Luận án tiến sĩ: Synthesis and characterization of functional nanostructures

HARVARD UNIVERSITY GRADUATE SCHOOL OF ARTS AND SCIENCES DISSERTATION ACCEPTANCE CERTIFICATE The undersigned, appointed by the: Department of Chemistry and Chemical Biology have examined a thesis entitled: Synthesis and Characterization of Functional Nanostructures presented by: Lian Ouyang candidate for the degree of Doctor of Philosophy and hereby certify that it is worthy of acceptance. Signature Typed name. Professor Hongkun Park, Advisor Š1pnalun. Professor Charles Lieber, Chemistry SRE oypJor OE he.

Typed name Professor Xiaowei Zhuang, Chemistry Date, 22 August 2006 Synthesis and Characterization of Functional Nanostructures A thesis presented by Lian Ouyang to The Department of Chemistry and Chemical Biology in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Chemistry Harvard University Cambridge, Massachusetts Submitted in August 2006 UMI Number: 3245177 Copyright 2006 by Ouyang, Lian All rights reserved. INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted.

Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. ® UMI UMI Microform 3245177 Copyright 2007 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code.

ProQuest Information and Learning Company 300 North Zeeb Road P. Box 1346 Ann Arbor, MI 48106-1346 ©2006 Lian Ouyang All rights reserved. This thesis is dedicated to my husband and my parents. ill Synthesis and Characterization of Functional Nanostructures Advisor: Prof.

Hongkun Park Lian Ouyang Harvard University August 2006 Abstract Nanostructured materials or nanomaterials are generally considered to possess at least one dimension on the nanometer scale. The physical properties of nanomaterials often differ significantly from those of bulk materials, largely due to quantum size effects and surface effects. Because of these unique properties and their potential applications, there is a great deal of interest in developing methods for controlling the composition and morphology of nanostructures. This thesis describes approaches to the synthesis and characterization of several functional materials in a nanostructured form, including metal oxides, metal silicides, and compound semiconductors.

These materials were chosen because they exhibit unique and useful electronic, magnetic, and optical properties. The first chapter provides a brief introduction to nanotechnology, nanomaterials, and the organization of this thesis. The second chapter describes the synthesis and structural, elemental, and magnetic characterization of bartum-doped lanthanum manganite nanocubes. Manganite is an attractive transition-metal-oxide system because there is an incredible variety in their electronic and magnetic properties that may be tuned by chemical doping.

We developed a hydrothermal synthesis of manganite nanocubes 1V whose chemical doping was adjusted by changing the relative abundance of chemical precursors and the solution pH levels. The third chapter presents a vapor-phase synthesis of iron monosilicide nanowires and the characterization of the product. The cubic B20-type intermetallic compound ¢- FeSi is a narrow band-gap semiconductor and a Kondo insulator. The synthesis yields straight and branched single-crystalline FeSi nanowires.

Magnetic and electrical measurements were performed on the nanowire ensembles and on individual nanowires and the results were discussed. The following two chapters focus on semiconductor nanorods and axial nanorod heterostructures. Specifically, the fourth chapter explores a solution—liquid—solid method for the synthesis of cadmium chalcogenide nanorods with built-in heterojunctions. Structural, electrical and optical characterization of the heterostructures consistently demonstrated the success of this synthetic strategy.

The final chapter presents an electroluminescence study on individual colloidal CdSe nanorods devices with a transistor geometry. The electrical and optical properties of the devices were measured simultaneously at low temperature. The devices displayed Coulomb blockade behavior at low bias voltages. At higher bias voltages, we observed a superlinear increase in current with bias, accompanied by electroluminescence with a broad spectral distribution.

These measurements enabled us to explore the interplay between charge transport and light emission in a single-nanocrystal transistor and propose a light emission mechanism. Acknowledgement If I can live up to the average lifespan—eighty years, I only have 16 five-years. I consider myself extremely fortunate to have spent one sixteenth of my life at the graduate school of Harvard University. The last five years has been the most rewarding and unimaginable period of my life.

