Search

The nonlinearity inherent in the traveling wave tube (TWT) amplifier distorts amplified signals and results in reduced efficiency and bandwidth, limiting its use in communication and electronic countermeasure applications. Signal predistortion is an effective technique for suppressing nonlinear distortion in TWTs that provides high suppression and requires simple circuits for implementation. While conventional predistortion linearizers are based on third-order intermodulation (3IM) injection, this paper proposes using second-order (second-harmonic) signal injection in predistortion circuits. A detailed experimental investigation and comparison of second-order versus third-order signal predistortion is presented. It is observed that both schemes result in suppression of up to 30 dB (55 dBc) for the 3IM distortion products. However, experimental results indicate that second-harmonic signal injection performs better than 3IM in suppressing higher order products. The paper also investigates spatial evolution of the wave spectrum along the TWT axis with and without injection, and sensitivity of the suppression to injected signals amplitude, phase and the fundamental frequency.

Hermetic stainless-steel open-ended coaxial probes have been designed for precision dielectric spectroscopy of biological tissue, such as breast tissue, over the 0.5-20-GHz frequency range. Robust data-processing techniques have also been developed for extracting the unknown permittivity of the tissue under test from the reflection coefficient measured with the precision probe and a vector network analyzer. The first technique, referred to as a reflection-coefficient deembedding method, converts the reflection coefficient measured at the probe's calibration plane to the desired aperture-plane reflection coefficient. The second technique uses a rational function model to solve the inverse problem, i.e., to convert the aperture-plane reflection coefficient to the tissue permittivity. The results of the characterization and validation studies demonstrate that these precision probes, used with the prescribed measurement protocols and data-processing techniques, provide highly accurate and reliable in vivo and ex vivo biological tissue measurements, including breast tissue spectroscopy.

The physics of signal injection to shape the output spectrum in a traveling wave tube (TWT) is studied using an analytic solution to the approximate nonlinear S-MUSE model and with the large signal code LATTE. The results verify the long-standing conjecture that a frequency canceled by signal injection is composed of a component due to the injected signal and a component due to the nonlinearity of the TWT. Furthermore, the structures of the solutions are exploited to explain and predict behavior for various signal injection schemes. The scenarios studied include second harmonic injection to reduce the second harmonic and enhance the fundamental, multiple harmonic injection to eliminate the sensitive output power dependence on injected phase, second harmonic injection to reduce intermodulation distortion, and multiple signal injection to reduce the intermodulation spectrum. Insights are given regarding the effectiveness of an injection depending on whether the injected signal is within or outside the linear gain bandwidth of the TWT.

Microfabricated folded waveguide traveling-wave tubes (TWTs) are potential compact sources of wide-band, high-power terahertz radiation. We present feasibility studies of an oscillator concept using an amplifier with delayed feedback. Simulations of a 560-GHz oscillator and experimental evaluation of the concept at 50 GHz are presented. Additionally, results from various fabrication methods that are under investigation, such as X-ray lithography, electroforming, and molding (LIGA), UV LIGA, and deep reactive ion etching are presented. Observations and measurements are reported on the generation of stable single-frequency oscillation states. On varying the feedback level, the oscillation changes from a stable single-frequency state at the threshold to multifrequency spectra in the overdriven state. Simulation and experimental results on amplifier characterization and dynamics of the regenerative TWT oscillator include spectral evolution and phase stability of the generated frequencies. The results of the experiment are in good agreement with the simulations.

The helix traveling-wave tube (TWT) is a vacuum electronic device which utilizes an electron beam to amplify electromagnetic waves. Although having a broad frequency gain bandwidth compared to other vacuum electron devices, the helix TWT has been used in relatively narrowband ways in its applications in communications and electronic countermeasures. Recent interest in ultrawideband (UWB) radio and radar, combined with the recent development of UWB helix TWTs, has stimulated interest in the amplification of very broadband multifrequency signals and impulses. A number of studies have been conducted on the harmonic and intermodulation effects of multiple signals in a TWT, but there has not been much investigation into impulse amplification. Utilizing a nonlinear time-domain model developed for this purpose, the response of a wideband (helix) TWT to an input Gaussian pulse is examined. Differences between the large signal response to positive and negative Gaussian inputs are examined, and it is shown that a positive impulse input yields better pulse shape preservation, higher saturation level, and possibly greater efficiency. The growth and saturation mechanisms of a positive input Gaussian are then investigated, showing distinct differences from steady-state growth and saturation mechanisms. This study indicates that the possibility of amplification of impulses in a TWT is very promising. The results and conclusions of this study generally apply to all types of TWTs with appreciable bandwidth (e.g., couple-cavity, folded waveguide). However, as the helix TWT has the largest bandwidth, it is the most interesting and is the specific TWT studied here.

