High-speed Charge Research Articles

New Magnetically Recyclable Reduced Graphene Oxide rGO/MFe2 O4 (M= Ca, Mg)/Ag3 PO4 Nanocomposites With Remarkably Enhanced Visible-light Photocatalytic Activity and Stability.

New magnetically separable CaFe2 O4 /Ag3 PO4 , MgFe2 O4 /Ag3 PO4 , rGO/CaFe2 O4 /Ag3 PO4 and rGO/MgFe2 O4 /Ag3 PO4 photocatalysts were synthesized by the hydrothermal and ion-exchange deposition method. These four types of photocatalyst were used for degradation of Methylene blue (MB), Methyl orange (MO) and 4-chlorophenol (4-CP) in aqueous solution under visible-light illumination. The optimized photocatalyst, i.e. rGO/CaFe2 O4 /Ag3 PO4 with a mass ratio of (1:3:9) composite not only shows the highest photocatalytic performance for the degradation of MB, MO and 4-CP under visible light irradiation among the other synthesized photocatalysts but also exhibits high reusability and stability for at least five cycles. It was found that the impressive separation of electron-hole pairs as well as presence of rGO sheets which act as a high speed charge transfer were responsible for increasing photocatalytic activity over the optimized photocatalyst under visible-light irradiation. A possible mechanism for the increased photocatalytic activity of the rGO/CaFe2 O4 /Ag3 PO4 with a mass ratio of (1:3:9) composite was discussed in detail.

Design and analysis of low-power high-speed shared charge reset technique based dynamic latch comparator

Circuit intricacy, high-speed, low-power, small area requirement, and high resolution are crucial factors for high-speed and low-power applications like analog-to-digital converters (ADCs). The delay analysis of classical dynamic latch comparators is presented to add more insight of their design parameters, which effects the performance parameter. In this research, a new architecture of dynamic latch comparator is presented, which is able to provide high-speed, consumes low-power and requires smaller die area. The proposed comparator benefits from a new shared charge logic based reset technique to achieve high-speed with low-power consumption. It is shown by simulation and analysis that the delay time is significantly reduced compared to a conventional dynamic latched comparator. The proposed circuit is designed and simulated in 90 nm CMOS technology. The results show that, for the proposed comparator, the delay is 51.7 ps and consumes only 33.62 μW power, at 1 V supply voltage and 1 GHz clock frequency. In addition, the proposed dynamic latch comparator has a layout size of 7.2μm × 8.1μm.

A Distance Measurement Method Using A Time-of-Flight CMOS Range Image Sensor with 4-Tap Output Pixels and Multiple Time-Windows

In this study, advanced range measurement method using a TOF sensor with 4-tap output pixels and small-duty short light pulse is presented. A CMOS TOF range imager with pinnedphotodiode high-speed charge modulator pixels using lateral electric field (LEF) control has been implemented by a 0.11-μm CIS process with high near infrared sensitivity. In order to improve the range resolution while maintaining the measurable range, multiple time-windows are used for range measurements. Compared with the conventional single time window, the use of N time-windows theoretically improve the range resolution by a factor of N1.5 if the back ground light shot noise is dominant. In the measurement for N=2, the range resolution is improved by a factor of 2.8 compared with the case of N=1 while maintaining the same distance range.

Label-Free Biomedical Imaging Using High-Speed Lock-In Pixel Sensor for Stimulated Raman Scattering.

Raman imaging eliminates the need for staining procedures, providing label-free imaging to study biological samples. Recent developments in stimulated Raman scattering (SRS) have achieved fast acquisition speed and hyperspectral imaging. However, there has been a problem of lack of detectors suitable for MHz modulation rate parallel detection, detecting multiple small SRS signals while eliminating extremely strong offset due to direct laser light. In this paper, we present a complementary metal-oxide semiconductor (CMOS) image sensor using high-speed lock-in pixels for stimulated Raman scattering that is capable of obtaining the difference of Stokes-on and Stokes-off signal at modulation frequency of 20 MHz in the pixel before reading out. The generated small SRS signal is extracted and amplified in a pixel using a high-speed and large area lateral electric field charge modulator (LEFM) employing two-step ion implantation and an in-pixel pair of low-pass filter, a sample and hold circuit and a switched capacitor integrator using a fully differential amplifier. A prototype chip is fabricated using 0.11 μm CMOS image sensor technology process. SRS spectra and images of stearic acid and 3T3-L1 samples are successfully obtained. The outcomes suggest that hyperspectral and multi-focus SRS imaging at video rate is viable after slight modifications to the pixel architecture and the acquisition system.

