EVAPORATED CARBON FOILS
These are ultra-thin carbon foils having natural isotopic composition, made by evaporation from a vacuum arc onto glass microscope slides or other substrates. They are also known as SEM foils, TEM foils, stripper foils, and carbon slides. The foils are amorphous or nanocrystalline, with atomic binding primarily sp2, i.e., graphitic.
CARBON STRIPPER FOILS MOUNTED ON FORKS
Accelerators often use stripper foils to remove electrons from ions during or after the acceleration process. Carbon is usually the element of choice because of its strength and its low Z (atomic number Z = 6). For these purposes, foils may be mounted on special fork-shaped or L-shaped frames so that the foil has one or more free edges; in this way a beam of negative ions may be steered through the foil without the ions’ passing through a massive frame. Emgrid would be pleased to quote on producing foils on other mountings suggested by the customer.
POLYCRYSTALLINE GRAPHITE FOILS (PCG FOILS)
Thin polycrystalline graphite (PCG) free-standing foils are made by proprietary methods that yield foils composed of graphite microcrystals having natural isotopic composition and grain sizes of the order of 1 micrometer, aligned primarily (but not entirely) with their c-axes parallel to the foil’s normal. They have several advantages over standard (arc-evaporated) carbon foils. PCG foils can be made with greater areal densities, they are easier to handle, and in areal densities greater than 800 μg/cm2 (micrograms per square centimeter) they are less expensive than evaporated foils.
Thick, free-standing bulk density graphite foils in thicknesses of 20 μm (micrometers) and above can be provided upon special order. These are polycrystalline graphite having a density of approximately 1.84 grams per cubic centimeter. The maximum size and minimum order depend upon the thickness. Sizes up to 150 mm x 150 mm are available, depending upon thickness.
ISOTOPIC CARBON FOILS
Two types of foils are provided. For areal densities in the range 10-100 μg/cm2 (micrograms per square centimeter), enriched stable isotopes of carbon (12C or 13C) are electron-beam evaporated onto 25 mm x 75 mm glass slides, producing foils with size approximately 25 mm x 70 mm. Foils are fully annealed and are sold in minimum lots of 2, 3 or 4 slides, depending on areal density.
ELECTRON MICROSCOPY FOILS AND GRIDS
The use of a transmission electron microscope usually
requires specimens that are transparent to the electron
Frail specimens are often supported on very thin carbon
foils (usually called “films” by the microscopist), in turn
mounted on support grids. Carbon is used because of the
foils‘ relatively high strength, inertness and minimal
observable structure in the microscope. The thinnest and
purest carbon foils are made by electron-beam evaporation onto freshly-cleaved mica plates. These are ACF-Metals’ EM-Ultra-Smooth foils. The foils are then floated off and picked up onto conventional TEM grids, typically 3 mm in diameter and having a mesh structure to support the foil. For applications that do not require the highest purity and resolution, arc-evaporated carbon can be used at lower cost; however, particulates from the carbon arc may be present in such foils, and the parting agent adds to the uncertainties in the structure and in the purity of the foils.
EM-Ultra-Smooth Foils are electron-beam evaporated carbon foils on freshly water-cleaved mica substrates. No
contaminations appear due to parting agent, because
no parting agent is used. The foil has nominal
dimensions approximately 25 mm x 70 mm. Such
foils can be provided in nominal thicknesses from 2 nm
to 50 nm.
Carbon– and Metal-Covered Grids are standard 3mm diameter, 200-mesh copper TEM grids with the shiny sides covered with carbon films, or with metal or oxide films
specified by the customer. Some materials that have been
used in this way are: aluminum, aluminum oxide
(alumina), boron, gold, silicon, silicon dioxide (silica),
silicon monoxide, silver, titanium and zirconium. Lot size is 100 grids, coated with a film of carbon (either arc-evaporated or e-beam evaporated), or other material, at customer specified thickness, 10 nm or greater. Coated grids are packaged in conventional grid boxes having recesses to support the grids individually.
MOUNTED FOILS: FILTERS (EUV AND X-RAY) AND TARGETS
These are ultra-thin foils, sometimes isotopic foils, removed from their substrates, and mounted on frames. Frames may be washers, rings, or more-complicated assemblies. Except for the simplest standard assemblies, these products are made to the customer’s specifications and are priced by quotation.
Mounted foils are often used as bandpass filters, to transmit certain extreme-ultraviolet (EUV) or soft-x-ray wavelengths while absorbing others, typically in the wavelength range of