Transcript STM results: Co on Al 2 O 3 /NiAl(100)

Nano-materials
…size does matter
An opportunity to solve some present problems
related to applications in electronics, optics, catalysis,
mechanical materials and so on.
Meng-Fan Luo 羅夢凡
Department of Physics
National Central University
Nano-science course 9/23/2003
femto10 -15
pico10 -12
nano10 -9
micro10 -6
mini10 -3
meter
10 0
kilo10 3
fm
pm
nm
μm
mm
m
km
飛米
(胚？)米
奈米
微米
毫米
(公厘)
米
(公尺)
仟米
(公里)
忠
孝
新
生
站
假設全世界的人口已增加到一百億 (10 10 )，
若大家肩並肩地塞進一公尺寬的隊伍裡，
則每個人的肩寬應為 0.1 奈米，恰約氫原子的
直徑。
忠
孝
復
興
站
92.03.03 美國家奈米科學計畫( NNI) 2004年 奈米研究預算達 8.47億美元
美國政府日前公布2004年「國家奈米科學計畫」（National
Nanotechnology Initiative, NNI）的預算，總金額為8.47億美元，較
2003年成長了9.5%。
自從政府宣布奈米材料為未來重點發展技術後，
(民國八十八年) 國科會也通過「奈米計畫」成為國家型科技計畫，
而預計在6年內 (民國九十二至九十七年間) 將投入192億元，
92.03.20 2012年我奈米技術產值達兆元
經濟部十九日預估，到二○○八年時我國奈米技術應用影響相
關產業產值將達新台幣三千億元，
至二○一二年擴大應用到電子、半導體等八大產業後，這八大
產業的產值可升至一兆元。
Shrink…
Store the library on a device with the size of a sugar cube
10 times the strength of steel at a fraction of steel’s weight
Cell-repair nano-machine
Reduce people and machinery to nanoscale
Nano-device infiltrates a person brain to correct weakness
Image copyright Scott Barrows, University of Illinois at Chicago
Nano-biotechnology
Nano-electronics
Nano-science
Nano-materials
Single atom
~Å
?
Nanocluster
~ nm
Bulk
~ m
Electronic Structures
Semiconductor
Energy
Metal
Density of states
Geometric structures
Magic numbers are found in nanoclusters, nanowires,
and thin films…
Hot sodium nanoclusters with numbers of
8, 20, 40, 58, 92, 138… [1]
Gold nanowires with magic radii and
geometry: 7-1, 11-4, and 14-7-1[2].
Magic structural stability of silver films
with 1, 2, and 5 monolayer thickness [3]
[1] M. Brack, Sci. Am. Dec. (1997) 30; [3]D.A. Luh, et. al., Sci. 292 (2001) 1131;
[2] Y. Kondo et. al., 289 (2000) 606.
Size effects
By varying the size, a enormous range of fundamental properties is
realized in a material of single chemical component.
Electrical conductivity
Optical properties
Hardness, melting temperature
Catalytic reactivity and selectivity
An opportunity to solve some present problems related to
applications in electronics, optics, catalysis, mechanical materials and
so on.
The band gap in CdS can be tuned between 4.5 eV and 2.5 eV as the
size is varied from the molecular regime to macroscopic crystal [1].
Silicon clusters containing around 50 atoms emit a strong red light
which is not seen in either crytsalline or amorphous forms of silicon [2].
The melting temperature of CdS increase from 400 to 1600 C as the
size is varied [3]; films made from carbon clusters with 900 atoms
behave like graphite, while films made from 20-atoms clusters behave
like diamond [2].
[1] T. Vossmeyer et. al., J. Phys. Chem. 98 (1994) 7665; [2] R. Palmer, New Scientist 2070
(1997) 38; [3] A.N. Goldstein, Science 256 (1992) 1425.
Catalytic reactivity and selectivity
Bulk Au surfaces are chemically inert, however, supported Au
nanoclusters with diameters smaller than 5 nm are active.
Propane
Au/TiO2
at 80 C
Propylene oxide
CO + O2
H2 + O2 + Propylene
From M. Haruta, Catalysis Today 36 (1997) 153
New building blocks
for new materials…
The placement of nanoparticles in automotive catalytic converters
Science 299 (2003) 1688
DMFC Application
 MOTOROLA
 CASIO
 TOSHIBA
How Does DMFC Work?
