<< Chapter < Page Chapter >> Page >

RHEED Gun-Reflection High Energy Electron Diffraction Gun gives a beam of electron which can be made incident on the epitaxially grown film. The diffraction pattern of electrons is studied on the fluorescent screen. This shows a maximum when there is a completed monolayer and a minimum when there is a partial layer as this produces more scattering. Thus RHEED Gun is used for in-situ monitoring of the growth of the epitaxial film mono-layer by mono-layer.

Computer controlled shutters of each furnace allows precise control of the thickness of each layer, down to a single layer of atoms.

Substrate Heating- to obtain high quality epitaxial layer, growth temperature must be relatively high. The substrate wafer must be heated to allow the atoms to move about the surface and reach the proper ordered site. Growth must be at a temperature where growth rate is insensitive of minor temperature variation. Atoms arriving at the substrate surface may undergo absorption to the surface, surface migration, incorporation into the crystal lattice, and thermal desorption. Which of the competing pathways dominates the growth will depend strongly on the temperature of the substrate. At a low temperature, atoms will stick where they land without arranging properly - leading to poor crystal quality. At a high temperature, atoms will desorb (reevaporate) from the surface too readily - leading to low growth rates and poor crystal quality. In the appropriate intermediate temperature range, the atoms will have sufficient energy to move to the proper position on the surface and be incorporated into the growing crystal.

The Inventors of MBE are : J.R. Arthur and Alfred Y. Chuo (Bell Labs, 1960).

MBE is a technique for epitaxial growth of single crystal atomic layer films on single crystal substrate. It gives precise control in chemical composition and doping profiles. To avoid contamination of the epitaxial films, Ultra High Vacuum within MBE chamber is imperative. It requires Very/Ultra high vacuum (10 -8 Pa or 10 -11 Torr). This implies that Epitaxial film is grown at slow deposition rate (1 micron/hour). This permits epitaxial growth of single atomic layer if desired. Slow deposition rates require proportionally better vacuum. Ultra-pure elements are heated in separate quasi-knudson effusion cells (e.g., Ga and As) until they begin to slowly sublimate. Gaseous elements then condense on the wafer, where they may react with each other (e.g., GaAs). The term “beam” in MBE means the evaporated atoms do not interact with each other or with other vacuum chamber gases until they reach the wafer. Each gas beam may be turned on and off rapidly with a shutter or a valve. Beam intensity (called the flux) is adjusted for precise control of layer composition. A collection of gas molecules moving in the same direction constitute the molecular beam. Simplest way to generate a molecular beam is Effusion cell or Knudsen cell . Oven contains the material to make the beam. Oven is connected to a vacuum system through a hole. The substrate is located with a line-of-sight to the oven aperture. From kinetic theory, the flow through the aperture is simply the molecular impingement rate on the area of the orifice. Impingement rate is: The total flux through the hole. The spatial distribution of molecules from the orifice of a knudsen cell is normally a cosine distribution. The intensity drops off as the square of the distance from the orifice. Intensity is maximum in the direction normal to the orifice and decreases with increasing θ, which causes problems. Use collimator, a barrier with a small hole; it intercepts all of the flow except for that traveling towards the sample.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Solid state physics and devices-the harbinger of third wave of civilization. OpenStax CNX. Sep 15, 2014 Download for free at http://legacy.cnx.org/content/col11170/1.89
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Solid state physics and devices-the harbinger of third wave of civilization' conversation and receive update notifications?

Ask