#physics lab

A selection of evaporation sources in our cleanroom. Evaporation is a thin film deposition technique where the material is heated up to above its melting point in vacuum, typically using an electron beam. The molten material evaporates and is redeposited on your samples which are positioned near the source. Common materials that can be deposited using this technique include gold, copper, titanium, platinum, nickel, iron, silicon dioxide, and carbon.

Metal stock in our department’s machine shop.  Basic machining skills are often necessary to build an experiment, and so many experimental physicists are encouraged to take a course in machining.  The final project is to make a nut and bolt from scratch.

Ion gauges on one of our deposition systems.

Ionization gauges are commonly used to measure pressure in high vacuum. They look and operate very much like a light bulb. Electrons are emitted from a central heated filament (the glowing part) and accelerated toward a helical wire or “grid” around the filament. Some of these electrons collide with gas molecules and ionize them. The ions are then attracted to a collector filament, creating a current which can be measured. The magnitude of the ion current depends on the pressure and composition of the gas.

Aluminum target for our sputter system. If you look closely you can see individual crystal grains.

Sputtering is a technique used to deposit thin films of material. The material source is called a target because it is bombarded with high energy atoms which remove bits of material that are then redeposited on your sample or wafer. The ring is a result of the magnetic field confining the plasma to that region.

Sample stage controls for an ion mill, allowing for rotation about two different axes.

Ion milling is a type of dry etch process used to remove parts of a sample by bombarding it with ions, typically argon, in a vacuum chamber. It can be thought of as an atomic sand blaster. Ions (the “grains of sand”) physically expel, or sputter, chunks of material from the surface. The sample is rotated to ensure uniform coverage.

Some of the controls for our sputter system.

Patterned silicon wafers in the clean room.

Photolithography is a technique similar to photography used to make very small micron (~0.00004 inch) sized features.  Wafers are coated in light sensitive chemicals called photoresist and then certain areas are exposed to light to create a pattern. The processing room is lit with yellow light to avoid exposing the resist. Photolithography is commonly used to make integrated circuits in electronics, but it is also used in basic research in fields such as physics, material science, engineering, and even biology.

Electron beam lithography is a technique used to write nanometer-size features using a narrow beam of electrons to trace out the desired pattern on your sample.  This is a form of maskless lithography - custom patterns can be written without the need for a mask.  However, ebeam lithography has a low throughput and it is expensive, making it impractical for industrial purposes.  This form of lithography is mainly used in research, mask writing, and prototyping, rather than for mass producing devices. 

In the past, I have used this system to make nanowires that are less than 100 nm wide. This is 1/1000th the diameter of a human hair!

One of the older graduate students posted this near our sputter system.

Cryopump on a sputter system.

Cryopumps are a common type of high vacuum pump. They operate by condensing or freezing gases in the vacuum chamber onto an array that is typically cooled down to 10-12 kelvin. Compressed helium gas enters a chamber below the condenser array, where a piston (the displacer) allows the gas to expand, removing heat from the system. The piston then pushes the helium out and back into a compressor, and the cycle repeats. The displacer and compressor in a cryopump make a distinctive rhythmic high pitched whistle that is a common sound in clean rooms and condensed matter physics labs.

Togging room for our cleanroom.

Cleanrooms, often used in industrial and scientific research, are environments with a controlled number of particles of a certain size per unit area in the air. This is to prevent contamination of samples during fabrication - large particles can ruin electrical devices and decrease yield.

To decrease the number of particles in the air, researchers are required to wear full body “bunny suits” and certain particle-generating items, such as pencils and normal paper, are not allowed. The room is slightly pressurized and the flow of air is controlled to push particles toward the floor and out of the cleanroom.

Our cleanroom is Class 1000, meaning there is approximately 1/100th the number of particles in regular air.

A sputter system in our lab.