The creation of low resistivity, ultrashallow source/drain regions in MOS device structures requires rapid thermal processing (RTP) techniques that restrict diffusion and activate a significant percentage of the implanted dopant species. While current heating techniques depend upon illumination based heating, a new technology, electromagnetic induction heating (EMIH), achieves a rapid heating of the silicon by coupling electromagnetic radiation directly into the silicon wafer. Heating rates of 125/spl deg/C/s to temperatures in excess of 1050/spl deg/C have been achieved for 75- and 100-mm-diameter wafers at input powers of 1000 and 1300 W, respectively. These ramp rates are suitable for ultrashallow junction formation, and junctions shallower than 30 nm with sheet resistances lower than 600 /spl Omega//square have been achieved. This paper details the application of electromagnetic heating using radiation in the microwave, 2450 MHz, frequency regime. Experimental results, comparing microwave annealed implants to the well documented SEMATECH requirements, and simulations, utilizing a coupled electromagnetic-thermal computer model, of the heating process are discussed.

We have used open-ended coaxial probes to determine the dielectric properties of freshly excised normal and diseased breast tissue specimens. The considerable variability in size and composition of these specimens predicates the need for determining the minimum surgical specimen size that yields accurate measurements for a given probe diameter. We investigate the sensing volume of 2.2- and 3.58-mm-diameter flange-free coaxial probes for both lowand high-water-content tissue using standard liquids that exhibit dielectric properties similar to breast tissue over the microwave frequency range from 1 to 20 GHz. We also present an innovative graphical technique based on the use of Cole-Cole diagrams to determine the error thresholds in the magnitude and phase of the reflection coefficient, which bound the errors in the measured complex permittivity to an acceptable level. Results from self-consistent experiments and finite-difference time-domain simulations indicate that a tissue specimen with a thickness of 3.0 mm and a transverse dimension of 1.1 cm is the minimum size that yields accurate measurements with the 3.58-mm-diameter probe. For the 2.2-mm-diameter probe, the specimen's thickness and width should be at least 1.5 and 5 mm, respectively. These conclusions are relevant not only to breast tissue characterization, but also more generally to the dielectric characterization of a variety of low- and high-water-content biological tissues.

Critical to the development of improved solid oxide fuel cell (SOFC) technology are novel compounds with high oxygen reduction reaction (ORR) catalytic activity and robust stability under cathode operating conditions. Approximately 2145 distinct perovskite compositions are screened for potential use as high activity, stable SOFC cathodes, and it is verified that the screening methodology qualitatively reproduces the experimental activity, stability, and conduction properties of well-studied cathode materials. The calculated oxygen p-band center is used as a first principle-based descriptor of the surface exchange coefficient (k*), which in turn correlates with cathode ORR activity. Convex hull analysis is used under operating conditions in the presence of oxygen, hydrogen, and water vapor to determine thermodynamic stability. This search has yielded 52 potential cathode materials with good predicted stability in typical SOFC operating conditions and predicted k* on par with leading ORR perovskite catalysts. The established trends in predicted k* and stability are used to suggest methods of improving the performance of known promising compounds. The material design strategies and new materials discovered in the computational search help enable the development of high activity, stable compounds for use in future solid oxide fuel cells and related applications.

A novel heating technique, electromagnetic induction heating (EMIH), uses electromagnetic radiation, ranging in frequency from a few megahertz to tens of gigahertz, to volumetrically heat silicon above 1000/spl deg/C in only a few seconds. Typical power requirements fall between 900 to 1300 W for silicon wafers 75 to 100 mm in diameter. This technique has successfully produced direct silicon wafer-to-wafer bonds without the use of an intermediate glue layer. Infrared images indicate void free bonds that could not be delaminated with knife-edge tests. In addition, four pairs of stacked wafers were bonded simultaneously in 5 min, demonstrating the potential for multiwafer bonds and high-throughput batch processing.

We derive from Eulerian electron beam equations the multifrequency spectral Eulerian (MUSE) model, a new one-dimensional (1-D) nonlinear multifrequency model of a traveling wave tube (TWT). We also derive from the same equations a Lagrangian "disk" model, LATTE, so that MUSE may be directly compared to a Lagrangian approach. The models are compared to the large signal code Christine 1-D on a set of TWT parameters which are based on a single section of the Hughes 8537H L-band TWT. Aspects of the physics, nonlinearities, and simulation dimensions of the MUSE model are discussed, as well as its relation to the method of collective variables. A simplified MUSE model S-MUSE useful for analysis is also presented and its applications are discussed.

