NanopowderCarbon nanotubes

Silver Nanopowder. Image Credit: SkySpring                      Carbon nanotubes. Image Credit: RSC

Nanomaterials have features or particle sizes in the range of 1 to 100 nm. They can be natural or manmade and they have a wide variety of applications

What are Nanomaterials?

Nanomaterials are materials possessing one or more dimensional features having a length on the order of a billionth of a meter, or 10-9, to less than 100 billionths of a meter. To illustrate this size, there are 25,400,000 nanometers in an inch and on a comparative scale, if a marble were a nanometer, than one meter would be the size of the earth.

Nanotechnology Description

The term nanomaterial includes all nanosized materials, including materials that can be engineered or found in nature. They are important because they exhibit unique properties because of the size of their features and scientists and engineers have learned how to manipulate and understand the relationship of their properties to size. The National Nanotechnology Initiative (NNI) website puts these ideas in a simple phrase, "At the nanoscale, the physical, chemical, and biological properties of materials differ in fundamental and valuable ways from the properties of individual atoms and molecules or bulk matter."

nanoscale

NanoScale. Image Credit: Nano.gov

Recent discoveries in areas such as microscopy have given scientists and engineers new tools to observe and manipulate the phenomena that occur when matter is organized at the nanoscale level. The scanning tunneling microscope (STM) and the atomic force microscope (AFM) have made nanotechnology possible to enable scientists to utilize the unique physical, chemical, mechanical, and optical properties of materials that naturally occur at that scale. Nanomaterials fall under the field of nanotechnology and the events that occur at the nanoscale level are based on "quantum effects" and physical effects such as expanded surface area.

How Are Nanomaterials Made?

'Nanomaterials' is a term that includes all nanosized materials, including engineered nanoparticles, incidental nanoparticles, and nano-objects like those that exist in nature. Nanomaterials exist in nature in the form of biological materials or a byproduct of human activities. For instance, hemoglobin is 5.5 nanometers in diameter and biological ion channels can be as small as a few tenths of a nanometer. Natural nanomaterials such as smoke from fire and sea spray exist in the air around us. Manmade nanomaterial byproducts include automobile exhaust and welding fumes. Scientists have already copied the nanostructure of several natural items including the lotus leave to create water repellent surfaces beings used to make stain proof clothing and spider silk, which is naturally reinforced with Nanoscale crystals.

Nanomaterials can also be engineered and are made through a process called nanomanufacturing. Nanomanufacturing has two basic approaches.

  • Bottom-up builds products by building them up from atomic- and molecular-scale components. The process involves manipulation or synthetic methods of biochemistry in direct assembling subnanoscale building blocks, such as atomic molecular and supramolecular elements into required nanoscale patterns. It can be a very time consuming process and is therefore better for biomedical, chemical and physical sensors than large scale molecular electronics and computer parts. The fabricaion strategy must occur in parallel or in arrays to self-form groups of atoms fast enough to produce useful structures of macroscopic size. Further research is being done to create self-assembling structures that will put themselves together and reduce the waste of top-down approaches. Currently, the best bottom-up approach is nano-manipulation which allows for precise control over single atoms and nanoscale particles for the formation of nanostructures.
  • Top-down reduces large pieces of materials to the Nanoscale level. The process has evolved from lithographic techniques, requiring larger amounts of materials which can lead to waste from the discarding of excess material. Another difference from the bottom up approach is that in the top-down approach, the parts or chips are both patterned and built in place so that no assembly step is needed. It is a very useful process for the evolution of the electronics, computer, photonic, and microsystem industries.
  • Combined bottom-up and top-down approaches will soon be the standard practice.

