Transcript Pt/SrTiO3 Interface - Nc State University

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GaAs
Si
2 nm
[001]
[110]
[110]
The World of Atoms
Instructor:
Dr. Gerd Duscher
http://www4.ncsu.edu/~gjdusche
email: [email protected]
Office:
Office Hours:
2156 Burlington Nuclear Lab.
Tuesday: 10-12pm
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The World of Atoms
Objective
Johann Wolfgang von Goethe (1749-1832): Faust
Faust is searching for the first principles, for
"that inner force which holds the world together,"
“was die Welt im Innersten zusammenhält”.
So do we, in this lecture
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Atomic Structure
Bohr Model
that is too simple
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Atomic Structure
Bohr Model
Wavemechanic Model
1
probability
probability
1
Energy
distance
Nucleus
radial distance
Nucleus
electrons
Some Links
Bonding :
http://info.lu.farmingdale.edu/depts/met/met205/atomicbon
ds.html
(pictures of different kinds of bonding)
Orbitals :
http://web.mit.edu/3.091/www/orbs/
(computer simulation of electron positiond for certain
orbitals)
Crystal Structure :
http://web.mit.edu/3.091/www/cryst/
(Pictures of several crystal structures)
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Electron Energy States
Electrons...
increasing energy
• have discrete energy states
• tend to occupy lowest available energy state.
4p
n=4
4s
n=3
3s
n=2
n=1
2s
1s
3d
3p
2p
Adapted from Fig. 2.5,
Callister 6e.
3
Stable Energy Configurations
• have complete s and p subshells
• tend to be unreactive.
Z
2
Element Configuration
He
1s2
10
18
Ne
Ar
36
Kr
Adapted from Table 2.2,
Callister 6e.
1s22s 22p6
1s2 2s22p63s23p6
1s2 2s22p63s23p63d10 4s24p6
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Survey of Elements
• Most elements: Electron configuration not stable.
Element
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
...
Neon
Sodium
Magnesium
Aluminum
...
Argon
...
Krypton
Atomic #
1
2
3
4
5
6
10
11
12
13
18
...
36
Electron configuration
1s 1
1s 2
(stable)
1s 2 2s 1
1s 2 2s 2
Adapted from Table 2.2,
1s 2 2s 2 2p 1
Callister 6e.
1s 2 2s 2 2p 2
...
1s 2 2s 2 2p 6
(stable)
2
2
6
1
1s 2s 2p 3s
1s 2 2s 2 2p 6 3s 2
1s 2 2s 2 2p 6 3s 2 3p 1
...
1s 2 2s 2 2p 6 3s 2 3p 6
(stable)
...
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
• Why? Valence (outer) shell usually not filled completely.
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give up 1egive up 2egive up 3e-
• Columns: Similar Valence Structure
Metal
accept 2eaccept 1einert gases
The Periodic Table
Nonmetal
H
He
Intermediate
Li Be
Ne
O
F
Na Mg
S
Cl Ar
K Ca Sc
Se
Br Kr
Rb Sr
Te
Y
Cs Ba
Po
I
Xe
At Rn
Fr Ra
Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.
Adapted from
Fig. 2.6,
Callister 6e.
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attraction
attractive force FA
repulsion
0
Net force FN
repulsive force FR
repulsion
attraction
potential energy E
force F
Bonding
repulsive energy ER
0
net energy EN
attractive energy EA
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Properties from Bonding: Tm
• bond length, r
F
• melting temperature, Tm
Energy (r)
F
r
• bond energy, Eo
ro
r
Energy (r)
smaller T m
unstretched length
ro
r
Eo =
“bond energy”
larger T m
Tm is larger if Eo is larger.
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Properties from Bonding: E
• coefficient of thermal expansion, a
• Elastic modulus, E
cross
sectional a is smaller
length,
E is larger if
E0 is Lmore
negative.
if Eo Liso more negative
length,
o
area A o
undeformed
DL
deformed
1
DL
heated, T 2
F
• a ~ symmetry at ro
energy
• E ~ curvature at ro
energy
unheated, T
unstretched length
ro
r
smaller Elastic Modulus
larger Elastic Modulus
ro
larger a
smaller a
r
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Ionic Bonding
•
•
•
•
Occurs between + and - ions.
Requires electron transfer.
Large difference in electronegativity required.
Example: NaCl
Na (metal)
unstable
Cl (nonmetal)
unstable
electron
Na (cation)
stable
-
+
Coulomb
attraction
Cl (anion)
stable
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Ionic Bonding
+
-
Electron density difference
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Examples: Ionic Bondings
• predominant bonding in ceramics
NaCl
MgO
CaF 2
Cs Cl
H
2.1
Li
1.0
Be
1.5
Na
0.9
Mg
1.2
K
0.8
Ca
1.0
Sr
1.0
Rb
0.8
Cs
0.7
Fr
0.7
Ti
1.5
Cr
1.6
Fe
1.8
Ni
1.8
He
O
3.5
Zn
1.8
As
2.0
Ba
0.9
Ne
-
Br
2.8
I
2.5
Kr
Xe
Rn
-
At
2.2
Ra
0.9
give up electrons
F
4.0
Cl
3.0
acquire electrons
Ar
-
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Covalent Bonding
• requires shared electrons
• example: CH4
C: has 4 valence e,
needs 4 more
H
CH4
H
H: has 1 valence e,
needs 1 more
C
H
shared electrons
from carbon atom
H
shared electrons
from hydrogen
atoms
H
Electronegativities
are comparable.
