Nano-science and Nano-technology in China

发布时间：2016年05月06日 来源：中国化学会

Li-Jun Wan & Chun-Li Bai
Institute of Chemistry,  Nanoscience and Nanotechnology Center of the Chinese Academy of Sciences,  Beijing 100080,  China

Abstract:  Nanoscience and nanotechnology is an important emerging field of research and development focusing on the artificially fabricated structures in the nanometer range (1~100 nm). The shrinking sizes of structures will lead to a whole new world of quantum phenomena actively made use of in electronic, magnetic and optical devices. Chinese scientists have followed with the main stream in the development of the nanoscience and nanotechnology since its initial stage. In the present paper, the achievements and present status of China in relative researches such as characterization of nanostructures, preparation of nanomaterials and fabrication of nanodevices are described.

1. Introduction 

Nanoscience and nanotechnology is the creation and utilization of materials, devices, and systems through the control of matter on the nanometer-length scale. Its essence is the ability to work at these levels to generate larger structures exhibiting novel physical, chemical, and biological properties and phenomena. The aim of nanoscience and nanotechnology is to learn to exploit these properties and efficiently manufacture and employ the structures. Control of matter on the nanoscale already plays an important role in scientific disciplines as diverse as physics, chemistry, materials science, biology, medicine, engineering, and computer simulation. For example, it has been shown that carbon nanotubes are ten times as strong as steel with one sixth of the weight, and that semiconductor nanoparticles can be used in biolabeling. Nanoscale systems have the potential to make supersonic transport cost effective and to increase computer efficiency by millions of times.

As understanding developments of the way natural and living systems are governed by molecular behavior at nanometer scale, and as this understanding begins to be felt in science and medicine, researchers seek systematic approaches for nanoscale-based manufacturing of human-made products. In many countries, programs and initiatives on nanostructured materials have started. In China, some financial supports were given to support the research endeavors in this field [1]. The total funds supported by the government for nanoscience and nanotechnology research have reached about seven million US dollars during the past 10 years. 

Some public funds also contributed to the industrialization of nanomaterials. In the middle of 1980s, the Chinese Academy of Sciences (CAS) and National Natural Science Foundation of China (NSFC) initiated support on the development of SPM and other scientific issues at the nanometer scale (1987-1995). The Ministry of Science and Technology of China approved the 'Climbing up' project and supported nanomaterial science for ten successive years from 1990 to 1999. In 1999, the Ministry of Science and Technology started a national key basic research project 'Nanomaterial and Nanostructure', to continually support the basic research on nanomaterials such as nanotubes. The National High Technology Plan also establishes a series of projects for nanomaterial applications. However, compared with those in the developed countries, the funding is clearly too limited. Appreciable differences of overall level still exist between China and other developed countries, especially in the area of nanoscale devices and in industrialization.

It is noteworthy that the drive of nanoscale science and technology in China and outside China began at almost the same starting line. Tens of nation-wide conferences have been held in China since 1990 covering a wide range of topics in the related fields. In Beijing, CAS sponsored the 7th International Conference on Scanning Tunneling Microscopy (STM'93) and the 4th International Conference on Nanoscale Science and Technology (Nano IV)[2]. These conferences have severed academic exchanges and collaborations both nationally and internationally. 

To date, more than 50 universities, 20 institutes of CAS and 300 enterprises have engaged in the research and development of nanoscience and nanotechnology. Several centers for research and development of nanoscience and technology have been established in CAS, Tsinghua University, Peking University, Nanjing University, East China University of Science and Technology, and others.

Among these research centers, CAS pioneered the investigation on nanoscience and technology in China. A series of significant research projects were carried out in the late 1980s. The principal fields supported by CAS are as follows: bond-selective chemistry under the control of laser and the manipulation of single atoms with scanning tunneling microscopy (STM); molecular electronics research on molecular materials and molecular devices; giant-magneto resistance materials and related physics; photo catalytical and photoelectronic chemistry study of anosemiconductor; SPM studies on surface and interface as well as macromolecules; study on carbon nanotubes and other nanomaterials; study on the structure and physical properties of artificial "super-atom", and others. In addition, CAS is also undertaking a number of national key projects. 

