Master Course - "Introduction to Surface Chemistry"

Prof. Dr. Ulrich Jonas
Macromolecular Chemistry
Department Chemistry - Biology
University of Siegen
Adolf-Reichwein-Strasse 2
AR-G 213
D-57076 Siegen
Germany
Tel.: +49 (0) 271 740-4713
Fax: +49 (0) 271 740 14713
E-Mail: jonas@chemie.uni-siegen.de

-> Suggested Literature List
 
Acknowledgment:

In these lecture notes a lot of ideas and material was gathered from the world wide web and airily used, often without an explicit reference to the origin (which would rather clog up the transparencies).  Some major sources are given in the literature list, but sometimes I do not even recall the source.  Nevertheless, I want to express my sincere thanks to everyone who contributed (unknowingly) to this script and invite everybody to freely use my material in the same way.  If you find your work in my script and you are not happy about it, please let me know so I can resolve the issue.  At the end, it is a gift to the students and used solely for teaching without any commercial interests.

1. Introduction to Surfaces:

- definition of a surface / interface [liquid / gas (vacuum), solid / gas (vacuum), solid / liquid, liquid1 / liquid2, solid1 / solid2)]

- practical examples:
    a) gold nanoparticle (surface layer to prevent precipitation)
    b) Teflon (PTFE) frying pan
    c) lotus leaf effect
    d) antireflecting surfaces
    e) semiconductor chips
    f) biochips
    -> important features of a surface: 1) surface material, 2) topography

        -> handouts: lecture_IntroSurfChem_1a.pdf  (2.0 MB)

- simple theoretical treatment of surfaces:
        > 3D crystal structures, crystal planes, Miller indices
        > surface lattices (single crystal surfaces)
        > surface reconstruction ("Überstruktur")
        > surface structure features (terrace, step, kink, adatoms)
        > surface defects (point defect, line defect (steps), domain borders, screw
             dislocation, surface reconstruction, facets, mosaic)
        > surface sites (relates to adsorption)
        > electronic and vibronic structure of surfaces

       -> handouts: lecture_IntroSurfChem_1b.pdf  (1.9 MB)

- definition of surface tension and surface (free) energy [Atkins 7.6a, p.151]

- definition of cohesion and adhesion energy
    a) cohesion in amorphous solid or liquid (isotropic, independent of orientation of
     separation plane)
    b) cohesion in crystalline solid (anisotropic, depends on orientation of separation
     plane with respect to crystal planes, e.g. silicon single crystal for wafers)
    c) measurement of cohesion and adhesion forces
    d) adhesion mechanisms in adhesive tapes (practical examples)

       -> handouts: lecture_IntroSurfChem_1c.pdf  (0.2 MB)

- types of interactions:
    > fundamental forces (strong, weak, electromagnetic -> intermolecular!,
     gravitational interactions)
    > pair potentials (Mie, Lennard-Jones)
    > all intermolecular forces are essentially electrostatic in origin (Hellman-Feynman theorem)
    > classification in long-range and short-range forces
        a) covalent bonds, ionic bond, metallic bond, coordinative bond
        b) electrostatic (Coulomb)
        c) van der Waals
        d) hydrogen bonding
        e) the force "zoo" extended: hydrodynamic, surface tension / capillary forces,
     magnetic, gravitation, buoyancy, hydrophobic interactions, solvation forces,
     topological bonds, dipole-dipole, dipole / induced-dipole interaction,
     dispersion forces = induced-dipole / induced-dipole interactions, charge
     transfer, form anisotropy, electric double layer forces, ...

       -> handouts: lecture_IntroSurfChem_1d.pdf  (1.7 MB)

- adsorption at surfaces: physisorption / chemisorption [Henzler / Göpel, p.364,368]
    a) Langmuir isotherms
    b) BET isotherm
    c) Temkin isotherm
    d) Freundlich isotherm
    -> surface sites

- surface layer growth models:
    a) Frank van der Merwe (2D layer growth)
    b) Volmer-Weber (3D island growth)
    c) Stranski-Krastanov (initial 2D layer growth, subsequent 3D island)
    d) columnar (highly defective columns by low atom / molecule mobility)
 
    -> definition of 1) epitaxy, 2) commensurability, 3) lattice strain, 4) incoherence

- preparation of highly defined surfaces:
    a) UHV (ultrahigh vacuum), single crystal [Henzler / Göpel, p.62]
    -> advantage: very well defined surface structure, full control over environment,
     many characterization methods work in UHV
    -> disadvantage: labor and money intense equipment, very sensitive to contamination
    - UHV preparation methods: sputtering, chemical vapor deposition, ...)
    b) "real live", surfaces under environmental conditions (laboratory)
    -> advantage: relative simple equipment and handling, can be more easily
     implemented in industrial processes
    -> disadvantage: very complex situation / chemistry / dynamics at the surface
     (adsorption of different and varying contaminants from surrounding air,
     chemical surface reactions (oxidation O2, hydrolysis and wetting H2O,
     electrochemical and light induced reactions)
    - environmental / ambient preparation methods: cleaving of substrates (mica,
     HOPG, ...), cleaning of substrate surfaces (SiO2 in "Piranha" or "NoChromix",
     plasma cleaner), deposition from solution or vapor phase

