Ultrashort Voltage Pulses Research Articles

Theoretical and experimental investigation on electrochemical micromachining

Based on the principle of electrochemical reactions, the mechanism of electrochemical micromachining with ultra short voltage pulses was investigated and the theoretical model was developed. The effects of electrode gap and pulse parameters on the result of electrochemical micromachining were discussed. Using the self-developed experimental system, microtool-electrode and the complex microstructures were sequentially machined. Upon the application of ultrashort voltage pulses, the troughs with 20 μm in width were fabricated by φ 10 μm tool electrode produced.

Large capacitance in the nanosecond-scale transient response of quantum point contacts

The transient electrical response of split-gate quantum point contacts (QPCs) is investigated using ultrashort voltage pulses with rise times as small as 2ns. Our measurements reveal a large (∼1nF) parallel capacitance under conditions where the QPC is formed. The capacitance is independent of the QPC gate geometry, and the amplitude and rise time of the applied transient pulse. Some speculations on the source of this capacitance are offered.

Zap [extreme voltage for fighting diseases

Bioelectrics is an emerging field of research that combines the disciplines of high voltage engineering and cell biology to gain a better understanding of the effects of powerful, ultrashort voltage pulses on living tissue. Bioelectrics depends on advanced pulsed power technology, which is the ability to switch on and off thousands of amperes of current and just as many volts in mere nanoseconds. The most promising and practical result so far has been the recent discovery that certain pulsed electric fields can wipe out skin tumors in mice. Although many years will pass before it will even be worth testing on humans, bioelectrics offers a totally new therapeutic avenue - one that could lead to a therapy free of the debilitating side effects of chemotherapy drugs and tissue damage of radiation

Etch Trends in Electrochemical Machining with Ultrashort Voltage Pulses

We present analytical and computational models used to investigate the dependence of etch resolution on pulse duration, tool radius, and etched feature aspect ratio in electrochemical machining with ultrashort voltage pulses. Our results predict that, for the high aspect ratio system in which the effect of trench top and bottom edges can be ignored, the increase of etch resolution with pulse length is a strong function of tool radius, while there is a significant dependence on etch depth for the low aspect ratio system in which the edge effects become important. A detailed analysis of the etch trends is presented.

Computational Analysis of Intratool Interactions in Electrochemical Micromachining with Multitip Tool Electrodes

We have investigated the use of complex tool electrodes (templates) in electrochemical machining with ultrashort voltage pulses using a three-dimensional computational model. Through a systematic study of profile evolution varying pulse durations and separations between features, we have quantified the degree to which the performance of these templates is decreased relative to that of a simple tool electrode. We have found both the discrepancies and the separation at which the maxima occur are reduced with decreasing pulse duration. We explain these discrepancies through examining for the first time the effects of intratool electrode interactions on the overpotential and dissolution current at the substrate electrode. These studies have revealed that overpotential is largely additive among the individual components of a tool electrode above a critical separation between components, while the exponential nature of the dissolution current with respect to overpotential leads to increased dissolution when using a complex tool electrode.

A study of the characteristics for electrochemical micromachining with ultrashort voltage pulses

Electrochemical micromachining (EMM) has traditionally been used in highly specialized fields, such as those of the aerospace and defense industries. It is now increasingly being applied in other industries, where parts with difficult-to-cut material, complex geometry and tribology, and devices of microscopic-scale are required. EMM, which is not normally considered as a precision process, is presented in this paper. The application of voltage pulses between a tool electrode and a workpiece in an electrochemical environment allows the three-dimensional machining of conducting materials with micrometer precision. In this paper, tool electrodes (5 μm in diameter, 1 mm in length) are developed by EMM and microholes are manufactured using these tool electrodes. Microholes with a size of below 50 μm in diameter can be accurately achieved by using ultrashort voltage pulses (1–5 μs).

Electrochemical machining with ultrashort voltage pulses: modelling of charging dynamicsand feature profile evolution

A two-dimensional computational model is developed to describe electrochemicalnanostructuring of conducting materials with ultrashort voltage pulses. The model consistsof (1) a transient charging simulation to describe the evolution of the overpotentials at thetool and workpiece surfaces and the resulting dissolution currents and (2) a feature profileevolution tool which uses the level set method to describe either vertical or lateral etchingof the workpiece. Results presented include transient currents at different separationsbetween tool and workpiece, evolution of overpotentials and dissolution currents as afunction of position along the workpiece, and etch profiles as a function of pulse duration.

