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Tailoring metal film texture by use of high atomic mobility at metal-semiconductor interfaces
摘要： The difference in the microstructural and texture evolution of Al films grown on amorphous SiO2 (a-SiO2) and amorphous Ge (a-Ge) substrates have been investigated. Surprisingly, the a-Ge substrate was found to change the preferred orientation of Al grains from the conventional (1 1 1) to the unconventional (1 1 0). The effect of the high mobility of Ge atoms at the metal-semiconductor interface on the microstructural and texture evolution of the metal thin film was studied. The diffusion of the Al adatoms on the a-Ge substrate was suppressed owing to the segregation of Ge atoms at the film surface. The mobility of Al grain boundaries was also suppressed because of grain-boundary wetting by the Ge atoms. It is concluded that the a-Ge substrate could tailor the Al grain orientation from (1 1 1) to (1 1 0) owing to the change in the film-growth mode from three-dimensional to two-dimensional nucleation. The concept of interaction-induced island-growth model, which is based on the Volmer–Weber growth model, is also discussed here. This work thus demonstrates how the atomic mobility at the interface of the metal thin film and the semiconductor substrate controls the film microstructure and texture during deposition.
关键词： Substrate,Microstructure,Surface diffusion,Texture,Metal thin film,Grain-boundary wetting
更新于2025-09-23 15:23:52
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Roles of alloying elements in wetting of SiC by Al
摘要： Wetting of SiC by Al alloys is a key issue in the preparation of SiC-reinforced Al matrix composites. The wettability could be improved by alloying of Al, yet controversial results widely exist in the literature. We investigated the effects of four important alloying elements (Si, Cu, Ti and Mg) and their concentrations on the wettability in the Al/SiC system using a dispensed sessile-drop method. The results demonstrate that Si could weaken or even inhibit the formation of Al4C3 and substantially improve the wettability via an adsorption effect; Cu slightly deteriorates the wettability, but alleviates the formation of Al4C3 by decreasing the activity of Al; Ti strongly adsorbs at the solid?liquid interface, forming TiCx instead of Al4C3, and thus significantly improves the wettability; Mg may also favor the wettability due to its help in the disruption of the oxide film covering the Al surface via evaporation and its strong affinity for the silica film on the SiC surface; but for a clean Al/SiC system, the effect of Mg is essentially limited. In addition, the evaporation of Mg always leads to a reduction in the drop volume, which causes a decrease in the apparent contact angle, but this effect is usually neglected.
关键词： Contact angle,Interface,Wetting
更新于2025-09-23 15:23:52
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Wetting Transition from the Cassie–Baxter State to the Wenzel State on Regularly Nanostructured Surfaces Induced by an Electric Field
摘要： When droplets are placed on hydrophobic textured surfaces, different wetting state Cassie-Baxter (CB) state or Wenzel (W) state may occur depending on materials and structures of surfaces, types and sizes of droplets, thermal fluctuations, and external stimuli. The wetting transition from the CB to the W state and the opposite process have attracted a great deal of attention due to their primary importance for designing and fabricating textured surfaces. In this work, molecular dynamics (MD) simulations are employed to understand the mechanism behind the CB-to-W transition for a nanoscale water film placed on a surface decorated with a single nanogroove when an external electric field is applied. The free energy variation during the transition process is computed on the basis of the restrained MD simulations. Water intrusion into the groove is observed by simulation snapshots, which provides a direct evidence for the electric-field-induced CB-to-W transition. In the previous experiments, however, only a sharp reduction in the apparent contact angle is employed to judge whether the transition takes place. The free energy curves reveal that there are two energy barriers separating the CB and W states (?E1) as well as separating the W and CB states (?E2). Owing to the presence of ?E1, although the CB state has a higher free energy than the W state, it cannot spontaneously convert to the W state. When the external energy input exceeds ?E1, the CB-to-W transition can be triggered, otherwise the transition will stop, and the water film will return to the CB state. Moreover, it is found that the maximum of free energy always occurs after the film touches the groove bottom. Thus, the requirement of the film touching the groove bottom is responsible for the presence of the energy barrier ?E1. Finally, the dependences of the two energy barriers on the electric field strength, groove aspect ratio, and intrinsic contact angle of the groove are also discussed.
关键词： Cassie-Baxter state,wetting transition,Wenzel state,energy barrier,free energy,molecular dynamics simulations.
