Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Reexamination Certificate
1998-10-01
2001-02-13
Kiliman, Leszek (Department: 1773)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
C205S121000, C205S123000, C205S124000, C205S131000, C428S690000, C428S900000
Reexamination Certificate
active
06187165
ABSTRACT:
BACKGROUND OF THE INVENTION
Magnetic nanostructures, such as multilayers (e.g., Co/Cu) and granular solids (e.g., Co—Ag) with metallic constituents, have attracted a great deal of attention due to the realization of new phenomena such as giant magnetoresistance (GMR) and interlayer coupling. These structures are of technological interest for applications in field-sensing devices. For the case of GMR, the effect size is generally on the order of a few to a few tens of percent, except in nearly perfect superlattices which show the largest GMR effect of about 150% at 4.2 K.
Recently, advances in materials processing techniques have resulted in the fabrication of other novel nanostructures, such as arrays of nanowires. Metallic nanowires, as well as multilayered nanowires, have been successfully fabricated by electrodeposition. The nanowires are grown by electrochemical deposition into nanometer-sized cylindrical pores in a suitable insulating medium, such as polycarbonate, or mica. The nanowires are typically up to 10 micrometers in length, arranged in a parallel manner. The diameter of the wire can be controlled from tens of nanometers to microns, and the number density can be varied from 10
4
wires/mm
2
to 10
7
wires/mm
2
. Arrays of nanowires are a new type of nanostructure with quasi-one dimensional characteristics and they provide new means to study the intricate physics as well as the practical applications in nanostructured materials.
To date, the constituent materials in the overwhelming majority of magnetic nanostructures include transition metals, alloys, and noble metal elements. Bismuth (Bi) has been used to study both classical and quantum finite size effects, for which the characteristic lengths are the carrier mean free path and Fermi wavelength, respectively. The pursuit of quantum size effects since the 1960's, initiated by the observation of resistivity oscillations in Bi thin films as the thickness is varied, has continued to attract attention. Most of these studies involve Bi thin films, for which film thickness is a convenient variable. However, fabrication of high quality Bi thin films through traditional vapor deposition has proven to be technically challenging. The properties of Bi thin films fabricated by vapor deposition depend sensitively on the purity and the concentration of crystal defects, which are further compounded by the low melting point of Bi.
SUMMARY OF THE INVENTION
In the present invention, nanowires are fabricated by electrodeposition using semi-metallic bismuth. In this novel form of nanowire, positive magnetoresistance (MR) as high as 300% at low temperatures and 70% at room temperature, with a quasi-linear field dependence has been achieved. The MR effect in these semi-metallic nanostructures not only has much larger magnitude than, but also is characteristically different from, the negative GMR previously obtained in metallic nanostructures.
This invention takes advantage of the electronic properties of semi-metallic Bi which are fundamentally different from those of common metals.
The invention solves all the limitations noted of the known structures with the novel construction and use of semi-metallic bismuth. The MR effect exhibited by the semi-metallic Bi nanowires is much larger in magnitude than that of all GMR materials previously reported for magnetic nanostructures. Equally important for device applications is the quasi-linear field dependence of MR at all temperatures. Magnetoresistive devices based on metallic nanostructures must meet stringent requirements in layer thickness on the nanometer scale and sufficiently high resistance of the sensing element. The high resistivity of the Bi nanowires and the variable wire density can readily accommodate a very wide resistance range without sacrificing sensitivity.
REFERENCES:
patent: 5747180 (1998-05-01), Miller
patent: 5989406 (1999-11-01), Beetz
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Chien Chia-Ling
Liu Kai
Searson Peter C.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Kiliman Leszek
The John Hopkins University
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