Introduction to Nanoscience and Nanotechnology ENS 463 by Alexander M. Zaitsev alexander.zaitsev@csi.cuny.edu Tel: 718 982 2812 Office 4N101b 1
What is the size for a nano? 10-3 m, (milli) Macroobjects, e.g. discrete power transistor 10-6 m, (micro) Microobjects, e.g Microelectronics, transistor in a small integrated circuit. 10-9 m, (nano, meso) Nanoobjects, e.g. Nanoelectronics, transistor in a very large integrated circuit. Typical size of nanoobjects ranges from 1 to 100 nm. Clusters of atoms 0.1nm 1nm 10nm 100nm 1 m 10 m Large molecules (e.g. biomolecules) 2
Size scale compared to atom Bohr radius = 0.5292Å 0.05 nm C atom (VdW radius)=0.17 nm In a 1nm line: In a 1nm 2 surface: In a 1nm 3 cube: In a 1m 3 cube: 3 C atoms 9 C atoms 27 C atoms 2.7 10 28 C atoms A typical nanosystem (nanoobject) may contain from hundreds to tens of thousands of atoms. 3
Subject of Nanotechnology - Controllable manufacturing and characterization of materials and systems with predetermined and artificially modified atomic and molecular structure. - Nanoscience is Materials Science at atomic level. To accomplish that, one needs to manipulate with atoms and molecules at nanoscale. The importance of Nanoscience and Nanotechnology is determined by the fact that the specificity of the properties of materials and their functionality form at Nano-scale" by the atomic composition and the interaction between atoms and molecules. True Nanotechnology starts where one can manipulate both with atoms (molecules) and interactions between them. 4
Subject of Nanoscience Nanoscience is where atomic physics converges with the physics and chemistry of complex systems. Nanoscience is about the phenomena that occur in systems with nanometer dimensions. Quantum Mechanics Statistical Mechanics Quantum Mechanics dominates the world of atoms, but typical nanosystems may contain from hundreds to tens of thousands atoms. Emergent behavior How much a system is quantum mechanical? 5
Scaling down Physics and Chemistry 1. Below a certain length scale (that depends on interaction strengths) systems must be described using quantum mechanics. Ex. quantum dots, nanocatalysts, electronic transport through nanowires and thin films 2. Many processes depend on the number of available energy states per unit energy. This quantity varies with the dimensionality of the system. 3. The effective concentration of reactants that are confined in nanostructures may be very high. 6
Physical properties depend on size At nano-scale, - the material properties change - melting point, fluorescence, electrical conductivity, and chemical reactivity; - surface size is larger so a greater amount of the material comes into contact with surrounding materials and increases reactivity. Nanomaterial properties can be tuned by varying the size of the particle (e.g. changing the fluorescence color so a particle can be identified) Their complexity offers a variety of functions to products. CdSe nanoparticles (quantum dots) 7
Dependence on size Sensitivity of nano-structures As objects are scaled down the ratio of the surface to volume increases sharply. This makes surface effects more pronounced. E.g. isolated small size electrode will possesses high sensitivity due to non-linearity effects. 8
Areas of Nanotechnology Advance Materials & Textiles Information Technology Energy & Environment Mechanical Engineering / Robotics NANOTECHNOLOGY Aerospace Medicine / Health Biotechnology Transportation National Security & Defense Food and Agriculture 9
Examples of nanomaterials in products Amorphous silica fume (nano-silica) in Ultra High Performance Concrete. Nano platinum or palladium in vehicle catalytic converters - higher surface area to volume of particle gives increased reactivity and therefore increased efficiency. Crystalline silica fume is used as an additive in paints or coatings, giving e.g. self-cleaning characteristics it has a needle-like structure and sharp edges so is very toxic and is known to cause silicosis upon occupational exposure. References: http://www.efbww.org/pdfs/nano.pdf http://www.landscapeforms.com/en-us/sitefurniture/pages/prima-marina-table.aspx http://www.nano.gov/nanotech-101/speci al http://old.vscht.cz/monolith/ http://www.efbww.org/pdfs/nano.pdf 10
What do we expect from Nanotechnology? Design and fabrication of artificial (never met in Nature) materials and devices with entirely new properties, capabilities and functionality. Carbon Rope Space Elevator will come true once the technology of crosslinking and binding the carbon nanotubes in continuous fibers becomes possible. 11
