Transcript Nanotechnology - Bristol ChemLabS

Nanotechnology
(Dr Paul May)
What is it?
1 nm = 10-9 m
Or 1 millionth of a mm
Or ~5 atoms.
Nanotechnology is making or manipulating things
on the nanoscale, i.e. the scale of a few atoms.
(But actually it’s used to mean any microscopic
physical process, e.g. making Si chips,
manipulating DNA, colloid science, etc.)
Scanning Electron Microscope (SEM) – down to ~100 nm.
Transmission Electron Microscope (TEM) – down to ~5 nm.
How is it done?
• Usually with a Scanning Probe Microscope
(STM, AFM,…)
Scanning Tunnelling Microscope (STM) – down to ~0.01 nm.
Direct write ion/electron beams can draw 3D microscopic shapes
Chemical Vapour Deposition of Thin
Diamond Films
(or....Grow Your Own Diamonds)
Dr Paul May
School of Chemistry
University of Bristol
Diamond The Ultimate Engineering Material
Extreme Properties:
1. Hardest known material
2. Highest atomic number density
3. Highest Elastic Modulus (stiffest)
4. Least compressible
5. Highest thermal conductivity (at 300 K)
6. Thermal expansion at 300 K < invar
7. Transparent from deep UV to far IR
8. Very low coefficient of Friction
9. Chemically inert
10. Biologically compatible
11. Very good electrical insulator
12. When doped, becomes semiconducting
13. Radiation hard
14. Exhibits 'Negative Electron Affinity'
Uses for Diamond Thin Films
1. Wear resistance, hard, little lubrication
•Machine parts
•Cogs, gears, bearings
•Cutting tools, saws, razors, etc.
2. Transparency IR-UV
•Optics, especially IR or high power laser lenses
•Windows (Pioneer spacecraft)
3. High Thermal Conductivity
•Heat sinks and heat spreaders for PCBs or ICs
4. Stiffness
•Reinforcements in composite structures
5. Electrical Properties
•Inert Electrochemical Sensors .
6. Semiconducting Properties
•High power devices, high V and T (500°C, 400 V)
•Computers, denser and therefore faster circuitry
7. Negative Electron Affinity
•Ultra-fast switches (transistors, computers,...)
•Flat panel displays (TVs, monitors, watches,....)
How to Make Diamond
1) Geological
•Take carbon (coal), bury it underground
at very high T and high p, wait a few
million years...
 Natural Diamond (gemstones).
2) High Pressure – High Temperature
•Copy of Nature's method.
•Take graphite, place in a hydraulic press
at 120 kbar, and 3000°C, with a suitable
catalyst (Fe, Cr, Pt)...
 Industrial Diamond
3) Chemical Vapour Deposition, CVD
•Since ~1985
 Thin Film Diamond (nm, m, mm, cm?)
Recipe for CVD Diamond
•Vacuum Chamber (10s of Torr)
•Source of Carbon (methane, ethanol,...)
•Activate Gas (hot filament, plasma...)
•Substrate (Si, Mo, quartz, etc)
If you do this you get....
... only Graphite or amorphous Carbon.
Need a few more 'tricks of the trade'.
Tricks of the Trade
•Excess H2 essential (1% CH4 / 99% H2)
•etches graphite, not diamond
•stabilises diamond surface
•removes polymers from gas phase
•Hot Substrate (> 700°C)
•gives species mobility on surface
•Pre-abrade surface
•provides nucleation sites
•and/or seed crystals
Now we get Diamond!
Hot Filament Reactor
Microwave Plasma Reactor
SEM Examples
Initial stages of diamond nucleation on a Ni substrate
A typical polycrystalline CVD diamond film
A cross-section through the film, showing columnar growth
A nanocrystalline film grown with 2% methane
SEM Examples
A thick (125 µm) W wire coated in ~40 µm of diamond
A thin (25 µm) W wire coated in ~40 µm of diamond
Diamond tubes
Diamond fibre reinforced composites
Ti metal matrix
composite
PMMA plastic
matrix composite
Diamond biosensors
Replace H termination with a C-C bond, linking the diamond
surface to a molecule of your choice, e.g. DNA, proteins, etc.




Reusable biosensors
genetic screening
disease diagnosis
in situ monitoring (glucose, insulin?)
Electron Emission Devices
Diamond has:
a negative electron affinity, or work function ~0.
Extraction of electrons from surface easy – no energy loss.
Harness those electrons to do something useful….
Field emission devices
•Extract electrons using a high voltage
•Electrons accelerated to hit a
phosphor screen
•Cheap, bright flat panel displays
•But competing with large existing
market, LCDs, Plasmas, OLEDs, etc.
Electron Emission Devices
Diamond has:
a negative electron affinity, or work function ~0.
Extraction of electrons from surface easy – no energy loss.
Harness those electrons to do something useful….
Thermionic emission devices
•Extract electrons using heat
•Electrons collected on cold electrode,
then returned to other electrode by an
electric circuit.
•Converts heat into electricity
•Diamond can be CVD coatings or
sprayed nanoparticles.
•Very efficient, large area Solar cells!
Diamond-neuron connection
Computer-brain interfaces?
Ordered growth of mice neurons on a
laminin-coated hydrophilic CVD
diamond surface.
C.G. Specht, O.A. Williams, R.B. Jackman, R.
Schoepfer, Biomaterials, 25, (2004) 4073.
Diamond is biocompatible – cells don’t produce immune
response when grown on diamond.
Can make patterned diamond grids, mice neurons can be
grown to follow the pattern and join up….artificial neural
network…’grow your own brain’
Diamond Quantum Computers
The nitrogen-vacancy (NV)
defect in diamond lattice.
 Single photon source
 very long spin lifetime at RT
 emits in visible at 637 nm
Ultrafast computers
 Unbreakable codes
 secure communications

Summary
Diamond Technology has Arrived...
We should soon see CVD diamond in:
• Medical Applications
• Car/Aircraft Components
• Optics
• (Quantum?) Computers
• TVs
• Engagement rings?
BUT, we still have problems with:
• low growth rates
• high substrate temperature
• n-doping
• single crystal growth
Web site
http://www.chm.bris.ac.uk/pt/diamond/