系列专贴－－Nature China Research Highlights
[size=2][font=Verdana][i][color=red][b]Nature China[/b][/color][/i] highlights the best research coming out of Mainland China and Hong Kong, providing scientists from around the world with a convenient portal into publications drawn from across all scientific disciplines. Each week, our editors select the best published research and provide a summary of the results. By organizing this research into a comprehensive, regularly updated, one-stop web portal, we hope to help you quickly reach the resources you need to study, and to keep you up-to-date with the most significant research coming out of Mainland China and Hong Kong.[/font][/size][font=Verdana][size=2][/size][/font]
[url=http://www.nature.com/nchina/index.html]http://www.nature.com/nchina/index.html[/url]
[b][size=3][color=red]------------------------------------------------------------------------------------------[/color][/size][/b][table=540][tr][td=2,1][font=verdana, arial, helvetica, sans-serif][size=2][color=#000000][b]24 September 2008[/b][/color][/size][/font]
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[url=http://www.nature.com/nchina/2008/080924/full/nchina.2008.224.html][size=3][color=blue]Porous materials: Forced to order[/color][/size][/url]
Vicki Cleave
Abstract
High-temperature drying of composite solutions leads to ordered pores in polymer films
Original article citation
You, B. [i]et al.[/i] [url=http://dx.doi.org/10.1021/ma801417c][color=#0000ff]A facile method for fabrication of ordered porous polymer films[/color][/url]. Macromolecules doi: 10.1021/ma801417c (2008).
Introduction[img]http://www.nature.com/nchina/2008/080924/images/nchina.2008.224-i1.jpg[/img] © (2008) ACS
Porous films — especially those with three-dimensionally ordered pores — are useful for many applications, such as photonics, biosensing and catalysis. However, the fabrication of ordered pores in films often requires complex procedures, including the making, use and removal of a template, as well as precise controls that are unsuitable for mass production. To address these problems, Limin Wu and co-workers at Fudan University in Shanghai[url=http://www.nature.com/nchina/2008/080924/full/nchina.2008.224.html#B1][color=#800080]1[/color][/url] have introduced a 'forced drying' method that has just one step, can be used with any substrate, and enables control of the pore size.
The researchers stirred latex polymer nanoparticles and silica nanoparticles, which were hundreds and tens of nanometres in diameter, respectively, into water. They then cast the polymer solution — by spin-coating, brush-coating or pouring — onto a variety of substrates, such as glass, silicon wafer and plastic. After drying the sample at high temperatures (above 120 °C) for two hours or more, a periodic array of pores was formed in the film (pictured).
Changing the polymer nanoparticle size controls the pore sizes and distribution. The exact formation mechanism has yet to be explained, but Wu and co-workers showed that silica particles are vital — without them, no porous structure would form.
The authors of this work are from:
Department of Materials Science and Advanced Materials Laboratory, Fudan University, Shanghai, China.
Reference
[list=1][*]You, B. [i]et al.[/i] A facile method for fabrication of ordered porous polymer films. Macromolecules doi: 10.1021/ma801417c (2008). | [url=http://dx.doi.org/10.1021/ma801417c][color=#0000ff]Article[/color][/url] |[/list]
[size=3][color=blue]Hybrid materials: Well spread[/color][/size]
Vicki Cleave
Abstract
A chemical approach ensures nanoparticles are well dispersed in hybrid materials
Original article citation
Liu, X. [i]et al.[/i] [url=http://dx.doi.org/10.1021/la8020639][color=#0000ff]Organic–inorganic nanohybrids via directly grafting gold nanoparticles onto conjugated copolymers through the Diels–Alder reaction[/color][/url]. Langmuir doi: 10.1021/la8020639 (2008).
Introduction[img]http://www.nature.com/nchina/2008/080924/images/nchina.2008.223-i1.jpg[/img] © (2008) ACS
Hybrid materials are a topic of intense interest at present because they provide the potential to combine the best properties of different components into one material. Unfortunately, favourable properties are often lost as a result of the poor dispersion of components within the material. Yuliang Li at the Chinese Academy of Sciences in Beijing and co-workers[url=http://www.nature.com/nchina/2008/080924/full/nchina.2008.223.html#B1][color=#800080]1[/color][/url] have developed a chemical approach that avoids this problem.
The researchers produced a composite of two electronically active components — namely, conjugated polymers and gold nanoparticles. They functionalized the gold nanoparticles with maleimide groups, and used a polymer with furan pendant groups branching off from its conjugated backbone (pictured), so that they could bring them together using the Diels–Alder reaction.
