Nanoscience and Nanotechnology Notes

Nanoscience Overview

• Nanoscience involves studying and manipulating materials at the nanometer scale ($10^{-9}$ meters).

• Deals with phenomena at the atomic and molecular levels.

• Atoms are approximately a few tenths of a nanometer in diameter.

• Molecules are typically a few nanometers in size.

Nanotechnology

• Nanotechnology is the creation of functional materials, devices, and systems through controlled manipulation of matter at the nanometer scale.

• Exploits novel physical, chemical, and biological properties at this scale.

• Richard Feynman introduced the concept in 1959.

• Feynman's lecture "There’s Plenty of Room at the Bottom":

  • Discussed writing the Encyclopaedia Britannica on a pinhead.

  • Envisioned miniaturizing computers.

  • Proposed arranging atoms to synthesize any chemical substance.

Nanoscale Properties

• At the nanoscale, material properties can be directly altered.

  • Making materials harder, lighter, or more durable.

• Size reduction can change properties:

  • Chemicals may exhibit new colors.

  • Materials may start conducting electricity.

• Nanoscale particles have increased chemical reactivity due to higher surface area.

• Nanotechnology involves fundamentally changing the internal structure of compounds.

Carbon Nanotubes (CNTs)

• Carbon nanotubes are part of the fullerene structural family.

• They have long, hollow structures with walls made of single-atom-thick sheets of carbon called graphene.

Classification of Nanomaterials

• Classified based on:

  • Size: Typically 1-100 nanometers in at least one dimension.

  • Shape

  • Composition: E.g., Metal-based nanomaterials.

  • Structure: E.g., Core-shell nanoparticles, Hollow nanoparticles.

  • Surface characteristics: Surface chemistry affecting interactions with biological systems.

• Examples based on dimensions:

  • 1 dimension < 100nm: Nanoparticles, Nanorods, nanowires.

  • 2 dimensions < 100nm: Tubes, fibers, platelets.

  • Zero or three dimensions < 100nm: Particles, quantum dots, hollow spheres.

• Examples based on phase:

  • Single phase solids: Crystalline, amorphous particles and layers.

  • Multiphase solids: Matrix composites, coated particles.

  • Multiphase systems: Colloids, aero gels, ferro fluids.

• Dimensional classification:

  • Zero-dimensional: Nanoparticles.

  • One-dimensional: Whiskers, fibers, nanowires, nanorods, nanocables, nanotubes.

  • Two-dimensional: Thin films.

  • Three-dimensional: Colloids with complex shapes.

Interdisciplinary Nature of Nanoscience

• Nanoscience integrates physics, chemistry, biology, and engineering.

• Involves nanomechanics.

• Quantum effects are significant.

Quantum Mechanics in Nanoscience

• Quantum mechanics governs the behavior of materials at the nanoscale.

• Materials exhibit unique properties not seen at larger scales.

• Applications include quantum computation and quantum teleportation.

• Research into artificial atoms.

Physical Properties of Nanomaterials

• Quantum mechanical and thermodynamic properties become important.

• Size-dependent properties:

  • Melting point

  • Fluorescence

  • Electrical conductivity

  • Magnetic permeability

  • Chemical reactivity

• Examples of altered properties:

  • Copper becomes transparent.

  • Platinum becomes a catalyst.

  • Aluminum becomes combustible.

  • Silicon insulators become conductors.

Manufacturing Approaches

• Two main approaches:

  • Bottom-up: Building from single molecules using covalent forces.

    • Examples: AFM, sol-gel processing, CVD, laser pyrolysis, molecular self-assembly.

    • Components arrange themselves into complex assemblies atom-by-atom or molecule-by-molecule.

  • Top-down: Starting with bulk material and creating smaller structures.

    • Methods: Cutting, carving, molding.

    • Traditional workshop or microfabrication methods are used.

    • Examples: Attrition and milling, nanolithography, laser ablation, electroplating.

Revolution of Nanoscience

• Potential to transform science and technology.