In the year 2000, CAS organized 11 institutes of CAS to take joint efforts in a major research project of "Nanoscience and Nanotechnology", which was sponsored by the Knowledge Innovation Program, with an investment of more than three million US dollars. The main target of this project is as follows: to improve or to invent new synthetic methods and techniques for nanostructures, to produce new nanomaterials and nanodevices with important significance.

In the present paper, we focus on the progress of nanoscale science and technology in China. The discussions are divided into three sections: (1) characterization of nanoscale structures, (2) preparation of nanomaterials and (3) fabrication of nanodevices.

2. Characterization of nanoscale structures

The recent rapid advances in nanoscience and nanotechnology are due in part to our newly acquired ability to measure and manipulate individual structures on the nanoscale. Whether it should be scanning probes, optical tweezers, high-resolution electron microscopes, or other new tools, instruments available to researchers in science and technology now permit them to create new structures, measure new phenomena, and explore new applications. There are limitations for various properties, such as the chemical composition of a single nanostructures and local electronic and thermal characteristics. A research group at the Institute of Chemistry of CAS has independently developed a series of instrumentations such as STM, AFM, BEEM, LT-STM, UHV-STM, SNOM and so on, which have been extensively used in the characterizations on the nanoscale structures [3]. The Peking University has designed and constructed UHV-SEM-STM-EELS system and LT-SNOM system. They also set up a set of complete system consisting of SNOM-Near field spectrum, and classical optical methods, by which the structure of cancer cells was investigated.

With the development of these instrumentations, the Institute of Chemistry and Laboratory for Vacuum Physics, of CAS began the surface lithography experiments by STM on the nanometer scale and even on atomic scale as early as 1990 [3,4]. They successfully fabricated "CAS", the map of China, and Chinese characters of "China". These progresses in nanoscale fabrication helped to stimulate the awareness of the research of nanoscience and nanotechnology. Recently, a group in Institute of Chemistry has achieved good progress in the ordered self-assembly of organic molecules, aiming at the exploratory research on the nanoscale devices [5]. A group in the University of Science and Technology of China observed single C60 molecules by STM. Remarkably, the positional order and the bonding orientational order are both fully preserved across domain boundary [6,7].

3. Preparation of Nanomaterials

Synthesis and processing of nanostructures are employing in a diverse materials-organic, inorganic and biological-well beyond examples already realized. The driving forces will be creativity in broad areas of science, technology, and economics. Increasing emphasis will be placed on synthesis and assembly at a very high degree of precision, achieved through innovative processing. The result will be control of the size, shape, structure, morphology, and connectivity of nanostructured materials. Chinese scientists have devoted much attention to the preparation of nanomaterials. And numerous achievements have been obtained in the nanoparticles, nanotubes and nanorods, and. nanocrystals.

In respect of the preparation of nanoparticles, the Institute of Solid State Physics of CAS manufactured the silicon based nano-oxide (SiO2-x) with high specific surface area (~640 m2/g), and established a one-hundred-ton-scale production line in cooperation with enterprises. East China University of Science and Technology is establishing a 150,000 tons/year super-fine CaCO3 production line based on the industrial test of 3,000 tons/year. The Peking University has achieved good results in the production of nanoscale powder of Ni and applied the material with the largest Ni-H battery company in China. Based on the super-gravity synthesis methods, the Beijing University of Chemical Engineer developed a production line of 3,000 tons/year nanoscale powder, whose scale and techniques ranked in the first class in the world in 1994. The successful preparation of nanoscale iron powder by Tianjin University made China the second country in which nanoscale metal powder can be industrially produced. Qingdao University of Chemical Engineering has accumulated a wealth of experience in the research and development of nanoscale Cu catalyst. To date, there are more that 20 production lines with ton-scale capacity to prepare nanoscale powder materials. The great varieties include: nano-oxides (ZnO, TiO2, SiO2, ZrO, MgO, Co2O3, NiO, Cr2O3, MnO2, Fe2O3, etc.), nano-metal and nano-alloy (Ag, Pd, Cu, Fe, Co, Ni, Ti, Al, Ta, Ag-Cu alloy, Ag-Sn alloy, In-Sn alloy, Ni-Al alloy, Ni-Fe alloy and Ni-Co alloy, etc.), nano-carbonate (W2C3, C powder, SiC, TiC, ZrC, NbC, B4C3, etc.), nano-nitronate (Si3N4, AlN, Ti3N4, BN, etc.).

