Outline of the talk. FIB fabrication of ZnO nanodevices. Properties of ZnO 4/19/2011. Crystal structure of ZnO. Collaborators. Wurtzite structure

Transcription

1 FIB fabrication of ZnO nanodevices Crystal structure of ZnO Wurtzite structure Lee Chow Department of Physics University of Central Florida 1 4 Collaborators X-ray diffraction pattern of ZnO nanorods 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 2 5 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 Properties of ZnO ZnO is a key functional material exhibiting : near ultraviolet emission, transparent conductivity semiconducting, magnetic, and piezoelectric properties. It has awide direct band gap (3.37 ev), & large exciton binding energy (60 mev) excellent chemical, mechanical, and thermal stability 3 6 1

2 Zinc oxide is an old material and has been used in the past 100 years as: Results SEM images of the branched and flower like ZnO nanorods Paint, feeds, adhesives, additives, & etc. Current interests in ZnO are in the following areas: Optoelectronics Nano/microelectronics Sensors, transducers. Morphology controlled by Zn 2+ concentration, ph and Temp Results Hydrothermal synthesis of ZnO nanorods and nano structures 8 11 Methodology The ZnO nano architectures were deposited on Si, glass, & quartz substrates using a hydrothermal method. Aligned ZnO nanorods 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: Zn(SO 4 ) + NH 4 OH ZnO + NH 4 (SO 4 ) or Zn (OH) - ZnO + 2(OH) - + H 2 O 9 4/18/ /4/19 University Lecture of Central #10 Florida 12 2

3 Zn ZnO Core Shell microspheres XRD pattern TEM & SAED Self assembly of ZnO nanorods based 3 D architectures 4/18/ /4/19 Lecture # ZnO microspheres Aligned bi layer of ZnO array SEM images of the ZnO chemically grown by biopolymer self assistance method are : (a) overall morphology of ZnO nanorodbased 2011/4/19 University of Central Florida 14 microspheres; 17 Intensity (a.u.) ZnO (100) Other Results ZnO microspheres ZnO (002) ZnO (101) ZnO (102) XRD pattern ZnO (112) ZnO (201) ZnO (004) (degree) ZnO (110) ZnO (103) ZnO (202) Intensity (a.u.) 100 cm -1 (low-e 2 ) Raman spectra 331 cm -1 (E 2H -E 2L ) 382 cm -1 (A 1T ) 438 cm -1 (high-e 2 ) 423 cm -1 (E 1T ) ZnO spheres fig1a Wavenumbers (cm -1 ) 586 cm -1 (E 1L ) During our doping investigations, we discovered that under certain conditions, we were able to grow aligned bi layer of ZnO nanorod array 2011/4/

4 Physics We demonstrated that a layer of Zincowoodwardite, Zn 1 xal x (OH) 2 SO 4 was first formed and acted as a template for the ZnO nanorod array. This is a schematic diagram of a simple FIB Physics Functions of Focused Ion Beam Focused ion beam fabrication of ZnO nanodevices Milling/Sputtering Deposition Imaging This is an FEI Dual Beam FIB/SEM instrument, NanoLab 600 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 SiO 2 covered silicon substrate. 4. Use electron flood gun for charge neutralization m 24 4

5 by in-situ lift-out technique In-situ lift-out fabrication of ZnO nanosensor 4/18/ /4/19 University Lecture of Central #10 Florida 25 4/18/ /4/19 University Lecture of #10 Central Florida 28 Individual ZnO nanorod Hydrogen sensor 4/18/ /4/19 University Lecture of Central #10 Florida our 1D, 2D and 3D nano/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. 4/18/ /4/19 University Lecture of Central #10 Florida 27 4/18/ /4/19 University Lecture of Central #10 Florida 30 5

6 The conductivity response of the ZnO-branched rod-based UV photosensor fabricated by insitu lift-out technique in the FIB system Results Device characterization Fabrication of ZnO nanocross Sensitivity = 0.09 % Scale bar is 3 μm 4/18/ /4/19 Lecture # /19/ Results nanorod arrays based sensors Fabrication of Tetrapod devices 4/18/ /4/19 University Lecture of Central #10 Florida 32 4/19/2011 4/18/2011 E MRS 2009 Fall Lecture Meeting, #10Poland 35 Focused Ion Beam Fabrication of ZnO nano cross Electric characterization Fig. I-V characteristics of the single ZnO tetrapod device through leg pair /19/ m 4/19/

7 Results characterization Gas response values of ZnO tetrapodbased sensor to different gases of 100 ppm. Sensitivity = 0.7 % 4/19/ Results characterization Typical spectral response of the ZnO tetrapod sensor under identical intensity of 300 nw/cm 2. Insert shows relative response versus bias voltage. Recent results using MOCVD method 4/19/ Response to H 2 gas CVD grown ZnO nanowires Fig. Response of the ZnO tetrapod sensor to 100 ppm H 2 gas at the room temperature. 4/19/

8 CVD grown ZnO nanowires Not all nanowires can be fabricated by FIB, it seems that ZnO nanowires is a special case rather than the norm. Scale bars are 2 m Summary CVD grown ZnO nanowires 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 MOCVD grown ZnO nanowires Summary 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

9 Summary 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. 49 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. 2011/4/