Automated Dielectrophoretic Tweezers-Based Force Spectroscopy System in a Microfluidic Device.

We reported an automated dielectrophoretic (DEP) tweezers-based force spectroscopy system to examine intermolecular weak binding interactions, which consists of three components: (1) interdigitated electrodes and micro-sized polystyrene particles used as DEP tweezers and probes inside a microfluidic device, along with an arbitrary function generator connected to a high voltage amplifier; (2) microscopy hooked up to a high-speed charge coupled device (CCD) camera with an image acquisition device; and (3) a computer aid control system based on the LabVIEW program. Using this automated system, we verified the measurement reliability by measuring intermolecular weak binding interactions, such as hydrogen bonds and Van der Waals interactions. In addition, we also observed the linearity of the force loading rates, which is applied to the probes by the DEP tweezers, by varying the number of voltage increment steps and thus affecting the linearity of the force loading rates. This system provides a simple and low-cost platform to investigate intermolecular weak binding interactions.

Preparation of 2D/2D g-C3N4 nanosheet@ZnIn2S4 nanoleaf heterojunctions with well-designed high-speed charge transfer nanochannels towards high-efficiency photocatalytic hydrogen evolution

In this work, we design and construct a novel 2D/2D g-C3N4 nanosheet@ZnIn2S4 nanoleaf via a simple one-step surfactant-assisted solvothermal method for photocatalytic H2 generation. Its unusual 2D/2D heterojunction structure provides far more contact areas and much faster charge transport rate than the 2D/0D heterojunction structure of g-C3N4 nanosheet@ZnIn2S4 microsphere. More importantly, this unique 2D/2D heterojunction leads the g-C3N4 nanosheet@ZnIn2S4 nanoleaf composite to generate numerous intimate high-speed charge transfer nanochannels in the interfacial junctions, and which could considerably enhance the photogenerated charge separation and migration efficiency, thus yielding a remarkable visible-light-driven H2 evolution rate without the additive Pt cocatalyst (HER=2.78mmolh−1g−1), nearly 69.5, 15.4, 8.2 and 1.9 times higher than that of pure g-C3N4 nanosheet, pure ZnIn2S4 microsphere, 2D/0D g-C3N4 nanosheet@ZnIn2S4 microsphere and pure ZnIn2S4 nanoleaf, respectively. Additionally, the 2D/2D g-C3N4 nanosheet@ZnIn2S4 nanoleaf exhibits an outstanding stability and recyclability, manifesting a promising potential application in sustainable energy conversion. This work would provide a platform for the design and synthesis of binary heterojunction composite system with highly-efficient charge separation and transfer.

Construction of an all-solid-state artificial Z-scheme system consisting of Bi2WO6/Au/CdS nanostructure for photocatalytic CO2 reduction into renewable hydrocarbon fuel

An all-solid-state Bi2WO6/Au/CdS Z-scheme system was constructed for the photocatalytic reduction of CO2 into methane in the presence of water vapor. This Z-scheme consists of ultrathin Bi2WO6 nanoplates and CdS nanoparticles as photocatalysts, and a Au nanoparticle as a solid electron mediator offering a high speed charge transfer channel and leading to more efficient spatial separation of electron–hole pairs. The photo-generated electrons from the conduction band (CB) of Bi2WO6 transfer to the Au, and then release to the valence band (VB) of CdS to recombine with the holes of CdS. It allows the electrons remaining in the CB of CdS and holes in the VB of Bi2WO6 to possess strong reduction and oxidation powers, respectively, leading the Bi2WO6/Au/CdS to exhibit high photocatalytic reduction of CO2, relative to bare Bi2WO6, Bi2WO6/Au, and Bi2WO6/CdS. The depressed hole density on CdS also enhances the stability of the CdS against photocorrosion.

