Nanoparticles-chemistry, new synthetic approaches, gas phase clustering and novel applications

In this paper, an overview of the synthesis, chemistry and applications of nanosystems carried out in our laboratory is presented. The discussion is divided into four sections, namely (a) chemistry of nanoparticles, (b) development of new synthetic approaches, (c) gas phase clusters and (d) device structures and applications. In ‘chemistry of nanoparticles’ we describe a novel reaction between nanoparticles of Ag and Au with halocarbons. The reactions lead to the formation of various carbonaceous materials and metal halides. In ‘development of new synthetic approaches’ our one-pot methodologies for the synthesis of core-shell nanosystems of Au, Ag and Cu protected with TiO₂ and ZrO₂ as well as various polymers are discussed. Some results on the interaction of nanoparticles with biomolecules are also detailed in this section. The third section covers the formation of gas phase aggregates/clusters of thiol-protected sub-nanoparticles. Laser desorption of H₂MoO₄, H2WO₄, MoS₂, and WS₂ giving novel clusters is discussed. The fourth section deals with the development of simple devices and technologies using nanomaterials described above.     

Quantum interference effect in few-layered transition metal dichalcogenide

Van der Waals layered transition metal dichalcogenides (TMDCs), as atomically flat two-dimensional materials, have been studied extensively in both fundamental science and application fields in recent years. The reduced-dimensional properties of TMDCs not only provide a route for the fabricating of efficient field effect transistors and optoelectronic devices but also suggest the possibility of the devices that utilize quantum coherency. In this work, we characterize the electron transport properties of ReS₂, one of the TMDCs, at both room temperature and low temperature. Of particular note, we measured strong quantum conductance oscillations as a function of the gate voltages and source-drain voltages at reduced temperature, which is evidence of quantum coherent transport. This work unambiguously establishes ReS₂ as a promising candidate for future quantum materials.     

Recent advances on Fe- and Mn-based cathode materials for lithium and sodium ion batteries

The ever-growing market of electrochemical energy storage impels the advances on cost-effective and environmentally friendly battery chemistries. Lithium-ion batteries (LIBs) are currently the most critical energy storage devices for a variety of applications, while sodium-ion batteries (SIBs) are expected to complement LIBs in large-scale applications. In respect to their constituent components, the cathode part is the most significant sector regarding weight fraction and cost. Therefore, the development of cathode materials based on Earth’s abundant elements (Fe and Mn) largely determines the prospects of the batteries. Herein, we offer a comprehensive review of the up-to-date advances on Fe- and Mn-based cathode materials for LIBs and SIBs, highlighting some promising candidates, such as Li- and Mn-rich layered oxides, LiNi_0.5Mn_1.5O₄, LiFe_1-xMn_xPO₄, Na_xFe_yMn_1-yO₂, Na₄MnFe₂(PO₄)(P₂O₇), and Prussian blue analogs. Also, challenges and prospects are discussed to direct the possible development of cost-effective and high-performance cathode materials for future rechargeable batteries.     

Nanoparticles from the Gas Phase as Building Blocks for Electrical Devices

Electrical device development is driven by miniaturization and possibilities to use new chemical and physical effects. Nanotechnology offers both aspects. The structural dimensions of materials and devices are small and because of that large exchange surfaces are provided but also effects like quantum effects may occur and be used to get new or at least improved properties of nanostructured materials and devices.Nanoparticles are of special interest because of their nanodimensions in all three directions, so that nanoeffects become most prominent. They can be synthesized in solid materials, in liquids and in gases. Gas synthesis has several advantages compared to the other phases, especially the high cleanliness which can be achieved. In case of electrical devices the particles have to be deposited onto substrates in a structured way.The substrate may consist out of microelectronic devices in which the deposited nanoparticles are introduced for the basic function. In case of a transistor this would be the gate function, in case of a sensor this would be the sensing layer, where the contact with the measurement object takes place. For two kinds of particles SnO₂ and PbS, synthesized in the gas phase, we demonstrate the way how to create devices with improved sensor properties.     

