Introduction to Nanomaterials and nanotechnology

difference between nanomaterials and nanotechnology how are nanomaterials different from bulk materials how nanomaterials are different from bulk materials
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University of Tartu Institute of Physics Tallinn Technical University Institute of Mechanical Engineering Frantsevich Institute for Problems of Materials Science of National Academy of Sciences of Ukraine Vladimir Pokropivny Rynno Lohmus Irina Hussainova Alex Pokropivny Sergey Vlassov INTRODUCTION TO NANOMATERIALS AND NANOTECHNOLOGY Tartu 2007 V. Pokropivny, R. Lohmus, I. Hussainova, A. Pokropivny, S. Vlassov. Introduction in nanomaterials and nanotechnology. – University of Tartu. – 2007, 225p. (Special lecture course for bachelors, MSc, post-graduates and specialists in nanotechnology) Physics and chemistry of nanostructures or nanophysics and nanochemistry are relatively new areas of science arisen in last decade of past century after discovery of fullerenes and nanotubes. It is introduction into more extent interdisciplinary integrated modern science known now as nanotechnology rapidly developing. At this stage of growing knowledge authors have shortly outlined the subject and classifications of nanostructures, interesting milestones, main principles, methods, techniques, as well as general directions of future perspective research to be a guideline in a see of modern research. Main mechanisms of physico-chemical processes affected formation of nanostructured materials and their properties are clearly expressed, in particular, a dielectric permittivity as a principal characteristic of electric, magnetic, acoustic, optic transparency, superconducting, and other properties of nanoceramics and nanometals. The peculiar properties of nanostructures are emphasized to be result of size effects, external and internal, classical and quantum ones, that arise in zero-dimensional quantum dots, one-dimensional wires, and two-dimensional layers. Numerous applications are considered including microlasers, photonic crystals, probe microscopy, left-handed materials with negative refraction index, etc. Novel idea is advanced that new discovery of novel fundamental laws, phenomena and applied effects are possible only in artificially fabricated nanostructures with new effect theoretically predicted and designed in advance. Content of the course covers the types, classification and peculiarities of nanostructures, size effects, synthesis and growth, fullerenes, nanotubes, microlasers, photonics, scanning probe microscopy, nanomanipulation, etc. The course is based on the lectures given during several years for students of Kiev National University (Ukraine), Tartu University and Tallinn Technical University (Estonia). RAK/NSF Meede 1.1 Project has supported this work. Also Estonian Science foundation grants no. 6658,6537, 6660 and Ukraine Nanotechnology Science Founda- tion. Estonian Nanotechnology Competence Center projects were also engaged to this work Copyright: Vladimir Pokropivny (Tartu University, Tallinn University, Frantsevich Institute for Problems of Materials Science of NASU), Rynno Lohmus (Tartu University), Irina Hussainova (Tallinn University of Technology), Alex Pokropivny (Frantsevich Institute for Problems of Materials Science of NASU), Sergey Vlassov (Tartu University). ISBN: 978–9949–11–741–3 Tartu University Press www.tyk.ee CONTENTS 1. INTRODUCTION.................................................................................................. 7 2. CLASSIFICATION OF NANOSTRUCTURES .................................................. 14 2.1. Gleiter's classification of nanostructured materials ....................................... 14 2.2. Classification of nanostructures by dimensionality....................................... 16 2.3. Concept of “surface form engineering” in nanomaterial science .................. 18 3. PECULIARITIES OF NANOSTRUCTURED MATERIALS ............................. 20 3.1. Introduction..................................................................................................... 20 3.2. Extended internal surface................................................................................ 22 3.3. Increasing of surface energy and tension........................................................ 23 3.4. Grain boundaries............................................................................................. 25 3.5. Instability of 3D0 NSM due to grain growth.................................................. 26 4. SIZE EFFECTS IN NSM ....................................................................................... 29 4.1. Definition and types........................................................................................ 29 4.2. Internal classic (IC) size effects...................................................................... 30 4.2.1. Reduction of lattice parameter.............................................................. 30 4.2.2. Decrease in melting point ..................................................................... 31 4.2.3. Decreasing of thermal conductivity...................................................... 31 4.2.4. Diffusion enhancement......................................................................... 32 4.2.5. Increasing of plastic yield strength and hardness of polycrystal ......... 32 4.3. External classic (EC) size effects at interaction of light with matter.............. 33 4.4. Intrinsic quantum (IQ) size effects ................................................................. 34 4.4.1. Transformation of absorption spectra of sodium from atom to solid ... 34 4.4.2. Blue shift – the increasing of band gap and luminescence frequency.. 35 4.4.3. Broadening of energetic bands ............................................................. 36 4.4.4. Phase transitions in ferromagnetic and ferroelectrics........................... 37 4.5. Extrinsic quantum (EQ) size effects in semimetallic bismuth Bi.................. 39 5. TECHNIQUES FOR SYNTHESIS AND CONSOLIDATION OF NSM............. 41 5.1. Vapor – phase synthesis.................................................................................. 41 5.1.1. Gas-Vapor deposition ........................................................................... 42 5.1.2. Plasma – based synthesis...................................................................... 42 5.1.3. Molecular beam epitaxy ....................................................................... 44 5.1.4. Inert gas condensation .......................................................................... 45 5.1.5. Flame pyrolysis..................................................................................... 45 5.2. Liquid phase synthesis.................................................................................... 46 5.2.1. Colloidal methods................................................................................. 46 5.2.2. Solution precipitation............................................................................ 47 5.2.3. Electrodeposition .................................................................................. 47 5.3. Sol-gel technique ............................................................................................ 48 5.3.1. Introduction........................................................................................... 48 5.3.2. Sol-gel process...................................................................................... 48 5.3.3. Sol-gel coating processes...................................................................... 50 5.3.4. Sol-gel applications .............................................................................. 53 5.4. Solid – state phase synthesis........................................................................... 53 5.4.1. Mechanical milling, attriction and alloying.......................................... 