Carrier Modulation Research Articles

Heterogeneous Functional Dielectric Patterns for Charge‐Carrier Modulation in Ultraflexible Organic Integrated Circuits (Adv. Mater. 45/2021)

Flexible Electronics In article number 2104446, Takafumi Uemura, Tsuyoshi Sekitani, and co-workers report the modulation of charge carriers in ultraflexible organic integrated circuits. This is achieved by introducing heterogeneous functional dielectric patterns through ultraviolet-light irradiation. Consequently, the threshold voltage is precisely controlled from negative to even positive values, and performance metrics of ultraflexible integrated circuits are maximized.

Conductometric NO2 gas sensor based on nanolayered amorphous tellurium for room temperature operation

A fast operating NO2 sensor based on amorphous Te layer of a nanometric thickness, enclosed between Pt electrodes has been developed and investigated. The gas sensor operates at room temperature and by sensitivity ~ 60% / ppm it exhibits a response time around 5 s. The long – term stability of the sensor tested by operating it 12 weeks showed no appreciable changes in the characteristics. To elucidate the mechanism of so fast gas detection, the sensor structure and active material have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, energy-dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM), being followed with its characterization via studying the current - voltage characteristics, dynamic response, long – term stability, effects of temperature, humidity and other gases. It is shown that combination of used materials as well as the developed sensor design allow the simultaneous involvement of contact, and surface phenomena in sensor mechanism of operation, making possible the gas induced modulation of charge carriers simultaneously on Te film surface, accumulation regions at contacts, which include the portions of the degenerate (metallic) p-Te, as well as in contact gaps (transition regions), originated from microscopically roughness, formed since during electrode deposition. The last referred process leads to increasing the portion of the semiconducting Te nanolayer turned into metal of p-type Te, which at closed – circuit conditions results in a sharp increasing of the current flow through the device. Such explanation of obtained results reflects the fundamentals of metal – semiconductor junctions, the properties of used materials and meets the modern models proposed for interpretation of adsorption processes in similar devices.

Physical model for effects of microwaves on nucleoids in living cells: role of carrier frequency, modulation and DC and AC magnetic field

The effect of static and alternating magnetic fields on the conformation of nucleoids in cells of different types is considered. The model of slow and nonuniform rotation of the charged DNA domain is used. An equation is obtained for the resonance frequencies of the alternating magnetic field.

Polymer‐Mediated Electron Tunneling Towards Solar Water Oxidation

AbstractExploiting emerging artificial photosystems with regulated vectorial charge transfer pathways is retarded by the difficulties in precise interface modulation at the nanoscale level, deficiency of suitable assembly methodologies, and ultra‐short charge lifetime. Herein, it is first conceptually demonstrated the general design of transition metal chalcogenides quantum dots (TMCs QDs)‐insulating polymer‐metal oxides (MOs) electron‐tunneling photosystems, wherein TMCs QDs are controllably layer‐by‐layer self‐assembled on the MOs substrates assisted by an ultrathin insulating polymer interim layer. It is ascertained that electrons photoexcited over TMCs QDs in spatially highly ordered MOs/(TMCs QDs/polymer)n multilayered heterostructures can be unidirectionally extracted and tunneled to the MOs substrates across the intermediate insulating polymer layer by engendering the tandem charge transfer to accelerate the interfacial charge migration kinetics, thereby triggering the significantly boosted net efficiency of solar‐driven photoelectrochemical water oxidation. This study would spark new inspirations for designing novel electron‐tunneling photosystems for fine carrier modulation towards solar energy harvesting and conversion.