Two-dimensional computational model for electrochemical micromachining with ultrashort voltage pulses

We have developed a computational model to simulate electrochemical micromachining of conducting substrates with ultrashort voltage pulses. This theoretical approach integrates (i) a circuit model to describe charging and discharging of electrochemical double layers and electric field variation in electrolytes and (ii) the level set method to simulate feature profile evolution during electrochemical etching. Our simulation results of transient current responses and etch profile evolution are qualitatively in agreement with experimental observations. From our simulations, we find that the resolution of etched features is a strong function of the substrate double layer capacity which may be controlled by electrolyte concentration and pulse duration.

Electrochemical micromachining with ultrashort voltage pulses–a versatile method with lithographical precision

Upon the application of ultrashort voltage pulses electrochemical reactions can be spatially confined with nanometer accuracy, which allows for high precision machining of electrochemical active materials. As an example, electrochemical machining parameters for the micromachining of Ni are derived from conventional electrochemical cyclic voltammetry. Depending on the average potentials of tool and workpiece, overall corrosion of the workpiece and the location of the counter reaction of workpiece dissolution can be controlled. The pulse duration provides a direct control for setting the machining accuracy. Machining precisions below 100 nm were achieved by the application of 500 ps voltage pulses.

Electrochemistry and microsystems

Electrochemistry takes a key position in products and manufacturing processes of microtechnology, which has established a multi-billion dollar market with applications in information, entertainment, medical, automotive, telecom and many other technologies. In combination with microlithographic pattern generation electrochemical deposition processes are applied in manufacturing CDs and DVDs, nozzle plates for ink jet printers, read–write heads for hard magnetic disks and solder bumps for flip-chip technology. Three-dimensional microstructures with extremely high precision and aspect ratio are manufactured by means of LIGA technology, which combines deep lithography, electroforming and moulding process steps. Field assisted etching processes with ultra-short voltage pulses, anodization of silicon and field assisted ion exchange in glass have been successfully used for generating microstructures. Meanwhile, there are a huge number of microdevices, which utilize electrochemical phenomena. ISFETs and ion sensitive electrodes are standard components in the field of microsensors, microfuel cells will become high-performance power supply systems for mobile IT and entertainment products. In communication technology electrophoresis-based on electronic ink displays will become more and more important products. The most challenging development is dealing with so-called labs-on-a-chip which utilize electrochemical phenomena like electrophoresis, isoelectric focussing and electroosmosis to create a novel platform for ultra-miniaturized analytics in life sciences, medical diagnosis, environmental technologies and many other areas of modern development.

Single-step electrochemical machining of complex nanostructures with ultrashort voltage pulses

We show that complex patterns including three-dimensional structures, lines, curved features, and arrays can be machined in substrates in single-step processing without the need for rastering. High-aspect-ratio nanometer accurate features were machined in nickel using ultrashort voltage pulse electrochemical machining. Experiments were conducted with two different tool shapes. The first was a combination of rectangles, squares, and a half circle; the second was a 2×2 array. The effect of pulse duration and electrolyte concentration on feature resolution was studied. Structures with 90 nm widths were made by applying 2 ns voltage pulses.

Electrochemical Micromachining of Stainless Steel by Ultrashort Voltage Pulses

Abstract Application of ultrashort voltage pulses to a tiny tool electrode under suitable electrochemical conditions enables precise three-dimensional machining of stainless steel. In order to reach submicrometer precision and high processing speed, the formation of a passive layer on the workpiece surface during the machining process has to be prevented by proper choice of the electrolyte. Mixtures of concentrated hydrofluoric and hydrochloric acid are well suited in this respect and allow the automated machining of complicated three-dimensional microelements. The dependence of the machining precision on pulse duration and pulse amplitude was investigated in detail.

