Overview of Nanotechnology with emphasis on Optical Properties of Nanomaterials. Highly recommended for basic understanding of Nanotechnology.

1. Nanotechnology An overview Manoranjan Ghosh

2. What Is All the Fuss About Nanotechnology? Any given search engine will produce 1.6 million hits Nanotechnology is on the way to becoming the FIRST trillion dollar market Nanotechnology influences almost every facet of every day life.

3. History Richard Feynman: 1959– “There's Plenty of Room at the Bottom," He predicted - a process to manipulate individual atoms and molecules might be developed, using one set of precise tools to build and operate another proportionally smaller set, so on. At this scale, gravity would become less important, surface tension and Van der Waals attraction would become more important, etc. The term "nanotechnology" was defined by Tokyo Science University Professor Norio Ta in 1974s: "'Nano-technology' mainly consists of the processing, separation, consolidation, and deformation of materials by one atom or by one molecule." 1980: Dr. K. Eric Drexler – First book Engines of Creation: The Coming Era of Nanotechnology (1986) and Nanosystems: Molecular Machinery, Manufacturing, and Computation. Nanotechnology started with the birth of cluster science, scanning tunneling microscope (STM) and fullerenes in 1985 and carbon nanotubes a few years later. Buckminsterfullerene C 60 , the simplest of the carbon structures are a major subject of research falling under the nanotechnology umbrella.

5. Small Things A fish egg is 2 mm Most human cells are 7 - 30 µm Size of a average molecule, cluster of atoms atom nucleus 0.1 pm Size of a proton Size of a quark 3.280 ft 1,000 meters 150x10 6 km (Earth to Sun Distance) 9.46x10 12 km 3.26 light years A million parsecs Big Things Centimeter (10 -2 m) Millimeter (10 -3 m) Micrometer (10 -6 m) Nanometer (10 -9 m) Picometer (10 -12 m) Femtometer (10 -15 m) Attometer (10 -18 m) Meter Killometer Astro-nomical Unit Light-year Parsec Megaparsec

6. Planets to Scale: Jupiter is 142,796 km in diameter Outer Solar System: Pluto’s orbit is 12 billion km in diameter. Milky Way Galaxy: Diameter = 150,000 light Years A. micrometer µm (or micron)- Cells B. Nanometer - Molecule Small Things Big Things

8. ZnO quantum dots

12. Novel properties of Nanomaterials

19. Quantum Dots – Basic properties J . Ma t e r . C h em., 2 0 0 4 , 1 4 , 6 6 1 – 6 6 8

20. Quantum dots' electron energy levels are discrete rather than continuous. So the addition or subtraction of just a few atoms to the quantum dot has the effect of altering the boundaries of the bandgap . Quantum Dots - A tunable range of energies Quantum confinement describes the increase in energy which occurs when the motion of a particle is restricted in one or more dimensions by a potential well. A quantum dot is a well that confines in all three dimensions such as a small sphere, a quantum wire confines in two dimensions, and a quantum well confines in one dimension. 3D potential well

28. Optical properties of ZnO nanostructures Luminescence is an optical phenomenon mostly found in cold bodies, in which the molecular absorption of a photon triggers the emission of another photon with a longer wavelength. Generally ZnO nanocrystals show two line patterns viz. sharp excitonic emission in the Ultra Violet region and broad defect related emission in the visible region.

30. Quantum confinement effect Emission energy as well as intensity ratio of which depends upon the surface to volume ratio of the nancrystals.

