1. Materials Science & Engineering (MSE) PhD lecture.
Advanced Materials Synthesis.
Thin Films.
By Toru Hara, PhD
Oct. 23, 2014
1

2. Research history of the lecturer.
1. Thin film capacitor
Sputtering
Chemical Solution Deposition (CSD)
Chemical Vapor Deposition (CVD)
O
O e
2
Electric Current
(From top electrode)
Electric Current
(From botom electrode)
Dielectric material
Magnetic Ffux
Solder ball
+ - +
-
2. Thin film oxygen sensor
Electron-Beam Evaporation
Sputtering
Pulsed Laser Deposition (PLD)
Atomic Layer Deposition (ALD)
Sr
O
Sr
O
O
Sr
O
Sr
Sr
O
Sr
O
Ti
O
Ti
3. Novel batteries (in progress)
Plating
Electrospray Deposition
Polaron diameter
Larger polaron diameter:
Higher conductance
(Lower resistance)
Smaller polaron diameter:
Lower conductance
(Higher resistance)
Film
thickness
TiO6 unit cell

3. Why thin film?
3
Flexible Solar Cell
Smaller Electronic Circuit
퐶 = ε0ε푟
퐴
푑
C, Capacitance;
ε0, vacuum permittivity;
εr, relative dielectric constant of a material;
A, electrode area;
d: thickness of a dielectric material.
The thinner the dielectric layer, the higher
the capacitance  even small capacitors can
give great enough capacitance.
Polaron diameter
Larger polaron diameter:
Higher conductance
(Lower resistance)
Smaller polaron diameter:
Lower conductance
(Higher resistance)
Film
thickness
TiO6 unit cell
New functional device

4. Contents.
Definition of thin films.
General applications & Required theory.
Brief introduction on each application.
Thin film deposition technique as an advanced
materials synthesis method
Research topics.
4

5. Definition of thin films.
General applications & Required theory.
Brief introduction on each application.
Thin film deposition technique as an advanced
materials synthesis method
Research topics.
5

6. Definition of thin films.
A thin film is a layer of material ranging from
fractions of a sub-nanometer to several micrometers in
thickness.
Help for imagining.
Bulk: 1022-1023 atoms exist in 1.0*1.0*1.0 cm3
Thin Film: 1015-1016 atoms exist in 1.0*1.0 cm2
(one-atom-thick thin film)
6

7. Definition of thin films.
General applications & Required theory.
Brief introduction on each application.
Thin film deposition technique as an advanced
materials synthesis method
Research topics.
7

8. General applications & Required theory.
1. Electronic semiconductor devices
Band engineering
2. Optical coatings
Refractive indices engineering
3. Optoelectronic semiconductor devices
Band engineering &
Refractive indices engineering
4. Quantum devices
Quantum dynamics/design
8

9. 1. Electronic semiconductor devices
Band engineering
It uses semiconductor alloys, in which a wide-gap
semiconductor and a narrow-gap semiconductor are combined
to give a substance with a desired intermediate band gap.
The left figure shows the
band gaps and lattice
parameters for some of the
more common elemental and
binary semiconductors.
*The practical band
engineering involves making
ternary alloys such as
(Ga,Al)As and (Hg,Cd)Te.
9

10. 2. Optical coatings
Refractive indices engineering
Optical transmission/reflection can be modulated by refractive
indices engineering (destructive/constructive interferences).
10
http://www.intechopen.com/books/electromagnetic-waves/propagation-of-electromagnetic-
waves-in-thin-dielectric-and-metallic-films

11. 3. Optoelectronic semiconductor devices
Band engineering & Refractive indices engineering
Band gap modulation causes the refractive indices modulation
at the same time, resulting in “optical guide.”
http://www.tf.uni-kiel.de/matwis/amat/semitech_en/kap_2/backbone/r2_3_1.html
http://optipedia.info/lsource-index/fiberlaser-index/fiber/parameters/numerical_aperture/
11

12. 4. Quantum devices Quantum dynamics/design
(L) Quantum well structure is made by the combination of a layer of a wider gap
material such as (Ga,Al)As, and a very thin layer of a narrower gap material such as
(GaAs). The narrower-gap material forms a one-dimensional potential well in the
conduction and valence bands; thus, the electron and hole levels are bound states of the
well, known as subbands. The well will contain three sets of subbands, the electron
subbands, the light hole subbands and the heavy hole subbands. By intersubband
absorption/emission of light realizes the use of long-wavelength light. The merits of
quantum well structure are (1) all of the transitions are excitonic (i.e. sharp features at a
well-defined energy, rather than broad edges), even at 300 K; (2) electrons and holes are
held in close proximity, to encourage more efficient recombination in lasers and LEDs.
(R) A superlattice contains a set of quantum wells which are sufficiently closely spaced
for the carriers to tunnel between wells. The subbands will broaden out to form
minibands with minigaps, resulting in the longer-wavelength (far-infrared) light
12
response.

