Migration of nano metals in semisolid and solid matrix under the influence of selectively triggered heterogeneous nucleation and growth

Abstract

Use of heterogeneous nucleation allows the localized reduction of metal salt and also cross-link the carbon precursor in the same region. This cross-linked matrix act as the secondary heterogeneous sites for spontaneous Nano particle synthesis and growth during the process of pyrolysis. Selectively creating heterogeneous sites and reducing the metal precursor using highly focused energy beams create various metal-carbon composites with controlled metal positioning. This is such a unique process where a pretreatment process will control the fabrication of complex metal-carbon composite nano and microstructures. This greatly simplifies the fabrication process, facilitating nanostructures like Nano metal bulbs, nanometal pointed nanogaps and metal sandwich structures with such process. With several advantages ranging from electronics, catalysis, optics and several other bio-functionalization technologies, this enables materials with unique and hybrid advantages. Moreover, fabrication of micro and Nano level structures provides a CMEMS and BIOMEMS relevant approach for wide range of applications.

Claims

1. A method for selective accumulation of nano-metals particles in a composite, the method comprising: providing a mixture of a photoresist and a metal salt embedded within the photoresist, wherein the metal salt is selected from the group consisting of titanium oxide, zinc oxide, silicon oxide, aluminum oxide, aluminum nitride, copper oxide, iron oxide, and combinations thereof, and wherein the mixture in the form of a solid or semisolid thin film, a nano/micro fiber, a suspended nano/micro wire, flakes, powder, or a nano/micro electrode; applying focused energy to a localized region of the mixture, wherein the focused energy is selected from the group consisting of a focused electron beam, one or more photon beams, ultraviolet and infrared wavelength exposure, and combinations thereof, in order to reduce the metal salt embedded in the mixture in the localized region, and cross-link the photoresist in the localized region, thereby creating secondary heterogeneous nucleation sites for spontaneous synthesis and growth of nano-metal particles.

2. The method according to claim 1, further comprising biologically functionalizing the composite so that a surface of the composite comprises proteins, enzymes, antibodies, antigens, peptides, aptamers, nucleotides, human/animal origin cells, microbes, viruses, or combinations thereof.

3. The method according to claim 1, further comprising chemically functionalizing the composite so that a surface of the composite comprises polymers, dyes, therapeutic chemicals, lipids, cationic/ionic resins, chelating agents, complexation moieties, or combinations thereof.

4. The method according to claim 1, wherein the composite presents surface conductivity, bulk conductivity, capacitance, and surface kinetics.

5. The method according to claim 1, wherein the composite material is biocompatible.

Description

BRIEF DESCRIPTION OF EACH FIGURE

(1) FIG. 1. Schematic of the basic mechanism representing the use of focused energy beam to create heterogeneous nucleation sites.

(2) FIG. 2. Schematic of the Nano-bulb fabrication process on a nanofiber.

(3) FIG. 3. Schematic of the nano-metal writing on precursor thin films.

(4) FIG. 4. Scanning electron microscopy of the gold Nano-bulbs fabricated in the carbon nanofibers.

(5) FIG. 5. Nanometal decorated nanogaps created by two different methods where the properties and surface composition of nanogaps is controlled by inducing metal accumulated nanogaps in the center of suspended carbon based nanofiber.

DETAILED DESCRIPTION OF THE INVENTION

(6) This invention opens a new prospective of controlling and localizing the metal nanoparticles nucleation and growth on as well as inside a substrate. The process relies on a precise pretreatment of the precursor substrate mixture with a focused energy beam. The localization and accumulation of the nano-metals is an in situ process during the carbonization of the pretreated substrate. This invention allows the selective growth of Nano metals in situ during the transformation of the metal-carbon substrate into a nanometal carbon composite. The process require a pretreatment process with focused energy beam to create heterogeneous nucleation sites in the metal-carbon substrate.

(7) Writing metal structures or fabricating metal Nano structures inside a solid matrix is a challenging process. Researchers are using intense energy beam to reduce metal precursor salts inside these solid or semisolid substrates. These processes are very harsh, non-uniform and may damage the substrate properties. A much easier solution is required to control and localize this nanometal fabrication in a solid matrix like carbon, which will further allow to reach the fabrication of structures like metal carbon based Nano bulbs, sandwiches and coaxial/core shell structures. Similar procedure. The problem relies in the fact that all the researchers have tried the complete reduction of metal precursors using high intensity/energy sources. No such research is reported where passive accumulation of Nano metals is tried during the process of substrate transformation.

(8) Carbon MEM/NS (Microstructure and Nanostructures) Fabrication

(9) This invention includes the fabrication of C-MEMS microstructure and nano-structures scaled microelectronic devices for wide range of application. One of the most prominent application of this invention is the writing of predefined patterns of metals/nano metals in a solid carbon matrix. These microstructures are created by pretreating the photo cross-linking polymer precursor containing metal precursor to create selective nucleation (by virtue of site selective reduction of metal precursor) as well as creation of secondary heterogeneous nucleation and growth platform. This heterogeneous nucleation sites further determines the patterning of the nanometal structures inside the transforming carbon precursor from a polymer state to solid carbon matrix during the process of high temperature carbonization. As explained in FIG. 1, the heterogeneous nucleation sites creation are responsible for the relatively higher nucleation and growth of metal nano-structures. Diffusion rate of reduced metal ions during the growth of nanostructure is highly dependent on the concentration of metal ions and the diffusivity/porosity of the surrounding matrix. This invention reports the selective accumulation of metal ions around the self-created heterogeneous sites resulting in the creation of 2D and 3D nano and microstructures inside the solid carbon matrix. These structures are represented as nano/micro bulb created on the suspended micro or nano fibers/wires and writing with the nano/micro metal structures on the surface and even inside the carbon matrix FIGS. 2, 3 and 4. 2D and 3D pretreatment using selective energy source are used to create metal carbon sandwich structures and coaxial structure of metal and carbon fibers/wires. Invention also presents the fabrication of nano metals/metal pointed nanogaps fabricated on the suspended nanofibers/wires. In molecular electronics, individual molecules are integrated with the rest of the circuit by positioning them in electrode gaps of the order of the molecule size. Such nanoscale gaps (nanogaps) have emerged as important experimental platforms for the electrical characterization of molecules, capturing unique transport phenomena of both organic and inorganic materials. These nanogaps are created using the metal-carbon composite fibers/wires, which are designed to have an accumulated metal/nanometal region at a certain region of the suspended nano fiber/wire FIG. 5.