Physical and Mechanical Properties of Dendrimer-Metal ......Physical and Mechanical Properties of...

Center for Materials for Information Technologyan NSF Materials Science and Engineering Center

Physical and Mechanical Properties of Dendrimer-Metal Nanocomposites

Michael L. Curry and Shane C. Street

MRSEC IRG-1Mint Fall Review, November 2002

Hybrid Organic/Inorganic Nanostructures and Interfaces


Hybrid Organic/Inorganic Nanostructuresand Interfaces

Hybrid organic/inorganic nanocomposites formed from dissimilar and typically incompatible components can yield novel physical/mechanical/structural behavior and function.Dendrimer-based organic/inorganic nanostructures are uniquely flexible: the size of the dendrimers is controllable, they are monodisperse, and the chemistry of both the core and shell can be designed to suit the application.

Applications: Probe-based molecular datastorage, biochemical sensors, optics, functionalcoatings, lubrication/adhesion, friction/roughness,tribology, etc.

This work is supported by the National Science Foundation (DMR-0213985)


Dendrimers as Functional ComponentsStarburst PAMAM Dendrimers

N N

N

N

N

N

N

N N

N

N

NN

N

NN

N

N

N

N

N

NNN

N

N

N

N

NN

NN N N NN N

N

NN

NN

NN

NN

NNNNNN

NN

NN

N

N

NN

NN

XX

XXXX XX X X XX

XX

XX

XX

XX

XX

XX

XX

XX

XX

XX

XX

X XXXXXXXXXXX

XXXX

XX

XXXX

XX

XXX

X

XX

Repeated UnitsN- (CH2)2 -N

(CH2)2 - CO -NH - (CH2)2-N

(CH2)2 - CO -NH - (CH2)2-N

Core

Dendrimers are 3d, highly branched, macromoleculeswith a core/repeat unit/terminal shell structure.

Generally classified by generation, e.g., G8: -NH2 terminated1024 endgroupsMW = 233,383 amuDiam. = 9.7 nm (solution)


Sample Configuration SchematicsMetal/G8 Dendrimer Monolayer System

Si (100) wafer (a)Si

2.5 nm Si oxidedendrimers

(b)D/Si

12 nm Metal/Si

(c)M/Si

Metal/dendrimer/Si

(d)M/D/Si

Schematic of samplesSchematic of samplesin the metal/dendrimerin the metal/dendrimerexperiments: a) nativeexperiments: a) nativesilicon, b) dendrimer silicon, b) dendrimer monolayer, c) metal monolayer, c) metal layer without dendrimer,layer without dendrimer,d) metal layer with d) metal layer with dendrimer interlayerdendrimer interlayer..

4.6 nm

14.2 nm


AFM: structure with and without dendrimer interlayer

12.5 nm Au, scan 5 µm

10 nm Cu, scan 1 µm

Almost no changes was found for Al deposition.


Nanomechanical Response

Nanoindentation

Load (P)

Hardness, H = P/A

Contact Area (A)

•The composite with the dendrimer interlayer is twice as hard as the gold layer alone. 0 5 10 15 20 25 30

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Without dendrimer interlayer With dendrimer interalyer

Hard

ness

(GPa

)

Contact Depth (nm)


TEM Plan View of 10 nm Au Films

TEM results shows a significant change in the grain size of the deposited metal film in the presence of the dendrimer interlayer.

(a) Au/Si (b) Au/D8/Si


Interfacial interactions of reactive metals

• Investigation of the metal-organic interfacial interactions using much more reactive metals (Cr and Co)– Can a bilayer be formed if we change the kinetic energy

or the reactivity of the incoming metal atom?

• How would the dendrimer monolayer respond to these types of changes– Would it survive intact?


3.5 nm Cr/G4

408 406 404 402 400 398 396 394 392

3.5 nm Cr/G10

Binding Energy (eV)

2x103 counts/sec

G8/Si

3.5 nm Cr/G8

XPS Results: N 1 s Region Cr/D/Si

•Formation of nitride layer at the interface•Consumption of dendrimer nitrogen exceeds that associated with the amine shell: ~ 50% of internal amide nitrogen involved•Degree of metal penetration decreases as the generation number increases •Nitride N 1s/total N 1s signal: 62, 56, 53%

Evaporative deposition


Sputtered deposition•Formation of nitride layer at the interface for Cr and Co.•Low binding feature apparently indicates bond-breaking in dendrimer adlayer.•Consumption of dendrimer nitrogen exceeds that associated with the amine shell: ~ 50% of internal amide nitrogen involved.•Degree of metal reaction (penetration) decreases as the generation number increases.

XPS Results: N 1s Region M/G8/Si

408 406 404 402 400 398 396 394 392

3.5nm Cu/G8

Binding Energy (eV)

G8/Si2*103 counts/sec

103

3.5nm Co/G8

3.5nm Cr/G8


10 nm sputtered 10 nm evaporated AFM Images of M/D/Si

1 µm x 1µm•AFM images showing the surface topography of metals deposited (10nm) on dendrimer (G8) mediated substrates.•Comparable rms roughness (<1nm) observed for all metals. Increase in apparent “feature size” from evaporated to sputtered metal.•Measurements without dendrimer interlayer were scanned in each experiment resulting in slightly rougher films (not shown).

Cr Cr

Co Co

Cu Cu


TEM Plan View of 10 nm Cr films.

(a) (b)

TEM results shows no significant change in the grain size of thedeposited metal film in the presence of the dendrimer interlayerfor the more reactive metals.

300nm 300nm 60nm 60nm

(a) Cr/Si (b) Cr/D/Si


Conclusions• The presence of the dendrimer monolayer influences the morphology, nanomechanical properties and chemical composition of overlayer metal ultrathin films• The reactivity of the overlayer metal and the deposition kinetics play roles in the nature of the nanocomposite (growth modes, grain size, chemical composition of the interface)•Comparable results on the surface topography of sputtered and evaporatively deposited films as monitored by AFM (RMS roughness <1nm).

Physical and Mechanical Properties of Dendrimer-Metal ......Physical and Mechanical Properties of...

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