2-D Nanostructure Synthesis (Making THIN FILMS!)

Examples of thin films: Hydrophobic coating on windshield Plating on a car bumper Anti-reflective coating Solar cells have a transparent conductive coating Soap bubbles Gasoline puddle

Rough Vacuum Science 101 Pressure: The result of gas particles colliding & exerting force Vacuum: The absence of pressure (or very little pressure) Atmospheric Pressure ~ 760 torr For film deposition, decrease pressure < torr – Particles don’t collide into each other very often – Particles mostly collide with surfaces Decreasing pressure Medium High Ultrahigh (UHV) – – < Instruments: Surface / Analytical Sputtering; CVD Electron microscopes P (torr) 

Some Terms… Source: The same chemical as the species, just in a different state of matter, size or location (Ex: Gold) Species: The chemical you wish to grow (ex: Titanium Oxide) Substrate: The surface you are growing the thin film on (ex: Silicon)

Physical Vapor Deposition (PVD) Involves the transferring of the species from source to a substrate (ex: Vaporized gold is transferred to a substrate and deposited as a thin layer of gold atoms) Thickness: 0.1 nm - millimeters 2 main types: #1: Evaporation (heat) #2: Sputtering (impact of plasma)

Evaporation Source material is evaporated Material deposits on substrate Vacuum (10 -3 – torr) Control concentration of growth species in vapor Fun fact, it’s $60,000 for one of these! Intel, for example, has many of these instruments

Demo: Beaker & watch glass

Sputtering Argon plasma (Ar + ) accelerated towards target As Ar + hits target, neutral atoms are ejected Ejected atoms deposit on substrate

Challenge: Make a model!

Chemical Vapor Deposition Similar to PVD, but reactions between two gases to produce a solid deposit on a substrate

Self-Assembly Ordered arrangement of molecules that occurs spontaneously due to forces (e.g. chemical reactions, electrostatic attraction) Chemical bonding between molecules and substrate, as well as between molecules – Sulfur LOVES Cu, Ag, Au

2D Film Synthesis: Coating Methods Dip-Coating: – Immerse, Deposit/Drain, – Evaporate, Repeat Spin-Coating: –Deliver sol to substrate center –Spin up; Spin-off –Evaporate; Repeat Resulting Films are porous & amorphous —Unique properties (low thermal conductivity) —Applications (electrodes in solar cells)