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Showing papers by "Zhong Chen published in 2010"


Journal ArticleDOI
TL;DR: The N-doped TiO(2) nanotubes exhibited higher photocatalytic activity in degradating methyl orange into non-toxic inorganic products under both UV and simulated sunlight irradiation.

231 citations


Journal ArticleDOI
TL;DR: In this article, the authors used pulse current deposition to prepare evenly distributed and uniformly sized Ag nanoparticles on a TiO2 nanotube array photoelectrode, and the resulting electrode contained intimately coupled, three-dimensional Ag/TiO2 structures with greatly improved photocurrent generation and charge transfer compared to a two-dimensional random Ag particle layer.
Abstract: In the current work, pulse current deposition has been used to prepare evenly distributed and uniformly sized Ag nanoparticles on a TiO2 nanotube array photoelectrode. The Ag particle size and loading were controlled by the pulse deposition time. The Ag/TiO2 nanotube arrays were characterized by SEM, TEM, XRD, XPS and UV-vis diffuse reflection absorption. The resulting electrode contained intimately coupled, three-dimensional Ag/TiO2 structures with greatly improved photocurrent generation and charge transfer compared to a two-dimensional random Ag particle layer deposited directly on top of the nanotube array by the regular photoinduction method. A model mechanism is proposed to illustrate the uniform Ag nanoparticle deposition via the new deposition technique developed in the current work that promotes the uniform distribution of the Ag particles whilst minimizing their deposition at tube entrances, thus effectively preventing the pores from becoming clogged.

176 citations


Journal ArticleDOI
Xiaobo Qu1, Weiru Zhang1, Di Guo1, Congbo Cai1, Shuhui Cai1, Zhong Chen1 
TL;DR: Simulation results demonstrate that contourlet-based CS-MRI can better reconstruct the curves and edges than traditional wavelet- based methods, especially at low k-space sampling rate.
Abstract: Reducing the acquisition time is important for clinical magnetic resonance imaging (MRI). Compressed sensing has recently emerged as a theoretical foundation for the reconstruction of magnetic resonance images from undersampled k-space measurements, assuming those images are sparse in a certain transform domain. However, most real-world signals are compressible rather than exactly sparse. For example, the commonly used two-dimensional wavelet for compressed sensing MRI (CS-MRI) does not sparsely represent curves and edges. In this article, we introduce a geometric image transform, the contourlet, to overcome this shortage. In addition, the improved redundancy provided by the contourlet can successfully suppress the pseudo-Gibbs phenomenon, a tiresome artefact produced by undersampling of k-space, around the singularities of images. For numerical calculation, a simple but effective iterative thresholding algorithm is employed to solve l 1 norm optimization for CS-MRI. Considering the recovered information ...

156 citations


Journal ArticleDOI
TL;DR: In this paper, MoS 2 -metal composite coatings were analyzed by energy dispersive analysis of X-ray (EDX), X-rays diffraction (XRD), and nanoindentation experiments.
Abstract: Solid-lubricant MoS 2 coatings have been successfully applied in high vacuum and aerospace environments. However, these coatings are very sensitive to water vapor and not suitable for applications in moist environments. In this work, Cr- and T-doped MoS 2 composite coatings were developed. The results demonstrated that these composite coatings are promising for applications in high humidity environments. MoS 2 –Cr and MoS 2 –Ti composite coatings with different Cr or Ti content were deposited on high speed steel substrate by unbalanced magnetron sputtering. The composition, microstructure, and mechanical properties of the as-deposited MoS 2 -metal composite coatings were analyzed by energy dispersive analysis of X-ray (EDX), X-ray diffraction (XRD), and nanoindentation experiments. The tribological properties of the coatings were evaluated against an alumina ball under different relative humidity atmosphere using a ball-on-disc tribometer. The MoS 2 –Cr and MoS 2 –Ti coatings showed a maximum hardness of 7.5 GPa and 8.4 GPa at a dopant content of 16.6 at.% Cr or 20.2 at.% Ti, respectively. The tribological test results showed that, with a small amount of Cr and/or Ti doping, the tribological properties of MoS 2 coatings under humid atmosphere could be significantly improved. The optimum doping level was found to be around 10 at.% for both MoS 2 –Cr coatings and MoS 2 –Ti coatings to show the best tribological properties, with both the lowest friction coefficient and wear rate. The excellent tribological properties of the MoS 2 –Cr and MoS 2 –Ti coatings with an appropriate metal doping level in moist atmosphere are found due to their ability to form stable transfer layer on the surface of the counterbody, which supplies lubrication for the contact surface.

