Resonant Energy Transfer can Trigger Multiexciton Recombination in Dense Quantum Dot Ensembles

Core/shell quantum dots/quantum rods are nanocrystals with typical application scenarios as ensembles. Resonance energy transfer is a possible process between adjacent nanocrystals. Highly excited nanocrystals can also relax energy by multiexciton recombination, competing against the energy transfer. The two processes have different dependencies and can be convolved, resulting in collective properties different from the superposition of the individual nanocrystals. A platform to study the interplay of energy transfer and multiexciton recombination is presented. CdSe/CdS quantum dot/quantum rods encapsulated in amphiphilic micelles with an interparticle distance control by spacer ligands are used for time‐resolved photoluminescence and transient absorption experiments. At exciton populations around one, the ensemble starts to be in a state where energy transfer can trigger multiexciton Auger recombination, altering the collective dynamics.     

Ultrasensitive Surface‐Enhanced Raman Spectroscopy Detection Based on Amorphous Molybdenum Oxide Quantum Dots

Surface‐enhanced Raman spectroscopy (SERS) based on plasmonic semiconductive material has been proved to be an efficient tool to detect trace of substances, while the relatively weak plasmon resonance compared with noble metal materials restricts its practical application. Herein, for the first time a facile method to fabricate amorphous H_xMoO₃ quantum dots with tunable plasmon resonance is developed by a controlled oxidization route. The as‐prepared amorphous H_xMoO₃ quantum dots show tunable plasmon resonance in the region of visible and near‐infrared light. Moreover, the tunability induced by SC CO₂ is analyzed by a molecule kinetic theory combined with a molecular thermodynamic model. More importantly, the ultrahigh enhancement factor of amorphous H_xMoO₃ quantum dots detecting on methyl blue can be up to 9.5 × 10⁵ with expending the limit of detection to 10^?9 m . Such a remarkable porperty can also be found in this H_xMoO₃‐based sensor with Rh6G and RhB as probe molecules, suggesting that the amorphous H_xMoO₃ quantum dot is an efficient candidate for SERS on molecule detection in high precision.     

两款木包装箱的生命周期影响分析及对比

目的 研究木包装箱在全生命周期过程中对环境的影响,对比钢边箱和传统木箱对环境的影响.方法 通过全生命周期分析软件eBalance分析2款木包装箱从产品生产、物流运输到使用后的废物管理整个生命周期的物耗、能耗及向环境中的排放,对其数据清单进行分类、特征化和归一化计算,得到木包装箱3个流程的主要环境影响类型和对应指标值.结果 传统木箱在产品生产、物流运输和废物管理流程的LCIA加权综合指标分别为6.87514×10?9,1.93549×10?12,5.20×10?13,其中胶合板生产在产品生产过程中的占比为99.86％,胶合板处理在废物管理过程中的占比为99.82％;钢边箱在产品生产、物流运输和废物管理流程的LCIA加权综合指标分别为6.53463×10?9,3.57256×10?13,2.96531×10?13,其中胶合板生产在产品生产过程中的占比为97.43％,胶合板处理在废物管理过程中的占比为99.38％;钢边箱对环境影响的总量比传统木箱小约5％.结论 木包装箱全生命周期的环境影响主要体现在胶合板的生产和废物管理过程中,木包装箱在设计、生产加工、运输、废弃物处理等方面都有较大的改进余地,钢边箱比传统木箱更具有环境友好性,对木包装箱绿色化的生产设计具有参考意义.     

Recommendations for accurate heat capacity measurements using a Quantum Design physical property measurement system

A commercial instrument for determination of heat capacities of solids from ca. 400 K to 0.4 K, the physical property measurement system from Quantum Design, has been used to determine the heat capacities of a standard samples (sapphire [single crystal] and copper). We extend previous tests of the PPMS in three important ways: to temperatures as low as 0.4 K; to samples with poor thermal conductivity; to compare uncertainty with accuracy. We find that the accuracy of heat capacity determinations can be within 1% for 5 K < T < 300 K and 5% for 0.7 K < T < 5 K. Careful attention should be paid to the relative uncertainty for each data point, as determined from multiple measurements. While we have found that it is possible in some circumstances to obtain excellent results by measurement of samples that contribute more than ca. 1/3 to the total heat capacity, there is no “ideal” sample mass and sample geometry also is an important consideration. In fact, our studies of pressed pellets of zirconium tungstate, a poor thermal conductor, show that several samples of different masses should be determined for the highest degree of certainty.     

