Tetsuo Hanaguri has been devoted to develop instruments, particularly low-temperature scanning tunneling microscope (STM). I always take a lot of work to buy appropriate materials, to find good machine shops and to find tips for handicraft. Followings are part of my experiences. If you would like to know more about these, please feel free to email me. I would like to hear your feedback as well.

Remarks on cryogen use

Presentation file (PowerPoint 1.8MB) which I present every year at the orientation seminar of nano-science lab. in RIKEN.

Technical drawings of our STM unit

• All joints are glued with Epotek H74.
• Outside of the part #3 is covered with gold film made from Noritake resinate paste D-24 for shielding.
• Assembly manual is here. (Sorry, in Japanese...)
• Leaf springs on the main unit push 3.5mm-diameter sapphire balls.
• Leaf springs on the chuck push 1.5mm-diameter carbide balls.

Piezo tube design

It is very important to enhance the mechanical resonant frequency of the scanning piezo tube for stable STM operation. You should pay attention to the loaded mass at the end of the tube (tip holder etc.) because even small mass suppresses the (bending) resonant frequency. This is an MS-Excel worksheet which calculates the resonant frequency and scan area of the tubes made of various PZT materials. (If you want to try this, please use it at your own risk.)

UHV-compatible soldering

Low-outgas conductive epoxy such as Epotek H20E can be used for UHV-compatible wire connection. But, of course, soldering is much easier. Unfortunately, good-and-old Pb-Sn solder is not UHV compatible. I have been using indium to attach the wires to the piezo tube and Castolin Eutectic 157 for UHV compatible soldering. In both cases, fluxing is necessary but commercial fluxes are usually toxic and contain unknown materials. Try lactic acid as flux. Lactic acid consists of C, H and O and is not toxic. Lactic acid can easily be removed by rinsing with water.

Wires

• California Fine Wire provides various magnet wires which are suitable for low-temperature ultrahigh-vacuum wiring and heaters.
• Cooner wire Inc. provides thin custom coax cables.

Machining ceramics

• Otsuka Seiko Co. Ltd. (in Japanese) can make an M1.6 threaded hole into SiC.
• Sartonworks Co. Ltd. (in Japanese) can make an M1.6 threaded hole into sapphire.

Cutting tungsten wires

Tungsten is a common material for STM tips. In various cases, you may want to cut tungsten wires. If you use a conventional wire cutter, wires tend to split off and the cutter is easily damaged. Use a tungsten-carbide tipped cutter. This is expensive but works perfectly.

I am using MEISEI HOTweezers(R) for teflon coated wires and it works perfectly. But HOTweezers(R) is not good for polyimide coated (ML) magnet wires and I should use razor blade etc. If you know a good method to strip ML wires, please let me know...