This letter presents the application of electrostatic pull-in instability to study the size-dependent effective Young's Modulus Ẽ ͑ϳ170-70 GPa͒ of ͓110͔ silicon nanocantilevers ͑thickness ϳ1019-40 nm͒. The presented approach shows substantial advantages over the previous methods used for characterization of nanoelectromechanical systems behaviors. The Ẽ is retrieved from the pull-in voltage of the structure via the electromechanical coupled equation, with a typical error of Յ12%, much less than previous work in the field. Measurement results show a strong size-dependence of Ẽ . The approach is simple and reproducible for various dimensions and can be extended to the characterization of nanobeams and nanowires.

In this contribution, a capillary electrophoresis microdevice with an integrated on-chip contactless four-electrode conductivity detector is presented. A 6-cm-long, 70-microm-wide, and 20-microm-deep channel was etched in a glass substrate that was bonded to a second glass substrate in order to form a sealed channel. Four contactless electrodes (metal electrodes covered by 30-nm silicon carbide) were deposited and patterned on the second glass substrate for on-chip conductivity detection. Contactless conductivity detection was performed in either a two- or a four-electrode configuration. Experimental results confirmed the improved characteristics of the four-electrode configuration over the classical two-electrode detection setup. The four-electrode configuration allows for sensitive detection for varying carrier-electrolyte background conductivity without the need for adjustment of the measurement frequency. Reproducible electrophoretic separations of three inorganic cations (K+, Na+, Li+) and six organic acids are presented. Detection as low as 5 microM for potassium was demonstrated.

The size-dependent elastic behavior of silicon nanocantilevers and nanowires, specifically the effective Young's modulus, has been determined by experimental measurements and theoretical investigations. The size dependence becomes more significant as the devices scale down from micro-to nano-dimensions, which has mainly been attributed to surface effects. However, discrepancies between experimental measurements and computational investigations show that there could be other influences besides surface effects. In this paper, we try to determine to what extent the surface effects, such as surface stress, surface elasticity, surface contamination and native oxide layers, influence the effective Young's modulus of silicon nanocantilevers. For this purpose, silicon cantilevers were fabricated in the top device layer of silicon on insulator (SOI) wafers, which were thinned down to 14 nm. The effective Young's modulus was extracted with the electrostatic pull-in instability method, recently developed by the authors (H Sadeghian et al 2009 Appl. Phys. Lett. 94 221903). In this work, the drop in the effective Young's modulus was measured to be significant at around 150 nm thick cantilevers. The comparison between theoretical models and experimental measurements demonstrates that, although the surface effects influence the effective Young's modulus of silicon to some extent, they alone are insufficient to explain why the effective Young's modulus decreases prematurely. It was observed that the fabrication-induced defects abruptly increased when the device layer was thinned to below 100 nm. These defects became visible as pinholes during HF-etching. It is speculated that they could be the origin of the reduced effective Young's modulus experimentally observed in ultra-thin silicon cantilevers.

In this work, we present a technology for fabrication of nanochannels created in glass with which bio-analysis can be performed in combination with fluorescence microscopy. The technology is based on a glass-to-glass anodic bonding process. In the bonding process, an intermediate layer (thin insulating film) is deposited on one of the two glass wafers. The channel is then defined, with one or two photo-patterning steps, in the intermediate layer. In our approach, a 33 nm thick amorphous silicon layer deposited by low-pressure chemical vapor deposition (LPCVD) was used as an intermediate layer. The depth of the channel is defined during the etching of this layer.

In this paper, we demonstrate for the first time that insulative dielectrophoresis can induce size-dependent trajectories of DNA macromolecules. We experimentally use ͑48.5 kbp͒ and T4GT7 ͑165.6 kbp͒ DNA molecules flowing continuously around a sharp corner inside fluidic channels with a depth of 0.4 m. Numerical simulation of the electrokinetic force distribution inside the channels is in qualitative agreement with our experimentally observed trajectories. We discuss a possible physical mechanism for the DNA polarization and dielectrophoresis inside confining channels, based on the observed dielectrophoresis responses due to different DNA sizes and various electric fields applied between the inlet and the outlet. The proposed physical mechanism indicates that further extensive investigations, both theoretically and experimentally, would be very useful to better elucidate the forces involved at DNA dielectrophoresis. When applied for size-based sorting of DNA molecules, our sorting method offers two major advantages compared to earlier attempts with insulative dielectrophoresis: Its continuous operation allows for highthroughput analysis, and it only requires electric field strengths as low as ϳ10 V / cm.