154 citations


Journal ArticleDOI
TL;DR: In this paper, a chalcogenide, [Mn{sub 2}Sb{sub 3]Sb[sub 2]S{sub 5}(N{ sub 2}H{sub 4}(sub 3}]-sub 4]-sub 3]-sub 5] (1) has been synthesized by hydrazine-hydrothermal method, which has an optical band gap of about 2.09 eV and displays photocatalytic behaviors under visible light irradiation.

122 citations


Journal ArticleDOI
TL;DR: It is shown that sperm entry was sufficient to trigger central cell mitotic division, suggesting the existence of signaling events associated with sperm cell fusion with female gametes, and that the paternal genome plays an essential role during early seed development.
Abstract: Fertilization in flowering plants involves two sperm cells and two female gametes, the egg cell and the central cell, progenitors of the embryo and the endosperm, respectively. The mechanisms triggering zygotic development are unknown and whether both parental genomes are required for zygotic development is unclear. In Arabidopsis, previous studies reported that loss-of-function mutations in CYCLIN DEPENDENT KINASE A1 (CDKA;1) impedes cell cycle progression in the pollen leading to the production of a single sperm cell. Here, we report that a significant proportion of single cdka;1 pollen delivers two sperm cells, leading to a new assessment of the cdka;1 phenotype. We performed fertilization of wild-type ovules with cdka;1 mutant sperm cells and monitored in vivo the fusion of the male and female nuclei using fluorescent markers. When a single cdka;1 sperm was delivered, either female gamete could be fertilized leading to similar proportions of seeds containing either a single endosperm or a single embryo. When two cdka;1 sperm cells were released, they fused to each female gamete. Embryogenesis was initiated but the fusion between the nuclei of the sperm cell and the central cell failed. The failure of karyogamy in the central cell prevented incorporation of the paternal genome, impaired endosperm development and caused seed abortion. Our results thus support that the paternal genome plays an essential role during early seed development. However, sperm entry was sufficient to trigger central cell mitotic division, suggesting the existence of signaling events associated with sperm cell fusion with female gametes.

111 citations


Journal ArticleDOI
Jingjing Xu1, Shuyu Yang1, Shuhui Cai1, Jiyang Dong1, Xuejun Li1, Zhong Chen1 
TL;DR: The results from the PCA of all four groups indicated that diet plays a greater role in influencing metabolite differences than gender, and the potential of metabolomics when applied to nutritional and physiological studies is shown.
Abstract: A vegetarian diet has been demonstrated to have a profound influence on human metabolism as well as to aid the prevention of several chronic diseases relative to an omnivorous diet. However, there have been no systematic metabolomic studies on all of the biochemical changes induced in human subjects by long-term vegetarianism. In this study, (1)H NMR spectroscopy in combination with multivariate statistical analysis was applied to explore the variability in the metabolic urinary profiles of healthy populations from four groups: lactovegetarian male (VEGMALE), lactovegetarian female (VEGFEMALE), omnivorous male (OMNMALE), and omnivorous female (OMNFEMALE). Differences in metabolic profiles were examined in relation to diet and gender by principal component analysis (PCA) and spectral integrals. It was found that the most influential low molecular weight metabolites responsible for the differences between the diet groups were N-acetyl glycoprotein (NAG), succinate, citrate, trimethylamine-N-oxide (TMAO), taurine, glycine, hippurate, phenylalanine, methylhistidine and formate, whereas for the differences in gender groups the most discriminatory metabolites were NAG, succinate, creatinine, arginine, TMAO, taurine, hippurate, mannitol, phenylalanine, and methylhistidine. The results from the PCA of all four groups indicated that diet plays a greater role in influencing metabolite differences than gender. As an exploration, this work shows the potential of metabolomics when applied to nutritional and physiological studies, and it will aid further studies.

