Chenfei Song

Fabrication mechanism of friction-induced selective etching on Si(100) surface.

As a maskless nanofabrication technique, friction-induced selective etching can easily produce nanopatterns on a Si(100) surface. Experimental results indicated that the height of the nanopatterns increased with the KOH etching time, while their width increased with the scratching load. It has also found that a contact pressure of 6.3 GPa is enough to fabricate a mask layer on the Si(100) surface. To understand the mechanism involved, the cross-sectional microstructure of a scratched area was examined, and the mask ability of the tip-disturbed silicon layer was studied. Transmission electron microscope observation and scanning Auger nanoprobe analysis suggested that the scratched area was covered by a thin superficial oxidation layer followed by a thick distorted (amorphous and deformed) layer in the subsurface. After the surface oxidation layer was removed by HF etching, the residual amorphous and deformed silicon layer on the scratched area can still serve as an etching mask in KOH solution. The results may help to develop a low-destructive, low-cost, and flexible nanofabrication technique suitable for machining of micro-mold and prototype fabrication in micro-systems.

Maskless and low-destructive nanofabrication on quartz by friction-induced selective etching.

A low-destructive friction-induced nanofabrication method is proposed to produce three-dimensional nanostructures on a quartz surface. Without any template, nanofabrication can be achieved by low-destructive scanning on a target area and post-etching in a KOH solution. Various nanostructures, such as slopes, hierarchical stages and chessboard-like patterns, can be fabricated on the quartz surface. Although the rise of etching temperature can improve fabrication efficiency, fabrication depth is dependent only upon contact pressure and scanning cycles. With the increase of contact pressure during scanning, selective etching thickness of the scanned area increases from 0 to 2.9 nm before the yield of the quartz surface and then tends to stabilise after the appearance of a wear. Refabrication on existing nanostructures can be realised to produce deeper structures on the quartz surface. Based on Arrhenius fitting of the etching rate and transmission electron microscopy characterization of the nanostructure, fabrication mechanism could be attributed to the selective etching of the friction-induced amorphous layer on the quartz surface. As a maskless and low-destructive technique, the proposed friction-induced method will open up new possibilities for further nanofabrication.

Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching

In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface.

Nondestructive tribochemistry-assisted nanofabrication on GaAs surface

A tribochemistry-assisted method has been developed for nondestructive surface nanofabrication on GaAs. Without any applied electric field and post etching, hollow nanostructures can be directly fabricated on GaAs surfaces by sliding a SiO2 microsphere under an ultralow contact pressure in humid air. TEM observation on the cross-section of the fabricated area shows that there is no appreciable plastic deformation under a 4 nm groove, confirming that GaAs can be removed without destruction. Further analysis suggests that the fabrication relies on the tribochemistry with the participation of vapor in humid air. It is proposed that the formation and breakage of GaAs-O-Si bonding bridges are responsible for the removal of GaAs material during the sliding process. As a nondestructive and conductivity-independent method, it will open up new opportunities to fabricate defect-free and well-ordered nucleation positions for quantum dots on GaAs surfaces.

Rapid and maskless nanopatterning of aluminosilicate glass surface via friction-induced selective etching in HF solution

Protrusive nanostructures were fabricated with the proposed friction-induced selective etching method, which involves the combined techniques of scanning with an atomic force microscopy diamond probe and selective etching in HF solution. Various patterns, including slope and hierarchical stages, were produced by programming the loading mode and scanning traces. The height of such nanostructures increased as the scan load and number of scan cycles increased. X-ray photoelectron spectroscopy analysis indicated that the mechanism of the friction-induced selective etching should be attributed to the formation of AlF3 on the fabrication area during HF etching. Given that the friction-induced selective etching could be completed in several seconds without any templates, the proposed method may provide high efficiency and serve as a convenient nanofabrication technique for glass.

Nanotribological behaviors of friction-induced hillocks on monocrystalline silicon

With an atomic force microscope, friction and wear behaviors of the friction induced hillocks on monocrystalline silicon were investigated. With the increase of normal load from one to twelve microNewtown, the friction force on silicon substrate showed a sharp increase at eight microNewtown, while the friction force on the hillocks kept a stably linear increase. Since no scratch damage was detected on the hillock below a contact pressure of ten point three gigaPascal, the friction induced hillocks on silicon can withstand the typical contact and sliding in dynamic devices. It was also noted that the friction induced hillock presented anisotropic friction and wear behaviors during scratching. The sliding parallel to the scanning direction for producing the hillock can reduce the friction in dynamic devices. This study can shed new light on potential application of the friction induced nanostructures.