RC Time Research Articles

Square Wave Electrogravimetry Monitors Transient Submonolayer Adsorption of Redox-Active Molecules with a Precision of Less Than 1% of a Monolayer

Square wave voltammetry on electrolytes containing the reversible redox pairs flavin adenine dinucleotide (FAD) and methyl viologen (MV) was complemented by a new form of acoustic microgravimetry. The analytes FAD and MV have promising applications in bacterial fuel cells and redox flow batteries. The instrument operates similarly to a quartz crystal microbalance with dissipation monitoring (EQCM-D). It reports shifts in resonance frequency and half bandwidth on several overtones. Compared to the existing instruments, the time resolution was improved by a factor of 40 down to 2.5 ms by multifrequency lockin amplification, which is important for the analysis of the transients in electrochemistry. The frequency noise after accumulation was reduced below 10 mHz ≙ 0.12 ng/cm2 ≙ 1.2 pm (assuming ρ = 1 g/cm3) by employing modulation and averaging. Square wave modulation of the electrode potential is superior to linear ramps (cyclic voltammetry) because it reduces the contribution of non-Faraday currents and, also, improves sensitivity. The shifts of frequency,Δf, and half bandwidth, ΔΓ, are in line with the Sauerbrey prediction (Δf/n ≈const. and ΔΓ/n < -Δf/nwith n the overtone order). Small deviations (Figure B and D) presumably are caused by the layer’s softness. The apparent shear modulus, G app, of this layer is in the GPa range. The frequency difference, Δf/n|CT (Figure E), amounts to an apparent mass transfer rate. Plots of Δf/n|CT versus potential sometimes show curves similar to the electric current as observed for e. g. MV. For FAD, the results obtained depended on pH and the apparent mass transfer rates are much different from the current (Figure C and E). This difference is most likely caused by adsorbed molecules that are intermediates of the underlying two-electron process. The explanation is further corroborated by the response time of the QCM signals being much larger than the RC time of double layer recharging as determined with EIS. An interpretation in terms of adsorption/desorption is more plausible than an interpretation in terms of changed viscosity in the diffuse double layer.[1] Caption: Currents and frequency shifts obtained on a solution containing FAD. Df/n|av evidences the preferred adsorption of the intermediate state (FADH).

DLC: Flexible bridge across heterogeneous interface between alumina filler and epoxy resin matrix

The heterogeneous interface between filler and matrix within composites often acts as a bottleneck for material performance. Carbon materials, particularly Diamond-Like Carbon (DLC), are representing a novel trend in interface design. This study investigates the nanoscale mechanical and electrical properties of the heterogeneous interface between DLC-coated alumina fillers and an epoxy resin matrix. The results demonstrate that the DLC layer is instrumental in creating a harmonious modulus transition between materials that exhibit significant variance in their elastic moduli, characterized by an exponential relationship, and approximately 50% enhancement in interfacial adhesion. Additionally, the DLC layer exhibits elevated sensitivity in dielectric response, attributed to a small RC time constant. This interface transition technology offers new tools for composite material design.

Electrochemical performance of boron- and nitrogen-doped tetrahedral amorphous carbon