SiO2/Si(111)表面Ge量子点的生长研究

Si衬底用化学方法清洗后,表面大约残余1.0 nm厚SiO2薄膜.利用原子力显微镜(AFM)和反射高能电子衍射(RHEED)来研究温度和Ge蒸发厚度对在SiO2薄膜表面生长的Ge量子点的影响.实验结果表明,当衬底温度超过500 ℃时,SiO2开始与Ge原子发生化学反应,并形成与Si(111)表面直接外延的Ge量子点.在650 ℃时,只有Ge的厚度达到0.5nm时,Ge量子点才开始形成.     

Effects of hydrogen dilution on CNx film properties deposited using rf PECVD from a mixture of ethane,nitrogen and hydrogen

Carbon nitride (CN_x) thin films were deposited using radio frequency plasma enhanced chemical vapor deposition (rf PECVD) from a mixture of ethane (C₂H₆), nitrogen (N₂) and hydrogen (H₂) gases. The C₂H₆ and N₂ flow rates were kept constant, while the H₂ flow rate was varied. The effects of hydrogen dilution on the growth rate and structural properties of the films were studied. It was found that a significant increase in the films growth rate was observed with the introduction of H₂ at as low as 25 standard cubic centimeters per minute (sccm). A set of CN_x films deposited from C₂H₆:N₂ mixture without any inclusions of H₂ were also presented in this work as a reference to compare the differences between those two sets and to understand the roles of H₂ to the films properties. At highest H₂ flow rate, the structure of the films changed from polymeric to graphitic and the quenching of PL was observed. Furthermore, higher N incorporation with lower E_g was obtained for these films compared to those of C₂H₆:N₂ films. The change in the structure of the films corresponds to changes in their chemical bonding. As N incorporation increased, the porosity of the films increases and thus affects the disorder in the film structures.     

Quantum beat spectroscopy on excitons in GaN

We present four wave mixing experiments on excitons in GaN. The four wave mixing transients exhibit strong modulations yielding a splitting of the A- and the B-exciton of 7.98 meV. In addition, we obtain a biexciton binding energy for A-excitons of 5.7 meV.     

Single Nucleobase Identification Using Biophysical Signatures from Nanoelectronic Quantum Tunneling

Nanoelectronic DNA sequencing can provide an important alternative to sequencing‐by‐synthesis by reducing sample preparation time, cost, and complexity as a high‐throughput next‐generation technique with accurate single‐molecule identification. However, sample noise and signature overlap continue to prevent high‐resolution and accurate sequencing results. Probing the molecular orbitals of chemically distinct DNA nucleobases offers a path for facile sequence identification, but molecular entropy (from nucleotide conformations) makes such identification difficult when relying only on the energies of lowest‐unoccupied and highest‐occupied molecular orbitals (LUMO and HOMO). Here, nine biophysical parameters are developed to better characterize molecular orbitals of individual nucleobases, intended for single‐molecule DNA sequencing using quantum tunneling of charges. For this analysis, theoretical models for quantum tunneling are combined with transition voltage spectroscopy to obtain measurable parameters unique to the molecule within an electronic junction. Scanning tunneling spectroscopy is then used to measure these nine biophysical parameters for DNA nucleotides, and a modified machine learning algorithm identified nucleobases. The new parameters significantly improve base calling over merely using LUMO and HOMO frontier orbital energies. Furthermore, high accuracies for identifying DNA nucleobases were observed at different pH conditions. These results have significant implications for developing a robust and accurate high‐throughput nanoelectronic DNA sequencing technique.     

