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.)
How is it done? • Usually with a Scanning Probe Microscope (STM, AFM,…)
Chemical Vapour Deposition of Thin Diamond Films (or....Grow Your Own Diamonds) Dr Paul May School of ChemistryUniversity of Bristol
Diamond - The Ultimate Engineering Material • Extreme Properties: • Hardest known material • Highest atomic number density • Highest Elastic Modulus (stiffest) • Least compressible • Highest thermal conductivity (at 300 K) • Thermal expansion at 300 K < invar • Transparent from deep UV to far IR • Very low coefficient of Friction • Chemically inert • Biologically compatible • Very good electrical insulator • When doped, becomes semiconducting • Radiation hard • 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!
SEM Examples Initial stages of diamond nucleation on a Ni substrate
SEM Examples A thick (125 µm) W wire coated in ~40 µm of diamond
Diamond fibre reinforced composites Ti metal matrix composite PMMA plasticmatrix 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 connectionComputer-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/