Tetrahedral amorphous carbon (ta-C) is one of the most versatile carbon electrode materials available. The incorporation of various dopants in ta-C alters the structural, electrochemical, physical, and chemical properties which are tunable for various applications. Furthermore, doped ta-C (ta-C:X) can be deposited on many different substrate materials (metals, ceramics, plastics) and geometries (micro-electrodes to ultra large areas at continuous coating lines). In this work, we present a comparison in electrochemical performance of ta-C electrodes prepared by filtered laser-arc (a physical vapor deposition process), doped with nitrogen (ta-C:N) at various levels, doped by boron (ta-C:B), and doped by boron and nitrogen together (ta-C:B:N). The ta-C:N films were doped via N2 gas in the deposition chamber, while ta-C:B and ta-C:B:N were deposited via incorporation of the dopant into the graphite cathode used for film synthesis. Films coated on silicon (Si) and titanium (Ti) substrates were compared through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The Fe(CN)63-/4− and Ru(NH3)63+/2+redox systems were used to investigate the electrochemical characteristics of each ta-C:X film type. Boron-doped diamond (BDD), glassy carbon (GC), and undoped ta-C were used as control electrodes. It was found that all ta-C:X films exhibited appropriate rates of electron transfer, wide working potential window (ca. 3.7 V in KCl), and low capacitance. Specifically, the boronated films produced high heterogenous rate constant (k), the lowest double layer capacitance (Cdl), and a consequentially smaller RC time constant than BDD and GC. Incorporating boron into undoped and nitrogenated ta-C films stabilizes the formation of sp3 bonded content during deposition leading to films with a smoother surface and increased hardness. It is shown that the B-incorporated films exhibit no compromise in their electrochemical performance despite the increase in sp3 content. Due to its versatile nature, ta-C stands out as a material with a wide range of tunable properties for various applications.

Insights into RC time curve fit analysis of pulmonary artery pressure decay

The notion of a constant relationship between resistance and capacitance (RC time) in the pulmonary circulation has been challenged by more recent research. The RC time can be obtained using either a simplified empirical approach or a semilogarithmic equation. Although direct curve-fit analysis is a feasible and ostensibly reference approach for RC analysis, it remains largely unexplored. We aimed to study the relationship between various RC methods in different states of pulmonary hemodynamics.Methods In total, 182 patients underwent clinically indicated right heart catheterization. The pressure curves were exported and processed using the MATLAB software. We calculated the RC time using the empirical method (RCEST), semilogarithmic approach (RCSL), and direct measurement of curve fit (RCFIT).Results Among 182 patients, 137 had pulmonary hypertension due to left heart disease (PH-LHD), 35 had pulmonary arterial hypertension (PAH), and 10 demonstrated normal hemodynamics (non-PH). RCEST consistently overestimated the RCFIT and RCSL measurements by a mean of 75%. With all three methods, the RC values were longer in the PAH (RCFIT = 0.36 ± 0.14 s) than in the PH-LHD (0.27 ± 0.1 s) and non-PH (0.27 ± 0.09 s) groups (p < 0.001). Although the RCSL and RCFIT values were similar among the three subgroups, they exhibited broad limits of agreement. Finally, the RCEST demonstrated a strong discriminatory ability (AUC = 0.86, p < 0.001, CI = 0.79–0.93) in identifying PAH.Conclusion RC time in PAH patients was substantially prolonged compared to that in PH-LHD and non-PH patients. The use of the empirical formula yielded systematic RC overestimation. In contrast, the semilogarithmic analysis provided reliable RC estimates, particularly for group comparisons.

On the realization of an amplifier‐tuned low/high frequency family of oscillators

SummaryWe propose a family of equal‐R equal‐C dual amplifier oscillators with gain‐tunable start‐up condition and oscillation frequency. In particular, while one of the amplifiers can be used to satisfy the oscillator start‐up condition, the second amplifier can be used to tune the oscillation frequency. In this regard, it is observed that the oscillation frequency can be made very low or very high independent of the RC time constant of the circuit by properly choosing the amplifier gain and the circuit topology. In one possible topology, the oscillation frequency is directly proportional to the tuning amplifier gain, while in a second topology, it is inversely proportional to this gain. Both topologies generate two outputs which also have a gain‐tunable leading or lagging phase shift. Circuit simulations and experimental results are presented to verify the theory in addition to a non‐conventional application in chaos generation.

Nanostructured Black Silicon as a Stable and Surface-Sensitive Platform for Time-Resolved In Situ Electrochemical Infrared Absorption Spectroscopy.

Attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is a powerful method for probing interfacial chemical processes. However, SEIRAS-active nanostructured metallic thin films for the in situ analysis of electrochemical phenomena are often unstable under biased aqueous conditions. In this work, we present a surface-enhancing structure based on etched black Si internal reflection elements with Au-coatings for in situ electrochemical ATR-SEIRAS. Using electrochemical potential-dependent adsorption and desorption of 4-methoxypyridine on Au, we demonstrate that black Si-based substrates offer advantages over commonly used structures, such as electroless-deposited Au on Si and electrodeposited Au on ITO-coated Si, due to the combination of high stability, sensitivity, and conductivity. These characteristics are especially valuable for time-resolved measurements where stable substrates are required over extended times. Furthermore, the low sheet resistance of Au layers on black Si reduces the RC time constant of the electrochemical cell, enabling a significantly higher time resolution compared to that of traditional substrates. Thus, we employ black Si-based substrates in conjunction with rapid- and step-scan Fourier transform infrared (FTIR) spectroscopy to investigate the adsorption and desorption kinetics of 4-methoxypyridine during in situ electrochemical potential steps. Adsorption is shown to be diffusion-limited, which allows for the determination of the mean molecular area in a fully established monolayer. Moreover, no significant changes in the peak ratios of vibrational modes with different orientations relative to the molecular axis are observed, suggesting a single adsorption mode and no alteration of the average molecular orientation during the adsorption process. Overall, this study highlights the enhanced performance of black Si-based substrates for both steady-state and time-resolved in situ electrochemical ATR-SEIRAS, providing a powerful platform for kinetic and mechanistic investigations of electrochemical interfaces.

Grain-size adjustment in Hf0.5Zr0.5O2 ferroelectric film to improve the switching time in Hf0.5Zr0.5O2-based ferroelectric capacitor

By adjusting the rising time in annealing ferroelectric HfO2-based films, the grain size of the film can be controlled. In this study, we found that increasing the rising time from 10 to 30 s at an annealing temperature of 700 °C in N2 atmosphere resulted in improved ferroelectric switching speed. This is because the larger grain size reduces the internal resistance components, such as the grain bulk resistance and grain boundary resistance, of the HZO film. This in turn lowers the overall equivalent resistance. By minimizing the RC time constants, increasing the grain size plays a key role in improving the polarization switching speed of ferroelectric films.

Abstract 15854: Pulmonary Arterial Waveform Analysis and Supervised Machine Learning Predicts Outcomes in Heart Failure: An Analysis of the CHAMPION Trial

Introduction: Pulmonary artery (PA) pressure monitors have been shown to prevent hospitalizations in heart failure patients using mean pressure values. PA waveform analysis offers an overall assessment of right ventricular load that combines resistance and compliance. Hypothesis: We hypothesised that clinical outcomes can be predicted from PA waveform analyses from patients with an implanted PA monitor. Methods: The CHAMPION trial database was analysed. Information about the demographics and data collection methods for this cohort have been published previously. All waveforms were analysed automatically using Python. Tau or RC time, respiratory rate, respiratory range, P asymptote, mean pulmonary arterial pressure (mPAP), diastolic pulmonary arterial pressure (dPAP) and systolic pulmonary arterial pressure (sPAP) were derived from the raw waveforms. Tau and P asymptote were calculated using phase plane analysis. Outcomes of hospitalization or mortality were adjudicated as part of the original trial. Statistics were performed in R. A decision tree statistical approach using the XGBoost algorithm was used. Contribution to the model was assessed using Shapley Additive Explanations (SHAP) values. The dataset was split into 70% train and 30% test sets. Results: 296,948 PA pressure traces from 547 patients were analysed. 3 patients had insufficient quality of trace to analyse. There were 1340 outcome events throughout the follow up period, median 664 days. The trained algorithm was able to predict clinical outcomes in the test dataset with 100% accuracy. The most significant contributors according the mean SHAP value were RC time (SHAP = 1.1), respiratory range (SHAP = 1.1) and heart rate (SHAP = 1.1). Conclusions: Detailed analysis of the PA waveform from PA pressure monitors is feasible and yields clinically relevant information. A supervised machine learning algorithm trained on this data can accurately predict hospitalization or mortality events in heart failure patients.