更新于2025-09-23 15:23:52
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Meniscus Shape Control Using Electrowetting and Its Application to Optical Devices
摘要： Electrowetting is a technique to modify wettability and meniscus shapes on electrodes by applying voltage to the electrodes. In the present article, we introduce principles of electrowetting deriving the equation connecting voltage and contact angle. Then we reviews related articles on optical devices using electrowetting including our previous works; a liquid prism controlling optic-axis using electrowetting. Numerical simulation solved meniscus shapes between each liquid to predict the relation between applied voltage and optic angle. Results in experiments and simulations are briefly reported.
关键词： Meniscus,Electrowetting,Numerical simulation,Optical devices,Wetting
更新于2025-09-23 15:21:21
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High-throughput laser generation of Si-nanoparticle based surface coatings for antibacterial applications
摘要： High-productivity regime of nanosecond IR-laser ablative generation of silicon colloidal solutions in water for anti-bacterial applications was found in terms of GW/cm2-level laser intensity and scanning velocity by measuring multi-shot ablative mass loss and extinction coefficients of the colloids as sub-linear and third-power intensity functions, respectively. This advantageous regime implies sub-linear mass loss versus laser intensity at the simultaneous third-power yield of nanoparticles, resulting from the subcritical-density, opaque ablative plasma regulating the sample ablation rate and the related plasma-mediated dissociation (dispergation) of the ablation products. In contrast, at higher intensities, there is a drastic increase in mass loss with the corresponding increased yield of (sub) micrometer-sized particles owing to intense plasma-driven expulsion of micro-scale melt droplets and the corresponding saturation of the extinction coefficient of the colloidal solutions because of their dynamic local “self-limiting” effect during the high-rate ablation. The optimal low-intensity regime for Si nanoparticle production demonstrates the monotonous correlated increase of mass loss and extinction coefficient in terms of increasing laser scanning velocity, indicating the diminished cumulative effects. Surface coatings prepared from the generated Si nanoparticles exhibit minor surface oxidation, as acquired as their elemental composition via energy-dispersive X-ray spectroscopy, making their contact angle for water droplets (≈51°) close to that of bare Si wafer (≈58°) with its nanometer-thick native oxide layer. Owing to good wetting, the nanoparticle-based surface coatings show strong antibacterial response regarding Gram-negative Pseudomonas auereginosa bacteria even despite their minor oxidative passivation.
关键词： Silicon nanoparticles,Colloids,Surface oxidation,Extinction coefficient,Wetting,Antibacterial tests,Gram-negative bacteria Pseudomonas auereginosa,Sub-critical ablative plasma,Nanosecond laser ablation,Mass loss
更新于2025-09-23 15:21:21
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Wetting and spreading behaviors of Al-Si alloy on surface textured stainless steel by ultrafast laser
摘要： An ultrafast laser was used to ablate the surface of stainless steel. Periodical surface micro-textures including micro-grooves, micro-pits and micro/nano-ripples were successfully fabricated. As a typical reactive wetting system, Al-Si alloy was used to study the wetting and spreading behaviors on the laser patterned surfaces of stainless steel. The results showed that initial, rapid spreading and gradient balance stages were found in the spreading process. By comparing to the primitive surface, Al-Si alloy exhibited worse wettability on the surface with micro-grooves and micro-pits because of the geometrical characteristics and nano-scale oxides residuals after laser processing; however, Al-Si alloy showed better wettability on the surface with micro/nano-ripples owing to the formation of micro/nano hierarchically patterns and the resultant improved capillary actions. The interfacial reaction layer formed during wetting and spreading processes were also investigated. The surface micro-textures were found to enhance the interfacial metallurgical reactions, thus increasing the thickness of the reaction layer. This work provides a new method to improve the wettability, spreadability and metallurgical reactions of Al-Si/stainless steel reactive wetting system and may extend its use in other reactive wetting systems. This method may be able to improve brazing, soldering, coating and other processes involving solid/liquid interfacial interactions.
关键词： Reactive wetting system,Wetting and spreading,Intermetallic compounds,Ultrafast laser processing,Surface micro-textures
更新于2025-09-23 15:21:01
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Wetting-Layer-Free AlGaN Quantum Dots for Ultraviolet Emitters
摘要： We exhibit both experimentally and theoretically a novel growth mode for the epitaxy of AlGaN quantum dots (QD), where they are eventually produced without their usual surrounding wetting layer. If the generic evolution of QD is ruled by the elastic relaxation and capillary effects, evaporation occurs here on a time scale similar to that of growth. Using a dedicated surface diffusion model accounting for elasticity, wetting and anisotropy, we evidence numerically different kinetic regimes as a function of the evaporation flux, that rationalize the experimental outcome. The resulting QD are characterized by enhanced optical properties compared to the common QD with a wetting layer. These nanostructures are promising candidates for deep ultraviolet light emitting diodes.
