Combined Temperature Compensation Method for Closed-Loop Microelectromechanical System Capacitive Accelerometer.

This article describes a closed-loop detection MEMS accelerometer for acceleration measurement. This paper analyzes the working principle of MEMS accelerometers in detail and explains the relationship between the accelerometer zero bias, scale factor and voltage reference. Therefore, a combined compensation method is designed via reference voltage source compensation and terminal temperature compensation of the accelerometer, which comprehensively improves the performance over a wide temperature range of the accelerometer. The experiment results show that the initial range is reduced from 3679 ppm to 221 ppm with reference voltage source compensation, zero-bias stability of the accelerometer over temperature is increased by 14.3% on average and the scale factor stability over temperature is increased by 88.2% on average. After combined compensation, one accelerometer zero-bias stability over temperature was reduced to 40 µg and the scale factor stability over temperature was reduced to 16 ppm, the average value of the zero-bias stability over temperature was reduced from 1764 µg to 36 µg, the average value of the scale factor stability over temperature was reduced from 2270 ppm to 25 ppm, the average stability of the zero bias was increased by 97.96% and the average stability of the scale factor was increased by 98.90%.

Improving the performance of quantum dot light-emitting diodes by tailoring QD emitters.

As the emitters of quantum dots (QDs) light-emitting diodes (QLEDs), QDs, which are responsible for the charge injection, charge transportation, and especially exciton recombination, play a significant role in QLEDs. With the crucial advances made in QDs, such as the advancement of synthetic methods and the understanding of luminescence mechanisms, QLEDs also demonstrate a dramatic improvement. Until now, efficiencies of 30.9%, 28.7% and 21.9% have been achieved in red, green and blue devices, respectively. However, in QLEDs, some issues are still to be solved, such as the imbalance of charge injection and exciton quenching processes (defect-assisted recombination, Auger recombination, energy transfer and exciton dissociation under a high electric field). In this review, we will provide an overview of recent advances in the study and understanding of the working mechanism of QLEDs and the exciton quenching mechanism of QDs in devices. Particular emphasis is placed on improving charge injection and suppressing exciton quenching. An in-depth understanding of this progress may help develop guidelines to direct QLED development.

Distance-dependent resonance energy transfer in alkyl-terminated Si nanocrystal solids.

Understanding and controlling the energy transfer between silicon nanocrystals is of significant importance for the design of efficient optoelectronic devices. However, previous studies on silicon nanocrystal energy transfer were limited because of the strict requirements to precisely control the inter-dot distance and to perform all measurements in air-free environments to preclude the effect of ambient oxygen. Here, we systematically investigate the distance-dependent resonance energy transfer in alkyl-terminated silicon nanocrystals for the first time. Silicon nanocrystal solids with inter-dot distances varying from 3 to 5 nm are fabricated by varying the length and surface coverage of alkyl ligands in solution-phase and gas-phase functionalized silicon nanocrystals. The inter-dot energy transfer rates are extracted from steady-state and time-resolved photoluminescence measurements, enabling a direct comparison to theoretical predictions. Our results reveal that the distance-dependent energy transfer rates in Si NCs decay faster than predicted by the Förster mechanism, suggesting higher-order multipole interactions.

A blockchain-based lightweight identity authentication scheme for the IEDs of security and stability control system.

As an important part of the second defense line of the power system, the Security and Stability Control System (SSCS) is of great significance to ensure the reliable operation of the power system. However, SSCS still lacks an effective security mechanism and is easily accessed by attackers, thus posing a threat to the stable and reliable operation of the power system. To tackle this issue, we propose a blockchain-based identity authentication scheme for Intelligent Electronic Devices (IEDs) of SSCS. We first propose an identity authentication system model for IEDs and design the deployment of consortium chain nodes on IEDs, with architectural characteristics of SSCS and the working scenario of IEDs taken into consideration. The consortium chain is used to store credentials required for authentication, ensuring that they are tamper-proof. We combine IP address, port number and physical ID, and propose the unique identification of IEDs, with a data structure designed for the identification. We also propose a lightweight identity authentication method based on renewable hash chains, with hash chains used as one-time authentication passwords, and introduce a renewal mechanism of hash chains. Further, the detailed processes of registration and authentication phase are designed. Finally, the security analysis shows that our identity authentication scheme can resist various attacks, and the feasibility of our scheme is verified by experiments.