 

Within the top-down and bottom-up categories of nanomanufacturing, there are a growing number of new processes that enable nanomanufacturing. Among these are:

  • Chemical vapor deposition (CVD) is a process in which chemicals react to produce very pure, high-performance films. CVD involves flowing a precursor gas or gasses into a chamber containing one or more heated objects to be coated. A chemical reaction occurs on or near the heated surfaces, resulting in the deposition of a thin film on the surface. CVD can be done with a variety of chemicals for a wide range of applications. The process can be enhanced with plasmas and ions to increase deposition rates and/or lower temperatures.

Chemical Vapor Deposition

o   Advantages include the conformability of the deposition; the film thickness is the same on all sides of the piece so products with odd shapes can be properly covered. Other advantages of CVD are that a variety of materials can be deposited with  high purity and relatively high deposition rates, and also requires less vacuum pressure.

o   Disadvantages for CVD include the properties of the precursors which need to be volatile at near-room temperature. The byproducts of the reactions and the precursors can be hazardous. The type of substrate is limited since the films are deposited at higher temperatures and mechanical stress can occur if the materials have different thermal expansion coefficients.

  • Molecular beam epitaxy (MBE) is a technique for epitaxial growth via the interaction of one or several molecular or atomic beams that occur on a surface or heated substrate. Epitaxy means the arrangement of atoms on an order substrate. Three factors define the MBE process; Thermal -energy molecular or atomic beams, substrate with elevated temperature, and high vacuum (10x 10-3 to 10x10-9 Torr). The processes occurring during film growth include surface adsorption, surface dissociation and migration, lattice incorporation and thermal desorption.
    • Advantages include precise control of the beam fluxes and growth condition and compatibility with other high vacuum thin- film processing methods. MBE is easy implementation of in situ diagnostic instruments and provides a clean growth environment for deposition.
    • Disadvantages of MBE are the sophisticated and expensive equipment needed, and the slow speed of the process. Another disadvantage is that it is difficult to control the multi-element rate.

molecular beam epitaxy works

Molecular beam epitaxy (MBE) means creating a single crystal by building up orderly layers of atoms on top of a substrate (base layer). Image Credit: explainthatstuff.com

  • Atomic layer epitaxy, also called atomic layer deposition, is a process for depositing one-atom-thick layers on a surface. Films are deposited by a repetitive sequence of single layer deposition cycles composed of several gas-surface interactions that are all self-limiting. The crystal lattice structure achieved is thin, uniform and aligned with the structure of the substrate.

Atomic Layer Deposition

o   Advantages of atomic layer epitaxy include the ability to accurately control the thickness of the layer. The process is simple and multilayer structures are easy to grow. Additional advantages include the wide range of film materials available, high density, and low impurity levels; all of which are done at a lower temperature so sensitive substrates are not affected.

o   Disadvantages include the potential for residue to be left behind from the precursors. The process is time consuming and usually only a fraction of a monolyer is deposited in one cycle. Also, several technologically important materials are too expensive to be deposited by the technique

  • Dip pen lithography is a process in which the tip of an atomic force microscope is "dipped" into a chemical fluid and then used to "write" on a surface, like an old fashioned ink pen onto paper. This is an effective technique for transporting molecules from the tip of an atomic force microscope (AFM) to substrates at resolutions comparable to those achieved with much more expensive and sophisticated lithographic methods.
    • Advantages of dip pen lithography are that it is easy and inexpensive. Patterns for the experiments are easy to create and can be specific to an application since it can be applied to a large selection of substrates.
    • Disadvantages include the limiting factors of the experiments such as solubility of the desired ink, the transfer and stability of the material within the water meniscus, and the adsorption of the material on the substrate surface. Inks can be molecules, sol-gel materials, and biological species like proteins

dip pen nanolithography

Schematic diagram showing how dip pen nanolithography works. Image Credit: Azonano.com

