Week 11 frontier chemistry

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Week 11 frontier chemistry

  1. 1. Chapter 6 Frontier Chemistry Nanomaterials Nanoscience Nanotechnology Prepared by: Mrs Faraziehan Senusi PA-A11-7C Characterization Fabrication Synthesis Reference: Inorganic Chemistry4th ed, 2006, Shriver & Atkins, Oxford
  2. 2. Nanomaterials • Materials having critical dimension between 1-100 nm. • Nano material is taken to be a solid material and exhibits ‘novel’ properties related to this scale. ‘novel’: New or unusual in an interesting way • Novel optical properties appear in nanoparticle are being exploited for – Information – Biological – Sensing – Energy technologies – Example: semiconducting nanoparticle and metallic nanoparticle
  3. 3. Nanomaterials - DNA • Original version of nanotechnology occurred in nature, where organisms developed an ability to manipulate light and matter on a atomic scale to build devices that perform specific functions, such as stored information, reproducing themselves and moving about. • DNA ~ ultimate nanomaterial. • It stores information as the sequence of base pairs that are spaced about 0.3 nm apart. • Folded DNA molecules have an information density of more than about 1 Tb cm-2 (1 Tb = 1012 bits), which is much greater than achieved in most current data storage system.
  4. 4. Nanoscience • Study of the properties of matter that have length scales between 1 and 100 nm. • Study of the new effects that arise only in materials that exist on the nanoscale.
  5. 5. Nanotechnology • Collection of procedures for manipulating matter on this scale in order to build nanosized entities for useful purposes. • Study of the procedures that creates new functionalities that are possible only by manipulating matter on the nanometre scale. • Photosynthesis – example of biological nanotechnology Nanostructures are exploited to: – absorb light – Separate electric charge – Shuttle proton around – Convert solar energy into biologically useful chemical energy
  6. 6. • Human have practised nanotechnology for centuries • Example:  Gold and silver salts have been used to colour glass Gold – produce red stained glass Silver – produce yellow  Photosensitive nanosized particle in silver halide emulsions used in photography  Nanosized carbon granules in the ‘carbon black’ used for reinforcing tyres and in printer’s ink  Biomedical technology metallic nanopigment ~ used to tag DNA and other nanoparticles
  7. 7. • Began to take shape in the latter half of the twentieth century • Significant contribution – Gerd Binnig and Heinrich Rohrer developed the scanning tunneling microscope – Scanning probe tip was used to rearrange atoms on a surface to spell out words – Demonstrating an ability to manipulate and characterize nanoscale structure
  8. 8. Characterization • Areas of nanomaterials, nanoscience and nanotechnology were intimately tied in characterization and fabrication methods. • Great advances made in these areas would not have occurred without the ability to characterize the nanostructural, chemical and physical properties of materials. • Methods:  Scanning probe microscopy  Electron microscopy techniques
  9. 9. Scanning probe microscopy Scanning tunneling microscopy • Scanning tunneling microscopy (STM) was the first of a series of Scanning probe microscopy, which are techniques that allow 3D imaging of the surface of materials by using sharp and sensitive physical probes. • This technique use a sharply pointed probe brought into close proximity with the specimen and construct image by scanning the probe over the surface of the specimen • Monitoring the spatial variation in the value of physical parameter, such as potential difference, electric current, magnetic field and mechanical force. – In STM, an atomically sharp conductive tip is scanned at about 0.3 – 10 nm above the surface. – Uses tunnelling current from a sharp tip to image and characterize a surface
  10. 10. Scanning tunneling microscopy
  11. 11. Scanning probe microscopy Atomic force microscopy • In AFM, atoms at the tip of the probe interact with the surface atoms of the sample through intermolecular forces such as van der waals interactions. • The cantilever holding the probe bends up and down in response to the forces and the extent of deflection is monitored with a reflected beam. • Variations on AFM include:  Frictional force microscope – measures variations in the lateral forces on the tip based on chemical variations on the surface  Magnetic force microscope – uses magnetic tip to image magnetic structures  Electrostatic force microscope - uses tips that can sense electric fields  Scanning capacitance microscope - tip is used as an electrode in a capacitor • Scanning near-field optical microscopy (SNFOM) – Combines the local interactions of a scanning probe and a specimen with well –established methods of optical spectroscopy.
  12. 12. Atomic force microscopy
  13. 13. Electron microscopy techniques • Electron beams are accelerated through 1-200kv and electric and magnetic field are used to focus the electron • In transmission electron microscopy (TEM) – the electron beam passes through the thin sample being examined and is imaged on a phosphorescent screen – Often used for imaging electron-transparent biological samples because it offers atomic resolution for highresolution metarials studies. • In scanning electron miscroscopy (SEM) – the beam is scanned over the object and the reflected (scattered) beam is then imaged by the detector. • In both microscopes, the electron probes caused the production of X-rays with energies characteristic of the elemental composition of the material.
  14. 14. Electron microscopy techniques
  15. 15. Fabrication • Two basic techniques for the fabrication of nanoscale entities. 1. Top-down approaches  A macroscale (or microscale) object and to carve out nanoscale patterns.  In this approaches, patterns are first designed on a large scale, their lateral dimensions are reduced and then used to transfer the nanoscales features into or onto the bulk material.  Physical interaction • Lithography ~ method for making printed circuits • Mechanical stamping • Nanoscale printing  Most common approach is photolithography, the technique used to fabricate very large scale integrated circuits having feature dimension on the 100 nm scale
  16. 16. Top - down 1m Bulk material Thin films Top-down technique starts with larger objects that are whittled down into nanoscale objects Heterostructures Litographic wires Quantum dots 1 nm Nanocrystals Molecular wires Proteins Molecules 100 pm Atoms Bottom - up Bottom-down technique starts with smaller objects that are combined into nanoscale objects
  17. 17. 2. Bottom – up approaches – Build larger objects by controlling the arrangements of their component smaller-scale objects – Start with control over the arrangements of atoms and molecules – Bottom up approach to nanoscale fabrication because of its focus on the interactions of atoms and molecules and their arrangement into larger functional structures
  18. 18. Synthesis • Methods widely used to prepare nanomaterials.  Solution based synthesis of nanoparticles – Main techniques for nanoparticle synthesis because they have atomically mixed and highly mobile reagents • Allow for the incorporation of stabilizing molecule • Widely successful in practise • Two stages of crystallization from solution are nucleation and growth – Basic stages in solution chemistry are: • Solvate the reactant species and additives • Form stable solid nuclei from solution • Grow the solid particles by addition of material until the reactant species are consumed.
  19. 19.  Vapour phase synthesis of nanoparticle • Alternative techniques for nanoparticle synthesis because they have atomically mixed and highly mobile reagents • It can be controlled by varying the condition and also widely succesful in practice. • It as a attractive synthesis methods for particles when continuous operation is required or when solution method do not produce good quality nanoparticles.
  20. 20.  Synthesis using frameworks, supports and substrates  Nanosized reaction vessel • By carrying out reactions in nanoscale reaction vessels, the ultimate dimensions of solid products are confined to the vessel size; a reverse micelle has an aqueous core in which reactions can occur  Physical vapour deposition • A vapour of atoms, ions or clusters physically adsorb to the surface and combine with other species to create a solid • Molecular beam epitaxy (MBE) is a technique where evaporated species from elemental charges are directed as a beam at a substrate where growth occurs  Chemical vapour deposition • A vapour of molecules chemically interact or decompose at or near the substrate, where they adsorb to the surface and combine with other species to create a solid and residual gaseous product.

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