Second harmonic generation as a probe of structure and dynamics of ionic liquids at the electrode interface

Electrochemical second harmonic generation (ESHG) has been applied as a probe of the slow dynamics in the electric double layer (EDL) at the ionic liquid (IL)/Au interface. When the electrode potential was stepped, the SHG signal from the interface was relaxed on the time scale longer than tens of seconds, which is distinctively slower than the RC time constant of the cell. This ultraslow relaxation in ESHG was quantitatively analyzed and discussed for several ILs, revealing that the ultraslow relaxation itself is a common phenomenon for the EDL in the ILs studied but the asymmetry of the time constants to the potential-step directions depends on the IL ions, which is likely to reflect the structure ordering of the interfacial ionic layer in the EDL depending on both ILs and the potential. The EDL structure in equilibrium has also been investigated via SHG measurements with a potential scan at a sufficiently slow rate; the potential dependence of the SHG signal was found to deviate from a simple parabolic one, reflecting the camel-shaped static differential capacitance for the EDL in ILs.

Retinomorphic Motion Detector Fabricated with Organic Infrared Semiconductors.

Organic retinomorphic sensors offer the advantage of in-sensor processing to filter out redundant static backgrounds and are well suited for motion detection. To improve this promising structure, here, the key role of interfacial energetics in promoting charge accumulation to raise the inherent photoresponse of the light-sensitive capacitor is studied. Specifically, incorporating appropriate interfacial layers around the photoactive layer is crucial to extend the carrier lifetime, as confirmed by intensity-modulated photovoltage spectroscopy. Compared to its photodiode counterpart, the retinomorphic sensor shows better detectivity and response speed due to the additional insulating layer, which reduces the dark current and the RC time constant. Lastly, three retinomorphic sensors are integrated into a line array to demonstrate the detection of movement speed and direction, showing the potential of retinomorphic designs for efficient motion tracking.

Measuring carrier diffusion in MAPbI3 solar cells with photocurrent-detected transient grating spectroscopy.

Conventional time-of-flight methods can be used to determine carrier mobilities for photovoltaic cells in which the transit time between electrodes is greater than the RC time constant of the device. To measure carrier drift on sub-ns timescales, we have recently developed a two-pulse time-of-flight technique capable of detecting drift velocities with 100-ps time resolution in perovskite materials. In this method, the rates of carrier transit across the active layer of a device are determined by varying the delay time between laser pulses and measuring the magnitude of the recombination-induced nonlinearity in the photocurrent. Here, we present a related experimental approach in which diffractive optic-based transient grating spectroscopy is combined with our two-pulse time-of-flight technique to simultaneously probe drift and diffusion in orthogonal directions within the active layer of a photovoltaic cell. Carrier density gratings are generated using two time-coincident pulse-pairs with passively stabilized phases. Relaxation of the grating amplitude associated with the first pulse-pair is detected by varying the delay and phase of the density grating corresponding to the second pulse-pair. The ability of the technique to reveal carrier diffusion is demonstrated with model calculations and experiments conducted using MAPbI3 photovoltaic cells.

Role of Proportion of Surrounding Gate on the Improved Transient Behavior of MIS Tunnel Diode with Ultra-Thin Metal Surrounded Gate (UTMSG)