54 5.4.2. Severe plastic deformation ................................................................... 56 5.5. Other methods................................................................................................. 59 4 5.6. Consolidation of nanopowders ........................................................................ 60 5.6.1. Sintering of nanoparticles..................................................................... 61 5.6.2. Non- conventional processing .............................................................. 64 5.6.2.1. Microwave sintering................................................................. 64 5.6.2.2. Field – assisted sintering (FAS) ............................................... 65 5.6.2.3. Shockwave consolidation......................................................... 67 6. PROPERTIES OF 3D0 NANOSTRUCTURED MATERIALS (NSM)................ 68 6.1. Mechanical properties..................................................................................... 68 6.1.1. Hardness and strength........................................................................... 69 6.1.2. Ductility ................................................................................................ 71 6.1.3. Applications of Mechanical Properties of NSM................................... 75 6.2. Thermal properties of NSM............................................................................ 76 6.3. Electrical Properties of NSM.......................................................................... 78 6.4. Optical Properties of NSM ............................................................................. 80 6.5. Chemical Properties of NSM.......................................................................... 82 6.6. Magnetic Properties of NSM .......................................................................... 83 7. MEZO-NANO-POROUS MATERIALS............................................................... 84 7.1. Nanoporous materials ..................................................................................... 84 7.2. Zeolites and zeolite-like materials .................................................................. 85 7.3. Mesoporous materials..................................................................................... 86 8. PHYSICAL BACKGROUND OF NANOSTRUCTURES .................................. 88 (QUANTUM DOTS, WHISKERS, AND WELLS) ................................................. 88 8.1. Quantization and Heisenberg's indeterminacy principle ................................ 88 8.2. Energy states and wave functions in quantum well........................................ 89 8.2.1. Rectangular infinite potential ............................................................... 89 8.2.2. Rectangular finite potential................................................................... 91 8.2.3. Parabolic finite potential....................................................................... 92 8.2.4. Rise of energy bands in periodical potential within the Kronig-Penny model ............................................................................ 92 8.3. Quantum well in the gallium arsenide GaAs/AlGaAs heterostructure........... 94 8.4. Density of electronic states for bulk 3D and low dimensional 2D, 1D, 0D systems............................................................................................................ 95 8.4.1. General case for bulk 3D system.......................................................... 96 8.4.2. Case for 2D-quantum well.................................................................... 96 8.4.3. 1D-Case for quantum wire.................................................................... 97 8.4.4. 0D-Case for quantum dot...................................................................... 97 8.5. 2D-Electronic gas (2D-EG) in metal-oxide-semiconductor (MOS) structures.......................................................................................................... 98 9. FULLERENES ........................................................................................................ 99 9.1. History of fullerene discovery and Nobel Prices............................................ 99 9.2. Allotropic forms of carbon .............................................................................. 100 9.3. Fullerenes – the closed carbon cages consistent of 5- and 6-membered rings 102 9.4. Fullerites – the crystals of fullerenes ............................................................... 103 9.5. Fullerides – doped fullerites ............................................................................ 103 9.6. Synthesis of fullerenes..................................................................................... 104 9.7. Spectral properties of С ................................................................................ 106 60 9.8. Application of fullerenes ................................................................................. 106 5 10. CARBON NANOTUBES (C-NT) ........................................................................ 108 10.1. Geometrical structure..................................................................................... 108 10.2. Symmetry....................................................................................................... 110 10.3. Unit cell and Brillouin zone........................................................................... 110 10.4. Band structure................................................................................................ 112 10.4.1. Band structure graphite ..................................................................... 112 10.4.2. Band structure of C-NTs ................................................................... 112 10.4.3. Electronic density of state in NT....................................................... 114 10.5. Phonon spectra............................................................................................... 116 10.6. Thermal physical properties........................................................................... 120 10.7. Thermal conductivity..................................................................................... 120 10.8. Electric conductivity...................................................................................... 121 10.9. Electron interference (Aaronov-Bohm effect).............................................. 122 10.10. Nanotubular superconductivity.................................................................... 124 10.11. Mechanical properties.................................................................................. 127 10.12. Vibrations of C-NTs .................................................................................... 131 10.13. Nanothors from carbon nanotubes............................................................... 132 11. NONCARBON NANOSTRUCTURES AND NANOTUBEs.............................. 133 11.1. Fulborenes and fulborenites, the BN analogues of fullerenes and fullerites . 133 11.2. Boron-nitride nanotubes ................................................................................ 135 11.3. Dichalcogenide NTs ...................................................................................... 137 11.4. Oxide NTs...................................................................................................... 138 11.5. Other kinds of noncarbon nanotubes ............................................................. 139 12. APPLICATIONS OF NANOTUBES ................................................................... 141 12.1. Field Emitting Transistor (FET) based on C-NTs ........................................ 141 12.2. Logical circuits .............................................................................................. 141 12.2.1. Voltage inverter................................................................................. 