Simulations of electroporation dynamics and shape deformations in biological cells subjected to high voltage pulses

The temporal dynamics of electroporation of cells subjected to ultrashort voltage pulses are studied based on a coupled scheme involving the Laplace, Nernst-Planck, and Smoluchowski equations. It is shown that a finite time delay exists in pore formation, and leads to a transient overshoot of the transmembrane potential V/sub mem/ beyond 1.0 V. Pore resealing is shown to consist of an initial fast process, a 10/sup -4/ second delay, followed by a much slower closing at a time constant of about 10/sup -1/ s. This establishes a time window for effective killing by a second pulse. The results are amply supported by our experimental data for E.-coli cells, and the time constant also matches experiments. An electromechanical analysis for analyzing cell shape changes is also presented. Our calculations show that at large fields, the spherical cell geometry can be significantly modified, and even ellipsoidal forms would be inappropriate to describe the deformation. Values of surface forces obtained are in very good agreement with the 1-10-nN/m range reported for membrane rupture. It is also demonstrated that, at least for the smaller electric fields, both the cellular surface area and volume change roughly in a quadratic manner with electric field. Finally, it is shown that the bending moments are generally quite small and can be neglected for a simpler analysis.

Ultrashort pulsed barrier discharges and applications

Abstract Atmospheric pressure nonequilibrium plasmas have made a recent remarkable progress in formation techniques including atmospheric pressure glow discharge (APG), dielectric barrier discharge (DBD), corona discharge, surface discharge, ultrashort pulsed discharge, etc., and are expanding their applications into the field of energy and environment as well as material conversion processes. This paper will especially focus on a large improvement of DBD by combining it with squared ultrashort high voltage pulses and various applications.

Electrochemical machining of stainless steel microelements with ultrashort voltage pulses

An electrochemical pulse technique enables the fabrication of three-dimensional microelements from stainless steel. The method is based on the application of ultrashort (nanosecond) voltage pulses, whereupon electrochemical reactions are locally confined with submicrometer precision. Employing properly shaped tool electrodes enables the machining of freestanding cantilevers or microstructures directly to a metal sheet. Due to gentle removal of the material, the grain structure of the material is revealed without any chemical or mechanical modifications. This is demonstrated by measuring the vibration frequency of a cantilever, and agrees well with the value derived from the bulk material properties.

Self-consistent simulations of electroporation dynamics in biological cells subjected to ultrashort electrical pulses.

The temporal dynamics of electroporation of cells subjected to ultrashort voltage pulses are studied based on a coupled scheme involving the Laplace, Nernst-Plank, and Smoluchowski equations. A pore radius dependent energy barrier for ionic transport, accounts for cellular variations. It is shown that a finite time delay exists in pore formation, and leads to a transient overshoot of the transmembrane potential V(mem) beyond 1.0 V. Pore resealing is shown to consist of an initial fast process, a 10(-4) s delay, followed by a much slower closing at a time constant of about 10(-1) s. This establishes a time-window during which the pores are mostly open, and hence, the system is most vulnerable to destruction by a second electric pulse. The existence of such a time window for effective killing by a second pulse is amply supported by our experimental data for E. coli cells. The time constant for the longer process also matches experiments. The study suggests that controlled manipulation of the pore "open times" can be achieved through multiple, ultrashort pulses.

A strong electromagnetic field generated by a dipole

A strong electromagnetic field generated by a steep current pulse passing in a conductor dipole was measured. The current was created by an ultrashort voltage pulse formed in a coaxial transmitting line of a high-current picosecond electron accelerator.

Electrochemical micromachining

The application of ultrashort voltage pulses between a tool electrode and a workpiece in an electrochemical environment allows the three-dimensional machining of conducting materials with submicrometer precision. The principle is based on the finite time constant for double-layer charging, which varies linearly with the local separation between the electrodes. During nanosecond pulses, the electrochemical reactions are confined to electrode regions in close proximity. This technique was used for local etching of copper and silicon as well as for local copper deposition.

Partial dephasing in interacting many-particle systems and current echo

Current echos as a response to a sequence of two ultrashort voltage pulses and their delay dependence are studied for interacting particles. The echo amplitude is reduced compared to its noninteracting counterpart, and decays even without an external bath coupling. However, it ends up with a nonzero value in the large-delay limit. This partial dephasing can be traced back to correlated energy differences in the many-body system. It is expected for all echo phenomena in small isolated systems. The time-dependent Hartree-Fock approximation fails to describe the current echo's dephasing even qualitatively.

Transient response of Josephson-coupled multilayers

We investigate the response of a Josephson-coupled multilayer to an ultra-short voltage pulse. The response is understood in terms of the dynamics of the phase differences across the layers, calculated from both the microscopic theory and the resistively shunted junction (RSJ) model. We discuss how such response might play a role in novel multilayered switching devices for use in electronics applications, such as flux quantum digital circuitry.