Xiaojun Tian

Force Analysis of Top-Down Forming CNT Electrical Connection Using Nanomanipulation Robot

Carbon nanotube (CNT) is an ideal candidate for future nanoelectronics because of its small diameter, high current-carrying capability, and high conductance in a one-dimensional nanoscale channel. The most challenging part in fabricating nanosystems could be the formation of CNT connections. Existing techniques in forming CNT connections are suffered from problems in forming a single CNT connection or not being able to precisely deposit CNTs on specific locations. One of the efficient and reliable ways to form CNT connections is to make connections between CNTs and beforehand-fabricated electrodes by using an atomic force microscopy based nanomanipulation robot, which has the ability to manipulate single CNT with nanometre precision in a controllable manner. But even this, it often happens that CNT cannot be manipulated onto the top surface of electrodes, because there are some restrict conditions among electrode thickness, CNT radius and attitude of AFM tip, this paper study this problem in detail, some experimental results are also presented

3D nano forces sensing for an AFM based nanomanipulator

Atomic force microscope (AFM) has been proven to be a useful tool to characterize and change the sample surface down to the nanometer scale. However, in the AFM based nanomanipulation, the main problem is the lack of real-time sensory feedback for a user, which makes the manipulation almost in the dark and inefficient. In this paper, the AFM probe micro cantilever-tip is used not only as an end effector but also as a three dimensional (3D) nano forces sensor for measuring the interactive forces between the AFM probe tip and the object or substrate in nanomanipulation. The nano forces acting on cantilever-tip is modeled and the real-time PSD signals are used to calculate the forces. With new parameters calibration method used, the real 3D nano forces can be easily got and then fed to a haptic/force device for operator to feel, thus real-time manipulation forces information is obtained, with which the efficiency of nanomanipulation can be significantly improved. Nanoimprint experiments verify the effectiveness of 3D forces sensing system and efficiency improvement of nanomanipulation using this system.

Purification of SWNTs using high-speed centrifugation

For eventual commercial applications of single- walled carbon nanotubes (SWNTs) in nanoscale devices, it will be very important to realize effective purification of SWNTs. We have developed a simple method to purify as-synthesized SWNTs by centrifugal force in an aqueous solution of sodium dodecyl sulfate (SDS). The method proposed in this paper can effectively remove impurities such as metal catalyst particles, graphitic nanoparticles and amorphous carbon. Our method takes advantage of the fact that more massive particles sediment faster than less massive particles. Through adjusting relative centrifugal force, we can respectively remove metal catalyst particles and carbon nanoparticles from SWNTs by centrifugation. SEM results indicate that the concentration of the SWNT solution decreased when the number of times of centrifugation is increased. Raman spectra suggest that the purity of the SWNT solution increased when the number of times of centrifugation is increased. These experimental results indicate that the centrifugal technique can provide a rapid and repeatable purification of SWNTs.

A Study on Theoretical Nano Forces in AFM Based Nanonmanipulation

As it is important to understand the basic mechanics principle in nanofabrication process, much research has been done about nano mechanics with different tools in different nano enviroments, and various kinds of nano force formula have been proposed. However, as the special case of AFM based nanomanipulation is considered, little about its mechanics principle under the micro probes operation is known, such as what kinds of nano forces are the decisive factors and how they work, which are important to perform accurate control in nanomanipulation. To explore this subject, nano forces among tip, substrate and particle are analyzed, and simulation & experiments are performed to verify the rationality of the analysis.

The Assembly and Fabrication of Single CuO Nanowire Electronic Device Based on Controllable DWS-DEP Technology

CuO nanowire is an important one-dimensional semiconductor material to assemble and fabricate novel nanoelectronic device, especially molecular or atom device based on single nanowire. However, how to assemble and fabricate nanoelectronic device based on single CuO nanowire remains a big challenge. Here, we proposed a new controllable dielectrophoresis assembly technology, namely dielectrophoretic working space-dielectrophoresis technology, to realize the assembly and fabrication of single CuO nanowire nanoelectronic device. Theoretical analysis and assembly experiments verified the effectiveness of the new technology. By this technology, currently we have successfully fabricated two kinds of single CuO nanowire nanoelectronic device, photodetector and alcohol sensor, from CuO nanowires preparation, dispersion to assembly. Due to the high sensitivity of single CuO nanowire, the novel alcohol sensor can work at room temperature compared to the CuO nanowires arrays-based sensor working only at high temperature. The proposed technology can also be utilized to assemble and fabricate single-nanowire electronic device based on other materials.