Two main aspects of Nanotechnology (i) NanoFabrication (ii) NanoCharacterization 12
Nano-Fabrication: Top-Down and Bottom-Up 0.1nm 1nm 10nm 100nm 1 m 10 m bottom-up Organic synthesis Self-assembly of atoms and molecules top-down Photolitography Microprinting 13
TOP-DOWN Nano-Fabrication The principle of TOP-DOWN methods of nanofabrication is the deliberate control of fabrication of every element of a nanosystem unit by unit (ideally atom by atom). Atomic content and interaction between atoms and molecules can be controlled at nanoscale with nanotools. Top-Down fabrication is an essentially "artificial" approach rarely found in nature. Physical methods Advantage: Top-down methods allow control of the nanofabrication process at every moment. Disadvantage: Manipulating with small amounts of atoms at a time. Low fabrication throughput. 14
BOTTOM-UP Nano-Fabrication Selection and combining naturally occurring building nanoblocks (atoms, molecules, nanoclusters) in a predetermined manner. The principle of the bottom-up nanofabrication is to put together in a specific time sequence certain atoms and molecules in appropriate quantities and leverage this way naturally occurring chemical, physical and biological processes. Advantage: manipulation with large quantities of atoms at a time. High fabrication throughput. Chemical method (self-assembly) Disadvantage: The bottom-up methods do not allow control of interatomic interactions). The predetermined interactions are taken as ready-to-use building blocks. However, a great variety of available atoms and molecules allows to put the interaction process in almost any pathway and form a great many of different nanostructures. 15
Nano-Characterization Nanofabrication is the major part of nanotechnology. A minor one, but equally important part is nano-charactrization. The fabricated novel nanostructures have to be tested for their advanced properties and functionality. Also one needs to monitor and control the process of nanofabrication. Direct characterization methods are those based on microscopy techniques. These methods allow direct observation of nanostructures and to test quality of their individual elements. The most common of the direct methods are Scanning Electron Microscopy (SEM), optical Near-Field microscopy, Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM). 16
SEM: Using electrons to see Scanning electron microscopes, invented in 1930s, let us see objects as small as 0.5 nm! High resolution of SEM is due to small size of electrons. SEM image is created by electrons bouncing off of the object surface. High-resolution scanning electron microscope (HRSEM) image of mesoporous hollow silica used as a nanocarrier for drag delivery. 200 nm 17
Touching the surface 18
Indirect characterization methods Indirect characterization methods comprise techniques of traditional electrical, optical and mechanical characterization. These techniques provide information on macroscopic properties of nanomaterials and nanosystems. Examples of the indirect methods are electrical measurements (e.g. current-voltage characterization), optical spectroscopy (e.g. absorption, emission, Raman spectroscopies). 19
Risky nanotechnology... Development of something entirely new and unknown may be highly risky... Once we start to manipulate materials at the level of their fundamental basis, the unwanted and unpredictable side effects of this manipulation can be as disastrous as its positive results are beneficial. Nanotechnology may help the human race to survive the global problems we have created, or, if dealing imprudently, may accelerate our downfall. E.g. absolute catalytic converters for combustion engines based on Pt and Pd nanoparticles increase concentration of these nanoparticles in air and this increases risk of cancer. Scientists hope to use C60 fullerenes (buckyballs) as drug delivery systems, components of fuel cells and as tools to clean up contaminated soil. But buckyballs can also steal electrons from surrounding molecules -- a process known as oxidation and a common mechanism of tissue damage and aging. Some nanoparticle are freely mobile. Their penetration in natural ecosystems and human bodies may have negative health and environmental impacts. Nanotechnology for the military...? 20