60 V tolerance full symmetrical switch for battery monitor IC**Project supported by the National Natural Science Foundation of China (No. 61334003).

For stacked battery monitoring IC high speed and high precision voltage acquisition requirements, this paper introduces a kind of symmetrical type high voltage switch circuit. This kind of switch circuit uses the voltage following structure, which eliminates the leakage path of input signals. At the same time, this circuit adopts a high speed charge pump structure, in any case the input signal voltage is higher than the supply voltage, it can fast and accurately turn on high voltage MOS devices, and convert the battery voltage to an analog to digital converter. The proposed high voltage full symmetry switch has been implemented in a 0.18 μm BCD process; simulated and measured results show that the proposed switch can always work properly regardless of the polarity of the voltage difference between the input signal ports and an input signal higher than the power supply.

A Lateral Electric Field charge Modulator with Bipolar-gates for Time-resolved Imaging

This paper reports high time-resolved imaging technique using a lateral electric field charge modulator with bipolar-gates. The proposed pixel structure achieved high time-resolved signal detection by using negative bias effect by work function difference between the p-type gate and p-substrate. The test chip fabricated in 0.11 um CIS technology demonstrates the high-speed charge modulation, and the modulation contrast is measured to be 97%.

In-cylinder combustion visualization of Jatropha straight vegetable oil and mineral diesel using high temperature industrial endoscopy for spatial temperature and soot distribution

Endoscopic optical visualization technique is reliable for investigations in harsh environments such as IC engine combustion chambers. In this study, high temperature industrial endoscopy was employed to a production grade diesel engine for optical diagnostics of in-cylinder combustion. Engine cylinder-head was suitably modified for visual access of combustion. Combustion characteristics such as in-cylinder pressure, heat release rate (HRR), start of combustion (SoC), combustion duration (CD), etc., for Jatropha straight vegetable oil (SVO) and mineral diesel were investigated using Industrial endoscope, which can withstand such harsh environment. In-cylinder combustion images were recorded using a high-speed charge coupled device (CCD) camera. Recorded images were corrected using calibration tool to remove endoscopic lens distortions (spherical aberration). Spatial soot and flame temperature distributions were analysed from the corrected combustion images using soot analysis and correlated colour temperature (CCT) methods. Spatial soot and temperature distributions for the test fuels indicated that luminous regions in the combustion chamber were the prime locations for soot formation. These regions also indicated peak temperature zones in the field of view. This study is unique, where in-situ combustion characteristics were determined for SVO and baseline diesel using endoscopic visualization. This study generated valuable information about in-cylinder spatial combustion of SVO, which can be utilized for combustion and emission optimization of SVO fuelled engines.

A Stimulated Raman Scattering CMOS Pixel Using a High-Speed Charge Modulator and Lock-in Amplifier.

A complementary metal-oxide semiconductor (CMOS) lock-in pixel to observe stimulated Raman scattering (SRS) using a high speed lateral electric field modulator (LEFM) for photo-generated charges and in-pixel readout circuits is presented. An effective SRS signal generated after the SRS process is very small and needs to be extracted from an extremely large offset due to a probing laser signal. In order to suppress the offset components while amplifying high-frequency modulated small SRS signal components, the lock-in pixel uses a high-speed LEFM for demodulating the SRS signal, resistor-capacitor low-pass filter (RC-LPF) and switched-capacitor (SC) integrator with a fully CMOS differential amplifier. AC (modulated) components remained in the RC-LPF outputs are eliminated by the phase-adjusted sampling with the SC integrator and the demodulated DC (unmodulated) components due to the SRS signal are integrated over many samples in the SC integrator. In order to suppress further the residual offset and the low frequency noise (1/f noise) components, a double modulation technique is introduced in the SRS signal measurements, where the phase of high-frequency modulated laser beam before irradiation of a specimen is modulated at an intermediate frequency and the demodulation is done at the lock-in pixel output. A prototype chip for characterizing the SRS lock-in pixel is implemented and a successful operation is demonstrated. The reduction effects of residual offset and 1/f noise components are confirmed by the measurements. A ratio of the detected small SRS to offset a signal of less than 10−5 is experimentally demonstrated, and the SRS spectrum of a Benzonitrile sample is successfully observed.