When operated in high-power pulsed systems, frequency selective surfaces (FSS) are susceptible to breakdown. Breakdown in these devices changes the frequency response of the device and can result in permanent damage in certain situations. Recently, it has been demonstrated that breakdown induced at a certain location in an FSS can result in breakdown at other locations (e.g. neighboring unit cells) where the intensity of the incident EM wave is not high enough to cause breakdown under normal circumstances. In this paper, we examine the physical cause of this phenomenon and demonstrate that this is caused by the generation of vacuum ultraviolet (VUV) radiation, at the location of the initial discharge, which facilitates breakdown at other locations. Furthermore, through a series of experimental studies, we identify the distances over which this VUV radiation has a high enough intensity to facilitate breakdown at the neighboring unit cells. The results presented in this paper are expected to be useful in mitigating and localizing the adverse impacts of breakdown in HPM FSSs covering large aperture dimensions or in designing devices that generate large scale breakdown (e.g. periodic plasmas).

We present a formulation for achieving stable high-concentration (up to 20 mg/ml) aqueous dispersions of carbon nanotubes (CNTs) with exceptionally high microwave-frequency (0.5-6 GHz) dielectric properties. The formulation involves functionalizing CVD-synthesized CNTs via sonication in nitric and sulfuric acid. The overall chemical integrity of the CNTs is largely preserved, as demonstrated via physical and chemical characterizations, despite significant shortening and functionalization with oxygen-containing groups. This is attributed to the protected inner walls of double-walled CNTs in the samples. The resulting CNT dispersions show greatly enhanced dielectric properties compared to a CNT-free control. For example, at 3 GHz, the average relative permittivity and effective conductivity across several 20 mg/ml CNT samples were increased by ∼ 70% and ∼ 400%, respectively, compared to the control. These CNT dispersions exhibit the stability and extraordinary microwave properties desired in systemically administered theranostic agents for microwave diagnostic imaging and/or thermal therapy.

The efficacy of protecting electronics from high power microwaves (HPM) through plasma creation depends on how quickly the plasma forms in the protective gas chamber when illuminated with microwave radiation. A cylindrical chamber with polycarbonate windows was filled with a neon, krypton gas mixture and illuminated with a train of ∼25kW, 800ns long pulses at 43Hz repetition rate as a simulation of the HPM attack scenario. In order to facilitate the formation of a plasma, a set of metamaterial, stainless steel masks for the incident polycarbonate window were created to increase the effective electric field. In addition to the masks, we investigated the effect chamber pressure had on the breakdown delay.

We find that the surface resistance of smooth copper exceeds that predicted by classical electromagnetic theory. We have fabricated copper surfaces with controlled roughness and grain size. We will present measurements of the reflectivity of these copper surfaces and compare these results to theoretical predictions for the THz resistance of surfaces.

Perovskite oxides are promising materials for a new class of electron emitting materials because they possess intrinsically low work functions without the need for an additional surface dipole coating. Density Functional Theory (DFT) was used to examine a series of LaBO 3 (B=transition metal) perovskites, and it was found that LaVO 3 exhibited the lowest work function of 1.52 eV.

In this paper, we present an experimental study of the microwave-frequency dielectric properties and heating response of aqueous dispersions of single- and double-walled carbon nanotubes (CNTs). The CNTs were chemically treated using a method that enables the creation of stable dispersions of isolated tubes at very high concentrations. The CNT dispersions show significantly enhanced dielectric properties and heating response compared to the control (an aqueous sample without CNTs). The observed enhancement with this specific CNT dispersion formulation is far greater than any previously reported. The results suggest that these modified CNTs are promising candidates as contrast agents for microwave diagnostic imaging and heating agents for nanoparticle-mediated microwave thermal therapy for cancer.

Under high power illumination, electromagnetic metamaterials and periodic structures experience internal breakdown that alters their frequency responses. It was recently demonstrated that a breakdown discharge created at a given location within the unit cell of a metamaterial mediates the breakdown at other locations within that unit cell or at the neighboring unit cells in spite of the fact that the intensity of the incident field is not high enough to cause breakdown at these other locations under normal situations. In this paper, we investigate the physics behind this phenomenon and examine three candidate mechanisms for these simultaneous breakdown discharges. These include energetic electron transport, ultraviolet (UV) radiation, and vacuum ultraviolet (VUV) radiation. By experimentally examining the unit cell of a metamaterial composed of multiple resonators, we were able to selectively isolate the coupling influence of the candidate mechanisms. It was established that VUV radiation from the initial discharge yields simultaneous breakdown at the other locations of interest.