The Diels–Alder reaction is one of the most important ways in which chemists make new carbon–carbon bonds, and here it proceeds under very mild conditions: at room temperature, in chloroform and away from light. As the polymer and nanoparticles come together, their electronic spectra are influenced by each other's presence, so the reaction can be monitored simply from the change in the mix's ultraviolet-to-visible spectrum.
The components were well dispersed throughout the final hybrid, giving it the cumulative properties of their electronic and optical signatures and pronounced nonlinear optical properties that promise novel device applications.
The authors of this work are from:
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China; Graduate University of Chinese Academy of Sciences, Beijing, China; Suzhou University, Suzhou, China; Department of Physics, Harbin Institute of Technology, Harbin, China.
Reference
[list=1][*]Liu, X. [i]et al.[/i] Organic–inorganic nanohybrids via directly grafting gold nanoparticles onto conjugated copolymers through the Diels–Alder reaction. Langmuir doi: 10.1021/la8020639 (2008). | [url=http://dx.doi.org/10.1021/la8020639][color=#0000ff]Article[/color][/url] |[/list]
[size=2][color=blue][/color][/size][size=2][color=blue]Fullerenes: Symmetry breakers[/color][/size]
Felix Cheung
Abstract
Researchers in Xiamen are close to making symmetry-breaking buckminsterfullerenes
Original article citation
Tan, Y. Z. [i]et al.[/i] [url=http://www.nature.com/doifinder/10.1038/nmat2275][color=#0000ff]Two [i]I[/i]h-symmetry-breaking C60 isomers stabilized by chlorination[/color][/url]. Nature Mater. doi: 10.1038/nmat2275 (2008). [url=http://www.nature.com/uidfinder/10.1038/nmat2275?referral=true][color=#0000ff]Full text article available for download[/color][/url] free
Introduction[img]http://www.nature.com/nchina/2008/080924/images/nchina.2008.221-i1.jpg[/img] © (2008) Nature Materials
Buckminsterfullerene (C60) was discovered more than two decades ago. However, icosahedrally symmetric C60 ([i]I[/i]h-C60), which resembles a soccer ball, remains the only C60 species that can be made in an experiment. Structural variations of C60 — especially those without icosahedral symmetry — might be possible, but nobody has figured out how to make them yet. Suyuan Xie and co-workers at Xiamen University[url=http://www.nature.com/nchina/2008/080924/full/nchina.2008.221.html#B1][color=#800080]1[/color][/url] have now produced two chlorinated symmetry-breaking C60 species — just one step away from an actual symmetry-breaking C60 structure.
The carbon atoms of [i]I[/i]h-C60 are arranged in hexagons and pentagons, in which no two pentagons share an edge. Fusing pentagons together would make the C60 structure unstable, so Xie and co-workers overcame this problem by adding chlorine atoms at the edges of the fused pentagons. They managed to produce two symmetry-breaking species, C60Cl8 and C60Cl12 (pictured), both of which contained fused pentagons in their structure.
When the researchers optimized the reaction conditions, they could improve the yield of the C60Cl8 to 3.5% the weight of the crude product, which is comparable to the 4.2% yield of [i]I[/i]h-C60. The yield of C60Cl12 is much lower, but still enough for detailed characterization and property investigations in future studies.
The authors of this work are from:
State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China.
Reference
[list=1][*]Tan, Y. Z. [i]et al.[/i] Two [i]I[/i]h-symmetry-breaking C60 isomers stabilized by chlorination. Nature Mater. doi: 10.1038/nmat2275 (2008). | [url=http://www.nature.com/doifinder/10.1038/nmat2275][color=#0000ff]Article[/color][/url] |[/list]
[color=red][fbox=Random Bonus]Congratulations to sally208, who obtained 5 token(s) from the system by posting this thread.[/fbox][/color]
[[i] 本帖最后由 sally208 于 2008-9-25 11:35 编辑 [/i]] 谢谢提供！
:victory: 好帖。
希望越来越多的中国人的工作引起世界的注意。
也希望这里面看到chem8er的工作。 多谢分享！
回复 1# sally208 的帖子
support. :) 多谢分享！支持 支持中国人的nature! GOOD JOB 支持国货Nanotubes: Confusing conduction
Published online: 1 October 2008 | doi:10.1038/nchina.2008.231[size=1][color=red][b]Nanotubes: Confusing conductionTim Reid[/b][/color][/size]
Abstract
Carbon nanotubes made with lots of deliberate defects could conduct electricity in strange nonlinear ways
Original article citation
Li, Y. F., Li, B. R. & Zhang, H. L. [url=http://dx.doi.org/10.1088/0953-8984/20/41/415207][color=#0000ff][i]Ab initio[/i] investigations of the transport properties of Haeckelite nanotubes[/color][/url]. J. Phys.: Condens. Matter 20, 415207 (2008).