• Creation of new fields of study.

• New properties and behaviors:

  • Increased strength

  • Reactivity

  • Electrical conductivity

  • Changes in optical, magnetic, and thermal properties.

• Precision engineering:

  • Precise manipulation of matter.

  • Creation of structures and devices with unprecedented control.

• Cross-disciplinary collaboration:

  • Enables discoveries and breakthroughs.

• Potential for new technologies:

  • Transformation of electronics, medicine, energy, and more.

Applications of Nanotechnology

• Electronics

• Health and Medicine

• Transportation

• Energy and Environment

• Space exploration

Electronics

• Smaller transistors lead to more powerful and energy-efficient devices.

• Improved materials, such as carbon nanotubes and graphene, enable flexible electronic devices.

• Increased computing power due to smaller device sizes.

• Improved energy efficiency.

Health and Medicine (Nanomedicine)

• Early detection and prevention of diseases.

• Improved diagnosis, treatment, and follow-up.

• Nanoscale particles used as tags and labels.

• Efficient gene sequencing.

• Tissue engineering to reproduce or repair damaged tissue.

• Biosensors for real-time health monitoring.

Transportation

• Aerospace applications and space flight.

• Reduced emissions from cars.

• Improved catalysts.

• Nanocoating of surfaces for hardening and corrosion protection.

• "Smart" materials for self-monitoring and repair.

• Cerium oxide nanoparticles for fuel efficiency.

• Nanoparticles of inorganic clays and polymers will replace carbon black in tires.

• Iran Polymer and Petrochemical Institute designed high-friction tires using nanotechnology.

• Nanotechnology will affect every aspect of transportation.

Energy and Environment

• Solar technology, nano-catalysis, fuel cells, and hydrogen technology.

• Carbon nanotube fuel cells are used to store hydrogen.

• Nanoporous filters.

• Catalytic converters based on nanoscale noble metal particles.

• Environmentally safe and green technologies minimize by-products.

• More efficient lighting or combustion systems.

• Lighter and stronger materials in transportation.

Space Exploration

• Electric propulsion.

• Lighter space plane structures improve viability.

• Solar-powered ion engines.

• AI and nanorobotics reduce the time and cost of developing new technologies.

• Nanosensors and nanorobots on spacecraft exteriors increase mission rates and lower costs.

Silver Nanoparticles

• Historical uses as an antimicrobial:

  • Herodotus in 450 BC.

  • Ancient Romans kept silver in milk containers.

  • Silver nitrate for open wounds in the 17th and 18th centuries.

  • Silver nitrate to prevent eye infections in newborns (still used).

  • Silver sulphadiazine for burns in the late 1940s.

• Current antimicrobial uses:

  • Band-aids coated with silver colloids.

  • Aseptic covers for surgery, wounds, ulcers.

  • Catheter coatings.

  • Water distribution systems (e.g., Brita).

  • Sterilizing drinking water (Russian space station, NASA space shuttle).

  • Mixed into plastics in Japan (telephones, calculators, toys).

  • Embedded in sports fabric and sleeping bags.

• Properties in bulk vs. nano form:

  • Bulk silver is shiny silver.

  • Silver nanoparticles vary in color based on size and shape: spherical particles below 20 nm are yellow or amber and absorb light strongly.

Silver as an Antimicrobial

• Silver ions and compounds are toxic to microorganisms.

• Effective against bacteria (e.g., Escherichia coli) and fungi.

• Mechanism of toxicity:

  • Interaction with cellular membranes, binding to proteins or lipids.

  • Destabilizes membranes, causing ion leakage and cell rupture.

  • Disrupts mitochondrial membranes, interfering with energy production (ATP).

  • Interferes with cellular enzymes and DNA.

• Nanoparticles insert within the membrane, releasing silver ions locally.

• Continuous release of silver ions from nanoparticulate form overcomes biotoxicity limitations.

• Effective concentration of nanoparticles is much less than silver ions.

• Nanoparticle size is important for biotoxic activity.

