Have Au nanowires defined by EBL electron beam lithography, 100 nm across and 18 nm deep, contacted by contact wires that expand from that 100 nm width to 10 um wide over 10 um.
Want to clean them of organics using an oxygen RF plasma, was thinking 40 W of power for 1 minute at 1.0 sccm of O2. I'm worried about roughening of the Au surface however, even though the Au shouldn't oxidize at equilibrium. I'm concerned that could damage the nanowires.
If anyone has relevant experience, I'd appreciate it!
Hi Darin,
40 W for 1 minute might not alter the surface roughness much (just an assumption). Yet, oxygen plasma can oxidize the Au surface. You might think of cleaning the nanowires by a combination of alkanethiols and hydrogen plasma. See Raiber et al., Surface Science 595 (2005) 56–63.
Cheers
Martin.
Thanks Martin!
That's valuable information, I was afraid of that. I'll see if I can put together a viable hydrogen alternative. Otherwise I'll try to keep the oxygen plasma exposure light. I was hoping that the Au oxide would rapidly reduce in air, leaving surface roughening as the only effect, but appears that there are oxides of Au stable beyond 100C.
Fortunately, oxidation of Au nanoparticles appears to be very slow, see Wu et al. http://pubs.acs.org/doi/abs/10.1021/jp301009f
Based on their results, at 40 W for 1 min we should see negligible oxidation. They only saw measurable Au oxide after more than 15 minutes at 160 W of power.
Control of the plasma conditions may be vital to the outcome of the experiment. We (and others) have done quite some experimentation on removing organics from transition metal and alloy nanoparticles using exposure to oxygen plasma first, and hydrogen plasma next. Results were controlled by element specific spectroscopy.
We found it nontrivial to control the plasma (home built apparatus) such as not to damage the nanoparticles and to securly avoid deposition of sputtered material from other parts of the vacuum chamber.
These procedures have also been applied to gold nanoparticles, and gold oxidation was actually seen in these experiments, with notable exceptions. Generally, I'd tend to believe that rf power and time of exposure is not what primarily matters, but rather the geometry and other parameters (potentials) which define the plasma.
Concerning the work I was involved with, you'll find it browsing my publications on RG. Concerning the Au related work, I enclose two links to references below.
http://www.sciencedirect.com/science/article/pii/S0039602800009869
http://www.sciencemag.org/content/297/5586/1533
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