Introduction[img]http://www.nature.com/nchina/2008/081001/images/nchina.2008.231-i1.jpg[/img] © (2008) IOP
The performance of carbon nanotubes is strongly affected by structural defects. This has led researchers to propose novel carbon structures, known as haeckelite nanotubes (HNTs), which could have improved electronic properties. Bingrui Li and co-workers at Lanzhou University[url=http://www.nature.com/nchina/2008/081001/full/nchina.2008.231.html#B1][color=#800080]1[/color][/url] have performed calculations showing that HNTs could demonstate some unusual conduction phenomena, including 'negative resistance'.
Haeckelite nanotubes are largely composed of Stone–Wales defects, in which the usual hexagon structure switches to pentagons and heptagons (pictured). This type of defect is thought to lower the electronic bandgap of nanotubes, leading to semiconducting or even conducting behaviour.
Li and co-workers simulated the electronic properties of a short segment of HNT suspended either between electrodes made from other HNTs, or between two gold electrodes. Both systems were predicted to have clear metallic (conducting) behaviour. The conduction was not linear, however, and at some points the current was found to decrease with voltage, indicating negative resistance.
The researchers suggest that the negative resistance arose because the conduction energy bands of the electrodes and the sample did not match up. This implies that more unusual transport properties could be discovered in nanoscale carbon electronics, especially when the 'leads' are on the same small scale as the components.
The authors of this work are from:
State Key Laboratory of Applied Organic Chemistry (SKLAOC), College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, China.
Reference
[list=1][*]Li, Y. F., Li, B. R. & Zhang, H. L. [i]Ab initio[/i] investigations of the transport properties of Haeckelite nanotubes. J. Phys.: Condens. Matter 20, 415207 (2008). | [url=http://dx.doi.org/10.1088/0953-8984/20/41/415207][color=#0000ff]Article[/color][/url] |[/list]
Left-handed materials: Different Dopplers
Published online: 1 October 2008 | doi:10.1038/nchina.2008.232[color=red][b]Left-handed materials: Different DopplersTim Reid[/b][/color]
Abstract
The Doppler shift in left-handed materials depends on whether the movement is straight or rotational
Original article citation
Luo, H. [i]et al.[/i] [url=http://dx.doi.org/10.1103/PhysRevA.78.033805][color=#0000ff]Rotational Doppler effect in left-handed materials[/color][/url]. Phys. Rev. A 78, 033805 (2008).
Introduction[img]http://www.nature.com/nchina/2008/081001/images/nchina.2008.232-i1.jpg[/img] © (2008) APS
Artificial left-handed materials, which exhibit negative refraction, have attracted attention for the unusual effects they have on light waves. Shuangchun Wen and co-workers at Hunan University in Changsha[url=http://www.nature.com/nchina/2008/081001/full/nchina.2008.232.html#B1][color=#800080]1[/color][/url] have shown that although left-handed materials can reverse the Doppler frequency shift for a source moving in a straight line, it is not reversed for rotational movement.
In the usual Doppler shift, observers experience an increased wave frequency as they move towards a wave source. This effect is reversed for waves propagating in a left-handed material. Wen and co-workers investigated what would happen to the Doppler shift for a rotating observer. The finding is important for applications that use Laguerre–Gaussian laser beams, which have a spiral-shaped wavefront.
The researchers calculated the effective refractive index experienced by a Laguerre–Gaussian beam in a left-handed material. They found that the rotational Doppler shift stays the same as in a right-handed substance.
This counterintuitive phenomenon occurs because both the phase velocity and screwing motion of the spiral wavefront are reversed (see image). These two effects cancel out, and the left-handed material may actually transfer angular momentum to the beam. The effect could shed light on the Abraham–Minkowski dilemma — a long-standing disagreement over how to quantify the momentum of photons.
The authors of this work are from:
Key Laboratory for Micro/Nano Opto-Electronic Devices, Ministry of Education, School of Computer and Communication, Hunan University, Changsha, China.
