Jiangbo Zhang

Sensor Referenced Real-Time Videolization of Atomic Force Microscopy for Nanomanipulations

The main problem of atomic force microscopy (AFM)-based nanomanipulation is the lack of real-time visual feedback. Although this problem has been partially solved by virtual reality technology, the faulty display caused by random drift and modeling errors in the virtual reality interface are still limiting the efficiency of the AFM-based nanomanipulation. Random drift aroused from an uncontrolled manipulation environment generates a position error between the manipulation coordinate and the true environment. Modeling errors due to the uncertainties of the nanoenvironment often result in displaying a wrong position of the object. Since there is no feedback to check the validity of the display, the faulty display cannot be detected in real time and leads to a failed manipulation. In this paper, a real-time fault detection and correction (RFDC) method is proposed to solve these problems by using the AFM tip as an end effector as well as a force sensor during manipulation. Based on the interaction force measured from the AFM tip, the validity of the visual feedback is monitored in real time by the developed Kalman filter. Once the faulty display is detected, it can be corrected online through a quick local scan without interrupting manipulation. In this way, the visual feedback keeps consistent with the true environment changes during manipulation, which makes it possible for several operations to finish without an image scan in between. The theoretical study and the implementation of the RFDC method are elaborated. Experiments of manipulating nanomaterials including nanoparticles and nanorods have been carried out to demonstrate its effectiveness and efficiency.

Investigation of human keratinocyte cell adhesion using atomic force microscopy

UNLABELLED Desmosomal junctions are specialized structures critical to cellular adhesion within epithelial tissues. Disassembly of these junctions is seen consequent to the development of autoantibodies directed at specific desmosomal proteins in blistering skin diseases such as pemphigus. However, many details regarding cell junction activity under normal physiological and disease conditions remain to be elucidated. Because of their complex structure, desmosomal junctions are not well suited to existing techniques for high-resolution three-dimensional structure-function analyses. Here, atomic force microscopy (AFM) is used for detailed characterization and visualization of the cell junctions of human epithelial cells. We demonstrate the ability to image the detailed three-dimensional structure of the cell junction at high magnification. In addition, the effect of specific antibody binding to desmosomal components of the cell junction is studied in longitudinal analyses before and after antibody treatment. We show that antibodies directed against desmoglein 3 (a major component of the desmosomal structural unit, and the major target of autoantibodies in patients with pemphigus vulgaris) are associated with changes at the cell surface of the human keratinocytes and alterations within keratinocyte intercellular adhesion structures, supporting the assertion that cell structures and junctions are modified by antibody binding. The present study indicates that the molecular structure of gap junctions can be more completely analyzed and characterized by AFM, offering a new technological approach to facilitate a better understanding of disease mechanisms and potentially monitor therapeutic strategies in blistering skin diseases. FROM THE CLINICAL EDITOR Disassembly of desmosomal junctions is seen in blistering skin diseases such as Pemphigus. This present study demonstrates that the molecular structure of gap junctions can be more completely analyzed and characterized by atomic force microscopy.

Adaptable End Effector for Atomic Force Microscopy Based Nanomanipulation

Nanomanipulation using the atomic force microscope (AFM) has been extensively investigated for many years. But the efficiency and accuracy of AFM-based nanomanipulation are still major issues due to the nonlinearities and uncertainties in nanomanipulation operations. The deformation of the cantilever caused by manipulation force is one of the most major nonlinearities and uncertainties. It causes difficulties in accurately controlling the tip position, and results in missing the position of the object. The softness of the conventional cantilevers also causes the failure of manipulation of sticky nano-objects because the tip can easily slip over the nano-objects. In this paper, an active atomic force microscopy probe is used as an adaptable end effector to solve these problems by actively controlling the cantilevers flexibility or rigidity during nanomanipulation. A control voltage is applied to the piezo layer of the adaptable end effector to exert a reverse bending moment on the cantilever to balance the bending moment caused by the interaction force during manipulation. Thus, the adaptable end effector is controlled to maintain straight shape during manipulation. A detailed model of the adaptable end effector is presented in the paper. Control of the adaptable end effector employing an optimal LQR control law is derived and implemented. The experimental results verify the validity of the model and effectiveness of the controller. The nanomanipulation results also prove the increased efficiency of AFM-based nanomanipulation using the adaptable end effector

Design, Manufacturing, and Testing of Single-Carbon-Nanotube-Based Infrared Sensors

As a 1-D nanostructural material, carbon nanotube (CNT) has attracted lot of attention and has been used to build various nanoelectronic devices due to its unique electronic properties. In this paper, a reliable and efficient nanomanufacturing process was developed for building single-CNT-based nanodevices by depositing the CNTs on the substrate surface and then aligning them to bridge the electrode gap using the atomic force microscopy (AFM) based nanomanipulation. With this technology, single CNT-based IR sensors have been fabricated for investigating CNTs electronic and photonic properties. The fabrication of single-CNT-based IR sensors demonstrated the reliability and efficiency of the nanomanufacturing process. Experimental tests on single-multiwalled-CNT-based IR sensors have shown much larger photocurrent and quantum efficiency than other reported studies. It has also been shown that a high signal to dark current ratio can be accomplished by single-walled-CNT (SWNT) based IR sensors. Moreover, the testing of SWNT-bundle-based IR sensors verified that the performance of CNT bundle/film-based nanoelectronic devices was limited by the mixing of semiconducting CNTs and metallic CNTs, as well as the unstable CNT-CNT junctions in a CNT bundle or network.