142 12.2.2. Chips with logical elements .............................................................. 142 12.3. Indicators and flat displays ............................................................................ 144 12.4. Thermometer.................................................................................................. 145 13. PHOTONIC CRYSTALS ..................................................................................... 146 13.1. Physical ideas for light control via Bragg diffraction................................... 146 13.2. Methods for fabrication of photonic crystals and membranes....................... 147 13.3. Phenomenon of photon-trapping by defects in PC ........................................ 148 13.4. Photonic band structure ................................................................................. 149 13.5. Application..................................................................................................... 151 13.5.1. Waveguide......................................................................................... 151 13.5.2. Hollow concentrators of light............................................................ 152 13.5.3. Filters................................................................................................. 152 13.5.4. Fibers................................................................................................. 153 13.5.5. Prisms, lenses, interferometers.......................................................... 153 14. SEMICONDUCTOR MICROLASERS ON BASE OF NANOSTRUCTURES . 155 14.1. Introduction to injection lasers ..................................................................... 155 14.2. Laser on base of double heterojunction ......................................................... 157 14.3. Cascade multi-layered laser........................................................................... 158 14.4. Microdisc laser............................................................................................... 158 14.5. Nanowire laser ............................................................................................... 159 14.6. Zeolite-dye laser ............................................................................................ 160 14.7. Laser with distributed feedback (DFB) ......................................................... 160 6 14.8. Vertical cavity surface emitting laser – VCSEL............................................ 161 14.9. Surface-emitting 2D photonic-crystal laser with multidirectional distributed-feedback ...................................................................................... 161 14.10. Laser on defect mode of photonic crystal.................................................... 162 14.11. Quantum dots laser ...................................................................................... 162 14.12. Laser light diode on base of nanotube ......................................................... 164 15. ELECTRODYNAMICS OF “LEFT-HANDED” METAMATERIALS WITH ε 0 AND µ 0 .............................................................................................. 166 15.1. General remarks and determinations ............................................................. 166 15.2. Veselago theory of left-handed matter........................................................... 167 15.3. Inverse Doppler effect ................................................................................... 168 15.4. Inverse Cherenkov effect............................................................................... 169 15.5. Inverse Snell law or negative refractive index.............................................. 170 15.6. Optical units from left-handed media ............................................................ 171 15.7. Light pressure from left-handed media.......................................................... 172 15.8. Superprizm phenomenon ............................................................................... 172 15.8. General ε − µ -diagram.................................................................................. 173 16. SCANNING PROBE MICROSCOPY.................................................................. 175 16.1. Introduction – from Hooke to Binnig ............................................................ 175 16.2. Basics of SPM................................................................................................ 175 16.3. SPM techniques ............................................................................................. 177 16.3.1. Scanning tunneling microscopy ........................................................ 177 16.3.2. Atomic-force microscopy (AFM) ..................................................... 178 17. MEMS and NEMS ................................................................................................ 182 17.1. Introduction.................................................................................................... 182 17.2. Fabrication of MEMS and NEMS ................................................................. 182 17.2.1. Surface micromachining.................................................................... 182 17.2.2. Bulk Micromachining........................................................................ 182 17.2.3. Fabrication stages.............................................................................. 183 17.2.3.1. Deposition........................................................................... 183 17.2.3.2. Patterning............................................................................ 185 17.2.3.3. Etching................................................................................. 186 17.3. Examples........................................................................................................ 187 TEST QUESTIONS .................................................................................................... 190 LITERATURE ............................................................................................................ 192 1. INTRODUCTION Nanoscience primarily deals with synthesis, characterization, exploration, and exploita- tion of nanostructured materials. These materials are characterized by at least one –9 dimension in the nanometer range. A nanometer (nm) is one billionth of a meter, or 10 m. One nanometer is approximately the length equivalent to 10 hydrogen or 5 silicon atoms aligned in a line. The processing, structure and properties of materials with grain size in the tens to several hundreds of nanometer range are research areas of considerable interest over the past years. A revolution in materials science and engineering is taking place as researchers find ways to pattern and characterize materials at the nanometer length scale. New materials with outstanding electrical, optical, magnetic and mechanical properties are rapidly being developed for use in information technology, bio- engineering, and energy and environmental applications. On nanoscale, some physical and chemical material properties can differ signifi- cantly from those of the bulk structured materials of the same composition; for example, the theoretical strength of nanomaterials can be reached or quantum effects may appear; crystals in the nanometer scale have a low melting point (the difference can be as large as 1000°C) and reduced lattice constants, since the number of surface atoms or ions becomes a significant fraction of the total number of atoms or ions and the surface energy plays a significant role in the thermal stability. Therefore, many material properties must now be revisited in light of the fact that a considerable increase in surface-to-volume ratio is associated with the reduction in material size to the nanoscale, often having a prominent effect on material performance. Historically, fundamental