13. Definition of thin films.
General applications & Required theory.
Brief introduction on each application.
Thin film deposition technique as an advanced
materials synthesis method
Research topics.
13

14. Brief introduction on each application.
1. Electronic semiconductor devices
Schematic diagrams of a GaAs metal-semiconductor
field effect transistor (MESFET). Si3N4 is deposited by using
Chemical Vapor deposition (CVD) in order to passivate the
single-crystal-based GaAs electronic device.
A. R. Barron, CVD of Nonmetals, Ed. W. S. Rees, Jr., Wiley, NY (1996).
14

15. Brief introduction on each application.
2. Optical coatings
Optical coating films are deposited onto the substrate,
which is a usually optically transparent glass, in order to
modulate the optical reflection. Electron beam physical vapor
deposition is often used in order to modulate the optical
reflection.
http://www.calctool.org/CALC/phys/optics/thin_film
15

16. Brief introduction on each application.
3. Optoelectronic semiconductor devices
One of the most famous application is probably Light
Emitting Diodes (LEDs) application. Each layer is deposited
by Chemical Vapor Deposition (CVD).
http://creativentechno.wordpress.com/2012/01/07/how-led-works/
16

17. Brief introduction on each application.
17
4. Quantum devices
One of the important
concept in order to realize
quantum devices is the concept,
“Superlattice.” This is a periodic
structure of layers of two or more
materials; the thickness of one
layer is typically several
nanometers. Molecular beam
epitaxy (MBE) is a popular
deposition technique in order to
make superlattice structures.
http://www.semiconductor-today.
com/news_items/2011/FEB/MEIJO_0202
11.htm

18. Definition of thin films.
General applications & Required theory.
Brief introduction on each application.
Thin film deposition technique as an advanced
materials synthesis method
Research topics.
18

19. Thin film deposition technique as an advanced
materials synthesis method
1. Chemical deposition
2. Physical deposition
19

20. Thin film deposition technique as an advanced
materials synthesis method
1. Chemical deposition
Fluid/Gas precursor undergoes a chemical change at a
solid surface, leaving a solid layer.
20

21. Thin film deposition technique as an advanced
materials synthesis method
Various types of chemical deposition technique
- Plating
- Chemical Solution Deposition (CSD)
- Chemical Vapor Deposition (CVD)
- Atomic Layer Deposition (ALD)
21

22. Plating
(1)Liquid precursors (a solution of water with a salt of
the metal to be deposited) are used.
(2) Some plating processes are driven by reagents,
e.g., reducing agents, in the solution.
(3) Electroplating is done through the use of an
external electron supply. Electroplating is a process in
which a metal or two or more metals is/are reductively
deposited onto the surface of a negatively biased
electrode.
22

23. http://worldofsecrets.org/en/2014/06/batte
rie-von-bagdad/
This is the world oldest
electroplating equipment that
found in an ancient tomb in
Bagdad in 1936. It consists of a
14-centimeter-high egg-shaped
clay jar with an asphalt stopper.
An iron rod protruding out of
the asphalt is the anode, which
is surrounded by a copper
cylinder used as the cathode.
Filled with vinegar as an
electrolytic solution.
23

24. http://www.sparknotes.com/chemistry/ele
ctrochemistry/electrolytic/section1.rhtml
This is the setup for gold
electroplating. At the cathode
surface, Au3+ ion will be
reduced into metal Au.
Thanks to this technique, we
can use golden spoons at an
inexpensive cost.
24

25. In today's nanoscience researches, electroplating is quite
popular. This is the picture of electroelectroplated patterned
surface.
P. Kim et al., Nano Lett. ,12 (2012) 527–533.
25
5 μm

26. Electroplating can be used for novel battery research. At the
conductive carbon fiber surface, nano-sized electrochemically
active materials are directly plated: highly durable (expected
life = 25 years) battery will be realized.
http://toruhara.page.tl/_-Research-plan-
26
1.htm
For this purpose, nano-crystals are
preferred rather than thin films.

