Niandong Jiao

Fabrication of SWCNT-Graphene Field-Effect Transistors

Graphene and single-walled carbon nanotube (SWCNT) have been widely studied because of their extraordinary electrical, thermal, mechanical, and optical properties. This paper describes a novel and flexible method to fabricate all-carbon field-effect transistors (FETs). The fabrication process begins with assembling graphene grown by chemical vapor deposition (CVD) on a silicon chip with SiO2 as the dielectric layer and n-doped Si substrate as the gate. Next, an atomic force microscopy (AFM)-based mechanical cutting method is utilized to cut the graphene into interdigitated electrodes with nanogaps, which serve as the source and drain. Lastly, SWCNTs are assembled on the graphene interdigitated electrodes by dielectrophoresis to form the conductive channel. The electrical properties of the thus-fabricated SWCNT-graphene FETs are investigated and their FET behavior is confirmed. The current method effectively integrates SWCNTs and graphene in nanoelectronic devices, and presents a new method to build all-carbon electronic devices.

Nanochannel system fabricated by MEMS microfabrication and atomic force microscopy

A silicon nanochannel system with integrated transverse electrodes was designed and fabricated by combining micro-electro-mechanical systems (MEMS) micromachining and atomic force microscopy (AFM)-based nanolithography. The fabrication process began with the patterning of microscale reservoirs and electrodes on an oxidised silicon chip using conventional MEMS techniques. A nanochannel, approximately 30 [micro sign]m long with a small semi-circular cross-sectional area of 20 nm × 200 nm, was then mechanically machined on the oxide surface between the micro reservoirs by applying AFM nanolithography with an all-diamond probe. Anodic bonding was used to seal off the nanochannel with a matching Pyrex cover. Continuous flow in the nanochannel was verified by pressurising a solution of fluorescein isothiocyanate in ethanol through the nanochannel in a vacuum chamber. It was further demonstrated by translocating negatively charged nanobeads (diameter approximately 20 nm) through the nanochannel by using an external DC electric field. The passage of the nanobeads caused a sharp increase in the transverse electrical conductivity of the nanochannel.

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.

An asymmetric PI hysteresis model for piezoceramics in nanoscale AFM imaging

A modified Prandtl-Ishlinskii (PI) model, referred to as an asymmetric PI model, is implemented to reduce the displacement error between the model and the actual trajectory of a piezoceramic actuator used for AFM-based nanoscale imaging. The fact that the standard PI model is symmetric, while the actual hysteresis loop of a piezoceramic actuator is asymmetric, assures scanning errors if the standard PI operator is used. In order to improve the accuracy of the model, instead of using the same slope values in the entire PI model, different slope values to describe the forward loop (voltage increase) and the backward loop (voltage decrease) is proposed. The accuracy of the asymmetric PI model is validated on a custom-built AFM by comparing the experimental results derived from it with the results for the standard PI model.

Automatic Path Tracking and Target Manipulation of a Magnetic Microrobot

Recently, wireless controlled microrobots have been studied because of their great development prospects in the biomedical field. Electromagnetic microrobots have the advantages of control agility and good precision, and thus, have received much attention. Most of the control methods for controlling a magnetic microrobot use manual operation. Compared to the manual method, the automatic method will increase the accuracy and stability of locomotion and manipulation of microrobots. In this paper, we propose an electromagnetic manipulation system for automatically controlling the locomotion and manipulation of microrobots. The microrobot can be automatically controlled to track various paths by using visual feedback with an expert control algorithm. A positioning accuracy test determined that the position error ranges from 92 to 293 μm, which is less than the body size (600 μm) of the microrobot. The velocity of the microrobot is nearly proportional to the applied current in the coils, and can reach 5 mm/s. As a micromanipulation tool, the microrobot is used to manipulate microspheres and microgears with the automatic control method. The results verify that the microrobot can drag, place, and drive the microstructures automatically with high precision. The microrobot is expected to be a delicate micromachine that could play its role in microfluidics and blood vessels, where conventional instruments are hard to reach.