A Time-of-Flight CMOS Range Image Sensor Using 4-Tap Output Pixels with Lateral-Electric-Field Control

This paper presents a 160×240-pixel CMOS Time-of-Flight (TOF) range imager with a 4-tap charge modulator using pinned-photodiode high-speed lock-in pixels in a 0.11μm CIS process. The proposed lock-in pixel structure using lateral electric field (LEF) control is suitable for implementing a multiple-tap charge modulator while achieving high-speed charge transfer for high time resolution. A CMOS TOF range imager with the multiple-tap charge modulators is expected to have background light cancelling capability in one frame and to improve range resolution with shifted short double light pulses. In this paper, we report the design, implementation and evaluation results of the TOF range imager using the 4-tap LEF modulator (LEFM). The TOF range imager has a range resolution of less than 3.2mm for the range from 1.0m to 2.0m at the frame rate of 15.7fps.

Observation of Impact Ionization of Shallow States in Sub-Kelvin, High-Purity Germanium

We report on the observation of impact ionization processes involving shallow impurity states in a sub-Kelvin, high-purity n-type germanium detector similar to those used by direct detection dark matter experiments such as the Cryogenic Dark Matter Search. An optical fiber is used to generate packets of charge carriers near one surface of the detector. The charge carriers drift to the opposite surface by application of an electric field. The resulting drift current is measured by a high-speed charge amplifier. The onset of impact ionization for both electron and hole transport is clearly observed in the drift current as the applied electric field is increased above \(\approx \)5 V/cm. We present the effective charge collection efficiency and trapping length as a function of applied electric field for electrons and holes. We estimate the impact ionization cross section to be on the order of \(5\times 10^{-13}\,\mathrm {cm}^2\).

Phase-shifting interferometer with pulse modulation based on a downsampling technique

A phase-shifting interferometer that uses pulse modulation and downsampling is proposed and demonstrated. Pulse modulation is a direct modulating technique that realizes a rapid, large change in the wavelength of a laser diode with a constant optical power. For instance, an interference signal of 10 kHz is observed after the injection of pulse current. However, an expensive high-speed charge coupled device (CCD) camera is required to acquire a high-speed interference signal. If we consider a periodical signal, the same waveform repeats at every period. Therefore, the signal varying with high frequency can be captured by a low-frequency sampling pulse. This signal processing technique, the so-called downsampling, enables us to acquire rapid interference signals with a standard CCD camera. The experimental results using a flat mirror and a concave mirror showed measurement errors of 10 and 28 nm in root mean square (RMS), respectively. The repeatability of the experimental result between the first and the second is 13 nm in RMS.

A Time-of-Flight Range Image Sensor With Background Canceling Lock-in Pixels Based on Lateral Electric Field Charge Modulation

This paper presents a CMOS time-of-flight (ToF) range image sensor using high-speed lock-in pixels with background light canceling capability. The proposed lock-in pixel uses MOS gate-induced lateral electric field control of depleted potential of pinned photodiode for implementing a multiple-tap charge modulator while achieving a high-speed charge transfer for high-time resolution. A TOF image sensor with 320 x 240 effective pixels is implemented using a 0.11-μm CMOS image sensor process. The TOF sensor has a range resolution of less than 12 mm without background light and 20 mm under background line for the range from 0.8 to 1.8 m and integration time of 50 ms. The effectiveness of in-pixel background light canceling with a three-tap output pixel is demonstrated.

Linear Tunable Analog Front-End Electronics for Silicon Charged-Particle Detectors

A linear front-end electronic system based on a high-speed charge sensitive amplifier and a tunable shaping amplifier suitable for silicon detectors has been presented. The designed charge sensitive amplifier features simplicity and compactness. It is based on the combination of a low-noise field-effect transistor input device and a current feedback opamp ensuring high frequency and small rise time. The circuit provides both an energy signal and a timing signal. The shaping amplifier is a fifth-order complex filter based on an opamp- RC topology providing a nearly Gaussian response. The shaper also includes a pole-zero cancellation circuit and a base line restorer to preclude the pileup of subsequent input signals. A control system has been developed to adjust the main parameters of the channel. The designed readout channel has been optimized for a medium energy range up to 50 MeV coupled to silicon detectors up to 100 pF. Its feasibility for nuclear physics applications has been experimentally validated.