Metal-doped (Ti, WC) diamond-like-carbon coatings: Reactions with extreme-pressure oil additives under tribological and static conditions

In contrast to non-doped diamond-like-carbon (DLC) coatings, reliable chemical evidence of the reactions between metal-doped DLC coatings and oil additives under tribological conditions using state-of-the-art surface-sensitive chemical analyses is still scarce. In this study we have investigated the reactivity of metal-doped (Ti, WC) DLC coatings with the extreme-pressure (EP) dialkyl dithiophosphate additive — without the presence of a steel counter body in the contact that befogs the actual coating reactions. Static “reactivity” experiments without any tribological or mechanical effects were also performed to provide a further insight into the lubrication mechanisms. The results confirmed the chemical reactions between the EP additive and all the DLC coatings, as well as their oxidation during the tribological contacts. We measured an about 10-times higher chemical activity (a 25-fold P/S ratio increase) for the Ti-doped DLC compared to the WC-doped or non-doped DLC, which also agrees with it having the lowest amount of wear in this study. We suggest that the Ti-DLC boundary lubrication is achieved via binding sites at the O vacancies present in the Ti-doped DLC coating. The data also clearly show, in contrast to most of literature reports, that even though small, some direct chemical activity between the W-DLC and the dialkyl dithiophosphate EP additive is also possible without any iron catalytic effect. However, the chemical changes were significantly smaller, also allowing coating graphitization, which might be one of the reasons for the 50% higher wear of the WC-doped compared to the Ti-doped DLC.     

过滤阴极真空电弧法制备四面体非晶碳薄膜

利用离面双弯曲过滤阴极其空电弧沉积系统，在Ф200mm单晶硅片上制备四面体非晶碳薄膜。利用Dectek3型表面轮廓仪检验膜厚均匀性(小于5％)，并利用扫描电子显微镜(SEM)、原子力显微镜(AFM)、激光拉曼光谱(Raman)、X射线光电子谱(XPS)以及纳米压痕(Nano—Indenter)仪器测试薄膜的性能和结构。结果表明：试验制备的薄膜是四面体非晶碳薄膜，其中sp^3键含量高达80％以上，薄膜表面纯净，几乎没有大颗粒的污染，表面粗糙度(Rq)小于0．3nm(取样面积1μm^2)，薄膜硬度可达50GPa，杨氏弹性模量高于550GPa。     

Core level and valence band investigation of WO3 thin films with synchrotron radiation

In this work, the electronic properties of the surface of WO₃ films with thickness of 150 nm, thermally evaporated in high vacuum onto Si(100) substrates and pre-treated in air by a 24-h-long annealing at 300 °C and 500 °C (obtaining polycrystalline monoclinic samples) have been studied by surface and bulk sensitive core level (W 4f) and angle integrated valence band photoemission using synchrotron radiation (ELETTRA Synchrotron). The photon energy ranged from 50 eV to 200 eV. The line shape analysis of W 4f core level spectra has shown that the surface presents a sub-stoichiometric WO₃ component assigned to oxygen vacancies ultimately responsible for the gas sensitivity of this material. Correspondingly, valence band spectra show well-defined metallic states W 5d in the gap and near the Fermi level. The variations of surface chemical composition caused by Ultra High Vacuum annealing, and prolonged exposure to UV beam has been monitored by changes in spectral line shape. A general consequence of annealing in vacuum is the segregation of oxygen from the bulk toward the surface as confirmed by independent scanning tunnelling spectroscopy measurements.     

X-ray photoelectron spectroscopy (XPS) and FTIR studies of vanadium barium phosphate glasses

Barium vanadophosphate glasses, having composition 50BaO–xV₂O₅–(50 − x)P₂O₅, (x = 0–50 mol%), were prepared by conventional melt quench method. Density, molar volume and glass transition temperature (T_g) were measured as a function of V₂O₅ content. Structural investigation was done using XPS and FTIR spectroscopy. First, substitution of the P₂O₅ by the V₂O₅ in the metaphosphate 50BaO–50P₂O₅ glass increases the density and T_g and decreases the molar volume. When the amount of V₂O₅ increases, all these properties show a reverse trend. XPS measurement found in the O1s, P2p, and V2p core level spectra indicate the presence of primarily P–O–P, P–O–V and V–O–V structural bonds, the asymmetry in the P 2p spectra indeed arises from the spin-orbit splitting of P 2p core level, and more than one valence state of V ions being present. IR spectroscopy reveals the depolymerization of the phosphate glass network by systematic conversion of metaphosphate chains into pyrophosphate groups and then orthophosphate groups. Even though metaphosphate to pyrophosphate conversion is taking place due to breaking of P–O–P linkages, formation of P–O–V and P–O–Ba linkages provide cross linking between short P-structural units, which make the glass network more rigid. Above 10–20 mol% V₂O₅ content, network is highly depolymerized due to the formation of orthophosphate units and V–O–V bridge bonds, resulting in poor cross-linking, making the glass network less rigid.     

