Etching a substrate: processes – Nongaseous phase etching of substrate – Relative movement between the substrate and a confined pool...
Reexamination Certificate
2000-05-09
2002-10-15
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Nongaseous phase etching of substrate
Relative movement between the substrate and a confined pool...
C216S096000, C216S100000, C216S106000, C216S105000
Reexamination Certificate
active
06464893
ABSTRACT:
BACKGROUND OF THE INVENTION
The ability to prepare and manipulate organic thin-film-metal structures in a well-defined way is critically important in areas as diverse as sensing, adhesion, tribology, corrosion and nanoscale electronics. For example, FTIR spectroscopy in the Attenuated Total Reflection mode (ATR-FTIR) is a widely used surface analytical method for investigating an organic-metal interface. One of the most popular ATR attachments employs a 45° ZnSe single crystal with an available sample area of 10 mm×70 mm (Horizontal Contact Sampler, Spectra-Tech, Inc.). In order to obtain the maximum possible ATR-FTIR signal strength, it is necessary to ensure maximum interfacial contact between the ZnSe crystal and the sample. Thin, smooth metallic foils are, therefore, a practical requirement for such surface studies.
Many types of thin metallic foils necessary as substrates in this area of research are commercially available but the cost of such materials is frequently too high for researchers with limited resources. For instance, single crystal pieces of any metal, whether precious or non-precious, and polycrystalline pieces of all precious metals typically cost at least about $1500 cm
−2
. Thus, each 4 cm
2
piece of commercial thin copper foil costs about $16 and many such pieces must be used during an investigation. Accordingly, an inexpensive way to obtain high quality thin metallic foils is desirable.
There has been a surge of interest in fundamental studies involving the properties in chemical reactivity of organic films on metallic copper evident in the recent scientific literature. A method of producing thin copper foils is therefore expected to be of particular interest to those presently involved in organic-copper interfacial chemistry, as well as people who are contemplating entry into this area.
SUMMARY OF THE INVENTION
This invention provides a new method for the preparation of thin metallic foils and organic thin film-metal composites using such foils. More particularly, the invention provides a method in which a metallic substrate is rotated and contacted with an etchant so as to reduce the thickness of the metal substrate by corrosion and realize the desired foil thickness. The resulting thin foil can then be contacted with the organic material so as to form a thin film of the organic material on the surface of the foil.
DESCRIPTION OF THE INVENTION
The process of the present invention is applicable to any metal substrate. While it can be applied to precious and rare metals, because the process depends on a controlled corrosion, it is generally impractical for such metals because of the cost involved. A non-precious metal is therefore preferred. At present, the most preferred metal to which the process of the present invention can be applied is copper.
The thickness and other dimensions of the metal substrate employed are not restricted as long as the substrate can be rotated. Relatively thick metallic foils are commercially available and the use of such substrates is generally preferred. In general, it is preferred to employ a substrate having a thickness in the range from about 0.01 to about 1 mm and preferably from about 0.1 to 0.6 mm. It is also generally preferred, although not essential, that the substrate employed be in the form of a circular disk.
The metal substrate is rotated in any convenient manner, for instance by being mounted on a suitable rotatable supporting structure. The mounting also serves to protect one of the major faces of the substrate from the etchant and thereby minimize point breakthroughs which are more likely to occur when two opposing surfaces are being simultaneously etched. The speed of rotation can be adjusted as desired depending on the particular metal substrate employed, the particular etchant, the temperature and pressure conditions employed, and the desired rate of etching. In general, the rotation is usually within the range of about 100-1000 rpm, preferably 200-600 rpm.
Any etchant which acts chemically on the metal substrate to remove surface from that substrate can be employed. In general, inorganic acids such as hydrochloric acid, sulphuric acid, nitric acid and hydrofluoric acid can be used, with nitric acid being particularly preferred, but the range of etchants usable is not limited to this list. The etchant and metal substrate are contacted under etching conditions. For some combinations of etchant and metal, elevated temperature and/or pressure may be appropriate while other combinations can be processed under ambient or other conditions.
The etchant and metal substrate are contacted under the etching conditions for a time sufficient to reduce the substrate thickness to the foil thickness desired. If desired or convenient, the contacting may be done a plurality of times until the desired foil thickness is achieved. For example, the metal substrate can be separated from the etchant periodically and the exposed surface washed or otherwise cleaned before contact with the etchant is reestablished. The thickness of the desired thin foil is typically on the order of about 1 to 100 &mgr;m and preferably about 10 to 90 &mgr;m. Frequently about 60-90% and more frequently about 70-85% of the initial mass of the metal is eliminated as a result of the etching procedure.
Forming an organic thin film on a thin metal foil is per se known. The foil and the organic material are brought into contact under suitable conditions so as to form an organic thin film on the surface of the metal foil. Any procedure and any organic material which has been used heretofore can be used in accordance with the present invention which differs from such prior procedures by using the thin metal foil produced by the rotating etching procedure described above.
In order to further illustrate the present invention, experimental procedures and results are described below. It will be understood that these examples are intended to be illustrative and non-limiting. Unless otherwise indicated, all temperatures are in degrees Centigrade and all parts and percentages are by weight throughout this specification and claims.
General. Kinetic data were obtained with copper sheet (Johnson Matthey, 0.60 mm thickness, 99.9% purity). Copper “Heavy Foil” (J. T. Baker, 0.127 mm thickness, ≧99.90% purity) was used for all other experiments. Water was deionized (DI) via reverse osmosis (Barnstable Nanopure II system, resistivity 16.7 M&OHgr;). Anhydrous ethanol (Phannco), hexane (Fisher, HPLC grade), acetone (Fisher, reagent grade), dichloromethane (Fisher, HPLC grade), dodecane (Aldrich, 99.9+%), concentrated nitric acid (Fisher, reagent grade), dodecanethiol (Aldrich, 98+%), 11-mercapto-1-undecanol (Aldrich, 97%) and acetyl chloride (Aldrich, 97%) were used as received. Visible spectroscopy was carried out on a Milton Roy Model Spectronic 20 spectrophotometer. FTIR spectra were obtained on a Mattson Galaxy Model 3000 spectro-photometer, using Win 1st software for processing (DTGS detector, 2-cm
−1
resolution). ATR-FTIR spectra were obtained using a Horizontal Contact Sampler (Spectra-Tech, Inc.) fitted with a 10-mm×70-mm ZnSe crystal (45°, 12 internal reflections). Two 10 mm×35 mm strips were cut from each sample and were laid end-to-end on the ZnSe crystal before application of pressure by the gripper. The ATR-FTIR sample compartment was purged with nitrogen before analysis of samples. IR spectral assignments were assigned, in part, with the aid of molecular modeling data (PC Spartan Plus™, Wavefunction, Inc.), using a PM3 basis set.
Kinetics. A circular disk 48 mm in diameter was cut from copper sheet of nominal 0.60-mm thickness (8.28 g, 0.130 g-atom, 99.9% purity). The center of the disk was fastened to the circular end of a wooden dowel (6 mm in diameter, 15 cm in length) with two-part “5-minute” epoxy adhesive. After the adhesive cured, the disk/dowel assembly was attached to a digital stirring motor (IKA Tech, Inc., Eurostar™ model). The disk was vigorously abraded with emery paper and then lowered into 6 N HNO
3
Ahmed Shamim
Gulakowski Randy
Ostrolenk Faber Gerb & Soffen, LLP
Pace University
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