Water-Soluble Luminescent Silicon Nanocrystals by Plasma-Induced Acrylic Acid Grafting and PEGylation.

Luminescent silicon nanocrystals are promising nanomaterials for biomedical applications due to their unique optical properties and biocompatibility. Here, we demonstrate a two-step surface modification approach coupling gas-phase and liquid-phase methods to synthesize PEGylated acrylic acid grafted silicon nanocrystals with near-infrared emission in water and biological media. First, acrylic acid grafted silicon nanocrystals are synthesized by an all-gas-phase approach on a millisecond time scale, omitting high temperature and postpurification processes. Subsequently, room-temperature PEGylation is carried out with these acrylic acid grafted silicon nanocrystals, yielding stable colloidal dispersions in both water and high ionic strength Tyrode's buffer with 20-30 nm hydrodynamic diameters. The PEGylated silicon nanocrystals exhibit photoluminescence in the 650-900 nm near-IR window with quantum yields of ∼30% and ∼13% in deionized water and Tyrode's buffer, respectively, after a 7-day oxidation in water. The surface-functionalized Si NCs exhibit relatively small toxicity to MDA-MB-231 cells at concentrations relevant to bioimaging applications.

Comparative Study of NO and CO Oxidation Reactions on Single-Atom Catalysts Anchored Graphene-like Monolayer.

Noble metal single-atom catalysts (NM-SACs) anchored at novel graphene-like supports has attracted enormous interests. Gas sensitivity, catalytic activity, and d-band centers of single NM (Pt and Pd) atoms at graphenylene (graphenylene-NM) are investigated using first-principle calculations. The adsorption geometries of gas reactants on graphenylene-NM sheets are analyzed. It is found that the adsorption energies of reactant species on graphenylene-Pt are larger than those on graphenylene-Pd, because the d-band center of the Pt atom is closeser to the Fermi level. The NO and CO oxidation reactions on graphenylene-NM are investigated via four catalytic mechanisms, including Langmuir-Hinshelwood (LH), Eley-Rideal (ER), New ER (NER), and termolecular ER (TER). The results show that the NO and CO oxidations via LH and TER mechanisms can occur owing to the relatively small energy barriers. Moreover, the interaction of 2NO+2CO via ER mechanism is the energetically more favorable reaction. Although the NO oxidation via the NER mechanism has rather low energy barriers, the reaction is unlikely to occur due to the low adsorption energy of O2 compared with CO and NO. This research may provide guidance for exploring the catalytic performance of SACs on graphene-like materials to remove toxic gas molecules.

The effect of strain on water dissociation on reduced rutile TiO2(110) surface.

The effect of external uniaxial strain on water dissociation on a reduced rutile TiO2(110) surface has been theoretically studied using first-principles calculations. We find that when the tensile strain along [11̄0] is applied, the energy barrier of water dissociation substantially decreases with the increase of strain. In particular, water almost automatically dissociates when the strain is larger than 3%. Besides, the water dissociation mechanism changes from indirect to direct dissociation when the compressive strain is larger than 1.3% along [11̄0] or 3% along [001]. The results strongly suggest that it is feasible to engineer the water dissociation on the reduced rutile TiO2(110) surface using external strain.

Aluminum Oxide Nanoparticle Films Deposited from a Nonthermal Plasma: Synthesis, Characterization, and Crystallization.