77 citations


Journal ArticleDOI
TL;DR: In this article, the growth kinetics of the Cu-Al IMCs were correlated to the diffusion process during aging; their combined activation energy was estimated to be 1.01 eV.
Abstract: Interface evolution caused by thermal aging under different temperatures and durations was investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that approximately 30-nm-thick and discontinuous Cu-Al intermetallic compounds (IMCs) were present in the initial bonds before aging. Cu-Al IMCs grew under thermal aging with increasing aging time. The growth kinetics of the Cu-Al IMCs was correlated to the diffusion process during aging; their combined activation energy was estimated to be 1.01 eV. Initially, Al-rich Cu-Al IMCs formed in the as-bonded state and early stage of aging treatment. Cu9Al4 was identified by selected-area electron diffraction (SAD) as the only type of Cu-Al IMC present after thermal aging at 250°C for 100 h; this is attributed to the relatively short supply of aluminum to the interfacial reaction.

76 citations


Journal ArticleDOI
TL;DR: In this article, the PMI2 Project Grant No. 41 through the UK Department for Innovation, Universities and Skills DIUS was used to support the work of the authors in this paper.
Abstract: This research was funded as a PMI2 Project Grant No. RC 41 through the UK Department for Innovation, Universities and Skills DIUS.

63 citations


Journal ArticleDOI
TL;DR: In this paper, the authors use first-principles calculations to clarify the origin of the visible light absorption in chalcogen element-doped TiO2 and show that interstitial doping is not the origin for visible light absorbing under any equilibrium growth conditions, but rather, sensitization is achievable via substitutional doping of O (or Ti) at Ti-rich (or O-rich) conditions, respectively.
Abstract: We use first-principles calculations to clarify the origin of the visible light absorption in chalcogen elementdoped TiO2. Our results show that interstitial doping is not the origin of visible light absorption under any equilibrium growth conditions, but rather, sensitization is achievable via substitutional doping of O (or Ti) at Ti-rich (or O-rich) conditions, respectively. With increasing atomic number (from S to Te), it is harder to form anion-doped TiO2 but easier to achieve cationic doping. Both anionic and cationic doping can confer visible light absorption, but the former is more effective. The effect increases with increasing atomic number of the chalcogen element. Dopant pairing is found in anionic S-, Se-, and Te- and cationic S-doped TiO2 .W e further identified that anion pairing induces a bathochromic shift in the absorption, whereas cationic pairing causes the opposite, that is, a hypsochromic (blue) shift, predictions that agree well with the experimental findings.

60 citations


Journal ArticleDOI
TL;DR: A simple method to control the phase and morphology of titanium-based oxides is demonstrated and excellent performance has been shown in the MB adsorption test by the sodium titanate nanostructures.
Abstract: Titania (TiO2) and sodium titanate nanostructures with controllable phases and morphologies were synthesized by a hydrothermal method with titanium disulfide (TiS2) as the starting material. Sodium titanate nanobelts could be synthesized under a relatively low alkaline concentration (1 mol L−1 NaOH) and short duration (6 h). At 3 mol L−1 HCl, rutile TiO2 nanorods were synthesized. Anatase TiO2 nanoparticles were obtained at pH values ranging between 2 and 13. FTIR analysis confirmed the phase change as the pH of the reacting medium increased from highly acidic to highly alkaline. The adsorption of Methylene Blue (MB) on the as-synthesized sodium titanate nanobelts fitted well with the Langmuir monolayer model, with an adsorption capacity as high as 312.5 mg g−1. The kinetics of MB adsorption was found to be a pseudo-second-order kinetic model. In brief, this study demonstrates a simple method to control the phase and morphology of titanium-based oxides. Excellent performance has been shown in the MB adsorption test by the sodium titanate nanostructures.

Journal ArticleDOI
TL;DR: In this paper, a chemical solution approach modified with both diethanolamine (DEA) and ethylenediaminetetraacetic acid (EDTA) as stabilizing agents was used to obtain a remarkably low leakage current and well-saturated polarization hysteresis loop.
Abstract: (K0.5Na0.5)NbO3 (KNN)-based ferroelectric thin films were prepared by a chemical solution approach modified with both diethanolamine (DEA) and ethylenediaminetetraacetic acid (EDTA) as the stabilizing agents. The obtained KNN thin films exhibited a remarkably low leakage current and well-saturated polarization hysteresis loop. The effective piezoelectric strain coefficient d33 and voltage coefficient g33 under the clamping of the substrate were improved to 74.0 pm/V and 28.3 mm V/N, respectively. The reason for the superior properties was found that the addition of EDTA and DEA was effective in suppressing the volatilization of K and Na at moderate temperature before the crystallization.