Dual-carrier modulation (DCM) is used to implement a species of tone reservation to reduce the PAPR of COFDM, wherein the reserved tones convey coded digital data (CDD) a second time. The same CDD is conveyed by carriers in a lower-frequency sub-band of the COFDM and by carriers in a higher- frequency sub-band. Each pair of carriers conveying the same CDD

Dual-carrier modulation (DCM) is used to implement a species of tone reservation to reduce the PAPR of COFDM, wherein the reserved tones convey coded digital data (CDD) a second time. The same CDD is conveyed by carriers in a lower-frequency sub-band of the COFDM and by carriers in a higher- frequency sub-band. Each pair of carriers conveying the same CDD are separated by a subband width, enabling receivers better to ameliorate the effects of multipath reception. There is labeling diversity between the QAM symbol constellations that respectively govern modulation of carriers in the lower- frequency sub-band and modulation of carriers in the higher-frequency subband, which labeling diversity is designed to reduce PAPR of the COFDM. The labeling diversity also improves bit-error ratio (BER) for increased-size QAM symbol constellations used to increase CDD throughput despite the halving of CDD throughput owing to the use of DCM.

Improved photodegradation efficiency in Fe3+-doped Bi3TiNbO9 nanosheets through oxygen vacancies introduction and ferroelectric polarization enhancement simultaneously

Suffering from wide bandgaps and poor charge carrier mobility, most of the ferroelectric photocatalysts are still faced with low efficiency in spite of the advanced intrinsic ferroelectric polarization. Herein we proposed a simple Fe3+-doping strategy to induce oxygen vacancies and enhance ferroelectric polarization in Bi3TiNbO9 nanosheets simultaneously, realizing band structure modulation and charge carrier kinetics steering. Combining DFT calculations and systematic experimental characterizations, it was demonstrated that the introduction of Fe not only reduce the bandgaps but also improve electron-hole separation. The promoted carrier transport and increased carrier density was related to the Fe3+/Fe2+ redox cycle and oxygen vacancies (OVs) arising from the substitution of Ti4+ with Fe3+. More importantly, the enlarged ferroelectric polarization strength after doping verified by hysteresis loop can provide further driving force for charge carrier migration. Benefitting from these optimized properties, under the optimum doping concentration, the photocatalytic degradation rate of antibiotic tetracycline hydrochloride and organic dye rhodamin B under visible light were about 1.6 times and 2.1 times of that in pure Bi3TiNbO9 respectively, outperforming the benchmark P25 and the majority of bismuth layer structured ferroelectrics. This work shed light on the feasibility of defect engineering and ferroelectric polarization modulation for efficient ferroelectric photocatalysts development.

Defect Engineering of Graphene to Modulate pH Response of Graphene Devices.

Graphene-based pH sensors are a robust, durable, sensitive, and scalable approach for the sensitive detection of pH in various environments. However, the mechanisms through which graphene responds to pH variations are not well-understood yet. This study provides a new look into the surface science of graphene-based pH sensors to address the existing gaps and inconsistencies among the literature concerning sensing response, the role of defects, and surface/solution interactions. Herein, we demonstrate the dependence of the sensing response on the defect density level of graphene, measured by Raman spectroscopy. At the crossover point (ID/IG = 0.35), two countervailing mechanisms balance each other out, separating two regions where either a surface defect induced (negative slope) or a double layer induced (positive slope) response dominates. For ratios above 0.35, the pH-dependent induction of charges at surface functional groups (both pH-sensitive and nonsensitive groups) dominates the device response. Below a ratio of 0.35, the response is dominated by the modulation of charge carriers in the graphene due to the electric double layer formed from the interaction between the graphene surface and the electrolyte solution. Selective functionalization of the surface was utilized to uncover the dominant acid-base interactions of carboxyl and amine groups at low pH while hydroxyl groups control the high pH range sensitivity. The overall pH-sensing characteristics of the graphene will be determined by the balance of these two mechanisms.

Galileo E5 AltBOC Signals: Application for Single-Frequency Total Electron Content Estimations

