Yichun Liu

The properties and application of nano-ZnO Y.C. Liu （刘益春） Key Laboratory of UV Light-Emitting Materials and Technology, Ministry of Education, Northeast Normal University, Changchun

Environmental issues TiO2 Photocatalysis: Advantages and Shortcomings Advantages: 1) Cheap material 2) Nontoxic and stable 3) Suitable valence and conduction band positions

Shortcomings: 1) Charge recombination problem Resolution: “Photochemical diode” type photocatalysts such as TiO2/SnO2, TiO2/Pt 2) Transparent for visible light Resolution: non-metal doping, such as N, C, S-doped TiO2 3) Low extinction coefficient in UVA range due to its nature of indirect bandgap semiconductor

How to resolve this problem?

Our Strategy for Highly Efficient Semiconductor Photocatalysis ZnO: a direct wide band-gap semiconductor with intense absorption in UVA; a chemically unstable oxide material, easy to be dissolved in acidic or alkaline medium

TiO2: a indirect band-gap semi-conductor with weak absorption in UVA; a chemically stable oxide material, stable in acidic or alkaline medium either in dark or under excitation.

E vs vacuum level TiO2/shell as reaction site

-2 -4

ZnO/nanorode core as antenna for UV light

e-

e-

O2 O2-

-5 -6

In such a array structure, UVabsorption and photoreaction can be site-separately carried out, which may favor the efficiency of photocatalytic process.

RH

-7 -8

h+ ZnO

h+ TiO2

R•

PVP/ZnO tubes ZnO/TiO2 nano-fibers for photocatalysis Langmuir,23 (2007)10920， J.Chem.Phys, 2008

J.Chem.Phys., (2009)

The top view FESEM images of the to be accepted as-prepared well-aligned ZnO nanorod arrays on aMapping ZnO-coated Si Resonance Raman to Identify nano-ZnO Array Orientation substrate

Langmuir,25 (2009)xxxx

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/SiO2 core-shell nanowire array.

Figure 2. Evolution of water contact angle on ZnO nanowire and ZnO/SiO2 core-shell nanowire arrays modified with octadodecyltrimethylsilane monolayers during irradiation with ultraviolet light.

n-nano-ZnO/p-GaN LED P-NiO/n-nanoMgZnO UV-detector

A great breakthrough from in ZnO homojunction LED The★results of n-ZnO/p-GaN ----------Kawasaki et al. nature materials, 4, 47 (2005)

A homostructural ZnO p-i-n light emitting diode

n-ZnO/p-GaN diode by ZN Technology, CA,USA EL from p-GaN

na tur e

ma te

GaN

ria

ls,

4,

20

05

¾Why choose to construct GaN/ZnO heterojunction LED ?

p-ZnO

pn homojunction

UV LED & LD

ZnO ZnMgO, GaN, SiC, AlN, et al

pn heterojunction

¾Researching progresses in GaN/ZnO heterojunction LED Why choose GaN? ¾Similar material properties GaN

ZnO

Crystal Structure

Wurtzite

Wurtzite

Lattice Constant (Å)

a = 3.189 c = 5.186

a = 3.249 c = 5.205

Bandgap (eV)

3.42

3.37

¾Commercial availability of high-quality p-GaN

p-GaN/n-ZnO异质结器件的电学性质 Samples

ρ (Ωcm)

μ (cm2V-1s-1)

N (cm-3)

p-GaN

1.63

5.34

7.13×1017

n-ZnO

3.15×10-2

26.21

7.57×1018

n-ZnO p-GaN

p-GaN/n-ZnO

p-GaN/n-ZnO异质结器件的电致发光性质

蓝色电致发光来自p-GaN层

Why does EL originate from p-GaN? conduction and valence band offset : ΔEc=0.15 eV and ΔEv=0.12 eV

electrons in n-ZnO and holes in pGaN 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

¾UV LED based on p-GaN/i-ZnO/n-ZnO heterojunction ‹Device structure

n-ZnO i-ZnO p-GaN

Mg doped p-GaN: MOCVD i-ZnO: rf reactive magnetron sputtering Zn-rich n-ZnO: electron beam evaporation

‹Electrical properties Samples p-GaN i-ZnO n-ZnO

ρ (Ωcm) 1.63 1.12×103 4.14×10-2

μ (cm2V-1s-1) N (cm-3) 5.34 7.13×1017 1.28 4.38×1015 20.0 7.53×1018

¾p-i-n heterojunctions exhibites a rectifying, diode-like behavior. ¾The forward turn-on and reverse breakdown voltages is ~9 and ~11 V.

p-GaN/i-ZnO/n-ZnO异质结器件的电致发光性质

‹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

Appl. Phys. B 80 (2005) 871

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 iZnO to one at 3.08 eV from pGaN vs. the injection currents ‹Mechanism The i-ZnO has the lowest carrier concentration and mobility among the three layers, thus, the carriers including holes from p-GaN and electrons from n-ZnO can inject into iZnO layer, where the radiative recombination occurs.

