Silicon nanotubes are nanoparticles which create a tube-like structure from silicon atoms. As with silicon nanowires, they are technologically important due to their unusual physical properties, which differ fundamentally to those of bulk silicon. [2] The first reports on silicon nanotubes appeared around the year 2000. [3]
One method to prepare silicon nanotubes is using a reactor employing an electric arc without the use of any catalyst. [4] To ensure purity, the reactor is evacuated and filled with the nonreactive noble gas argon. The actual formation of the nanotubes relies on the process of chemical vapor deposition. [5]
A more common laboratory-scale method involves the use of germanium, carbon or zinc oxide nanowires as a template. Silicon, coming typically from either silane or silicon tetrachloride gas, is then deposited onto the nanowires, and the core is dissolved leaving behind a silicon tube. [6] The growth of template nanowires, silicon deposition and nanowire etching, and consequently the geometry of resulting Si nanotubes, can be accurately controlled in the second method; however, the smallest inner diameter is limited by tens of nanometers. [1]
The conventional vapor-liquid-solid (VLS) and solid-liquid-solid (SLS) mechanisms are favorite techniques to grow one-dimensional silicon nanostructures. However, they usually incorporate only one type of metal as catalyst and therefore can not be used for growing tubular (hollow) silicon nanostructures. In a recent attempt, a nickel-gold bilayer catalyst layer has been used to take the advantage of the uneven growth rate of constituent metal catalysts. Using these modified VLS and SLS techniques, multiwall silicon nanotubes with a sidewall thickness of few nanometers have been grown. [7]
As a result of their ballistic conductivity, silicon nanotubes and nanowires have been considered for use in electronics, e.g. in thermoelectric generators. [8] Since the structure can accommodate molecules of hydrogen so it might resemble coal without the CO2, it appears that silicon nanomaterials may behave like a metal fuel. [9] [10] A silicon nanotube charged with hydrogen delivers energy and in the process leaves residual water, ethanol, silicon and sand. However, as hydrogen production requires considerable energy, this is only a proposed method of storing energy, not producing it.
Silicon nanotubes and silicon nanowires can be used in lithium-ion batteries. Conventional Li-ion batteries use graphitic carbon as the anode, but replacing this with silicon nanotubes experimentally increases the specific (by mass) anode capacity by a factor of 10 (though the overall capacity improvement is lower due to the far lower specific cathode capacities). [11]
Another emerging application of silicon nanotube is light emission. Since silicon is an indirect band gap semiconductor, the quantum yield of radiative recombination in this material is very low. As the thickness of silicon-based nanostructures reduces below the effective Bohr radius (about 9 nm, in silicon) the quantum efficiency of light emission from this material increases owing to the quantum confinement effect. Relying on this fact, photoemission capability of silicon nanotubes with very thin sidewalls has been demonstrated. [7]
Nanotechnology was defined by the National Nanotechnology Initiative as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing properties of matter. The definition of nanotechnology is inclusive of all types of research and technologies that deal with these special properties. It is therefore common to see the plural form "nanotechnologies" as well as "nanoscale technologies" to refer to the broad range of research and applications whose common trait is size. An earlier description of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macroscale products, also now referred to as molecular nanotechnology.
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre. More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important—which coined the term "quantum wires".
Nanosensors are nanoscale devices that measure physical quantities and convert these to signals that can be detected and analyzed. There are several ways proposed today to make nanosensors; these include top-down lithography, bottom-up assembly, and molecular self-assembly. There are different types of nanosensors in the market and in development for various applications, most notably in defense, environmental, and healthcare industries. These sensors share the same basic workflow: a selective binding of an analyte, signal generation from the interaction of the nanosensor with the bio-element, and processing of the signal into useful metrics.
Nanomaterials describe, in principle, materials of which a single unit is sized between 1 and 100 nm.
Nanomaterial-based catalysts are usually heterogeneous catalysts broken up into metal nanoparticles in order to enhance the catalytic process. Metal nanoparticles have high surface area, which can increase catalytic activity. Nanoparticle catalysts can be easily separated and recycled. They are typically used under mild conditions to prevent decomposition of the nanoparticles.
