Surface Review and Letters

We present a new theoretical approach to determine the interaction energy due to the coupling of adsorbed molecules to their environment in scanning tunneling microscopy. In fact, the above coupling energy is estimated by assuming the involved adsorbed molecules as Morse oscillators and their environment (electrodes, leads) as external reservoir.

The (100)-oriented Ca_0.4Sr_0.6Bi₄Ti₄O₁₅(C_0.4S_0.6BTi) thin film was successfully prepared by a sol-gel method on Pt/Ti/SiO₂/Si substrate. The orientation and formation of thin films under different annealing schedules were studied using XRD and SEM. XRD analysis indicated that (100)-oriented C_0.4S_0.6BTi thin film with degree of orientation of I₍₂₀₀₎/I₍₁₁₉₎ = 1.60 was prepared by preannealing the film at 400°C for 3 min followed by rapid thermal annealing at 800°C for 5 min. SEM analysis further indicated that the (100)-oriented C_0.4S_0.6BTi thin film with a thickness of about 800 nm was mainly composed of equiaxed grains. The remanent polarization and coercive field of the film were 16.1 μC/cm² and 85 kV/cm, respectively.

Surface photovoltage of semiconductors depend strongly on their electronic structures, in particular, their Fermi energy level. This offers a possibility to characterize photoelectronic behavior using the Kelvin probe structure by measurements of work function (WF). In this paper, ZnO films were prepared using the CVD method and their microstructures and morphology were characterized using the XRD and SEM. Furthermore, photovoltage evolution and WF of selected ZnO samples were measured using a scanning Kelvin probe (SKP) system. It is found that the surface photovoltage and its time-resolved evolution process as well as the energy level structure of ZnO films can be correlated to WF very well. The present study therefore provides a simple and practical methodology for the characterization of photovoltaic behavior of semiconductor films.

We report the preparation of ZnO quantum dot hybrid luminescent resists for nanoimprint lithography. Photoluminescence spectra indicate that ZnO QDs@AMONIL have a significant increase in the luminescent intensity, an obvious blue-shift of emission peak and the Stoke's shift, revealing that ZnO QDs@AMONIL have dramatic luminescent property change instead of inhibiting or only preserving the optical properties of pure ZnO QDs. The fabrication of two-dimensional (2D) photonic crystal structure on the ZnO QDs@AMONIL by UV-based nanoimprint lithography is demonstrated at last, which confirms the luminescent ZnO QDs@AMONIL reliable processing capabilities in wavelength-scale and envisions its promising applications in the optoelectronic micro-/nanodevices.

We prepared gradated nano-transient layers at different interfaces between deposited film and substrates by high-intensity pulsed ion beam (HIPIB) irradiation. The deposited film was (Al–Si) alloy and substrates were Ni and Ti, respectively. The gradated nano-transient layers at different interfaces were measured by Rutherford backscattering, its spectra were solved by SIMNRA code and then the microstructures of the gradated nano-transient layers at the interfaces of these two irradiated samples were obtained. The experimental results were analyzed by STEIPIB code. The formation of the gradated distribution of element contents in nano-transient layer at the interface can eliminate the abrupt changes of thermal and elastic characteristics at the interface. And, it can greatly reduce the mismatch of thermal expansion coefficients and Young's modulus at the interface between deposited film and substrate. Thus, after the formation of the gradated nano-transient layer, the adhesion at the interface between different materials can be enhanced and the level of thermal stresses can also be reduced in the case of thermal loading.

The problem of the CO dissociation on Mo(110) has been addressed by means of temperature-programmed desorption (TPD) and density-functional (DFT) calculations. The TPD spectra show a first-order CO desorption, which indicates the desorption from a "virgin" state, not a recombinative form of desorption. The height of the potential barrier for the dissociation (2.75 eV), estimated from DFT calculations, substantially exceeds the energy of CO chemisorption (2.1 eV), which makes the thermally induced CO dissociation on Mo improbable. Monte Carlo simulations of TPD spectra, performed using estimated chemisorption energies, are in good agreement with experiment and demonstrate that the two-peak shape of the spectra can be explained without involving the CO dissociation. Thus, the results of the present study finally refute the concept of a dissociative form of CO adsorption on Mo surfaces.

Pb-9.3wt.%Sb alloy was directionally solidified upwards under argon atmosphere under the two conditions; with different temperature gradients, (G = 0.93–3.67 K/mm) at a constant growth rate (V = 17.50 μm/s) and with different growth rates (V = 8.30–497.00 μm/s) at a constant (G = 3.67 K/mm) in a Bridgman furnace. The dependence of characteristic microstructure parameters such as primary dendrite arm spacing (λ₁), secondary dendrite arm spacing (λ₂) and dendrite tip radius (R) on the growth rate (V) and the temperature gradient (G) were determined by using a linear regression analysis. A detailed analysis of microstructure were also made and compared with the theoretical models and similar experimental works on dendritic solidification in the literature.

To prevent the carbon/carbon (C/C) composites from ablation, a new type of ablation protective coating was prepared on the surface of the C/C composites by a step pack cementation technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis show, the coatings obtained by pack cementation were silicon carbide/tantalum silicide (SiC-TaSi₂). The ablation behavior of the coated samples were evaluated by the oxyacetylene flame. The results show that, the SiC-TaSi₂ coating can improve the anti-ablative properties of C/C composites effectively. The mass ablation rate for the coated C/C composites was only 7.7 × 10^-4 g/s, which was lower by 79% than that of the C/C composites after ablation for 30 s.

In this work, a convenient and efficient procedure to control the morphologies of Au nanocrystals has been reported. The Au nanospheres are generated in polyvinyl-pyrrolidone/ethanol glycol system through a thermal chemical method. However, by adding a small amount of K₂CO₃ which influences the growth rate of various facets during the crystal growth, Au nanoplates with broad surface plasmon resonance band in 500–800 nm can be obtained.

In this work, a series of polycrystalline ZnO samples have been synthesized from Zn thin films deposited on Si(100) substrates by using thermal oxidation technique. The ZnO thin film samples grown by this technique were then characterized by a variety of structural and optical characterization tools. The results revealed that the use of novel annealing process i.e. the application of temperature gradient in the thermal treatment could enhance the structural and optical quality of the ZnO thin films significantly as compared to the normal annealing process, i.e. a fixed temperature under different durations. Apart from the improvement of structural and optical properties of ZnO thin films, another striking feature of this novel annealing process was the promotion of the growth of ZnO nanostructures.