Global navigation satellite system signals are known to be an efficient tool to monitor the Earth ionosphere. We suggest Galileo E5 AltBOC phase and pseudorange observables—a single-frequency combination—to estimate the ionospheric total electron content (TEC). We performed a one-month campaign in September 2020 to compare the noise level for different TEC estimations based on single-frequency and dual-frequency data. Unlike GPS, GLONASS, or Galileo E5a and E5b single-frequency TEC estimations (involving signals with binary and quadrature phase-shift keying, such as BPSK and QPSK, or binary offset carrier (BOC) modulation), an extra wideband Galileo E5 AltBOC signal provided the smallest noise level, comparable to that of dual-frequency GPS. For elevation higher than 60 degrees, the 100 s root-mean-square (RMS) of TEC, an estimated TEC noise proxy, was as follows for different signals: ~0.05 TECU for Galileo E5 AltBOC, 0.09 TECU for GPS L5, ~0.1TECU for Galileo E5a/E5b BPSK, and 0.85 TECU for Galileo E1 CBOC. Dual-frequency phase combinations provided RMS values of 0.03 TECU for Galileo E1/E5, 0.03 and 0.07 TECU for GPS L1/L2 and L1/L5. At low elevations, E5 AltBOC provided at least twice less single-frequency TEC noise as compared with data obtained from E5a or E5b. The short dataset of our study could limit the obtained estimates; however, we expect that the AltBOC single-frequency TEC will still surpass the BPSK analogue in noise parameters when the solar cycle evolves and geomagnetic activity increases. Therefore, AltBOC signals could advance geoscience.

Time-domain dual component computation diversity based on generalized hybrid carrier

In this paper, the concept of computation diversity is proposed by employing generalized hybrid carrier (GHC) system. The signal is backed up by transform-domain computation to enhance the anti-fading capability. Theoretical analysis is presented to demonstrate the superiority of the proposed method. Numerical simulations in doubly-selective fading channels are provided to verify the results. The bit error rate (BER) performance is guaranteed with a small computational complexity increment. The proposed method not only extends the new diversity dimension, but also improves the diversity gain of the system without occupying additional wireless resources. Moreover, the proposed method shows good adaptability with single carrier modulation and improves diversity performance. As the simulation results shown, time-domain dual component computation diversity (TDC-CD) has 1dB BER gain and 0.1 diversity gain at high signal-to-noise ratio, and single carrier system with TDC-CD achieves 2dB BER gain at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> .

Simultaneous directional full-field OCT using path-length and carrier multiplexing.

Full-field swept-source optical coherence tomography (FF-SS-OCT) is an emerging technology with potential applications in ophthalmic imaging, microscopy, metrology, and other domains. Here we demonstrate a novel method of multiplexing FF-SS-OCT signals using carrier modulation (CM). The principle of CM could be used to inspect various properties of the scattered light, e.g. its spectrum, polarization, Doppler shift, or distribution in the pupil. The last of these will be explored in this work, where CM was used to acquire images passing through two different optical pupils. The two pupils contained semicircular optical windows with perpendicular orientations, with each window permitting measurement of scattering anisotropy in one dimension by inducing an optical delay between the images formed by the two halves of the pupil. Together, the two forms of multiplexing permit measurement of differential scattering anisotropy in the x and y dimensions simultaneously. To demonstrate the feasibility of this technique our carrier multiplexed directional FF-OCT (CM-D-FF-OCT) system was used to acquire images of a microlens array, human hair, onion skin and in vivo human retina. The results of these studies are presented and briefly discussed in the context of future development and application of this technique.

Highly Enhanced Thermoelectric and Mechanical Properties of Bi-Sb-Te Compounds by Carrier Modulation and Microstructure Adjustment.

Bi0.42Sb1.58Te3 + x wt % Cu1.8S (x = 0, 0.03, 0.05, and 0.1) bulk materials with enhanced thermoelectric and mechanical properties were fabricated by a solid-state reaction and spark plasma sintering. The thermoelectric properties, such as electrical transport properties and thermal conductivity, are highly dependent on the Cu1.8S content. The highest value of ZT obtained for Bi0.42Sb1.58Te3 with 0.05 wt % Cu1.8S is 1.23 at 373 K, and an optimistic average ZT of 1.2 is achieved at temperatures in the range of 323-448 K, which is 34% higher than that of the pristine sample. The highly enhanced ZT of the doped sample is attributed to the increased electrical conductivity and reduced lattice thermal conductivity caused by the effective element doping and the multiscale phonon scattering by quantities of point defects, twin boundaries, and nanopores. Further, the hardness obtained for this sample is 1.02 GPa, which is increased by 16% in comparison with that of the pristine sample. The conversion efficiency of the doped sample is also significantly higher than that of the pristine sample. Therefore, Cu1.8S is considered to be a promising dopant for enhancing the thermoelectric and mechanical properties of Bi-Sb-Te-based thermoelectric materials.