Controlled regular locomotion of algae cell microrobots

Algae cells can be considered as microrobots from the perspective of engineering. These organisms not only have a strong reproductive ability but can also sense the environment, harvest energy from the surroundings, and swim very efficiently, accommodating all these functions in a body of size on the order of dozens of micrometers. An interesting topic with respect to random swimming motions of algae cells in a liquid is how to precisely control them as microrobots such that they swim according to manually set routes. This study developed an ingenious method to steer swimming cells based on the phototaxis. The method used a varying light signal to direct the motion of the cells. The swimming trajectory, speed, and force of algae cells were analyzed in detail. Then the algae cell could be controlled to swim back and forth, and traverse a crossroad as a microrobot obeying specific traffic rules. Furthermore, their motions along arbitrarily set trajectories such as zigzag, and triangle were realized successfully under optical control. Robotize algae cells can be used to precisely transport and deliver cargo such as drug particles in microfluidic chip for biomedical treatment and pharmacodynamic analysis. The study findings are expected to bring significant breakthrough in biological drives and new biomedical applications.

Nanoscale welding by AFM tip induced electric field

The most difficult challenges in fabricating SWCNT-based nanosystems or nanodevices have proven to be the assembly and anchoring of SWCNTs to form a stable physical and electric contact between SWCNTs and the electrodes. For example, for SWCNT-based nanosensors or field effect transistors (FETs), the need to fix the SWCNT between electrodes is extremely important, i.e., it affects the electronic transport properties at the connection point. Currently, researchers usually focus on the assembly between SWCNTs and the electrodes by using dielectrophoresis (DEP), direct growth, or atomic force microscopy (AFM). In this paper, we present a new method to realize nanoscale welding by using an AFM tip coated with conductive materials. This method is very useful in welding the SWCNTs on the micro electrodes after the manipulation of the SWCNTs in between the microelectrodes by AFM-based or DEP-based manipulation. In our experiments, we first assembled individual SWCNTs or bundles of SWCNTs between two electrodes using DEP force. Then, SWCNTs are welded on the surface of the electrodes when a bias impulse voltage is exerted between the AFM tip and sample, which produces an electric field. The experimental results have demonstrated that SWCNTs can effectively be welded on the surface of the electrodes.

Atomic force microscope deposition method for nano-lines

Nano-devices have many potential applications. However, how to connect the nano-components is a problem during fabrication of nano-devices. This paper introduces a nano-line deposition method with atomic force microscope(AFM). This method is expected to be used as a nano-welding technique, which can improve the physical and electrical connections between the various components of nano-devices. With this method, nano-lines can be deposited continuously, rather than depositing a row of nano-dots to form a nano-line. The method comprises two features. One is current-induced deposition rather than voltage. Experiments show that current-induced method can fabricate more continuous and smoother nano-lines than voltage-induced method.The other is a simple tip-substrate distance control means. AFM deposition is based on field emission theory, so tip-substrate distance is an important factor for field emission. A simple tip-substrate distance control means is introduced in this paper, which makes the deposition process easier.

A nanochannel system fabricated by MEMS microfabrication and atomic force microscopy

A silicon nanochannel system with integrated transverse electrodes was designed and fabricated by combining MEMS microfabrication and AFM nanolithography. The fabrication process began with the patterning of microscale reservoirs and electrodes on an oxidized silicon chip using conventional MEMS techniques. A nanochannel, approximately 30µm long with a small semi-circular cross-sectional area of 20nm by 200nm, was then mechanically machined on the oxide surface between the micro reservoirs by applying AFM nanolithography with an all-diamond probe. Anodic bonding was used to seal off the nanochannel with a matching Pyrex cover. Continuous flow in the nanochannel was verified by pressurizing a solution of fluorescein isothiocyanate (FITC) in ethanol through the channel in a vacuum chamber. It was further demonstrated by driving carboxyl-modified FluoSpheres® (diameter ∼ 20 nm) through the nanochannel with an external electric field. Presence of the FluoSpheres® in the channel was indicated by a sharp increase in current between the transverse electrodes.

Nanochannels on silicon oxide surface fabricated by atomic force microscopy

An experimental study was conducted to investigate the feasibility of fabricating relatively long nanochannels on hard and brittle silicon dioxide surface using atomic force microscopy (AFM) based lithography. Specifically, the relationship between the applied AFM tip force and the resultant nanochannel depth was measured and analyzed. The nanochannels were fabricated by two different AFM lithographic methods. In the first method, a constant tip force was applied and the maximum channel depth achievable was about 15nm. In the second method, a gradually increasing tip force was used and a much larger channel depth of 28nm was achieved. The average depth along the entire channel length was about 15nm. Based on the current results, it can be concluded that AFM based lithography is a viable nanomachining technique for realizing long nanochannels on silicon based substrates.