- structure of solid / liquid interfaces:
    a) metal surface in contact with ions in liquid (Helmholtz, Gouy-Chapman, Stern, Nernst)
    b) silica surface in water (pH dependence)
    c) grafted polymer layer in good / bad solvent
    d) molecular surface layers (SAM, LB)

       -> handouts: lecture_IntroSurfChem_1e.pdf  (0.6 MB)
 

2. Surface Characterization Methods:

imaging methods:
- breath patterns
- optical microscopy (bright field, dark field, crossed polarizers, phase contrast,
  differential interference contrast DIC, fluorescence)
-scanning probe microscopy SXM:
    a) scanning force microscopy SFM or AFM (topography in contact / noncontact,
     phase mode, friction, chemical force, ...)
    b) scanning tunneling microscopy STM (constant current, constant hight, spectroscopy)
    c) near-field scanning optical microscopy NSOM
- scanning electron microscopy SEM
- transmission electron microscopy TEM
- low energy electron microscopy LEED
- field emission microscopy FEM and field ionization microscopy FIM

       -> handouts: lecture_IntroSurfChem_2a_1.pdf  (2.2 MB)

       -> handouts: lecture_IntroSurfChem_2a_2.pdf  (2.1 MB)

force measurements:
- SFM
- surface force apparatus SFA

surface energy and surface tension:
- contact angle microscopy
- SFA
- SFM

surface layer thickness:
- ellipsometry

chemical composition:
- secondary ion mass spectrometry SIMS
- x-ray photoemission spectroscopy XPS / ESCA
- energy dispersive x-ray emission EDX (also imaging)
- scanning Auger microscopy (also imaging)

spectroscopic methods:
- Fourier transform infrared spectroscopy FTIR (grazing-angle, attenuated total reflection ATR)
- Raman spectroscopy
- ultraviolet spectroscopy UV (transmission, reflection)
- surface plasmon resonance spectroscopy SPR

diffraction methods:
- small angle x-ray scattering SAXS
- low energy electron diffraction LEED
- reflection high energy electron diffraction RHEED
- helium diffraction

       -> handouts: lecture_IntroSurfChem_2b.pdf  (0.8 MB)
 

3. General Techniques for Surface Modification

- chemical surface transformation:
    a) chemical reactions at Si-H surfaces (inorganic and organic)
    b) chemical modification of polymer surfaces (plasma and photochemically)

- layer deposition:
    a) Langmuir-Blodgett films (LB)
        - structure of amphiphilic molecules
        - application of LB films

       -> handouts: lecture_IntroSurfChem_3a.pdf  (2.2 MB)

    b) self-assembled monolayers (SAM)
        - structure of SAM molecules
        - chemical reactions at SAM
        - application of SAM
    c) chemical vapor deposition (CVD)
    d) polymer layers ("layer-by-layer" polyelectrolyte films, "grafting from",
     "grafting onto", plasma polymerization)
    e) film casting, spin coating

- etching:
    a) isotropic and anisotropic etching
    b) wet- and dry-etching methods
    c) ion milling

- modification of polymer surfaces:
    a) structural classes with polymer surfaces
         (polymers as: substrates, surface layers, surface molecules, particles)
    b) polymer surface modification / chemical transformations
         (flame-, corona-, plasma-, chemical-, and ion beam treatment, UV irradiation)
    c) material deposition
         (metalization, plasma polymerization, grafting from/to, polymer adsorption, LbL)
    d) surface segregation
         (rearrangement of functional groups as response to environmental changes)
    e) interactions between polymer surfaces / particles
         (charge-, steric-, flocculation-, and depletion interactions)

       -> handouts: lecture_IntroSurfChem_3c.pdf  (2.1 MB)

4. Patterning Techniques

- photolithography:
    a) general procedure
    b) positive and negative resists: principles and chemical examples
    c) monolayer photolithography

- electron-beam lithography:
    a) principles
    b) materials

       -> handouts: lecture_IntroSurfChem_4a_1.pdf  (0.8 MB)

- soft lithography:
    a) microcontact printing (µCP)
    b) replica molding (REM)
    c) microtransfer molding (µTM)
    d) micromolding in capillaries (MIMIC)
    e) solvent-assisted micromolding (SAMIM)

- proximal probe lithography

- embossing

- printing

       -> handouts: lecture_IntroSurfChem_4a_2.pdf  (2.5 MB)
 

5. Applications of Micropatterned Surfaces

- lotus leaf effect, shark skin
- microelectronics
- biosensors, DNA chips
- microfluidics, microreactors
- optics (antireflecting surfaces, planar lenses, gratings, couplers...)