• Antimicrobial paints with silver nanoparticles prevent bacterial growth.

Viewing Nanoparticles

• Imaging techniques:

  • Scanning Tunneling Microscopy (STM)

  • Atomic Force Microscopy (AFM), also known as Scanning Probe Microscopy (SPM)

  • Scanning Electron Microscopy (SEM)

Scanning Tunneling Microscopy (STM)

• Scans a sharp metal tip over a sample to generate an image.

• Does not rely on visible light, so resolution is higher than optical microscopes.

• STM Operation:

  1. A conductive tip is brought within a nanometer of a conductive surface.

  2. A voltage is applied between the tip and the surface.

  3. Electrons tunnel from the tip to the surface.

  4. A small electrical current (tunneling current) is produced.

• The tunneling current is exponentially dependent on the distance between the tip and the surface.

• Feedback loop keeps the tunneling current constant by adjusting the tip height.

• Images are generated by plotting the tip height as it scans the surface.

• STM images contain information about both topography and electrical conductance.

• Surfaces must be electrically conductive for STM to work.

• Used for investigating surfaces in detail and manipulating single atoms and molecules.

• IBM logo created by positioning 35 individual xenon atoms on a nickel surface.
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Atomic Force Microscopy (AFM)

• High-resolution imaging technique that can resolve features as small as an atomic lattice.

• Enables observation and manipulation of molecular and atomic level features.

• AFM Operation:

  1. A cantilever tip is brought in contact with the surface.

  2. Ionic repulsive force bends the cantilever upwards.

  3. The bending is measured by a laser spot reflected onto a split photo detector.

  4. The force is kept constant while scanning, and the vertical movement of the tip is recorded as surface topography.

• STM is limited to conducting surfaces, while AFM can image any surface.

• AFM Applications:

  • Imaging cells (e.g., red blood cells, fibroblast).

  • Monitoring cell behavior (e.g., beating of cardiac cells).

  • Manipulating living cells.

  • Imaging DNA fragments and molecules.

Scanning Electron Microscopy (SEM)

• Produces images by scanning a sample with a focused electron beam.

• Electrons interact with atoms, producing signals with information about surface topography and composition.

• Signals Detected:

  • Secondary electrons

  • Backscattering electrons

• Electron Source (Electron Gun):

  • Hot cathode source (tungsten filament) heated to emit electrons.

  • Positively charged plate (anode) attracts electrons.

  • Negatively charged plate repels electrons.

  • Hole in the plates allows an electron beam to pass through.

• Electromagnetic Lenses:

  • Coils around an iron cylindrical core create a magnetic field that acts as a lens.

  • Condenser lens controls the size and amount of electrons in the beam.

  • Objective lens focuses the beam into a spot on the sample.

• Scanning:

  • Plates around the beam deflect it.

  • Scan generator scans the beam across the sample.

  • Image is formed on a CRT synchronized with the scanning beam.

• Image Formation:

  • Beam passes through the sample.

  • Beam collides with electrons, forming secondary electrons.

  • Beam collides with the nucleus, creating backscattering electrons.

• Electron Detectors:

  • Placed in the sample chamber with a positive potential.

  • Attract secondary electrons.

• Secondary Electron Imaging Mode:

  • Holes appear as black spots.

  • Hills appear as bright spots.

• Backscattering Electron Imaging Mode:

  • Sensitive to differences in atomic number.

  • Higher atomic number materials appear brighter.

Energy-Dispersive X-ray Spectroscopy (EDX)

• Incident electron beam creates secondary and backscattering electrons.

• Outer shell electrons lose energy and emit X-rays.

• Each element has characteristic X-ray lines for elemental composition identification.

Comparison of Techniques

Conclusion

• Nanotechnology will affect almost every field of human life.

• It is an enabling technology impacting electronics, computing, medicine, materials, manufacturing, catalysis, energy, and transportation.

• Revolutionizes future world by changing material use.

• Opportunities to make things smaller, lighter, and stronger.