  • Nanoimprint lithography is a process for creating nanoscale features by "stamping" or "printing" them onto a surface. A hard mold (mask) with a surface relief pattern is used to emboss a layer of resist. After heat and pressure are applied the mold is revoked and the residual layer of resist is (dry) etched away to leave behind a fully patterned resist.
    • Advantages of this process include the ability to clean and reuse the mask which allows for imprint uniformity and defect free fabrication. It is a simple process with simple machines that produce three-dimensional patterns on a variety of substrate materials
    • Disadvantages come from user error in overlaying the mask correctly, as well as from defects and debris on the template. Also, the higher the resolution the slower the throughput.

nanoimprint lithography

Process of nanoimprint lithography. Image Credit: what-when-how.com

  • Roll-to-roll processing (R2R) is a high-volume process to produce nanoscale electronic devices on a roll of ultrathin plastic or metal. The process is similar to nano-imprint lithography but rollers allow for a larger substrate to be patterned faster.
    • Advantages include a lower substrate cost, steady state processing with high-throughput and high yield, lower cleanroom requirements and less expensive equipment. It has a high throughput and has been able to demonstrate 100nm resolution as well as self-alignment.
    • Disadvantages of R2R include the limited equipment available because there is no previous generation equipment to model, and challenges with patterning and defect repair.

roll to roll process

Roll-to-roll process. Image Credit: Nitto Denko

  • Self-assembly describes the process in which a group of components come together to form an ordered structure without outside direction. Self -assembly is the ultimate goal for many nanomaterial making processes because of the reduced chance for error and reduction of waste.

The properties exhibited by a nanomaterial are related to the composition, and process that the material was created by. Controlling the process parameters such as temperature and pressure as well as composition makes the material stronger, lighter, more durable, water-repellent, anti-reflective, self-cleaning, ultraviolet-or-infrared-resistant, antimicrobial, electrically conductive, etc.

Product Selection

The GlobalSpec SpecSearch database allows industrial buyers to select nanomaterials by type of nanotechnology, material type, design specifications and application.

Nanotechnology Type

Two general constructions include,

  • Single Walled (SWNT) materials which are constructed of a single plane of atoms. SWNTs have superior properties compared to doubled walled for certain applications
  • Double Walled (DWNT) materials are constructed of two or more planes of atoms.

 Different types of nanomaterials and nanotechnology products are named for their individual shapes and dimensions.

Type

Description

Application

Fullerenes or buckyballsFULLERENESImage Credit: chemical-engineering.com

Carbon (C60) molecules with a cage-like structure of 60 or more atoms. 

Computer memory, electronic wires, and materials science

Nanotubes

Image Credit: hochgeladen von Schwarzm am

Toroidal-shaped fullerene molecules or strings of stacked C60 carbon molecules. Greater mechanical strength at less weight per unit volume than that of conventional materials.

Baseball bats, tennis racquets, and some car parts. Flat panel displays in TVs, batteries, and other electronics.

Nanocrystals or quantum dotsImage Credit: Nanotechnology Now

Aggregates of anywhere from a few hundred to tens of thousands of atoms that combine into a crystalline form of matter known as a "cluster." Their energies or optical properties are determined by particle size and shape due to quantum confinement effects and not the bulk material properties.

Optical displays,computer memory, cryptography, photovoltaics,storage media flexible electronics,neural networks, telecommunications components, and quantum computing, enhance biological imaging for medical diagnostics.

NanogelsImage Credit:advancedglazings.com

A pore structure on the nanometer scale. Silica aerogel's pore network (2 to 50 nm) accounts for 95% of the material's volume. A fine, open porosity.

Thermal insulation, as scaffolds for nanocomposite manufacturing, to capture fragrances, chemical catalysts and biochemicals.

  • aerogels,
  • hydrogelsand
  • other nanoporous materials

NanodevicesnanofibersImage Credit: thesingularityprinciple.blogspot.com

Electronic, optical, mechanical or elecromechanical products built on a nanosacle or with nanosized components.

Medical diagnostics and treatment, information technology, food and drug applications and environmental monitoring.

