YiChun Liu

8/14/2019 YiChun Liu

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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

Documents

YiChun Liu