Parallel connected GaN E‐HEMT VSI‐based servo drives for PMSMs

The operation of parallel-connected servo drives has the advantages of increasing the torque (hence the power) capacity, reliability, redundancy and modularity. However, smaller discrepancies of the system clocks of the independent microcontrollers, asynchronous pulse width modulation (PWM) carrier signals and hardware differences can make the output voltages of the parallel modules non-identical, which results in circulating currents. These circulating currents limit the parallel operation, introduce additional power dissipation, cause unbalanced power distribution and degrade the control performance. To eliminate the circulating currents separated DC supplies, coupled inductors (CIs), PWM techniques, modified control techniques etc. are proposed in the literature. In this study, a fault-tolerant parallel-connected gallium nitride enhancement-mode high electron mobility transistor voltage source inverter-based servo drive scheme that eliminates the need for CIs and separate DC supplies and also enables the use of a standard proportional-integral current control and a standard space vector PWM approach is proposed and tested. To evaluate the performances of the proposed scheme, up to six servo drives (limit-6 × 7 Arms) are connected in parallel and tested under various conditions with a 24 V permanent magnet synchronous motor (nominal-61.9 Arms). The results show that the parallel operation not only increases the torque capacity of the system but also increases modularity, flexibility, reliability and also redundancy.

Controllable band offset in monolayer MoSe2 driven by surface termination and ferroelectric field of BiFeO3(0001) substrate

Integration of 2D van der Waals crystals into ferroelectric materials is a reliable way for the technological leap toward next-generation (opto)electronic applications. In present work, first-principles density functional theory calculations were performed to describe nonvolatile carrier modulation and ferroelectric field effect caused by interface coupling of MoSe2 monolayer with ferroelectric BiFeO3(0001) substrate. The Fermi level of MoSe2 monolayer on BiFeO3(0001) surface showed strong dependence on surface termination and polarization direction. Furthermore, polarization switching made MoSe2/BiFeO3(0001) heterointerface evolve into energetically metastable state and remarkable ferroelectric field effect on band offset in MoSe2 monolayer was observed due to distinct interface charge transfer. Therefore, the results of this work open up new prospects for surface chemistry and domain structure engineering of MoSe2 homojunctions for MoSe2/BiFeO3(0001)-based ferroelectric field effect devices.

A p–n–n heterostructure composite for low-temperature solid oxide fuel cells

Recent advances have presented a promising p-n heterostructure strategy to develop highly ionic conducting electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs). In this study, a p–n–n heterostructure approach is further proposed to develop new electrolytes for LT-SOFCs based on p-type Ni0.8Co0.15Al0.05LiO2−δ (NCAL), n-type ZnO, and n-type SnO2. Material characterization reveals that the developed NCAL-ZnO-SnO2 electrolyte gains a desirable heterostructure with homogenous distribution and hetero-interface as well as enriched oxygen vacancies. Electrochemical studies find that the electrical conductivity and fuel cell performance are significantly correlated with the mass ratios of p/n phases in the samples. The 2NCAL-1(ZnO-SnO2) exhibits a highest ionic conductivity of 0.389 S cm−1 at 530 ℃ along with a remarkable fuel cell power density of 1267 mW cm−2, which are apparently superior to those of p–n heterostructure electrolytes of NCAL-ZnO and NCAL-SnO2. By considering the semiconductor features of the used materials, further investigation in terms of energy band structure and rectifying characteristic studies indicate the possible existence of p-n-n heterojunction in the NCAL-ZnO-SnO2 fuel cell with rectifying behavior for charge carrier modulation. On basis of which, an energy band alignment effect is propounded to illustrate the electronic blocking and ionic acceleration processes of the p–n–n heterostructure electrolyte. The successful demonstration of 2NCAL-1(ZnO-SnO2) thus provides a new approach to develop advanced electrolytes for LT-SOFCs.