material properties such as elastic modulus have been characterized in bulk specimens using macroscopic, and more recently microscopic, techniques. However, as nanofabrication advances continue, these bulk properties are no longer sufficient to predict performance when devices are fabricated with small critical dimensions. Although nanotechnology is a new area of research, nanomaterials are known to be used for centeries. For example, the Chinese used gold nanoparticles as an inorganic dye to introduce red color into their ceramic porcelains more than thousand years ago. Roman glass artifacts contained metal nanoparticles, which provided beautiful colours. In medivial times, nanoparticles were used for decoration of cathedral windows. What really new about nanoscience is the combination of our ability to see and manipulate matter on the nanoscale and our understanding of atomic scale interactions. Advances in the materials processing along with the precipitous rise in the sophistication of routine, commonly available tools capable for characterization of materials with force, displacement and spatial resolutions as small as picoNewtons (pN –12 –9 –10 = 10 N), nanometer (nm = 10 m) and Angstrom (A = 10 m), respectively, have provided unprecedented opportunities to probe the structure and mechanical response of materials on nanoscale. In addition, major improvements in computer support have allowed the simulations of material structures and behavior with a degree of accuracy unimaginable as recently as a decade ago. Although study on materials in the nanometer scale can be traced back for centuries, the current fever of nanotechnology is at least partly driven by the ever shrinking of devices in the semiconductor industry. The continued decrease in device dimensions has followed the well-known Moore’s law predicted in 1965 and illustrated in Fig. 1. The trend line illustrates the fact that the transistor size has decreased by a factor of 2 every 18 months since 1950. 8 Fig. 1. “Moore’s Law” plot of transistor size versus year. There are many nanoscale electronic devices available now: tunneling junctions; devices with negative differential electrically configurable switches; carbon nanotube transistor; and single molecular transistor; ultrahigh density nanowires lattices and circuits with metal and semiconductor nanowires; etc. Devices have also been connected together to form circuits capable of performing single functions such as basic memory and logic function. Computer architecture based on nanoelectronics (also known as nanocomputers) has also been intensively studied. Various processing techniques have been applied in the fabrication of nanoelectronics such as focused ion beam (FIB), electron beam lithography, and imprint lithography. Major obstacles preventing the development of such devices include addressing nanometer-sized objects such as nanoparticles and molecules, molecular vibrations, robustness and the poor electrical conductivity. Certainly, nanomaterials play an important role not only in semiconductor – based electronics. Nano-sized materials currently are used in numerous industries, e.g., carbon black particles make rubber tires wear resistant; nanofibers are used for insulation and reinforcement of composites; iron oxide creates the magnetic material used in disk drives and audio-video tapes; nano-zinc oxides and titania are used as sunblocks for UV rays; etc. Nanoscale particles and nanothin layers of materials are being used, among other things, to make products lighter, stronger or more conductive. Some of the products on the market using nanotechnology are: magnetic recording tapes; computer hard drivers; bumpers on cars; solid – state compasses; protective and glare – reducing coatings for eyeglasses and windows; automobile catalyc converters; metal – cutting tools; dental bonding agents; longer – lasting tennis ball; burn and wound dressing; ink; etc. Promising applications of nanotechnology in medicine and/or biology have attracted a lot of attention and have become a fast growing field. One of the attractive applications in nanomedicine is the creation of nanoscale devices for improved therapy and diagnostics. Such nanoscale devices or nanorobots serve as vehicles for delivery of therapeutic agents, detectors or guardians against early disease and perhaps repair of metabolic or genetic defects. For applications in medicine, the major challenge is “miniaturization”: new instruments to analyze tissues literally down to the molecular level, sensors smaller than a cell allowing to look at ongoing functions, and small 9 machines that literally circulate within a human body pursuing pathogens and neutralizing chemical toxins. Researchers expect to develop new commercial applications for nanotechnology for the next several years. They include: advanced drug – delivering systems, including implantable devices that automatically administer drugs and sense drug levels; medical diagnostic tools, such as cancer – tagger mechanisms and “lab-on-a-chip” diagnostics for physicians; cooling chips or wafer to replace compressors in cars, refrigerators, air conditioners and other devices, using no chemicals or moving parts; sensors for airborne chemicals or other toxins; solar fuel cells and portable power to provide inexpensive, clean energy; etc. Nanotechnology (NT) is proposed presently to define as the complex of fundamental and engineering sciences that integrates a chemistry, physics and biology of nanostructures with a materials science, electronics, and processes technologies focused on a comprehensive research of nanostructures, on a development of atomistic physical- chemical processes, self- and automatic-assembling of nanomaterials and workpieces using complex probe microscopes combined with other tools, resulted in a fabrication and manufacturing of nanodevices, nanomachines, ultra-low integrated circuits, micro- opto-electro-mechanical systems, nanobiorobots, etc. In reality the NT have been arisen in early 80-th, when the scanning tunneling micro- scopy, the atomic force and other probe microscopes were invented. These have given the opportunity to realize the main concept of NT formulated by Richard Feynman, namely, to assemble artificially the nanoworkpieces and nanodevices from single atoms and molecules. Huge advantage of Pentium-4 over IBM-360 have been achieved by a miniaturizing 9 2 of integrated circuits and fabricating of microchips containing ca. 10 units/cm of 200nm in size. And this is not a limit; the size of individual units may be decreased at least on the orders of magnitudes. With regard to nanoworld, a natural question has arisen “where are its boundaries?” Formally it is restricted by size of nanoparticles, d 100nm. Physically it is determined by a variety of size effects. Decrease in size results in the particles physical- chemical properties changing and, consequently, the properties of nano-materials are changed dramatically and sometime cordially. The size effects may be divided into two types, the internal and external ones, as well as the classical and quantum effects. Internal or intrinsic size effects are determined as a change of the properties peculiar to particles (the lattice parameters, melting temperature, hardness, band gap, luminescence, diffusion coefficients, chemical activity, sorption, etc.) irrespective of external dis- turbances. External size effects arise inevitably and always in the processes of interaction between different physical fields and matters under decreasing of their building units (the particles, grains, domains) down to a crucial value, when this size becomes to be comparable with a length of physical phenomena (the free length of electrons, phonons, coherent length, screening length, irradiative wave length, etc.). In turn the classical size effects appear to become apparent in variation of lattice parameters, hardness, plasticity, thermal conductivity, diffusion, etc. The quantum size effects manifest themselves in a blue shift of luminescence, in the rise of peculiar low- dimensional quantum states, in the quantization of electroconductivity in magnetic field, in the oscillation of the superconductivity critical temperature, magnetoresistance and other physical characteristics, in the generation of hypersound, etc. Hence, studying the size effects in novel nanostructured materials activated by different external fields one can hope for the discovery of novel effects and phenomena and for the development of novel nanotechnology on this base. 10 Nanotechnology therefore is the complex interdisciplinary science including: 1. Nanochemistry (nanocolloid, sol-gel and quantum chemistry) destined for self- assembling and synthesis of nanoparticles as well as for research of their intrinsic size effects. 