Photovoltaic effect in single carbon nanotube-based Schottky diodes

Photovoltaic effects in individual single-walled carbon nanotube (SWCNT) based Schottky diodes were investigated for infrared detection in this paper. Different contact conditions (symmetric and asymmetric CNT-metal contacts) have been studied for optimising the performance of SWCNT-based infrared detector. Experiments demonstrated that the asymmetric structure could improve the photodiode performance by increasing the signal-to-dark current ratio up to two orders of magnitude higher than a symmetric device. With the perfect photodiode I-V characteristic curves, SWCNTs show a strong potential of applications in solar collection, infrared sensing and nanogenerators.

Automated Nanomanufacturing System to Assemble Carbon Nanotube Based Devices

In this paper we report the design and implementation of a novel automated manufacturing system for carbon nanotube (CNT)-based nanodevices, which integrates a new dielectrophoretic (DEP) microchamber into a robotic-based deposition workstation. The microchamber has been fabricated to separate and select CNTs with the desired electronic property by using DEP force. Moreover, a series of tools for mass-producing consistent nanodevices has been developed with the CNT deposition workstation, such as computer-controllable micromanipulators and a micro-active nozzle. Detailed experimental studies of the CNT separation and deposition processes have been performed on both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Preliminary results show that CNTs could be manipulated to multiple pairs of microelectrodes repeatedly. Consistent I—V characteristics and CNT formations of the fabricated devices were obtained. The yield of semi-conducting CNTs was also increased by using our system. Therefore, by using the proposed CNT separation and deposition system, CNT-based nanodevices with specific and consistent electronic properties can be manufactured automatically and effectively.

Modeling and Control of Active End Effector for the AFM Based Nano Robotic Manipulators

Nanomanipulation using Atomic Force Microscope (AFM) has been extensively investigated for many years. However, control of tip position during nanomanipulation is still a major issue because of the deformation of the cantilever caused by manipulation force. The softness of the conventional cantilevers also cause the failure of the manipulation of relatively large and sticky nano-object because the tip can easily slip over the nano-object. In this paper, an active atomic force microscopy probe is used to solve these problems by changing the cantilever’s flexibility or rigidity through different control strategies in imaging and manipulation modes respectively. During imaging mode, the active probe is controlled to bend up with respect to the interaction force between the tip and samples, thus making the tip response faster and increase the imaging speed. During manipulation mode, the active probe is controlled to bend down with respect to the interaction force between tip and the samples; thus increasing its nominal rigidity to avoid tip slipping over object. A detailed model of the active probe is presented in this paper and the controller designed based on the proposed active probe model is also implemented on the augmented reality system, which is an AFM based nanomanipulation system with both real-time visual and haptic feedback. The simulation results for the control strategies and the preliminary experimental results for the AFM based nanmomanipulation verified the validity of the model and effectiveness of the controller.

Single carbon nanotube based photodiodes for infrared detection

The photobehavior of carbon nanotubes (CNTs) has attracted great attention because of their unique cylinder structure and outstanding electrical properties. Much experimental progress toward nanotubes based photodetector has been reported. But it is still unclear whether the photoinduced conductivity change is caused by heating effect or quantum effect for the reported results. Moreover, the sensitivity of the CNT based IR detector needs to be further improved for real applications. In this paper, a single carbon nanotube based photodiode for infrared (IR) detection is constructed by assembling a single CNT to form connections with a pair of electrodes. By forming Schottky contact with an electrode, a semiconductive CNT is assembled into a Schottky diode. The photogenerated electron-hole pairs within the Schottky barrier are separated by an external electric field or the built-in field, producing a photocurrent. Since a semiconductive CNT normally forms Schottky contacts with both electrodes, the photocurrents generated by the two reversely connected Schottky diodes will cancel each other. Experimental results show that, at zero bias, the photocurrent varied from positive to negative as the IR spot center was moved from one electrode to another one. This proved that the photocurrent is caused by the photovoltaic effect in stead of the heating effect. To optimize the performance of the detector, a heterogeneous electrodes structure is designed to maximize the difference between the photocurrents of the two Schottky barriers. Different contact metals are selected such as an Ohmic contact is formed at one electrode and a Schottky barrier is formaed at another electrode. Experimental results show that the signal to dark current ratio of a heterogeneous detector is thousand times higher than the ratio of a homogeneous detector.

Atomic force yields a master nanomanipulator

A nanorobotic system enables researchers to better handle nano-objects.To facilitate the nanomanipulation and improve efficiency, an AFM-based nanorobotic system was developed. The objective of this system is to provide operator real-time visual and force feed-back during manipulation.

Single carbon nanotube based infrared sensor

As a one-dimensional nanostructural material, carbon nanotube (CNT) has been used to build different nanoelectronic devices due to its unique electrical properties. In this paper, the infrared (IR) responses of individual single-wall carbon nanotube (SWNT) and SWNT film are studied. A single-wall carbon nanotube is assembled onto a pair of electrodes to form Schottky contacts. The photongenerated electron-hole pairs within the carbon nanotube are seperated by an external electric field between the two electrodes. The separated carriers contribute to the current flowing through the carbon nanotube and form photocurrent. By monitoring the photocurrent, the incident infrared can be detected and quantitated. The single-wall carbon nanotube based infrared sensor is designed and a series of efficient and reliable fabrication and assembly processes are developed for the sensor fabrication. With an atomic force microscope based nanomanipulation system as the assembly tool, a single carbon nanotube can be easily assembled onto the electrodes. Since the assembly process is controllable and reliable, it becomes possible to fabricate an individual carbon nanotubes based infrared sensor array, which was difficult to fabricate with other fabrication method. The photocurrent responses of individual SWNT IR sensor and SWNT film IR sensor are measured and analyzed. Experimental results show the good sensitivity of SWNTs to the infrared light. Our results shows a three orders higher photocurrent than the previous reported results. It has also been shown that an individual SWNT IR sensor is more sensitive than a SWNT film IR sensor.