CAPITOLO III MATERIALI ASSEMBLATI E AUTOASSEMBLATI. Photonics and Biophotonics Organics Synthesis - PhoBOS

Transcription

1 CAPITOLO III MATERIALI ASSEMBLATI E AUTOASSEMBLATI 1

2 Outline and motivation SA mono and multilayers on silica and silicon native oxide The chemistry of the process the effect of moisture the effect of the solvent the effect of temperature From mono to multi layers. Reactive functionalities on a surface Case study I Electro-optic modulators the electro-optic effect in organic materials Self-limiting chemisorptive siloxane self assembly Case study II Organic Field Effect Transistors structure and components the gate insulator role SAM as very thin gate insulator the Self Assembled Nano Dielectric (SAND) concept 2

3 Weak and ordered forces, nanostructured films Langmuir-Blodgett films 3

4 The Langmuir isotherms deposition Compression 4

5 Experimental Setup 5

6 The Langmuir isotherms Branching effect 6

7 The Langmuir isotherms Head group effect 7

8 Morphology Films X, Y and Z Transfer ratio A L τ = 100 AS 8

9 Self-Assembled Mono and Multilayer on hydroxy-functionalized surfaces 9

10 Outline and motivation SA mono and multilayers on silica and silicon native oxide The chemistry of the process the effect of moisture the effect of the solvent the effect of temperature From mono to multi layers. Reactive functionalities on a surface Case study I Electro-optic modulators the electro-optic effect in organic materials Self-limiting chemisorptive siloxane self assembly Case study II Organic Field Effect Transistors structure and components the gate insulator role SAM as very thin gate insulator the Self Assembled Nano Dielectric (SAND) concept 10

11 Mechanism of deposition the role of the solvent 1. Moisture extraction from the substrate 2. Chlorosilane hydrolisis 3. Surface adsorption and polymerization of the silanole Optimum condition: H 2 O 0.15 mg/100 ml solvent Hydrophobic solvents: - Low water concentration in solution (reduced hydrolysis) - lanole low solubility (surface deposition favorable) Hydrophilic solvents -High water extraction capability -Solution polymerization (silanoles and low oligomers are soluble) 11

12 Coverage and reproducibility The role of moisture ) Excess water leads to polymerization in solution and polysiloxane deposition ) Rigorous absence of water gives Incomplete monolayers 12

13 Mechanism of deposition the role of the temperature On silica contact angle Cl Cl Cl low temperature low silanole solubility favored absorption reduced wated solubility controlled hydrolysis higher order due to WDW interactions Optimal T growt: C18 silane 18 C C10 silane 10 C 13

14 Surface grafting mechanism and SAM morphology Possible trimeric (soluble) precursor HO OH OH Not all of the silanoles bind to the surface. Statistically one over 5 silanoles reacts with the surface. The preformed silica oligomer bridges over defects. 14

15 Wide range of possible functionalization HO HO OH n R R = X, CN, SCN, OCH 3, COOCH 3, CSOCH 3, OCOCH 3, (CH 3 ) 3 perfluorinated chains, benzyl halides,.. Strongly basic functionalities lead to disordered films, interactions with surface and lateral chain silanoles. Free alchools, amine, free thiols and nucleophylic functionalities in general are incompatible. Multilayers, functional structures? 15

16 Iteration: multilayered structures Construction of self-assembled multilayers from methyl 23- (trichlorosilyl)tricosanoate Tillman, N.; Ulman, A.; Penner, T. L. Langmuir 1989, 5,

17 Condensation Chemistry Surface modification through the SAM approach The general idea Cl H 2 O OH Hydroxylated surface Solvent Temperature Reagents Time Surface reactivity - Dense, conformal coverage - robust, covalent bonding - wet process - wide range of accessible functionalities 17

18 Self Assembled Acentric Multilayers Synthesis 18

19 Self Assembled Acentric Multilayers Synthesis repeat Substrate (i) (ii) (iii) (i-iii) (i) Coupling reagent, I X 3 (ii) Organic Chromophore, N O R O Et S HCN OH OH (iii) Capping reagent, Cl Cl Cl O Cl Cl O Cl Cl Cl X = Cl, I, OR 19

20 OH Organized self assembled monolayers with Zwitterionic Chromophores OH OH GLASS, QUARZ, SILICON I X 3 X = Cl, I, OR O I O O O I O O O I O O N S IN SOLUTION CN Na CN UV-Vis INCOLORE NC S NC CN S CN S NC CN 0.7 Absorbance N N N Wavelength (nm) BLU O O O O O O O O O Facchetti, A. ; van der Boom, M. E.; Abbotto, A. ; Beverina, L.; Marks, T. J.; Pagani, G. A. Langmuir 2001, 17,