Fuel：
CH3OH +
H2 O
Load
CO2
6e
H2O
CH3OH
6e
-
-
3/2O2
Air
+
6H
3H2O
+
6H
PEM
Tank
Anode
Cathode
Membrane Electrode Assembly
Direct Methanol Fuel Cell
Gf = -698.2
kJ/mole
E = -Gf / nF =
1.21 V
@ 25℃
Size effects on catalytic properties
Bulk Au surfaces are chemically inert, however, supported Au
nanoclusters with diameters smaller than 5 nm are active.
Propane
Au/TiO2
at 80 C
Propylene oxide
CO + O2
H2 + O2 + Propylene
From M. Haruta, Catalysis Today 36 (1997) 153
Which one is correct?
Au nanoclusters on oxides
Ru/TiOX
Pt/carbon-silica aerogel
from H.J. Freund et. al. Cryst. Res. Technol.
Comparison of model systems and real systems:
CO oxidation catalytic activity of Au/TiO2
(B)
(A)
300K
(A)prepared by deposition-precipitation
method; (B)Vapor-deposited Au atoms
on planar TiO2(110).
From M. Valden et al. Science 281 (1998) 1648.
350 K
奈米觸媒催化反應機制之探索
目標: 探索奈米觸媒催化反應之基本機制與過程，以期提供
設計與製造奈米觸媒所需知識。
主要課題: 1. 奈米微粒在反應中之尺寸效應(size effects)
2.尺寸效應之產生機制
3.氧化物擔體(oxides support)在奈米觸媒中扮演之角色
研究方法:在超高真空(UHV)系統中使用各式表面探測技術(surface
probe techniques)針對模型系統(model systems)進行研究，
以求對反應過程與奈米觸媒的結構達到原子層級的了解
(atomic-level understanding)。
模型系統:包含樣品(觸媒本身)和反應進行的環境
樣品部分: 將在單晶金屬基座(metal substrates)成長金屬氧化薄膜
(metal oxide thin films)，之後於氧化薄膜上成長奈米金微粒。
metal substrates
O2 exposure
grow metal oxides
grow nanoparticles via CVD
運用各式表面探測技術(surface probe techniques)嚴格掌控氧化薄膜與
奈米金微粒的尺寸和結構，以利尺寸效應之分析。
X-ray
STM&STS
反應進行的環境:在超高真空環境下吸附反應氣體分子於奈米金
觸媒，再利用各式表面探測技術精確觀測反應率(reactivity)與反應
選擇性(selectivity)隨奈米金微粒尺寸的變化。
EELS
TOF
STM&STS
Laser desorption
反應率與反應
選擇性隨奈米金微粒尺寸
的變化:尺寸效應
尺寸效應與結構
的關聯性
尺寸效應的起源
氧化薄膜與奈米金
微粒的結構
UHV-Chemical reactions system
LEED & AES
UHV STM
Leak valve
Evaporator
Evaporator
Sample
Load-lock system
And reaction chamber
Mass Spectrometer
RGA
Ion gun
Transfer rod
Co nanoclusters/ Al2O3/ NiAl(100)
Co nanoclusters
Al2O
3
NiAl(100)
Importance of Al2O3
•Acid-Base Catalyst
•Metallic Catalyst Support
•Solid Oxide Fuel Cell for Methanol Oxidation
•Heterogeneous Atmospheric Chemistry
•Mineral Dust
•82,000,000 ppbw Al in the earth’s crust
•Rocket Fuel Exhaust
•16% atomized Al powder
•70% ammonium perchlorate
•Space shuttle: 1,100,000 lb/booster
3Al(s) + 3NH4ClO4(s)
Al2O3(s) + AlCl3(s) + 3NO(g) + 6H2O(g
Advantage of Al2O3/NiAl(100)
Al2O3 is produced on the surface of NiAl by oxidation.
Reduced charging effects, so the electronic spectroscopies
can be applied.
Highly ordered (Franchy and Freund)
~ 10 Å thick
Thermal control of Al2O3 Phase
High melting temperature of NiAl (1911 K)
Available as a Single Crystal
Surf. Sci. 1994, 319, 95.;J. Electron Spect. Related Phenomena 1993, 64/65, 315.
Surf. Sci. 1991, 259, 235;Surf. Sci. 1994, 318, 61.