First-principles studies on mechanical,electronic, magnetic and optical properties of new multiferroic members BiLaFe2O6 and Bi2FeMnO6: Originated from BiFeO3

Recently multiferroic materials have attract great interest for the applications on memorial, spintronic and magneto-electric sensor devices for their spontaneous magneto-electric coupling properties. Research and development of the various kinds of multiferroics are indispensable factor for a new generation multifunctional materials. In this research, mechanical, electronic, magnetic and nonlinear optical properties of La modified BiLaFe₂O₆ (BLFO) and Mn modified Bi₂FeMnO₆ (BFMO) were studied as new members of multiferroic BiFeO₃ (BFO) series by first-principles calculations, and compared with the pure BFO to discover the optimized properties. Our results show that BLFO and BFMO have good mechanical stability as revealed by elastic constants that satisfy the stability criteria. All these compounds exhibit anisotropic and ductile nature. The enhanced properties by La and Mn substitution, such as increased hardness, improved magnetism, decreased band gap and comparable second harmonic generation responses reveal that the new multiferroic members of BLFO and BFMO would get wider application than their BFO counterpart. Our study is expected to providing an appropriate mechanical reference data as guidance for engineering of high efficiency multifunctional devices with the BFO series.     

高k介质在新型半导体器件中的应用

当CMOS器件特征尺寸缩小到45 nm以下, SiO₂作为栅介质材料已经无法满足性能和功耗的需要, 用高 k材料替代SiO₂是必然选择. 然而, 由于高 k材料自身存在局限性, 且与器件其他部分的兼容性差, 产生了很多新的问题如界面特性差、 阈值电压增大、 迁移率降低等. 本文简要回顾了高 k栅介质在平面型硅基器件中应用存在的问题以及从材料、 结构和工艺等方面采取的解决措施, 重点介绍了高k材料在新型半导体器件中的应用, 并展望了未来的发展趋势.     

A comparison of algainas and InGaAsP-based 1.3 μm semiconductor lasers using high pressure

Abstract

We have compared the effect of hydrostatic pressure on the threshold current, I_th, and lasing energy, E_lase, of 1.3 pm quantum-well devices based upon AlGaInAs and InGaAsP. Whilst we observe a very similar dependence of E_lase on pressure for the two materials, we measure strikingly different variations of I_th. By applying pressure to 1.3 μm InGaAsP lasers, I_th typically decreases by ～ 10% over 1 GPa consistent with the reduction of Auger recombination, which forms ～ 50% of I_th at room temperature. However, for the 1.3 μm AlGaInAs-based lasers, we observe an increase in I_th by ～ 8% over the same pressure range. From these results we conclude that non-radiative recombination accounts for only ～ 20% of I_th in AlGaInAs-based devices. This is in good agreement with previous temperature dependence measurements and shows why AlGaInAs-based devices exhibit a reduced temperature sensitivity of I_th which is very important for telecommunications applications.     

Elastic and photo-elastic characteristics of laser crystals potassium rare-earth tungstates KRE(WO4)2, where RE = Y,Yb, Gd and Lu

The elastic and photo-elastic characteristics of four laser crystals KY(WO₄)₂, KGd(WO₄)₂, KYb(WO₄)₂, and KLu(WO₄)₂ are presented. The first pair was reported early, and the last two materials have been investigated for the first time. The full matrix of elastic constants of these monoclinic crystals has been determined. Also, acousto-optical figure of merit for all the basic geometries of isotropic diffraction has been measured. It is proved that potassium rare-earth tungstates has rather good acousto-optical properties and particularly can take place of fused silica in technical applications required high power laser radiation. All the results demonstrate good prospect of these optically bi-axial laser crystals for development of new effective acousto-optical devices.     

Theoretical study of enhanced ferromagnetism and tunable magnetic anisotropy of monolayer CrI3 by surface adsorption

Magnetic anisotropy energy (MAE) plays a key role for 2D magnetic materials, which have attracted significant attention for their promising applications in spintronic devices. Based on first-principles calculations, we have investigated the influence of surface adsorption on the ferromagnetism and MAE of monolayer CrI₃. We find that Li adsorption can dramatically enhance its ferromagnetism, and tune its easy magnetization axis to the in-plane direction from original out-of-plane at certain coverage of Li. The monotonic enhancement of in-plane magnetism in CrI₃ as the coverage of Li increases are attributed to electrostatic doping induced by charge transfer between Li atoms and I atoms, as supported by the charge doping simulation. The tunable robust magnetic anisotropy may open new promising applications of CrI₃–based materials in spintronic devices.     

