1. Solid Surfaces Analysis Group & Electron Microscopy Laboratory
Nanophysics
Michael Hietschold
Solid Surfaces Analysis Group &
Electron Microscopy Laboratory
Institute of Physics
Portland State University, May 2005

2. Content of the Whole Course
1st Lecture
1. Introduction
2. The Nanoscale in 2,1,0, and 3 Dimensions
3a. Surfaces and Interfaces – Geometrical Structure

3. Intermediate Lecture – SPM Nanoanalysis
I. Nature of Resolution Limits – Near-Field Principle
II. Scanning Tunneling Microscopy / Spectroscopy / Manipulation
III. Scanning Force Microscopies
IV. Other Near-Field Microscopies

4. 2nd Lecture
3b. Surfaces and Interfaces – Electronic Structure
4. Semiconductor Heterostructures
3rd Lecture
5. 2-Dimensional Electron Gas
6. Quantum Interference, Molecular Devices, and Self-Assembling
7. Outlook

5. 1.Introduction History: Richard Feynman 29th December 1959
(APS Meeting at Caltech):
„There is plenty of room at the bottom“
Fiction : Molecular electronics (F.L.Carter 1982)
Reality: Daily-life nanotechnology (e.g. ultrathin films,
ultra-precision manufacturing, self-organized
and -assembled structures, ...)
Breakthrough: Scanning probe techniques
Nanotechnology needs Nanoscience !!!

6. Dimensional Considerations
1 nm = 10-9 m = µm
1/1000 extension of a malaria
bacterium
A few nearest-neighbor distances
in solids
Fe (bcc): d = 0.25 nm
1 nm

7. Role of surface effects increases with decreasing dimensions
A / V = 6a2 / a3 = 6 / a = 6 V-1/3
V = a3 (2a)3 = 8 a3 (5a)3 = a (10a)3 = a3
Percentage of „surface atoms“:
100% 100% ,4% ,8%
Macroscopic: V = (108a)3 = a3 A = 6 (108a)2 = a2
Percentage of surface atoms: % !!! (negligible)

8. Behavior of extensive physical quantities
Classical macroscopic physics (thermodynamics):
E = ε V = e N
Geometry-dependent mesoscopic quantities:
Sphere:
E = ε V + εSurface(R) A = e N + eSurface(R) N2/3
Cube:
E = ε V + εSurface A + εEdge L + εCorner 8
≈ e N + eSurface N2/3 + eedge N1/3 + eCorner N0
εSurface = εSurface (∞)

9. Quantum Electrodynamics
Application of Basic Physical Theories – Classical vs. Quantum Physics:
Classical Mechanics
Electrodynamics
Thermodynamics
Quantum Mechnics
Quantum Electrodynamics
Quantum Statistics
mesoscopic phenomena (quasiclassical regime)

10. Bottom-up and top-down approaches
„chemical/syntheti-cal approach“ (scaling-up from the atomic entities)
Top-down:
classical approach of miniaturization (scaling down from the macroscopic world)

11. 2. The Nanoscale 1, 2, 3 Dimensions
Number of Nano-Dimensions:
1 – Nanofilms
2 – Nanowires
3 - Nanodots
One can start by creating Nanofilms on a substrate and
proceed to Nanowires and Nanodots by lateral lithography

12. Other Nanoobjects Nanocomposites Nanoporous Systems
High-velocity deformed nanostrucutred Ni
Nanoporous luminescent Si

13. Supramolecular Architectures
J.-M.Lehn
3-dimensional functional structures
according to the molecular geometri-
cal and electronic structures
C.J.Kuehl

14. 3. Surfaces and Interfaces 3.1. Macroscopic Description
Surface Energy:
E = ε0 V < 2 [ ε0 (½ V) + εSurface A ]
 εSurface > 0
Relaxation
„frozen“ surface relaxes
towards equilibrium
Classical cleavage

15. Wulff‘s Construction Surface tension γ: γ = ∂ F / ∂ A ∫ γ(n) dA  Min.  
∫ γ(n) dA  Min.
(whole surface)
γ-plot:
inner enveloppe of γ(n)
determines crystal
shape in equilibrium

16. Phase Boundaries Interfacial tensions Young‘s equation:
γS = γS/F + γF cos Ф
determines modes of thin film growth:
Frank - van der Merwe (complete wetting)
Vollmer-Weber (islands)

17. Frank-van der Merwe Stranski-Krastanov Vollmer-Weber
Ф = 0; γS > γS/F + γF Ф > 0; γS < γS/F + γF
Atomic interactions:
Sub-Ads > Ads-Ads Ads-Ads > Sub-Ads
only valid in equilibrium  supersaturation changes conditions

18. 3.2. Structure and Crystallography of Surfaces
TLK model
(terraces, ledges,
kinks)
Burton, Frank,
Cabrera 1935

19. Fundamental Surface Lattices
5 Bravais lattices in 2 dimensions belonging to 10 point groups
in 3 dimensions: 14 Bravais lattices, 32 point groups

20. Miller Indices z Sections cutted from the axis Take inverse of them
Multipy to get the smallest
Integers
Axes parallel to surface –
index 0 y x
(1-10)
(211)

21. varying distances between lattice planesz
Surface Relaxation
varying distances between lattice planes
(metals)
Surface Recon-struction
Change of (lateral) atomic arrangement on the surface
(semiconductors)

22. Adsorbate Structures z

23. Description of superstructures:
R = m a1 + n a2
Adsorbate / Rec. Surface Lattice:
b1 = m11 a1 + m12 a2
b = M a
b2 = m21 a1 + m22 a2
Area of new unit cell:
|b1 x b2| = det M |a1 x a2|
integer simple
det M rational  coincidence superlattice
irrational incommensurate

24. Exemples:
Real space diffraction image

25. Structure of interfacesz
crystallinity and sharpness
characterize solid-solid interfaces