Department of Electrical Engineering

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The paper presents the design of discrete-time chatter free sliding mode control for the two-time-scale full system using the slow subsystem. It has been shown that a sliding mode control designed for the slow subsystem gives similar performance for the full system. Also, the obtained state feedback based control is converted into output feedback based control using fast output sampling approach. The state computation method presented here can avoid ill-conditions in dealing with full two-time-scale system. The method is successfully illustrated by numerical example which is reported in literature. © 2008 IEEE.

World University root node

IECON Proceedings (Industrial Electronics Conference)

Discrete-time sliding mode control for two-time-scale systems

The field emission of a carbon nanotube (CNT) pillar array has been improved significantly by plasma treatment in a mixture of hydrogen and nitrogen gases. The plasma treatment for 30 s on a pillar array decreased the turn-on electric field from 0.48 to 0.37 Vμm and increased the field enhancement factor from 6200 to 6900. The emission current density increased by a factor of ≈40. We report in this letter the technique of generating nanotips on CNT pillars with an enormous potential to become a tool for the control and manipulation of CNTs and nanostructures. © 2008 American Institute of Physics.

Fulltext

Applied Physics Letters

Nanotip formation on a carbon nanotube pillar array for field emission application

A technique is demonstrated to detect DNA hybridization at low concentrations, based on Surface-Enhanced Raman Scattering (SERS) using silicon nanostructures coated with gold-silver as substrate. Standard silicon process technologies were employed to fabricate the SERS substrates featuring nanogaps with a characteristic distance of 15 ± 10 nm. Target DNA was hybridized with cysteine-modified Peptide Nucleic Acids (PNA), which was previously fixed into the nanogaps as the capture sites. After hybridization, the introduced phosphate groups from the backbone of the target DNA showed strong affinity to an inorganic linker, Zr4+, so that resulting in the assembly substrate-PNA-DNA-Zr. Since PNA does not possess phosphate groups, the linker is avoided when there is no hybridization from the complimentary DNA. Subsequently, the assembly of substrate-PNA-DNA-Zr was incubated with a Raman label, Rhodamine B (RB). The carboxylic acid group in RB reacted with the linker Zr4+ allowing this Raman Label to be attached to the assembly substrate-PNA-DNA-Zr. The Raman peaks corresponding to RB were selected to detect the target DNA, with a detection limit of 1 × 10-12 M. © 2008 Elsevier B.V. All rights reserved.

Biosensors and Bioelectronics

DNA detection using nanostructured SERS substrates with Rhodamine B as Raman label

To provide a comprehensive understanding of the field effect in silicon nanowire (SiNW) sensors, we take a systematic approach to fine tune the distance of a charge layer by controlling the hybridization sites of DNA to the SiNW preimmobilized with peptide nucleic acid (PNA) capture probes. Six target DNAs of the same length, but differentiated successively by three bases in the complementary segment, are hybridized to the PNA. Fluorescent images show that the hybridization occurs exclusively on the SiNW surface between the target DNAs and the PNA. However, the field-effect response of the SiNW sensor decreases as the DNA (charge layer) moves away from the SiNW surface. Theoretical analysis shows that the field effect of the SiNW sensor relies primarily on the location of the charge layer. A maximum of 102% change in resistance is estimated based on the shortest distance of the DNA charge layer (4.7 Å) to the SiNW surface. © 2008 American Chemical Society.

Nano Letters

DNA sensing by silicon nanowire: Charge layer distance dependence

A highly sensitive and specific copper ion sensor using single crystalline silicon nanowires (SiNWs) configured as field-effect transistors (FETs) is reported. The surface of SiNWs is functionalized with a His-containing tripeptide which serves as a copper sensitive layer. It is found that the complexation between copper ions and His-containing tripeptides leads to an increase in the SiNW conductance, and the position of His residue in the tripeptide plays an important role for the binding of copper ions. Only Gly-Gly-His-modified SiNWs exhibit selectivity for copper ions in the presence of zinc ions whereas Gly-His-Gly-modified SiNWs do not. Our experimental results demonstrate the potential utility of oligopeptide-modified SiNWs as metal ion sensors. © 2008 Elsevier B.V. All rights reserved.