2. Nanophysics (quantum physics, spintronics, photonics) destined for artificial assempling and fabrication of nanostructures as well as for research of their external size effects. 3. Nanomaterials science (nanopowder technology, nanoceramics compounds, nano- tribology, nanosintering and other nanoprocesses) destined for research, development and production of novel nanostructured architectures, functional nanomaterials and smart nanocomponents with unique properties. 4. Nanoelectronics, optoelectronics and nanoengineering destined for development of novel technological processes, nanomotors, nanoactuators, nanodevices, micro-opto- electro-mechanical systems (MEMS, MOEMS), ultra-large integrated circuits (ULCI), nanorobots, etc. 5. Nanobionics destined for development of novel biomachine complexes, such as nanobiochips, nanobiorobots, etc. 6. Nanometrology, nanodevice-building and nano-hand-craft destined for development of special nanotools, instrumentations, information and computational systems for support of NT itself. The association of these sciences in nanotechnology reflects both their inherent inter- connection around the nanoobjects and the change in technology paradigm, namely, the nanomaterial, nanodevice or nanosystem seems to be fabricated by the automatic artificial assembling or self-assembling from molecules or clusters in whole, in situ, in place, in the single technological process incorporating them then in microdevices, rather then by aggregating of different components as now. In place of the traditional processes of thermo mechanical treatment ( the rolling, cutting, welding, soldering, molding, etc.) and of microelectronics processes ( the chemical and physical vapor depositions, lithography, etc.) the novel atomistic nanotechnology processes (the nanomanipulation, artificial- and self-assembling, nanolithography, membrane- templating synthesis, sol-gel synthesis, molecular-beam epitaxy, etc.) are expected to will come. Living in macroworld human come into controllable tunable contact with nanoworld mainly by means of a tip of probe microscope, so the contact “tip-surface” is the contact of macroworld with nanoworld. Therefore the key problem of novadays nanotechnology is a comprehensive research of atomistic mechanisms of the nanocontact phenomena (adhesion, indentation, friction, wear, etc.) in dependence on a type of interatomic intermolecular bonds, type and structure of contact materials, size of tip and nanostructure, value of load, width of gap, environment, temperature, external electric and magnetic fields, frequency and intensity of electromagnetic waves, and so on. These researches have to be expressed in development of the techniques for tunable manipulation, characterization, control, and position assembling of nanostructures, particulary, seizure, gripping, restraining, turning, moving, breaking, reset and adhesion of a molecular building block onto prescribed place. Such operations at atomic and molecular level are just the ones which become to be principal for nanotechnology. It should be emphasized that NT has not intended to replace the existence micro- technologies, but to stay in close connection with them to complement them in the deeper study and advanced control of nanoworld. Atoms, molecules, clusters, fullerenes, supramolecular structures, their crystals, nanotubes, nanowires, nanorodes, their arrays and photonic crystals serve as NT objectives. 11 Fullerenes and atomic clusters are the smallest zero-dimensional (0D) nanostructures called quantum dots possessing the properties inherent for nanomaterial rather than for single atom. Note that for fullerenes it should mean not only the buckyball С , but the 60 multitude of another carbon C and noncarbon clusters and metcarbes МеC . n n Presently a number of experimental nanodevices was developed on this base, e.g. the switchers, diodes, transistors, amplifiers, sensors, optical filters, solar cells, magneto- optical recorders, etc. Nanotubes, nanorodes, nanowires, nanofibers manifest more advanced and pro- mising properties as being the 1D quantum wires nanoscopic in diameter but micro- scopic in length. Their unique properties stem from capability of the ring and cylindrical types of acoustic and electromagnetic waves to propagate that makes them a unique nanolaboratory for research of quantum resonance phenomena. All stated above also concern to noncarbon 1D nanowires and nanotubes based on boron-nitride, oxides, chalcogenides, dichalcogenides, chalogenides, and some other III–V and II–VI compounds possessing of the most manifold physical-chemical characteristics. Reduced two-dimensional 2D heterostructures, nanolayers and nanodisks as being the well known 2D quantum wells are believed to migrate from micro- to nano- electronics. In addition the 2D arrays of nanowires and nanotubes ordered in 2D forest arrays or 2D crystals seem to be novel and very perspective core of NT. Their unique properties have to be determined by new principles of electromagnetic waves propagation based on the Bragg diffraction law rather than on the total internal reflection. They are the quantum and, in the same time, the macroscopic 2D crystals in which the various quantum states and resonance effects are expected. Actually such resonance states can be recognized as the novel state of matter, research of which appears to become the advanced direction in nanophysics. On this base the waveguides, laser emitting diodes, infrared sensors and other nanodevices have already been developed. Design and assembling of such artificial media, search for new unusual effects and phenomena, as well as development of the up-to-date nanodevices on their base seems to be the most promising way in the nearest NT development. The example is the discovery of “left” matter or metamaterials, in which unconventional inverse refraction law, inverse Doppler and inverse Cherenkov effects were observed. In nanomaterials science the structure-form engineering will put in the forefront in addition to the impurity engineering. Material becomes not a raw or a pig but it is forming at once as a nano-workpiece. Note that advantage of nanomaterials is hoped to proclaim itself just at developing of nanodevices, the electronic gnat for example, rather than in the large scale industry. By peculiarity of the nanoworld is the cancellation of distinctions between the living and inorganic matter. The exchange of substance being the indication of life manifests itself on the supramolecular level rather than a molecular one. Proteins, membranes, and nuclein acids refer to giant natural nanostructures built in result of self-assembling. The analogy opens a fantastic opportunity for nanomaterials and nanodevices fabrication by such biomimicry. Artificial growth of pearls inside mussels, as well as ordering of non- equilibrium defects into 2D nanostructures on a surface of semiconductors under the ion bombardment and implantation are the examples. Principal question is “what are the peculiar features inherent to nowadays