Concerning the preparation of carbon nanotubes, a research group at the Institute of Physics of CAS invented a template method based on chemical vapor deposition catalyzed by iron nanoparticles embedded in mesoporous silica in 1996 [8]. The obtained nanotubes are approximately perpendicular to the surface of the silica and form an aligned array of isolated tubes with spacings between the tubes of about 100 nm. This approach avoids the possible problems such as entanglements compared with other methods. In 1998, this group produced very long, multiwalled carbon nanotubes that reach about 2 mm in length through the pyrolysis of acetylene over iron/silica substrates, which is an order of magnitude longer than that described in most previous reports [9]. In 2000, the thinnest carbon nanotube with a diameter of 0.5 nm was first produced in the same group [10]. Then, the Department of Physics in Hong Kong University of Science and Technology prepared the thinnest single-wall carbon nanotube (0.4 nm) arrays using zeolite as template [11]. Afterwards, Peng et al. demonstrated the existence of small single wall carbon nanotubes with diameters of 0.5 and 0.33 nm by high resolution transmission electron microscopy. The 0.33 nm carbon tube observed is likely a (4,0) tube [12]. In 1999, masses of single-walled carbon nanotubes with a large mean diameter of about 1.85 nanometers were synthesized by a semicontinuous hydrogen arc discharge method in the Institute of Metal Research of CAS. They also investigated the characteristics of hydrogen-storage, and reported that the mass capacity of hydrogen storage in carbon nanotubes can reach 4.2% [13].

In respect of the synthesis of nanoscale inorganic materials, scientists in the University of Science and Technology of China developed the hydrothermal synthetic route to prepare GaN microcrystal [14]. They manufactured, for the first time, the GaN microcrystal with a size of 30 nm at about 300 ˚C. The research team also applied a reduction-pyrolysis-catalysis method to prepare the diamond powder, and therefore developed a technological route with high economic values [15]. Through a carbon nanotube-confined reaction, a research group in Tsinghua University prepared one-dimensional GaN nanocrystals, which have a diameter of 4 to 50 nm and a length of up to 25 mm [16]. This study demonstrated the possibility to synthesize other nitride nanorods through similar carbon nanotube-confined reactions. A research group in the Institute of Metal Research of CAS synthesized a bulk nanocrystalline pure copper with high purity and high density by electrodeposition [17]. For the first time, an extreme extensibility (elongation exceeds 5000%) without a strain harden effect was observed when the nanocrystalline copper specimen was rolled at room temperature. This behavior demonstrates new possibilities for scientific and technological advancements with nanocrystalline materials. This discovery was considered as of "a breakthrough in this field".

4. Fabrication of Nanodevices

In the broadest sense, nanodevices are the critical enablers that will allow mankind to exploit the ultimate technological capabilities of electronic, magnetic, mechanical, and biological systems. While the best examples of nanodevices at present are clearly associated with the information technology industry, the potential for such devices is much broader. Nanodevices will ultimately have an enormous impact on our ability to enhance energy conversion, control pollution, produce food, and improve human health and longevity. In the past decade, our ability to manipulate matter from the top- down and bottom-up strategy, combined with advances and in some cases unexpected discoveries in the synthesis and assembly of nanometer-scale structures, has resulted in advances in a number of areas. Particularly striking examples include the following: quantum electronics devices, ultra-high density data storage, etc.

