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Planar resonant tunneling sensor and method of fabricating and using the sameRelated Patent Categories: Measuring And Testing, Surface And Cutting Edge Testing, RoughnessPlanar resonant tunneling sensor and method of fabricating and using the same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060230818, Planar resonant tunneling sensor and method of fabricating and using the same. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The quantum mechanical phenomenon of "resonant tunneling" was first analyzed in 1969 by Esaki and Tsu in 1969 (Esaki et al., IBM J. Res. and Develop. 14:61-69 (1970). The concept of "resonant tunneling" has since evolved into that of the "resonant tunneling diode" (RTD), wherein a central region containing some central moiety, for example a quantum dot, is placed between two quantum mechanical tunneling barriers. Two conducting electrodes in contact with the two quantum mechanical tunneling barriers can therefore allow the injection of electrical current from a first electrode, across a first barrier to the moiety, and from the moiety across a second barrier to the second electrode. [0002] If an energy level in the central moiety matches the electron energy in the first electrode, some enhancement of electrical current through the RTD occurs. This phenomenon can be called matched-level resonance. [0003] If the matched-level resonance condition is present, and if in addition the two quantum mechanical tunneling barriers are equal in magnitude, a tremendous additional enhancement in electrical current through the RTD occurs. This second phenomenon wherein the two quantum mechanical tunneling barriers are equal in magnitude can be called matched-barrier resonance. [0004] A variant of the resonant tunneling diode is used with a scanning tunneling microscope (STM) in a procedure called "resonant tunneling spectroscopy," which has been refined into a procedure called "shell tunneling spectroscopy" (Bakkers, et al., Nano Letters, 1(10):551-556 (2001)). [0005] The prior shell-tunneling spectroscopy work has been limited because the sample under test is fixed in place in a single position on top of an insulator of constant thickness. In order for the desirable phenomenon matched-barrier resonance to be employed in such a device, the magnitude of the upper quantum mechanical tunneling barrier due to the separation of the STM tip from the sample under test must be matched to the magnitude of the lower quantum mechanical tunneling barrier due to the presence of the insulator between the sample under test and the conducting substrate, and this is difficult to achieve in practice. [0006] Thus there exists a need for a tunneling spectrometer in which the phenomenon of matched-barrier resonance can be effectively employed, and at the same time the phenomenon of matched-energy resonance can also be made to occur, in order to obtain a complete density of states for a test sample. The present invention addresses this need. Relevant Literature [0007] Bakkers et al., Nano Letters, 1(10):551-556 (2002); Chang et al., Applied Physics Lett., 24(12):593-595 (1974); Goodhue et al., Applied Physics Lett., 49(17): 1086-1088 (1986); Sollner et al., Applied Physics Lett., 43(6):588-590 (1983); Esaki et al., IBM J. Res. Dev., 14:61-65 (1970); and Sollner et al., Applied Physics Lett., 45(12):1319-1321 (1984). SUMMARY OF THE INVENTION [0008] Planar resonant tunneling sensors and methods for using the same are provided. The subject sensors include first and second electrodes present on a surface of a planar substrate and separated from each other by a nanodimensioned gap. The devices further include a first member for holding a sample, and a second member for moving said first member and planar resonant tunneling electrode relative to each other. Also provided are methods of fabricating such a device and methods of using such a device for improved detection and characterization of a sample. [0009] One feature of the invention provides a device including a planar resonant tunneling sensor including first and second electrodes present on a surface of a planar substrate and separated from each other by a nanodimensioned gap, a first member for holding a sample, and a second member for moving said first member and planar resonant tunneling electrode relative to each other. In some embodiments, the first and second members comprise an integrated structure. In further embodiments, the integrated structure is an atomic force microscopy (AFM) tip. In other embodiments, the nanodimensioned gap has a width ranging in length from about 1 to about 8 nm. In some embodiments, the second member moves the first member sequentially across the first electrode, nanodimensioned gap and second electrode at a distance ranging from about 0.1 nm to about 10 nm. [0010] In some embodiments, the nanodimensioned gap includes an insulating material. In such embodiments, the insulating material may be silicon dioxide. In some embodiments, the first and second electrodes comprise platinum or polycrystalline silicon. In further embodiments, the planar substrate includes single-crystal silicon. [0011] Another feature of the invention provides a method for fabricating a planar resonant tunneling sensor, the method including providing a first insulating layer atop a planar substrate, depositing a first conductive layer on a first portion of a surface of the first insulating layer, depositing a spacer layer over the first conductive layer and a second portion of the surface of the first insulating layer, depositing a second conductive layer over a portion of the surface of the second insulating layer, and removing a portion of the deposited second conductive layer and the insulator layer to produce a planar resonant tunneling electrode sensor comprising first and second electrodes present on a surface of a planar substrate and separated from each other by a nanodimensioned gap. A portion of the spacer layer in the nanodimensioned gap, and extending from the upper extent of the nanodimensioned gap downward to the first insulating layer, may subsequently be removed, for example by chemical etching. If the spacer layer comprises an insulating material it may be left in place. [0012] A further feature of the invention provides a method of forming a nanodimensioned gap suitable for various purposes, for example to serve as electrical contacts to nanoscale devices comprising diodes, transistors, and the like. [0013] In some embodiments the removal of a portion of the deposited second conductive layer includes polishing the surface to produce a flat surface. In further embodiments, the polishing includes using a chemomechanical polishing protocol. In some embodiments, the method further includes positioning the sensor in a device that further includes a first member for holding a sample and a second member for moving the first member and planar resonant tunneling sensor relative to each other. [0014] Yet another feature of the present invention provides a method including positioning a sample on a first member of a device including a planar resonant tunneling sensor comprising first and second electrodes present on a surface of a planar substrate and separated from each other by a nanodimensioned gap, a first member for holding a sample, and a second member for moving said first member and planar resonant tunneling electrode relative to each other, and moving the positioned sample relative to the planar resonant tunneling sensor while monitoring the current between the first and second electrodes. [0015] In some embodiments, the method includes maintaining a constant first voltage applied to the sensor while the sample is moved relative to said sensor. In some embodiments the method further includes reiterating moving the positioned sample relative to the planar resonant tunneling sensor while monitoring the voltage between the first and second electrodes at least once at a second voltage that is different from the first voltage. In some embodiments, the method is a method for characterizing a quantum dot, a macromolecule, or a nanocrystal. BRIEF DESCRIPTION OF THE DRAWINGS [0016] The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: [0017] FIG. 1 is a schematic illustration of a cross-section at plane 1a of FIG. 3 of an embodiment 100 of the present invention. [0018] FIGS. 2A and 2B are schematic illustrations of cross-sections at plane 1a of FIG. 3 of an embodiment 100 of the present invention with additional elements and a sample 116 present in the first member for holding a sample 107. The arrow shows the direction the sample is moved over the nanodimensioned gap [0019] FIG. 3 is a schematic illustration of a top plan view of an embodiment 100 of the present invention. [0020] FIGS. 4A-4F illustrate sequential steps of a method of fabricating embodiment 100 of the present invention. Continue reading about Planar resonant tunneling sensor and method of fabricating and using the same... 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