Ionized physical vapour deposition (IPVD) is of current interest to the semiconductor industry for the deposition of thin metal films as diffusion barriers and seed layers in high aspect ratio features. One of the aims of IPVD is to collimate depositing particle fluxes by ionizing a significant fraction of the incident metal vapour and applying an electric potential bias to the substrate. A system consisting of a dc-powered, 15 cm diameter copper sputter source and a RF induction plasma powered by a single-turn, 36 cm diameter, loop antenna internal to the vacuum chamber has been examined. Measurements made with a biased quartz crystal microbalance in an argon background of 10-90 mTorr demonstrate that, at low magnetron sputtering levels of 100 W, ionized metal flux fractions (IMFFs) as high as 90% can be observed. However, further measurements of the IMFFs and plasma density indicate rarefaction of the background argon gas as the metal flux to the plasma increases. Results are presented from an experimental investigation of methods to reduce the gas rarefaction. These include the modulation of the metal flux on the timescale of the process gas residence time and increasing the target-to-substrate height.

Optical absorption spectroscopy has been used to measure absolute, average gas phase densities of neutral copper, ground and metastable states, and neutral argon, metastable and resonance states, in an ionized physical vapor deposition plasma. Spectroscopic measurements were carried with a xenon arc lamp as a high intensity, continuum light source, and an optical multichannel detector. Copper radiative transitions in the wavelength range of 324.8–510.6 nm and argon radiative transitions in the 706.7–811.5 nm range were employed. The curve of growth method has been used to calculate the absolute line average densities from fractional absorption data. For a copper–argon plasma of neutral pressure 30 and 10 mTorr copper metastable state densities were found to lie in the range of 1010–1012 cm−3. Comparison of these densities with neutral copper densities derived from independent measurements of neutral copper flux at the substrate indicate gas phase temperatures greater than 1500 K under certain experimental...

A recoil implantation technique is investigated for ultrashallow p+/n junction formation. In this method, a 3–35 nm thick B layer is deposited on the wafer by magnetron sputtering. Then a medium energy (10–40 keV) Ge implant drives the boron atoms into Si by means of ion beam mixing. The remainder of the boron film is chemically etched away prior to the annealing step. Sub-60 nm deep p+/n junctions with sheet resistance less than 1000 Ω/sq and test diodes with leakage current density below 2 nA/cm2 have been formed using this method.

Langmuir probe, optical emission spectroscopy, and biased quartz crystal microbalance measurements were used to investigate an argon and copper plasma used for ionized physical vapor deposition of copper. Copper vapor generated by a magnetron sputter discharge is ionized upon passing through an argon discharge excited by an internal rf induction antenna. Argon plasma characteristics such as electron temperatures Te, plasma densities ne, and plasma and floating potentials Vp and Vf, were studied as a function of argon pressure and rf power. An increase of plasma density versus rf discharge power and argon pressure was observed. The radial profile of plasma density measured by a Langmuir probe reveals a peak ion density at the center of the rf antenna and an increase in the radial ion concentration gradient with argon pressure. The ratios of optical emission intensities from Cu+ ion and Cu neutral lines increase with rf discharge power and argon pressure. The biased quartz crystal microbalance measurements ...

Numerical and theoretical analyses show that stable, two-plane focusing of finite width, elliptical cross section, sheet electron beams with high space charge (low voltage, high current density) can be accomplished using periodically cusped-magnetic (PCM) fields. Magnetic field strength requirements for focusing high-space-charge sheet beams are within technological capabilities of modern permanent magnet technology. Both an offset-pole PCM stack and a PCM stack combined with a periodic quadrupole magnet (PQM) edge array are shown to be effective for two-plane sheet beam confinement. The PCM-PQM hybrid configuration offers inherent advantages for independent adjustment of confinement fields to achieve beam matching (minimum ripple) in both transverse dimensions. The offset-pole configuration offers the advantage of open-side access for applications such as vacuum electronic microwave devices. It is also shown that PCM-focused sheet beam envelope stability obeys criteria equivalent to that previously identified for round-cross-section electron beams in periodic permanent magnet focusing.

Ionized physical vapor deposition is a technique for sputtering metal into small trenches, by ionizing sputtered metal atoms so that their trajectories can be controlled by electric fields. To this date no one has quantified exactly what fraction of the metal vapor is ionized, although the trends of how ionization varies with input parameters is known. This article describes and demonstrates a new quartz crystal microbalance design, which can be used to measure the ionized metal flux fraction arriving at the substrate location. Instead of using grids to repel ions as similar devices do, this analyzer works by applying a voltage bias to the front surface of the crystal in order to repel ions. A magnetic field adjacent to the face limits electron current to the microbalance, minimizing its perturbation of the plasma. The measurement tool described in this article does not suffer from complications caused by placing grids in front of the monitor and is an attractive method for characterizing ionized physical vapor deposition systems. Ion and neutral metal fluxes as a function of ionizer power are presented for an argon/copper discharge.

