4/19/2011

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FIB fabrication of ZnO nanodevices

Lee Chow

Department of Physics

University of Central Florida4/18/2011 1Lecture #10

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Collaborators

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Synthesis, XRD Dr. O. Lupan

FIB, SEM Dr. G. Chai

XPS – Dr. B. Roldan,

Micro-Raman – Dr. A. Schulte

CL spectra – Dr. L. Chernyak

TEM – Dr. H. Heinrich

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Outline of the talk

• General review of ZnO properties

• Hydrothermal synthesis of ZnO nanorods & nano‐structures

• Chemical bath deposition of ZnO thin films

• Focused ion beam (FIB) fabrication of ZnO nanodevices

• Summary

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Crystal structure of ZnO

Wurtzite structure

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X-ray diffraction pattern of ZnO nanorods

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Properties of ZnO

• ZnO is a key functional material exhibiting :near‐ultraviolet emission , transparent conductivity semiconducting, magnetic, and piezoelectric properties. 

• It has a wide direct band gap (3.37 eV), &large exciton binding energy (60 meV) excellent chemical, mechanical, and thermal stability 

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• Zinc oxide is an old material and has been used in the past 100 years as:

Paint, feeds, adhesives, additives, & etc.

• Current interests in ZnO are in the following areas:

OptoelectronicsNano/microelectronicsSensors, transducers.

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Hydrothermal synthesis of ZnO nanorods and nano‐structures

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Methodology

The ZnO nano‐architectures were deposited on Si, glass, & quartz substrates using a hydrothermal method.   

The cleaned substrates were immersed in an aqueous solution bath for definite periods of time. There are many reactions that can be used.  For example:

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Zn(SO4) + NH4OH → ZnO + NH4(SO4)

orZn2+ + 4(OH)- → ZnO + 2(OH)- + H2O

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Results ‐ SEM images of the branched and 

flower‐like ZnO nanorods

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Morphology controlled by Zn2+ concentration, pH and Temp.

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Results

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Aligned ZnO nanorods

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Self‐assembly of ZnO nanorods‐based 3‐D 

architectures 

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ZnO microspheres

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SEM images of the ZnO chemically grown by bio-polymer self assistance method are : (a) overallmorphology of ZnO nanorod-based microspheres;

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Other Results – ZnO microspheres

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30 40 50 60 70 80

2 (degree)

Inte

nsit

y (a

.u.)

ZnO

(20

2)

ZnO

(00

4)Z

nO (

201)

ZnO

(11

2)

ZnO

(10

3)

ZnO

(11

0)

ZnO

(10

2)ZnO

(10

1)Z

nO (

002)

ZnO

(10

0)

100 200 300 400 500 600 700 800

586

cm-1 (

E1L

)

438

cm

-1(h

igh-

E2)

423

cm-1 (

E1T

)3

82 c

m-1 (

A1T

)

331

cm

-1 (

E2H

-E2L

)

100

cm-1(lo

w-E

2)

Wavenumbers (cm-1)

Inte

nsit

y (a

.u.)

ZnO spheres fig1aXRD pattern Raman spectra

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Zn‐ZnO Core‐Shell microspheres

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XRD pattern TEM & SAED

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Aligned bi‐layer of ZnO array

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During our doping investigations, we discovered that under certain conditions, we were able to grow aligned bi‐layer of ZnO nanorod array

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We demonstrated that a layer of Zincowoodwardite, Zn1‐xAlx(OH)2∙SO4 was first formed and acted as a template for the ZnO nanorod array.

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Focused ion beam fabrication of ZnO nanodevices

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This is an FEI Dual Beam FIB/SEM instrument, NanoLab 600

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Physics

This is a schematic diagram of a simple FIB

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Functions of Focused Ion Beam

Milling/Sputtering 

Physics

Deposition Imaging

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FIB fabrication procedures

1. Transfer individual nanostructure from the growth substrate to a clean silicon substrate. (For easy pick up of the nanostructure)

2. Use an intermediate nanorod to pick up the nanostructure. (to add an extra degree of freedom to manipulate the nanostructure)

3. Prepare contacts on a SiO2 covered silicon substrate.

4. Use electron flood gun for charge neutralization.

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Results‐ Device Fabrications

by   in-situ lift-out technique

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In-situ lift-out fabrication of ZnO nanosensor

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Results‐ Device Fabrications

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Results‐ Device Fabrications

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our 1D, 2D and 3Dnano/microrods

can be easily transferred to other substrates opening the possibility of studying the assembly of different functional units in novel nanodevices, nanosensors and single crystal logic nanogates.

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Results‐ Device Fabrications

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Individual ZnO nanorod Hydrogen sensor

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Results‐ Device Fabrications

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Results‐ Device characterization

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The conductivity response of the ZnO-branched rod-based UV photosensorfabricated by in-situ lift-out technique in the FIB system

Sensitivity = 0.09 %

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Results‐ nanorod arrays  ‐ based sensors

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Focused Ion Beam Fabricationof ZnO nano‐cross

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Fabrication of ZnO nano‐cross

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Scale bar is 3 μm

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Fabrication of Tetrapod devices

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Electric characterization

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Fig. I-V characteristics of the single ZnO – tetrapod device through leg pair 1-2.

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Sensitivity = 0.7 %

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Results‐ characterization

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Typical spectral response of the ZnO tetrapod sensor under identical intensity of 300 nW/cm2. Insert shows relative response versus bias voltage.

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Response to H2 gas

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Fig. Response of the ZnO tetrapod sensor to 100 ppm H2 gas at the room temperature.

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Results‐ characterization

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Gas response values of ZnO tetrapod-based sensor to different gases of 100 ppm.

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Recent results using MOCVD method

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CVD grown ZnO nanowires

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Scale bars are 2 m

CVD grown ZnO nanowires

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CVD grown ZnO nanowires

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MOCVD grown ZnO nanowires

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Not all nanowires can be fabricated by FIB, it seems that ZnO nanowires is a special case rather than the norm.

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Summary

• ZnO is a multi‐functional material that can have important applications in the near future.

• Hydrothermal method is a very simple technique to study the nano‐structure of ZnO.

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Summary

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Focused ion beam technique (FIB) is used to fabricate individual ZnO nano-sensor to detect Hydrogen gas and UV radiation.

Detail step of the FIB fabrication procedures were described.

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Summary

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The fabricated ZnO nano-sensors were tested for the detection of Hydrogen gas and UV radiation.

This is possible due to the fact that ZnO is an excellent radiation hardened material. So the exposure to Ga ion beam seems to have no effect on the properties of fabricated ZnO devices.

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Acknowledgements

This work was funded through the U.S. Civilian Research and Development Foundation (CRDF) with support from U.S. Department of State, Apollo Technology Inc., Florida I‐4 Corridor, FEI, and US Department of Agriculture.  

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