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The hot deformation and dynamic recrystallization (DRX) behaviors of 7055 aluminum alloy were studied at temperatures of 390−470 °C and strain rates of 0.01−1 s−1. A low DRX fraction between 1% and 13% was observed by using EBSD technique. A modified JMAK-type DRX model was proposed for such low DRX fraction problems. The model was used together with commercial FEM software DEFORM-3D to simulate the hot compression of 7055 aluminum alloy. There was a good agreement between experimental and predicted DRX fractions and grain size with an average absolute relative error (AARE) of 13.7% and 6.3%, respectively. In order to further verify the validity of the proposed model, the model was also used to simulate DRX in industrial hot rolling of 7055 aluminum alloys. The results showed that the distribution of DRX fraction was inhomogeneous, and agreed with experimental observations.

Using aerobic oxidative coupling of thiophenol in organic media as a model reaction, we show that photogenerated holes in CdSe/CdS core–shell nanorods can be efficiently extracted. As a result, CdSe/CdS nanorods can serve as an efficient visible-light photocatalyst at a very low concentration (∼1.5 × 10−4 mol%). We show that primary amines play an important role in the transformation of thiols into disulfides by forming a soluble thiolate in nonpolar solvent. Using time-resolved optical spectroscopy and electron paramagnetic resonance spectroscopy, we show that thiolate can efficiently extract the photogenerated holes from CdSe/CdS nanorods and transform into disulfide in organic solvent. Our data indicate that there are two reaction pathways responsible for S–S coupling of thiolate upon illumination of CdSe/CdS nanorods. We demonstrate that instead of scavenging of photogenerated holes by sacrificial species for prevention of photo corrosion of CdSe/CdS nanorods, the photogenerated holes can be efficiently used for oxidative organic synthesis.

Background: Docetaxel and doxorubicin combination has been widely used in anaplastic thyroid cancer/ATC treatment but often results in serious adverse effects and drug resistance. Resveratrol effectively inhibits ATC cell proliferation in vitro without affecting the corresponding normal cells, while its in vivo anti-ATC effects especially on the ones with docetaxel/doxorubicin-resistance have not been reported due to its low bioavailability. Nanoparticles with sustained-release and cancer-targeting features may overcome this therapeutic bottleneck. Methods: The resveratrol nanoparticles with sustained-release and IL-13Rα2-targeting capacities (Pep-1-PEG3.5k-PCL4k@Res) were prepared to improve the in vivo resveratrol bioavailability. Human THJ-16T ATC cell line was employed to establish nude mice subcutaneous transplantation model. The tumor-bearing mice were divided into four groups as Group-1, without treatment, Group-2, treated by 30 mg/kg free resveratrol, Group-3, treated by 30 mg/kg Pep-1-PEG3.5k-PCL4k@Res and Group-4, treated by 5 mg/kg docetaxel/5 mg/kg doxorubicin combination. TUNEL staining was used to detect the apoptotic cells in the tumor tissues. Docetaxel/doxorubicin resistant xenografts named as THJ-16T/R were isolated and subjected to 2D and 3D culture. The docetaxel/doxorubicin and resveratrol sensitivities of the original THJ-16T and THJ-16T/R cells were analyzed by multiple methods. Results: Docetaxel/doxorubicin and Pep-1-PEG3.5k-PCL4k@Res but not free resveratrol significantly delayed tumor growth (P 10%) and 2/3 of them died within 3 times of treatment and the chemotherapy was stop to avoid further animal loss. One week after drug withdrawal, the subcutaneous tumors regrew and the tumor volume increased 55.28% within 14 days. The cells isolated from the regrowing tumors (THJ-16T/R) were successfully cultured under 2D and 3D condition and underwent drug treatments. Compared with THJ-16T, the death rate of docetaxel/doxorubicin-treated THJ-16T/R population was lower (39.3% vs 18.0%), which remained almost unchanged in resveratrol-treated group (45.3% vs 49.3%). Conclusion: Resveratrol sustained-release targeting nanoparticles effectively inhibit in vivo ATC growth. Docetaxel/doxorubicin suppresses ATC xenografts but causes obvious side effects and secondary drug resistance that can be overcome by resveratrol.

