Branchlike nickel oxide nanocrystals with narrow size distribution are obtained by a solution growth method. The size-dependent of magnetic properties of the nickel oxides were investigated. The ...results of magnetic characterization indicate that the NiO nanocrystals with size below 12.8 nm show very weak ferromagnetic state at room temperature due to the uncompensated spins. Both of the average blocking temperature (T
b) and the irreversible temperature (T
irr) increase with the increase of nanoparticle sizes, while both the remnant magnetization and the coercivity at 300 K increase with the decrease of the particle sizes. Moreover, the disappearance of two-magnon (2M) band and redshift of one-phonon longitudinal (1LO) and two-phonon LO in vibrational properties due to size reduction are observed. Compared to the one with the spherical morphological, it is also found that nano-structured nickel oxides with the branchlike morphology have larger remnant magnetization and the coercivity at 5 K due to their larger surface-to-volume ratio and greater degree of broken symmetry at the surface or the higher proportion of broken bonds.
By integrating CdSeTe alloy into CdTe based thin-film solar cells, high efficiency above 19% has been obtained. However, the role of O2 during the CdSeTe deposition has not been studied since the ...current reported CdSeTe deposition process by close space sublimation (CSS) is free of oxygen. We found the oxygen performed an important role in this process. Here, we prepared CdSeTe films under O2/N2 ambient and apply them as absorb-layer together with CdTe. The effects of O2 on the CdSeTe deposition, material performance, and devices have been studied. Oxygen in the ambient can increase Se content in the CdSeTe alloy for the as-deposited films. A two-step reaction process of “oxidation - sublimation” is proposed to explain the role of oxygen. The oxygen facilitates the amount of Se content into the vapor then in the film. With the oxygen appearance, the composition of as-deposited CdSeTe films and the source can be controlled relative stable. This technique makes the process of depositing CdSeTe thin film by CSS for long time operation feasible. The short circuit current density (Jsc) and fill factor (FF) of the cells are promoted with the introduce of oxygen. A process of high efficiency (Eff.) (≥19%) CdSeTe/CdTe cells with oxygen in the CSS deposition is developed, which is repeatable and also compatible with both the existing manufacturing and laboratory CdTe process and equipment.
•We found the oxygen performed an important role in CdSeTe deposition process by close space sublimation (CSS).•The effects of O2 on the CdSeTe deposition, material performance, and devices have been studied.•Oxygen in the ambient can increase Se content in the CdSeTe alloy for the as-deposited films.•With the oxygen appearance, the composition of as-deposited CdSeTe films and the source can be controlled relative stable.•The short circuit current density (Jsc) and fill factor (FF) of the cells are promoted with the introduce of oxygen.
4H silicon carbide (4H‐SiC) holds great promise for high‐power and high‐frequency electronics, in which high‐quality 4H‐SiC wafers with both global and local planarization are cornerstones. ...Chemical–mechanical polishing (CMP) is the key processing technology in the planarization of 4H‐SiC wafers. Enhancing the performance of CMP is critical to improving the surface quality and reducing the processing cost of 4H‐SiC wafers. In this review, the superior properties of 4H‐SiC and the processing of 4H‐SiC wafers are introduced. The development of CMP with chemical, mechanical, and chemical–mechanical synergistic approaches to improve the performance of CMP is systematically reviewed. The basic principle and processing system of each improvement approach are presented. By comparing the material removal rate of CMP and the surface roughness of CMP‐treated 4H‐SiC wafers, the prospect on the chemical, mechanical, and chemical–mechanical synergistic improvement approaches is finally provided.
Recent progress on the CMP of 4H‐SiC wafers are discussed after a brief overview of the basic properties of 4H‐SiC. Chemical, mechanical, and chemical–mechanical synergistic approaches for the efficiency improvement of CMP are highlighted. By discussing the advantages and disadvantages of the efficiency‐improvement approaches, the challenges of using these approaches in industry are analyzed. Finally, prospects on the development of the CMP of 4H‐SiC wafers are presented.
Abstract
Silicon is vital for its high abundance, vast production, and perfect compatibility with the well-established CMOS processing industry. Recently, artificially stacked layered 2D structures ...have gained tremendous attention via fine-tuning properties for electronic devices. This article presents neuromorphic devices based on silicon nanosheets that are chemically exfoliated and surface-modified, enabling self-assembly into hierarchical stacking structures. The device functionality can be switched between a unipolar memristor and a feasibly reset-able synaptic device. The memory function of the device is based on the charge storage in the partially oxidized SiNS stacks followed by the discharge activated by the electric field at the Au-Si Schottky interface, as verified in both experimental and theoretical means. This work further inspired elegant neuromorphic computation models for digit recognition and noise filtration. Ultimately, it brings silicon - the most established semiconductor - back to the forefront for next-generation computations.
This paper reports a novel self-templating methodology for the formation of SnO2-carbon hybrid hollow spheres by using Sn spheres as sacrificing templates. The time-sequenced structural evolution of ...the templates indicates that the nanoscale Kirkendall effect plays a critical role in the transformation from Sn spheres to the hybrid hollow spheres. Moreover, the as-synthesized SnO2–carbon hybrid hollow spheres have been applied as anode materials for lithium-ion batteries, which exhibit a much higher initial Coulombic efficiency and better cycling performance than pure SnO2 hollow spheres.