27. Chemical Solution Deposition (CSD)
Chemical Bath Deposition (CBD)
(1)Liquid precursor, usually a solution of
organometallic powders dissolved in an organic
solvent, are used in order to gain thin films.
(2)This is a relatively inexpensive, simple thin film
process that is able to produce stoichiometrically
accurate crystalline phases.
(3)This technique is also known as the sol-gel method
because the 'sol' (or solution) gradually evolves
towards the formation of a gel-like system.
27

28. K Sarkar et al., J. Mater. Chem. A, 2
(2014) 6945-6951.
This is a schematic of the sol-gel
process for zinc-oxide-based
28
solar cell. Onto the
silicon substrate, a solution is
spin-coated; then, dehydrated;
and finally, calcinated.

29. Chemical vapor deposition (CVD)
It uses a gas-phase precursor, often a halide or hydride
of the element to be deposited. In the case of
MOCVD, an organometallic gas is used. Commercial
techniques often use very low pressures of precursor
gas.
29

30. This shows the schematic mechanism of CVD. Precursors
deposit onto the substrate surface; then, surface reaction takes
place; and finally, reaction products form thin films.
http://cnx.org/contents/1096167b-8518-4159-a88d-3b2ae4df6645@9.4:35
30

31. Atomic layer deposition (ALD)
It uses gaseous precursor to deposit conformal thin
films one layer at a time. The process is split up into
two half reactions, run in sequence and repeated for
each layer, in order to ensure total layer saturation
before beginning the next layer. Therefore, one
reactant is deposited first, and then the second reactant
is deposited, during which a chemical reaction occurs
on the substrate, forming the desired composition.
31

32. This shows ALD process of Strontium Titanate thin film, (20-
nm-thick) which is used for novel oxygen sensor [T. Hara et
al., Sens. Actuators B 136 (2009) 489.].
32

33. Thin film deposition technique as an advanced
materials synthesis method
2. Physical deposition
Mechanical, electromechanical or thermodynamic
energy is used in order to produce a thin film of solid.
Since most engineering materials are held together by
relatively high energies, and chemical reactions are not
used to store these energies, commercial physical
deposition systems tend to require a low-pressure
vapor environment to function properly; most can be
classified as physical vapor deposition (PVD).
33

34. Thin film deposition technique as an advanced
materials synthesis method
Various types of physical deposition technique
- Thermal Evaporation
- Electron-Beam Evaporation
- Molecular Beam Epitaxy (MBE)
- Sputtering
- Pulsed Laser Deposition (PLD)
- Cathodic Arc Deposition
- Electrospray Deposition
34

35. Thermal Evaporation
It uses an electric resistance heater to melt the material
and raise its vapor pressure to a useful range. This is
done in a high vacuum, both to allow the vapor to
reach the substrate without reacting with or scattering
against other gas-phase atoms in the chamber, and
reduce the incorporation of impurities from the
residual gas in the vacuum chamber.
35

36. This is the schematic of
thermal evaporation
equipment. Under the high
vacuum atmosphere, heated
material will evaporate and
deposit onto the substrate.
http://www.ece.utep.edu/research/cdte/Fab
rication/index.htm
36

37. Electron-Beam Evaporation
It fires a high-energy beam from an electron gun to
boil a small spot of material; since the heating is not
uniform, lower vapor pressure materials can be
deposited. The beam is usually bent through an angle
of 270° in order to ensure that the gun filament is not
directly exposed to the evaporant flux.
37

38. This is the schematic of
electron-beam evaporation
equipment. Under the high
vacuum atmosphere, heated
material will evaporate and
deposit onto the substrate. The
difference between the
thermal evaporation and
electron-beam evaporation is
the heating method.
http://www.optics.rochester.edu/workgrou
ps/cml/opt307/spr13/greg/
38

39. Molecular Beam Epitaxy (MBE)
Slow streams of an element can be directed at the
substrate, so that material deposits one atomic layer at
a time. Compounds such as gallium arsenide are
usually deposited by repeatedly applying a layer of
one element (i.e., gallium), then a layer of the other
(i.e., arsenic), so that the process is chemical, as well
as physical. The beam of material can be generated by
either physical means (that is, by a furnace) or by a
chemical reaction (chemical beam epitaxy).
39

40. This is the schematic of
molecular beam epitaxy
equipment.
http://en.rusnano.com/portfolio/com
panies/semiteq
40

41. Sputtering
It relies on a plasma (usually a noble gas, such as
argon) to knock material from a "target" a few atoms
at a time. The target can be kept at a relatively low
temperature, since the process is not one of
evaporation, making this one of the most flexible
deposition techniques. It is especially useful for
compounds or mixtures, where different components
would otherwise tend to evaporate at different rates.
41