In the process of ‘surviving’ graduate school, trying- failing-trying different projects, meeting all kinds of incredible people in and out of Harvard, I have had a chance to know myself better, to know this country better, and hopefully to know science better. I have to thank many people for their support during this unforgettable period of my life, without whom the research presented in this thesis could not have been accomplished. I must first thank my advisor, Professor Hongkun Park, for his shepherding and guidance throughout my five years as a group member. I will be always indebted to him because I would have been separated from my husband for the last five years without his kind help.

I have learned from him not only the scientific thinking but also the effective communication of thoughts, honesty and courage of self-criticizing. I would like to thank Professor Lieber and Professor Zhuang for serving on my Graduate Advising Committee and giving valuable suggestions to this thesis. I am deeply appreciative to my husband, Nan, who has always been supportive and giving. I am grateful for his indulgence and trust in me.

I am blissful to have him as my closest friend, a “mentor”, a “cheer leader’, a “chauffeur”, and most importantly a loving and caring husband. Jeff Urban has been an integral part of my research and non-scientific experience at Harvard. He never hesitated in giving me advice and help whenever I vi asked him. He taught me how to put septa onto flasks in the glove box (believe me, it is absolutely a critical training for someone who has no previous experience in using the glove box); how to clean schlenk line; how to seal quartz tubes; how to differentiate ‘tower’ and ‘towel’; how to learn new things—wun poco per dia.

I want to thank Junqiao, Qian and Kristin who have always been around to answer my questions no matter how trivial they are. I owe a lot of thanks to all the current and former group members who have made my life in the group a memorable experience. I also want to thank Dr. Chenyan Wen, Mr.

Xi Wang and Dr. David Bell for their selfless help with the high-resolution TEM. I couldn’t get those beautiful TEM images of the nanostructures I made without them. I have to thank many of my classmates: Yi-wen, Ked, Daina, Amethyst, Chen, Carl, Yue, Isaac, Vijay, Jake, Ping, Gengfeng and Xiaolin.

(If I forget any names, please believe me that I appreciate their friendship as much.) Besides having fun with them, I also learned quite different yet invaluable lessons from them outside classroom and laboratory. Finally, my greatest thanks go to my parents for their understanding and encouragement through the way. Their ineffable influence contributes a totally different yet absolutely essential part of this thesis work. They have been always worried about what I was worried about and excited about what I was excited about.

I don’t know how to truly thank them. Vil Table of Contents Chapter 1: InfroducfÏOI. NANOTECHNOLOGY AND NANOMATTERIALS. Terminology and history 0ƒ nanofechHOÏOBV.

Nanomaterials and ways t†o make th€HN. àcccctnTt Tnhh ng the 4 1. QVERVIEW OF THE THESIS. --LÁ Ă HT TH HH nà TH Hệ 10 1.

ốẳốắ 12 Chapter 2: Synthesis and Characterization of Mixed-Valence Manganite Nanocubes. INTRODUCTION TO MIXED-VALENCE MANGANITES. LH ng ưêc 17 PIN NT, 42. Rich phase điagrams 0ƒ ItAHBGHÌ[€S.

sàng HH noi 22 2. HYDROTHERMAL SYNTHESIS OF LA¡. Brieƒfintroduction to Hydrothermal methodi. Synthesis of LBMO nanocubes with controllable doping.

Characterization oƒ mangqnite nahOCH€. HYDROTHERMAL SYNTHESIS OF LA¡. CONCLUSION AND FUTURE DIRECTIONS. nh HH Hư HH Hy 42 "N00 901.

43 Chapter 3: Vapor Phase Synthesis and Characterization of ¢-FeSi E111. INTRODUCTION TO E-FESI. ngĐT ng 49 Vill 3. VAPOR-PHASE SYNTHESIS OF 8-FESI NANOWIRES.