This paper describes the synthesis of three-dimensionally porous Fe3O4 via template-assisted and subsequent electrochemical deposition methods. When used as anode materials of lithium-ion batteries, ...the porous Fe3O4 electrodes show better cyclability and enhanced rate capabilities compared to planar Fe3O4 electrodes. The superior performance can be attributed to improved electrical contact, fast electron transport and good strain accommodation of the porous electrodes. The effect of the thickness of the porous Fe3O4 electrodes on the lithium-ion battery performance has also been investigated.
Integrated circuit anti-counterfeiting based on optical physical unclonable functions (PUFs) plays a crucial role in guaranteeing secure identification and authentication for Internet of Things (IoT) ...devices. While considerable efforts have been devoted to exploring optical PUFs, two critical challenges remain: incompatibility with the complementary metal-oxide-semiconductor (CMOS) technology and limited information entropy. Here, we demonstrate all-silicon multidimensionally-encoded optical PUFs fabricated by integrating silicon (Si) metasurface and erbium-doped Si quantum dots (Er-Si QDs) with a CMOS-compatible procedure. Five in-situ optical responses have been manifested within a single pixel, rendering an ultrahigh information entropy of 2.32 bits/pixel. The position-dependent optical responses originate from the position-dependent radiation field and Purcell effect. Our evaluation highlights their potential in IoT security through advanced metrics like bit uniformity, similarity, intra- and inter-Hamming distance, false-acceptance and rejection rates, and encoding capacity. We finally demonstrate the implementation of efficient lightweight mutual authentication protocols for IoT applications by using the all-Si multidimensionally-encoded optical PUFs.
As a leading surface-modification approach, hydrosilylation is critical to the practical use of silicon nanocrystals (Si NCs). However, the effect of hydrosilylation-induced surface chemistry on the ...electronic and optical properties of Si NCs is rather limitedly understood. By means of first-principles calculation at 0 K we show thermodynamically favored surface bonding for hydrosilylation of 1.4 nm Si NCs and the relative reactivity of alkenes and alkynes. The optical properties of hydrosilylated Si NCs are elucidated on the basis of their energy-level schemes and radiative recombination rates. The chain length (up to C12) of ligands hardly affects the absorption and emission of Si NCs. The increase of the surface coverage (up to 29%) of ligands causes the absorption onset to slightly redshift, hardly rendering changes to the light emission from Si NCs. As an added advantage, hydrosilylation may lead to enhanced light emission from Si NCs. Radiative recombination is very sensitive to surface chemistry for Si NCs. Only the coexistence of CC and functional groups at the NC surface significantly modifies the electronic structures and optical behavior of Si NCs.
One-step approach for doping and interface engineering of the Gr/Si solar cells was realized by using the fluorographene(FG) as an insulator interlayer. Metal/insulator/semiconductor (MIS) like solar ...cells with a structure of Gr/FG/Si were composed. The F atoms of FG serve as electron acceptors and yield p-type doping, which is beneficial for improving the Schottky barrier. The carrier recombination of the solar cell can be effectively suppressed by the employment of the FG interlayer and the PCE of the solar cell increased from 3.17% to 7.52%. More interestingly, the performance of Gr/FG/Si solar cell can be further enhanced by applying a temporary voltage bias, which was likely associated with rotation of the C―F bonds or/and enhancement of the Gr/FG coupling in electrical field. A PCE up to 13.38% was achieved by combining the AR technology and chemical doping from the top-side of the Gr.
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•We fabricated metal/insulator/semiconductor (MIS) solar cells with a structure of Gr/FG/Si.•Underside p-type Gr doping was obtained in the Gr/FG heterostructure.•One-step approach for doping and interface engineering of the Gr/Si solar cells was realized.•Performance of Gr/FG/Si solar cell was further enhanced by applying a temporary voltage bias.•PCE of 7.52% and 13.38% were achieved for the pristine Gr/FG/Si solar cell and after AR technique and chemical doping.
The optical and electrical properties of quantum dots (QDs) have generated great interest in the use of QDs for photovoltaics. The optical coupling of QDs with currently manufactured solar cells is ...one of the most promising photovoltaic applications of QDs. Here we demonstrate that by spin-coating Si-QD ink at the solar cell surface the efficiency of screen-printed Si solar cells may be improved. The enhancement of solar cell efficiency results from the porous Si-QD film induced increase of light absorption. The solar cell efficiency may be further improved as the efficiency of down-shifting short-wavelength light to red light by Si-QDs increases.
By spin-coating silicon-quantum-dot (Si-QD) ink at the solar cell surface the efficiency of commercially produced Si solar cells may be improved. The enhancement of solar cell efficiency results from the porous Si-QD film induced increase of light absorption. The solar cell efficiency may be further improved as the efficiency of down-shifting short-wavelength light to red light by Si-QDs increases.
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► Silicon quantum dots (Si-QDs) form porous films at the surface of Si solar cells. ► The porous Si-QD film induced increase of light absorption leads to the enhancement of solar cell efficiency. ► The solar cell efficiency may be further improved as required down-shifting efficiency of Si-QDs is reached.
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