Nadine Geyer

Bio: Nadine Geyer is an academic researcher from Max Planck Society. The author has contributed to research in topics: Nanowire & Etching (microfabrication). The author has an hindex of 13, co-authored 20 publications receiving 2463 citations. Previous affiliations of Nadine Geyer include Martin Luther University of Halle-Wittenberg.

Metal-Assisted Chemical Etching of Silicon: A Review

Abstract: This article presents an overview of the essential aspects in the fabrication of silicon and some silicon/germanium nanostructures by metal-assisted chemical etching. First, the basic process and mechanism of metal-assisted chemical etching is introduced. Then, the various influences of the noble metal, the etchant, temperature, illumination, and intrinsic properties of the silicon substrate (e.g., orientation, doping type, doping level) are presented. The anisotropic and the isotropic etching behaviors of silicon under various conditions are presented. Template-based metal-assisted chemical etching methods are introduced, including templates based on nanosphere lithography, anodic aluminum oxide masks, interference lithography, and block-copolymer masks. The metal-assisted chemical etching of other semiconductors is also introduced. A brief introduction to the application of Si nanostructures obtained by metal-assisted chemical etching is given, demonstrating the promising potential applications of metal-assisted chemical etching. Finally, some open questions in the understanding of metal-assisted chemical etching are compiled.

Model for the Mass Transport during Metal-Assisted Chemical Etching with Contiguous Metal Films As Catalysts

Abstract: Metal-assisted chemical etching is a relatively new top-down approach allowing a highly controlled and precise fabrication of Si and Si/Ge superlattice nanowires. It is a simple method with the ability to tailor diverse nanowire parameters like diameter, length, density, orientation, doping level, doping type, and morphology. In a typical metal-assisted chemical etching procedure, a Si substrate is covered by a lithographic noble metal film and etched in a solution containing HF and an oxidant (typically H2O2). In general, the function of the metal is to catalyze the reduction of H2O2, which delivers electronic holes necessary for the oxidation and subsequent dissolution of the Si oxide by HF. However, the details of the etching process using contiguous metal thin films, especially the mass transport of reactants and byproducts are still not well understood. In this study, the etching mechanism was systematically investigated. Several models of metal-assisted chemical etching using a contiguous metal film...

Oxidation Rate Effect on the Direction of Metal-Assisted Chemical and Electrochemical Etching of Silicon

Abstract: Assisted by noble metal particles, non-(100) Si substrates were etched in solutions with different oxidant concentrations at different temperatures. The etching directions of (110) and (111) Si substrates are found to be influenced by the concentration of oxidant in etching solutions. In solutions with low oxidant concentration, the etching proceeds along the crystallographically preferred ⟨100⟩ directions, whereas the etching occurs along the vertical direction relative to the surface of the substrate in solutions with high oxidant concentration. These phenomena are found for both n- and p-type substrates as well as in experiments with different oxidants. The experiments on metal-assisted chemical etching are complemented by additional experiments on metal-assisted electrochemical etching of (111) Si substrates with different current densities. As a function of current density, a change of etching directions is observed. This shows that the change of the etching directions is mainly driven by the oxidati...

Sub-100 nm silicon nanowires by laser interference lithography and metal-assisted etching

Abstract: By combining laser interference lithography and metal-assisted etching we were able to produce arrays of silicon nanowires with uniform diameters as small as 65 nm and densities exceeding 2 × 107 mm − 2. The wires are single crystalline, vertically aligned, arranged in a square pattern and obey strict periodicity over several cm2. The applied technique allows for a tailoring of nanowire size and density. Using a controlled and scalable process to fabricate sub-100 nm silicon nanowires is an important step towards the realization of cost-effective electronic and thermoelectric devices.

Metal-assisted electrochemical etching of silicon.

Abstract: In this paper the metal-assisted electrochemical etching of silicon is introduced. By electrochemical measurement and sequent simulation, it is revealed that the potential of the valence band maximum at the silicon/metal interface is more negative than that of the silicon/electrolyte interface. Accordingly, holes injected from the back contact are driven preferentially to the silicon/metal interface. Consequently, silicon below metal is electrochemically etched much faster than a naked silicon surface without metal coverage. Metals such as Ag and Cu have been utilized to catalyze the electrochemical etching. Feature sizes as small as 30 nm can be achieved by metal-assisted electrochemical etching. Meanwhile, the metal-assisted electrochemical etching method enables convenient control over the etching direction of non-(100) substrates, and facilitates the fabrication of orientation-modulated silicon nanostructures.

Metal-Assisted Chemical Etching of Silicon: A Review

Abstract: This article presents an overview of the essential aspects in the fabrication of silicon and some silicon/germanium nanostructures by metal-assisted chemical etching. First, the basic process and mechanism of metal-assisted chemical etching is introduced. Then, the various influences of the noble metal, the etchant, temperature, illumination, and intrinsic properties of the silicon substrate (e.g., orientation, doping type, doping level) are presented. The anisotropic and the isotropic etching behaviors of silicon under various conditions are presented. Template-based metal-assisted chemical etching methods are introduced, including templates based on nanosphere lithography, anodic aluminum oxide masks, interference lithography, and block-copolymer masks. The metal-assisted chemical etching of other semiconductors is also introduced. A brief introduction to the application of Si nanostructures obtained by metal-assisted chemical etching is given, demonstrating the promising potential applications of metal-assisted chemical etching. Finally, some open questions in the understanding of metal-assisted chemical etching are compiled.

Silicon-based Nanomaterials for Lithium-Ion Batteries - A Review

Abstract: There are growing concerns over the environmental, climate, and health impacts caused by using non-renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium-ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid-electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described.

An 18.2%-efficient black-silicon solar cell achieved through control of carrier recombination in nanostructures

Abstract: The efficiency of solar cells with high-area, nanostructured surfaces is limited by surface and Auger charge-recombination processes, which can be slowed through appropriate levels of junction doping

Porous One-Dimensional Nanomaterials: Design, Fabrication and Applications in Electrochemical Energy Storage.

Abstract: Electrochemical energy storage technology is of critical importance for portable electronics, transportation and large-scale energy storage systems. There is a growing demand for energy storage devices with high energy and high power densities, long-term stability, safety and low cost. To achieve these requirements, novel design structures and high performance electrode materials are needed. Porous 1D nanomaterials which combine the advantages of 1D nanoarchitectures and porous structures have had a significant impact in the field of electrochemical energy storage. This review presents an overview of porous 1D nanostructure research, from the synthesis by bottom-up and top-down approaches with rational and controllable structures, to several important electrochemical energy storage applications including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and supercapacitors. Highlights of porous 1D nanostructures are described throughout the review and directions for future research in the field are discussed at the end.