yichun liu
TRANSCRIPT
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Key Laboratory of UV Light-Emitting Materials andTechnology, Ministry of Education, Northeast Normal
University, Changchun
The properties and application ofThe properties and application of
nanonano--ZnOZnO
Y.C. Liu
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TiO2 Photocatalysis: Advantages and ShortcomingsAdvantages:
1) Cheap material
2) Nontoxic and stable3) Suitable valence and conduction band positions
Shortcomings:
1) Charge recombination problemResolution: Photochemical diode type photocatalystssuch as TiO2/SnO2, TiO2/Pt
2) Transparent for visible light
Resolution: non-metal doping, such as N, C, S-doped TiO23) Low extinction coefficient in UVA range due to its nature of
indirect bandgap semiconductor
How to resolve this problem?
Environmental issues
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Our Strategy for Highly Efficient Semiconductor Photocatalysis
ZnO: a direct wide band-gap semi-conductor with intense absorption inUVA; a chemically unstable oxidematerial, easy to be dissolved inacidic or alkaline medium
TiO2: a indirect band-gap semi-conductorwith weak absorption in UVA; achemically stable oxide material, stable inacidic or alkaline medium either in dark orunder excitation.
E vs vacuum level
ZnO TiO2
e- e-
h+ h+
O2
O2-
RH
R
-2
-5
-6
-7
-8
-4
In such a array structure, UV-absorption and photoreactioncan be site-separately carried
out, which may favor theefficiency of photocatalyticprocess.
ZnO/nano-rode coreas antennafor UV light
TiO2/shell asreaction site
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PVP/ZnO t ubes
ZnO/TiO2 nano-f ibers for phot oc at a lys is
Langm uir ,23 (2007)10920
J .Chem .Phys, 2008
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J.Chem.Phys., (2009)
to be acceptedThe top view FESEM images of the
as-prepared well-aligned ZnO
nanorod arrays on a ZnO-coated Si
substrate
Resonance Raman Mapping to Identify nano-ZnO Array Orientation
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Scheme 1. Schematic illustration of the
super-hydrophobicity ZnO/SiO2 core-shell
nanowire array. Figure 1.The SEM images of the top and tilt
view of nanowire array before UV irradiation.
(a, b) ZnO nanowire array; (c, d) ZnO/SiO2core-shell nanowire array.
Figure 2. Evolution of water contact angle onZnO nanowire and ZnO/SiO2 core-shell
nanowire arrays modified with
octadodecyltrimethylsilane monolayers during
irradiation with ultraviolet light.
Langmuir,25 (2009)xxxx
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n-nano-ZnO/p-GaN LED
P-NiO/n-nanoMgZnO UV-de t ec t or
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EL from p-GaN
The results of n-ZnO/p-GaN from
n-ZnO/p-GaN diode by ZN Technology, CA,USA
GaN
A homostructural ZnO p-i-n light emitting diode
naturematerials
,4,2005
A great breakthrough in ZnO homojunction LED----------Kawasaki et al. nature materials, 4, 47 (2005)
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Why choose to construct GaN/ZnO heterojunction LED ?
ZnOUV LED
& LD
pn homojunction
pn heterojunction
p-ZnO
ZnMgO, GaN,
SiC, AlN, et al
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Researching progresses in GaN/ZnO heterojunction LED
Why choose GaN?
Similar material properties
GaN ZnO
Crystal Structure Wurtzite Wurtzite
Lattice Constant()
a = 3.189c = 5.186
a = 3.249c = 5.205
Bandgap (eV) 3.42 3.37
Commercial availability of high-quality p-GaN
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p-GaN/n-ZnO
Samples (cm) (cm2V-1s-1) N (cm-3)
p-GaN 1.63 5.34 7.131017
n-ZnO 3.1510-2 26.21 7.571018
p-GaN/n-ZnO
n-ZnO
p-GaN
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p-GaN/n-ZnO
p-GaN
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Why does EL originate from p-GaN?
conduction and valence band offset :
Ec=0.15 eV andEv=0.12 eV
electrons in n-ZnO and holes in p-
GaN overcame almost equal barrier
to realize the carrier injection.
The source of EL would be mainly determined by the differences
of carrier mobility and concentration between n-ZnO and p-GaN.
Idea of designing p-GaN/i-ZnO/n-ZnO device
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UV LED based on p-GaN/i-ZnO/n-ZnO heterojunction
Device structure
Mg doped p-GaN: MOCVD
i-ZnO: rf reactive magnetron sputtering
Zn-rich n-ZnO: electron beam evaporation
p-GaN
n-ZnO
i-ZnO
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Samples (cm) (cm2V-1s-1) N (cm-3)p-GaN 1.63 5.34 7.131017i-ZnO 1.12103 1.28 4.381015n-ZnO 4.1410-2 20.0 7.531018
p-i-n heterojunctions exhibites a
rectifying, diode-like behavior.