Aluminum oxide, both in amorphous and crystalline forms, is a widely used inorganic ceramic material because of its chemical and structural properties. In this work, we synthesized amorphous aluminum oxide nanoparticles using a capacitively coupled nonthermal plasma utilizing trimethylaluminum and oxygen as precursors and studied their crystallization and phase transformation behavior through postsynthetic annealing. The use of two reactor geometries resulted in amorphous aluminum oxide nanoparticles with similar compositions but different sizes. Size tuning of these nanoparticles was achieved by varying the reactor pressure to produce amorphous aluminum oxide nanoparticles ranging from 6 to 22 nm. During postsynthetic annealing, powder samples of amorphous nanoparticles began to crystallize at 800 °C, forming crystalline θ and γ phase alumina. Their phase transformation behavior was found to be size-dependent in that powders of small 6 nm amorphous particles transformed to form phase-pure α-Al2O3 at 1100 °C, while powders of large 11 nm particles remained in the θ and γ phases. This phenomenon is attributed to the fast rate of densification and neck formation in small amorphous aluminum oxide particles.

Synthesis of PEG-grafted boron doped Si nanocrystals.

Silicon nanocrystals are intriguing materials for biomedical imaging applications because of their unique optical properties and biological compatibility. We report a new surface functionalization route to synthesize biological buffer soluble and colloidally stable silicon nanocrystals, which is enabled by surface boron doping. Harnessing the distinctive Lewis acidic boron surface sites, postsynthetic modifications of plasma synthesized boron doped nanocrystals were carried out with polyethylene glycol (PEG-OH) ligands in dimethyl sulfoxide under photochemical conditions. The influence of PEG concentration, PEG molecular weight, and boron doping percentage on the nanocrystal solubility in a biological buffer has been investigated. The boron doping facilitates the surface functionalization via two probable pathways, by providing excellent initial dispersiblity in polar solvents and providing available acidic boron surface sites for bonding. These boron doped silicon nanocrystals have nearly identical absorption features as intrinsic silicon nanocrystals, indicating that they are promising candidates for biological imaging applications.

Se/S Ratio-Dependent Properties and Application of Gradient-Alloyed CdSe1- xS x Quantum Dots: Shell-free Structure, Non-blinking Photoluminescence with Single-Exponential Decay, and Efficient QLEDs.

Colloidal quantum dots (QDs) are promising optical and optoelectronic materials for various applications. The excited state properties are important indexes to assess the quality of QDs and may directly affect their applications. Different from controlling surface engineering (surface ligands, shell thickness, etc.) to adjust excited state properties, high-quality shell-free alloyed CdSe1- xS x (simplified as CdSeS) QDs with controlled excited state properties were synthesized by tuning the composition and using diphenylphosphine as a beneficial additive at a low temperature (∼180 °C). The optimized CdSeS shell-free alloyed QDs (Se/S = 1:8) exhibited excellent optical properties with tuning of the excited state, including single-exponential photoluminescence (PL) decay dynamics, a narrow full width at half maximum of 28 nm, and non-blinking emission behavior (>98% "on" time). Furthermore, all-solution-processed, multilayered quantum dot light-emitting diodes were fabricated using the conventional device structure to assess the performance of QDs with composition-controlled excited states. The best device displayed a maximum luminance of 92,330 cd m-2, a current efficiency of 50.3 cd A-1, and an external quantum efficiency of 14.5%.

Aerosol-Phase Synthesis and Processing of Luminescent Silicon Nanocrystals.

Silicon quantum dots are attractive materials for luminescent devices and bioimaging applications. For these light-emitting applications, higher photoluminescence efficiency is desired in order to achieve better device performance. Nonthermal plasma synthesis successfully allows for the continuous production of silicon nanocrystals, but postprocessing is necessary to improve photoluminescence quantum yields so that nanocrystals can be used for luminescence applications. In this work, we demonstrate an all-aerosol-phase synthesis and processing route that integrates nonthermal plasma synthesis, plasma-assisted surface functionalization with alkene ligands, and in-flight annealing within one flow stream. Here, luminescent silicon nanocrystals are synthesized and postprocessed on a time scale of only 100 ms, which is orders of magnitude faster than previous synthesis and functionalization schemes. The as-produced silicon nanocrystals have photoluminescence quantum yields exceeding 20%, which is a 5-fold increase compared to previous silicon nanocrystals synthesized with all-aerosol-phase approaches. We attribute the enhanced photoluminescence to the reduced "dark" nanocrystal fraction due to reduction of dangling bond density and desorption of surface silyl species induced by the in-flight annealing. We also demonstrate that the ligand coverage plays a minor role for the photoluminescence properties, but that the nature of the silicon hydride surface groups is a major factor.

