DNP-NMR of surface hydrogen on silicon microparticles

Dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR) offers a promising route to studying local atomic environments at the surface of both crystalline and amorphous materials. We take advantage of unpaired electrons due to defects close to the surface of the silicon microparticles to hyperpolarize adjacent 1H nuclei. At 3.3 T and 4.2 K, we observe the presence of two proton peaks, each with a linewidth on the order of 5 kHz. Echo experiments indicate a homogeneous linewidth of 150 - 300 Hz for both peaks, indicative of a sparse distribution of protons in both environments. The high frequency peak at 10 ppm lies within the typical chemical shift range for proton NMR, and was found to be relatively stable over repeated measurements. The low frequency peak was found to vary in position between −19 and −37 ppm, well outside the range of typical proton NMR shifts, and indicative of a high-degree of chemical shielding. The low frequency peak was also found to vary significantly in intensity across different experimental runs, suggesting a weakly-bound species. These results suggest that the hydrogen is located in two distinct microscopic environments on the surface of these Si particles

The modeling and experiments of a PVDF mirco-force sensor

This paper aims at designing a kind of advanced micro-force sensor that can measure force in the range of submicro-Newton (μN). To accurately measure the micro interactive force (For example, adhesion, surface tension, friction, and assembly force) acting on micro devices during micromanipulation, the polyvinylidene fluoride (PVDF) is fabricated highly sensitive force sensors. This paper illustrates the modeling method of a PVDF sensor. The transformation between the micro interactive force and the output of the sensor is described. To calibrate the transformation, the model of the PVDF cantilever beam that shows the relationship between the interactive force and the deflection of the sensor probe tip is built first. Then, by given deflection, the interactive force can be calculated with the model. Finally, the transformation can be calibrated. Experiment results verify the effectiveness and accuracy of the transformation model, and the sub-μN sensitivity of the sensor. This micro force sensing technology will solve an important problem that restricts the development of micromanipulation and batch assembly of micro devices. © 2008 IEEE.Link_to_subscribed_fulltex

The design and development of a mirco-force sensing device

An advancing micro-force sensing device that can measure force in the range of sub-micro-Newton (μN) is designed and realized in this paper. To accurately measure the micro interactive force (For example, adhesion, surface tension, friction, and assembly force) between the tool and the object during micromanipulation, the polyvinylidene fluoride (PVDF) is used to fabricate a highly sensitive force sensing device. In this paper, the relationship model of the interactive force and the charge generated on the PVDF surface, the design of the signal processing method of PVDF output are illustrated. The transformation model between the micro interactive force and the signal of the sensing device is built. A new calibration method of the sensing device is presented. Experiment results verify the accuracy of the sensing device's transformation model, the effectiveness of the signal processing method. The results also show the sub-μN sensitivity of the sensing device. The micro-force sensing technology developed in this paper will promote the efficiency, and decrease the cost of micromanipulation and microassembly. © 2008 IEEE.Link_to_subscribed_fulltex

Research on signal processing method and calibration method of sub-μN micro-force sensor

To develop a novel micro-force sensor that can reliably measure force in the range of sub-micro-Newton (μN), the signal processing method and a novel indirect calibration method are designed and realized in this paper. The relationship model between the micro-force acting on the sensor's probe tip and the deflection of the probe tip is built up. With the above model and the standard deflection input, the novel indirect calibration method completes calibrating the relationship model between the micro-force and the output voltage of the sensor and solves the problem that standard micro-force used in calibration is difficult to find. Experiment results show the signal processing method and the new indirect calibration method are effective and correct. The signal processing method and the indirect calibration method are indispensable to developing the sub-μN micro-force sensor and providing a feasible and versatile solution in micro contact-force sensing and feedback control for micro/nano assembly and manipulation.Link_to_subscribed_fulltex

Research on sub-μN micro-force sensor based on PVDF

A novel micro-force sensor that can reliably measure force in the range of sub-micro-Newton (μN) and its calibration method are designed in this paper. Reliable and sensitive micro-force sensing and corresponding control method is quite important to improve the efficiency of microassembly. At present, sub-μN micro-force in microassembly is not able to be reliably measured by the existing force sensors. In this paper, the polyvinylidene fluoride (PVDF) is used to fabricate a highly sensitive force sensor. The relationship model of micro-force and the sensor's output voltage is built up, and corresponding signal processing circuit is designed and realized. Furthermore, the relationship model is calibrated. Experiment results show the sub-μN sensitivity of the sensor. The results also verify the accuracy of the sensor's relationship model, the effectiveness of the signal processing method and calibration method. The micro-force sensor developed in this paper provides a feasible and versatile solution in micro-force sensing and feedback control for micro/nano assembly and manipulation, and will promote the technology of automating the micro/nano assembly and manipulation.Link_to_subscribed_fulltex

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 will study this problem in detail, some experimental results will be also presented. ©2006 IEEE.Link_to_subscribed_fulltex