Sample holder assembly instructions

Required materials: 1/32” spring pins (McMaster-Carr part #93740A005) .057” OD stainless steel compression springs (Lee Spring part #CI 006A 01 S) 3D printed base and clamps (see this post.) Wire cutters File Tweezers The sample base should be free standing while multiple clamps can be printed onto one piece. The clamps are cut out with wire cutters. There may be residual material sticking out after cutting out the piece, but the material can be filed down

Camera mount for CF-2.75

This is a hinged plastic clamp that attaches to the outside of a 2.75” Conflat flange, serving as a mount for a small digital camera for in-chamber inspection. We used a $15 camera (from China via Amazon) intended to be used as an after-market vehicle backup camera. It comes with built-in LED lighting and works beautifully (when it works – we bought two and one had its LEDs die after a month or so of intermittent use – but at the price we won’t complain.

Electrometer build instructions

Preface to the tutorial: This tutorial is written in such a way that beginners to DIY electronics can follow along; more experienced builders may not need many of the steps. We’d be happy to discuss rationale for component selection and other design choices over e-mail. Also e-mail if you’d like us to send you printed circuit boards, as we have a few extras we can give away. What you will need: Box enclosure (Hammond 1590A) Box enclosure (Hammond 1590Q) 3 printed circuit boards (see this post) Reasonably thin wire Soldering iron Solder Shunt Jumpers 3/8” 6⁄32 threaded (both sides) standoffs (x4) 1/4” 6⁄32 threaded socket head screws (x12) 1/2” 4⁄40 threaded (both sides) standoffs (x2) 1/2” 4⁄40 threaded hex screws (x4) 1/8” 2⁄56 threaded hex screws (x12) Small-pattern 2⁄56 hex nuts (x12) Electrometer Circuit: BNC Connector BNC 2-Hole standoff (3D-printed) JP2 - JP8 - M jumper pins JP1 - F jumper pins Integrated Circuits IC1 - INA116 IC2 - AMP02 IC3 - OP07D IC4 - MAX6225 Resistors R1, R2, R11 - 10 KΩ R3 - 505 Ω R4 - 20 KΩ (Trim) R5 - 5.

Tip grabber

Of all the parts of the STM, the tip grabber was probably the most difficult to design and went through the most iterations. The idea is that the grabber will be loaded into the microscope like a sample holder, at which point its pincers will open to release a tip into the microscope, or close to remove one. The pincers need to open as wide as possible, but there’s very little space for the mechanism … this is our best solution so far.

Sample holders (and grabber)

This is our 3D-printed sample holder, printed in metal as a base piece and two clamping pieces. The clamps pivot on 1⁄32” spring pins (from McMaster-Carr) and derive clamping force from extremely small 0.057” OD stainless steel compression springs (from, of all places, Amazon.com). We use a magnetically coupled linear-rotary motion feedthrough to move samples in and out of the microscope. The sample grabber here has pincers that hold onto the back knob of the sample holder.

Piezo assembly

This is the single-tube STM scanner design currently in use in the Kandel lab. The tip sits in a carrier made from 1/16” OD capillary tube, and the tube rests on four ball bearings that are press fit into a metal frame. Coarse motion then comes from inertial slip-stick cycles driven by the scanning piezo. Three thumb screws around the perimeter of the base are used for initial alignment of the scanner in the XY plane, relative to a larger ceramic tube that supports the scanner assembly.

Transimpedance amplifiers

We recently published “Circuit design considerations for current preamplifiers for scanning tunneling microscopy” (link). We consider the standard feedback transimpedance design: We considered the IC used for the operational amplifier, the composition of resistor R1, and the value of capacitor C1. The capacitor C1 is required to prevent the circuit from going into unstable oscillations, at the cost of limiting the bandwidth of the amplifier. We found a value of 5 pF was sufficient for all of the op amps we tested, but a value of 1-2 pF could be used for the LT1169, which was also one of the lowest-noise ICs.

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