Metal-Insulator-Semiconductor tunnel diodes (MISTD) are widely used in modern integrated circuits, and have shown the potential in dynamic memory [1], [2]. To recognize the memory states more easily, efforts should be made to enhance the transient behavior. Recently, MISTD with ultra-thin metal surrounded gate (UTMSG) had been proposed in [3] and [4], presenting improved transient current and transient capacitance. In this work, we further modulated the proportion of surrounding gate, S, and found increased transient behavior for larger S.Fig. 1(a) and (b) illustrate the structure of UTMSG and planar MISTD, respectively. For UTMSG, the total gate is composed of a thick metal center gate and a resistive thin metal surrounding gate. Fig. 2 shows the process flow and the anodic oxidation system. For UTMSG, after defining the center gate by photolithography, dilute nitric acid was used to form a very thin aluminum oxide layer on the edge. 10 nm Al was then evaporated as the resistive surrounding gate. Table 1 lists the detailed parameters and the proportion of surrounding gate, S. Fig. 3(a) shows the transient read currents for UTMSG and planar, with inset illustrated the voltage program. Fig. 3(b) shows the read currents extracted at 40 ms under different read voltages after a 2 V write pulse. All UTMSG show larger transient current than planar. Besides, UTMSG with larger S would have better performance. The reason could be explained by Fig. 3(c). The insulating aluminum oxide interlayer and the resistive thin metal surrounding gate together result in a distributed resistance, leading to an RC time delay during voltage switching. During read, the electrons stored under the surrounding gate would take longer to response. Therefore, larger current could be read out, due to the edge late response. Consequently, more electrons would be delayed for larger S, and larger transient current would be expected.Fig. 4(a) and (b) show the AC signal model and the reverse-bell shape capacitance-voltage (C-V) characteristics of UTMSG, which were discussed in detail in previous work [5]. When Rsi, determined by the electron density under gate, is small enough such that the cut-off frequency 1/2πRsiCs,o is larger than the AC frequency, Cs,o could be read out. Fig. 5 shows the frequency dispersion of C-V curves. For lower frequencies, lower VG is needed for the AC signal to pass through.Fig. 6(a) shows the 10kHz C-V curves, on which ± 0.5 V voltage pulse were performed to read out two capacitance states. Fig. 6(b) shows the transient capacitance read at 0 V. When switching from + 0.5 V to 0 V, excess electron would be stored under gate initially. To balance the gate voltage, depletion region would shrink and high capacitance state would be measured, which would be more significant for UTMSG due to more delay of electron. For UTMSG at – 0.5 V and 0 V, depletion capacitance under center gate Cs,i and under total gate Cs,i + Cs,o would be read out, respectively. This means after applying a - 0.5 V pulse and then read at 0 V, UTMSG devices would experience a larger change of capacitance. Moreover, since the capacitance at - 0.5 V is lower for UTMSG with larger S, the change of capacitance would be larger. The two state capacitance windows measured at 30 ms are shown in Fig. 6(c), where larger capacitance window could be observed for UTMSG with larger S. Finally, the capacitances when sweeping voltage forwardly and backwardly and the separation between them were shown in Fig. 7(a) and (b) for UTMSG and planar devices. All UTMSG show larger separations, which further confirms the improved transient capacitance window observed in Fig. 6.In conclusion, transient behavior could be further improved by increasing the proportion of surrounding gate in UTMSG MISTD, and 17x read current and 14x capacitance window could be measured. The discovery in this work might be beneficial for the future dynamic memory design.Acknowledgement: This work was supported by the Ministry of Science and Technology of Taiwan, ROC, under Contract No. MOST 111-2221-E-192-MY3 and NSTC 111-2622-8-002-001[1] M. A. Green, F.D. King and J. Shewchun, Solid-State Electronics, 17, 6, pp. 551-561, (1974).[2] S.-W. Huang and J.-G. Hwu, IEEE Trans. on Electron Dev., 68, 12, pp. 6580-6585 (2022).[3] K.-H. Tseng, C -S. Liao and J. -G. Hwu, IEEE Trans. on Nanotech., 16, 6, pp. 1011-1015, (2017).[4] C.-D. Lin and J.-G. Hwu, ECS Trans., 85, 51, (2018).[5] S.-W. Huang and J.-G. Hwu, IEEE J. of the Electron Devices Soc., 9, pp. 1041-1048, (2021). Figure 1

Capacitance characterization of graphene/n-Si Schottky junction solar cell with MOS capacitor

