The surface quality of the thin films is tested using either atomic force microscopy (AFM) or scanning tunnelling microscopy (STM).
Atomic Force Microscopy
The next tree images are AFM images with lateral size respectively of 1.6 μm x 1.6 μm, 1.1 μm x 1.1 μm and 1.1 μm x 1.1 μm. The z scale is 5 nm for the first image and 3 nm for the last two.
Scanning Tunneling Microscopy
The next image is a 0.5 μm x 0.5 μm STM image of a 2 month old sample kept inside its box. The Z scale is 2 nm.
The size of the terraces may vary from one sample to another. We observe sometime terraces as large as 1 μm2. During the production process, we regularly control the surface quality of our films.
Epitaxial Au(111) thin films are grown in controlled high vacuum deposition systems using a magnetron sputtering technique. Details on the deposition technique can be found here. The gold source target is made of pure gold 99.99%. The films are grown at high temperature in a controlled argon atmosphere.
Epitaxial growth of thin films refers to extended single-crystal film formation on top of a crystalline substrate. The structural crystalline quality of the films is checked by X-ray-diffraction analysis. The next figure shows an example of a θ-2θ X-ray analysis performed on a typical 70nm thick gold film.
The analysis shows a pure (111) growth with a c-axis lattice parameter of 2.36 Å. Moreover, the finite number of diffracting planes leads to oscillations of diffracted intensities whose period is related to the layer thickness. The occurrence of these oscillations around the (111) reflection indicates a high degree of crystallinity of the samples and allows us to precisely control the thickness of the films.
Substrates
Phasis gold thin films are grown on high grade muscovite mica sheets freshly cleaved. The quality of the mica is classified from V-1 to V-10 according to the ASTM international standard. V-1 is considered as the best quality. It is a visual system of classifying the quality of natural muscovite mica based upon relative amounts of visible foreign inclusion. At Phasis we are using muscovite mica with quality higher of equal to V-2. The mica sheets are cleaved just before their introduction into the deposition system. The thickness of the final cleaved mica sheets may vary from 0.080mm to 0.130mm. The mica cleaving process is of random nature and the final thickness of the mica sheets cannot be controlled with better accuracy.
Gold size and thickness
Phasis offers the gold films in various geometries and sizes. The largest gold deposited region is 2 cm x 2 cm and the smallest 4 mm x 4 mm. The complete list of available geometries can be found under products.
Cutting a gold thin film grown on mica into smaller parts degrades the gold surface. Mica is indeed a very hard material and thus difficult to cut. With the different proposed geometries, the cutting process becomes easier because it can be done in-between the gold areas without damaging the gold surface. It is thus possible to maximise the number of possible measurements. Do not hesitate to contact us if you have a request for a special gold geometry not proposed in our list. If you need cutting tools, you can get at Phasis special scissors with a titanium nitrate coating layer improving the cutting process. These scissors are very useful to cut thin sheets of mica.
The typical gold thickness we provide is 200 nm. With our experience, we know that 200 nm thick films present good surface quality. We can grow thinner of thicker films upon request. For very thin film however, the gold surface will present islands with holes in-between, the film being not thick enough to allow a better covering.
Shelf life
We observe that the quality of the gold surface degrades with time due to some contamination. In order to slow down this process, we package the gold thin films in pure nitrogen immediately after the deposition process. This procedure allows the extension of the shelf life of the product to three to four months. All our films are freshly grown, we keep no stock of this product and we strongly recommend the use of the films in a short time scale after reception.
Cutting tools
Phasis provides special scissors: the Swissors 500 made by Wenger SA, a Swiss company producing the Swiss army knife.
Mica is a very hard material and thus difficult to cut. Mica pieces are usually prepared by die cutting with special carbide tools that are not available to our customers cutting mica in the laboratory. To help our customers who need to cut mica, Phasis provides special scissors made by Wenger SA, a Swiss company fabricating the famous Swiss army knife. The scissors have blades with a titanium nitride coating layer improving the cutting process. With those scissors you will minimise the edge fracturing on the mica compared to the cutting with standard scissors. Phasis also provide separated blades that can be changed on the scissors once the blades are worn out.
| Catalog # | Product | Description | Picture | |
|---|---|---|---|---|
| 50020010 | Swissors 500 | Scissors with blades for the gold on mica products |  |
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50020011 |
Separated blades for Swissors 500 |
Separated blades for the scissors for the gold on mica products |  |
Precautions
While cutting mica, wear adequate eyes protections. Customers have to be cautious not to touch or destroy the gold surface and to minimise the number of particles falling onto the gold surface during the cutting process. Pay also attention not to bend the samples during the cutting process.
Tweezers
Phasis also provides special tweezers made by Ideal-Tek SA, another Swiss company. These tweezers are ideal for the gold on mica products. They have indeed very fine tips made of plastic with a high rigidity and good chemical resistance. With these tips you will reduce the possibility scratching or destroying your samples while being able to hold your sample in a secure way.
Phasis also provide tweezers for the Bionano gold products.
| Catalog # | Product | Description | Picture | |
|---|---|---|---|---|
| 50030010 | tweezers | Tweezers for the gold on mica products |  |
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| 50030011 | tweezers | Tweezers for the BioNano gold products |  |