Selective Etching of Si versus Si_1−xGe_x in Tetramethyl Ammonium Hydroxide Solutions with Surfactant

We investigated the selective etching of Si versus Si1−xGex with various Ge concentrations (x = 0.13, 0.21, 0.30, 0.44) in tetramethyl ammonium hydroxide (TMAH) solution. Our results show that the Si1−xGex with a higher Ge concentration was etched slower due to the reduction in the Si(Ge)–OH bond. Owing to the difference in the etching rate, Si was selectively etched in the Si0.7Ge0.3/Si/Si0.7Ge0.3 multi-layer. The etching rate of Si depends on the Si surface orientation, as TMAH is an anisotropic etchant. The (111) and (010) facets were formed in TMAH, when Si was laterally etched in the and directions in the multi-layer, respectively. We also investigated the effect of the addition of Triton X-100 in TMAH on the wet etching process. Our results confirmed that the presence of 0.1 vol% Triton reduced the roughness of the etched Si and Si1−xGex surfaces. Moreover, the addition of Triton to TMAH could change the facet formation from (010) to (011) during Si etching in the -direction. The facet change could reduce the lateral etching rate of Si and consequently reduce selectivity. The decrease in the layer thickness also reduced the lateral Si etching rate in the multi-layer

Self-attachable Flexible Transparent Electrodes with Robust Mechanical Adhesion and low Contact Resistance

With the recent development of low-dimensional nanomaterials such as nanowires, carbon nanotubes (CNTs), and graphene, flexible and transparent conductive electrodes (FTCEs) are being developed. Based on the high mechanical flexibility, optical transparency, and electrical conductivity, FTCEs are key elements of the emerging flexible optoelectronic devices, including flexible displays, touch panels, heaters, solar cells, electronic skins, and smart windows. Such electrodes should form an intimate physical contact with various active components of flexible devices to ensure stable, low-resistant electrical contacts. However, contact formation techniques are based largely on conventional soldering, conductive pastes, mechanical clamping, and thin film deposition. These generally result in damaged, contaminated, bulky, and uncontrollable contact interfaces. Herein, we report a selfattachable, flexible, transparent, and conductive electrode (AF-TCE) that can simultaneously form strong mechanical adhesive contacts and low-resistant electrical contacts with diverse planar and curvilinear surfaces of flexible devices. The AF-TCE has a distinctive design of regular grid patterns into which bioinspired adhesive architectures and percolating Ag nanowires are integrated. Based on the integrated design, the AF-TCE can form low-resistant electrical ohmic contacts and ultra-clean, damage-free contact interfaces with active components of flexible devices by attaching it onto the components even when they are highly bent. Moreover, specific electronic circuits can be formed on the surface of the AF-TCE by depositing Ag nanowires selectively. This enables interconnections among the diverse electronic components on its surface. The advantages of the proposed AF-TCE are demonstrated by utilizing it for flexible electronics

The Rho-associated kinase inhibitor fasudil can replace Y-27632 for use in human pluripotent stem cell research.

Poor survival of human pluripotent stem cells (hPSCs) following freezing, thawing, or passaging hinders the maintenance and differentiation of stem cells. Rho-associated kinases (ROCKs) play a crucial role in hPSC survival. To date, a typical ROCK inhibitor, Y-27632, has been the primary agent used in hPSC research. Here, we report that another ROCK inhibitor, fasudil, can be used as an alternative and is cheaper than Y-27632. It increased hPSC growth following thawing and passaging, like Y-27632, and did not affect pluripotency, differentiation ability, and chromosome integrity. Furthermore, fasudil promoted retinal pigment epithelium (RPE) differentiation and the survival of neural crest cells (NCCs) during differentiation. It was also useful for single-cell passaging of hPSCs and during aggregation. These findings suggest that fasudil can replace Y-27632 for use in stem research