The Three-Carrier Quasi Switched Boost Inverter Control Technique

This paper presents a carrier modulation technique to control the three-phase, two-level quasi switched boost inverter. This PWM algorithm uses three carrier waves, the first of which is for the inverter while the others are for the booster. The boost factor depends on the short circuit interval on the DC/DC booster and the inverter. When the short circuit interval on the DC boost is twice that on the inverter, the modulation index can be enlarged. The new algorithm is analyzed, calculated, simulated, and tested. The analysis and calculation results show that the proposed technique can reduce the voltage on the DC link capacitor compared to a conventional approach. It can reach 22.16% when the ratio of the DC source voltage to the effective reference voltage is 0.5. The modulation index can extend to 29% under these conditions and the current ripple in the boost inductor can be reduced by 4.8%. The simulation and experimental results also show similarities, thereby confirming the analysis and calculation.

Tunable Band-Edge Potentials and Charge Storage in Colloidal Tin-Doped Indium Oxide (ITO) Nanocrystals.

Degenerately doped metal-oxide nanocrystals (NCs) show localized surface plasmon resonances (LSPRs) that are tunable via their tunable excess charge-carrier densities. Modulation of excess charge carriers has also been used to control magnetism in colloidal doped metal-oxide NCs. The addition of excess delocalized conduction-band (CB) electrons can be achieved through aliovalent doping or by postsynthetic techniques such as electrochemistry or photodoping. Here, we examine the influence of charge-compensating aliovalent dopants on the potentials of excess CB electrons in free-standing colloidal degenerately doped oxide NCs, both experimentally and through modeling. Taking Sn4+:In2O3 (ITO) NCs as a model system, we use spectroelectrochemical techniques to examine differences between aliovalent doping and photodoping. We demonstrate that whereas photodoping introduces excess CB electrons by raising the Fermi level relative to the CB edge, aliovalent impurity substitution introduces excess CB electrons by stabilizing the CB edge relative to an externally defined Fermi level. Significant differences are thus observed electrochemically between spectroscopically similar delocalized CB electrons compensated by aliovalent dopants and those compensated by surface cations (e.g., protons) during photodoping. Theoretical modeling illustrates the very different potentials that arise from charge compensation via aliovalent substitution and surface charge compensation. Spectroelectrochemical titrations allow the ITO NC band-edge stabilization as a function of Sn4+ doping to be quantified. Extremely large capacitances are observed in both In2O3 and ITO NCs, making these NCs attractive for reversible charge-storage applications.

Modular‐Peptides‐Based Ternary Complex for Precisely Tracking the Targeted Process and Delivery of Gene/Chemo‐Drug

AbstractHighly effective transporting and real‐time monitoring of the drug delivery system (DDS) has attracted much attention from researchers. However, separately tracking the multiple components in a complex DDS as well as its delivery process is challengeable. Here, a multi‐fluorescence‐labeled ternary complex is designed for delivering the therapeutic agents and monitoring the multiple components. Ternary complex (A@TR) is formed by three parts, including a) the carrier module TFD, which is a cell‐penetrating peptide (TAT) conjugated with anti‐cancer drug doxorubicin (DOX) and fluorescent molecule fluorescein isothiocyanate (FITC); b) therapeutic genes (ASO); c) the targeting module RDP based on a cyclic RGDFK peptide and aggregation‐induced‐emission luminogen PyTPE. The labeling of FITC through the covalent bond can stably track the location of anticancer drugs and genes in the long term. Meanwhile, the mark of PyTPE can monitor the process of targeting‐mediated endocytosis over time. After being internalized by tumor cells selectively, chemodrug and therapeutic genes can achieve a superior tumor inhibited effect. By utilizing the multi‐channel fluorescence, this ternary complex could achieve precisely monitoring the targeted binding process of DDS and delivery processes of therapeutic agents.