This work examines the effect of iron as a contaminate implant impurity on the characteristics of boron p/sup +/n silicon diodes. Plasma-based doping processes [e.g., plasma source ion implantation (PSII)] are subject to concerns about the introduction of contaminant impurities. Here, a relevant database on iron contaminant effects was acquired through a controlled study using conventional ion-beam implantation. Uncontaminated control diodes had leakage current densities of 6-9 nA-cm/sup -2/ at -5 volts and ideality factors

Nitrogen of doses of 5×10 16 , 1×10 17 and 5×10 17 ions cm −2 was implanted into bearing steel (52100) samples for surface corrosion protection. The implantation was performed by using nitrogen plasma source ion implantation (PSII). The nitrogen distribution and nitride identification were determined by Auger electron spectroscopy and glancing angle X-ray diffraction (XRD), respectively. The corrosion resistance was monitored by using a linear polarization test. XRD measurements confirmed that a thin layer of multiphase iron nitrides was formed on top of the samples after the PSII treatment. The treated bearing steel samples showed a significantly improved corrosion resistance compared with the untreated samples.

The finite difference time domain (FDTD) method is widely used as a computational tool for development, validation, and optimization of emerging microwave breast cancer detection and treatment techniques. When expressed in terms of Debye parameters, dispersive breast tissue dielectric properties can be efficiently incorporated into FDTD codes. Previously, we experimentally characterized the dielectric properties of a large number of excised normal and malignant breast tissue samples from 0.5 to 20 GHz. We subdivided the large database of normal tissue data into three groups based on the percent adipose tissue present in a particular sample. In addition, we formed a group of all cancer samples that contained at least 30% malignant tissue. We summarized the data using one-pole Cole-Cole models that were rigorously fit to the median dielectric properties of the three normal tissue groups and one malignant tissue group. In this letter, we present computationally simpler one- and two-pole Debye models that retain the high accuracy of the Cole-Cole models. Model parameters are derived for two sets of frequency ranges: the entire measurement frequency range from 0.5 to 20 GHz, and the 3.1-10.6 GHz FCC band allocated for ultrawideband medical applications. The proposed Debye models provide a means for creating computationally efficient FDTD breast models with realistic wideband dielectric properties derived from the largest and most comprehensive experimental study conducted to date on human breast tissue.

An important characterization parameter associated with ionized physical vapor deposition systems is the amount of metal vapor that is actually ionized. In such systems, metal ions, in this case copper, formed by passing sputtered metal vapor through a high density plasma are used for ion plating applications. Here, a Langmuir probe technique is utilized which takes advantage of changes in the ratio of the ion saturation current to the electron saturation current to determine the variations in both copper and argon ion concentrations as a function of sputter power. The data indicate that at fixed rf power, the copper ion concentration increases rapidly with increasing sputter rate, eventually overtaking argon as the dominant ion species in the discharge. These findings also suggest that the fraction of electrons with sufficient energy to ionize argon neutrals decreases as a function of magnetron power. Optical emission spectra collected as a function of magnetron sputter power provide supporting evidence that the electron population in the tail of the electron energy distribution function is depleted by the introduction of the copper vapor. This quenching is attributed to inelastic collisions with copper associated with the low threshold energies and large excitation and ionization cross sections as compared to argon, and the resulting reduction in the measured plasma potential.

The shape of the gain curve and physics of interaction between microwave fields and the electron beam for a periodic rectangular grating slow-wave Traveling Wave Tube (TWT) amplifier are investigated. This research focuses on the collective (ωpτ≫1) low-voltage (⩽10 kV) interaction in the backward wave regime for the Ku-band (12.5–17.5 GHz) range of frequencies. For amplifier experiments, a round “probe” beam (10 kV, 0.25 A, 1 mm diameter) confined by a 1 kG solenoidal focusing magnetic field was utilized. Simultaneous single-pass collective gain and electron-beam velocity spread measurements are performed by means of a Faraday cup repeller energy analyzer configured as the beam collector. Experiments near 13.0 GHz show the maximum normalized single-pass gain to be in agreement with the theoretical prediction for several axial velocity spreads (δv‖/v‖). Collective single-pass experimental results are presented and compared with theory. The effect of an increased interaction length which is accomplished by ...

A numerical model was developed to simulate and study microwave-induced transport in ionic solids. The model is based on continuum equations, is very general, and could be applied to many materials. The assumptions, boundary conditions, initial conditions, and numerical techniques used in the model are described. Results are presented from a study of microwave driven defect transport in sodium chloride. Static, high-frequency, and quasistatic results show that ponderomotive rectification of vacancy fluxes will act to deplete the vacancies in a near-surface region and will continue to pull vacancies to the surface through diffusion kinetics. The ponderomotive driving force for this transport is characterized over a wide range of variable space. The magnitude of the driving force falls right in the range such that it can explain why microwave-enhanced mass transport is observed in some experimental cases but not in others.

Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating of a variety of ceramic, glass, and polymer materials. An explanation for these controversial observations has eluded researchers for over a decade. This paper describes a series of recent experimental and theoretical investigations that provide an explanation for these intriguing observations in terms of ponderomotive forces acting on mobile ionic species. The ponderomotive phenomenon, like its conventional-plasma analog, can be described in the continuum model limit by combining the continuity, Poisson’s, and transport equations. However, the solid-state plasma version typically manifests as a result of gradients in mobile charge mobility (e.g., near physical surfaces or interfaces), whereas the conventional plasma ponderomotive transport is typically a consequence of gradients in the radiation field intensity. Both cases can be captured in a single, general, mathematical articulation developed in terms of the mobile particle fluxes.

A spreadsheet based cost model was used to explore the installation and operating costs for a PSII system based on various operating conditions and equipment configurations. It was found that plasma density and implantation voltage were operating specifications which can significantly aVect capital costs. The plasma density is an important factor since operating at lower plasma density levels requires larger vacuum chambers and pump systems which significantly increase capital costs. Comparisons of the cost eYciency of operating at relatively high versus low implantation voltages were made. Results indicated that high dosage levels favor a higher implant voltage whereas high plasma densities favor a lower voltage, with the plasma density being the dominant factor. When capital expenses are amortized, the cost of operation comprises the majority of total annual costs, with personnel expenses being the most significant of these. Therefore, any cost comparisons with other technologies should emphasize the number and expertise (salary) of personnel. © 1998 Elsevier Science S.A.

A method of forming TiN films for Si/Cu metallization by using plasma source ion implantation (PSII) of nitrogen into Ti is described. The PSII process utilizes a dose of 1 × 1017 ions/cm2 and peak voltages of –10, –15, and –20 kV. The properties of such TiN films as diffusion barriers between Cu and Si were investigated by annealing Cu(2000 A)/TiN/Ti/Si films in vacuum from 500 °C to 700 °C, and by analyzing with four-point probe sheet resistance measurements, Rutherford backscattering spectrometry (RBS), and Auger electron spectroscopy (AES). The TiN films made at peak voltages of –15 and –20 kV were stable barriers against Cu diffusion after annealing at temperatures higher than 600 °C.

Background The use of pulsed electric fields (PEFs) to irreversibly electroporate cells is a promising approach for destroying undesirable cells. This approach may gain enhanced applicability if the intensity of the PEF required to electrically disrupt cell membranes can be reduced via exposure to a molecular deliverable. This will be particularly impactful if that reduced PEF minimally influences cells that are not exposed to the deliverable. We hypothesized that the introduction of charged molecules to the cell surfaces would create regions of enhanced transmembrane electric potential in the vicinity of each charged molecule, thereby lowering the PEF intensity required to disrupt the plasma membranes. This study will therefore examine if exposure to cationic peptides can enhance a PEF’s ability to disrupt plasma membranes. Methodology/Principal Findings We exposed leukemia cells to 40 μs PEFs in media containing varying concentrations of a cationic peptide, polyarginine. We observed the internalization of a membrane integrity indicator, propidium iodide (PI), in real time. Based on an individual cell’s PI fluorescence versus time signature, we were able to determine the relative degree of membrane disruption. When using 1–2 kV/cm, exposure to >50 μg/ml of polyarginine resulted in immediate and high levels of PI uptake, indicating severe membrane disruption, whereas in the absence of peptide, cells predominantly exhibited signatures indicative of no membrane disruption. Additionally, PI entered cells through the anode-facing membrane when exposed to cationic peptide, which was theoretically expected. Conclusions/Significance Exposure to cationic peptides reduced the PEF intensity required to induce rapid and irreversible membrane disruption. Critically, peptide exposure reduced the PEF intensities required to elicit irreversible membrane disruption at normally sub-electroporation intensities. We believe that these cationic peptides, when coupled with current advancements in cell targeting techniques will be useful tools in applications where targeted destruction of unwanted cell populations is desired.

&p.1: Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating or processing of a variety of ceramic, glass, and polymer materials. These empirical observations of microwave enhancements have been broadly called the “microwave effect”. In the past, these claims have been the source of significant controversy, due in part to the lack of a credible and verifiable theoretical explanation. Moreover, certain notable microwave heating experiments have failed to observe any resolvable reaction or transport rate enhancements. This paper describes a series of recent experimental and numerical investigations that have established the fact that strong microwave electric fields induce a (previously unknown) nonlinear driving force for (ionic) mass transport near surfaces and structural interfaces (e.g., grain boundaries) in ceramic materials. This driving force can influence reaction kinetics by enhancing mass transport rates in heterogeneous solid-state reactions. Most of the previously reported observations regarding “microwave effects” (both for and against) are consistent with the characteristics of this newly identified microwave-induced driving force. &kwd: Microwave processing · Microwave effect · Ponderomotive force · Ionic transport · Nonthermal · Sintering&bdy