Reference
[list=1][*]Luo, H. [i]et al.[/i] Rotational Doppler effect in left-handed materials. Phys. Rev. A 78, 033805 (2008). | [url=http://dx.doi.org/10.1103/PhysRevA.78.033805][color=#0000ff]Article[/color][/url] |[/list]
Nanoparticles: Easy beadwork
Published online: 8 October 2008 | doi:10.1038/nchina.2008.237[color=red][b]Nanoparticles: Easy beadwork[/b][/color]
[b][color=black]Vicki Cleave[/color][/b]
Abstract
A simple chemical approach links nanoparticles like beads on a chain
Original article citation Zhu, L., Xue, D. & Wang, Z. [url=http://dx.doi.org/10.1021/la802207m][color=#0000ff]Metallic cation induced one–dimensional assembly of poly(acrylic acid)–1–dodecanethiol–stabilized gold nanoparticles[/color][/url]. Langmuir doi: 10.1021/la802207m (2008).
Introduction[img]http://www.nature.com/nchina/2008/081008/images/nchina.2008.237-i1.jpg[/img] © (2008) ACS
Nanoparticles come in various shapes, but doing something practical with them often relies on being able to construct a more complex assembly. Zhenxin Wang at the Chinese Academy of Sciences in Changchun and co-workers[url=http://www.nature.com/nchina/2008/081008/full/nchina.2008.237.html#B1][color=#800080]1[/color][/url] have added a useful tool to the box of assembly methods available — the ability to create 'chain networks' from gold nanoparticles. Their simple method is based on adding metal cations to a solution of stabilized nanoparticles.
Wang and co-workers stabilized their nanoparticles with poly(acrylic acid)-containing ligands. Poly(acrylic acid) has several carboxylic acid units, which are well-known to have a strong affinity to some metallic cations. When lead cations are added to the solution, they bind to the ligands, bringing the particles together to form chains (pictured). Adding more lead cations extends the average length of the chains, and their absorption spectrum signatures change as a result, so their growth can be tracked.
Nanoparticles form chain networks instead of aggregates because, in solution, the ligands produce a uniformly distributed negative charge across the surface of the nanoparticles. When a metal cation is bound to one ligand, its positive charge repels the negative cloud, creating a dipole. Further metal cations are therefore attracted to the opposite side of the particle, forming chains.
The authors of this work are from:
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, China; School of Biological Engineering, Changchun University of Technology, Changchun, China.
Reference
[list=1][*]Zhu, L., Xue, D. & Wang, Z. Metallic cation induced one–dimensional assembly of poly(acrylic acid)–1–dodecanethiol–stabilized gold nanoparticles. Langmuir doi: 10.1021/la802207m (2008). | [url=http://dx.doi.org/10.1021/la802207m][color=#0000ff]Article[/color][/url] |[/list]
Electrospinning: Taking it to the third dimension
Published online: 8 October 2008 | doi:10.1038/nchina.2008.238[color=red][b]Electrospinning: Taking it to the third dimension[/b][/color]
Vicki Cleave
Abstract
Manipulating electric fields enables the production of three-dimensional electrospun structures
Original article citationZhang, D. & Chang, J. [url=http://dx.doi.org/10.1021/nl801667s][color=#0000ff]Electrospinning of three–dimensional nanofibrous tubes with controllable architectures[/color][/url]. Nano Lett. doi: 10.1021/nl801667s (2008).
Introduction[img]http://www.nature.com/nchina/2008/081008/images/nchina.2008.238-i1.jpg[/img] © (2008) ACS
Electrospinning is a versatile technique for creating continuous fibres with diameters on the nanoscale. Usually, two-dimensional sheets of randomly arranged fibres are created by the process, but Daming Zhang and Jiang Chang at the Chinese Academy of Sciences in Shanghai[url=http://www.nature.com/nchina/2008/081008/full/nchina.2008.238.html#B1][color=#800080]1[/color][/url] have developed an approach that could produce three-dimensional fibrous structures. A wide range of structures can be made through this approach, providing opportunities for applications in tissue engineering, blood-vessel reconstruction and filtration.
In a typical electrospinning system, a charged polymer solution is extruded as a jet from the tip of a syringe by electrostatic repulsion. The jet, which still carries a charge, is drawn towards a grounded collector template (usually a metal plate) placed some distance away. As the solvent in the polymer solution evaporates, a charged polymer fibre is left to accumulate on the grounded collector.
Zhang and Chang replaced the collector plate with a three-dimensional 'working collector' (usually a metal cylinder) that was coupled with two assistant collectors (a plane assistant collector and a stick assistant collector). Using these three collectors, the researchers could manipulate the electric fields to cause the electrospun fibres to deposit on the three-dimensional collector template, forming tubes with different shapes, open or closed ends, and even interconnected tubes (pictured). They could also create different nanofibre patterns on the structures, which have been shown to have an effect on cell activities in tissue engineering.
