行政院國家科學會專題研究計畫成果報告
半導體奈米物質在發光元件上的應用及高排列之半導體奈
米線的製作
Applications of Semiconductor Nano-sized Materials on Light Emitting Devices and Fabrications of Highly-Oriented Semiconductor Nanowires.
計畫類別：個別型計畫
計畫編號：89-2113-M-003-024
執行期間：89/08/01 90/07/31
計畫主持人：陳家俊 教授
計畫參與人員：研究生: 余敏源 陳俊和 李勇志 葉怡
君 蘇雅雯 李奕成
郭聰榮
楊正義
鍾順宏
本成果報告包括以下應繳交之附件：
l 出席國際學術會議心得報告及發表之論文各一份
執行單位：國立台灣師範大學化學系
中華民國 90 年 1 月 07 日
行政院國家科學委員會專題研究計畫成果報告
合成半導體奈米線/棒(量子線)並探討它們光學上的特質
計畫編號：89-2113-M-003-024
執行期限：89 年 8 月 1 日至 90 年 07 月 31 日
主持人：陳家俊 國立台灣師範大學化學系
一、中文摘要 我們在過去的一年裡，已經完成十篇論文。分 別發表在 Advanced Materials 與 Journal of the American Chemical Society, Chemical Physics Letter, Applied Physics letter, Journal of Physical Chemistry, 半導體月刊, 物理雙月刊, 科儀新知等中英文論文 期刊 (see reference). 另外二篇論文於 2001/11 及 2002/01 已經投稿 關鍵詞：硒化鎘、硫化鎘、奈米棒、氮化鎵、奈米 線、碳奈米管 Abstr actA novel two-step catalytic reaction is developed
to synthesize gallium nitride nanowires encapsulated inside carbon nanotubes (GaN@CNT). The nanowires are prepared from the reaction of gallium metal and ammonium using metals or metal alloys as a catalyst. After the formation of the nanowires, carbon nanotubes are subsequently grown along the nanowires by chemical vapor deposition of methane. The structural and optical properties of pure GaN nanowires and GaN@CNT are characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and Raman spectroscopy. The results show that GaN nanowires are indeed encapsulated inside carbon nanotubes. The field emission studies show that the turn-on field of GaN@CNT is higher than that of carbon nanotubes, but substantially lower than that of pure GaN nanowires. This work provides a wide route toward the preparation and applications of new one-dimensional semiconductor nanostructures.
二、緣由與目的
Since the discovery of carbon nanotubes by Iijima, the materials always offer intriguing possibilities for
fundamental studies of nanoscale well-defined structures and provide high potential for technological applications. Significant progresses have been made recently on the studies of mechanical, electronic transport and structural properties of individual carbon nanotubes and the results indicated that they exhibited high tensile strength, discrete electronic states and structural helicity. On the application side, carbon nanotubes have been applied in the fabrications of various devices, for examples, scanning probes, biological sensors, electronic transistors, field emitting devices, and energy storage.
Filling materials into the inner hollow cavity of carbon nanotubes have brought great attention because the new filled one-dimensional (1-D) structures are expected to exhibit different physical properties than those of empty nanotubes. Many attempts have been made to encapsulate various materials into carbon nanotubes. For examples, capillary force has been utilized to fill lead and bismuth into an open nanotube. Also, different transition metals such yttrium,
manganese, iron or gadolinium have been
encapsulated into nanotubes using an arc-discharge method. In addition, a direction chemical vapor deposition (CVD) of metal organic complexes of Fe(CO)5 and Co(CO)5 has been used to generate the carbon nanotubes filled with Fe and Co nanoparticles. However, in those methods the overall yield of the encapsulated nano-materials is rather low and they are difficult to scale up. Moreover, to our knowledge, still there are few reports on how to fill binary semiconductor materials into carbon nanotubes, although it has been known that 1-D semiconductor nanostructures (nanowires) are electronic confined systems ideal for fundamental studies of their physical
properties and for the fabrications of optoelectronic nanodevices.