Nanochemistry is an emerging sub-discipline of the chemical and material sciences that deals with the development of new methods for creating nanoscale materials. The term "nanochemistry" was first used by Ozin in 1992 as 'the uses of chemical synthesis to reproducibly afford nanomaterials from the atom "up", contrary to the nanoengineering and nanophysics approach that operates from the bulk "down"'. Nanochemistry focuses on solid-state chemistry that emphasizes synthesis of building blocks that are dependent on size, surface, shape, and defect properties, rather than the actual production of matter. Atomic and molecular properties mainly deal with the degrees of freedom of atoms in the periodic table. However, nanochemistry introduced other degrees of freedom that controls material's behaviors by transformation into solutions. Nanoscale objects exhibit novel material properties, largely as a consequence of their finite small size. Several chemical modifications on nanometer-scaled structures approve size dependent effects.
Nanoelectronics refers to the use of nanotechnology in electronic components. The term covers a diverse set of devices and materials, with the common characteristic that they are so small that inter-atomic interactions and quantum mechanical properties need to be studied extensively. Some of these candidates include: hybrid molecular/semiconductor electronics, one-dimensional nanotubes/nanowires or advanced molecular electronics.
Nanobatteries are fabricated batteries employing technology at the nanoscale, particles that measure less than 100 nanometers or 10−7 meters. These batteries may be nano in size or may use nanotechnology in a macro scale battery. Nanoscale batteries can be combined to function as a macrobattery such as within a nanopore battery.
As the world's energy demand continues to grow, the development of more efficient and sustainable technologies for generating and storing energy is becoming increasingly important. According to Dr. Wade Adams from Rice University, energy will be the most pressing problem facing humanity in the next 50 years and nanotechnology has potential to solve this issue. Nanotechnology, a relatively new field of science and engineering, has shown promise to have a significant impact on the energy industry. Nanotechnology is defined as any technology that contains particles with one dimension under 100 nanometers in length. For scale, a single virus particle is about 100 nanometers wide.
The following outline is provided as an overview of and topical guide to nanotechnology:
A nanowire battery uses nanowires to increase the surface area of one or both of its electrodes, which improves the capacity of the battery. Some designs, variations of the lithium-ion battery have been announced, although none are commercially available. All of the concepts replace the traditional graphite anode and could improve battery performance. Each type of nanowire battery has specific advantages and disadvantages, but a challenge common to all of them is their fragility.
Green nanotechnology refers to the use of nanotechnology to enhance the environmental sustainability of processes producing negative externalities. It also refers to the use of the products of nanotechnology to enhance sustainability. It includes making green nano-products and using nano-products in support of sustainability.
An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode. Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells.
Nanoarchitectures for lithium-ion batteries are attempts to employ nanotechnology to improve the design of lithium-ion batteries. Research in lithium-ion batteries focuses on improving energy density, power density, safety, durability and cost.
Anodic aluminium oxide, anodic aluminum oxide (AAO), or anodic alumina is a self-organized form of aluminium oxide that has a honeycomb-like structure formed by high density arrays of uniform and parallel pores. The diameter of the pores can be as low as 5 nanometers and as high as several hundred nanometers, and length can be controlled from few tens of nanometers to few hundred micrometers. Porous AAO is formed by electrochemical oxidation (anodization) of aluminum in acid electrolytes in the conditions that balance the growth and the AAO films are formed with limited thickness.
Carbon nanotube supported catalyst is a novel supported catalyst, using carbon nanotubes as the support instead of the conventional alumina or silicon support. The exceptional physical properties of carbon nanotubes (CNTs) such as large specific surface areas, excellent electron conductivity incorporated with the good chemical inertness, and relatively high oxidation stability makes it a promising support material for heterogeneous catalysis.
The applications of nanotechnology, commonly incorporate industrial, medicinal, and energy uses. These include more durable construction materials, therapeutic drug delivery, and higher density hydrogen fuel cells that are environmentally friendly. Being that nanoparticles and nanodevices are highly versatile through modification of their physiochemical properties, they have found uses in nanoscale electronics, cancer treatments, vaccines, hydrogen fuel cells, and nanographene batteries.
Research in lithium-ion batteries has produced many proposed refinements of lithium-ion batteries. Areas of research interest have focused on improving energy density, safety, rate capability, cycle durability, flexibility, and cost.
In materials and electric battery research, cobalt oxide nanoparticles usually refers to particles of cobalt(II,III) oxide Co
3O
4 of nanometer size, with various shapes and crystal structures.
Silicon nanowires, also referred to as SiNWs, are a type of semiconductor nanowire most often formed from a silicon precursor by etching of a solid or through catalyzed growth from a vapor or liquid phase. Such nanowires have promising applications in lithium ion batteries, thermoelectrics and sensors. Initial synthesis of SiNWs is often accompanied by thermal oxidation steps to yield structures of accurately tailored size and morphology.