The authors of this work are from:
Biomaterials and Tissue Engineering Research Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China.
Reference
[list=1][*]Zhang, D. & Chang, J. Electrospinning of three–dimensional nanofibrous tubes with controllable architectures. Nano Lett. doi: 10.1021/nl801667s (2008). | [url=http://dx.doi.org/10.1021/nl801667s][color=#0000ff]Article[/color][/url] |[/list] Published online: 15 October 2008 | doi:10.1038/nchina.2008.240
[size=3][color=red][b]Fluorescent spectroscopy: Mercury exposed[/b][/color][/size]
Felix Cheung
Abstract
New fluorescent sensors can be used to quantify the biological effects of mercury ions in living cells
Original article citation
Zhang, X., Xiao, Y. & Qian, X. [url=http://dx.doi.org/10.1002/anie.200803246][color=#0000ff]A ratiometric fluorescent probe based on FRET for imaging Hg2+ ions in living cells[/color][/url]. Angew. Chem. Int. Ed. doi: 10.1002/anie.200803246 (2008).
Introduction[img]http://www.nature.com/nchina/2008/081015/images/nchina.2008.240-i1.jpg[/img] © (2008) Wiley Interscience
Mercury ions (Hg2+) can enter the human body through the skin and lungs, causing serious damage to the brain and kidneys. Fluorescence spectroscopy has become the tool of choice for sensing and imaging the biological effects of Hg2+ in living cells; the technique determines the degree of cellular damage by the change in the fluorescence intensity in cells that have been stained with fluorescent sensors. Yi Xiao at Dalian University of Technology and co-workers[url=http://www.nature.com/nchina/2008/081015/full/nchina.2008.240.html#B1][color=#800080]1[/color][/url] have developed a sensor that can selectively detect amounts of Hg2+ on the scale of parts per billion.
Typical fluorescent sensors give off light with a single emission peak, the intensity of which can be affected by factors such as probe concentration. These sensors are therefore no good for quantitative measurements.
Xiao and co-workers developed a BODIPY–rhodamine system (BODIPY and rhodamine are both fluorescent sensors) that has two characteristic peaks. In the presence of Hg2+, the emission peak of the system changes from 514 nm (the characteristic peak of BODIPY; pictured top) to 589 nm (the characteristic peak of rhodamine; pictured bottom) through a mechanism known as fluorescence resonance energy transfer. The intensity ratio of the two characteristic peaks is independent of probe concentration and can be used for calibration prior to quantitative measurements.
The sensor can be dissolved in water as well as organic solvents — an important property that ensures the sensor gets inside the cell for intracellular fluorescent imaging. The researchers have shown that, in experiments, the probe can be used in the Hg2+ imaging of living cells.
The authors of this work are from:
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, China; Laboratory of Chemical Biology, East China University of Science and Technology, Shanghai, China.
Reference
[list=1][*]Zhang, X., Xiao, Y. & Qian, X. A ratiometric fluorescent probe based on FRET for imaging Hg2+ ions in living cells. Angew. Chem. Int. Ed. doi: 10.1002/anie.200803246 (2008). | [url=http://dx.doi.org/10.1002/anie.200803246][color=#0000ff]Article[/color][/url][/list]
Dinitrogen cleavage: Breaking up is hard
Published online: 15 October 2008 | doi:10.1038/nchina.2008.243[size=3][color=red][b]Dinitrogen cleavage: Breaking up is hard[/b][/color][/size]
Vicki Cleave
Abstract
Researchers in Nanjing provide mechanistic insight into potential low-temperature, low-pressure ammonia production
Original article citation
Li, J. & Li, S. [url=http://dx.doi.org/10.1002/anie.200801668][color=#0000ff]Energetics and mechanism of dinitrogen cleavage at a mononuclear surface tantalum center: A new way of dinitrogen reduction[/color][/url]. Angew. Chem. Int. Ed. doi: 10.1002/anie.200801668 (2008).
