Surface Review and Letters

Using the effective-mass approximation within a variational scheme, we have calculated the diamagnetic susceptibility and binding energy of a hydrogenic donor in a quantum well under different temperatures and hydrostatic pressure conditions. Our calculation have revealed the dependence of the diamagnetic susceptibility and the impurity binding on temperature and hydrostatic pressure.

The influence of structural, thermal and electronic properties on collective electronic excitations (plasmon modes) has been investigated for thin Ag films grown at room temperature on Cu(111). For the (9 × 9)-Ag/Cu(111) structure the excitation of the two-dimensional plasmon, observed in Ag/Si(111), is forbidden by both the high corrugation of the Ag layer and the presence of the underlying metal substrate. The increase of the sp density of states at the Fermi energy induces the appearance of a broad peak a 7–8eV, assigned to a free-electron collective excitation. For increasing Ag coverage (above 20 layers), surface plasmon is confined within Ag grains, as indicated by the analysis of its dispersion relation, which is dispersionless up to a critical wave-vector. Surface plasmon confinement is removed upon annealing at 400 K. The thermal treatment induces a flattening of the Ag adlayer with a merging of Ag islands, and moreover, a strong enhancement of surface conductivity.

We used scanning tunneling microscopy to investigate graphene formation on an SiC-on-insulator (SiC-OI) substrate. Annealing of an SiC-OI substrate with an SiC thickness of 1500 nm produced a graphene layer on the SiC surface. When the thickness of the SiC film was 5 nm, a graphene layer was not formed on the SiC surface. However, after annealing a C-covered SiC-OI substrate with an SiC thickness of 5 nm, a graphene layer formed on the SiO₂ surface.

A novel ordered-reinforced microscale polymer matrix composite based on electrophoresis and surface micromachining technologies has been proposed in the present work. The braid angle, volume content and width of the reinforcement in the composite has been designed and simulated by ANSYS finite element software. Based on the simulation and optimization, the Ni fibers reinforced polymer matrix composite sample (3 mm length × 0.6 mm width × 0.04 mm thickness) was successfully fabricated utilizing the surface micromachining process. The fabricated samples were characterized by microtensile test on the dynamic mechanical analysis (DMA) equipment. It is indicated that the tested tensile strength and Young's modulus are 285 MPa and 6.8 GPa, respectively. In addition, the fracture section of the composite sample has been observed by scanning electron microscope (SEM) and the corresponding fracture process was also explained and analyzed in detail. The new presented composite is promising for hot embossing mold in microfluidic chip and several transducers used in accurately controlled biomedical systems.

Magnetoelectric (ME) Ni/Pb(Zr_0.52Ti_0.48)O₃ bilayers have been successfully prepared by hydrothermal method using Ti as buffer layer. The hydrothermal mechanism of PZT thin film deposited onto Ni layer has been discussed. The structure and ferroelectric properties of the deposited PZT thin films are characterized by X-ray diffraction and ferroelectric testing. The ME voltage coefficient of the Ni/PZT bilayers gradually decreases as the thickness of buffer layer increases because the interface coupling of the Ni/PZT layers gradually decreases. The large ME coefficient makes these Ni/PZT bilayers possible for applications in multifunctional devices such as electromagnetic sensor, transducers and microwave devices.

A novel aluminium matrix surface composite added Al-based amorphous, whose layer depth was 5 mm, was fabricated by friction stir processing (FSP), at an air cooling. The surface composite region shows the obvious sandwich structure. It is considered to be a combination between the base metal and the amorphous strip via the FSP. The average hardness of the surface composite is about HV97, higher than the base metal is about HV80. The maximum tensile strength of the processed aluminium plate with the surface composite is 410 MPa. XRD results indicate that the constituent phases of the surface composite mainly include α-Al, Mg₂Al₃, MnAl₆ and La₃Al₁₁ Moreover, no obvious amorphous diffraction peaks are observed in the XRD results. However, a large number of ultrafine grained structures can be observed in the surface composite. The average grain size of them is ~90–400 nm constitutes the surface composite. These ultrafine grained structures are composed of the α-Al and α-Al amorphous structures.

A series of Zn_1-xMg_xO(x = 0 ~ 0.16) films have been prepared on glass substrates by RF magnetron sputtering. The structure, surface morphology, composition, optical and electrical properties of the films were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, UV-Vis spectrophotometer and Hall measurement, respectively. It reveals that the obtained films are uniform hexagonal wurtzite polycrystalline with grain size about 100 nm.The optical transmittance are over 80% and the band gap (Eg) has linear relationship with Mg content: Eg = 1.67x + 3.274 (eV) (0 < x < 0.16). The resistivity of the films increases with the increase of Mg content. The Raman spectra of the films show that the position of E₂ peaks (473 cm^-1) has not changed, but the A₁(LO) mode (577 cm^-1) frequency shifts to lower wavenumbers with the increase of Mg content, indicating that Mg-doping does not cause intensive lattice deformation, but results in the decrease of the carrier concentration, which is corresponding to the degradation of the conductivity of ZnMgO films with the increase of Mg content.

Indium oxide (In₂O₃) films have been prepared by thermal oxidation of pre-deposited indium films onto glass substrate kept at room temperature (35°C). These films were dipped into an aqueous solution (0.1 M) of lithium chloride (LiCl) and aluminum chloride (AlCl₃) followed by being fired at 500°C. Based on X-ray diffraction results, it has been observed that pure and Li modified In₂O₃ films are polycrystalline in nature while Al modified In₂O₃ film has a prominent peak corresponding to 222 plane of In₂O₃. Field emission scanning electron microscopy of pure film shows smaller grains which get transformed to bigger ones for Li modified In₂O₃ film. In case of Al modified In₂O₃ film agglomerated small grains are observed. This film also reveals the response of 60% for 100 ppm of ammonia vapors at room temperature. The transparency increased from 23–36% to 53–67% in visible region with Li modification of pure In₂O₃ film.

The evolution of the fatigue behaviors in Bi_3.5Nd_0.5Ti₃O₁₂ (BNT) ferroelectric thin films deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by chemical solution deposition (CSD) method effected by amplitude, frequency and profile of the driving electric field were reported. It is found that the switching with lower frequency and higher amplitude of the external voltages resulted in higher fatigue rates and only bipolar waveform type voltage can result in fatigue, whereas a unipolar voltage cannot. An empirical function with N/f is proposed in the frequency-dependence of polarization fatigue, where N is the number of switching cycles and f is the frequency of driving. It is indicated that injected charges from electrodes into films, the trapped charges, and suppression of the seeds of opposite domain nucleation are the main mechanism of fatigue in ferroelectric BNT thin films.

Anisotropic surfaces with micropillar- or micropillar/nanobump structures and anisotropic wetting behavior were fabricated. Structures were arranged as three parallel zones where the structure of the middle zone differed from that of the edge zones. The widths of the middle zones were increased systematically, and the effects of the middle zone structures and widths on the contact and sliding angles of water were investigated. Structures were fabricated on PP by injection molding. Microstructured mold inserts for injection molding were obtained by structuring aluminum foils with a microworking robot, and hierarchically structured mold inserts by anodizing the microstructured foils. It was possible to create surfaces where the microstructure in the middle zone was lower or higher than on the edges, or where the middle zone had only nanostructure or was unstructured. The behavior of water on the surfaces was characterized by measuring the dynamic contact angles and sliding angles parallel and perpendicular to the zones. Hydrophobic surfaces were achieved. With appropriate middle zone widths, clearly differing parallel and perpendicular contact angles were measured and elongation of droplets along the middle zones was detected.