Physical and Mechanical Properties of Dendrimer- Metal Nanocomposites

Transcription

1 Physical and Mechanical Properties of Dendrimer- Metal anocomposites Shane Street Faculty: J. Barnard, G. Zangari Post-Docs: A. Rar, J. Zhang, P. Evans, W.J. Liu Graduate Students: D. Arrington, M. Curry, F. u, P.P. Ye J.. Zhou MIT Fall Review, ovember 2001 An SF Materials Research Science and Engineering Center

2 Related Poster Presentations Molecular Interlayers and the Mechanism of Abrasive Wear of Ultrathin Metal Films F.T. u, M. Curry, F. Huang, P.P. Ye, J. A. Barnard and S.C. Street Kinetic Energy Influences on the Growth Mode of Metal Over-layers on Dendrimer Mediated Substrates M. Curry, F. T. u, J. A. Barnard, and S. C. Street Patterning of Dendrimers and Dendrimer-assisted Metal Electrodeposition D. Arrington, P. Evans, G. Zangari, and S.C. Street MIT Fall Review, ovember 2001 An SF Materials Research Science and Engineering Center

3 Dendrimer Monolayers as Tribological Interlayers - Wear resistance - Mechanical hardness (?) But even a mechanically hard, wear resistant overlayer will transmit the force of an impact to the substrate, potentially deforming it inelastically. A model Hard, wear resistant overlayer Soft, flexible interlayer Substrate An SF Materials Research Science and Engineering Center

4 Dendrimer Mediated Adhesion Baker et al., Dendrimer-Mediated Adhesion between Vapor-Deposited Au and Glass or Si Wafers Anal. Chem. 71 (1999) Demonstrated that polyamidoamine (PAMAM) dendrimers of sufficient size (generation number) can be used as an adhesion layer between silica and thick Au, replacing metallic adhesion layers (Cr, Ti). A Physical Representation of the Model? Gold Layer Dendrimer Interlayer SiO x /Si An SF Materials Research Science and Engineering Center

5 An SF Materials Research Science and Engineering Center Dendrimers as Functional Components Starburst PAMAM Dendrimers Repeated Units - (CH 2 ) 2 - (CH 2 ) 2 - CO -H - (CH 2 ) 2 - (CH 2 ) 2 - CO -H - (CH 2 ) 2 - Core Dendrimers are 3d, highly branched, macromolecules with a core/repeat unit/terminal shell structure. Generally classified by generation, e.g., G8: -H 2 terminated 1024 endgroups MW = 233,383 amu Diam. = 9.7 nm (solution)

6 AFM Images: 12 nm Au Films 5 µm 5 µm Without Dendrimer Interlayer With Dendrimer Interlayer An SF Materials Research Science and Engineering Center

7 anomechanical Response anoindentation Load (P) Contact Area (A) Hardness, H = P/A Hardness (GPa) Without dendrimer interlayer With dendrimer interalyer The composite with the 1.0 dendrimer interlayer is twice as hard as the gold layer alone Contact Depth (nm) An SF Materials Research Science and Engineering Center

8 SEM Images of anoscratch Events 4 m constant load, Berkovitch tip (face forward) 10 nm Cu/D8/Si 10 nm Cu/Si An SF Materials Research Science and Engineering Center

9 AFM Images of anoscratch Events 10 nm Cu/D8/Si 10 nm Cu/Si An SF Materials Research Science and Engineering Center

10 TEM Images: Grain Size 15 nm Cu/D8/Si 15 nm Cu/Si An SF Materials Research Science and Engineering Center

11 AFM Images 1µm x 1µm PS Results: 1s Region G8 Thermal Deposition G8 Sputtered Deposition An SF Materials Research Science and Engineering Center

12 Three Parameter Roughness Analysis R: Point to point distance W: RMS roughness ξ: Correlation length α: Roughness exponent H(nm 2 ) Cu/G8/Si sputtered Cu/G8/Si evaporated 0.01 (10nm) Evaporated Sputtered W(nm) ξ(nm) α E R (nm) Height correlation function H(R) = AVE{[h(R) - h(0)] 2 } from AFM profile; fit to H(R) = 2 W 2 [1-exp(-(R/ξ) 2α )] An SF Materials Research Science and Engineering Center

13 G8/Si 3.5 nm Cr/G nm Cr/G 8 PS Results: 1 s Region Cr/D/Si 2x10 3 counts/sec Binding Energy (ev) sputter deposition 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 itride 1s/total 1s signal: 68, 58% comparable with 63, 56% in thermal methods of evaporation. An SF Materials Research Science and Engineering Center

14 10 nm sputtered 10 nm evaporated AFM Images of M/D/Si Cr Co Cr Co 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 grain size for sputtered. Measurements without dendrimer interlayer were scanned in each experiment resulting in slightly rougher films (not shown). Cu Cu An SF Materials Research Science and Engineering Center

15 Electrochemical Deposition of Copper Cu/G8/Si Si Electroplating solution: 0.2M CuSO 4 ; 0.25M a 2 SO 4 ; 0.42M H 3 BO 3 ; distilled water Substrate: doped Si (ntype, 0.01 Ω/cm) The dendrimer monolayer can be used to promote adhesion of copper electroplated from an acidic copper bath onto the native oxide of doped Si. An SF Materials Research Science and Engineering Center

16 Patterning Surfaces Using Microcontact Printing Microcontact printing is a means of forming chemical patterns onto surfaces. A polydimethylsiloxane (PDMS) stamp is used as the template. The stamp is treated with the chemical ink and is subsequently transferred to the substrate. An SF Materials Research Science and Engineering Center

17 AFM Image of G4 Patterned Dendrimer Multilayer Features are over 60 nm high, indicative of multilayer formation of G4 An SF Materials Research Science and Engineering Center

18 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) Dendrimer layers improve adhesion of electrodeposited metals and they may be patterned by microcontact printing MIT Fall Review, ovember 2001 An SF Materials Research Science and Engineering Center