Effect of precursor on growth and morphology of MoS2 monolayer and multilayer

The rise of two-dimensional (2D) material is one of the results of successful efforts of researchers which laid the path to the new era of electronics. One of the most exciting materials is MoS₂. Synthesis has been always a major issue as electronic devices need reproducibility along with similar properties for mass productions. Chemical vapor deposition (CVD) is one of the successful methods for 2D materials including graphene. Furthermore, the choice of starting materials for Mo and S source is crucial. The different source has different effects on the layers and morphology of MoS₂ films. In this work, we have extensively studied the CVD technique to grow few layers of MoS₂ with two precursors MoO₃ and MoCl₅, show remarkable changes. The MoO₃ source gives a triangular shaped MoS₂ monolayer while that of MoCl₅ can achieve uniform MoS₂ without triangle. The absence of geometric shapes with MoCl₅ is poorly understood. We tried to explain with MoCl₅ precursor, the formation of continuous monolayer of MoS₂ without any triangle on the basis of chemical reaction formalism mostly due to one step reaction process and formation of MoS₂ from gas phase to the solid phase. The film synthesized by MoCl₅ is more continuous and it would be a good choice for device applications.     

Nanoscale Transition Metal Dichalcogenides: Structures,Properties, and Applications

Transition metal dichalcogenides (TMDs), such as MoS₂, MoSe₂, WS₂, and WSe₂, are layered materials with strong in-plane ionic-covalent bonds and weak out-of-plane van der Waals interactions, enabling formation of various nanostructures, such as nanotubes, nanoribbons, nanoflakes, and fullerene-like nanoparticles. Various remarkable properties have been found recently in these nanostructures, opening up brand new opportunities for their applications in nanoelectronics, optoelectronics, spintronics and structural materials. In this article, we present recent advances in the study of two-dimensional TMDs and their derivatives with special emphasis on structures, morphologies, properties (electronic, magnetic, thermal, mechanical), and applications (transistors, sensors, catalysts, lubricants, and composite materials). In addition, routes for modifying these properties by chemical doping, defect engineering, strain engineering, and electric fields are discussed. Our intent is to present a state-of-the-art view in this fast evolving field, with a balanced theoretical and experimental perspective.     

Electrochemical open circuit voltage (OCV) characterization of SOFC materials

In this paper, we are reporting an extensive characterization, by means of open circuit voltage measurements, of Ce_0.8Gd_0.2O₂, La_0.9Sr_0.1Ga_0.8Mg_0.2O₃, and La₂Mo_0.6W_1.4O₉ oxide-ions and BaCe_0.8Y_0.2O₃ and BaCe_0.55Zr_0.3Y_0.15O₃ proton-conducting electrolyte materials for solid oxide fuel cell (SOFC) applications. This simple and common technique, well known for a long time in the electrochemical study of solid oxide fuel cells, has been here proposed for the electrical characterization of these ceramic materials, in order to define their ionic transport numbers, the maximum voltage performances, the thermal and chemical stability, and also to suggest the ideal temperature range for different applications, as in the electrochemical devices, sensors, and SOFC field. In the paper, controlled and reproducible working conditions have been applied in a wide range of temperature, by means of ultrapure gas (H₂ and O₂), under operational conditions found in real SOFC devices and, mainly, without the usual problems related to the chemical compatibility, the depolarization efficiency, and the high current density required to the electrode materials in the design of a more efficient SOFC device.     

