Gold-Coated Substrates
Does Platypus clean the substrates before coating them with gold?
All of our substrates are cleaned with oxygen plasma prior to coating.
Do I have to be careful not to scratch the gold on the substrates?
We use source gold that is 99.999% pure - the coatings essentially are "24-karat," which means that the surface is somewhat prone to being scratched if it is not handled carefully.
This is not a defect with the coating, it simply is the nature of this metal. Coating adhesion to
the substrate is excellent due to the thin titanium layer that is deposited between the substrate
and the gold layer. Our own researchers routinely wash gold-coated surfaces with a variety of solvents
with no problem.
Why does Platypus use titanium as the adhesion layer?
We use titanium, not chromium, as the adhesion layer, because chromium has been known to diffuse
into the overlying gold over time more quickly than titanium.
Which substrate provides the smoothest surface?
That depends. If you need a smooth substrate surface, choose Platypus� Gold-coated Silicon Wafers (AU.1000.SL1 or AU.1000.SL2). However, if you want the actual surface of the gold to be as flat as possible, choose Gold-coated Mica (AU.2000.MC1 or AU.2000.MC2) and thermally anneal it by flame or furnace. This will result in gold with atomically flat terraces. The Gold-coated aluminosilicate slides also allow for annealing to improve surface roughness.
Why might I want atomically flat terraces of gold on my substrates?
Flame annealed gold substrates can provide atomically flat terraces that may be used in many surface science fields including the following:
What is the orientation of the gold surface on the substrates (what lattice plane is 'up')?
On several substrates (glass, mica) evaporated gold shows a significant tendency, but not an absolute driver, to assume a <111> orientation, which can be greatly enhanced if the coating is properly annealed for a few hours at around 450°C. Deposited onto Silicon (100), however, the gold coating appears to be highly polycrystalline, with <111> orientation being perhaps marginally preferred. Please note that this information is derived from the literature (see below).
We measure ellipsometric constants for one substrate (not all of the substrates) from a given deposition. The constants are sent with the coated substrates when such data are requested by the customer at the time the original order is placed. This assumes that the coating being ordered is sufficiently reflective (i.e., thick) to allow ellipsometric measurements to be properly made.
Can I purchase glass microscope slides coated with just titanium
(and not gold)?
Yes, we can custom coat glass with just titanium. This will be a custom order.
Can I purchase gold-coated substrates that are gold coated but
without a titanium adhesion layer?
Yes, we can custom coat gold without titanium. This will be a custom order.
Glass Microscope Slides
Can I immerse gold-coated slides in thiol-based solutions?
Glass slides coated with 100/500 angstroms of gold over a thin titanium adhesion layer may
be immersed in a solution of 1.0 millimolar thiol in ethanol. The slides certainly may
be immersed for one hour at room temperature; however, they have also been immersed for
as long as 24 hours at room temperature with good success.
What are the glass specifications of the microscope slide substrates?
Glass Description and Specifications:
Mica
Can I cut the mica?
Gold-coated mica may be cut with either a sheet metal bench shear or a sharp pair of scissors.
We do not suggest using a scalpel or hobby knife as they might tear the coating along the edge
of the mica.
If you plan to anneal the gold and want to preserve this flatness as much as possible, we suggest that our standard mica substrates first be coated, then cut to size, then annealed. It may be of benefit to first cut to size prior to coating if preserving coating properties is absolutely critical.
Silicon Wafers
What is the difference between surface 'flatness' and surface 'roughness'?
Surface 'flatness' is typically measured from an imaginary plane across the center of the wafer.
Data points are then taken from that imaginary plane to the top surface of the wafer. The specification
is given as GTIR (Global Total Indicated Readout) which covers multiple data points across the wafer.
The typical GTIR for the wafers coated by Platypus (test grade wafers) is <15 microns. We can also custom coat 'prime grade wafers', which have a typical GTIR of <5 microns. Superflat wafers with a GTIR of <3 microns are also available for coating on a custom basis. This flatness can be achieved only with a double side polished wafer.
Surface 'roughness' is measured in angstroms rms. It is a measurement of the hills and valleys on the topical surface, polished side. This number is not specified or measured much for the typical semiconductor user. We cannot quote this specification for a test grade wafer; however, a standard of 20 angstroms rms or better for a prime grade wafer is a good approximation