NanofibersnanofibersImage Credit: University of Nebraska-Lincoln

A diameter of less than one micron, or one dimension of 100 nanometer (nm) or less. polymeric nanofibers produced by electrospinning, Low density, large surface area to mass, high pore volume, and tight pore size 

Medical, filtration, barrier, wipes, personal care, composite, garments, insulation, and energy storage

Nanowires nanowiresImage Credit: National Cancer Institute

Depending on what it's made from, a nanowire can have the properties of an insulator, a semiconductor or a metal.

Identification of biomarkers and cells, electronics such as mircoprocessors and nanorobotos,

NanopowdersnanoparticlesImage Credit: TPL, INC.

Composed of nanoparticles having an average diameter below 50nm

Targeted drug delivery, solid fuels, conducting pastes, and specialized paints and glazes, finished coatings

NanoparticlesnanoparticlesImage Credit: nanogloss.com

Particles that have one dimension that is 100 nanometers or less in size, have a greater surface area per weight than larger particles,

Can safely be injected into the body and will preferentially bind to cancer cells making it visible.

Nanocatilevers NanocatileversImage Credit: National Cancer Institute

Microscopic, flexible beams built using semiconductor lithographic techniques.  Can be coated with molecules capable of binding specific substrates. When that substrate is detected it deflects the cantilever, changing the conductance of the device.

Identification of biomarkers and cells

Nanoshells NanoshellsImage Credit: National Cancer Institute

Spherical nanoparticle consisting of a dielectric core covered by a thin metallic shell

Target specific cells, imaging, drug delivery

NanofilmsnanofilmImage Credit: Nanofilm.com

Nanomaterial used in thin films. Can beinvisible if small enough.  

Used to make thin films water-repellent, anti-reflective, self-cleaning, antifog, or electrically conductive. Used on eyeglasses, computer screens, and cameras.

Material Properties

Generally, materials types include crystalline or amorphous properties. Nanomaterials represent materials from a structural perspective somewhere in between the two types.

  • Crystalline materials are composed of an orderly repeating array of atoms, molecules or ions. They come in two general forms; single crystalline, which have single atoms arranged periodically on a three dimensional lattice; and polycrystalline, which is a consolidated assembly of small single crystals. This material has short and long range order meaning that the manner in which atoms are arranged at any one location within a crystal is identical to the arrangement at any other location. Most metals are polycrystalline and when they break the grains or crystallites can be observed randomly orientated within the material. The surface between grains is called the grain boundary.
  • Amorphous materials are non-crystalline. They have short range order but not long range order. This material is not composed of grains. A broken edge is observed at a smooth surface because they are considered a cooled liquid rather than a true solid. Polymers and ordinary glass are amorphous materials.

Material Type

Description

Application

Carbon

Based on carbon or built from carbon atoms

Diamonds, pigment, organic compounds

Ceramic/Carbide

Non-metallic, inorganic compounds that include oxides, carbides, or nitrides. High melting points, low wear resistance, and a wide range of electrical properties.

Suitable for applications requiring wear resistance, high temperature strength, electrical or thermal insulation or other specialized characteristics.

Chemical / Precursor

Precursors are chemicals which are thermally decomposed, deposited or processed

Produce ceramics, metals or other materials.

 

Ferrite / Magnetic

Metals with magnetic properties

Data storage media, electronics

Metal

Broad category of elements that usually have a shiny surface and grayish color. 

Good conductors of electricity and heat, can be melted or fused, hammered into thin sheets, or drawn into wire.

Mineral / Nanoclay

Forms of silicates, clays, calcium carbonate, wollastonite, aggregates and other additives

Used to extend, fill, strengthen or modify plastics, coatings, adhesives, and other materials. Nanoclay additions to resin compounds can enhance strength and flame retardancy beyond the level of strengthening provided by a micron-sized clay filler.

Nanocomposite

 

Composite materials typically consist of a matrix and a dispersed second phase. The second phase can be particulate, fibrous or continuous.

