We have applied this etching mode to the machining of a Ge surface in O2-containing water. So far, we revealed fundamental etching properties such as pore formation and patterning in this system with noble metals (Pt and Ag), and recently, we demonstrated Pt-assisted chemical flattening.[4,5] In this scheme, a catalyst plate comprising a soft elastomer coated with a sputtered Pt film, and a Ge wafer were brought into contact and rotated independently in the same plane in water. The processed Ge surface includes few protrusions with a lateral size on the order of 10 nm, which is probably caused by the selective removal of protrusions from the Ge surface by the catalytic activity of Pt.
However, a problem in this system is the use of noble metals as catalysts. After metal-assisted chemical etching, residual metals on a semiconductor surface have to be removed. For example, aqua regia is effective for dissolving Pt. However, such a strong oxidative solution causes severe damage to a Ge surface. To solve this issue, graphene can be used as a substitute for noble metals to achieve catalyst-assisted chemical etching.
In this talk, we discuss the etching properties of a p-type Ge(100) surface loaded with reduced graphene oxide (RGO) in O2-containing water. In order to obtain the RGO, a graphene oxide (GO) ink, used as a starting material, was either heated at 900°C in Ar ambient for 10 min or immersed in a solution comprising the GO ink, hydrazine and N,N-dimethylformamide. Then we deposited the obtained RGO on a Ge surface in the form of aggregated particles or dispersed flakes. After immersing the samples into water exposed to air, we found that the Ge surface was preferentially etched around the loaded RGO. The etching rate as well as the etched morphology was revealed by atomic force microscopy observations, and the etching mechanism is proposed. These findings show the possibility of using RGO as a catalyst to enhance the chemical etching of a Ge surface in water.
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