nano- technology taking into consideration that atomic and molecular physics, chemical synthesis technologies, microelectronics, etc., were existed before NT era?” The novelty includes: – the artificial manipulating by nanoobjects and manual or automatic assembling of the nanodevices designed beforehand using a “bottom-up” approach; 12 – the deliberate meddling in processes mechanisms with the comprehensive control of a chemical self-assembling at molecular level; – the invention, design and production of nanodevices of submictometer size followed by their integration into micro-, mezo-, -and macro-systems. Entering into NT it should be warn of some illusions and problems. Firstly, decrease in particles size is restricted from below because it does not always result into improvement of the properties. For instance, the optimal size of disperse inclusions in oxide ceramics ca. 10–20 µk was shown to exist at which the optimal combination of hardness and durability is achieved. Secondly, with particles size decrease the processes of thermal instability and phase transitions were shown to take place resulting in nondurability of nanosystems. For instance, the well-known words IBM, NANO, and corals drown on substrate by atomic- force microscopy were turn out to be unstable due to fast surface diffusion of building atoms. Since the covalent bonded semiconductors and ceramics preferably appear to be stable and durable, the nanomaterials for NT are thought to be nonmetallic. Thirdly, a cosmic irradiation and radiation background are capable atoms to knock- out from nanostructures leading in degradation of their properties and in worsening of nanodevice operation. Fourthly, a thermal noise and vibrations will be significant circumstances influenced the properties and characteristics of nanodevices. In particular, it limits certainty of probe microscope position, which must never be less then a half-amplitude of thermal vibrations. Fifthly, even negligible concentration of inherent impurities and irremovable contamination enable to destroy the assembling processes, so a super-high-purity feed reagents and clean-room processes are required. Concluding, all physical discoveries in vacuum have been already made except further discovery of the vacuum itself. Novel discoveries, laws, phenomena, technical decisions, solutions, and inventions will be possibly made only in special designed and assembled artificial nanostructures to be fabricated by future materials science. Materials science concept is shown in fig. 2 illustrating the inherent interconnection between the composition, structure, properties, technology and applications. Fig. 2. Fundamental triad of materials science. 13 Material is not a dull bar, blank, block, pig, but it is the immense word, the Universe, the media in which new physical laws may be discovered. Actually, there are 100 pure natural elements in the Periodical Table on base of which 10,000 XY binary, 1,000,000 XYZ ternary, 100,000,000 quaternary, etc, compounds may theoretically exist accounting the chemical composition. This abundance in many times increases with account of physical structure including nanostructures. However only 500,000 compounds are known presently to exist in modern crystallography database. Hence the abundance of novel undiscovered compounds with new unique properties is very huge forming the challenging frontier of research for future nanotechnology. At present time we meet NT in child age. The announcement of grand projects, such as biochips and nanobiorobots for medicine, smart dust for space research, etc., have become as motivation for it's intense development, that may influence upon a civilization development. In USA, EC, Japan, Russia and other leading countries the great funds were released for NT projects. The perspectives of NT at the beginning of 21 century looks very optimistic, since a severe reality is capable to darken these somewhat naive prospects. However, in any case the development of NT is unavoidable and it is doomed to success. The aim of this book is to summarize the fundamentals and technical approaches in processing and behaviour of nanomaterials to provide the readers systematic, comprehensive and brief information in the challenging field of nanomaterials and nano technology. Therefore, this part is a general introduction for students of the physical science and technology, especially students of mechanical engineering and materials science, and for people just entering the field. 2. CLASSIFICATION OF NANOSTRUCTURES 2.1. Gleiter's classification of nanostructured materials The materials and/or devices sintered by means of the controlled manipulation of their microstructure on the atomic level may be divided into three categories. The first category comprises materials and/or devices with reduced dimensions and/or dimensionality in the form of isolated, substrate-supported or embedded nanometer-sized particles, thin wires or thin films. The techniques that are most frequently used to produce this type of microstructure are chemical vapor deposition (CVD), physical vapor deposition (PVD), various aerosol techniques, and precipitation from the vapor, supersaturated liquids or solids. Well-known examples of technological applications of materials the properties of which depend on this type of microstructure are catalysts and semiconductor devices utilizing single or multilayer quantum well structures. The second category comprises materials and/or devices in which the nanometer- sized microstructure is limited to a thin (nanometer-sized) surface region of a bulk material. PVD, CVD, ion implantation and laser beam treatments are the most widely applied procedures to modify the chemical composition and/or atomic structure of solid surfaces on a nanometer scale. Surfaces with enhanced corrosion resistance, hardness, wear resistance or protective coatings are examples taken from today's technology in which the properties of a thin surface layer are improved by means of creating a nanometer-sized microstructure in a thin surface region. For example, patterns in the form of an array of nanometer-sized islands (e.g. quantum dots) connected by thin (nanometer scale) wires. Patterns of this type may be synthesized by lithography, by means of local probes (e.g. the tip of a tunneling microscope, near-field methods, focused electron or ion beams) and/or surface precipitation processes. Such kind of processes and/or devices are expected to play a key role in the production of the next generation of electronic devices such as highly integrated circuits, terabit memories, single electron transistors, quantum computers, etc. The third category comprises bulk solids with a nanometer-scale microstructure. Those are solids in which the chemical composition, the atomic arrangement and/or the size of the building blocks (e.g. crystallites or atomic/molecular groups) forming the solid varies on a length scale of a few nanometers throughout the bulk. One of the basic results of the materials science is the insight that most properties of solids depend on the microstructure. A reduction in the spatial dimension, or confine- ment of particles or quasi-particles in a particular crystallographic direction within a structure generally leads to changes in physical properties of the system in that direction. Hence the another classification of nanostructured materials and systems essentially depends on the number of dimensions which lie within the nanometer range: (a) 3D-systems confined in three dimensions, e.g. structures typically composed of consolidated equiaxed crystallites; (b) 2D-systems confined in two dimensions, e.g. filamentary structures where the length is substantially greater than the cross-sectional dimensions; (c) 1D-systems confined in one dimension, e.g. layered or laminate structures; (d) 0D-zero-dimensional structures, e.g. nano-pores and nano-particles, Fig. 3. 