Gao-Xiang Ye

Growth behavior and surface morphology of Ag rough thin films deposited on silicone oil surfaces

The growth behavior and surface morphology of a rough film system, deposited on silicone oil drop surfaces by a r.f. magnetron sputtering method, have been studied. An anomalous film growth relaxation is observed during the deposition process. The relaxation rate is extremely sensitive to the substrate temperature. The surface morphology at the micrometer length scale is very susceptible to the substrate temperature, the incident r.f. capacity, and the nature of the solid substrate on which the oil drop is dripped. A discussion on the physical origins of these phenomena is also presented.

An internal stress pattern in free standing films

We report a sinusoid appearance of cracks existing in a continuous nickel (Ni) film system deposited on silicone oil surfaces. The sinusoid cracks start from the sample edges or from other cracks, then their oscillatory amplitudes decrease gradually as they extend and finally disappear. One crack may bifurcate into two or three cracks, or two cracks may coalesce harmoniously. The sinusoid appearance of the cracks represents a sinusoid stress pattern in the Ni films, which mainly results from the characteristic boundary condition and interactions among the atoms in these free sustained films.

Anomalous hysteresis properties of iron films deposited on liquid surfaces

A nearly free sustained iron film system, deposited on silicone oil surfaces by vapor-phase deposition method, has been fabricated and its crystal structure as well as magnetic properties has been studied. Both the temperature-dependent coercivity Hc(T) and exchange anisotropy field HE(T) of the iron films possess a maximum peak around the critical temperature Tcrit=10–15 and 4K, respectively. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase below freezing temperature Tf=30–50K.

Structural and electrical properties of an Au film system deposited on silicone oil surfaces

An Au thin film system, deposited on silicone oil surfaces by the thermal deposition method, has been fabricated and its structure as well as electrical properties has been studied. A web-shaped characteristic surface morphology of the films is observed. The dc sheet resistance R of the metal films on the liquid surfaces is measured during and after deposition in situ by the four-probe method. The time dependence of the sheet resistance can be explained in terms of the film growth mechanism on the oil surface. The anomalous I–V characteristics of the film system can be interpreted as a competition among the local Joule heating, hopping and tunnelling effects. It is found that the dc third-harmonic coefficient B0 and the zero-power resistance R0 satisfy the power-law relation B0 R02+w and the exponent w is close to zero. This result indicates that the hopping and tunnelling effects in the samples are much stronger than those of the other film systems. We also find Im R0−β with β = 0.79 ± 0.08 and Im B0−γ with γ = 0.49 ± 0.07, where Im is the critical current. The physical origins of the phenomena are discussed.

Preferred structures of the atomic Ag islands on silicone oil surfaces

Varying the substrate temperature T(s) from 285 to 353 K, both the aggregation behavior of Ag atoms and the preferred structures of the atomic Ag islands on silicone oil surfaces are investigated. After deposition, the deposited Ag atoms form isolated islands with a preferred height. Our observations reveal that, as T(s) increases, the preferred island height increases from 20.0 to 33.0 nm, which results in the decrease of the Ag apparent coverage, from 9.6 ± 0.1% to 6.5 ± 0.3%. Further, the crystal structure of the Ag islands changes from amorphous to polycrystalline as the substrate temperature T(s) goes up. Subsequently a 3D aggregation mechanism of the Ag atoms on the liquid substrates is proposed.

One-dimensional Growth of Zinc Crystals on a Liquid Surface

The catalyst-free growth of nanocrystals on various substrates at room temperature has been a long-standing goal in the development of material science. We report the growth of one-dimensional zinc nanocrystals on silicone oil surfaces by thermal evaporation method at room temperature (20 ± 2 °C). Uniform zinc nanorods with tunable size can be obtained. The typical length and width of the nanorods are 250–500 nm and 20–40 nm, respectively. The growth mechanism can be attributed to the effect of the liquid substrate and the preferential growth direction of the crystals. This result provides a novel and simple way to fabricate the precursors (zinc crystals) for preparation of Zn-based semiconductors and other metallic crystals on liquid substrates.

Aggregation Mechanism of Ag Atoms Deposited on Liquid Surfaces

We study the aggregation of silver (Ag) atoms deposited on silicone oil surfaces. It is observed that the apparent Ag coverage of the total area, � , increases linearly with the nominal film thickness h for h< 0:9 nm and its slope k decreases clearly as the deposition flux f increases. Our atomic force microscopy (AFM) observation shows that the average thickness of the atomic aggregates first increases with f , and then approaches a saturation value. Then, the aggregation mechanism of Ag atoms is presented.

Conductivity and dielectric constant in a wedge-shaped Pt-film percolation system☆

A wedge-shaped Pt-film percolation system was prepared by the magnetron sputtering method. A new nonlinear I-Vbehavior was found and can be well explained by the location-dependent hopping effect. Power-law behavior, σ(ω) α ωx and ϵ(ω) α ω−y, is observed near the percolation threshold. The exponents x and y are found to be 0.87±0.04 and 0.08±0.03, respectively, in agreement with the general scaling relation x + y = 1.

Anomalous Kinetic Roughening of Nanostructured Ag Islands on Liquid Surfaces

By atomic force microscopy, the surface evolution and kinetic roughening of nanostructured Ag islands on silicone oil surfaces are studied. It is found that the islands are composed of quasi-circular granules with planar size around 50.0 nm, which is approximately independent of nominal thickness d . Our measurement indicates that the geometrical shape of the granules changes from plateau to sphere as d goes up. The dynamic scaling analysis reveal that the roughness exponent α varies between 0.80 and 0.90 as d increases. The average roughness w rms shows power-law relationship with d and the growth exponent β= 0.53 ±0.03 when d ≤4.0 nm. However, w rms deviates obviously from the power-law relationship for the samples with d > 4.0 nm. This anomalous behavior of β is explained by the competition between the shadowing and reemission processes, and then the kinetic evolution and formation mechanism of the islands are presented.

GROWTH MECHANISM AND ELECTRICAL PROPERTIES OF METALLIC FILMS DEPOSITED ON SILICONE OIL SURFACES

The microstructure and the growth mechanism of the films, which were deposited on silicone oil surfaces by the rf-magnetron sputtering method, were studied systematically. It is found that, at the fixed incident rf capacity, the growth rate is not a constant and it depends on both the nominal film thickness and the substrate temperature. The film structure at the micrometer scale is highly sensitive to the substrate temperature. The dc resistance of the film increases with the increase of time, indicating that the behavior of the defects in the film is much different from that of the film deposited on a solid substrate. The effects of the liquid substrate are also discussed.