Journal ArticleDOI
TL;DR: It is shown that loss-of-function of the major DNA LIGASE I (AtLIG1) in Arabidopsis thaliana causes maternal effects in the endosperm, which is the seed tissue that nurtures embryo development.
Abstract: Maternal effects are defined by mutations that affect the next generation when they are maternally inherited. To date, most indepth studies of maternal effects in plants have attributed their origin to genomic imprinting that restricts expression to the maternal allele. The DNA glycosylase DEMETER (DME) removes methylated cytosine residues, causing transcriptional activation of the maternal allele of imprinted genes. In this study, we show that loss-of-function of the major DNA LIGASE I (AtLIG1) in Arabidopsis thaliana causes maternal effects in the endosperm, which is the seed tissue that nurtures embryo development. AtLIG1 expression is not imprinted and has a limited impact on imprinted gene expression. Genetic interaction analyses further indicate that AtLIG1 acts downstream of DME. The removal of methylated cytosine residues by DME involves the creation of DNA single-strand breaks and our results suggest that AtLIG1 repairs these breaks.

Journal ArticleDOI
TL;DR: A mechanism has been proposed to explain the formation of the OCP patterned film with hierarchically porous structure and distinct selectivity.

Journal ArticleDOI
TL;DR: In this article, an ultrafast and template-free method to synthesize three-dimensional (3D) hierarchical layered titanate microspherulite (TMS) particles with high surface area is reported.
Abstract: An ultrafast and template-free method to synthesize three-dimensional (3D) hierarchical layered titanate microspherulite (TMS) particles with high surface area is reported. The synthesis makes use of an electrochemical spark discharge spallation (ESDS) process, during which a fast anodic reaction on the titanium surface creates a layer of titanium dioxide that instantly breaks down by the applied electrical field into the solution in the form of titanium oxide particles. The spalled particles readily react with the heated NaOH electrolyte to form the titanate particles. A typical as-prepared TMS with a diameter of 0.4∼1.5 μm is synthesized by ESDS of Ti foils in 10 M NaOH solution under an applied current density of 0.5 A cm−2, leading to a reaction yield of approximately 0.10∼0.15 g per square centimetre of exposed Ti foil within 20 min. After hydrogen ion exchange, the surface area can reach as high as ∼406 m2 g−1. On the Ti surface, a crystalline rutile TiO2 nanosheet structure is formed, which is attributed to the local exothermic heat caused by the spark discharge. A formation mechanism of the TMS is discussed based on field emission scanning electron microscopy (FESEM), a transmission electron microscopy (TEM) study and Raman scattering spectroscopy analysis. The as-prepared TMS shows excellent adsorption performance compared with a titanate micro-particle (TMP), nanowire (TNW) and nanotube (TNT) when methylene blue (MB) and PbII ions are used as representative organic and inorganic pollutants. The mechanism of adsorption has also been discussed.