Shell-dependent blinking behavior and fluorescence dynamics of single ZnSe/CdS core/shell quantum dots.

An understanding of blinking behavior and photodynamics is crucial for improving the optical properties of quantum dots (QDs). Here we report the emission blinking behavior and dynamical mechanisms of single ZnSe/CdS core/shell QDs with the shell thickness varying from 1 to 6 monolayers. We find that the emission blinking behavior can be efficiently suppressed in the single-exciton regime and that the photoluminescence (PL) quantum yields (QY) and the corresponding fraction-bright of ZnSe/CdS QDs can be optimized by regulating the shell thickness. Specifically, the PL QY reaches a maximum of 93% when the shell thickness is 4 monolayers. The intensity-resolved and time-resolved fluorescence dynamics of single QDs indicate that three exciton decay pathways via trion emission, band-edge emission and shallow surface trap-state emission contribute to the blinking behavior of ZnSe/CdS QDs. The competitive contribution ratios of these three decay components are responsible for the significant difference in emission properties of ZnSe/CdS QDs with different shell thicknesses. Our findings in this work demonstrate that an effective way to improve the quantum yields and fraction-bright of core/shell QDs is to enhance the band-edge emission while suppressing the trion emission and surface trap-state emission.

High-efficiency, deep blue ZnCdS/CdxZn1-xS/ZnS quantum-dot-light-emitting devices with an EQE exceeding 18.

We report a facile and robust synthesis of ZnCdS core/shell quantum dots (QDs) with thick CdxZn1-xS (x = constant) uniform alloys as an intermediate shell which can provide effective confinement of excitons within the ZnCdS cores and ultrathin ZnS outermost shell to improve the stability by epitaxial growth at a relatively high temperature. The resulting nearly monodisperse ZnCdS/CdxZn1-xS/ZnS core/shell QDs have high photoluminescence quantum yield (near to 100%) and high color purity (full width at half maximum (FWHM) < 18 nm). More importantly, the ZnCdS/CdxZn1-xS/ZnS core/shell QDs have good chemical/photochemical stability and more efficient carrier transport performance compared with ZnCdS/ZnS core/shell QDs. Two types of QDs of ZnCdS/ZnS and ZnCdS/CdxZn1-xS/ZnS were incorporated into the solution-processed hybrid QD-based light-emitting device structure as the emissive layer. We find that the presence of the CdxZn1-xS shell makes a profound impact on device performances such as the external quantum efficiency and current efficiency. The corresponding light-emitting diodes exhibited a high EQE exceeding 18%, a peak current efficiency of 3.4 cd A-1 and low efficiency roll-off. Such excellent results of ZnCdS/CdxZn1-xS/ZnS-based QLEDs are likely attributable to the QD's high PL QY and very thin ZnS outermost shell which did not sacrifice the charge injection efficiency in QLEDs.

From coffee rings to coffee eyes.

We discuss how the stain left after evaporation of a suspension evolves with heating of the glass or plastic on which the liquid has been deposited. Upon increasing the substrate temperature, it is found that the stain gradually changes from the usually observed ring to an "eye" shape, that is, a combination of the thick central stain and the thin outer ring. Both the size and the relative volume of the central stain increase with the substrate temperature. The main mechanism for this phenomenon is proposed to be an enhanced Marangoni recirculation flow on hot substrates. These findings can be exploited to continuously tune the morphology of coffee stains, with potential applications in self-assembly and ink-jet printing.