42. This is the schematic of
sputtering equipment.
Argon atom is ionized
into argon cation under
static and/or alternative
electric field; argon cation
knocks the target surface;
knocked atoms will be
deposited onto the
substrte.
http://en.wikipedia.org/wiki/File:Spu
ttering.gif
42

43. Pulsed Laser Deposition
This systems work by an ablation process. Pulses of
focused laser light vaporize the surface of the target
material and convert it to plasma; this plasma usually
reverts to a gas before it reaches the substrate.
43

44. This is the schematic of
pulsed laser deposition
equipment. Target
materials are knocked by
laser irraduiation, then,
deposited onto the
substrte.
http://groups.ist.utl.pt/rschwarz/rsch
warzgroup_files/PLD_files/PLD.ht
m
44

45. Cathodic Arc Deposition
It is a kind of ion beam deposition where an electrical
arc is created that literally blasts ions from the
cathode. The arc has an extremely high power density
resulting in a high level of ionization (30–100%),
multiply charged ions, neutral particles, clusters and
macro-particles (droplets).
45

46. This is the schematic of
pulsed laser deposition
equipment. Target
materials are set as a part
of electrode, and
evaporated by a plasma-induced
excitation, then
deposited onto the
substrate.
http://groups.ist.utl.pt/rschwarz/rsch
warzgroup_files/PLD_files/PLD.ht
m
46

47. Electrospray deposition
The liquid to be deposited, either in the form of nano-particle
solution or simply a solution, is fed to a small capillary nozzle
(usually metallic) which is connected to a high voltage. The
substrate on which the film has to be deposited is connected to
ground. Through the influence of electric field, the liquid
coming out of the nozzle takes a conical shape and at the apex
of the cone a thin jet emanates which disintegrates into very
fine and small positively charged droplets. The droplets keep
getting smaller and smaller and ultimately get deposited on the
substrate as a uniform thin layer.
47

48. This is the schematic of electrospray deposition equipment. (1)
Precursors are fed to the nozzle. (2) The substrate is connected to ground.
(3) Through the influence of electric field, the liquid coming out of the
nozzle. (4) The liquid disintegrates into very fine and small positively
charged droplets. The droplets keep getting smaller and smaller and (5)
ultimately get deposited on the substrate as a uniform thin layer.
http://www.nanowerk.com/spotlight/spotid=9685.php
48
(1)
(4) (3)
(2)
(5)

49. Definition of thin films.
General applications & Required theory.
Brief introduction on each application.
Thin film deposition technique as an advanced
materials synthesis method
Research topics.
49

50. 50
Research Topics.
L. Bovo et al., “Restoration of the third law in spin ice thin films,” Nat. Commun. DOI:
10.1038/ncomms4439.
Spin liquid found in the pyrochlore structure is the apparent violation of the third law of
thermodynamics. The authors found that even in a pyrochlore compound the third law
can be restored by fabricating thin epitaxial films: this restoration results from strain-induced
(the lattice constant difference between the substrate and the film deposited
onto the substrate) ordering of the spins. showing how the physics of frustrated
pyrochlore magnets such as spin ice may be significantly modified in thin-film samples.

51. 51
Research Topics.
http://phys.org/news204201232.html
The third law of thermodynamics
is sometimes stated as follows,
regarding the properties of
systems in equilibrium at absolute
zero temperature: the entropy of a
perfect crystal, at absolute zero
(zero kelvins), is exactly equal to
zero. However, the large quantum
fluctuation of the magnetic spins
(see, it is tetrahedral) melt the spin
ice structure and form the spin
liquid (or spin liquid-crystal).

52. 52
Research Topics.
T. Hara et al., “Effect of Oxygen Adsorption on Polaron Conduction in Nanometer-
Scale Nb5+-, Fe3+-, and Cr3+-Doped SrTiO3 Thin Films,” Jpn. J. Appl. Phys., 50 (2011)
065807.
The polaron diameter in SrTiO3-based epitaxial thin films decreases owing to oxygen
adsorption, resulting in the decrease in electronic conductivity; this can be understood
by assuming that oxygen adsorbates induce local distortions of TiO6 unit cells at which
conduction electrons are frequently trapped.

53. 53
Research Topics.

54. 54
Research Topics.
What was new?
Although SrTiO3 is
paraelectric,
near the surface of STO
adsorbed oxygen can
induce the
ferroelectric-like
Ionic displacement.
Sr
O
Sr
O
O
Sr
O
Sr
Sr
O
Sr
O
O e
O
Ti
O
Ti