31. Band gap engineering of ZnO nanostructures by alloying with Mg and Cd S. G. P63mc Ionic radii = 0.60 Å Undoped ZnO Mg doped ZnO Cd doped ZnO Rock salt MgO and CdO S.G. Fm3m Ionic radii = 0.57 Å (Mg) and 0.72 Å (Cd) Wurtzite ZnO

32. Band gap engineering of ZnO nanostructures by alloying with Mg and Cd

33. Applications

34. Applications Change in the physical properties when the feature sizes are shrunk can be utilized. Nanoparticles for example take advantage of their dramatically increased surface area to volume ratio. Their optical properties, e.g. fluorescence , become a function of the particle diameter. When brought into a bulk material, nanoparticles can strongly influence the mechanical properties of the material, like stiffness or elasticity . For example, traditional polymers can be reinforced by nanoparticles resulting in novel materials which can be used as lightweight replacements for metals. Such nanotechnologically enhanced materials will enable a weight reduction accompanied by an increase in stability and an improved functionality.

35. Medicine Functionalities can be added to nanomaterials by interfacing them with biological molecules or structures. The size of nanomaterials is similar to that of most biological molecules and structures; therefore, nanomaterials can be useful for both in vivo and in vitro biomedical research and applications. Diagnostics Biological tests measuring the presence or activity of selected substances become quicker, more sensitive and more flexible when certain nanoscale particles are put to work as tags or labels. Magnetic nanoparticles, bound to a suitable antibody, are used to label specific molecules, structures or microorganisms. Gold nanoparticles tagged with short segments of DNA can be used for detection of genetic sequence in a sample. Multicolor optical coding for biological assays has been achieved by embedding different-sized quantum dots into polymeric microbeads. Nanopore technology for analysis of nucleic acids converts strings of nucleotides directly into electronic signatures. Drug delivery The overall drug consumption and side-effects can be lowered significantly by depositing the active agent in the morbid region only and in no higher dose than needed. This highly selective approach reduces costs and human suffering. An example can be found in dendrimers and nanoporous materials. They could hold small drug molecules transporting them to the desired location.

36. Chemistry and environment Nanotechnology can be applied in Chemical catalysis and filtration techniques. In this sense, chemistry is indeed a basic nanoscience. The synthesis provides novel materials with tailored features and chemical properties: for example, nanoparticles with a distinct chemical surrounding (ligands), or specific optical properties. Catalysis Chemical catalysis benefits especially from nanoparticles, due to the extremely large surface to volume ratio. Useful in Fuel cell to catalytic converters and photocatalytic devices. Catalysis is also important for the production of chemicals. Platinum nanoparticles are now being considered in the next generation of automotive catalytic converters. Filtration A strong influence of nanochemistry on waste-water treatment, air purification and energy storage devices is to be expected. By the use of membranes with suitable hole sizes, whereby the liquid is pressed through the membrane. Nanoporous membranes are suitable for a mechanical filtration with extremely small pores smaller than 10 nm (“nanofiltration”) and may be composed of nanotubes . Nanofiltration is mainly used for the removal of ions or the separation of different fluids.

37. Energy Energy storage, conversion, manufacturing improvements by reducing materials and process rates. Reduction of energy consumption A reduction of energy consumption can be reached by better insulation systems. Nanotechnological approaches like light-emitting diodes (LEDs) could lead to a strong reduction of energy consumption for illumination. Increasing the efficiency of energy production Today's best solar cells have layers of several different semiconductors stacked together to absorb light at different energies but they still only manage to use 40 percent of the Sun's energy. Commercially available solar cells have much lower efficiencies (15-20%). Nanotechnology could help increase the efficiency of light conversion by using nanostructures with a continuum of bandgaps . The use of more environmentally friendly energy systems An example for an environmentally friendly form of energy is the use of fuel cells powered by hydrogen, which is ideally produced by renewable energies.

38. Memory Storage Electronic memory designs in the past have largely relied on the formation of transistors. Two leaders in this area are Nantero which has developed a carbon nanotube based crossbar memory called Nano -RAM and Hewlett-Packard which has proposed the use of memristor material as a future replacement of Flash memory. Novel semiconductor devices An example of such novel devices is based on spintronics . The dependence of the resistance of a material (due to the spin of the electrons) on an external field is called magnetoresistance . This effect can be significantly amplified (GMR - Giant Magneto-Resistance) for nanosized objects, for example when two ferromagnetic layers are separated by a nonmagnetic layer, which is several nanometers thick (e.g. Co-Cu-Co). The GMR effect has led to a strong increase in the data storage density of hard disks and made the gigabyte range possible.

