Molecular Beam Epitaxy (MBE) : fabricating the nanoworld

https://www.reddit.com/r/Physics/comments/16hxd1i/molecular_beam_epitaxy_mbe_fabricating_the/

created by [deleted] on 13/09/2023 at 20:08 UTC

22 upvotes, 4 top-level comments (showing 4)

As I've done an internship on surface physics (and I used MBE) I will present you what MBE is.

Molecular beam epitaxy is a powerful technique to grow epitaxial thin films (which mean that the deposited material will have a direct structural relationship with its substrate). It consists in a UHV (ultravacuum) system which operates between 10^(-5) and 10^(-8) Pa and includes :

• Different sets of pumps and jauges in order to ensure the adequate pression
• Chambers which can be separated with valves, for instance you can have a preparation and a characterization chamber
• Different instruments like a quartz balance (to evaluate the growth rate), Auger spectrometer (to probe surface chemistry/stoechiometry), LEED (surface symmetry), STM (scanning tunneling microscopy for surface topography/structure) etc.

Example of a MBE system

Example of a MBE system with the different elements

The basic physical phenomenon underlying the MBE technique is that evaporated species (from effusion cells usually) will thereafter cristallize on the substrate. The molecular regime (meaning that molecules don't interact each other) is what allows the use of this technique.

MBE schematic principle

Low pressure has to be present because contamination from exterior sources has to be avoided in order to have a clean surface.

Deriving from the kinetic theory of gases (and notably Knudsen formula), you can estimate how much time it is needed before the whole surface is contaminated from one element, forming an unitary monolayer of adsorbed species.

┌─────────────────┬──────────────────────────────┐
│ Pressure (Torr) │ Time to form a monolayer (s) │
╞═════════════════╪══════════════════════════════╡
│ 1               │ 3*10^(-6)                    │
├─────────────────┼──────────────────────────────┤
│ 10^(-3)         │ 3*10^(-3)                    │
├─────────────────┼──────────────────────────────┤
│ 10^(-6)         │ 3                            │
├─────────────────┼──────────────────────────────┤
│ 10^(-9)         │ 3000                         │
└─────────────────┴──────────────────────────────┘

It signifies that we need to use pressures around 10^(-9)/10^(-10) Torr (roughly 10^(-7) Pa) to have a sufficiently clean surface to be studied.

To finish, MBE can be used for many applications :

• Fundamental studies in surface physics and condensed matter physics, you can probe easily all the structural and physical properties of systems that you create : functional oxides etc. As it is a bottom up approach, you can do pretty much everything you want (with physical limitations however)
• Semi-conductor industry : MBE is used a lot to grow organic semiconductors for example
• Heterostructure lasers

• *Bibliography** :

M. A. Hermann, H. Sitter. *Molecular Beam Epitaxy : Fundamentals and Current Status*, Springer, 1993.

J.R. Arthur. *Molecular beam epitaxy*, Surface Science, 500:189-217, 2002.

B. R. Pamplin et al. *Crystal growth* *- International Series on the science of solid state*, Pergamon Press, 1980.

D. P. Woodruff. *Modern Techniques of Surface Science*, Cambridge University Press, 1994.

​

Comments

Comment by gioco_chess_al_cess at 14/09/2023 at 19:43 UTC

11 upvotes, 2 direct replies

Ah yes, the Most Broken Equipment. I love the smell of bake-out in the morning.

Comment by WhenCaffeineKicksIn at 13/09/2023 at 21:35 UTC

6 upvotes, 1 direct replies

You forgot the proper visualization[1].

1: https://www.youtube.com/watch?v=NsGRKSV8yH8

Comment by Independent_Rip_8216 at 15/07/2024 at 15:40 UTC

1 upvotes, 0 direct replies

I am a Chemical Engineer. Making my way into semiconductor processing. I want to learn about MBE. Any online courses or certification courses?

Comment by ReasonablyBadass at 14/09/2023 at 19:55 UTC

1 upvotes, 1 direct replies

The first thing my dumbass thinks is: Replicator?

Do you think this could be improved/developed in the direction of molecular printing?