1.Cutting and flame annealing gold on mica calibration samples for nano G Ben MacLeod Laboratory for Atomic Imaging Research Oct 1 2013
2.Why gold on mica? Crashing on gold may not ruin the tip as badly as crashing on graphite does Can do tip conditioning via field- emmission on gold (and perhaps also crashing and drawing out w/ bias?) Calibration of the STM against the herringbone reconstruction and atomic lattice of Au(111) is possible Ex-situ flame annealed gold is commonly used as a STM sample SPI sells these samples (~$150 each) http://www.2spi.com/catalog/gold-sub.shtml SPI and other suppliers recommend to use these kind of samples within a few months of receiving them ( ours are much older ) We already have one 10mm x 10mm and plan to cut it into 4 , 5mmx5mm samples
3.Cutting the mica Cutting mica is not so easy because it deforms, cracks and scratches very easily (kind of like a flaky, brittle plastic) We found cutting with small surgical scissors yielded an ok cut, with less edge cracking near the edges of the cut and deformation of the mica sheet We expect cutting mica to dull the scissors quite quickly and bought new ones for this job See SPI tips on cutting mica: ( http://www.2spi.com/catalog/submat/mica-information-cutting.html ) SPI die-cuts their mica substrates
4.Inspecting a gold-on-mica sample cut with small scissors -cracking -crushing -peeling of film?
5.Flame annealing the gold Flame annealing gold on mica using an H2 torch is thought to remove contaminants and increase the microscopic flatness of the gold film http://dx.doi.org/10.1116/1.581536 SPI provides instructions for flame annealing their gold on mica samples : http://www.2spi.com/catalog/gold-sub2.html The hydrogen flame is very hot (measured with a thermocouple to be around 600 deg. C at 5-6 cm from the flame )
6.Flame annealing procedure Put mica on a quartz block, weigh down with another Turn off lights Turn on hydrogen, light, turn up until hissing Turn on oxygen, turn up until flame is short and sharp (few mm dia , ~6cm long) Pre-heat quartz around mica (~10 seconds) Pass torch tip over sample at about 1 Hz while watching color of spot (ideally dim orange according to SPI) for about 30-45 s
7.1 st try at annealing Held the torch ~4cm from sample (~750 deg. C) Torch spot on sample got bright yellow/white Gold seemed to disappear, leaving only a pink outline where the edges of the patch of gold had been on the mica
8.2nd try at annealing Before After Held torch ~5 cm from sample (~650 deg. C) Torch spot got bright orange / yellow during this anneal Note white area that appeared (melted mica?) Note change in texture of gold
9.3rd try at annealing Before After Held torch ~6cm from sample (~600 deg. C) Torch spot got dull orange during this anneal Bubble-like defects appeared
10.4th try at annealing Before After Held torch ~6cm from sample (~600 deg. C) Torch spot got dull orange during this anneal Again, bubble-like defects appeared Note peeling of film from bottom right corner
11.5 th annealing (dry run) Tried to anneal even more gently
12.6 th run Annealed using hydrogen only flame Very broad flame, temperature slightly lower?
13.To do Ask Sarah about quality of sample Ask people from Bizzotto group what they think Try in STM!