The forward turn-on and reverse
breakdown voltages is ~9 and ~11 V.
Electrical properties
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p-GaN/i-ZnO/n-ZnO
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UV EL from P-GaN/i-ZnO/n-ZnO
3.21 eV EL---UV NBE emission from
i-ZnO layer
2.1 eV EL---deep-level emission related
to native defects
3.08 eV EL---Mg-levels related emission
in p-GaN layer
App l. Phys . B 80 (2005 ) 871
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Mechanism
The i-ZnO has the lowest carrier
concentration and mobility among thethree layers, thus, the carriers
including holes from p-GaN and
electrons from n-ZnO can inject into i-
ZnO layer, where the radiative
recombination occurs.
RT EL spectra of p-GaN/i-ZnO/n-ZnO heterojunctions LED at
different injection currents;
inset shows the intensity ratios
of EL peak at 3.21 eV from i-
ZnO to one at 3.08 eV from p-
GaN vs. the injection currents
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EL from P-GaN/i-ZnO/n-ZnO (i-ZnO
EL of p-GaN/n-ZnO and p-GaN/i-ZnO/n-ZnO w it h
i -layer t h ic k ness of 20 nm , 40 nm , 80 nm
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Opt ic a l St orage and
Elec t r ic a l St orage Dev ic e
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AgTiO2
TiO2-Ag Film
TiO2
-Ag
Y. Ohko, et al.Nat. Mater. 2003 (2)29.
TiO2-Ag
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Ag/ZnO film
Interference fringe
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TiO2/ZnO-Ag
Ag
AgAg+
Ag+
Ag
Green
laser
UV
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Thin film transistor of amorphousoxide semiconductor
K. Nomura, et al., Nature 488 (2004) 432.
IGZO TFT17.2 cm2/v.s
IGZO TFT
0 10 20 30 40
0.0
1.0x10-6
2.0x10-6
3.0x10-6
4.0x10-6
5.0x10-6
0 10 20 30 40
-5.0x10-7
0.0
5.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
IDS
(A)
IDS
(A)
Vg (V)
VDS
(V)
Vg
increasing
VDS
increasing
a-IGZOSiO2
p-Si
Al Al
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S. H. Chang, et al., Phys. Rev. Lett. 102, 026801 (2009)
0.0 0.5 1.0 1.5 2.0
0.0
5.0x10-3
1.0x10-2
1.5x10-2
2.0x10-2
0.01 0.1 110
-7
10-6
10-5
10-4
10-3
10-2
10-1
Set
Current(A
)
Voltage (V)
ResetSetReset
ZnO:LiCu
Al
Unipolar memory ofreversible resistance switching
NiOAl
Al
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The application of nano-ZnO materialsin bioseparation and sensitive Immunoassays
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Au:ZnORamanZnOZnO ()/Au ()
ZnO (c ore)/Au (Ag) (she l l ) w i t h Ram anspec t rosc op ic f ingerpr in t s fo r DNA det ec t ion
TEM of ZnO (core)/Au (shell) nanocomposites
J . PHYS. CHEM. C 111 (2007) 3290-3293
ZnO
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A
target
B
probe
3.DNA detection
-S-A14-ATC-CTT-ATC-AAT-ATT
TAG-GAA-TAG-TTA-TAA-ATT-GTT-ATT-AGG-GAG
Nano-ZnO(core)/Au(shell)
TAA-CAA-TAA-TCC-CTC-A14-S-
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XPS
DNA
Zn
O/Auna
nocop
ositi
es
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EcE
F
Ev
= 5.2 eV
ZnO
EF
= 5.1 eV
AuE0
ZnO
Au SERS
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Im m unoassay based on ResonantRam an Sc at t e r ing of m agnet ic
Fe 3O4/ZnO/Au nanoc om posi t es
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(b)
Fig.3. Resonant Raman scattering for the nanocomposites.
Fig. 2 (a). TEM image of the nanocomposites.
Fig.2(b). HRTEM image of the red region in (a).
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The immunoassay process
analyteAu
Assay A:
AuAu
Fe3O4/ZnO/Au-antibody
analyte
Assay B:
Au
Fe3O4/ZnO/Au-antibody
Magnetic seperated
BSAanti-IgG
Magnet
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Assay A
Au
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Assay B
Au
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Thank you all