Single-Walled Carbon Nanotube-Based Gas Sensors for NO2 Detection

An efficient method for nitrogen dioxide (NO2) gas detection in single-walled carbon nanotubes (SWCNTs) ordered using dielectrophoretical (DEP) technology after dispersion in sodium dodecyl sulfate (SDS) surfactant solution. Atom force microscopy (AFM) and scanning electron microscopy (SEM) images revealed that SWCNTs were assembled between the microelectrodes. SWCNTs were affected by the electrophoretic force which was carried out by the related theoretical analysis in a nonuniform electric field. SWCNT field effect transistors (SWCNT-FETs) geometry was obtained. The electrical performance of NO2 gas sensor with SWCNT-FETs structure was tested before and after NO2 at room temperature. Experimental results that the efficient assembly of SWCNTs were obtained when the applied alternating current voltage has a frequency of 2 MHz and an amplitude of 10 V. SWCNTs-based gas sensor had high sensitivity to NO2, and the electrical conductance of NO2 gas sensor reduced two times. SWCNTs surface gas molecules were washed out by means of ultraviolet ray irradiation in 10 minutes. NO2 gas sensor could be duplicated. Meanwhile, it also provided an effective method of assembly and manufacture for other one-dimensional nanomaterials assembly of nanoelectronic devices.

Assembly and Fabrication of Single-Wall Carbon Nanotube Field Effect Transistor Using Dielectrophoresis Method

On account of their sizes and unique properties, single-wall carbon nanotubes are candidates for a number of building blocks in nanoscale electronics. With respect to the assembly of carbon nanotube field effect transistor, the dielectrophoresis technology is adopted, which assembles SWCNTs between the microelectrodes, SWCNTs are affected by the electrophoretic force which is carried out by the related theoretical analysis in a nonuniform electric field. The driving electric field of dielectrophoresis is simulated by the comsol software. According to the simulation results, a number of the experiments are done. The applied alternating current voltage has a frequency of 2 MHz and an amplitude of 10 V. It turns out that the required experimental parameters of the efficient assembly of SWCNT are obtained. AFM scanning and electrical properties of SWCNTs show that the method can achieve the effective assembly of carbon nanotube field effect transistor. SWCNTs are driven in the microelectrode gap, having a good arrangement of uniform orientation and assembly results, and proportional to the arrangement density along the electrode width direction and the duration of DEP. As a result, it also provides an effective method of assembly and fabrication for other one-dimensional nanomaterials assembly of nanoelectronic devices.

A Method Study on Assembly of Single-Wall Carbon Nanotube Field Effect Transistor Using Dielectrophoresis

Single-wall carbon nanotubes are candidates for a number of building blocks in nanoscale electronics. With respect to the assembly of carbon nanotube field effect transistor, the dielectrophoresis technology is adopted, which assembles SWCNTs between the micro-electrodes, SWCNTs are affected by the electrophoretic force which is carried out by the related theoretical analysis in a nonuniform electric field. The driving electric field of dielectrophoresis is simulated by the comsol software. According to the simulation results, a number of the experiments are done. It turns out that the required experimental parameters of the efficient assembly of SWCNT were obtained. AFM scanning and electrical properties of SWCNTs show that the method can achieve the effective assembly of carbon nanotube field effect transistor. SWCNTs are driven in the microelectrode gap, having a good arrangement of uniform orientation and assembly results, and proportional to the arrangement density along the electrode width direction and the duration of DEP. Meanwhile, it also provides an effective method of assembly and manufacture for other one-dimensional nanomaterials assembly of nanoelectronic devices.

A Study on the Assembly and Improvement of Electrical Contact between Carbon Nanotube and Microelectrode

Nowadays research on nano-electronic device based on carbon nanotube (CNT) raises much interest among researchers, but in the fabrication process, crucial problems exist in making and improving the electrical contact between CNT and microelectrode. Here pulse gas alignment method, combined with nanomanipulation technology based on atomic force microscope (AFM) if necessary, is proposed for the first time to assemble and make electrical contact between CNT and microelectrode. After the assembly, a processing technique of applying sweeping voltages is performed for producing electrical current induced local Joule heat, which will decompose and remove the sodium dodecyl sulfate (SDS) molecules adsorbed on the CNT and at the interface region, or even have some annealing effect, to reduce the contact resistance between CNT and microelectrode and thus to improve the electrical contact. Experiments of assembly and improvement of electrical contact between multi-wall carbon nanotube and microelectrode are performed to verify the effectiveness of the proposed methods

Manipulation of DNA origami nanotubes in liquid using a programmable tapping mode AFM

Deoxyribonucleic acid (DNA) origami [1] is expected to be a nanoscale functional block for Nano Electro Mechanical Systems (NEMS). It can be assembled on a substrate containing other MEMS components to realize a NEMS device in which nanostructures play an important role. We recently demonstrated a tapping mode atomic force microscopy (AFM) process that can manipulate DNA origami structures in liquid to desired positions with controlled orientations, which is a novel process that will eventually allow the constructions of complex nanostructures on substrate surfaces. The manipulation of DNA origami nanotubes with 6 nm in diameter and 400 nm in length placed on a mica substrate was executed by tapping mode AFM with 0-10 nm amplitude. The acting vertical force from the AFM tip to a DNA origami nanotube was calculated to be 25 - 30 nN numerically by using Simulink software (MathWorks). Experimental results shown that ~80% samples can be successfully manipulated if the tapping mode AFM tip amplitude is 3-4 nm.