Ung ng ng Hs nen ng vêy 52 3.3 CHARACTERIZATION OF FESI NANOWIRES. HH HH ng Hà HT Thy 55 3.1 Structural and compositional Characterization .2 Magnetic characterization 0ƒ FeSĩ HGHOWÌF§.3 Transport measurement of individual FeSi Hañ1OWÌY€S.- HH HH HH TH TH TT TT HH HH Tà TH TT TH TH TH 64 3. Ăn Hàn TH HH TH HH Ti TT 66 Chapter 4: Synthesis and Characterization of CdE (E = S, Se) Nanorod Heterostructures. Gv TT TH TH TT TH KH tiệt 70 4.

SYNTHESIS OF CDE NANOROD HETEROSTRUCTURES. nh HH HH TH TT HT HT ng HT HH 73 4. Ăn TH TH KT HH Hit 74 4. CHARACTERIZATION OF CDE NANOROD HETEROSTRUCTURES.

DISCUSSION ON THE EXPERIMENTAL RESULTS. TH TH KT KH TK kh cu 9 kg 6698190 11 87 Chapter 5: Electroluminescence from a Single CdSe Nanorod Transisfor. MOTIVATIONS OF RESEARCH ON INDIVIDUAL NANOCRYSTALS.- càng TH TH Hà nh TH HH TH ni ĐH Hit 93 3. Synthesis oƒ CdSe HaHOYOđÌS.

SH HH Hi Hư nai 93 5. Low-temperature electrolumin€esC€HC€ Il€ASUFGIHGHÍ. Inelastic scattering IHOđ€Ï. sàng HT ngư 100 1X 5.

REFERENCES Appendix 1: Experimental conditions assessed for work presented in Chapf€Y .0804 0600006000 106 Appendix 2: Experimental conditions assessed for work presented in Chapf€T Ổ. 0 T00 00940000900 0609080 0080080890 109 Appendix 3: Supporting information for work presented in Chapter 4 Chapter 1 Introduction Nano means extremely small. The word originated from Greek nanos, meaning dwarf. Nowadays, it is used as a standard prefix in the list of physical units and stands for one billionth (10°).

A size map of some representative small objects including ‘nano’- crystals is illustrated in Figure 1 [1]. The term nanotechnology broadly refers to the science and technology on the nanometer (1 nm = 10° meter) scale. It is an emerging field of research and development dedicated to increasing control over physical structures of nanoscale size (1 to 100 nm) in at least one dimension [2, 3]. This chapter serves as a brief introduction to certain aspects of this field and provides a general overview for the research work presented in this dissertation.

The first section is a brief review of the history and recent development in nanotechnology as well as nanomaterials. The following section explores the reasons why nanomaterials have been stunningly attractive over the past decade or so. The concluding section presents an overview of the following chapters of this thesis. 1,000 nrn— 100 nm — Figure 1.

Sizes of representative small objects. (Image copyright Bioimaging Laboratory, University of Wales.) (c) Polygonum pollen grain. (Image copyright David Scharf.) (d) Red blood cells. (Image copyright Tina Weatherby-Carvalho, MircroAngela.

Figure adapted from reference [1]. Nanotechnology and nanomaterials 1. Terminology and history of nanotechnology Nanotechnology should really be called “nanotechnologies” since there is no single field of nanotechnology. It is a “cluster of emerging techniques from solid-state technology, biotechnology, chemical technology and scanning-probe technology that converge “top- down’ and ‘bottom-up’ to the nanoscale” [3].

“Top-down” refers to the increasingly precise downsizing of macroscopic materials to nanometer scale while “bottom-up” refers to synthesis from individual molecules or atoms. The latter is the core idea that guided the work presented in this dissertation. The term "nanotechnology" was defined by Professor Norio Taniguchi of Tokyo Science University in a 1974 paper [6]. In the 1980s the basic idea of this definition was explored in much more depth by Dr.

Eric Drexler, who promoted the technological significance of nano-scale phenomena and devices through speeches and the books: “Engines of Creation: The Coming Era of Nanotechnology” and ‘““Nanosystems: Molecular Machinery, Manufacturing, and Computation”. Nonetheless, long before the term was coined, physicist Richard Feynman mentioned some of the distinguishing concepts in nanotechnology in the lecture “There's Plenty of Room at the Bottom” at an American Physical Society meeting in 1959.