Introduction[img]http://www.nature.com/nchina/2008/081015/images/nchina.2008.243-i1.jpg[/img] © (2008) Wiley Interscience
The Haber–Bosch process was devised in 1910, and is still used to make ammonia in the industry today. However, alternatives are sought because the process requires high temperatures and pressures to break the strong triple bond in dinitrogen (N2). A long-awaited low-pressure and room-temperature process to break the dinitrogen bond using tantalum hydride on silica has been reported[url=http://www.nature.com/nchina/2008/081015/full/nchina.2008.243.html#B1][color=#800080]1[/color][/url], but the underlying mechanism is still poorly understood. Shuhua Li and Jun Li at Nanjing University[url=http://www.nature.com/nchina/2008/081015/full/nchina.2008.243.html#B2][color=#800080]2[/color][/url] have calculated the possible reaction pathways, deciphered the two slowest steps in the reaction, and showed that metals other than tantalum could also be used.
The bond-breaking reaction begins with the catalyst (pictured) — tantalum hydride (Ta marked in light blue, H marked in white) supported on a silica surface (Si marked in yellow, O marked in red). Dinitrogen (N marked in dark blue) binds directly to the tantalum, and causes the hydride ion to move to one of the nitrogens. This hydride transfer was found to be one of the slowest steps in the reaction, limiting the rate at which the dinitrogen bond can be broken.
Afterwards, more hydride ions bind to the tantalum. Two further hydride transfers to the nitrogen atoms from the tantalum occur before the dinitrogen bond finally breaks. The third hydride transfer was found to be the other rate-limiting step.
The overall reaction is strongly energetically favoured, and the researchers showed that the bond breakage could still be achieved if tantalum is replaced with niobium.
The authors of this work are from:
School of Chemistry and Chemical Engineering, Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, Ministry of Education, Nanjing University, Nanjing, China.
References
1. Avenier, P. et al. Dinitrogen dissociation on an isolated surface tantalum atom. Science 317, 1056–1060 (2007). [url=http://dx.doi.org/10.1126/science.1143078][color=#0000ff]Article[/color][/url]
2. Li, J. & Li, S. Energetics and mechanism of dinitrogen cleavage at a mononuclear surface tantalum center: A new way of dinitrogen reduction. Angew. Chem. Int. Ed. doi: 10.1002/anie.200801668 (2008). | [url=http://dx.doi.org/10.1002/anie.200801668][color=#0000ff]Article[/color][/url] |
Spintronics: Finding the better half
Published online: 15 October 2008 | doi:10.1038/nchina.2008.244[size=3][color=red][b]Spintronics: Finding the better half[/b][/color][/size]
[size=3][color=red]
[size=2][color=black]Vicki Cleave[/color][/size][/color][/size]
Abstract
The range of potential materials for spin filters has expanded
Original article citation
Wang, L. [i]et al[/i]. [url=http://dx.doi.org/10.1021/nl8016016][color=#0000ff]Novel one-dimensional organometallic half metals: Vanadium-cyclopentadienyl, vanadium-cyclopentadienyl-benzene, and vanadium-anthracene wires[/color][/url]. Nano Lett. doi: 10.1021/nl8016016 (2008).
Introduction
Spintronics — an emerging technology that exploits the 'up' and 'down' spins of electrons — promises improved performance and enhanced functionality for next-generation solid-state devices. Spin filters, which let spins of only one orientation through, are particularly important spintronic components. Zhengxiang Gao at Peking University in Beijing and co-workers[url=http://www.nature.com/nchina/2008/081015/full/nchina.2008.244.html#B1][color=#800080]1[/color][/url] have applied density functional theory (DFT) to investigate the potential of using organic materials for making spin filters.
[img]http://www.nature.com/nchina/2008/081015/images/nchina.2008.244-i1.jpg[/img] © (2008) ACS
Half metals — materials that act as a conductor to electrons of one spin, but an insulator to electrons of the opposite spin — are known to be good candidates for making spin filters. It has been suggested that one-dimensional wires (see image) comprising metal atoms, such as vanadium (marked in red) and iron, stacked between aromatic molecules, such as benzene and cyclopentadienyl (marked in grey), could be an organic half metal.
By using DFT, the researchers predicted wires that contain only vanadium ions to be half metals, but those that contain both vanadium and iron to be semiconducting wires. When wires are coupled to gold electrodes at both ends, however, cyclopentadienyl wires with vanadium only or alternating vanadium and iron atoms can both become highly effective spin filters.
The researchers also showed that half-metal wires containing no iron make better spin filters than semiconducting iron-containing wires.
The authors of this work are from:
State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing, China; Department of Physics, University of Nebraska at Omaha, Omaha, Nebraska, USA; Student Information and Campus Administrative Systems (SICAS) Center, State University of New York (SUNY) College at Oneonta, Oneonta, New York, USA; School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, Dublin, Ireland.
