Quantum confinement in nanostructures leads to unique properties, like tunable optical emissions in quantum dots. This phenomenon occurs when particle size approaches the exciton Bohr radius, resulting in discrete energy levels instead of continuous bands.

Nanoparticles exhibit size-dependent properties, such as melting point depression and surface plasmon resonance. These characteristics, along with high surface-to-volume ratios, make nanostructures ideal for various applications, from display technology to drug delivery systems.

Quantum Confinement and Nanostructure Synthesis

Quantum confinement in quantum dots

• Quantum confinement effect occurs when particle size approaches exciton Bohr radius, leading to discrete energy levels instead of continuous bands
• Impact on optical properties includes size-dependent bandgap, tunable emission wavelength (red to blue shift), and increased oscillator strength
• Factors influencing quantum confinement include particle size, shape (spheres, rods), and composition (CdSe, InAs)
• Quantum dot energy levels described by particle-in-a-box model, energy gap increases as size decreases
• Photoluminescence in quantum dots exhibits enhanced quantum yield, narrow emission spectra, and Stokes shift

Synthesis and properties of nanowires

• Synthesis methods include vapor-liquid-solid (VLS) growth, solution-based methods (hydrothermal), and template-assisted growth (AAO templates)
• Growth mechanisms involve nucleation, axial growth along preferred crystal direction, and radial growth to increase diameter
• Unique properties of nanowires stem from high aspect ratio, quantum confinement in radial direction, and enhanced surface area-to-volume ratio
• Structural characteristics include single-crystalline nature and controllable diameter (10-100 nm) and length (μm to mm)
• Doping and heterostructure formation possible through axial and radial heterostructures (core-shell) and in-situ doping during growth

Nanoparticle Properties and Applications

Size effects in nanoparticles

• Size-dependent properties manifest as melting point depression (gold nanoparticles), surface plasmon resonance (silver nanoparticles), and superparamagnetism (iron oxide nanoparticles)
• Surface chemistry characterized by high surface energy, increased reactivity, and surface functionalization (ligands, polymers)
• Colloidal stability achieved through electrostatic stabilization (surface charge) and steric stabilization (polymer coatings)
• Surface-to-volume ratio increases as particle size decreases, affecting catalytic activity (platinum nanoparticles)
• Quantum size effects lead to discrete energy levels in small nanoparticles and band gap modification (semiconductor quantum dots)

Applications of nanoscale structures

• Quantum dot applications span display technology (QLED TVs), biomedical imaging (fluorescent labeling), photovoltaic cells, and quantum computing
• Nanowire applications include field-effect transistors, sensors and detectors (gas sensors), energy harvesting devices (piezoelectric nanogenerators), and optoelectronic components (LEDs)
• Nanoparticle applications encompass drug delivery systems (liposomes), catalysis (gold nanoparticles), magnetic resonance imaging contrast agents (iron oxide nanoparticles), and water purification (silver nanoparticles)
• Cross-cutting applications involve nanocomposite materials (polymer-clay nanocomposites), theranostics (combined therapy and diagnostics), nanoscale electronics (single-electron transistors), and environmental remediation (photocatalytic nanoparticles)