Abstract We have demonstrated a simple and accurate method for characterizing the capacitance of Graphene/n-Si Schottky junction solar cells (GSSCs) which embed the metal-oxide-semiconductor (MOS) capacitor. We measured two types of GSSCs, one with thermal annealing treatments (w-a) and one without (wo-a). It was found that the wo-a GSSC exhibits a two-step feature in the phase versus forward bias voltage relationship, which may be attributed to the presence of polymethyl methacrylate residues. By considering the capacitance of the MOS capacitor (Cmos) and its standard deviation, we successfully obtained the capacitance of the Schottky junction (CSch), and evaluated meaningful built-in potentials (Schottky barrier heights) which are 0.51 V (0.78 eV) and 0.47 V (0.75 eV) for the w-a and wo-a GSSCs, respectively, by the Mott–Schottky analysis. We also briefly discuss the relationship between CSch and the Nyquist and Bode plots, finding that the RC time constant decreases due to the subtraction of Cmos.

Measurements of variable capacitance using single port radio frequency reflectometry

A radio frequency (RF) reflectometry technique is presented to measure device capacitances using a probe station. This technique is used to characterize micro-electromechanical system (MEMS) variable capacitor devices that can be connected to create pull-up and pull-down networks used in digital gates for reversible computing. Adiabatic reversible computing is a promising approach to energy-efficient computing that can dramatically reduce heat dissipation by switching circuits at speeds below their RC time constants, introducing a trade-off between energy and speed. The variable capacitors in this study will be measured using single port RF reflectometry achieved with a custom-made RF probe. The RF probe consists of a micromanipulator with an on-board matching network and is calibrated by measuring a capacitive bank that shows a clearly visible frequency shift with the increase in capacitance. The RF probe worked well when measuring static capacitors with no parasitic resistance; however, the frequency shift is masked when measuring the MEMS variable capacitors due to their high in-series parasitic resistance (around 80 kΩ). Therefore, RF reflectometry has the potential to measure MEMS variable capacitors in the range of 0–30 fF when not masked by a high in-series parasitic resistance, creating a fast and versatile method for characterizing variable capacitors that can be used in energy-efficient computing.

High-Performance Normal-Incidence Ge/Si Meta-Structure Avalanche Photodetector

A high-speed and high-sensitivity avalanche photodetector (APD) is a critical component of a high-data-rate and low-power optical-communication link. In this paper, we study a high-speed and high-efficiency Ge/Si heterostructure APD. First, we numerically study the speed performance of the APD by analyzing frequency response. An optimized epitaxial structure of the high-speed APD is designed. In the absence of RC time effects, the APD exhibits a fast pulse response (full-width at half-maximum) of 10 ps and a high 3 dB bandwidth of 33 GHz at a high-gain value of 10. Taking device size and the corresponding RC time effects into account, the APD still achieves a high 3 dB bandwidth of 29 GHz at a gain value of 10. Moreover, a novel subwavelength periodic hole array is designed on the normal-incidence APD for enhancing light absorption without sacrificing speed performance. Near-perfect absorption is almost achieved by an infinite-period hole array due to the coupling of dual-resonance modes. A high-absorption efficiency of 64% is obtained by a limited-sized hole array in the high-speed APD. This work provides a promising method to design high-speed and high-efficiency normal-incidence Ge/Si heterostructure APDs for optical interconnect systems.

A Reactive Power Injection Algorithm for Improving the Microgrid Operational Reliability