One of the III-V 1-D semiconductor nanostructures,
GaN nanowires, has attracted much interest because of their great potential for new visible and UV
optoelectronic applications. Of recent, we have developed a large-scale synthesis of GaN nanowires from the catalytic reaction of gallium and ammonium using various metals as a catalyst. Subsequently, breakthroughs have been made to achieve high purity and high quality synthesis of the GaN nanowires by careful optimizing the growth conditions. From our previous results, we found that the resulting GaN nanowires from the catalytic reaction are usually terminated with a nanoparticle on the tip of each individual nanowires and the mechanism of the nanowire formation can be attributed to
vapor-liquid-solid (VLS) growth. It has been well known that single-wall and multi-wall carbon nanotubes can be prepared by a CVD of methane or ethylene using iron, nickel, cobalt or their alloys as a catalyst. There are several similarities between the proposed mechanisms and growth conditions of GaN nanowires and carbon nanotubes. First, the growths of the nanowires and nanotubes are both performed in a gas phase with the presence of metal catalysts. Second, the catalysts of cobalt, nickel and iron can commonly served in either one of the growths. Third, after the growth, catalytic nanoparticles were generally found on the tip of individual nanowires and
nanotubes. Thus, on the basis of the similarities between their growth conditions, we propose a two-step catalytic reaction in a gas phase for the growth of GaN nanowires encapsulated inside carbon nanotubes (GaN@CNT). The resulting materials of GaN@CNT were characterized using electron microscopy and Raman spectroscopy. In addition, their filed emission properties were measured to demonstrate their potential in an electronic device application.
三、研究結果與討論
In previous work, we have shown that metal (Fe,
Co, Ni) and their metal alloys are efficient catalysts for the growth of GaN nanowires. The imageshows typical SEM and TEM images of resulting materials obtained on the Substrate B after the first-step growth. A high yield (>95 %) of nanometer wire-like
structures (nanowires) with a diameter in the range of 20-50 nm is produced from the reaction of Ga metal and NH3. These nanowires are distributed over a large area of the substrate and have quite uniform diameters. The lengths between two entanglement points are up to several micrometers. The structural analysis on the nanowires using XRD and HRTEM showed that they can be indexed to a hexagonal wurtzite structure. The strong intensities of X-ray and electron diffraction peaks relative to the background signal suggested that the resulting products have high purity of GaN wurtzite phase. The image shows the TEM image that a single GaN nanowire is terminated with a nanoparticle on its tip. The structure and stoichiometry analyses using TEM and EDX on the nanowire suggested that the nanoparticle on the tip consists of GaN and catalyst, whereas the nanowires only contains gallium and nitrogen. The result agrees with the proposed mechanism of VLS growth of the nanowires as described in SEM image.
The catalytic nanoparticles terminated on the end of GaN nanowires can also served as a good catalyst for the growth of carbon nanotubes in methane. The SEM and TEM images show resulting materials on the Substrate B after the second-step growth. A thin layer of crystalline materials of light contrast is coated outside the surface of wire-like structures of dark contrast. The structural and stoichiometry analyses using HRTEM, EDX and Raman (see below) indicate that the outer thin layer structures and inner wire-like materials in the images are indeed consisted of carbon
nanotubes and GaN nanowires, respectively. The nanowires encapsulated inside the hollow core of the carbon nanotubes can extend over a substantial portion of the length (up to µm). The growth direction of carbon nanotubes follows the long axis of GaN nanowires. The diameters of nanotubes were
generally varied with the diameters of GaN nanowires. The number of graphite layers of carbon nanotubes depended on the total reaction time of the second-step growth. The longer reaction time, the more layers of carbon nanotubes outside the nanowires were obtained. Typically, the number of graphite layers calculated from HRTEM image (see below) are 15-20 under a reaction time of 10 minutes. Some parts of GaN nanorods are not successively connected inside carbon nanotubes and exhibited linear segments from several tenth to hundred nano-meters. The linear segments of GaN nanowires can be found either in the middle or at the end of carbon nanotubes. The structural analysis showed the segment is still a hexagonal structure, which suggests that GaN nanowires may be dissected into several segments without changing their crystal structures during the second-step growth at high temperature (1000 oC).