Polyaniline/Vanadium oxide composites: An effective control in morphology by varying reactant concentrations

A one pot synthesis protocol is presented for the realization of organic/inorganic hybrid nanostructures comprised of polyaniline and vanadium oxide. The polyaniline/vanadium oxide hybrid morphology is tailored by controlling the relative concentration of reactants which resulted in diverse morphologies ranging from nanorods, combined nano/microrods to porous nano/microspheres. Temporal evolution of morphology is investigated to elucidate the formation mechanism in detail. The prepared composites exhibit enhanced thermal stability in comparison to pure polyaniline which may be attributed to the strong chemical combination of vanadium oxide and polyaniline within the composites as prevailed by FTIR and TGA analysis of the products. This simple and controllable approach for synthesizing the organic/inorganic hybrid material should have future applications in energy storage devices, sensors and many more.     

Highly-Directional,Highly-Efficient Solution-Processed Light-Emitting Diodes of All-Face-Down Oriented Colloidal Quantum Well Self-Assembly

Semiconductor colloidal quantum wells (CQWs) provide anisotropic emission behavior originating from their anisotropic optical transition dipole moments (TDMs). Here, solution-processed colloidal quantum well light-emitting diodes (CQW-LEDs) of a single all-face-down oriented self-assembled monolayer (SAM) film of CQWs that collectively enable a supreme level of IP TDMs at 92% in the ensemble emission are shown. This significantly enhances the outcoupling efficiency from 22% (of standard randomly-oriented emitters) to 34% (of face-down oriented emitters) in the LED. As a result, the external quantum efficiency reaches a record high level of 18.1% for the solution-processed type of CQW-LEDs, putting their efficiency performance on par with the hybrid organic-inorganic evaporation-based CQW-LEDs and all other best solution-processed LEDs. This SAM-CQW-LED architecture allows for a high maximum brightness of 19,800 cd m⁻² with a long operational lifetime of 247 h at 100 cd m⁻² as well as a stable saturated deep-red emission (651 nm) with a low turn-on voltage of 1.7 eV at a current density of 1 mA cm⁻² and a high J₉₀ of 99.58 mA cm⁻². These findings indicate the effectiveness of oriented self-assembly of CQWs as an electrically-driven emissive layer in improving outcoupling and external quantum efficiencies in the CQW-LEDs.     

Er3+/Yb3+共掺氟硅酸盐玻璃陶瓷的制备及其量子剪裁发光行为

本文报道了一类组成为50SiO2-10Al2O3-20ZnF2-20SrF2-3YbF3-0.05ErF3(mol%)的氟氧化物玻璃陶瓷的制备及其量子剪裁发光行为。XRD和TEM分析结果显示,玻璃陶瓷中均匀分布有尺度10~40nm的SrF2析晶相。光谱研究表明,玻璃陶瓷在Er3+激发峰波长377nm激发下存在Er3+向Yb3+的有效能量传递,可实现包括量子剪裁效应在内的波长变换功能。随着热处理温度的升高,玻璃陶瓷的近红外977nm发光逐渐增强,荧光寿命显著增长。     

The formation of a SiOx interfacial layer on low-k SiOCH materials fabricated in ULSI application

The characterizations of SiOCH films using oxygen plasma treatment depends linearly on the O₂/CO flow rate ratio. According to the results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses, it was found that the carbon composition decreases with increasing O₂/CO flow rate ratio, because more carbon in the Si–O–C and Si–CH₃ bonds on the film surface would be converted by oxygen radicals. It was believed that the oxygen plasma could oxidize the SiOCH films and form a SiO_x interfacial capping layer without much porosity. Moreover, the result of FTIR analysis revealed that there was no water absorbed on the film. A SiO₂-like capping layer formed at the SiOCH film by the O₂/CO flow rate ratio of 0.75 had nearly the same dielectric properties from the result of capacitance–voltage (C–V) measurement in our research.