The second phase may reinforce (strengthen or stiffen), alter electrical, thermal or magnetic properties, or enhance wear or erosion resistance.

 

Polymer

 

High molecular weight compounds comprised of two or more repeating organic or synthetic base molecules

Plastics, elastomer or rubber materials, semi-finished plastics (stock shapes), elastomer shapes, molding compounds, liquid or casting resins, monomers and intermediates.

Silica / Silicate

Compounds of silicon and oxygen, contain additional elements or modifiers to form more complex compounds such as sodium silicates, borosilicates, or calcium aluminum silicates, can be glassy (e.g., borosilicate glass) or crystalline.  Silica-based glass is a hard, brittle material consisting or a mixture of silicates and usually transparent or translucent.

Quartz and high purity, amorphous fused silica are high performance ceramics with very low expansion, remarkable thermal shock resistance, low thermal conductivity, excellent electrical insulation up to 1000° C and excellent resistance to corrosion from molten metal and glass.  ptical, thermal, chemical, and electrical and electronics applications.

Shape and  Dimension

Nanomaterials are designed in a variety of shapes including particles, tubes, wires, films, flakes, or shells that have one or more nanometer-sized dimension.  For example, carbon nanotubes have a diameter in the nanoscale, but can be several hundred nanometers long or even longer. Nanofilms or nanoplates have a thickness in the nanoscale, but their other two dimensions can be much larger.

Particle and feature size is the diameter or width of nanomaterials and nanotechnology products. On consolidated nanomaterials or nanodevices, this is the diameter or width of the nanoscale feature or crystal. Size is an independent degree of freedom and can therefore be manipulated independent of composition, temperature and pressure to create materials that possess new properties. Scientists are trying to produce nanomaterials with tightly controlled size and size distribution so that the properties associated with size are observed and distinguishable. In order for the unique size-dependent properties to be utilized, the nanomaterials must be composed of monodisperse or nearly monodisperse nanoparticles. Often, specific surface features are responsible for the unique properties of the material so it is critical that processing is controlled to yield size and the particular surface features responsible for the materials unique characteristics.

The size of the particle or grain also influences properties of the grain boundary. As the grain size decreases the proportion of molecules or ions at the grain boundary increases. The rato of molecules or ions at the surface to the total in the grain is proportional to 1/r where r is the radius of the particle or grain. The size dependent properties that emerge in the nanometer length domain are in part a result of this increased ratio.

Design Specifications

Important specifications when selecting nanomaterials and nanotechnology products include,

  • Specific Surface Area (SSA)- SSA is measured in terms of mass per unit area and is easier to determine than crystal size. SSA can provide an indication of average particle size, but not particle size range or distribution. Nanoscale materials have far larger surface area then similar volumes of larger-scale materials, meaning more surface is available for interaction with other materials around them. Typically, gas absorption techniques such as the Brunauer-Emmett-Teller absorption (BET) technique are used to determine SSA.

Application

Nanomaterials and nanotechnology has a wide range of applications from baseball bats and tennis rackets to catalysts for refining cure oil and ultrasensitive detection and identification of biological and chemical toxins. The benefits of this technology come from the ability to tailor the structure of the material at the Nanoscale to achieve specific properties. According to the National Nanotechnology Initiative (NNI), there already exist over 800 everyday commercial products that rely on Nanoscale materials processes.

Application

Description

Biomaterials / Life Sciences 

Nanotube gene insertion, diagnostics or nanoparticulate drug delivery systems.

Click here for a video on Nanotechnology

Catalyst

Catalyst-type applications. The fine particle size and alternate properties due to nanoscale sizing may enhance a catalyst's ability to promote or initiate reactions. 

Chemical Sensing / Biomolecule Tagging 

Sensing chemicals, explosives, radioactive isotopes or biomolecules, includes nanomaterials for tagging or labeling proteins or biomolecules for analytical applications.

