Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2000-07-27
2002-05-28
Turner, Archene (Department: 1775)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S457000, C427S595000, C427S596000, C427S597000, C427S532000, C427S553000, C427S554000, C438S381000
Reexamination Certificate
active
06395350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to thin films comprising mesoporous transition metal oxide materials. The invention further relates to a method of producing mesoporous transition metal oxide thin films via pulsed laser ablation of appropriate mesoporous molecular sieve targets. The invention also relates to the use of mesoporous transition metal oxide thin films produced by the method of the invention to manufacture chemical sensors and electrochromic devices.
2. Description of Related Art
Two classes of materials with wide ranging uses as heterogeneous catalysts, adsorption media, and as components of chemical sensors and electrochromic devices, are microporous (pore diameter<20 Å) and mesoporous (pore diameter 20 Å-500 Å) inorganic solids. The utility of these materials is a consequence of their chemical structures, which allow guest molecules access to large internal void surfaces and cavities, thereby enhancing the catalytic activity and adsorptive capacity of these materials.
Typical of the microporous materials are the aluminosilicate molecular sieves known as zeolites. In zeolites, the micropores form regular arrays of uniformly-sized channels. Zeolites can act as hosts to ionic and neutral molecular guest species. However, the usefulness of sensors and devices fabricated from zeolites and other microporous materials is generally limited to those applications where the guest or analyte molecules have sufficiently small kinetic diameters to pass through the narrow microporous void openings.
Mesoporous materials offer the advantage of larger pore sizes, making them compatible with applications such as separation or sensing of relatively large organic molecules. Typical of the mesoporous materials are amorphous or polycrystalline solids such as pillared clays and silicates. Unfortunately, the pores in these materials are often irregularly spaced and broadly distributed in size, making them ill-suited for chemical separations, sensing and other device-oriented applications.
Considerable synthetic effort has therefore been devoted to developing molecular sieve frameworks with pore diameters within the mesoporous range, and a series of mesoporous molecular sieves having a hexagonal array of uniform mesopores has recently been developed (Beck et al., 1992). These materials, designated MCM-41, are of great interest because their large and uniform pore sizes allow otherwise sterically hindered molecules facile diffusion to internal active sites. However, the MCM-41 series of molecular sieves are silicate and aluminosilicate materials, and their aluminum and silicon centers do not have variable oxidation states, thus precluding the use of these materials in display applications and related electrochromic devices.
A method of precisely controlling deposition of a well-adhered mesoporous transition metal oxide thin film having redox active metal centers would be beneficial in extending the range of thin film materials available for use in applications such as electrochromic devices, chemical separations, and chemical sensing.
SUMMARY OF THE INVENTION
The present invention provides novel mesoporous transition metal oxide thin films, as well as processes for producing these thin films. The present invention further provides methods of fabricating useful chemical sensors and electrochromic devices from the thin films of the invention.
In forming the films of the present invention, a substrate is placed on a variable temperature substrate holder within a controlled-atmosphere chamber. The substrate is usually, though not always, heated in order to facilitate bond making between reactive molecular species produced during a laser ablation process. A pulsed laser beam is then directed into the controlled-atmosphere chamber and focused such that it impinges on a target of mesoporous transition metal oxide molecular sieve material, ablating the target. During the laser ablation process, a continuous, uniform film is deposited on the surface of the substrate. The film thickness is controlled primarily by adjusting the duration of the laser ablation/deposition process. Depending on the thickness of film desired, the time of deposition can range from a few seconds to over an hour.
In general, the thickness of the films will be dictated by their intended use. For example, electrochromic applications may require an extremely thin transparent film of about 50 nm thickness or less, whereas chemical sensing applications may require a somewhat thicker film in the range of about 200 nm to about 300 nm thickness.
The thin films of the present invention possess a mesoporous structure which can be further enhanced by means of a hydrothermal treatment. If necessary, the thickness of the thin films can actually be increased by means of the hydrothermal treatment step, as explained hereinbelow. The thin films can also be treated with an acid wash or other means of removing the templating agent originally used in the synthesis of the mesoporous target material.
The advantages of this invention over current technology are several. For example, the mesoporous transition metal oxide thin films have metal centers with variable oxidation states, allowing the fine tuning of catalytic, electronic and magnetic properties of these materials. Furthermore, the thin films of the present invention are deposited from a target of the desired mesoporous material using pulsed laser ablation, allowing more precise control of deposition of well-adhered thin films as compared with methods involving growth from solution at a substrate/solution interface. Also, the thin films of this invention may be deposited onto flexible polymer substrates, in addition to conventional metal, ceramic or glass substrates, thus decreasing the total weight of sensor or display devices manufactured therefrom.
In particular, the present invention provides thin films formed from mesoporous oxides of niobium, titanium, tantalum, zirconium, cerium, tungsten, molybdenum, iron, lead, and any other mesoporous oxides of transition metals. These mesoporous oxides of transition metals include, but are not limited to, Nb-TMS1, Ti-TMS1, Ta-TMS1, Zr-TMS1, Ce-TMS1, and related mesoporous oxides of tungsten, molybdenum, iron and lead.
Thin films, as used herein, are films that measure between about 10 nm and 100 &mgr;m in thickness. In one preferred embodiment, the thin films may measure between about 200 nm and about 300 nm in thickness. In an alternative embodiment, the thin F films may measure between about 10 nm and about 50 nm in thickness. The appropriate thickness of the thin film will vary according its intended use.
For example, it may be desirable to employ a thin film of a mesoporous transition metal oxide about 50 nm in thickness in electrochromic applications where the thin film should be transparent in its colorless state. In another application, it may be desirable to employ a thin film of a mesoporous transition metal oxide about 250 nm in thickness as the dielectric phase in a capacitive-type chemical sensor. In this latter application, a fine balance exists between films that are too thin, such that electrical breakdown occurs, and films that are too thick, such that the change in dielectric properties is too small to be accurately measured.
The substrates upon which the thin films may be deposited include, but are not limited to, titanium nitride-coated silicon, indium-doped tin oxide-coated glass, indium-doped tin oxide-coated polyester, and other inorganic supports such as alumina. The appropriate choice of substrate will vary according the intended use of the thin film.
The inventors contemplate that the mesoporous transition metal oxide thin films of the present invention may be employed as the dielectric phase of capacitive-type chemical sensors. These capacitive-type sensors are expected to detect adsorbed volatile compounds via specific interactions with the large surface area presented by the mesoporous films. For example, the response of capacitive-type chemical sensors
Balkus, Jr. Kenneth J.
Kinsel Mary E.
Board of Regents , The University of Texas System
Fulbright & Jaworski L.L.P.
Turner Archene
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