Journal ArticleDOI
TL;DR: A onestep, template-free method (electrochemical spark discharge spallation) to quickly fabricate layered titanate hierarchical microspherulites with a large surface area by carefully adjusting the applied electrical spark parameters in the experimental setup is reported.
Abstract: Recently, a new hydrothermal approach to fabricate titanate materials has attracted much attention. These layered titanate nanomaterials show excellent abilities in ion-exchange, absorption, photoelectronicity, and so on. To satisfy the requirement of different applications, there has been a drastic increase in research to develop new approaches to produce different types of semiconductor oxide nanostructures, especially titanium-based oxides. Up to now, the synthesis of 1D and 2D nanotitanate has been widely investigated with many interesting properties reported. For example, 1D titanate nanotubes, nanowires, nanorods, and 2D titanate nanosheets have been synthesized by hydrothermal, high-temperature oxidation, molten-salt synthesis, and exfoliation methods. Among which hydrothermal synthesis is most widely used. Recent investigations have demonstrated that 3D hierarchical nanostructures could improve the performance of the material in catalysis, biomedical, energy conversion, and water-treatment applications, among others, due to the superior properties derived from the high specific surface area and porous structure. However, it is still challenging to produce 3D hierarchically complex shapes of titanate over multiple scales and the synthetic method is usually not straightforward. Until now, the general approach for preparing hierarchical titanate structures involved the use of sacrificial templates, such as zinc oxide nanotemplate. Alternatively, the template-free methods for generating hierarchical titanates typically employ bottom-up methods, such as reacting agar gel containing a solution of titanium precursor in NH4OH, [5b] two-stage growth through an H2O2-enhanced oxidation process, [5c] twostep synthesis combining hydrolysis and hydrothermal treatment, the chimie douce route by heating TiO2 powder in 15m NaOH solution at reflux, and self-assembly by treating TiCl4 precursor in ethylenediamine at high temperaACHTUNGTRENNUNGtures.[5f] These approaches either take multiple steps or require a long time to ensure complete reaction, for example, the time taken for the reaction between agar gel with Ti precursor and NH4OH is one week. [5b] A simple, fast, and inexpensive method to form 3D hierarchical nanostructures is still lacking and will be of great interest. It is known that a TiO2 porous layer can be formed on a Ti foil surface by mild anodic oxidation in fluoride-containing solutions, rapid breakdown anodization in chloride-/perchlorate-containing electrolytes, or a plasma electrolytic oxidation method. However, to the best of our knowledge, there are no reports using these techniques to generate the titanate materials in powder form, which is traditionally prepared by hydrothermal method. Herein, we report a onestep, template-free method (electrochemical spark discharge spallation) to quickly fabricate layered titanate hierarchical microspherulites (TMSs) with a large surface area (406 mg ) by carefully adjusting the applied electrical spark parameters in the experimental setup (Figure S1 in the Supporting Information). The formation principle of the layered titanate is different from the formation of the TiO2 nanostructures, which include two important steps. First, an ultrahigh anodic reaction oxidizes the Ti surface layer and the formed oxide is immediately broken down by the applied electrical field into the solution in the form of small precipitates. This spallation of the oxide particle is driven by the continuously discharged sparks that simultaneously heat [a] Y. Tang, Dr. Y. Lai, D. Gong, Prof. Z. Dong, Prof. Z. Chen School of Materials Science and Engineering Nanyang Technological University, 50 Nanyang Avenue 639798 (Singapore) Fax: (+65)6790-9081 E-mail : zldong@ntu.edu.sg aszchen@ntu.edu.sg [b] Dr. Y. Lai State Key Laboratory of Physical Chemistry of Solid Surfaces College of Chemistry and Chemical Engineering Xiamen University, Xiamen, 361005 (China) [c] K.-H. Goh, Prof. T.-T. Lim School of Civil and Environmental Engineering Nanyang Technological University, 50 Nanyang Avenue 639798 (Singapore) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000330.

Journal ArticleDOI
TL;DR: In this article, position and orientation-controllable micropatterned ZnO/TiO2 nanostructures with different morphologies have been fabricated using a novel and versatile superhydrophilic/superhydrophobic template.
Abstract: Position- and orientation-controllable micropatterned ZnO/TiO2 nanostructures with different morphologies have been fabricated using a novel and versatile superhydrophilic/superhydrophobic template. Scanning electron microscopy, optical microscopy, electron probe microanalysis and X-ray diffraction were systematically used to confirm the successful fabrication of the patterns and to characterize the structure and morphology. The selective growth of ordered ZnO nanostructured patterns on the TiO2 nanotube surface employs a simple photocatalytic lithography technique with mild reaction conditions and in the absence of seeds and noble metal catalysts. The photoelectrical properties of the micropatterned ZnO/TiO2 nanocomposites with unique heterojunction structure and different density and orientation of the ZnO crystals were also investigated. It is expected that this novel micropatterned technique based on the superhydrophilic/superhydrophobic template will become a powerful tool for fabricating various types of micropatterned nanomaterials and devices.

Journal ArticleDOI
TL;DR: In this article, a wettability template-assisted process was applied to selectively deposit cadmium sulfide (CdS) nanospheres on TiO2 nanotube layers to form uniformly coupled CdS/TiO2 semiconductor heterojunction micropatterns.

Proceedings ArticleDOI
Xiaobo Qu1, Xue Cao1, Di Guo1, Changwei Hu1, Zhong Chen1 
14 Mar 2010
TL;DR: Simulation results demonstrate that the proposed method can improve image quality when comparing to single sparsifying transform, and is implemented via the state-of-art smoothed l0 norm in overcomplete sparse decomposition.
Abstract: Undersampling the k-space is an efficient way to speed up the magnetic resonance imaging (MRI). Recently emerged compressed sensing MRI shows promising results. However, most of them only enforce the sparsity of images in single transform, e.g. total variation, wavelet, etc. In this paper, based on the principle of basis pursuit, we propose a new framework to combine sparsifying transforms in compressed sensing MRI. Each transform can efficiently represent specific feature that the other can not. This framework is implemented via the state-of-art smoothed l 0 norm in overcomplete sparse decomposition. Simulation results demonstrate that the proposed method can improve image quality when comparing to single sparsifying transform.

