Reminders Quiz#2 and meet Alissa and Mine on Wednesday –Quiz covers Bonding, 0-D, 1-D, 2-D, Lab #2 –Multiple choice, short answer, long answer (graphical questions) Lab #3 due Thursday Thursday (5/7): Meet in library at 11 am 1

Nanostructure Formation: 2-D 2

2-D Structures: Thin Films Vapor Phase Deposition –Evaporation –Molecular Beam Epitaxy –Sputtering –Chemical Vapor Deposition Solution Phase Deposition –Electrochemical Deposition (Electroplating) –Self-Assembled Monolayers –Sol – gel –Chemical Bath / Layer – by –Layer Deposition 3

Fundamentals of Film Growth For 0-D, 1-D: –Change of volume of Gibbs free energy (due to supersaturation) and surface energy For 2-D: –Also need to consider film-growth surface interaction –“Heterogeneous Nucleation” –Usually done under vacuum 4

Fundamentals of Film Growth N & N, Fig

Single crystalline, polycrystalline, or amorphous? Single crystal films –Single crystal substrate (matches growth species) –Clean substrate –High temperature –Low impinging rate Amorphous films –Low growth temperature –Too much growth species Polycrystalline films –Moderate temperature –Moderately high levels of growth species 6

Rough Vacuum Science Pressure: result of gas molecules hitting container walls Atmospheric Pressure ~ 760 torr For film deposition, decrease pressure < torr –Particles don’t collide into each other –Particles only collide with surfaces Decreasing pressure Medium High Ultrahigh (UHV) – – < Instruments: Surface / Analytical Sputtering; CVD Electron microscopes P (torr)  7 Turbo Pump

Physical Vapor Deposition (PVD) Transfer species from source; deposit on substrate Mostly involves no chemical reactions Thickness: 0.1 nm - millimeters Methods: Evaporation (heat) Molecular Beam Epitaxy Sputtering (impact of plasma) Chemical Vapor Deposition Pulsed Laser Deposition 8

Evaporation Source material is evaporated Thermal or E-Beam Material deposits on substrate Vacuum medium/high (10 -3 – torr) Control concentration of growth species in vapor Source: Nanoatructures & Nanomaterials, Fig

Sputtering Argon plasma (Ar + ) accelerated towards target As Ar + hits target, neutral atoms are ejected (momentum transfer) Ejected atoms deposit on substrate Better for alloys 10 Source: Thermal Conductive Bonding, Inc.

Evaporation vs Sputtering 11Harvard MRSEC Applied Physics 298r

Chemical Vapor Deposition CVD: Reactions between two gases to produce a solid deposit on a substrate 12

Chemical Vapor Deposition APCVD (atmospheric pressure CVD) LPCVD (low pressure CVD) 13 pcvd_lpcvd_of_zno_tco_solar_applications/

CVD Diamond /8205diamonds.html

Atomic Layer Deposition Precise control of thickness Uniform films, no pinholes Sequential pulses of precursors Low to atmospheric pressures 50 – 500 deg C 15 dge%20savannah%20200%20ALD/index.html

Pulsed Laser Deposition High vacuum or carrier gas Laser hits target to form plasma Plasma deposits on substrate 16 Definitions/PLD/

Molecular Beam Epitaxy (MBE) Special evaporation for single crystal thin films UHV: torr (atoms do not collide with each other) Real-time characterization of film RHEED (Reflection High Energy Electron Diffraction) Product: Extremely pure Few defects Control of chemical composition 17 Source: Nanostructures & Nanomaterials, Fig. 5.7

Solution phase methods Electroplating SAM Sol-gel Chemical Bath Deposition/LBL 18

Electroplating Similar to electrodeposition of 1-D structures 19 Electroplating

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 Glass nanospheres on a mica surface in an evaporating drop of water Polydimethylsiloxane triangles with magnetized strontium ferrite along the edges 20

Sol-Gel Flexible solution based method Useful for metal oxides Heat required for dense crystalline film 21

Chemical Bath/Layer by Layer Deposition Solution phase chemistry All precursors in 1 pot (chemical bath) Separate precursors (layer by layer), analogous to ALD 22 Cu x S 0.figures-only