NiAl(100)
Grow Al2O3
Deposit Co and Au
Characterization
Nanoclusters/ Al2O3/ NiAl(100)
Auger spectroscopy (AES)
Electron energy loss spectroscopy (EELS)
Low energy electron diffraction (LEED)
Probe molecule adsorption
Scanning tunneling spectroscopy (STM)
Ultrathin -Al2O3 Film Growth
NiAl(100)
1000 L exposure
950 K
-Al2O3
NiAl(100)
NiAl(100)
~10 Å
Cleaned NiAl(100)
STM results
1000nm x 1000nm
Cycles of 2 keV ion sputtering and
annealing at 1000 K from 1 hour up
to a few hours
LEED results c(√2 x 3√2)R45°
56.7 eV
100.0eV
270 x 160 nm
LEED results (2 x 1) structure
56.3eV
100 eV
800 x 800 nm
1000 L exposure at 1000 K and
annealing at 1000 K for 1 hour
200 x 200 nm
Al2O3/NiAl(100)
STM results
STM results
1000 L exposure at 1000 K and
quenched to room temperature
190 x 250 nm
75 x 75 nm
Metal deposition
EFM 3 evaporator
300 K
Al2O3/NiAl(100)
surface with nanoclusters
Growth modes
(a)
Frank-Van der Merwe growth ( layer-by-layer growth )
(b)
Stranski-Krastanov growth ( layer-plus-island growth )
(c)
Volmer-Weber growth ( island growth )
STM results: Co on Al2O3/NiAl(100)
50 x 50 nm 0.4 ML
50 x 50 nm 2.4 ML
STM results: Co on Al2O3/NiAl(100)
150 x 150 nm 2.4 ML
300 x 300 nm 7.3 ML
High thermal stability (< 700 K)
50 x 50 nm 7.3 ML 350 K
50 x 50 nm 7.3 ML 800 K
Submitted to Appl. Phys. Lett.
Where dose the alignment come from?
150 x 150 nm
Carbon nanotubes
STM picture of a carbon nanotube
3d rendered STM image of carbon nanotube
Atomic structure of kinked nanotube
From Cees Dekker’s group at the Delft University of Technology
Artist’s nanotube Transistor
Advantages
When a positive voltage is applied on carbon nanotubes, strong electric
fields can be generated at the their extremely sharp tips, which are
sufficient to strip electrons from molecules.
Stability tests I
PHe = 4 x 10-5 mbar, Tip voltages: 7 kV (lower), 8 kV(higher)
What happened?

(a) before and (b) after high positive voltages
New measurements
Patterned multi-wall carbon nanotubes (MCNT)
MCNT Forests
Separated MCNT
Arrayed MCNT
Design of the detector
A
Thermocouple
V
Pi = 6 x 10-8 mbar, base voltage = 1600 V
nA
PHe=5 x 10-4 mbar
V = 2500 V
Both microelectronics and nanoelectronics have three levels
of organization:
1. The transistor or switch
2. Interconnection—the wires that link transistors
3. Architecture—constructing the circuit
From Science 293 (2001)
Transistor and switch
The conduction path thru a molecular switch is turned on by
an applied voltage. The applied voltage is believed to cause a
conformational shift which, in concert with the charging of the
molecule, opens the conduction pathway.
From Mark Reed’s group at Yale University
Carbon nanotubes as transistors
and nanowires
Carbon nanotube over Pt electrodes
AFM image of a nanotube between electrodes
3d rendered AFM image of kinked nanotube
on electrodes
From Cees Dekker’s group at the Delft University of Technology
Nanowires
DNA molecule
between electrodes
AFM image of DNA attached to
PNA-derivatized nanotube rope
Palladium particle trapped between two electrodes
From Cees Dekker’s group at the Delft University of Technology and C. Lieber’s group at Harvard University
Nanodevices are smaller enough
to enter cells…
Most animal cells are 10,000 to 20,000 nanometers in
diameter. This means that nanoscale devices (less than 100
nanometers) can enter cells and the organelles inside them
to interact with DNA and proteins.
Drug-delivery
vehicles
One might encapsulate drugs
within nanoscale packages
and control the medicines’
release in sophisticated ways.
Nanoshell attached to a capsule
made of a heat-sensitive polymer.
From National Cancer Institute, US
Gold nanoshell can absorb near-infrared
light which can penetrate several centimeters
of tissue. Heating from outside becomes
possible.
Using gold nanoshell attached
to antibodies that bind specifically
to tumor cells can destroy the
cancerous cells.
From National Cancer Institute, US