39. Displays The production of displays with low energy consumption could be accomplished using carbon nanotubes (CNT). Carbon nanotubes are electrically conductive and due to their small diameter of several nanometers, they can be used as field emitters with extremely high efficiency for field emission displays (FED). Quantum computers Entirely new approaches for computing exploit the laws of quantum mechanics for novel quantum computers, which enable the use of fast quantum algorithms. The Quantum computer will have quantum bit memory space termed qubit for several computations at the same time. Aerospace Lighter and stronger materials will be of immense use to aircraft manufacturers, leading to increased performance.

40. Optics The first sunglasses using protective and antireflective ultrathin polymer coatings are on the market. For optics, nanotechnology also offers scratch resistant surface coatings based on nanocomposites. Nano-optics could allow for an increase in precision of pupil repair and other types of laser eye surgery. Textiles The use of engineered nanofibers already makes clothes water- and stain-repellent or wrinkle-free. Textiles with a nanotechnological finish can be washed less frequently and at lower temperatures. Nanotechnology has been used to integrate tiny carbon particles membrane and guarantee full-surface protection from electrostatic charges for the wearer. Cosmetics One field of application is in sunscreens. The traditional chemical UV protection approach suffers from its poor long-term stability. A sunscreen based on mineral nanoparticles such as titanium dioxide and zinc oxide offer several advantages.

44. Dye sensitized solar cell (DSSC): The solar cell will consists of two conducting glass electrodes in a sandwich configuration, with a redox electrolyte separating the two [figure 1 (a)]. On one of these electrodes, a few micron-thick layers of ZnO/Zn1-xCdxO alloy nanostructures will be deposited from a colloidal preparation of monodispersed particles. The dye molecules will be coated by simply immersing the coated electrode (after appropriate heat treatment) in a dye solution of interest. The dye-coated electrode will be then put together with another conducting glass electrode and the intervening space will be filled with an organic electrolyte. A small amount of Pt (5-10 µg/cm2) is needed to the counter-electrode to catalyze the cathodic reduction of tri-iodide to iodide. After making provisions for electrical contact with the two electrodes, the assembly will be sealed.

45. Due to their large surface areas, nanostructured materials can be efficiently used in technologies such as PEC for hydrogen production [8, 9] and DSSC [10-12]. Morphologies and orientation of the nanostructures have great influence on the transport properties and therefore can play a key role in the performance of these devices [9, 12, 13, and 17]. It is thus important to find the appropriate nanostructures to achieve the best characteristics for device performance. In the simplest terms, the principle of photo-electrochemical water decomposition is based on the conversion of light energy into electricity within a cell involving two electrodes, immersed in an aqueous electrolyte, of which at least one is made of a semiconductor exposed to light and able to absorb the light. This electricity is then used for water electrolysis. We are planning to fabricate a photo-electrochemical cell for the photo-electrolysis of water [figure 1(b)]. The major components are a photo-anode (made of an oxide material) and cathode (made of Pt) immersed in an aqueous solution of a salt (electrolyte). The process results in oxygen and hydrogen evolution at the photo-anode and cathode, respectively. The related charge transport involves the migration of hydrogen ions in the electrolyte and the transport of electrons in the external circuit.

46. Photoresponse in film of ZnO nanostructures

47. Response to the 345 nm light on (a) nanostructured ZnO film of thickness ~ 2.5 μm sandwiched between ITO and conducting Al layer and (b) without ZnO film in between ITO and PEO/ LiClO 4 layer. Reference of bias is on ITO layer. Device is positively biased when the positive terminal of the source is connected to the top electrodes (Al or PEO/ LiClO 4) and the ITO is connected to the negative terminal.