Characteristics of nanoparticles relevant for health effects Size In addition to being able to cross cell membranes, reach the blood and various organs because of their very small size, nanoparticles of any material have a much greater surface to volume ratio (i.e. the surface area compared to the volume) than larger particles of that same material. Therefore, relatively more molecules of the chemical are present on the surface. This may be one of the reasons why nanoparticles are generally more toxicthan larger particles of the same composition. Chemical composition and surface characteristics The toxicity of nanoparticles depends on their chemical composition, but also on the composition of any chemicals adsorbed onto their surfaces. However, the surfaces of nanoparticles can be modified to make them less harmful to health. Shape Although there is little definitive evidence, the health effects of nanoparticles are likely to depend also on their shape. A significant example is nanotubes, which may be of a few nanometres in diameter but with a length that could be several micrometres. A recent study showed a high toxicity of carbon nanotubes which seemed to produce harmful effects by an entirely new mechanism, different from the normal model of toxic dusts. Crystalline silica fume used as an additive in paints or coatings has a needle-like structure and sharp edges so is very toxic and is known to cause silicosis upon occupational exposure. 21
Negative sides of nanotechnology for the environment: toxic nanoparticles Nanoparticles may impact the health and stability of ecosystems in ways that are difficult to predict. An example: Silver Nanoparticles Silver nanoparticles are being used in numerous technologies and incorporated into many products that take advantage of their optical, conductive, and antibacterial properties. Diagnostic Applications: in biosensors, as biological tags for quantitative detection. Antibacterial Applications: incorporated in apparel, footwear, paints, wound dressings, appliances, cosmetics, and plastics; Conductive Applications: conductive inks, composites with enhanced thermal and electrical conductivity; Optical Applications: used for efficient harvesting light, enhanced optical spectroscopies (metal-enhanced fluorescence and surface-enhanced Raman scattering) but Silver nanoparticles, though they are not toxic to humans, dissolve in water and release silver ions (which are antibacterial). If silver nanoparticles are released into the environment, these types of concentrated silver ion releases could devastate local bacterial populations, with drastic consequences for the affected ecosystems. 22
Negative sides of nanotechnology for the environment: reactive nanoparticles There are also several types of nanomaterials that may be detrimental to the environment because they facilitate chemical reactions that can harm plankton, bacteria, and small animals. Many metal and metal oxide nanomaterials are excellent catalysts (materials that speed up the rate of different chemical reactions). If these catalytic nanomaterials are released into the environment, they can enable chemical reactions that generate toxic chemicals, such as free radicals or reactive oxygen species (aka ROSs). One of these nanomaterials is titanium dioxide (TiO 2 ), which is an excellent photocatalyst (ultraviolet light exposure activates its catalytic properties). When illuminated by sunlight, titanium dioxide nanoparticles can catalyze chemical reactions that increase the concentrations of several ROSs (including hydroxide {-OH} or superoxide {-O 2 } radicals) in natural waters. These reactive oxygen species are known to be harmful to many aquatic organisms, including plankton and small fish. 23
How nanoparticles get into the environment 24
Nanotechnology has global impact As society becomes more interested in reaping the potential benefits of nanotechnology, nanoparticle production will increase, the number of nanoparticle-enabled products will increase. As a result, synthetic nanoparticles will join more traditional synthetic chemicals as environmental contaminants. By 2020, the total amount of nanomaterials produced by industry is expected to increase from 1000 to 58000 tons, making the release of nanomaterials during production a significant concern. Airborne pollutants are difficult to contain and can rapidly spread to other ecosystems (both near and far). 1 mole at STP occupies 22.4L, one breath is ca. 0.05 Mole N 2 Mass of earth s atmosphere is 5 10 18 kg (80% N 2 ), 1 mole of N 2 weights 28 g. Moles N 2 in atmosphere are ca. 2 10 20 Fraction exhaled by Caesar: 0.05/ 2 10 20 = 2.5 10-22 : 150 Caesar Molecules /mole In each breath we breath in: 0.05 150 or about 7 molecules of Caesar s Last Breath. 100-44 B.C. 25