THEORY EXAMINATION (SEM–IV) 2016-17 NANO SCIENCES

NANO SCIENCES (NOE042)

SECTION – A

(Attempt All | 10 × 2 = 20 Marks)
Explain all parts in short

(a) Nano diamond

Nano diamonds are carbon nanoparticles (2–10 nm) having diamond crystal structure. They exhibit high hardness, chemical stability, biocompatibility, and are used in drug delivery, polishing, and quantum sensors.

(b) Quantum dots

Quantum dots are zero-dimensional semiconductor nanocrystals where electrons are confined in all three dimensions. Their optical properties depend on size, leading to size-tunable emission.

(c) Fullerenes

Fullerenes are allotropic forms of carbon with closed cage structures (e.g., C₆₀). They have high strength, electrical conductivity, and applications in nanomedicine and electronics.

(d) Luminescence

Luminescence is the emission of light by a material not caused by heat, occurring due to electronic transitions (e.g., photoluminescence, electroluminescence).

(e) Face centered cubic (FCC) nanoparticles

FCC nanoparticles have atoms arranged at corners and centers of cube faces. This structure provides high packing efficiency and stability, common in metals like gold and silver.

(f) Lattice vibrations

Lattice vibrations are collective oscillations of atoms in a crystal lattice. They are quantized as phonons and affect thermal and electrical properties.

(g) Excitons

An exciton is a bound state of an electron and a hole formed due to Coulomb attraction in semiconductors and insulators.

(h) Magic numbers

Magic numbers refer to specific cluster sizes that exhibit enhanced stability due to closed electronic or atomic shells.

(i) Fermi surfaces

A Fermi surface represents the boundary in momentum space separating occupied and unoccupied electron energy states at absolute zero.

(j) Trap levels

Trap levels are defect-related energy states in the band gap that capture charge carriers, affecting conductivity and recombination processes.

 SECTION – B

(Attempt Any Five | 5 × 10 = 50 Marks)

(a) Carbon Nanotubes (CNTs) and Their Properties

Carbon nanotubes are cylindrical nanostructures of graphene sheets rolled into tubes.

Types:

Single-walled CNT (SWCNT)                 Multi-walled CNT (MWCNT)

Properties:

High tensile strength                            Excellent electrical and thermal conductivity

Low density                                           Chemical stability

Applications: nanoelectronics, composites, sensors, energy storage.

(b) Quantum Dot Laser & Superconductivity

Quantum dot laser:
Uses quantum dots as active medium, offering low threshold current, high efficiency, and temperature stability.

Superconductivity in nanomaterials:
At nanoscale, superconducting properties can be enhanced due to quantum confinement and surface effects, enabling applications in quantum devices.

(c) Electron–Material Interactions & Gold Coating in SEM

Interactions:                                          Elastic scattering

Inelastic scattering                                  Secondary electron emission

Backscattered electrons

Gold coating necessity:
Insulating samples are coated with gold to avoid charging, improve conductivity, and enhance image quality in SEM.

(d) Atomic Force Microscopy (AFM)

AFM is a scanning probe microscopy technique that maps surface topography at nanometer resolution.

Principle:
Interaction forces between a sharp tip and sample surface cause cantilever deflection.

Modes:                                                      Contact

Non-contact                                               Tapping

Applications: surface imaging, nanomechanics, biomaterials analysis.

(e) Growth Techniques of Nanomaterials & Thermal Evaporation

Growth techniques:                                  Sol–gel method

Chemical vapor deposition (CVD)              Molecular beam epitaxy (MBE)

Thermal evaporation

Thermal evaporation:
Material is heated in vacuum until it evaporates and deposits as thin film on substrate. It provides high purity films and simple setup.

(f) Graphene and Its Applications

Graphene is a single layer of carbon atoms arranged in hexagonal lattice.

Properties:

Extremely high electrical conductivity

High mechanical strength

Transparency

Applications: flexible electronics, sensors, energy storage, nano-composites.

(g) Localized Particles: Donors, Acceptors & Deep Traps

Donors: Provide extra electrons

Acceptors: Create holes

Deep traps: Energy levels deep in band gap that trap carriers

They significantly affect electrical and optical behavior of nanomaterials.

(h) Raman Spectroscopy

Principle:
Based on inelastic scattering of photons (Raman effect).

Applications:                                             Material identification

Phonon studies                                           Stress/strain analysis

Characterization of CNTs and graphene

 SECTION – C

(Attempt Any Two | 2 × 15 = 30 Marks)

 Time-Dependent Schrödinger Wave Equation

Starting from total energy:

E=p22m+VE = \frac{p^2}{2m} + VE=2mp2​+V

Using quantum operators:

E^=iℏ∂∂t,p^=−iℏ∇\hat{E} = i\hbar \frac{\partial}{\partial t}, \quad \hat{p} = -i\hbar \nablaE^=iℏ∂t∂​,p^​=−iℏ∇

Substituting:

iℏ∂ψ∂t=−ℏ22m∇2ψ+Vψi\hbar \frac{\partial \psi}{\partial t} = -\frac{\hbar^2}{2m}\nabla^2 \psi + V\psiiℏ∂t∂ψ​=−2mℏ2​∇2ψ+Vψ

This equation describes time evolution of quantum systems, essential in nanoscience.

 Inert Gas and Superfluid Clusters

Inert gas clusters:
Formed by weak van der Waals forces (He, Ne, Ar). They are used to study quantum size effects.

Superfluid clusters:
Helium clusters show zero viscosity and quantized vortices at nanoscale, important in low-temperature physics and spectroscopy.

 Microscope & Transmission Electron Microscopy (TEM)

A microscope is an instrument used to magnify small objects.

TEM:
Uses high-energy electron beam transmitted through thin specimen.

Components:                                  Electron gun

Magnetic lenses                               Specimen holder

Detector

Advantages:

Atomic-level resolution

Crystal structure analysis

Applications: nanomaterials, defects analysis, biological imaging.