Gas source molecular beam epitaxy and thermal stability of Si1-xGex/Si superlattice materials

Gas source molecular beam epitaxy has been used to grow Si1-xGex alloys and Si1-xGex/Si multi-quantum wells (MQWs) on (100) Si substrates with Si2H6 and GeH4 as sources. Heterostructures and MQWs with mirror-like surface morphology, good crystalline qualify, and abrupt interfaces have been studied by a variety of in situ and ex situ techniques. The structural stability and strain relaxation in Si1-xGex/Si heterostructures have been investigated, and compared to that in the As ion-implanted Si1-xGex epilayers. The results show that the strain relaxation mechanism of the non-implanted Si1-xGex epilayers is different from that of the As ion-implanted Si1-xGex epilayers.

Evaporation of Ethanol Drops on a Heated Substrate Under Microgravity Conditions

We present in this paper results obtained from a parabolic flight campaign regarding ethanol sessile drop evaporation under reduced gravity conditions. Drops are created using a syringe pump by means of injection through a PTFE (polytetrafluoroethylene) substrate. The drops are recorded using a video camera and an infrared camera to observe the thermal motion inside the drop and on the heating substrate. The experimental set-up presented in this paper enables the simultaneous visualization and access to the heat flux density that is transferred to the drop using a heat flux meter placed between the heating block and the PTFE substrate. We evidence original thermal spreading phenomena during the ethanol drop creation on a heated PTFE substrate. The drop exhibits specific behaviour which is discussed here. This work is performed in the frame of a French-Chinese collaboration (project IMPACHT) for future experiments in a Chinese scientific satellite.

Droplet Image Feedback Control System in Evaporation Experiment

In order to realize the steady-state droplet evaporation, image feedback control system is designed based on DSP. The system has three main functions: to capture and store droplet images during the experiment; to calculate droplet geometrical and physical parameters such as volume, surface area, surface tension and evaporation velocity at a high-precision level; to keep the droplet volume constant. The DSP can drive an injection controller with the PID control to inject liquid so as to keep the droplet volume constant. The evaporation velocity of droplet can be calculated by measuring the injected volume during the evaporation. The structure of hardware and software of the control system, key processing methods such as contour fitting and experimental results are described.

Coupling of thermocapillary convection and evaporation effect in a liquid layer when the evaporating interface is open to air

The coupling mechanism of thermocapillary convection and evaporation effect in evaporating liquids was studied experimentally. The experiments were carried out to study a thin evaporating liquid layer in a rectangular test cell when the upper surface was open to air. By altering the imposed horizontal temperature differences and heights of liquid layers, the average evaporating rate and interfacial temperature profiles were measured. The flow fields were also visualized by PIV method. For comparison, the experiments were repeated by use of another two non-evaporating liquids to study the influence of evaporation effect. The results reveal evidently the role that evaporation effect plays in the coupling with thermocapillary convection.