15 Fig. 3. Schematic classification of nano – materials: (a) three – dimensional structures; (b) two – dimensional; (c) one – dimensional; and (d) zero – dimensional structures. The most well-known example of the correlation between the atomic structure and the properties of a bulk material is probably the spectacular variation in the hardness of carbon when it transforms from diamond to graphite. Comparable variations have been noted if the atomic structure of a solid deviates far from equilibrium or if its size is reduced to a few interatomic spacing. An example of the latter case is the change in color of CdS crystals if their size is reduced to a few nano-meters. Three-dimensional structures or bulk materials with a nanometer-sized micro- structure are assembled of nanometer-sized building blocks or grains that are mostly crystallites. The schematic model of the nanostructured material is shown in Fig. 4. These building blocks may differ in their atomic structure, their crystallographic orientation and/or their chemical composition. If the building blocks are crystallites, incoherent or coherent interfaces may be formed between them, depending on the atomic structure, the crystallographic orientation and/or the chemical composition of adjacent crystallites. In other words, materials assembled of nanometer-sized building blocks are microstructurally heterogeneous consisting of the building blocks (e.g. crystallites) and the regions between adjacent building blocks (e.g. grain boundaries). It is this inherently heterogeneous structure on a nanometer scale that is crucial for many of their properties and distinguishes them from glasses, gels, etc. that are micro- structurally homogeneous. grain boundary atoms of grain boundary grain atoms Fig. 4. Schematic model of a nanostructured material (adapted from Gleiter H., Acta Mater., 2000, vol. 48). Nanostructured materials (NSMs) as a subject of nanotechnology are low-dimensional materials comprising building units of a submicron or nanoscale size at least in one direction and exhibiting size effects. Development of any science needs in classifi- cation. First classification scheme of NSMs was proposed by H. Gleiter in 1995 and further was extended by V.Pokropivny and V. Skorokhod in 2005. In recent years the 16 hundreds of new NSMs and abundance of novel nanostructures (NSs) have been obtained so the need in their classification is ripen. Crystalline forms and chemical composition was assumed by Gleiter as a basis of a classification scheme of NSMs where both intercrystalline grain boundaries and crystallites were regarded as building blocks (fig. 5). However this scheme seems to be incomplete because of zero- and one-dimensional (0D, 1D) structures such as fullerenes and nanotubes were not considered. Therefore in this scheme there are actually 3 classes and 4 types in each of them rather than 12 classes. Fig. 5. Gleiter's classification schema for NSM according to their chemical composition and the dimensionality (shape) of the crystallites (structural elements) forming the NSM. 2.2. Classification of nanostructures by dimensionality Nanostructures (NSs) should be separated from NSMs because the former (NSs) are characterized by a form and dimensionality while the last (NSMs) by a composition in addition. Hence NSs should be classified accurately upon one of these sign, namely, dimensionality, as being the general natural attribute, integrated a size and shape or form. Abundance of forms for bulk 3D materials is infinite. Under transition into nanoworld an atomic difference between some shapes can be neglected regarding these forms as the same due to their low dimension. Hence one can conclude that a number of NS-classes becomes to be finite. This brings up the problem of modern NSs classification. Under a nanostructure we understand the structure the one size of which d at least is 2 less or equal to a critical one d, dd≤≈ 10 nm. The value of d have not certain meanings because it is dictated by a critical characteristic of some physical phenomena (free path length of electrons, phonons, length of de Broglie wave, length of external electromagnetic and acoustical waves, correlation length, penetration length, diffusion length, etc.) giving rise to the size effects. We constitute our classification of NSs on their dimensionality. It may be one of the four, namely, 0D, 1D, 2D or 3D. All NSs can be build from elementary units (blocks) having low dimensionality 0D, 1D, and 2D. The 3D units are excluded because they 17 can't be used to build low dimensional NSs except 3D matrix. However 3D structures can be considered as NSMs if they involve the 0D, 1D, 2D NSs. This is just the case that Gleiter considered in his classification of NSMs. Let us introduce the notation of NSs kDlmn... (1) where k is a dimensionality of NS as a whole, while the integers l,m,n denotes the dimensionality of the NS's building units of different types. Each integer l,m,n refers to different type unit, so the number of these integers must be equal to the number of the different constituting units. From the definition of NSs the condition leads, namely, kl ≥,,mn , and k,l,m,n = 0,1,2,3. It follows from this conditions that restricted number of NSs classes exists, namely, 3 sorts of elementary units (0D, 1D, 2D), 9 single classes of kDl type built of 1 sort units, 19 binary classes of kDlm type built of 2 sort units, and variety of ternary, quaternary, etc., classes. Restricting the classification by 5 main ternary structures of kDlmn type built of 3 sort units, we obtain in the result 3+9+19+5=36 classes of NSs shown in fig. 6. Fig. 6. Dimensionality classification of nanostructures. 18 All kinds of NSs known in the literature belong to one of these classes. However some of classes still remain to be poor demonstrated although there is the predictive ability of the suggested classification. On this basis the combined classification of NSMs can be further developed with account of the secondry signs, in particular, the type and composition of materials, such as polymers, metals, dielectrics, semiconductors, ceramics (carbides, nitrides, borides, oxides, etc.), cermets, etc. 2.3. Concept of “surface form engineering” in nanomaterial science Concept of a “grain boundary engineering” is appereant from Gleiter's classification stated that the properties of NSMs strongly depend on the grain boundaries. In a similar manner the new concept of a “surface form engineering” follows from the classification proposed. In this classification the NSs properties strongly depend on free surface shape. It is based on the essential difference between intercrystalline grain boundaries and free surfaces. The boundaries give rise to the inner classical (IC) size effects, such as diffusion enhancement, decrease in melting point, lattice parameter, etc. The surfaces determine the form, shape, dimensionality, and thereby class of NSs. Sharp thin free surface can serve as a mirror for reflection of the electromagnetic, acoustic and de Broglie waves, in contrast to thickened diffusive grain boundaries, that only transmit and scatter these waves. This puts on forefront the indexes of refraction, absorption, and transmission of all the waves as main peculiar characteristics of NSs. Value of any classification is determined by an ability to predict some general properties. With the aim for any mesh, for each NS-class in our case, the general properties should be related to representative for this NS-class. Then, determining a class of NS, we are capable to predict its general properties. However at the present time the properties of NSs are studied insufficiently with rare exception. In particular, a general dependence of density of electron states (DOS) on the NS-dimensionality is 1 well known, namely, ρ()EE , ( ρ E) = const , ρ() E , and EE − 0 ρ()EE δ( −E) for the 3D, 2D, 1D, and 0D nanostructures, respectively. Hence we 0 can predict the general