Stand-alone microgrids have become reliable and efficient solutions for remote areas and critical infrastructures. However, the converters within these microgrids experience long-term complex power fluctuations caused by random variations in micro sources and loads. These power fluctuations induce thermal cycling in semiconductor chips, leading to thermal fatigue failure and compromising the safety and reliability of both the converter and microgrid operation. To address this issue, this paper proposes a reactive power injection algorithm aimed at reducing the output power fluctuation of the converter. The algorithm implements reactive power injection at the converter control level, thereby restructuring the output power profile and resulting in reduced junction temperature fluctuations in IGBTs. This approach effectively mitigates thermal stress within the material layers of the module, extending the lifetime of power devices and improving the operational reliability of the microgrid. The algorithm implementation is based on the PQ control strategy, integrating the power triangle with the envelope detection technique. Furthermore, the lifetime prediction process utilizes the electro-thermal coupling model, the rainflow counting algorithm, and the Lesit model. Simulation results demonstrate that, for an active power fluctuation range of 10 kW to 80 kW and an equivalent RC time constant of 22.5 s, the algorithm achieves a significant reduction of 62.64% in the amplitude of output power fluctuation and extends the lifetime of power devices by 74.13%. The obtained data showcase the effectiveness of the algorithm in enhancing the lifetime of power devices and further improving the microgrid operational reliability under specific parameter conditions.

Bandwidth Analysis of High-Speed InGaN Micro-LEDs by an Equivalent Circuit Model

High-speed light-emitting diodes (LEDs) are ideal light sources for low-cost plastic optical fiber communication in data-centers and vehicles. Here, high-speed micro-LEDs based on InGaN quantum dot (QD) active region with different diameters are fabricated and characterized. The -3dB bandwidth around 3.6 GHz and 1.4 GHz are achieved in the blue and green micro-LEDs under current density less than 1 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, which can work at an environmental temperature of 125 °C. An equivalent circuit model is proposed to analyze the limiting factors of the bandwidth, using which the effects of carrier recombination and RC time constant on modulation bandwidth are separated. It is found that carrier recombination rate is fast enough and the RC constant is still the main limiting factor for the blue micro-LEDs at an injection current density of more than 500 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> even when the diameter scales down to 20 μm, while the recombination rate mainly limits the bandwidth of the green micro-LEDs.

(738) The Effect of Acute Alterations in Left Atrial Pressure on Rc Time in the Pulmonary Circulation

(738) The Effect of Acute Alterations in Left Atrial Pressure on Rc Time in the Pulmonary Circulation

Transient Photocurrent From High-Voltage Vertical GaN Diodes Irradiated With Electrons: Experiments and Simulations

Radiation-hard high-voltage vertical GaN p-n diodes are being developed for use in power electronics subjected to ionizing radiation. We present a comparison of the measured and simulated photocurrent response of diodes exposed to ionizing irradiation with 70 keV and 20 MeV electrons at dose rates in the range of 1.4x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> - 5.0x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> rad(GaN)/s. The simulations correctly predict the trend in measured steady-state photocurrent and agree with experimental results within a factor of 2. Furthermore, simulations of the transient photocurrent response to dose rates with uniform and non-uniform ionization depth profiles uncover the physical processes involved that cannot be otherwise experimentally observed due to orders of magnitude larger RC time constant of the test circuit. The simulations were performed using an Exploratory Physics Development code developed at Sandia National Laboratories. The code offers the capability to include defect physics under more general conditions, not included in commercially available software packages, extending the applicability of the simulations to different types of radiation environments.

Effect of dielectric target properties on plasma surface ionization wave propagation

Surface ionization waves (SIWs) propagating along dielectric covered, grounded surfaces have been studied for various dielectric bulk and surface conditions; a dependence on the propagation velocity with respect to dielectric electrical thickness and near surface permittivity profiles are observed. SIWs generated by an atmospheric pressure plasma source are imaged interacting with planar dielectric surface. Surface wave velocity is obtained by tracking emission intensity as a function of time. Target dielectric thickness is varied from mm and dielectric constant is varied from . The propagation of SIWs can be generally predicted by relating their velocity to the RC time constant of the circuit generated between the plasma and the dielectric surface, but it is found that this approximation breaks down for dielectric substrates of sufficient thickness and wave velocity becomes constant. The results show that wave velocity is stable and predictable for target thicknesses beyond a certain point determined by the permittivity of the target material. It is also shown that SIW propagation is strongly driven by the dielectric material near to the surface of the target in addition to the bulk material. The possible mechanisms driving these thickness dependent behaviors is discussed.