EL from P-GaN/i-ZnO/n-ZnO (i-ZnO纳米结构）

EL of p-GaN/n-ZnO and p-GaN/i-ZnO/n-ZnO with i-layer thickness of 20 nm, 40 nm, 80 nm

Optical Storage and Electrical Storage Device

利用TiO2-Ag复合薄膜的光致变色现象实现全息信息存储 TiO2-Ag复合薄膜的多色光致变色现象

全息光栅的生成与擦除

Y. Ohko, et al. Nat. Mater. 2003 (2)29.

全息光栅的稳定性 TiO2 Ag

TiO2-Ag Film

全息光存储测量方法及原理

Ag/ZnO film

Interference fringe

利用TiO2/ZnO-Ag复合薄膜的全息信息存储

Ag Green laser Ag+

Ag

Ag+

UV

Ag

IGZO TFT

IGZO TFT的迁移率为

K. Nomura, et al., Nature 488 (2004) 432.

17.2 cm2/v.s

Thin film transistor of amorphous oxide semiconductor

-6

3.5x10

-6

-6

2.5x10

-6

IDS (A)

2.0x10

-6

1.5x10

Vg increasing

3.0x10

-6

1.0x10

-7

5.0x10

0.0 -7

-5.0x10

0

10

20

30

40

30

40

VDS (V) -6

5.0x10

-6

Al a-IGZO SiO2

-6

3.0x10

IDS (A)

Al

VDS increasing

4.0x10

-6

2.0x10

-6

1.0x10

p-Si

0.0 0

10

20

Vg (V)

Al

Unipolar memory of reversible resistance switching

NiO Al

S. H. Chang, et al., Phys. Rev. Lett. 102, 026801 (2009)

Cu

-1

10

Reset Set

Reset -2

Al

2.0x10

-2

10 Set -2

Current (A)

1.5x10

-3

10

-2

-4

1.0x10

10

-5

10

-3

5.0x10

-6

10 0.0

-7

10 0.0

0.5

1.0

1.5

2.0

Voltage (V)

0.01

ZnO:Li

0.1

1

The application of nano-ZnO materials in bioseparation and sensitive Immunoassays

为什么选择ZnO？ ZnO (core)/Au (Ag) (shell) with Raman spectroscopic fingerprints for DNA detection 优势：Au:生物兼容，环境友好；

ZnO电声子耦合强，共振多声子Raman指纹特征， 对ZnO材料要求不高，环境友好； ZnO (核)/Au (壳)结构： 光稳定性好，水溶性

TEM of ZnO (core)/Au (shell) nanocomposites

J. PHYS. CHEM. C 111 (2007) 3290-3293

3.DNA detection

target A probe

B -S-A14-ATC-CTT-ATC-AAT-ATT TAA-CAA-TAA-TCC-CTC-A14-S-

TAG-GAA-TAG-TTA-TAA-ATT-GTT-ATT-AGG-GAG

Nano-ZnO(core)/Au(shell)

Zn O /A u

D

A

op os iti es

N

na no c

XPS

Au Φ = 5.1 eV

E0

ZnO Φ = 5.2 eV

EF

Ec EF

ZnO Au

SERS

Ev

Immunoassay based on Resonant Raman Scattering of magnetic Fe3O4/ZnO/Au nanocomposites

(b)

Fig. 2 (a). TEM image of the nanocomposites.

Fig.2(b). HRTEM image of the red region in (a). Fig.3. Resonant Raman scattering for the nanocomposites.

The immunoassay process

anti-IgG

Magnet

Assay A:

Au

Au

Magnetic seperated BSA

analyte Fe3O4/ZnO/Au-antibody

Au

Assay B:

analyte Fe3O4/ZnO/Au-antibody

Au

Assay A

Au

Assay B

Au

Significance of the Superparamagnetism ¾Convenient separation Magnet

Fe3O4 /ZnO/Au

¾More faster detection under magnetic field

(a)

(b)

Magnet

Magnetic seperated

Conclusion ¾Multifunctional Fe3O4/ZnO/Au nanocomposites were used as biolabels. ¾The fingerprint resonant Raman Scattering could be used for sensitive immunoassay.

Au

Au

(assay A, 20 pM)

(assay B, 200 fM)

¾Rapid and convenient separation could be realized by an external magnet. ¾The detection time could be shorten by applying external magnetic field.

Thank you all