Objective: Anaplastic thyroid cancer/ATC is a highly aggressive malignancy with extremely poor prognosis. Resveratrol/Res promotes re-differentiation of cancer cells and exerts inhibitory effects on ATC cells. Sodium/iodide symporter/NIS and phosphate and tension homology deleted on chromsome ten/PTEN levels are positively correlated with the grade of thyroid cancer differentiation, while the impact of Res on them remain unknown. Materials and Methods: The patterns of NIS and PTEN expression and intracellular distribution in THJ-16T and THJ-21T ATC and Nthy-ori 3-1 normal thyroid cells and their relevance with Res-caused ATC suppression were investigated via multiple experimental methods. E-cadherin was cited as a re-differentiation biomarker of ATC cells. Results: MTT and EdU cell proliferation assays showed distinct growth suppression in ATC cells after Res treatment. TUNEL staining revealed extensive apoptosis of Res-treated THJ-16T and THJ-21T rather than Nthy-ori 3-1 cells. Western blotting, immunocytochemical/ICC and double-labeled immunofluorescent/IF staining showed increased PTEN levels accompanied with distinct NIS and PTEN nuclear co-translocation in Res-treated THJ-16T and THJ-21T cells. E-cadherin but not NIS appeared on the outer membrane. Conclusion: PTEN upregulation and the concurrent NIS and PTEN nuclear translocation in Res-suppressed ATC cells may indicate the better therapeutic outcome and would be a group of beneficial prognostic factors of ATCs.

Creating active and stable electrocatalysts remains a highly desirable and critical goal in the fields of catalysis and clean energy conversion. Single-atom catalyst (SAC), as a new research frontier in heterogeneous catalysis, has demonstrated emerging prospects for many electrocatalytic reactions. Support-assisted pyrolysis approaches are widely used in the synthesis of single-atom electrocatalysts. While extensive efforts have been devoted to increase the loading of the atomically dispersed metal sites, the role of the support in creating these active metal sites remains largely unexplored. Herein, we compare catalysts created by support-free and support-assisted pyrolysis of vitamin B12 and cobalt tetramethoxyphenylporphyrin, respectively, and demonstrate an important effect of support-induced structural reconstruction that directly controls the activation of SAC. Electrochemical studies show support-free catalysts are inactive for oxygen reduction reaction whereas the support-assisted pyrolysis yield...

Glioblastoma multiforme (GBM) is the most common lethal primary brain malignancy without reliable therapeutic drugs. IL-13Rα2 is frequently expressed in GBMs as a molecular marker. Resveratrol (Res) effectively inhibits GBM cell growth but has not been applied in vivo because of its low brain bioavailability when administered systemically. A sustained-release and GBM-targeting resveratrol form may overcome this therapeutic dilemma. To achieve this goal, encapsulated Res 30 ± 4.8 nm IL-13Rα2-targeting nanoparticles (Pep-PP@Res) were constructed. Ultraviolet spectrophotometry revealed prolonged Res release (about 25%) from Pep-PP@Res in 48 h and fluorescent confocal microscopy showed the prolonged intracellular Res retention time of Pep-PP@Res (&gt, 24 h) in comparison with that of free Res (&lt, 4 h) and PP@Res (&lt, 4 h). MTT and EdU cell proliferation assays showed stronger suppressive effects of Pep-PP@Res on rat C6 GBM cells than that of PP@Res (p = 0.024) and Res (p = 0.009) when used twice for 4 h/day. Pep-PP@Res had little toxic effect on normal rat brain cells. The in vivo anti-glioblastoma effects of Res can be distinctly improved in the form of Pep-PP@Res nanoparticles via activating JNK signaling, upregulating proapoptosis gene expression and, finally, resulting in extensive apoptosis. Pep-PP@Res with sustained release and GBM-targeting properties would be suitable for in vivo management of GBMs.

An electrooxidative direct arylsulfonlylation of ynones with sulfinic acids via a radical tandem cyclization strategy has been developed for the construction of sulfonated indenones under oxidant-free conditions. This method provides a simple and efficient approach to prepare various sulfonylindenones in good to excellent yields, demonstrating the tremendous prospect of utilizing electrocatalysis in oxidative coupling. Notably, this reaction could be easily scaled up with good efficiency.

Click chemistry has been widely used in bioconjugation, polymer synthesis, and the development of new anticancer drugs. Here, we report a nanoporous membrane made of AuCu alloy nanowires, which can effectively catalyze copper(I)-catalyzed 1,3-dipolar cycloaddition between azide and terminal alkyne (CuAAC) in flow condition with pressure less than one bar. Comparison studies of the nanowires before and after the reaction using X-ray photoelectron spectroscopy reveal Cu(0) and Cu(I) are main species that promote the reaction. This simple strategy can be used to synthesize a variety of compounds with triazole linkage and extended to gram level chemical production.