H
C
H
H
enhanced
electron
density
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Ni3Al–Superalloy Bonds Covalently
Ni
Al
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Examples: Covalent Bonding
H2
H
2.1
Li
1.0
column IVA
H2 O
C(diamond)
Si C
He
O
2.0
Na
0.9
K
0.8
Be
1.5
Mg
1.2
Ca
1.0
Rb
0.8
Cs
0.7
Sr
1.0
Ba
0.9
Sn
1.8
Pb
1.8
Fr
0.7
Ra
0.9
GaAs
•
•
•
•
Ti
1.5
Cr
1.6
Fe
1.8
Ni
1.8
Zn
1.8
C
2.5
Si
1.8
Ge
1.8
F2
Ga
1.6
Molecules with nonmetals
Molecules with metals and nonmetals
Elemental solids (RHS of Periodic Table)
Compound solids (about column IVA)
As
2.0
F
4.0
Ne
-
Cl
3.0
Ar
Kr
-
Br
2.8
I
2.5
At
2.2
Cl 2
Xe
-
Rn
-
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Metallic Bonding
• Arises from a sea of donated valence electrons
(1, 2, or 3 from each atom).
+
+
+
+
+
+
+
+
+
• Primary bond for metals and their alloys
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Van Der Waals Bonding
arises from interaction between dipoles
• fluctuating dipoles
ex: liquid H2
H2
H2
asymmetric electron
clouds
+
-
+
van der Waals
bonding
-
H H
H H
van der Waals
bonding
• permanent dipoles-molecule induced
-general case:
-ex: liquid HCl
-ex: polymer
+
-
H Cl
van der Waals
bonding
van der Waals
bonding
+
-
H Cl
Van Der Waals Bonding
fluctuating (Induced) dipols
permanent dipols
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Summary: Primary Bonds
Ceramics
(Ionic & covalent bonding):
Metals
(Metallic bonding):
Polymers
(Covalent & Secondary):
large bond energy
large Tm
large E
small a
variable bond energy
moderate Tm
moderate E
moderate a
directional Properties
van der Waals bonding dominates
small T
small E
large a
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• Non dense, random packing
energy
Energy And Packing
typical neighbor
bond length
typical neighbor
bond energy
energy
• Dense, regular packing
r
typical neighbor
bond length
typical neighbor
bond energy
Dense, regular-packed structures tend to have
lower energy.
r
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Materials And Packing
Crystalline materials...
• atoms pack in periodic, 3D arrays
• typical of:
-metals
-many ceramics
-some polymers
crystalline SiO2
Noncrystalline materials...
• atoms have no periodic packing
• occurs for: -complex structures
-rapid cooling
"Amorphous" = Noncrystalline
noncrystalline SiO2
Metallic Crystals
• tend to be densely packed.
• have several reasons for dense packing:
-Typically, only one element is present, so all atomic
radii are the same.
-Metallic bonding is not directional.
-Nearest neighbor distances tend to be small in
order to lower bond energy.
• have the simplest crystal structures.
We will look at three such structures...
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Simple Cubic Structure (sc)
• rare due to poor packing (only Po has this structure)
• close-packed directions are cube edges.
• Coordination # = 6
(# nearest neighbors)
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Body Centered Cubic Structure
(bcc)
• Close packed directions are cube diagonals.
--Note: All atoms are identical; the center atom is shaded
differently only for ease of viewing.
• Coordination # = 8
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Face Centered Cubic Structure
(fcc)
• Close packed directions are face diagonals.
--Note: All atoms are identical; the face-centered atoms are shaded
differently only for ease of viewing.
• Coordination # = 12
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Perovskite Strucutre
SrTiO3
Applications: non-linear resistors (PTC), SMD capacitors,
piezoelectric sensors and actuators, ferroelectric memory.
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Crystals as Building Blocks
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• Some engineering applications require single crystals:
--diamond single
crystals for abrasives
--turbine blades
• Crystal properties reveal features
of atomic structure.
--Ex: Certain crystal planes in quartz
fracture more easily than others.
POLYCRYSTALS
• Most engineering materials are polycrystals.
1 mm
• Nb-Hf-W plate with an electron beam weld.
• Each "grain" is a single crystal.
• If crystals are randomly oriented,
overall component properties are not directional.
• Crystal sizes typ. range from 1 nm to 2 cm
(i.e., from a few to millions of atomic layers).
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Single vs Polycrystals
• Single Crystals
E (diagonal) = 273 GPa
-properties vary with
direction: anisotropic.
-example: the modulus
of elasticity (E) in bcc iron:
• Polycrystals
-properties may/may not
vary with direction.
-if grains are randomly
oriented: isotropic.
(Epoly iron = 210 GPa)
-if grains are textured,
anisotropic.
E (edge) = 125 GPa
200 mm
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TEMs at NCSU
The NEW JEOL 2010F
This is a TEM/STEM,
which can do everything
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TEMs at NCSU
TEM Lab Course at the OLD TEM: Topcon
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STEM at
ORNL
This STEM provides the
smallest beam in the world.
It uses the brightest source
in the universe,
1000 times brighter than
a supernova.