PhD student DIYs super microscope to see atoms directly! Netizens: Too geeky, saving hundreds of thousands of yuan

Jin Leixiaocha from Aofei Temple
Quantum Bit Report | Public Account QbitAI

Scanning tunneling microscope (STM) may sound unfamiliar at first.

But its status in the scientific community is extraordinary - it allows humans to observe the local structure of the surface layer of single atoms , is an important tool in the field of nanotechnology, and has won a Nobel Prize.

There is no need to say much about the precision of the instrument.

Berard, a doctoral student from McGill University in Canada, made an STM at home and successfully "took" an image of graphite carbon atoms!

In terms of price , the price of a professional STM ranges from $30,000 to $150,000, but the cost for this doctoral student may only be around $1,000 !

This means you can save hundreds of thousands of dollars on equipment all at once, right?

This made netizens marvel:

This is too geeky!

STM Principle

The scanning tunneling microscope (STM) is a microscope with such high magnification that it can even see atoms on the surface of an object. Its principle is implied in its name.

Electrons are blocked when they encounter an insulator, just like a person encountering a wall. But when the insulator is thin enough, the role of quantum mechanics begins to emerge.

As the "wall" becomes thinner, electrons begin to be able to "pass through" the insulator and reach the conductor on the other side, as if a tunnel was opened in the insulator, hence the name tunnel effect.

△ Schematic diagram of quantum tunneling effect, some electrons pass through the wall to the right

Scanning tunneling microscope uses this principle.

When we apply voltage between the probe and the sample, the air between them acts as a wall. If the probe and the sample are close enough, electrons can jump through the air and reach the sample, and current will be generated in the circuit.

The magnitude of this current is related to the distance between the probe and the sample. The distance can be inferred based on the current magnitude, thereby obtaining the height data of the sample surface and drawing a microscopic image.

Although the STM principle is not complicated, there are still many technical difficulties in DIY.

First, to achieve atomic-level resolution, the probe tip must be fine enough, ideally with only one atom at the tip.

Secondly, the distance between the probe and the sample is very close, less than 1nm, and extremely weak thermal expansion or external vibration may cause the two to come into contact, resulting in the needle tip being destroyed.

The last challenge is how to accurately control the probe to scan on the plane.

How to DIY?

The production of STM probe is actually not complicated: take a platinum-iridium alloy wire or tungsten wire, cut it diagonally with wire cutters, and gently pull it to obtain the thinnest tip possible.

The next step is to make a vibration-damping table. The probe is fixed on three steel plates, which are bonded with rubber and then mounted on three long springs to minimize the resonant frequency of the system.

A magnet is also installed at the bottom of the steel plate. When the steel plate swings, the magnet will induce eddy currents on the aluminum block below, which in turn will generate a reverse magnetic field to suppress vibration.

The method to control the probe is to use piezoelectric ceramics. When voltage is applied to both ends of this material, it will expand and contract, and the amount of expansion and contraction is related to the size and direction of the voltage.

△ Longitudinal view of piezoelectric ceramics

△ Side view of piezoelectric ceramics

Piezoelectric ceramics are sandwiched between metal electrodes, and applying different voltages to the four areas can control the probe to move back and forth on the plane.

Since the tunnel current is very small, usually on the order of 1 nA, the acquired current signal must be amplified.

△ Probe current amplifier circuit

Berard also wrote a Windows software to control the scanning and output microscope images based on the current data. He also provides this STM control software and source code on his personal website.

He then used this homemade STM to scan materials such as gold, platinum, and graphite, and obtained very beautiful images.

about the author

The author of this project, Dan Berard , is a doctoral student at McGill University.

His research interests lie in nanotechnology and biophysics, with a focus on developing Convex Lens-Induced Confinement (CLiC) microscopy for linear expansion of DNA molecules for genomic analysis.

In addition, one of Berard's hobbies is DIY electronic products. As an extension of this, he co-founded ScopeSys with like-minded partners and served as co-founder and engineering director.

Netizen: Too geeky!

Berard's project has sparked quite a stir online.

While marveling at how he could DIY such a sophisticated instrument, some netizens also expressed their feelings about this "geek culture":

Geek culture is simply amazing!

People make all kinds of amazing machines at home, many of which have become world-class products and even changed human history.

But looking at the efforts Berard made here, it was not something that was accomplished "in one go", but rather took many years of hard work.

To this day, he still updates the progress of this project on his homepage.

Many netizens are also following his method to conduct experiments on their own. Berard will also actively respond and provide guidance to netizens on the bugs they encounter during the DIY process.

Do you also want to build a dedicated STM? Maybe you can try it yourself~

Reference links:
[1] https://dberard.com/home-built-stm/
[2] https://news.ycombinator.com/item?id=26740968
[3] http://e-basteln.de/other/stm/applications/