Concerning quantum electronics devices, several groups in China have studied the single electron tunneling effect at room temperature, single electron tunneling of single atom junction, Coulomb blockade effect at room temperature using UHV-STM, high performance opto-electrical detectors. The Tsinghua University has achieved 100 nm (0.1mm) level MOS devices, and a series of silicon based integrated sensors, microphones, micro-motors and micro-pumps, etc. They also developed new techniques and microsystems using 3-D microscopic lithography methods. Institute of Semiconductors of CAS has developed sensors based on infrared (13-15) adsorbing quantum dots, and semiconductor quantum dot laser (with the wavelength range of (0.7-2.0) [18]. A prototype single electron device has been achieved in Institute of Physics, CAS [19,20]. A model device of field emission display panel made of nanotube material has been fabricated in the Xian University of Transportation, and has already been under continuous test for over 3800 hours.

The research on the ultra-high density data storage using organic materials was carried out in CAS in collaboration with Peking University. The diameter of dots prepared on NBPDA organic thin films reached 1.3 nm in 1997, 0.7 nm in 1998 and finally 0.6 nm in year 2000 [21]. This data is an order of magnitude smaller than the reported one by groups in other countries, and could lead to an increase of nearly one million times in storage if commercialized CD. Groups in Peking University adapted binary composite material TEA/TCNQ as ultra-high density data storage material and obtained large area data arrays of 3 * 3 μm, with 8 nm dot diameter. Fudan University successfully fabricated high-speed, high-density memory unit by using bi-stable thin films, and synthesized several patented organic monomers as basic materials for organic integrated circuits. 

The well-defined nanostructure can be constructed at solid/liquid interface under potential control with inorganic ions, organic molecules or other objects. The molecule orientation and structure can be controlled by applying an electrode potential in electrolyte solution and the formation process can be monitored by electrochemical scanning tunneling microscopy. The so-constructed nanostructures are potentially useful in future nano-electronic devices fabrication [22].

It is noteworthy that Chinese scientists still remain at the level of the preparation and selection of materials for nanoscale devices, as well as at the level of the investigations for new physical phenomena. The investigation on the mechanism and structure of nanoscale devices are relatively weak and lack originality. To achieve a significant progress in the research of nanoscale devices, China is ready to throw much more funds into this field to alter the present experimental equipment and research conditions. Also, the collaborations between research units are encouraged.

5. Conclusion

In summary, Chinese government has been paying great attention to the development of nanoscience and nanotechnology. The total funds supported by the government for nanoscience and nanotechnology researches have reached about seven million US dollars during the past 10 years. However, the funding is clearly too limited compared with those in the developed countries. The financial supports are expected to be increased further compared with current level. In addition, a National Steering Committee for Nanoscience and Nanotechnology has also been established, which consist of scientists and administrators from Ministry of Science and Technology, State Development and Planning Commission, Ministry of Education, Chinese Academy of Sciences, Chinese Academy of Engineering, National Natural Science Foundation of China and so on. 

On the other hand, many achievements have been obtained in the field of nanoscience and nanotechnology in China, mainly focused on the preparation of carbon nanotubes and nanoparticles. The 2001 review report on nanoscience and nanotechnology by APEC ranks China as No.3 in the world in the terms of scientific publications. To date, about 20 production lines with ton-scalce capacity to prepare nanoscale powder materials have been established. Due to the limited research conditions, the research level is still low compared with the developed countries. Most researches are still remained at the level of preparation of nanomaterials and investigation of the new physical phenomena. Few attentions have been focused on the designation and fabrication of nanodevices. Well coordination should be made in order to organize different branches to realize the breakthrough of key techniques for nanoscale devices. The original and applied researches should be reinforced concerning nanoscale materials.

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