Highly uniform hole spacing micro brushes based on aligned carbon nanotube arrays
© Yang et al.; licensee Springer. 2013
Received: 20 October 2013
Accepted: 15 November 2013
Published: 25 November 2013
Highly uniform hole spacing micro brushes were fabricated based on aligned carbon nanotube (CNT) arrays synthesized by chemical vapor deposition method with the assistance of anodic aluminum oxide (AAO) template. Different micro brushes from CNT arrays were constructed on silicon, glass, and polyimide substrates, respectively. The micro brushes had highly uniform hole spacing originating from the regularly periodic pore structure of AAO template. The CNT arrays, serving as bristles, were firmly grafted on the substrates. The brushes can easily clean particles with scale of micrometer on the surface of silicon wafer and from the narrow spaces between the electrodes in a series of cleaning experiments. The results show the potential application of the CNT micro brushes as a cleaning tool in microelectronics manufacture field.
KeywordsMicro brushes Carbon nanotube arrays Chemical vapor deposition
Carbon nanotubes (CNTs) [1, 2], a typical one-dimensional nanostructure, have attracted great attention due to their unique combination of electronic, mechanical, chemical, and thermal properties [3–8]. In recent years, CNTs can be prepared mainly by arc discharge [9, 10], laser evaporation , and chemical vapor deposition (CVD) [12, 13]. Due to their mature preparation methods and outstanding properties, CNTs have been extensively exploited in a range of potential applications including nanodevices , sensor , field emission [16, 17], battery , and hydrogen storage .
The properties of CNTs can be highly enhanced when they are assembled into arrays, which can gain more applications in carbon nanotube devices and further strengthen the advantage of electronic nanodevices [20–23]. Although some material have been successfully aligned , it is very difficult to manipulate CNTs to form arrays, which makes it difficult to be economical and practical. Researchers have tried to realize the self-assembly growth of CNT arrays with the help of other auxiliaries [25, 26], among which anodic aluminum oxide (AAO) template is one of the important substrates for the growth of CNT arrays. Due to the uniform of the height and the nature, CNT arrays have great potential applications in many fields [25, 26].
Brushes are common tools for use in industry and our daily life. Typical materials for constructing brush bristles include animal hairs, synthetic polymer fibers, and metal wires. The performance of these bristles has been limited by the oxidation and degradation of metal wires, poor strength of natural hairs, and low thermal stability of synthetic fibers. CNT is one of the ideal materials for preparing micro brushes, owing to its small size, low density, high thermal stability, outstanding pressure-resistant elasticity, chemically inert, and excellent thermal conductivity properties. Micro brushes based on CNTs can be applied in many fields, such as the cleaning of the nanoscale particles on the integrated circuit, nanofilter to clean air and water and to kill bacteria, and selective adsorption to remove the organic matter and heavy metal ions in solution and the environment [27–29].
In the previous report , the hole spacing between the brush bristles was very hard to control. The CNT bristles were easy to take off from the substrate. The above-mentioned disadvantages have hindered their further potential applications. Here, we report a kind of micro brushes based on CNT arrays with the help of AAO template. Because of the regularly periodic pore structure of AAO template, the micro brushes have highly uniform hole spacing. The bristles, CNT arrays, are firmly grafted on the substrates. Finally the cleaning experiments are carried out to evaluate the performance of micro brushes.
Preparation of CNT arrays
At first, a quartz boat and the AAO template were sent into the CVD furnace and the system pressure was pumped to 1 × 10−2 Pa. Then, the temperature was raised to 500°C with the introduction of argon gas. After the temperature reaches 500°C, the furnace chamber pressure was controlled at 4,000 Pa for 1 h. Further, the chamber was heated to 700°C and 20 sccm of acetylene was introduced to the system, CNTs grew up in the hole of the AAO template. The reaction time was determined by the thickness of the AAO template. Typically, when the AAO template was 50 mm, the growth time was 2 h. Finally, the system was cooled down in a mixed gas atmosphere of argon and hydrogen. The samples were taken out until the CVD furnace was cooled below 300°C.
Preparation of micro brushes
The CNT arrays in AAO template were combined on silicon, glass, and polyimide substrates with the assistant of epoxy resin as the adhesive, respectively. The curing temperature was set at 50°C to 80°C for several hours. The samples were soaked into 2 M NaOH in order to completely remove AAO template framework and then washed by deionized water. The micro brushes were prepared after drying.
The cleaning experiments
Three types of cleaning experiments of particles on the silicon wafer and from the narrow spaces between the electrodes with the distance of 2 and 100 μm were carried out, respectively. The mixed particles are the silica with the diameter of 1 μm and epoxy resin powder with the diameter of 3 to 5 μm, including inorganic and organic particles. They were spilled on the surface of the substrate, the as-prepared micro brushes were used to clean for several times.
Transmission electron microscope (TEM) images were taken using a JEOL JEM-2100 microscope (JEOL, Akishima-shi, Tokyo, Japan) operating at 200 kV. The morphology of the samples was observed by scanning electron microscopy (SEM) using a Carl Zeiss (ULTRA 55, Carl Zeiss, Oberkochen, Germany) with energy dispersive X-ray (EDX, INCA PentaFET × 3, Model: 7426, Oxford Instruments, Abingdon, Oxfordshire, UK) spectrometry mode. The Raman spectra were obtained using a Senterra R200-L Raman spectrometer (Bruker, Germany) with a 514-nm line of laser source.
Results and discussion
In general, the diameter of CNTs is in consistent with pore size of AAO template. The roughness of CNTs has great relation with that of the hole wall of AAO template. In previously reported CVD experiments , the temperature of the system was increased quickly to reaction temperature and then immediately started the CVD experiment. In this process, the temperature directly rose from room temperature to reaction temperature; in other words, the sample has always been in a rapid heat treatment condition. Part of the internal thermal stress of the template was released through high-temperature deformation, but the majority of the thermal stress could not get released due to the rapid heating process. Thermal annealing is an effective method in thermal stress release . In order to improve graphitization degree of CNTs, a heat preservation pretreatment for 1 h under 500°C was added during the fast heating process so that the template could be fully stretched and the deformation stress will be released completely.
In summary, we have demonstrated that micro brushes based on CNT arrays were successfully fabricated. Firstly, the preparation of CNT arrays by a CVD method in AAO template was studied. The results show that the quality and degree of graphitization of CNT arrays can be improved significantly through a heat preservation pretreatment method. Secondly, three types of micro brushes were obtained on silicon, glass, and polyimide substrates with the assistance of epoxy resin, respectively. The hole spacing of the micro brushes is highly uniform owing to the regularly periodic pore structure of AAO template. The CNT arrays were firmly grafted on the substrates as bristles. The cleaning experimental results show that the particles on the surface of silicon wafer and between the electrodes can almost be swept away. The results expand the cleaning practicality of micro brushes in microelectronics manufacture field.
This work was supported by the National High-Tech R & D Program of China (863 program, 2011AA050504), National Natural Science Foundation of China (61376003), Program for New Century Excellent Talents in University (NCET-12-0356), Shanghai Science and Technology Grant (12JC1405700 and 12nm0503800), Shanghai Natural Science Foundation (13ZR1456600), Shanghai Pujiang Program (11PJD011), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, and Medical-Engineering Crossover Fund (YG2012MS40) of Shanghai Jiao Tong University, and the Foundation for SMC Excellent Young Teacher in Shanghai Jiao Tong University. We also acknowledge the analysis support from the Instrumental Analysis Center of Shanghai Jiao Tong University.
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