Colorant / Pigment 

Pigment or colorant applications in finishes, cosmetics, art

Energy

 

Energy equipment or process applications such as fuel cells, batteries, or clean fuel combustion. 

Lubricants / Lubrication 

Lubricant applications in industrial and mechanical industry  

Membranes / Filtration 

Membrane or filtration applications for waste water systems and medical technology

Storage / Magnetic

Storage media or magnetic applications. Nanostructuring can produce materials with high magnetic saturation and coercivity. 

Nanoelectronics 

Electronics applications such as flexible electronics, high density memory, nanoscale transistors, single electron devices (SEDs), or other electronic components. Over 10,000 nanoscale components can fit in the same area as a single microscale device. State-of-the-art commercial integrated circuits measure about 350 nm.   

Optoelectronics / Optical Components 

Optoelectronic or photonic applications such as light emitting diodes (LEDs), displays, lasers, or other optical components. 

Planarization Slurry (CMP) 

Chemical mechanical planarization or polishing applications. The fine particle size and modified properties due to nanoscale sizing may enhance chemical surface activity and improve surfacing characteristics. As microelectronic structures reach into nanoscale ranges, finer chemical mechanical polishing (CMP) solutions may be required. 

Photovoltaic / Energy Conversion

Nanomaterials such as quantum dots may increase the sensitivity of conventional solar cells to a broader spectral range, allowing increased energy absorption and efficiency. 

Reinforcement / Filler

The filler may enhance or produce specific electronic, thermal, structural or optical properties in the end-product or finished material. 

Structural Composites

Structural or composite strengthening applications including medical scaffolding support, sports technology, textiles and mechanical

Environmental

Eco-friendly applications such as providing clean water though filtration systems, cleaning up oil spills with special textiles and air purification.

Transportation

Improving highway and transportation infrastructure components while reducing cost and Nanoscale sensors monitor the condition and performance of bridges.

Food Industry

Nanocomposites in food containers to minimize carbon dioxide leakage out of carbonated beverages, or reduce oxygen inflow, moisture outflow, or the growth of bacteria in order to keep food fresher and safer, longer, warn against spoiled food, detect salmonella, pesticides, and other contaminates on food before packaging and distribution.

Specialty / Other

 

Other unlisted, specialized, or proprietary applications, including Nanoscale additives to or surface treatments of fabrics help them resist wrinkling, staining, and bacterial growth, and provide lightweight ballistic energy deflection in personal body armor.

Risks

Nanomaterials have been linked to several risks associated with material hazard and exposure to the material. Care should be taken when handling nanomaterials. Safety precautions such as engineering controls, administrative controls, and personal protective equipment is recommended to avoid exposure to nanoscale materials.

Industry Standards

According to the NNI, nanotechnology relies on standards through at least three concepts:

1.      Documentary standards define agreed-upon terminology or standard language for a field of science, engineering, or technology; they are agreed-upon means for conducting measurements; agreed-upon performance characteristics of instruments or commercial products; and particularly, they are documented agreements on means to facilitate trade and commerce.

2.      Standards often refer to standard reference materials, materials that are certified by a national standards laboratory to have specified characteristics traceable to an international system of the fundamental system of physical units of measurement.

3.      Standards generally refer to the fundamental physical realization of the units of measurement defined in the International System of Units (SI).

Around the world, there are numerous nanotechnology standards-setting groups that develop voluntary standards. Some of the leading standards setting organizations and their relevant nanotechnology committees are:

Resources

Introduction of Nanoimprint Lithography

Molecular Beam Epitaxy

Moving Roll to Roll Processing from the Lab to Manufacturing

Nanofacts

Nanofiber Nonwovens

Nanoshell particles: synthesis, properties and applications

Nanotechnology 101

Park, Jong-Hee, and T. S. Sudarshan. Chemical Vapor Deposition. Materials Park, OH: ASM International, 2001. Print.

Understanding Nanotechnology

 

 

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