Making An Appearance At The Nanoscale

Materials that interact with electromagnetic and other fields show a wide variety of spatial and temporal phenomena. 

The independence of any observation with regard to the choice of time, location, and units is a fundamental principle in physics. 

Physical quantities must rescale by the same amount throughout space-time, but this does not mean that physics is scale invariant. 

It is obvious that physics requires a quantized approach at the lowest scale, and Planck's constant h defines the least observable limit. 

Our world is governed by four basic forces: gravity, the weak force, the strong force, and the electromagnetic force, according to the standard model of constituent particles. 

Each of these forces has a distinct coupling strength as well as a distinct distance dependency. 

The gravitational and electromagnetic forces have a scale of 1/r 2 (known as the inverse-square rule) and may operate over vast distances, while the weak and strong forces only work over short distances. 

The strong force is virtually unobservable at distances larger than 1014 m, while the weak force has no effect at distances higher than 10 m. 

All of this indicates that we should be aware of the scale and units used to measure various amounts. 

All forces have the property of fading away as one travels away from the source. 

Using exchange particles, which are virtual particles produced from one item (source) and absorbed by the other, quantum field theory describes any force between two things (sink) Photons, gluons, weak bosons, and gravitons are four kinds of exchange particles that give birth to four forces; they all have a spin of one in units of h/(2 ) and transfer momentum between two interacting objects. 

The force produced between the two objects equals the rate at which momentum is transferred. 

Quantum field theory indicates that when the distance between objects grows, this force decreases. 

For example, the electromagnetic force between two charge particles diminishes as 1/r 2, while for dipole–dipole interactions, this dependency becomes 1/r4.

Because most physical or chemical characteristics can be traced back to interactions between atomic or molecular components, they all tend to retain vestiges of the inverse-distance dependency and appear as size-dependent traits for nanoscale objects. 

When at least one of the dimensions falls below 100 nm, the following material characteristics become size dependent (to varying degrees): 

• Mechanical properties: elastic moduli, adhesion, friction, and capillary forces; 

• Thermal properties: melting point, thermal conductivity; 

• Chemical properties: reactivity, catalysis; 

• Electrical properties: quantized conductance, Coulomb blockade; 

• Magnetic properties: spin-dependent transport, giant magnetoresistance; 

Engineers may adjust one or more characteristics of bulk materials by resizing them to the nano regime, which is a practical and beneficial element of this size dependency (1 nm to 100 nm). 

This property is at the heart of the idea of metamaterials, which are artificially created materials that enable nanotechnology to be used in real-world applications. 

~ Jai Krishna Ponnappan

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