48. I-V curves of the ITO-ZnO- PEO/LiClO 4 device for different intensity of UV illumination (345 nm) as indicated on the graph. Reference of bias is on the ITO layer. Device is positively biased when the positive terminal of the source is connected to the PEO/ LiClO 4 and the ITO is connected to the negative terminal.

49. Optical modulator AC voltage response of the visible luminescence intensity as a function of time collected at 544 nm exactly follows the amplitude and the polarity of the applied voltage. Nearly 100% modulation of the visible luminescence is achieved. Reference of bias is on ITO layer. The enhancement in the visible luminescence is observed when the negative terminal of the source is connected to the PEO/LiClO 4. Photoluminescence spectra of the device

50. Synthesis and Characterization

51. Synthesis Method The nanofabrication processes can be divided into two well defined approaches: 1) ‘ top-down’ and 2) ‘ bottom-up’ . The ‘ top-down ’ approach uses traditional methods to guide the synthesis of nanoscale materials. The paradigm proper of its definition generally dictates that in the ‘top-down’ approach it all begins from a bulk piece of material, which is then gradually or step-by-step removed to form objects in the nanometer-size regime. Well known techniques such as photo lithography and electron beam lithography , anodization , ion - and plasma-etching , that will be later described, all belong to this type of approach. The top-down approach for nanofabrication is the one first suggested by Feynman in his famous American Physical Society lecture in 1959.

52. High energy ball milling, a top-down approach for nanoparticle synthesis, has been used for the generation of magnetic, catalytic and structural nanoparticles. The technique, which is already a commercial technology, has been considered dirty because of contamination problems from ball-milling processes. However, the availability of tungsten carbide components and the use of inert atmosphere and/or high vacuum processes have reduced impurities to acceptable levels for many industrial applications. Common drawbacks include the low surface area, the highly polydisperse size distributions, and the partially amorphous state of the as-prepared powders.

53. The ‘ bottom-up ’ approach on the other hand takes the idea of 'top down' approach and flips it right over. In this case, instead of starting with large materials and chipping it away to reveal small bits of it, it all begins from atoms and molecules that get rearranged and assembled to larger nanostructures. It is the new paradigm for synthesis in the nanotechnology world as the ‘bottom-up’ approach allows a creation of diverse types of nanomaterials, and it is likely to revolutionize the way we make materials. It requires a thorough understanding of the short range forces of attraction such as Van der Waals forces, electrostatic forces, and a variety of interatomic or intermolecular forces.

54. Typical BOTTOM UP APPROACHES for Nanostructure Some examples of such a synthesis route starting from atoms and molecules are methods like: 1) chemical or electrochemical reactions for precipitation of nanostructures, 2) self-assembly of nanoparticles or monomer/polymer molecules, 3) sol-gel processing, 4) laser pyrolysis, 5) chemical vapor deposition, physical vapor deposition, 6) plasma or flame spraying synthesis, 7) atomic or molecular condensation, 8) Sputtering and thermal evaporation, 9) bio-assisted synthesis of nanomaterials.

55. CHEMICAL PRECIPITATION One of the basic ‘bottom-up’ techniques is chemical precipitation by which nanoparticles of metals, alloys, oxides, etc. are prepared in aqueous or organic solutions. PLUS: Cheap, can produce large quantities (i.e. coagulation or heterocoagulation of colloidal crystals from aqueous solutions) MINUS: The draw back of this straight-forward synthesis is related to the random distribution of particle size which is normally undesirable in nanoengineering applications.