An improved phase generated carrier demodulation scheme for sinusoidal phase-modulating interferometer to detect air-solid interface acoustic waves

When acoustic waves reach an air–solid interface, surface acoustic waves will be generated, and such waves may carry important acoustic information. In order to detect acoustic waves at air–solid interface, a non-contact detection method based on a partial-fiber sinusoidal phase-modulating interferometer (SPMI) is proposed in this paper. An improved phase generated carrier (PGC) demodulation scheme is also proposed to eliminate demodulation error caused by changes of interference signal parameters such as interference signal visibility, phase modulation depth and carrier phase delay. In our research, the improved PGC demodulation algorithm is first used to accurately calculate phase modulation depth and carrier phase delay, and then the in-phase and quadrature components of an interference signal are pre-normalized. Next, the visibility coefficient of the interference signal at each moment is derived by self-multiplying. Finally, the in-phase and quadrature components are completely normalized. The accuracy and effectiveness of the sinusoidal phase-modulating interferometer method and the improved PGC demodulation algorithm for detecting acoustic waves at air–solid interface are proven by numerical simulations and experiments. The air–solid interface acoustic waves excited by various acoustic sources are detected in experiments. The experiment results show that the detectable frequency range of the system is 100 Hz-3 kHz, the minimum detectable amplitude is 0.045 rad/√Hz, and the average signal-to-noise-and-distortion ratio (SINAD) is 28.98 dB.

Optimization of Passive Transmission Lines for Single Flux Quantum Circuits

Passive transmission lines (PTLs) provide an energy-efficient means of transporting pulsed single flux quantum (SFQ) signals between logic gates and blocks on a chip, or even between chips through a multi-chip module carrier. Although functional up to 70 GHz, our previous designs manifested sharp, length-dependent resonances resulting in diminished operating margins. These are particularly inconvenient since the resonant length is about 1 mm at 40–50 GHz, where most SFQ circuits currently function. To avoid the need to keep the PTLs < 1 mm in length, we have optimized the PTL driver-receiver pairs to sufficiently suppress these resonances; this helps facilitate the use of automated routing tools. We present experimental results, in the 10-70 GHz frequency range, for different driver-receiver pairs designed for PTLs in our dual RSFQ-ERSFQ cell library. This cell library, targeting MIT Lincoln Laboratory's SFQ5ee fabrication process, uses PTLs with two types of ground plane configuration. The first variant has signal in M1 and/or M3 with symmetrical ground planes in M0, M2 and/or M2, M4 respectively. The second variant has signal in M2 and/or M3 with asymmetrical ground planes in M1 and M4. We also present a comparison with wider, 4 Ω, PTLs that are more suitable for transport between distant logic blocks. Next, we present experimental results of PTL lengths ranging from 1.2-12 mm over the same 10-70 GHz frequency range. Finally, we report on the design of circuits for investigating crosstalk between two PTLs and their measurement results.

Novel Christmas Branched Like NiO/NiWO4/WO3 (p–p–n) Nanowire Heterostructures for Chemical Sensing

AbstractEstablishing a platform comprising different nanostructured oxides is an emerging idea to develop highly sensitive and selective sensing devices. Herein, novel 3D‐heterostructures (p–p–n) consisting of 1D nanowires of NiO and WO3 along with their intermediate reactive product, i.e., NiWO4 seed, are produced by a two‐steps vapor phase growth method. In‐depth morphological and structural investigations describing the growth mechanism of these heterostructures are presented. Finally, the p–p–n heterostructures are integrated into conductometric sensing devices and their performances are investigated toward different gases. It is observed that by modulating the charge‐carrier transport with temperature, the heterostructure sensors exhibit selective behavior toward different gas analytes. Indeed, at 300 °C, the heterostructure sensors show relatively selective behavior toward NO2, while at 400 °C, high selectivity toward VOCs is observed. The improvement in sensing performances is mainly based on charge carrier transport through the two interfaces (one at WO3/NiWO4 (n–p) and the other at NiWO4/NiO (p–p)) and the modulation of charge carriers in the electron depletion layer of WO3 and hole accumulation layer of NiO and NiWO4. The remarkable performance of these complex heterostructures with low ppb‐level detection limits makes them excellent candidates for chemical/ gas sensing applications in e‐noses.