关键词： epitaxy,ultra-violet emitters,evaporation,quantum dots,wetting-layer
更新于2025-09-23 15:21:01
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[IEEE 2019 20th International Conference on Electronic Packaging Technology(ICEPT) - Hong Kong, China (2019.8.12-2019.8.15)] 2019 20th International Conference on Electronic Packaging Technology(ICEPT) - Identification of essential factors causing solder bridging of right-angle solder interconnects in laser jet solder ball bonding process
摘要： Solder bridging is a commonly seen and serious processing defect in electronic packaging, which may lead to short circuit even absolute failure of electronic devices and products. Solder bridging may occur in all types of solder interconnects and in each of soldering processes during manufacturing journey, for example, in ball grid array solder interconnects and three-dimensional (3D) interconnects, as well as in wave soldering and reflow soldering assemblies. With the increasing trend towards miniaturization and multifunction, the pitch and size of solder interconnects have been scaling down. The finer pitch and decreased size of solder joints greatly increase the difficulty of soldering process and the solder bridging defect is more likely to appear. Notably, the laser jet solder ball bonding (LJSBB) with the advantages of localized heating and higher energy inputting provides a novel soldering technology for 3D packaging, for instance, the right-angle solder interconnects and temperature-sensitive components. When fabricating the right-angle solder interconnects, the liquid solder ball is blown by the protected N2 flow and hardly stays firmly in place during the LJSBB process, thus the solder bridging occurs more often in the LJSBB process. Under such circumstances, it is necessary to identify the essential factors causing solder bridging of right-angle solder interconnects and seeking the improvement measures for mass production.
关键词： displacement,solder bridging,poor wetting,laser jet solder ball bonding,right-angle solder interconnect
更新于2025-09-23 15:21:01
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Temperature and hydrostatic pressure effects on the electronic structure, optical properties of spherical segment quantum dot/wetting layer and group velocity of light
摘要： To investigate hydrostatic pressure and temperature effects on electron energy levels of an InAs spherical segment quantum dot with wetting layer embedded in GaAs barrier, we use the finite element method to solve the Schr?dinger equation in the effective mass approximation. Results show that the ground, the first and the second excited state energies decrease (increase) as the hydrostatic pressure (temperature) increases for the constant temperature (pressure). Moreover, given the optical properties of the system interacting with two laser fields, red (blue) shifts are observed in the linear and nonlinear absorptions and dispersions for the probe pulse as the hydrostatic pressure (temperature) increases. Furthermore, as the hydrostatic pressure increases, the maximum of the group velocity of light inside the slow light frequency range increases and the slow light frequency range shifts to the lower probe frequencies.
关键词： temperature,group velocity of light,hydrostatic pressure,optical property,quantum dot/wetting layer
更新于2025-09-23 15:21:01
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Investigations on the occurrence of different wetting regimes in laser brazing of zinc-coated steel sheets
摘要： In the automotive industry, the seam edge quality of laser brazed seams is a crucial factor for the required high optical quality standards of customer-visible connections of zinc-coated car body parts. The type of zinc coating is decisive for the resulting geometry of the seam edges, which are aspired to be straight. Especially brazing of hot-dip galvanised steel with conventional brazing setup is not resulting in seam edges which fulfil the required optical quality. In this study, the wetting of copper-based filler wire on electrogalvanised and hot-dip galvanised steel sheets is analysed to increase the understanding of the influence of the wetting fronts on the seam edge quality. For this, the wetting fronts are determined in high-speed camera images and the resulting seam edges are captured by microscopic pictures. The results show that two major wetting regimes occur on both types of zinc coatings but with a different occurrence probability: one with a steep wetting front and zinc evaporation in front of wetting (“steep-angle-wetting”) and one where liquid zinc connects with the wetting front and creates a flat wetting angle (“flat-angle-wetting”). It is found that the resulting seam edge quality is mainly depending on the present wetting regime. However, for flat-angle-wetting, in the regime with insufficient seam edge quality, a self-stabilising effect is identified, which is responsible for a missing process window for brazing of hot-dip galvanised steel with sufficient seam edge quality.
关键词： Wetting,Optical seam quality,Laser brazing,Zinc-coated steel
更新于2025-09-23 15:21:01