheet resistance and electrical resistivity of the film are of the minimum value. The sheet resistance and electrical resistivity of the film decrease with an increase of substrate temperature. Therefore, sputtering current density should be controlled between 0.3-0.4A, while the substrate temperature should be above 400°C. For a given modulation period and modulation ratio, with the change of number of cycles the films can present a unique set of colours, and its electrical resistivity decreases with an increase in the number of cycles. When the number of cycles is greater than 4, the sheet resistance is significantly reduced, and when the number is greater than 15, the prepared films come off. To keep the number of cycles at five and change the modulation period, it is shown that a minimum electrical resistivity exists.

Abstract: Zinc oxide thin films were prepared on the glass substrate by rf-magnetron sputtering technique and their structural, optical, and mechanical characteristics were then investigated. As the SEM images have revealed, the average grain size of ZMO thin film are influenced by pressure and sputter power, and the average value of the grain size is about 30~50 nm. The EDS analysis also revealed a successful doping of Mo in ZnO thin film. The transmittance property of ZMO thin film exhibited an excellent transparency in the visible range, where the transmittance was about 90% for ZMO film with Mo. Moreover, good transmittance was also demonstrated in the range of 350nm to 400nm (UV regime). Finally, the nano-mechanical properties of ZMO thin films were investigated using a nanoindentation technique. The corresponding result would show that the Young’s modulus and hardness both increased with decreasing pressure.

Abstract: In this study, cellulose nanofibers were obtained from wood pulp using a chemo-mechanical method and thin films were made of these cellulose nanofibers. The morphology of the films was studied by scanning electron microscopy (SEM). SEM image analysis revealed that the films were composed of cellulose nanofibers with an average diameter of around 32 nm. Other properties were also characterized, including the degree of crystallinity by X-ray diffraction, chemical bonding by infrared attenuated total reflectance analysis, and thermal properties by differential scanning calorimetry. The foldable, strong, and optically translucent cellulose nanofiber films thus obtained have many potential applications as micro/nano electronic devices, biosensors and filtration media, etc.

Abstract: This study presents the effect of iodine doping on optical and surface properties of polyterpenol thin films deposited from non-synthetic precursor by means of plasma polymerisation. Spectroscopic ellipsometry studies showed iodine doping reduced the optical band gap from 2.82 eV to 1.50 eV for pristine and doped samples respectively. Higher levels of doping notably reduced the transparency of films, an issue if material is considered for applications that require high transparency. Contact angle studies demonstrated higher hydrophilicity for films deposited at increased doping levels, results confirmed by XPS Spectroscopy and FTIR. Doping had no significant effect on the surface profile or roughness of the film.

Abstract: The surface displacement of the indented layered composite has been observed by AFM and TEM, and the elastic recovery due to the indentation residual stress is compared with the prediction of the triangular dislocation model. At the shoulders of the indentation, the upheaval of Al-4wt%Cu film is smoothly connected, whereas that of Al2Cu film is localized as the intensive sheared displacement. The magnitude of the elastic recovery in film/substrate composite is larger than the predicted value, which might be attributed to the repulsive interaction between the glide dislocations and the hard Si substrate.

Abstract: Structural stabilities in GaAs nanocrystals grown on the Si (111) substrate have been studied by transmission electron microscopy in order to see the structure and growth mechanism. The GaAs nanocrystals grown epitaxially on the Si (111) surface kept at 573 K have thin shapes consisting of a flat surface which is parallel to the Si (111) surface. The crystalline structure of the initial growth layer, below approximately 5 nm in thickness is zincblend, but with increasing thickness the structure changes to the wurtzite structure by formation of orderly-arranged stacking faults. The small difference in the driving force between wurtzite and the zincblende structure could lead to a situation where the kinetic rate of nucleus formation is higher for the wurtzite structure than for the zincblende structure. It would highly increase the probability that the wurtzite structure is formed as a non-equilibrium state.

Abstract: Preferred orientation of AlN film has been changed from random to c-axis textured by inserting the ultra-thin Pt/AlN underlayer. The ultra-thin Pt underlayer also exhibits the same effect on the preferred orientation control of AlN film. According to intensity distributions of diffracted X-ray collected as the function of 2θ and ψ on these films, it is clearly shown that c-axis of AlN is altered from titled to the surface normal. AlN film and AlN films with underlayers demonstrate tensile stress, and it can be reduced by inserting underlayers. The effects of underlayers on the development of the preferred orientation and the reduction of stresses are similar to that of decreasing sputtering gas pressure.

Abstract: Aluminum nitride (AlN) is one of the most popular piezoelectric materials for high frequency resonators, filters and sensors. The piezoelectric property, i.e. electromechanical coupling coefficient, of AlN thin film is highly related to its crystalline orientation. AlN thin films with various c-axis-tilted angles can be fabricated by the RF sputtering technique. The crystallization and grain growth orientations of AlN thin film are examined by XRD, SEM, and TEM, while the bonding condition and nano-mechanical properties are investigated by a raman system and a nano-indentation technique.

Abstract: This study aims to study the influence of surface topography on the photocatalytic reaction of TiO2 film surfaces. In this work, a textured TiO2 film surface was fabricated by anodic oxidizing a titanium plate with micro grooves, and its wettabilty was evaluated. Micro grooves were machined on a 3-axis NC control precision machine tool using a single point diamond cutter with a tip radius of several hundred nanometers. Anodic oxidation experiments were conducted by using the self-developed equipment with diluted acetic acid as the electrolyte. It was found that the wettability of the TiO2 film surface textured by microcutting was superior to that textured by polishing under the irradiation environment of ultraviolet rays. The wettability of photocatalytic film surfaces could be improved by increasing the surface area.

Abstract: We have investigated the growth and characteristics of heteroepitaxial Ge1-xSnx layers on various substrates. The low temperature growth and the large misfit strain between Ge1-xSnx and Si leads to the high density of defects such as vacancy in Ge1-xSnx layers. They effectively enhance the propagation of misfit dislocations and the strain relaxation with suppressing the precipitation of Sn atoms from Ge1-xSnx layers. We succeeded in growing strain-relaxed Ge1-xSnx layers with a Sn content over 9% by controlling the dislocation structure on Si substrates. We also characterized the Hall mobility of Ge1-xSnx layers and found that the incorporation of Sn into Ge effectively reduced the concentration of holes related with vacancy defects, and improved on the hole mobility.