DC Ionizer With Opposed $\phi$-Type Corona Electrodes for High-Speed Charge Elimination

The corona-type ionizer supplies air flow including positive and negative corona ions for the elimination of electrostatic charges on a charged target. DC ionizers placed close to the charged target are proposed to shorten the charge-elimination time. The ionizer is composed of a grounded mesh electrode and opposed positive and negative needle electrodes. Opposed φ-type electrodes are also evaluated to improve the ionizer performance. A strong electric field can be formed between the grounded mesh and the charged target; therefore, the ion drag force due to the electric field becomes dominant and plays an important role in charge elimination with this technique. A charge-elimination model that introduces a simplified charge-elimination current is also proposed to evaluate ionizer performance. The charge-elimination performance of the ionizer with opposed φ-type electrodes was much better than that with opposed needle electrodes.

Hierarchical Design for Fabricating Cost‐Effective High Performance Supercapacitors

The salient feature of a supercapacitor is its ability to deliver much higher power density than a battery. A hierarchical design and a cost‐effective approach to fabricate high performance supercapacitors using functional carbon nano‐particles is reported. A special arc synthesis method is used to produce amorphous/crystalline composite with nitrogen and boron co‐doped high charge density carbon nanoparticles. Upon etch removal of the amorphous phase in the composite nanoparticle, a crystalline carbon framework emerges, consisting of a mixture of nano‐graphitic sheets mostly in the middle and single nanohorns distributed around the surface of the nanoparticle. These nanoparticles have large internal/external surfaces with subnano channels and sharp nano‐tips for high speed charge transport and local charge accumulation. To deliver high power density, the internal resistance of the device is reduced by assembling the nanoparticles via electro‐spraying and compacting them into dense films (without any binder) under 700 MPa of pressure before supercapacitor assembly. Taken together, the hierarchical processed supercapacitor has a very high (compared to literature values) power density of nearly 4.5 kW cm−3 and a respectable energy density of 2.45 mWh cm−3. Combining these carbon nanoparticles with large area spraying coating, it can lead to a cost‐effective production of high performance supercapacitors.

Wide-bandwidth charge sensitivity with a radio-frequency field-effect transistor

We demonstrate high-speed charge detection at room temperature with single-electron resolution by using a radio-frequency field-effect transistor (RF-FET). The RF-FET combines a nanometer-scale silicon FET with an impedance-matching circuit composed of an inductor and capacitor. Driving the RF-FET with a carrier signal at its resonance frequency, small signals at the transistor's gate modulate the impedance of the resonant circuit, which is monitored at high speed using the reflected signal. The RF-FET driven by high-power carrier signals enables a charge sensitivity of 2 × 10−4 e/Hz0.5 at a readout bandwidth of 20 MHz.

Measurement of Tear Film Thickness Using Ultrahigh-Resolution Optical Coherence Tomography

To visualize the precorneal tear film with ultrahigh-resolution spectral domain optical coherence tomography, enabling quantification of tear film thickness in healthy subjects. A custom-built spectral domain optical coherence tomography system comprising a broadband titanium:sapphire laser operating at 800 nm and a high-speed charge coupled device (CCD) camera with a read-out rate of 47 kHz was used for measurement of precorneal tear film thickness. The system provides a theoretical axial resolution of 1.2 μm in tissue. The signal-to-noise ratio close to the zero delay was measured with 94 dB. A total of 26 healthy subjects were included in this study. Measurement was started immediately after blinking and averaged over a period of 1 second. In a subset of eight healthy subjects, the reproducibility of the approach was studied by measuring the tear film thickness every 10 minutes over 1 hour. The average central tear film thickness of the measured population was 4.79 ± 0.88 μm. Reproducibility was very high, with an intraclass correlation coefficient of 0.97. A breakup of the tear film was observed in one subject after 14 seconds. Our data indicate that the human precorneal tear film can be measured with excellent reproducibility using ultrahigh-resolution optical coherence tomography. This technique may be a valuable tool in the management of dry eye syndrome.