Reference
[list=1][*]Wang, L. [i]et al[/i]. Novel one-dimensional organometallic half metals: Vanadium-cyclopentadienyl, vanadium-cyclopentadienyl-benzene, and vanadium-anthracene wires. Nano Lett. doi: 10.1021/nl8016016 (2008). | [url=http://dx.doi.org/10.1021/nl8016016][color=#0000ff]Article[/color][/url][/list]
[[i] 本帖最后由 sally208 于 2008-10-15 18:02 编辑 [/i]]
Sonoluminescence: Baking bubbles
Published online: 15 October 2008 | doi:10.1038/nchina.2008.241[size=3][color=red][b]Sonoluminescence: Baking bubbles[/b][/color][/size]
Tim Reid
Abstract
Researchers in Nanjing are learning to measure the extremely high temperatures produced in a collapsing bubble
Original article citation
Chen, W., Huang, W., Liang, Y., Gao, X. & Cui, W. [url=http://dx.doi.org/10.1103/PhysRevE.78.035301][color=#0000ff]Time-resolved spectra of single-bubble sonoluminescence in sulfuric acid with a streak camera[/color][/url]. Phys. Rev. E 78, 035301 (2008).
Introduction[img]http://www.nature.com/nchina/2008/081015/images/nchina.2008.241-i1.jpg[/img] © (2008) istockphoto.com/Eric Madeja
Gas bubbles in liquids can emit bursts of light called sonoluminescence when they are 'popped' by ultrasound. Weizhong Chen and co-workers at Nanjing University[url=http://www.nature.com/nchina/2008/081015/full/nchina.2008.241.html#B1][color=#800080]1[/color][/url] have developed a new way of monitoring the wavelengths emitted in sonoluminescence, revealing the extreme conditions inside the bubble.
During sonoluminescence, the gas inside a collapsing bubble reaches pressures and temperatures so high that it ionizes to produce light. This has led to speculation that sonoluminescence could be used to achieve thermonuclear fusion, but the process is still poorly understood.
Chen and co-workers directed ultrasound onto bubbles of krypton gas dissolved in sulphuric acid. The emitted light was recorded on a spectrograph, then delivered to a streak camera, which deflects light to trace wavelengths over time. The streak images showed that the wavelength decreased from infrared to ultraviolet during the sonoluminescence pulse, which lasted around nine nanoseconds.
According to the laws of black-body radiation, the wavelength trend corresponds to an exponential increase in temperatures as high as 100,000 kelvins. However, this does not take into account the high pressures in the bubble, which could produce much higher peak temperatures on the scale of millions of kelvins.
The researchers were unable to record images fast enough to observe the cooling process. It remains a mystery exactly how the bubbles are able to cool down so rapidly.
The authors of this work are from:
Key Laboratory of Modern Acoustics, Ministry of Education, and Institute of Acoustics, Nanjing University, Nanjing, China.
Reference
[list=1][*]Chen, W., Huang, W., Liang, Y., Gao, X. & Cui, W. Time-resolved spectra of single-bubble sonoluminescence in sulfuric acid with a streak camera. Phys. Rev. E 78, 035301 (2008). | [url=http://dx.doi.org/10.1103/PhysRevE.78.035301][color=#0000ff]Article[/color][/url] |[/list]
回复 17# sally208 的帖子
看到了好多母校的文章。NJU。Supramolecular chemistry: Natural order
Published online: 22 October 2008 | doi:10.1038/nchina.2008.250[size=3][color=red][b]Supramolecular chemistry: Natural order[/b][/color][/size]
Vicki Cleave
Abstract
Organic nanostructures can be fabricated simply by exploiting intermolecular interactions
Original article citation
Zhang, X. [i]et al[/i]. [url=http://dx.doi.org/10.1021/jp803572f][color=#0000ff]One- or semi-two-dimensional organic nanocrystals induced by directional supramolecular interactions[/color][/url]. J. Phys. Chem. C doi: 10.1021/jp803572f (2008).
Introduction[img]http://www.nature.com/nchina/2008/081022/images/nchina.2008.250-i1.jpg[/img] © (2008) ACS
Creating high-purity, single-crystalline organic nanostructures without the need for surfactants, templates or catalysts is now possible, thanks to work by Xiaohong Zhang at the Chinese Academy of Sciences in Beijing, Shuit Tong Lee at City University of Hong Kong and co-workers[url=http://www.nature.com/nchina/2008/081022/full/nchina.2008.250.html#B1][color=#800080]1[/color][/url]. The researchers have demonstrated that a variety of intermolecular interactions can be used to form nanostructures, which could be used in future nanodevices.