Flame synthesis of 1-D complex metal oxide nanomaterials

One dimensional (1-D) complex metal oxide nanomaterials, such as ternary oxides, doped oxides, and hierarchical structures containing several oxides, not only benefit from large aspect ratios, but also offer exciting opportunities to design materials with desired properties by tuning their chemical compositions and tailoring their sizes and morphologies at the nanometer scale. Flame synthesis is an attractive method to grow 1-D complex metal oxide nanostructures because of its high temperature, scalability, low-cost and rapid growth rate. Here, we present three new combined flame synthesis methods: (1) simultaneous vapor–vapor growth, (2) simultaneous solid–vapor growth, and (3) sequential solid–vapor growth, to grow 1-D complex metal oxide nanostructures with well-defined compositions and morphologies. These three methods combine the previously reported flame vapor deposition and solid diffusion growth methods that were separately used to grow 1-D simple binary metal oxide nanostructures, and significantly advance the capabilities of existing flame synthesis methods for the growth of 1-D nanomaterials. The first method, simultaneous vapor–vapor growth, combines the flame vapor deposition growth of two different metal oxides by oxidizing and evaporating two different metal sources. With this we have successfully grown W-doped MoO₃ nanoplates and nanoflowers. In the second method, simultaneous solid–vapor growth, one precursor is again provided by oxidizing and evaporating metal oxide from a metal, while the other precursor diffuses out from a different growth substrate. With this we have successfully grown ternary Cu₃Mo₂O₉ nanowires. The third method, sequential solid–vapor growth, essentially uses the 1-D nanostructures firstly grown by solid diffusion as the substrates for subsequent flame vapor deposition. With this we have successfully grown hierarchical CuO/MoO₃ core/shell nanowires and MoO₃-branched CuO nanowires. We believe that these three new combined flame synthesis methods will provide a general platform for the synthesis of 1-D complex metal oxide nanostructures with tailored properties.     

Review of 5-V electrodes for Li-ion batteries: status and trends

Lithium-ion batteries have dominated the battery industry for the past several years in portable electronic devices due to their high volumetric and gravimetric energy densities. The success of these batteries in small-scale applications translates to large-scale applications, with an important impact in the future of the environment by improving energy efficiency and reduction of pollution. We present the progress that allows several lithium-intercalation compounds to become the active cathode element of a new generation of Li-ion batteries, namely the 5-V cathodes, which are promising to improve the technology of energy storage and electric transportation, and address the replacement of gasoline engine by meeting the increasing demand for green energy power sources. The compounds considered here include spinel LiNi_0.5Mn_1.5O₄ and its related doped-structures, olivine LiCoPO₄, inverse spinel LiNiVO₄ and fluorophosphate Li₂CoPO₄F. LiNi_0.5Mn_1.5O₄ thin films, nanoscale prepared materials and surface-modified cathode particles are also considered. Emphasis is placed on the quality control that is needed to guarantee the reliability and the optimum electrochemical performance of these materials as the active cathode element of Li-ion batteries. The route to increase the performance of Li-ion batteries with the other members of the family is also discussed.     

Detection of internal cracks and ultrasound characterization of nanostructured Bi₂Te₃-based thermoelectrics via acoustic microscopy

The search for thermoelectric (TE) materials for highly efficient devices aims at improving the TE efficiency and broadening their areas of applications. We created nanostructured thermoelectric Bi-Sb-Te-family materials by high energy (ball milling) pre-treatment of the parent materials followed by high-pressure/high-temperature treatment. Bi_0.5Sb_1.5Te₃ compositions with the superfluous maintenance of tellurium was used for the synthesis of the samples with p-type electrical conductivity. Acoustic microscopy was used to study elastic properties and bulk irregularities and to detection of internal cracks both in the parent materials and in the created nanostructured samples. The data has been used for optimization of parameters of synthesis of nanostructured thermoelectrics.     

A new superhard material: Osmium diboride OsB2

Superhard materials have many industrial applications, wherever resistance to abrasion and wear are important. The synthesis of new superhard materials is one of the great challenges to scientists. We re-examined the phase diagram of the binary osmium-boron system and confirmed the existence of two hexagonal phases, OsB_1.1, Os₂B₃, and an orthorhombic phase, OsB₂. Almost nothing is known about the physical properties of osmium borides. Microhardness measurements show that OsB₂ is extremely hard. Ab initio calculations show that this is due to formation of covalent bonds between boron atoms. OsB₂ is also a low compressibility material. It can be used as hard coating.     

