Methyl monolayers improve the fracture strength and durability of silicon nanobeams

Abstract

Micro-fabricated channel with ultra-thin yet ultra-strong windows enables electron microscopy under 4-bar pressure Applied Physics Letters 100, 081903 (2012);

Fracture strength of micro- and nano-scale silicon components

“…For instance, Alan et al examined the strength distributions of SCS notched nanobeams with hydrogen-terminated surfaces as a function of the number of days after release and found that r f decreased by 30% over the first 23 days after release. 176 Unexpectedly, m did not vary with time, indicating that only r h , and not the form of the r f distribution, was sensitive to the environmental conditions. It was noted that this observation is particularly concerning because it is common practice to finish the MEMS process with a HF-release step that renders components susceptible to this subsequent degradation.…”

“…Alan and Zehnder also used this test method to examine the role of surface chemistry on r f . 176 Both hydrogen-terminated and methyl-terminated SCS beams were fabricated and tested; to produce the methyl-terminated beams, hydrogenterminated beams were exposed to Cl 2 at 3 Torr, illuminated with a 254 nm pen lamp for 3 min, refluxed in methyl Grignard reagent under a constant Ar flow for 2.5 h, and then rinsed in anhydrous methanol and water.…”

“…For this reason, there are relatively few studies that have explored in detail the mechanisms governing mechanical reliability of Si MEMS under elevated temperatures or shock loading. For example, there is still no mechanistic explanation for why the strength of Si MEMS evolves significantly over the first few months after release, 176 and likewise controversy persists over the role of humidity on the fatigue strength. Yet there are already device packaging and application scenarios in which Si MEMS are challenged to survive sustained temperatures or dynamic loading or both.…”

Stronger silicon for microsystems

“…For example, Alan et al [25] has shown that the strength of single-crystal Si with hydrogen-terminated surfaces degrades by as much as 30% during the first month of air exposure after release. However, microfabricated single-crystal Si that has been coated with a methyl monolayer is initially stronger than H-terminated single-crystal Si and shows no degradation after a month of exposure to air.…”

Micro-fabricated channel with ultra-thin yet ultra-strong windows enables electron microscopy under 4-bar pressure

“…Mechanical properties of materials depend critically on process parameters and dimensional scales (higher strengths are expected for smaller sizes). [9][10][11] The nanoreactor is a multi-scale device with electron transparent windows that are 100 times thinner than the chamber ceilings. What are the maximum pressures which (2012) can be sustained by the thick chamber ceilings and ultra-thin windows during operation?…”