Journal ArticleDOI
Can Wu1, Mingfang Zhao1, Shuhui Cai1, Yulan Lin1, Zhong Chen1 
TL;DR: Comparisons between the experimental results and those of the previous real-time phase-modulated spatial encoding method demonstrate that the signal-to-noise ratio and resolution of the 2D COSY spectra are improved, and a good 2DCOSY spectrum is easier to achieve by using the proposed methods.

Journal ArticleDOI
TL;DR: A new pulse sequence based on intermolecular single-quantum coherences (iSQCs) is proposed to obtain high-resolution NMR spectroscopy in inhomogeneous magnetic fields via fast 2D acquisition and can recover useful information of chemical shifts, relative peak areas, J coupling constants, and multiplet patterns even when the field inhomogeneity is severe enough to erase almost all spectroscopic information.

Journal ArticleDOI
TL;DR: In this article, the feasibility of in vivo intermolecular double-quantum coherences (iDQC) high-resolution MR spectroscopy in the presence of large intrinsic and external field inhomogeneity was demonstrated in the whole cerebellum of normal volunteers in a scan time of about 6.5 min.
Abstract: Signals from intermolecular double-quantum coherences (iDQCs) have been shown to be insensitive to macroscopic field inhomogeneities and thus enable acquisition of high- resolution MR spectroscopy in the presence of large inhomogeneous fields. In this paper, localized iDQC 1H spectroscopy on a whole-body 3-T MR scanner is reported. Experiments with a brain metabolite phantom were performed to quantify characteristics of the iDQC signal under different conditions. The feasibility of in vivo iDQC high-resolution MR spectroscopy in the presence of large intrinsic and external field inhomogeneity (in the order of hundreds of hertz) was demonstrated in the whole cerebellum of normal volunteers in a scan time of about 6.5 min. Major metabolite peaks were well resolved in the reconstructed one-dimensional spectra projected from two-dimensional iDQC acquisitions. Investigations on metabolite ratios, signal-to-noise ratio, and line width were performed and compared with results obtained with conventional point-resolved spectroscopy/MR spectroscopy in homogeneous fields. Metabolite ratios from iDQC results showed excellent consistency under different in vitro and in vivo conditions, and they were similar to those from point-resolved spectroscopy with small voxel sizes in homogeneous fields. MR spectroscopy with iDQCs can be applied potentially for quantification of gross metabolite changes due to diseases in large brain volumes with high field inhomogeneity. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.

Journal ArticleDOI
TL;DR: In this paper, the morphological features of lift-off footprints on the aluminium metallization pads were investigated to gain an understanding of the effects of bonding parameters on formation of initial bonds during thermosonic gold ball bonding.

Journal ArticleDOI
Yuqing Huang1, Xi Chen, Shuhui Cai, Congbo Cai, Zhong Chen 
TL;DR: A new pulse sequence is proposed based on intermolecular zero-quantum coherences (iZQCs) to obtain high-resolution two-dimensional correlation spectroscopy (COSY) in inhomogeneous fields via three-dimensional (3D) acquisition to eliminate the influences of field inhomogeneity on the conventional COSY methods.
Abstract: A new pulse sequence is proposed based on intermolecular zero-quantum coherences (iZQCs) to obtain high-resolution two-dimensional (2D) correlation spectroscopy (COSY) in inhomogeneous fields via three-dimensional (3D) acquisition. This sequence extends the high-resolution iZQC approaches from one dimension to two dimensions. Since the iZQC evolution periods in the new sequence are insensitive to the field inhomogeneities, high-resolution COSY spectra can be recovered from inhomogeneous fields by projecting the 3D data onto the indirectly acquired 2D plane. Theoretical expressions were derived according to the distant dipolar field treatment combined with product operator formalism. Both the experimental observations and computer simulations are consistent with the theoretical predictions. The new sequence thus provides an attractive way to eliminate the influences of field inhomogeneity on the conventional COSY methods, which may be useful for the study of chemical and biological materials.