Lee and co-workers initially demonstrate their technique using intramolecular charge-transfer compounds. These compunds possess intramolecular dipoles — they contain both an electron-donating and an electron-withdrawing group connected by a conjugated [img]http://www.nature.com/__chars/pi/black/med/base/glyph.gif[/img]-bonded system, so their electron cloud is polarized. These dipoles promote crystallization in a preferred direction.
The researchers dissolve the molecules in an organic solvent, and then inject a little of this solution into another solvent in which the molecules do not dissolve. This causes supersaturation of the molecules in the first solvent, and causes them to form aggregated nuclei. One-dimensional crystals then grow in the direction of the dipole–dipole interaction, forming nanowires (pictured).
The researchers show that if two dipoles are present on one molecule — for instance if it has two electron-donating groups and one electron-accepting group — two-dimensional nanoribbons are formed instead of wires. Sheets, ribbons and wires were also made from molecules by exploiting different interactions such as hydrogen and [img]http://www.nature.com/__chars/pi/black/med/base/glyph.gif[/img]–[img]http://www.nature.com/__chars/pi/black/med/base/glyph.gif[/img] bonding.
The authors of this work are from:
Functional Nano and Soft Materials Laboratory (FUNSOM), Soochow University, Suzhou, China; Nano-organic Photoelectronic Laboratory and Laboratory of Organic Optoelectronic Functional Materials and Molecular Engineering, Technical Institute of Physics and Chemistry, Chinese Academy of Science, Beijing, China; Center of Super-Diamond and Advanced Film (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China.
Reference
[list=1][*]Zhang, X. [i]et al[/i]. One- or semi-two-dimensional organic nanocrystals induced by directional supramolecular interactions. J. Phys. Chem. C doi: 10.1021/jp803572f (2008). | [url=http://dx.doi.org/10.1021/jp803572f][color=#0000ff]Article[/color][/url] |[/list]
Nanotubes: Look what hatched!
Published online: 22 October 2008 | doi:10.1038/nchina.2008.249[size=3][color=red][b]Nanotubes: Look what hatched![/b][/color][/size]
Vicki Cleave
Abstract
Iron-oxide nanotubes have been successfully synthesized with the help of egg proteins
Original article citation
Geng, B., Zhan, F., Jiang, H., Guo, Y. & Xing, Z. [url=http://dx.doi.org/10.1039/b813071j][color=#0000ff]Egg albumin as a nanoreactor for growing single-crystalline Fe3O4 nanotubes with high yields[/color][/url]. Chem. Commun. doi: 10.1039/b813071j (2008).
Introduction[img]http://www.nature.com/nchina/2008/081022/images/nchina.2008.249-i1.jpg[/img] © (2008) RSC
Biological molecules found in nature can make great templates for the synthesis of structurally complex nanomaterials, but preparing and using these biological templates can involve complex and time-consuming processes. Baoyou Geng and co-workers at Anhui Normal University in Wuhu[url=http://www.nature.com/nchina/2008/081022/full/nchina.2008.249.html#B1][color=#800080]1[/color][/url] have now used egg albumin — a cheap and readily available protein found in egg whites — to assist the synthesis of iron-oxide nanotubes.
Geng and co-workers added egg albumin to a mixture of ferrous sulphate solution, ethanol and hydrazine hydrate. The concoction was vigorously stirred and then heated to 140 °C for 24 hours to form single-crystalline iron-oxide nanotubes. Some nanosheets were also found with the product, which suggested to the researchers that the nanotube formation proceeds through the rolling up of these nanosheets.
Their theory is that when egg albumin is added to ferrous sulphate solution, iron ions and albumin molecules form organic–inorganic complexes that aggregate into sheets. When the albumin is removed afterwards, two-dimensional iron-oxide sheets remain, which then curl into tubes (pictured).
The researchers also measured the nanotubes' magnetic properties and showed that they have a higher magnetic coercivity than bulk iron oxide, making them candidates for use in biotechnology or biomedicine.
The authors of this work are from:
College of Chemistry and Materials Science, Anhui Key Laboratory of Functional Molecular Solids, Anhui Normal University, Wuhu, China.
Reference
[list=1][*]Geng, B., Zhan, F., Jiang, H., Guo, Y. & Xing, Z. Egg albumin as a nanoreactor for growing single-crystalline Fe3O4 nanotubes with high yields. Chem. Commun. doi: 10.1039/b813071j (2008). | [url=http://dx.doi.org/10.1039/b813071j][color=#0000ff]Article[/color][/url] |[/list]
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