1.3 Comparison of micro and nano-scale systems

Micro and nano-scale systems behave differently from larger ones. Quantum effects, surface-to-volume ratios, and material properties change dramatically at tiny sizes. These differences impact how we make and use super small devices.

Manufacturing techniques like lithography and self-assembly create tiny structures with unique properties. Micro and nano-scale devices often perform better than bigger versions, using less energy and offering improved functionality in areas like sensors and energy harvesting.

Physical Properties at Different Scales

Quantum Effects and Surface-to-Volume Ratio at Small Scales

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• At micro and nano scales, quantum effects become more prominent due to the small size and confinement of particles
  • Quantum tunneling allows particles to pass through potential barriers that would be insurmountable in classical mechanics
  • Quantum confinement occurs when the size of a material is comparable to the wavelength of electrons, leading to discrete energy levels and unique optical and electronic properties (quantum dots)
• Surface-to-volume ratio increases significantly as the size of an object decreases
  • Nanomaterials have a much higher percentage of atoms on the surface compared to bulk materials
  • High surface-to-volume ratio leads to increased reactivity, improved catalytic properties, and enhanced sensitivity to external stimuli (nanoparticles for drug delivery)

Material Properties and Scale-Dependent Behavior

• Material properties can differ significantly between micro, nano, and macro scales
  • Mechanical properties such as strength, hardness, and elasticity can be scale-dependent
  • Electrical and thermal conductivity may change due to reduced dimensionality and increased scattering at small scales
• Size-dependent melting point depression occurs in nanoparticles
  • Melting point decreases as particle size decreases due to the increased surface energy contribution
  • Enables low-temperature processing and sintering of nanomaterials (nanoparticle-based inks for printed electronics)

Manufacturing and Performance

Fabrication Techniques for Micro and Nano-Scale Devices

• Lithography is widely used for patterning micro and nano-scale features
  • Photolithography uses light to transfer patterns from a mask to a photosensitive material (photoresist)
  • Electron beam lithography enables higher resolution patterning by using a focused electron beam to directly write patterns
• Bottom-up approaches such as self-assembly and chemical synthesis are used to create nanostructures
  • Self-assembly relies on the spontaneous organization of molecules or nanoparticles into ordered structures (self-assembled monolayers)
  • Chemical synthesis methods, including sol-gel processing and vapor deposition, allow precise control over composition and morphology (carbon nanotubes, quantum dots)

Performance Characteristics and Energy Efficiency

• Micro and nano-scale devices often exhibit improved performance compared to their macro-scale counterparts
  • Miniaturization enables faster response times, higher sensitivity, and increased functionality (MEMS accelerometers in smartphones)
  • Nanostructured materials can enhance mechanical strength, electrical conductivity, and optical properties (carbon nanotube-reinforced composites)
• Energy efficiency is a key advantage of micro and nano-scale systems
  • Reduced size leads to lower power consumption and improved energy conversion efficiency
  • Nanoscale heat transfer and thermoelectric effects can be exploited for energy harvesting and cooling applications (nanoscale thermoelectric generators)