Journal ArticleDOI
TL;DR: In this paper, a gold wire (20μm diameter/99.99 per cent wt%) was bonded to aluminium metallization pads (1μm thick) on a silicon chip using a commercial ball/wedge automatic bonder.
Abstract: Purpose – Optimization of the process parameters remains a challenging task in thermosonic wire bonding due to relatively poor understanding of the bonding mechanism. The purpose of this paper is to understand initial bond formation in thermosonic gold wire bonding on aluminium metallization pads and the effect of bonding time on the initiation of bonding.Design/methodology/approach – A gold wire (20 μm diameter/99.99 per cent wt%) was bonded to aluminium metallization pads (1 μm thick) on a silicon chip using a commercial ball/wedge automatic bonder. Bonding parameters were selected specifically to produce underdeveloped ball bonds so that ball lift‐off occurred during looping process. The lift‐off footprints on the aluminium metallization pads and their evolution were carried out using optical microscopy and scanning electron microscopy. A model is proposed to elaborate the effect of bonding time on initiation of bonding.Findings – The obtained results showed that metallurgical bonding initiated at the ...

Journal ArticleDOI
TL;DR: The results show that this sequence provides an attractive and efficient way to eliminate the influence of field inhomogeneities on 2D J-resolved spectra, which is potentially useful for characterizing complex chemical materials and studying biological metabolites in inhomogeneous fields.
Abstract: A new pulse sequence based on intermolecular single-quantum coherences (iSQCs) is proposed to achieve high-resolution two-dimensional (2D) J-resolved spectra in inhomogeneous fields via three-dimensional (3D) acquisition. Since the iSQC evolution period and spin echo evolution period in this sequence are intrinsically insensitive to magnetic field inhomogeneities, high-resolution 2D J-resolved spectra can be recovered from nuclei in inhomogeneous fields by projecting the 3D data onto the 2D plane. Analytical expressions of the resulting signals were derived assuming the secular dipole-dipole interaction. Analyses of a solution sample placed in a deliberately unshimmed magnetic field and of a biological sample with intrinsic field inhomogeneities were performed. The results show that this sequence provides an attractive and efficient way to eliminate the influence of field inhomogeneities on 2D J-resolved spectra, which is potentially useful for characterizing complex chemical materials and studying biological metabolites in inhomogeneous fields.

Journal ArticleDOI
TL;DR: In this article, a test scheme to evaluate solder joint interface fracture toughness using double cantilever beam (DCB) test has been successfully demonstrated, in terms of critical energy release rate, predict the joint failure based on the principle of fracture mechanics.
Abstract: In the current work, a test scheme to evaluate solder joint interface fracture toughness using double cantilever beam (DCB) test has been successfully demonstrated. The obtained results, in terms of critical energy release rate, predict the joint failure based on the principle of fracture mechanics. The results can be used as a materials property in the reliability design of various types of solder-ball joined packages. DCB specimens made of 99.9 wt% copper were selected in the current work. Eutectic Sn-37Pb and lead-free Sn-3.5Ag-0.5Cu solders were used to join two pieces of the copper beams with controlled solder thickness. The test record showed steady propagation of the crack along the solder / copper interface, which verifies the viability of such a testing scheme. Interface fracture toughness for as-joined, extensively-reflowed and thermally aged samples has been measured. Both the reflow treatment and the thermal aging lead to degradation of the solder joint fracture resistance. Reflow treatment was more damaging as it induces much faster interface reaction. Fractographic analysis established that the fracture has a mixed micromechanism of dimple and cleavage. The dimples are formed as a result of the separation between the hard intermetallic compound (IMC) particles and the soft solder material, while the cleavage is formed by the brittle split of the IMCs. When the IMC thickness is increased due to extended interface reaction, the proportion of IMC cleavage failure increases, and this was reflected in the decrease of the critical energy release rate.

Journal ArticleDOI
TL;DR: The results of density functional calculations provided a reasonable explanation on the relative reactivity of the pyrazole-like ligands as well as the important role of solvation in these reactions.

Journal ArticleDOI
TL;DR: In this paper, single-crystalline InVO4 nanotubes have been successfully synthesized by annealing electrospun precursor fibers using self-template-directed mechanism.
Abstract: Single-crystalline InVO4 nanotubes have been successfully synthesized by annealing electrospun precursor fibers. The products were characterized by X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy, which demonstrated that they are single-crystalline nanotubes. The growth of these nanotubes is considered to be a two-step process involving a self-template-directed mechanism.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a method to use the NNSF of China and the Research Fund for the Doctoral Program of Higher Education of China (RPHE) to support research at the University of Shanghai.