g., H2O2 or AgNO3) to form the nanostructures. Nanoparticles or thin films of noble metals (e.g., Au, Ag, or Pt) are used to catalyze the etching. Two-level nanoscaled porous Si nanowires were even synthesized with highly doped Si using MaCE, and Ag nanoparticles acted as JNK-IN-8 catalyst [15–17]. Zigzag Si nanowires were fabricated with (111)-oriented Si by MaCE (with Ag nanoparticles as catalyst) [18]. These zigzag Si nanowires were even fabricated
with (100)-oriented Si by a two-step MaCE (with Au film as catalyst) [19]. In general, the structural properties and morphologies of the nanostructured Si produced by MaCE are affected by three main factors: (1) the properties of the deposited noble metals, including the type and form of the metal, and its deposition method; (2) the properties of the Si wafer, including the doping type and level and the crystallographic this website orientation; and (3) the properties of the etchant, including etchant composition, concentration,
and temperature. By combining MaCE with nanolithography, many ordered nanostructures were fabricated. For example, ordered arrays of Si nanowires and nanopillars were fabricated using a combination of laser interference lithography or nanosphere lithography and MaCE [20–22]. An Au/Ag bi-layer metal mesh with an array of holes, prepared from an Wortmannin nmr anodic aluminum oxide membrane, was used to fabricate Si nanowires by MaCE [23]. In this paper, the fabrication selleck products of ordered arrays of nanoporous Si nanopillars, ordered arrays of nanoporous Si nanopillars with nanoporous base, and Si nanopillars with nanoporous shells using a combination of substrate conformal imprint lithography (SCIL) and MaCE (with Au film as catalyst) is presented. The mechanisms of MaCE are systematically investigated, and the fabricated nanoporous pillars should have the potential
for applications in sensors and optoelectronics. Methods The fabrication process is schematically represented in Figure 1a. As shown in Figure 1b, an array of elliptical pillars with hexagonal symmetry was defined using SCIL on two types of (100)-oriented p-Si wafers: one is highly doped (B-doped, ρ < 0.005 Ω cm), and the other is lightly doped (B-doped, ρ = (6.0−10.5) Ω cm). The periodicity (the distance between two adjacent pillars) is 1.0 μm, and the major and minor diameters of the ellipses are 613 and 385 nm, respectively. SCIL was developed by Philips Research and SÜSS MicroTec as a new technique of nanoimprint lithography, and this new technique possesses the advantages of both UV nanoimprint lithography techniques with a rigid stamp for best resolution and with a soft stamp for large-area patterning [24]. Two steps of reactive ion etching (RIE) were performed to transfer the structure into the Si substrate: the residual layer of the resist was removed using inductively coupled plasma RIE, and then the structure was transferred into the Si using RIE.