Semiconductor Physics and Computational Methods: Comprehensive Flashcards for Exam Review

Flashcards generated from lecture notes on Semiconductor Physics and Computational Methods, focusing on density of states, low-dimensional systems, nanotechnology, and electron microscopy.

What is the density of states function essential for in a semiconductor?

Determining the carrier concentrations and energy distributions of carriers within a semiconductor.

In low-dimensional systems, what role does quantum mechanics play as the semiconductor size approaches the nanoscale?

Quantum mechanics plays a major role.

What are quantum effects in systems that confine electrons to regions comparable to their de Broglie wavelength?

Phenomena that arise when the confinement occurs in two dimensions only, creating a one-dimensional system.

How does the density of states vary with energy for an electron confined to a 1D box?

It is a decreasing function of E and vanishes in the limit of large energy.

What is a key characteristic of the 2D density of states regarding energy?

It is a constant, independent of energy.

What replaces the k-space in defining the Density of States for a 0D structure (Quantum dot)?

No k-space is available as all dimensions are reduced.

What does 'Nano' mean?

A prefix that means very, very small; one billionth of something, or 0.000000001.

What length scale defines nanoscience where corresponding property depends on size and shape?

Nanometer scale

How does the surface to volume ratio change as particle size decreases, and what is the result?

Increases, resulting in a greater amount of a substance comes in contact with surrounding material.

How does the color of gold change at the nanoscale, and why?

Appears red because electron movement is restricted, leading to different light interaction.

What fields of study encompass nanoscience?

All sciences that work with the very small, including Biology, Physics, and Chemistry.

What are the main physical and chemical property differences at the nano-scale?

Electronic, optical, mechanical, thermal, and chemical properties can be different.

According to Dr. Richard P. Feynman, what is possible at the nanoscale?

Writing the entire Encyclopedia Britannica on the head of a pin.

What can be controlled at the nanoscale to create new materials with new properties?

Composition, size, and shape.

What is the Lycurgus Cup famous for and what material is responsible for its unusual optical effects?

An ancient Roman example of nanotechnology, colloidal gold is responsible.

What happens to the electron and VB hole as the nanocrystal radius becomes comparable to the Bohr radius?

Quantum confinement occurs.

Name at least three unique properties of nanomaterials.

Very high magneto resistance; lower melting point; high catalytic activity.

How does the melting point change as grain size decreases to less than about 10nm?

The melting point reduction is significant.

How is the strength of nanophase metals affected by their grain size?

They are exceptionally strong.

According to the lecture, what is the purpose of positional control in nanotechnology?

Enables assembling parts by precisely positioning them with respect to each other, even at the molecular scale.

Name one way nanotechnology could create shatterproof diamond.

By positioning diamond components atom by atom creating shapes directly with the material

What are the two general synthetic pathways to synthesize nanomaterials?

Top-down and bottom-up approach

List the main classification criteria for nanomaterials regarding their nanoscale confinement:

Zero-dimensional (0-D), one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D).

What happens when the size or dimension of a material is reduced continuously to below 100 nm?

Dramatic changes in properties can occur.

What is the structure known as if one dimension is reduced to the nanorange while the other dimensions remain large?

A quantum well.

What property can a quantum dot be used to synthesize?

High efficiency solar cells

What is the significance of the strength-to-weight ratio for space ships?

It is absolutely critical to the performance and economy of space ships.

What does lithography mean?

Stone writing.

If a medical technology were to have molecular precision, what could it achieve?

Directly heal injuries at the molecular and cellular level.

What element is used as the basis for fullerenes, graphene, and carbon nanotubes?

Carbon

What is a fullerene?

A molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube.

What is the most abundant form of fullerene and how many facets does it have?

C60 having 32 facets (12 pentagons and 20 hexagons)

What is graphene?

An one-atom-thick planar sheet of sp²-bonded carbon atoms densely packed in a honeycomb crystal lattice.

What is the electrical conductivity of graphene compared to copper?

Electrons are able to flow through graphene more easily than through even copper.

How do electrons move through Graphene?

They travel through the graphene sheet as if they carry no mass.

What are the properties of carbon nanotubes?

Extraordinary strength, unique electrical properties, and efficient conductors of heat.

What is a carbon nanotube?

A sheet of graphite rolled into a cylinder.

What are the two classifications of carbon nanotubes?

Single wall carbon Nanotube (SWNT) and Multiwall Carbon Nanotube (MWNT).

What are the three unique geometries, also referred to as flavors, of carbon nanotubes?

armchair, zig-zag, and chiral

Name 3 Applications of Carbon Nanotubes

conducting channel in Field emission Transistor, nanoprobes and sensors, and Composite materials

Name two advantages and two disadvantages of Arc Discharge method.

Advantages: Simple procedure, High quality product. Disadvantages: Requires further purification, Tubes tend to be short with random sizes

What gases are common for CVD Method?

Methane, Carbon monoxide, and Acetylene

What is chemical vapor deposition (CVD)?

A process in which a predefined mix of reactant gases and diluent inert gases are introduced at a specified flow rate into the reaction chamber.

What is the difference between homogenous and heterogenous reaction in the CVD process?

Homogeneous forms low-density films with lots of defects; Heterogeneous create good-quality films.

What is PECVD reactors dependence on thermal energy?

do not depend completely on thermal energy to accelerate the reaction processes.

How does physical vapor deposition (PVD) differ from chemical vapor deposition (CVD)?

PVD precursors start in solid form, whereas CVD precursors are introduced in the gaseous state.

What happens during Evaporation stage of in the physical vapor deposition?

Target is bombarded by a high energy for atoms to be dislodged.

Name three reasons to use physical vapor deposition coating.

Improved hardness and wear resistance, Reduced friction, and Improved oxidation resistance

What confirm that Electron do diffract as a wave and it varifies the De Broglie relation?

Davisson-Germer experiment

What is the primary function of the scanning electron microscope (SEM)?

To enlarge small features or objects otherwise invisible to human sight.

what is the electron beam's role in the Scanning electron microscope?

sweeps across the object building an image line by line as in a TV Camera

Name three uses for SEM.

identifying surface features composing a sample, determining its morphology

what detector cannot the EDS detector detect?

H, He, or Li.

TEM works much like a slide projector using rather than ?

electrons, light

How the production of backscattered electrons differ across compositions using different atomic numbers

higher atomic number elements to appear brighter than lower atomic number elements

What causes a slight energy loss and path change in the incident electron?

Cause by an incident electron passing near an atom in the specimen

What causes the Production of secondary electrons?

very topography related

What sort the electrons in an Auger Electrons process?

sorted according to energy to give compositional information about the specimen

what is the source of information from X-rays?

X-rays or Light emitted from the atom will have a characteristic energy which is unique to the element from which it originated.

Name three types of Machine Learning

Supervised, Unsupervised, and Semi-supervised learning

How can Machine Learning improve Electron Microscopy?

Explore time of the beam to reduce defect formation, Where is focus for a clean, high-resolution image and improving signal-to-noise ratio