Calibration and uncertainty estimation of one-dimensional reference grating using a metrological atomic force microscope

A one-dimensional reference grating with nominal pitch of 240 nm was calibrated using a tapping mode metrological AFM. Based on the analysis of the AFM structure and properties, measuring process, and data processing, the average pitch was obtained and its uncertainty was estimated. The expanded uncertainty of average pitch was in the order of sub-nano meter. According to the uncertainty analysis of this calibration, it is shown that the estimation of measuring uncertainty should be done based on the well understanding of the all factors in the measuring instrument and measuring process. Furthermore, the some secondary-order errors neglected in conventional measurement should be considered and estimated in nano measurement

Characteristics of the higher-order resonant cantilever in dynamic atomic force microscopy

In order to improve the performances of dynamic atomic force microscopy (AFM), a higher-order resonant cantilever which is driven at its second order or even higher-order resonant frequency instead of its first order resonant frequency is proposed. Due to the increase in the frequency and quality factor of the higher-order resonant cantilever, the response time, air damping coefficient are reduced and the detecting sensitivity of the cantilever is improved. Meanwhile, because the angular deflection of the cantilever under higher-order resonant vibration is larger than that under the first order resonant vibration, the optical magnification level of the higher-order resonant cantilever is several times larger than that of the first order when the optical lever method is adopted to detect the variation of the cantilever. Theoretical analysis and experimental results show that the scanning method done by a higher-order cantilever is effective and feasible, and the scanning characteristics of dynamic AFM with the higher-order resonant cantilever are promoted obviously compared with that of the AFM operated in the first-order. © 2013 SPIE

High speed scanning for dynamic atomic force microscope based on higher-order resonance of silicon cantilever

On the basis of higher-order resonant characteristics of silicon cantilevers of Atomic Force Microscopes (AFMs), a high speed scanning method for dynamic AFMs based on the higher-order resonant cantilever was put forward, and an AFM working at one-order resonant and higher-order modes was developed. The basic structure and working principle of the higher-order resonant AFM system were introduced and the feasibility of the method by using the higher-order resonant characteristics of cantilever to realize high speed scanning was demonstrated theoretically. With home-built AFM as the investigated object, the main factors influencing the scanning speed of the dynamic AFM were investigated, and the response time of each system module was analyzed and estimated by tests. It is experimentally proven that the settling time of the second-order resonant mode AFM is less than that the first-order resonant mode AFM obviously. Finally, the same area of a grating sample was scanned by the first-order and the second-order mode AFMs respectively and the experimental results demonstrate that the scanning speed of the second-order mode AFM is about 3.3 times faster than that of the first-order resonant mode under the same condition. Theoretical analysis and experimental results prove the feasibility and effectiveness to improve the dynamic AFM scanning speed by using the higher-order resonant cantilever

Dean-flow-coupled elasto-inertial three-dimensional particle focusing under viscoelastic flow in a straight channel with asymmetrical expansion-contraction cavity arrays

In this paper, 3D particle focusing in a straight channel with asymmetrical expansion-contraction cavity arrays (ECCA channel) is achieved by exploiting the dean-flow-coupled elasto-inertial effects. First, the mechanism of particle focusing in both Newtonian and non-Newtonian fluids was introduced. Then particle focusing was demonstrated experimentally in this channel with Newtonian and non- Newtonian fluids using three different sized particles (3.2 μm, 4.8 μm, and 13 μm), respectively. Also, the effects of dean flow (or secondary flow) induced by expansion- contraction cavity arrays were highlighted by comparing the particle distributions in a single straight rectangular channel with that in the ECCA channel. Finally, the influences of flow rates and distances from the inlet on focusing performance in the ECCA channel were studied. The results show that in the ECCA channel particles are focused on the cavity side in Newtonian fluid due to the synthesis effects of inertial and dean-drag force, whereas the particles are focused on the opposite cavity side in non-Newtonian fluid due to the addition of viscoelastic force. Compared with the focusing performance in Newtonian fluid, the particles are more easily and better focused in non-Newtonian fluid. Besides, the Dean flow in visco-elastic fluid in the ECCA channel improves the particle focusing performance compared with that in a straight channel. A further advantage is threedimensional (3D) particle focusing that in non-Newtonian fluid is realized according to the lateral side view of the channel while only two-dimensional (2D) particle focusing can be achieved in Newtonian fluid. Conclusively, this novel Dean-flowcoupled elasto-inertial microfluidic device could offer a continuous, sheathless, and high throughput (>10 000 s-1) 3D focusing performance, which may be valuable in various applications from high speed flow cytometry to cell counting, sorting, and analysis

An integrated dielectrophoresis-active hydrophoretic microchip for continuous particle filtration and separation

Microfluidic manipulation of biological objects from mixture has a significant application in sample preparation and clinical diagnosis. This work presents a dielectrophoresis-active hydrophoretic device for continuous label-free particle separation and filtration. This device comprises interdigitated electrodes and a hydrophoretic channel. According to the difference of lateral positions of polystyrene particles, the device can run at separation or filtration modes by altering the power supply voltages. With an applied voltage of 24 Vp-p, both 3 and 10 μm beads had close lateral positions and were redirected to the same outlet. Under a voltage of 36 Vp-p, beads with the diameters of 3 and 10 μm had different lateral positions and were collected from the different outlets. Separation of 5 and 10 μm particles was achieved to demonstrate the relatively small size difference of the beads. This device has great potential in a range of lab-on-a-chip applications