Electrochemistry Communications

Tripeptide-modified silicon nanowire based field-effect transistors as real-time copper ion sensors

Although CVD-grown nanowires are good for demonstration purposes, getting them into manufacturing calls for the utilization of CMOS fabrication methods. We present fully CMOS-compatible nanowire technology with applications and fabrication challenges. Gate-all-around (GAA) silicon nanowire FETs are demonstrated with excellent gate electrostatic control and near ideal turn-on behavior. The nanowire CMOS inverter logic operates down to VDD = 0.2V and is indicative of the potential of these devices for ultra-low power applications toward the end-of-silicon technology roadmap. Finally, we discuss the challenges specific to an advanced dielectric/electrode scheme in nanowire technology.

Solid State Technology

Fully gate-all-around silicon nanowire CMOS devices

For the end of the roadmap CMOS scaling, the non-classical device architecture, Gate All Around (GAA) FET with nanowire (NW) channel body offers the ultimate electro-static control and thus has the potential to push the gate length to few nanometers. The key challenge for NWs to be widely adopted in CMOS IC industry is that they have to be formed by large scale manufacturing methods and devoid of contamination issues. Top-down methods using lithography and etching suit CMOS applications in general and also provides a well-established CMOS based platform for creating devices for other applications. We have developed such a technology platform for Si NW fabrication with NW diameter down to 3 nm. This paper gives an overview of our technology approach, GAA Transistors, CMOS inverters, logic gates, ring oscillators, nanocrystal embedded SONOS memory devices and an introduction to high Ge content SiGe nanowires. © The Electrochemical Society.

ECS Transactions

Si nanowire CMOS transistors and circuits by top-down technology approach

This paper presents discrete time sliding mode control which uses multirate output feedback and power rate reaching law. The method proposed here uses only output samples and past control input for switching function evaluation and sliding mode control. The discrete time version of power rate reaching law has been obtained and then output samples based algorithm has been developed. It has been shown that it is possible to reduce chattering by suitably chosing the reaching law parameters. It has also been demonstrated that it is possible to avoid chattering completely for special case of controller parameters using only output information.The simulation study carried out on numerical example reveals effectiveness of the proposed algorithm. ©2008 IEEE.

IEEE 10th International Workshop on Variable Structure Systems, VSS'08

Discrete time output feedback sliding mode control algorithm for chattering reduction and elimination

Stability of power system has been and continues to be of major concern in system operation. Power system stabilizers are designed to enhance the damping of power system oscillations in order to extend power transfer limits of system and maintain the reliable operation of the grid. As a supplementary control to provide extra damping for synchronous generators, power system stabilizer (PSS) has been widely used in the electric power industry. Studies have shown that a well-tuned PSS can effectively improve power system dynamic stability. In this report we have used the design of PSS for single machine infinite bus system using multirate output feedback based digital redesign of sliding mode control, a robust controller design technique, to handel parametric uncertainty in power system and designed PSS for single machine infinite bus power system configuration. © 2008 IEEE.

Digital redesign of sliding mode control with application to power system stabilizer

Integral sliding mode(ISM) based composite nonlinear feedback(CNF)tracking controller to track step signal is proposed. The proposed controller combines advantages of CNF controller like quick response without overshoot and robustness of ISM controller. Integral sliding mode is used along with CNF controller to reject disturbances and track nominal trajectory. Actuator saturation effect is considered and the stability of overall system is guaranteed with saturated actuator. Chattering is reduced by use of sigmoid function and non-linear switching gain. Effectiveness of the proposed scheme is demonstrated by simulation results. Copyright © 2007 International Federation of Automatic Control All Rights Reserved.