Self-standing polyvinyl chloride film as flexible substrate for WSe2 based photodetector

Self-standing polymer materials have gained recognition as a flexible substrate for various optoelectronic devices. Here, we incorporated polyvinyl chloride (PVC) with tungsten diselenide (WSe₂) microcrystals. The WSe₂ microcrystals are added to PVC by solution mixing process. The WSe₂-PVC composite film possess excellent flexibility, electrical conductivity of 20 kΩsq⁻¹ at room temperature, high photoresponsivity of 0.3310 mAW⁻¹, detectivity of 1.527 x 10⁹ Jones and external quantum efficiency up to 8.7%. The free-standing WSe₂-PVC photodetectors show durability and reproducibility even after 7 months and show stable photoresponse in the bent state. The visible light WSe₂-PVC photodetector is sensitive to different monochromatic radiations (470 nm, 540 nm and 670 nm) and demonstrates potential applications in next-generation wearable optoelectronic devices.     

Robust Fabrication of Quantum Dots on Few‐Layer MoS2 by Soft Hydrogen Plasma and Post‐Annealing

Apart from unique properties of layered transition‐metal dichalcogenide nanosheets like MoS₂, quantum dots (QDs) from these layered materials promise novel science and applications due to their quantum confinement effect. However, the reported fabrication techniques for such QDs all involve the use of liquid organic solvents and the final material extraction from such liquid dispersions. Here a novel and convenient dry method for the synthesis of MoS₂ quantum dots interspersed on few‐layer MoS₂ using soft hydrogen plasma treatment followed by post‐annealing is demonstrated. The size of MoS₂ nanodots can be well controlled by adjusting the working pressure of hydrogen plasma and post‐thermal annealing. This method relies on the cumulative hydrogen ion bombardment effect which can destroy the hexagonal structure of the top MoS₂ layer and disintegrate the top layer into MoS₂ nanodots and even QDs. Post‐thermal annealing can further reduce the size. Such MoS₂ quantum dots interspersed on few‐layer MoS₂ exhibit two new photoluminescence peaks at around 575 nm because of the quantum confinement effect. This dry method is versatile, scalable, and compatible with the semiconductor manufacturing processes, and can be extended to other layered materials for applications in hydrogen evolution reaction, catalysis, and energy devices.     

Einstein relation in n-i-p-i and microstructures of nonlinear optical, optoelectronic and related materials: Simplified theory, relative comparison and suggestions for an experimental determination

We investigate the Einstein relation for the diffusivity-mobility ratio (DMR) for n-i-p-i and the microstructures of nonlinear optical compounds on the basis of a newly formulated electron dispersion law. The corresponding results for III-V, ternary and quaternary materials form a special case of our generalized analysis. The respective DMRs for II-VI, IV-VI and stressed materials have been studied. It has been found that taking CdGeAs₂, Cd₃As₂, InAs, InSb, Hg_1−xCd_xTe, In_1−xGa_xAs_yP_1−y lattices matched to InP, CdS, PbTe, PbSnTe and Pb_1−xSn_xSe and stressed InSb as examples that the DMR increases with increasing electron concentration in various manners with different numerical magnitudes which reflect the different signatures of the n-i-p-i systems and the corresponding microstructures. We have suggested an experimental method of determining the DMR in this case and the present simplified analysis is in agreement with the suggested relationship. In addition, our results find three applications in the field of quantum effect devices.     

Piezoelectricity in two‐dimensional group III–V buckled honeycomb monolayers

We studied the elastic and piezoelectric properties of buckled honeycomb group III–V monolayers (GaP, GaAs, GaSb, InP, InAs and InSb) by DFT calculations. Those buckled monolayers are ferroelectric and have nonzero e₁₁, e₃₁, d₁₁ and d₃₁ piezoelectric coefficients. Our calculations show that those monolayers are good piezoelectric materials and a pronounced periodic trend of the piezoelectric coefficients e₁₁, e₃₁, d₁₁ and d₃₁ was found. Group III–V monolayers are promising candidates for future atomically thin piezoelectric applications such as transducers, sensors, and energy harvesting devices.