Layer transfer techniques have been extensively explored for semiconductor device fabrication as a path to reduce costs and to form heterogeneously integrated devices. These techniques entail isolating epitaxial layers from an expensive donor wafer to form freestanding membranes. However, current layer transfer processes are still low-throughput and too expensive to be commercially suitable. Here we report a high-throughput layer transfer technique that can produce multiple compound semiconductor membranes from a single wafer. We directly grow two-dimensional (2D) materials on III-N and III-V substrates using epitaxy tools, which enables a scheme comprised of multiple alternating layers of 2D materials and epilayers that can be formed by a single growth run. Each epilayer in the multistack structure is then harvested by layer-by-layer mechanical exfoliation, producing multiple freestanding membranes from a single wafer without involving time-consuming processes such as sacrificial layer etching or wafer polishing. Moreover, atomic-precision exfoliation at the 2D interface allows for the recycling of the wafers for subsequent membrane production, with the potential for greatly reducing the manufacturing cost.
The effects of treatment processes on estrogenicity were evaluated by examining estradiol equivalent (EEQ) concentrations in influents and effluents of sewage treatment plants (STPs) located along Yeongsan and Seomjin rivers in Korea. The occurrence and distribution of estrogenic chemicals were also estimated for surface water in Korea and compared with seven other Asian countries including Laos, Cambodia, Vietnam, China, Indonesia, Thailand and Malaysia. Target compounds were nonylphenol (NP), octylphenol (OP), bisphenol A (BPA), estrone (E1), 17beta-estradiol (E2), 17alpha-ethynylestradiol (EE2) and genistein (Gen). Water samples were pretreated and analyzed by liquid-liquid extraction (LLE) and gas chromatography/mass spectrometry (GC/MS). The results showed that the treatment processes of Korean STPs were sufficient to reduce the estrogenic activity of municipal wastewater. The concentrations of phenolic xenoestrogens (i.e., NP, OP and BPA) in samples of Yeongsan and Seomjin rivers were smaller than those reported by previous studies in Korea. In most samples taken from the seven Asian countries, the presence of E2 and EE2 was a major contributor toward estrogenic activity. The EEQ concentrations in surface water samples of the seven Asian countries were at a higher level in comparison to that reported in European countries, America and Japan. However, further studies with more sampling frequencies and sampling areas should be carried out for better evaluation of the occurrence and distribution of estrogenic compounds in these Asian countries.