A typical HRTEM image and its corresponding
electron diffraction of the GaN@CNT were observed. A core-shell type structure is observed. The clear cross lattice fringes observed in the core indicated that GaN nanowires have a single crystal structure. In our previous report, both [001] and [110] directions were observed to be in parallel to the long axis of the wires, suggesting that they are common growth directions of the nanowires. A selected-area electron diffraction on the nanowires shows that they still keep a hexagonal wurtzite structure after the second heating process. The shell of the GaN@CNT consists of about 15 graphitene concentric layers with a uniform spacing of 0.34 nm between two consecutive layers, which consistent with previous experimental data
measured from multi-wall carbon nanotubes. The interface between nanowires and nanotubes was sharp with no gap or other phases under HRTEM. The result suggests that the first layer of carbon nanotubes could be directly formed on the surface of GaN nanowires.
四、參考文獻:
l "Controlled Growth of Cubic Cadmium Sulfide Nanoparticles Using Patterned Self-Assembled Monolayers as a Template", Chia-Chun Chen, J.-J. Lin, Advanced Materials, 13, 136 (2001).
l “Catalytic Growth and Characterization of Gallium Nitride Nanowires” Chia-Chun Chen, C.-C. Yeh, C.-H. Lang, C.-C. Lee, C.-H. Chen, M.-Y. Yu, H.-L. Liu, L.-C. Chen, Y.-S. Lin, K.-J. Ma, K.-H. Chen, J. Am. Chem. Soc.,123, 2791-2798 (2001).
l
“ Growth, Characterization and Applications of Semiconductor Nanomaterials (Invited paper, in Chinese) ” C.-I. Yang, C.-H. Chen, Chia-Chun Chen, Instruments today, 123, 27-40 (2001).l " Preparation and Characterization of Carbon Nanotubes Encapsulated GaN Nanowires (invited paper) ", Chia-Chun Chen, C.-C. Yeh, C.-H. Lang, C.-C. Lee, C.-H. Chen, M.-Y. Yu, H.-L. Liu, L.-C. Chen, Y.-S. Lin, K.-J. Ma, K.-H. Chen, J. Phys. Chem. Sol., 62, 1577-1586 (2001). l " Raman-Scattering in Single Crystalline
GaN Nanowires", H.-L. Liu, Chia-Chun Chen, C.-T. Chia, C.-C. Yeh, C.-H. Chen, M.-Y. Yu, S. Keller, S. P. DenBaars, Chem. Phys. lett.,
345, 245-251 (2001).
l " Optical Characterization of Wurtzite
Twu, Chia-Chun Chen, C.-H. Chen, Appl. Phys. lett., 79, 2693-2695 (2001).
l " Nanotechnology: From Basic Research to Industrial Development (Invited paper, in Chinese) " Chia-Chun Chen, C.-Y. Mou,
Solid State Technology, 22, 48 (2001). l " Developments and Applications of
Nanotechnology (Invited paper, in Chinese) " Chia-Chun Chen, Z..-H. Lang, Solid State Technology, 23, 44 (2001).
l " The Applications of Functionalized Metal and Semiconductor Nanoparticles in Biological Systems (Invited paper, in Chinese) ", C.-Y. Yang, J.-H. Chen, Y.-C. Yeh, C.-L. Chen, Chia-Chun Chen, Physics Bimonthly, 23, 667 (2001).
l " Electrochemical Fabrication of Photonic Crystals of ZnSe, PbSe, CdSe, CdS, CdTe and GaAs Semiconductors", Y.-C. Lee, T.-J. Kuo, C.-J. Hsu, Y.-W. Su Chia-Chun Chen,