behavior of DOS for each class of NSs combining the DOS of their building units and NS as whole. For instance, the DOS of 2D1 NS-class may 1 predicted to be ρ() E const + . EE − 0 In addition to dimensionality a size of NSs becomes to be the main factor determining their properties. In extreme case of nanoparticle d λ a size and external form have not affect its interaction with external electromagnetic field. In opposite extreme case of bulk 3D material of d λ a size and form have not affect its int ernal interaction with internal waves due to their intense scattering and vigorous attenuation. Only in case of d λ the size restriction of NSs leads to quantum confinement and causes the inner quantum (IQ) size effects manifested itself in optical spectra. Electron reflection from NS-surface when electron free path length becomes greater then NS- size, ld ≥ , may lead to decrease in electroconductivity, etc. Phonon reflection from el NS-surface when the phonon free path length stands out NS-size, ld ≥ , may lead to ph cut of a long wave phonon spectrum, and to decrease of thermal conductivity, heat 19 capacity, Debye temperature, hypersound generation, and other IQ size effects. Variety of external size effects, both classical (EC) and quantum (EQ) type, may arise under interaction of NSs with external field, when its wave length becomes to be compatible with NS-size, λ ≈ d . In this case a condition of total internal reflection or Bragg em reflection sindn ⋅= θ λ /2 may be fulfilled. For instance, the NSs of 2D11 class such em as photonic crystals can act as light waveguide and left-handed media, in which unusual unique phenomena were predicted, namely, negative refraction index, inverse Doppler and Cherenkov effects. Beside size effects the variety of resonance effects was shown to be possible in NSs, in particular, Aaronov-Bohm, magneto-acoustic, photogalvanic effects, in which NS serves as resonator for acoustic, electronic, elrctromagnetic waves. In special nano- tubular crystals on special sole super-frequency an unique photo-acousto-electronic super-resonance between microwave, hypersound, and matter waves was suggested to be possible. The state can be regarded as novel nanostructured state of matter, in which a lossless repumping and converting of the electromagnetic, acoustic and electronic energies, one to each other, was suggested to be possible. One can conclude that in accordance with suggested “surface form engineering” a geometry shape becomes to be a principal factor determining the properties of NSMs. In comparison with our 36 classes in fig. 6 there are only 4 classes in Gleiter's scheme in fig. 5 where more then 32 classes are absent, though there are just the new precise classes that belong to new excited field of nanotechnology. Geometry always plays an exceptional role in physics. Generalizing Einstein principle of general relative theory one can say that “physics is geometry plus physical laws”. This is in Universe. Applied to nanoworld this principle can be reformulated as follows: “nanophysics is geometry of surface and size of NSs plus critical characteristics of physical phenomena in materials". Geometric forms can be designed theoretically in couple with prediction of novel size effects and resonance phenomena. Excited idea arises of a theoretical design of novel size effects and resonance phenomena combining diversity of NSs-forms with the critical characteristics of materials. Suggesting their meaning is 36 and 10 respectively, one can obtain limited number (360) of the size effects and resonance phenomena. In the result nanoworld one can image as “multi-room ( 360) house” of size effects and resonance phenomena. Paraphrasing the well known Feynman's aphorism we can say “There are plenty rooms of restricted classes at a bottom". Hence, the principally new result of the proposed classification is an opportunity of a priori prediction and theoretical design of novel NSMs with unique properties. Attention should be focused on engineering of surface forms of NSs in addition to grain boundaries extending paradigm of nanostructured materials science and nanotechno- logy. 3. PECULIARITIES OF NANOSTRUCTURED MATERIALS 3.1. Introduction Nanostructured materials (NSM) have their own peculiar characteristic distinguished them from the bulk macroscopic 3D materials. Relative to microstructural (MSM) metals and alloys, the NSM contain a higher fraction of grain boundary volume (for example, for a grain size of 10 nm, between 14 and 27% of all atoms reside in a region within 0.5–1.0 nm of a grain boundary); therefore, grain boundaries play a significant role in the materials properties. Changes in the grain size result in a high density of incoherent interfaces or other lattice defects such as dislocations, vacancies, etc. As the grain size d of the solid decreases, the proportion of atoms located at or near grain boundaries relative to those within the interior of a crystalline grain, scales as 1/d. This has important implications for properties in ultra-fine-grained materials which will be principally controlled by interfacial properties rather than those of the bulk. The misfit between adjacent crystallites in the grain boundaries changes the atomic structure (e.g. the average atomic density, the nearest-neighbor coordination, etc.) of materials. At high defect densities the volume fraction of defects becomes comparable with the volume fraction of the crystalline regions. In fact, this is the case if the crystal diameter becomes comparable with the thickness of the interfaces. From the courses of physics and mechanics, the role of structural defects in material properties is well established. Vacancies are point defects in the crystalline structure of a solid that may control many physical properties in materials such as conductivity and reactivity. However, nanocrystals are predicted to be essentially vacancy-free; their small size precludes any significant vacancy concentration. This result has important consequences for all thermo mechanical properties and processes (such as creep and precipitation) which are based on the presence and migration of vacancies in the lattice. Planar defects, such as dislocations, in the crystalline structure of a solid are extremely important in determining the mechanical properties of a material. It is expected that dislocations would have a less dominant role to play in the description of the properties of nanocrystals than in the description of the properties of microcrystals (mc), owing to the dominance of crystal surfaces and interfaces. The free energy of a dislocation is made up of a number of terms: (i) the core energy (within a radius of about three lattice planes from the dislocation core); (ii) the elastic strain energy outside the core and extending to the boundaries of the crystal, and (iii) the free energy arising from the entropy contributions. In mc the first and second terms increase the free energy and are by far the most dominant terms. Hence dislocations, unlike vacancies, do not exist in thermal equilibrium. In nanocrystals, the elastic strain energy is reduced. The forces on dislocations due to externally applied stresses are reduced by a factor of about three and the inter-active forces between dislocations are reduced by a factor of about 10. Hence re-covery rates and the annealing out of dislocations to free surfaces are expected to be reduced, as well. Dislocations are positioned closer together and dislocations movement in the net is hindered by interaction between them. Together with the reduced elastic strain energy, this fact results in dislocations that are relatively immobile and the imposed stress necessary to deform a material increases with decrease in grain size. Moreover, nano- structures allow alloying of components that are commonly immiscible in the solid and/or molten state. For example, Fig. 4 schematically represents a model of the