61. SPUTTERING AND THERMAL EVAPORATION Preparing nanostructures from a supersaturated vapor was one of the earliest methods used to prepare nanoparticles. PLUSES: it is very versatile, easy to perform and to analyze the particles, produces high quantity, high purity materials, naturally produces films and coatings. MINUSES: costly, it is difficult to produce as large a variety of materials as compared to the one feasible by chemical means APPARATUS: consists of a vapor source inside a vacuum chamber containing and inert gas (usually Ar or He). The vapor source can be an evaporation boat or a sputtering target. Supersaturation is achieved by resistive heating, radio-frequency, heating, sputtering, electron beam heating, laser/plasma heating, or ion sputtering above the vapor source and nanoparticles are formed.

63. Imaging Techniques

64. The wavelength of light is a bit shorter than one µm . A ray of light can only resolve objects that are larger than its wave length. The human eye can recognize two objects if they are not closer than 0.1 mm at a normal viewing distance of 25 cm. Transmission Electron Microscope (TEM) at 60,000 volts has a resolving power of about 0.0025 nm. How can we see them?

66. The Philips CM200 transmission electron microscope Accelerating voltages is 200 kV Can achieve resolution up to 2 Angstroms. Transmission Electron Microscopy and Electron Diffraction

68. TEM is analogous to a Slide Projector

71. ZnO quantum dots

72. BRIGHT FIELD IMAGING ALLOWING TRNSMITTED BEAM

73. DARK FIELD IMAGING ALLOWING DIFFRACTED BEAM

74. SPECIMEN INTERACTION IN ELECTRON MICROSCOPY REACTIONS ON THE TOP SIDE ARE UTILIZED FOR EXAMINING THICK OR BULK SPECIMENS (SEM) RECTIONS ON THE BOTTOM SIDE ARE EXAMINED IN THIN OR FOIL SPECIMEN (TEM ) VARIOUS REACTIONS CAN OCCUR WHEN ENERGETIC ELECTRONS STRIKE THE SAMPLE SPECIMEN INTERACTION VOLUME FOR VARIOUS REACTIONS

75. COMPARISION OF LIGHT AND ELECTRON MICROSCOPE Optical glass lens, Small depth of Field, lower magnification, do not Require vacuum, Low price. Magnetic lens, Large depth of field, Higher magnification and better Resolution, Operates in HIGH vacuum, Price tag. LIGHT MICROSCOPE ELECTRON MICROSCOPE

78. Some fancy Diffraction Patterns

79. ATOMIC FORCE MICROSCOPE

80. Overview of Atomic Force Microscopy - General Principle of SPM A feedback system to control vertical position of the tip A tip as a probe  Means of sensing Vertical position of the tip Sample A coarse positioning system to bring the sample close to the proximity of the tip A Computer system, which drives the piezoelectric scanner, collects data from the tip, and converts in to an image X-Y Z Piezoelectric scanner

82. Working Principle Of An AFM

83. Optical Deflection System Laser (solid state) Tip and cantilever Scanner and positioner Quadrant photo detector

84. The total force gradient is the sum of the sample force gradient and the cantilever’s spring constant. FORCE DISTANCE CURVE

85. Different Modes of AFM Comparison of Contact and non-contact mode (a) (b) Non-Contact mode Contact mode Topography Measurement

86. Summary - Different Modes of AFM Apparent height is less. High lateral and force resolution Tapping mode Poor spatial resolution Nondestructive , high force resolution (~ ) Noncontact mode AC Potentially destructive Highest lateral resolution Contact mode Disadvantages Advantages Mode

87. Does Nanotechnology Address Teaching Standards? Nanotechnology Idea Standard it can address The idea of “Nano” – being small Structure of Atoms Nanomaterials have a high surface area (nanosensors for toxins) Structure and properties of matter, Personal and Community Health Synthesis of nanomaterials and support chemistry (space propulsion) Chemical Reactions Shape Memory Alloys Motion and Forces, Abilities of technological design, Understanding about science and technology Nanocrystalline Solar Cells Conservation of Energy and increase in disorder (entropy), Interactions of energy and matter, Natural Resources Nanocoatings resistive to bacteria and pollution Personal and Community Health, Population Growth, Environmental Quality, Natural and human-induced hazards