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)