Due to chemical etching, the surface energy is reduced [11] and the surface geometry is reconstructed [12]. Both sides will be conducive to the enhancement of intrinsic hydrophobic surface.

Local surface roughness is considered relevant to surface hydrophobicity [13]. We can use different chemical and physical approaches, such as nanocoating materials [14], femtosecond laser irradiation [15], photolithography [16, 17], etc., to modify surfaces, leading to the enhancement of surface hydrophobicity. Usually, selleck products these methods are complicated. In this paper, we report a hydrophobic property of black silicon surface. The micro- and nanospikes are prepared by metal-assisted wet chemical etching, without any complex nanomaterial coating deposition. Methods N-type single-crystal silicon wafers (100) with a resistivity of 6 to 8 Ω cm were cleaned by RCA standard cleaning procedure with each step for 15 min. After cleaning, the wafers were etched with HF in order to remove the unwanted native oxide layer. In the following step, the wafers were etched in

a mixed solution containing H2O2, C2H5OH, H2O, HF, and HAuCl4 with a typical ratio of 10:4:4:2:1, resulting in pores. This treatment occurred at room temperature for 8 min. As a control, one beaker (marked as A) was placed in a digital constant temperature water bath (HH-2, Guohua Electric Devices, Changzhou, China) and set at room temperature. The other (marked as B) was laid in a heat collection-constant temperature type magnetic stirrer (HCCT-MS; DF-101S, Wuhan, Sensedawn Selleck PLX3397 Science &Technology, Wuhan, China) at the same temperature. The samples in the beakers were correspondingly signed as A and B. The morphology of the textured silicon was characterized using a scanning electron microscope (SEM; JSM-5900 Lv, JEOL, Tokyo, Japan). An atomic force microscope (AFM; SPA-400 SPM UNIT, DAE HWA NI Tech, Pyeongtaek-si, South Korea) was used to characterize the topology of the black silicon in tapping mode. A UV-visible-near-infrared (UV–vis-NIR) spectrophotometer (UV-3600, Shimadzu, Tokyo, Japan) with an integrating sphere detector was used to measure the total (specular and diffuse) reflectance (R) and transmittance (T). The static contact

angles (CAs) were measured by capturing images of deionized water droplets using a drop shape Molecular motor analysis system, referred to as a sessile drop method. With a software equipped with an optical contact angle measuring instrument (OCAH200, Data Physics Instruments, Filderstadt, Germany), the CA values between the tangent of the drop and the horizontal plane at the point of contact with the black silicon surface were calculated. The mean value was calculated from at least four individual measurements, and each individual measurement contains independent values of the left and right contact angles. Results and discussion In the metal-assisted chemical etching procedure, the Si substrate is subjected to an etchant, which is composed of HF and H2O2 compound.