Nondestructive nanofabrication on Si(100) surface by tribochemistry-induced selective etching

Friction-induced selective etching on silicon by TMAH solution

Friction-induced selective etching provides a new thought direction in the field of nanotechnology with high resolution, low cost, flexibility and site control. In this work, it was found that the scratched area on a silicon surface can play a role as a mask against etching in tetramethyl ammonium hydroxide (TMAH) solution, resulting in the formation of protrusive hillocks. Friction-induced selective etching was found to depend on the temperature and etching time. The hillock height initially increased with the temperature or etching time, and then the hillock disappeared due to the mask etching off. In contrast, the applied normal load for scratching on silicon had little effect on the hillock height produced by selective etching in TMAH solution. Further analysis showed that crystal distortions or crystal amorphization could act as a mask against selective etching on silicon. Through control tip traces for scratching, different patterns can be produced on the silicon surface by friction-induced selective etching in TMAH solution. These results can enrich the fundamental aspects of scanning probe microscope (SPM)-based nanolithography, and provide an alternative method to produce nanostructures for various applications.

Friction-induced selective etching by TMAH solution was proposed for patterning a silicon surface with site control, high flexibility and low cost.

Fabrication of Nanoscale Pits with High Throughput on Polymer Thin Film Using AFM Tip-Based Dynamic Plowing Lithography

We show that an atomic force microscope (AFM) tip-based dynamic plowing lithography (DPL) approach can be used to fabricate nanoscale pits with high throughput. The method relies on scratching with a relatively large speed over a sample surface in tapping mode, which is responsible for the separation distance of adjacent pits. Scratching tests are carried out on a poly(methyl methacrylate) (PMMA) thin film using a diamond-like carbon coating tip. Results show that 100 μm/s is the critical value of the scratching speed. When the scratching speed is greater than 100 μm/s, pit structures can be generated. In contrast, nanogrooves can be formed with speeds less than the critical value. Because of the difficulty of breaking the molecular chain of glass-state polymer with an applied high-frequency load and low-energy dissipation in one interaction of the tip and the sample, one pit requires 65-80 penetrations to be achieved. Subsequently, the forming process of the pit is analyzed in detail, including three phases: elastic deformation, plastic deformation, and climbing over the pile-up. In particular, 4800-5800 pits can be obtained in 1 s using this proposed method. Both experiments and theoretical analysis are presented that fully determine the potential of this proposed method to fabricate pits efficiently.

Effect of crystal plane orientation on tribochemical removal of monocrystalline silicon

The effect of crystal plane orientation on tribochemical removal of monocrystalline silicon was investigated using an atomic force microscope. Experimental results indicated that the tribochemical removal of silicon by SiO₂ microsphere presented strong crystallography-induced anisotropy. Further analysis suggested that such anisotropic tribochemical removal of silicon was not dependent on the crystallography-dependent surface mechanical properties (i.e., hardness and elastic modulus), but was mainly attributed to various atomic planar density and interplanar spacing in different crystal planes. Phenomenological results speculated that higher density of silicon atom could promote the formation of Si-O-Si bonds between the SiO₂ microsphere and silicon substrate, resulting in more severe tribochemical material removal. Larger interplanar spacing with smaller energy barrier facilitated the rupture of the Si-Si network with the help of mechanical shearing stress, which caused more serious wear of the silicon surface. The results may help understand the material removal mechanism of silicon and provide useful knowledge for chemical mechanical polishing.

UV/ozone-assisted tribochemistry-induced nanofabrication on Si(100) surfaces

UV/ozone oxidation provides a simple and efficient method to prepare super-hydrophilic SiO_x films for tribochemistry-induced nanofabrication on Si substrates.

Temperature-Dependent Nanofabrication on Silicon by Friction-Induced Selective Etching

Friction-induced selective etching provides a convenient and practical way for fabricating protrusive nanostructures. A further understanding of this method is very important for establishing a controllable nanofabrication process. In this study, the effect of etching temperature on the formation of protrusive hillocks and surface properties of the etched silicon surface was investigated. It is found that the height of the hillock produced by selective etching increases with the etching temperature before the collapse of the hillock. The temperature-dependent selective etching rate can be fitted well by the Arrhenius equation. The etching at higher temperature can cause rougher silicon surface with a little lower elastic modulus and hardness. The contact angle of the etched silicon surface decreases with the etching temperature. It is also noted that no obvious contamination can be detected on silicon surface after etching at different temperatures. As a result, the optimized condition for the selective etching was addressed. The present study provides a new insight into the control and application of friction-induced selective nanofabrication.

Investigation of silicon wear against non-porous and micro-porous SiO2 spheres in water and in humid air

Tribochemical wear, a method to achieve controlled material removal without residual damage on substrates, plays a very important role in super-smooth silicon surface manufacturing.