Self-Assembled Monolayers

Transcription

1 Self-Assembled Monolayers

2 Literature and Further Information Surface Chemistry: venables.asu.edu/grad/lectures.html SAM s: F. Schreiber, Prog. Surf. Sci. 2000, 65, A. Ulman, Chem. Rev. 1996, 96, G. M. Whitesides, Chem. Rev. 2005, 105, (S on Metal surface) C Vericat, J. Phys.: Condens. Matter 2006, 18 R867- R900.

3 Schematic Diagram of an Ideal SAM

4 Combination of Headgroups and Substrates Used in Forming SAM s

5 Preparation of SAMs Preparation of Thin Metal Films as Substrates for SAM s: a) Electron Beam Evaporation of Au b) Of Pd c) Thermally evaporated Au film, treated with piranha and aqua regia solutions d) thermally annealed gold film deposited on a glass microscope slide functionalized with 3- aminopropyltrimethoxysilane e) gold film prepared by the templatestripping method while immersed in a solution of octadecanethiol f) gold film prepared by electroless deposition on a glass microscope slide

6 Electron Beam Evaporator

7 Preparation of SAMs Preparation of Thin Metal Films as Substrates for SAM s: a) Electron Beam Evaporation of Au b) Of Pd c) Thermally evaporated Au film, treated with piranha and aqua regia solutions d) thermally annealed gold film deposited on a glass microscope slide functionalized with 3- aminopropyltrimethoxysilane e) gold film prepared by the templatestripping method while immersed in a sol-ution of octadecanethiol f) gold film prepared by electroless deposition on a glass microscope slide

8 Template Stripping Method M. Textor,Langmuir 2003, 19,

9 Preparation of SAMs Preparation of Thin Metal Films as Substrates for SAM s: a) Electron Beam Evaporation of Au b) Of Pd c) Thermally evaporated Au film, treated with piranha and aqua regia solutions d) thermally annealed gold film deposited on a glass microscope slide functionalized with 3- aminopropyltrimethoxysilane e) gold film prepared by the templatestripping method while immersed in a sol-ution of octadecanethiol f) gold film prepared by electroless deposition on a glass microscope slide

10 Excurse: Metal Surfaces Surface Structures of Metals: a) bcc: body-centered cubic (e.g. Fe, W. Mo) b) fcc: face-centered cubic (e.g. Pt, Rh, Pd, Au) c) hcp: Hexagonal close packed (e.g. Co, Zn, Ti, Ru) bcc fcc hcp

11 Excurse: Metal Surfaces Description of exposed surface: a) The fcc(100) surface b) The fcc(110) surface c) The fcc(111) surface

12 Schematic Diagram of an Ideal SAM

13 How do Molecules Bond to Surfaces? Physical Adsorption: the only bonding is by weak Van der Waals - type forces. There is no significant redistribution of electron density in either the molecule or at the substrate surface. Chemisorption: a chemical bond, involving substantial rearrangement of electron density, is formed between the adsorbate and substrate. The nature of this bond may lie anywhere between the extremes of virtually complete ionic or complete covalent character.

14 Typical Characteristics of Adsorption Processes

15 Why is Gold the Standart? Gold forms good SAM s Gold is the historically most studied surface Easy to obtain Straightforward to prepare thin films Exceptionally easy to pattern by combination of lithograpgic tools Inert metal Binds thiols with high affinity and it does not undergo any unusual reaction with them Thin films of gold are common substrates for a number of existing spectroscopies and analytical techniques Gold is compatible with cells (no toxicity, SAM s are stable in complex liquid media reaquired for cell studies)

16 The Self-Assembly Process: Preparation of SAM s

17 The Self-Assembly Process: Preparation of SAM s

18 Wood s Notation

19 Mechanistic Considerations Au + HS(CH 2 ) n X 300K, EtOH H 2 (+O 2, H 2 O) Au S - (CH 2 ) n X 300K Au + [S(CH 2 ) n X] 2 Au S Bond~44kcal/mol X = C X = H X = F X = S Au N Bond ~8kcal/mol C X Au O Bond ~2kcal/mol S X

20 Thiol on Au(111)

21 The Basic Units θ = tilt angle, angle between the molecular backbone and the surface normal direction β = twist angle, rotation of the C C C bond plane relative to the plane of the surface normal and the tilted chain χ = azimuthal angle, tilt direction of the projection of the chain on the surface with respect to the next-nearest-neighbour direction.

22 Factors that Influence Monolayer Order 1. The cleanliness and purity of the original gold surface 2. The purity of the alkanethiol and assembly solution 3. The length and composition of the spacer chain 4. The type of head group (size and properties) 5. The amount of time the monolayer is allowed to assemble

23 Surface Structures 6 x x R30 a) zig-zag b) rectangular 2 x 4 x

24 Surface Defects Pinstripe Domain boundaries between rotated c(4 x 2) domains

25 Schematic Diagram of an Ideal SAM