Qingchun Tang

Optimized pre-thinning procedures of ion-beam thinning for TEM sample preparation by magnetorheological polishing

Ion-beam-thinning is a well-established sample preparation technique for transmission electron microscopy (TEM), but tedious procedures and labor consuming pre-thinning could seriously reduce its efficiency. In this work, we present a simple pre-thinning technique by using magnetorheological (MR) polishing to replace manual lapping and dimpling, and demonstrate the successful preparation of electron-transparent single crystal silicon samples after MR polishing and single-sided ion milling. Dimples pre-thinned to less than 30 microns and with little mechanical surface damage were repeatedly produced under optimized MR polishing conditions. Samples pre-thinned by both MR polishing and traditional technique were ion-beam thinned from the rear side until perforation, and then observed by optical microscopy and TEM. The results show that the specimen pre-thinned by MR technique was free from dimpling related defects, which were still residual in sample pre-thinned by conventional technique. Nice high-resolution TEM images could be acquired after MR polishing and one side ion-thinning. MR polishing promises to be an adaptable and efficient method for pre-thinning in preparation of TEM specimens, especially for brittle ceramics.

Flexible cold plasma jet with controllable length and temperature for hydrophilic modification

With the advantages of high efficiency, simple equipment, good controllability, and the fact that they do no surface damage, atmospheric-pressure cold plasma jets are used to make solid surfaces hydrophilic. To transport the plasma jet effectively to the region to be modified and to reduce the amount of thermal damage to the surface during the modification, it is essential to control the transmission and temperature of the plasma jet from the distance. Flexible transmission and pre-cooling methods are proposed in this paper to solve this problem. An experimental device is constructed that mainly comprises the working gas, a power source, and a plasma generator. The test results show that (i) using a flexible catheter can extend the plasma transmission distance significantly and (ii) adjusting the driving voltage and gas flow allows the cold flexible plasma jet (FPJ) to reach several meters. Specially shaped jets such as plasma jet brushes can be generated conveniently based on the FPJ principle, thereby expanding the application range of the plasma. Pre-cooling the working gas with a vortex tube can lead to an FPJ with a simple structure without additional energy input and with a controllable temperature as low as −7 °C. The developed FPJ with a controllable length and temperature can be used to quickly modify various common solid surfaces, convert superhydrophobic surfaces into superhydrophilic surfaces, and preserve the microstructure of workpiece surfaces during modification.With the advantages of high efficiency, simple equipment, good controllability, and the fact that they do no surface damage, atmospheric-pressure cold plasma jets are used to make solid surfaces hydrophilic. To transport the plasma jet effectively to the region to be modified and to reduce the amount of thermal damage to the surface during the modification, it is essential to control the transmission and temperature of the plasma jet from the distance. Flexible transmission and pre-cooling methods are proposed in this paper to solve this problem. An experimental device is constructed that mainly comprises the working gas, a power source, and a plasma generator. The test results show that (i) using a flexible catheter can extend the plasma transmission distance significantly and (ii) adjusting the driving voltage and gas flow allows the cold flexible plasma jet (FPJ) to reach several meters. Specially shaped jets such as plasma jet brushes can be generated conveniently based on the FPJ principle, thereby e...