Synthesis of free-standing, curved Si nanowires through mechanical failure of a catalyst during metal assisted chemical etching

Abstract

The fabrication of orderly arrays of free-standing, curved Si nanowires over large areas (1 cm × 1 cm) was demonstrated by means of interference lithography and intentional mechanical failure of a perforated Au catalyst during metal assisted chemical etching. Photoresist microgrooves were deposited on the perforated Au film to cause uneven etching which resulted in the build-up of bending stresses in the Au film to the point of catastrophic failure. By considering the initial positions of the holes in the perforated Au film relative to the photoresist constraints, the precise location of the fracture can be predicted using simple beam mechanics. Therefore, the type of curved nanowires obtained can be designed with a high degree of reliability and control. Four distinct types of nanowire arrangements were demonstrated for this study.

Minimizing Isolate Catalyst Motion in Metal-Assisted Chemical Etching for Deep Trenching of Silicon Nanohole Array

“…The unbalanced etching can possibly be prevented by the use of isotropic spherical particles, so that the etch rate variations caused by catalyst thickness variation or transport processes are reduced . The importance of geometry in affecting catalyst motion is also shown by Hildreth and co-workers when they found that small or asymmetric catalysts are generally most prone to movement during etching. ,,, Asymmetric catalysts can cause differences in etch rates due to the differences in shapes or exposed edges that can better facilitate the transport of etchant/reactant. The explanation using unbalanced etch rates can also be compared against the model proposed by Sakdinawat and Chang. , The latter reported on the nonuniform distribution of electrons and holes (etch rates) in the deviation of the isolate catalyst, which is reduced when larger catalyst strips are placed near the isolate catalysts to reduce the carriers splaying effect. , Finally, we believe that the unbalanced etch rate explanation is also consistent with the suggestion that the perturbation from hydrogen gas produced during etching is the cause for catalyst motion .…”

“…29 The importance of geometry in affecting catalyst motion is also shown by Hildreth and co-workers when they found that small or asymmetric catalysts are generally most prone to movement during etching. 16,18,23,31 Asymmetric catalysts can cause differences in etch rates due to the differences in shapes or exposed edges that can better facilitate the transport of etchant/reactant. The explanation using unbalanced etch rates can also be compared against the model proposed by Sakdinawat and Chang.…”

“…The latter scales with the size of the mesh, and thus a larger mesh requires a larger minimum force for deviating the catalyst motion . Hildreth et al found from deformation calculation that such a force should be at least ∼0.5 MPa while Lai and Choi estimated a value of ∼2.5 MPa for larger gold (Au) mesh. , Isolate catalyst, especially of smaller dimensions, requires much less minimum bending torques, and thus catalyst motion during etching is a common and persistent problem. ,− This poses a significant road block to the potential applicability of MacEtch in high aspect ratio hole etching in the field of biological/water filters, nanophotonics, and the through-silicon-via etching …”

Bacterial Attachment, Aggregation, and Alignment on Subcellular Nanogratings

“…The procedure for the fabrication of Si nanogratings in this study is similar to that previously reported for the synthesis of nanostructures on silicon (Si) and polymeric substrates. − Briefly, P-type (100) Si wafers were first cleaned with acetone and dipped in hydrofluoric acid (HF) for 60 s to remove the native oxide. Four hundred nanometers of Ultra-i-123 positive photoresist was then spin coated onto the surface and baked at 110 °C for 90 s. The wafers were diced into 1 cm × 1 cm samples and exposed to interference lithography using a He–Cd laser with a wavelength of 365 nm.…”

Kinked silicon nanowires-enabled interweaving electrode configuration for lithium-ion batteries

“…Under these conditions, the etching follows non-<100> directions (Figures S1 and S2 ). It was reported that at high ε, the amount of generated holes increases and can polarize more Si back-bonds resulting in non-<100> etching 31 , 36 . To generate the high aspect ratio k-SiNWs, the etching was quenched every 5 minutes by immersing the Si substrate in methanol.…”