School of Materials Engineering Thin Films and Interfaces Atomic Force Microscopy Studies of Gold Thin Films Dara Gough Advisor: Prof. King
Dec 21, 2015
School of Materials EngineeringThin Films and Interfaces
Atomic Force Microscopy Studies of Gold Thin Films
Dara Gough
Advisor: Prof. King
School of Materials EngineeringThin Films and Interfaces
Overview
• Brief Background• Purpose of the project• Project objectives• Why use gold films?• Experimental approach• Setbacks• Results
School of Materials EngineeringThin Films and Interfaces
Background
• The angle formed by the grain surfaces at the grain boundary is constant
• The triple junction was ignored in previous research– It is now believed to
have a line tension associated with it that affects the grains
School of Materials EngineeringThin Films and Interfaces
Background
• Theory: Groove (grain boundary and triple junction) depths increase with decreasing grain size
– The effects may be significant in Nano-scale
School of Materials EngineeringThin Films and Interfaces
PurposeEventual Goal:• Triple junctions may be “doped” to high levels (Via
Diffusion Along the Triple Junction) to make them conductive in an insulating material, or magnetic, or otherwise active regions of near-atomic dimension.
Courtesy of Prof. King
School of Materials EngineeringThin Films and Interfaces
Purpose• To study the
development of grooves as a function of the film thickness – The relative height (Hr)
is approximately equivalent to 4/3 and is derived by the expression:
zg
zgb
ztj
gbg
tjgr zz
zzH
School of Materials EngineeringThin Films and Interfaces
Objectives• To create gold thin films of varying
thicknesses• To anneal the film samples• To obtain surface profiles of the
samples
School of Materials EngineeringThin Films and Interfaces
Objectives
• To analyze the surface profiles and obtain data points– The data points are the height
differences between:• The center of the grain and the middle of
the grain boundary• The center of the grain and the triple
junction
School of Materials EngineeringThin Films and Interfaces
Why Gold?
• Gold is the ideal metal for this experiment because:– It is polycrystalline – It does not oxidize in atmospheric
conditions– It evaporates easily in high temperature-
low pressure environment
School of Materials EngineeringThin Films and Interfaces
Experimental Approach
• Evaporation coat glass substrates with a gold thin film– Thicknesses ranging
from (150-450nm)
• Anneal the samples at 350°C for 72 hours– To create dome-shaped
grains that are approximately equal in size to the film thicknessImage courtesy of Prof. King
School of Materials EngineeringThin Films and Interfaces
Experimental Approach
• Obtain profiles of the gold film using the Atomic Force Microscope (AFM)
– Multiple images must be taken of each film in order to obtain hundreds of data points
12 x 12 microns
Image courtesy of Raghavan Narayanan
School of Materials EngineeringThin Films and Interfaces
Experimental Approach
• The next step in the project is to analyze the images– This is done using Scanning Probe
Microscopy Software – The software analyzes changes in height
along the surface and provides relative height differences
School of Materials EngineeringThin Films and Interfaces
Setbacks
• Problems:– Multiple scan errors
with the AFM– Vibration lines in
images– Improper
engagement of the tip
1.0 x 1.0 micron
School of Materials EngineeringThin Films and Interfaces
SetbacksThis is an ideal image obtained using the AFM
1.0 x 1.0 micron
This is the type of image obtained from the AFM recently6 x 6 microns
Image courtesy of Raghavan Narayanan
School of Materials EngineeringThin Films and Interfaces
Setbacks
• My initial set of gold films was over-annealed– This resulted in the gold receding from
the substrate
School of Materials EngineeringThin Films and Interfaces
SetbacksThis optical microscopy image was taken using reflected light
This is the same image taken using transmitted light
School of Materials EngineeringThin Films and Interfaces
Results
• I was able to begin analyzing an image provided by Raghavan Narayanan
• Average grain size is 1270 nm2 (counted 252 grains)
1.0 x 1.0 micron
Image courtesy of Raghavan Narayanan
School of Materials EngineeringThin Films and Interfaces
ResultsHr Distribution
0
5
10
15
20
25
30
35
Data Range
Fre
qu
en
cy
170 Data Points
School of Materials EngineeringThin Films and Interfaces
Future Work
• Take more surface profiles using the AFM– Over a wider variety of film thicknesses
(grain sizes)
• Analyze the surface profiles using the Scanning Probe Microscopy Software
School of Materials EngineeringThin Films and Interfaces
Acknowledgements
• I would like to thank the National Science Foundation (REU Grant DMR-0243830) for financing my research alongside the Department of Energy
• I would like to thank Prof. Alex King for his support and guidance
• I would also like to thank Raghavan Narayanan for his assistance throughout the course of the project
School of Materials EngineeringThin Films and Interfaces
(Questions)