A periodic, rectangular grating slow-wave-structure is considered for forward and backward wave low-voltage (⩽10 kV) Ku-band traveling wave tube (TWT) amplifiers. For forward wave operation, it is required that the ratio of groove depth, d, to grating period, p, be large (i.e. d/p⩾5) while small values of d/p allow backward wave operation. For large d/p, skin effect losses in the grating slots are large and can substantially reduce the growth rate produced by the beam-slow wave interaction. Phase and amplitude measurements of the grating structures utilizing a slotted line and a fast Fourier transform (FFT) analysis have been carried out. The results show that the measured dispersion relations for both shallow (d/p= 0.446) and deep groove gratings (d/p= 7.43) agree very well with the theoretical dispersion relations. For amplifier experiments, a round “probe” beam (10 kV, 0.25 A, 1 mm radius) from a Litton Pierce electron gun (model M707) is utilized. The beam is confined by means of a 1 kG focusing solen...

It is established that nitridation of aluminum (Al) 6061-T4 by plasma source ion implantation (PSII) can dramatically enhance the pitting corrosion resistance of this alloy in marine environments (i.e., chlorine-ion-bearing aqueous solutions or humid atmospheres). Corrosion tests and microstructure analyses establish that the mechanism for successful passivation against chloride-induced pitting corrosion involves the formation of a multilayered microstructure, including the presence of a continuous layer of aluminum-nitride (AlN). Important process variables are the implantation voltage and the nitrogen dose (or total implantation time), as these two variables establish the implanted nitrogen concentration. Too high or too low an implanted nitrogen concentration will not yield the continuous AlN layer required for good corrosion resistance. PSII is attractive for this application as it provides for uniform, conformal implantation of irregularly shaped objects without masking, beam rastering, or object rotation.

The recent theory of averaged ponderomotive action of microwave fields in solids is expanded to describe quasistationary ionic currents driven by that action. Several limiting cases are explored in detail, and in all cases the effect is shown to depend upon the interfacial properties of the ionic crystal. Experimental results on the dynamics of the microwave-induced currents in AgCl and NaCl are presented. Agreement between experiment and theory provides further and stronger evidence for the general validity of the theoretical model.

Summary form only given. Development of high power microwave (HPM) distributed discharge limiters relies critically on minimizing the delay time between HPM incidence and diffuse plasma creation. We present a range of pulsed plasma experiments conducted in neon, argon, helium, and mixtures of these gases, from 50-760 torr. Breakdown is achieved by illuminating a gas cell with a ~25kW, ~2 kV/cm, 800ns-long pulse as well as 41Hz pulse trains. Current results focus on preliminary experiments with metamaterial window coatings that indicate significant improvement opportunities for controlling breakdown thresholds and reducing breakdown delay. New results with gas mixtures in which observed breakdown occurs in

Previous study on the surface resistivity of copper surfaces measured at 400 and 650 GHz has been extended to 850 GHz. These measurements were conducted using a high quality factor quasi-optical hemispherical resonator. The measurements of the surface resistance of rough metallic surfaces and the effect of roughness on reflectivity will be discussed. The results will be compared with measurements from theoretical predictions.

Observations of rapidly formed (

We find that the surface resistance of copper exceeds that predicted by classical electromagnetic theory. The small but significant discrepancy we find is consistent with results reported in adjacent frequency ranges. We will also present measurements of the reflectivity of rough copper surfaces and compare these results to theoretical predictions.

Density functional theory was used to calculate the surface electron emission barriers for the stable (011) and (111) surfaces of bixbyite Sc2O3 in the presence of adsorbed Ba and Ba-O. A low surface barrier of 1.21 eV for a defected BaO monolayer on Sc2O3 (011) was found to be thermodynamically stable. This result provides a straightforward explanation of low effective work function measurements obtained for scandate cathodes.

A theoretical model of microwave absorption in linear dielectric ~nonferroelectric! ionic crystals that takes into account the presence of point defects has been synthesized and specifically applied to NaCl single crystals by considering all relevant interaction mechanisms between a harmonic electric field and single-crystal ionic crystalline solids, including ionic conduction, dielectric relaxation, and multiphonon processes. The loss factor e9 has been measured by a cavity resonator insertion technique for nearly pure and Ca 21 doped NaCl single crystals at frequencies from 2 to 16 GHz and at the temperatures from 300 to 700 K. The experimental results are in good agreement with the theoretical model. The theoretical model predicts a transition between low- and high-temperature absorption processes that may partly account for the phenomenon of thermal runaway observed during microwave processing of ceramics.

Plasma source ion implantation (PSII) is a technique for modifying stafaces that places the object to he modified directly into a plasma and then negatively pulse biases the object so as to implant positive ions. If the voltage is high enough, X-rays can he generated by electrons that are also accelerated by the pulse. This work describes techniques for imaging and characterizing the X-rays A pinhole camera was used to image the X-rays being emitted as electrons collided with surfaces in the chamber. The images show that X-rays are generated at the chamber walls and near the target. The time dependence of these X-rays during each pulse was examined using a PIN diode X-ray detector. Then, using another X-ray sensor and pulseheight analyzer, the spectra of the emitted X-rays was determined. The object is to relate the X-ray intensity and spectrum to the temporal and spatial values of the implantation dose so that it may he used as a process monitor and a control sensor.

The surfaces of Lexan Polycarbonate (PC) and ABS polymers were treated with low energy (300 eV) ion bombardment prior to and during deposition of a thin (200 nm) Al film. The effects on the adhesion characteristics, the type of ions used (Ar, N), and the type of bombardment (sputtering or during deposition) were studied for eight different deposition conditions for each polymer. The adhesion characteristics were compared by the tape and stud pull tests. The ion beam treatment caused substantial improvement in adhesion strength in all seven cases where sputtering was involved. In the case of the stud pull test for the PC samples, the failure was along the interface for the non-sputtered case only. In all others, with sputtering, we observed cohesive failure within the polymer, as confirmed by SEM. This suggests that the actual interface strength in all the sputtered cases was higher than that of the polymer itself. SEM, RBS, and profilometry were used to study the failure modes, Al film quality, and the effect of morphology on adhesion characteristics, respectively. Surface roughness did not seem to be an important factor for adhesion improvement. XPS studies suggest that the Al is bonded in identical ways at the bombarded and virgin interfaces. Improved adhesion is likely due to surface sputter cleaning.

We present a new approach to perform beam steering in reflecting type apertures such as reflectarray antennas. The proposed technique exploits macro-scale mechanical movements of parts of the structure to achieve two-dimensional microwave beam steering without using any solid-state devices or phase shifters integrated within the aperture of the antenna. The principles of operation of this microwave beam steering technique are demonstrated in an aperture occupied by ground-plane-backed, sub-wavelength capacitive patches with identical dimensions. We demonstrate that by tilting the ground plane underneath the entire patch array layer, a phase shift gradient can be created over the aperture of the reflectarray that determines the direction of the radiated beam. Changing the direction and slope of this phase shift gradient on the aperture allows for performing beam steering in two dimensions using only one control parameter (i.e., tilt vector of the ground plane). A proof-of-concept prototype of the structure...

Many experimenters over the past few years have observed rate enhancements when using microwave processing compared to conventional processing. The results have remained somewhat controversial because the driving forces are not constant throughout the experiments and because of the possibility of inaccurate temperature measurement. This paper describes a different experimental approach that avoids the pitfalls of the previous experiments. Specifically, the alternative approach involves fixed driving forces and short duration experiments. Reliable and accurate knowledge of the sample temperature is ensured by restricting the amount of microwave heating to negligible levels and using conventional ohmic heating to control temperature. This approach has allowed us to confirm the presence of a ‘‘microwave effect’’ on kinetic processes in ionic ceramic materials. With this configuration, many further experiments are possible with different materials and conditions.

A system has been developed for measuring the complex permittivities of low loss ceramic materials at frequencies from 2 to 20 GHz and over a temperature range 20–1000 °C. The measurement technique involves a modified version of the conventional cavity perturbation method. Details of the design and fabrication of the circular cylindrical cavity and the input and output coupling transmission lines are discussed. Particular features related to high‐temperature operation and temperature cycling are described. Data are presented for an illustrative measurement of the complex microwave dielectric properties of NaCl single crystals between 20 and 400 °C. The experimental results are in excellent agreement with theoretical models.

An improved measurement technique to determine the complex dielectric properties of materials has been developed that extends the validity of the conventional cavity perturbation technique for circular cylindrical rod-shaped samples in circular cylindrical cavities resonating in TM/sub 0n0/ modes. The method is particularly useful for the dielectric characterization of fragile, low-loss materials that are difficult to machine to typically required thin dimensions. The method further allows for multi-frequency measurements using higher-order radial modes and somewhat alleviates the very small cavity dimensions typically required by the conventional perturbation technique at higher microwave frequencies. A validity criterion for the extended method is given. Measurements of the complex permittivity of NaCl single crystals are presented, showing excellent agreement with theory. >

Corrosion properties of 6061T aluminum alloy treated by nitrogen plasma source ion implantation (PSII) have been investigated. Results from corrosion tests demonstrate that the nitrogen PSII significantly increased the pitting resistance of implanted 6061T Al samples. Scanning electron microscopy of corrosion-tested samples found that both pit size and density of the PSII treated samples were smaller than those of untreated samples, although no significant changes in the corrosion potential or the corrosion current were observed. These results demonstrate PSII's potential for metal corrosion protection.