Low-cost transition metal oxides are actively explored as alternative materials to precious metal-based electrocatalysts for the challenging multistep oxygen evolution reaction (OER). We utilized the Kirkendall effect allowing the formation of hollow polycrystalline, highly disordered nanoparticles (NPs) to synthesize highly active binary metal oxide OER electrocatalysts in alkali media. Two synthetic strategies were applied to achieve compositional control in binary transition metal oxide hollow NPs. The first strategy is capitalized on the oxidation of transition-metal NP seeds in the presence of other transition-metal cations. Oxidation of Fe NPs treated with Ni (+2) cations allowed the synthesis of hollow oxide NPs with a 1–4.7 Ni-to-Fe ratio via an oxidation-induced doping mechanism. Hollow Fe–Ni oxide NPs also reached a current density of 10 mA/cm2 at 0.30 V overpotential. The second strategy is based on the direct oxidation of iron–cobalt alloy NPs which allows the synthesis of hollow FexCo100–x-ox...

Catalysis plays an essential role in the modern chemical industry. However, it still remains a great challenge to improve the efficiency of many heterogeneous catalysts based on a per metal atom basis. Single-site catalysts (SsCs) with isolated metal atoms/ions anchored to the supports are thus highly desirable, providing an innovative solution towards highly efficient usage of precious metal atoms in heterogeneous catalysts. Creating SsCs with high metal loading proves to be challenging because, without robust anchoring, atoms tend to diffuse to form large aggregates during catalytic reactions. We report a facile ligand exchange method to anchor a single-site Rh catalyst inside the individual channels of three-dimensional dendritic mesoporous silica nanospheres (MSNSs). The short porous channels inside MSNSs provide an easy access of reactants and the strong binding of the ligand prevents the aggregation of catalyst sites. The as-synthesized Rh1@MSNS-NH2 catalyst shows excellent activity, stability and reusability in the reduction of 4-nitrophenol. The same catalyst shows high regioselectivity in the hydrosilylation of terminal alkynes to yield α-vinylsilanes through the Markovnikov addition.

Ce0.8Pr0.2-xSmxO2-δ(x=0.02, 0.05, 0.1) solid solutions were synthesized by the sol-gel method. The XRD results show that all powders calcined at 800 °C are crystallized in a single cubic fluorite structure. The average grain sizes are between 19 nm and 28 nm. The Raman spectra analysis reveals that the solid solution Ce0.8Pr0.2-xSmxO2-δhas a cubic fluorite structure with oxygen vacancies. The oxygen vacancy concentration is increased by doping Sm in Ce0.8Pr0.2-xSmxO2-δ. Impedance spectra shows that the conductivity of rare earth co-doped ceria Ce0.8Pr0.15Sm0.05O2-δis higher than that of single rare earth doped ceria Ce0.83Sm0.17O2-y. The results also show that Ce0.8Pr0.15Sm0.05O2-δpossess maximum conductivity. At 600 °C, the conductivity is 1.20×10-2S/cm, which is assigned to the higher oxygen vacancy concentration and the hopping electron transition of small polarons in the sample Ce0.8Pr0.15Sm0.05O2-δ.

Ce0.8Pr0.2–xNdxO2-δ(x = 0.02, 0.05, 0.1) solid solutions were synthesized by the sol-gel method. The XRD results show that all powders calcined at 800 °C are crystallized in a single cubic fluorite structure. The average grain sizes are between 20 nm and 25 nm. The Raman spectra analysis reveals that the solid solution Ce0.8Pr0.2–xNdxO2-δhas a cubic fluorite structure with oxygen vacancies. The oxygen vacancy concentration is increased by doping Nd in Ce0.8Pr0.2–xNdxO2-δ. Impedance spectra shows that the conductivity of rare earth co-doped ceria Ce0.8Pr0.18Nd0.02O2-δis higher than that of single rare earth doped ceria Ce0.83Sm0.17O2−y. The results also show that Ce0.8Pr0.18Nd0.02O2-δpossess maximum conductivity. At 600 °C, the conductivity is 1.85×10-2S/cm, which is assigned to the higher oxygen vacancy concentration and the hopping electron transition of small polarons in the sample Ce0.8Pr0.18Nd0.02O2-δ.

Glioblastoma multiforme (GBM) is the commonest primary brain malignancy with extremely poor prognosis. Resveratrol posseses anti-cancer effects, while GBM cells respond differently to it due to certain unknown reason(s). Because the tumor-derived exosomes are supposed to influence chemosensitivity, the exosomic proteins released from resveratrol-sensitive U251 and resveratrol-resistant glioblastoma LN428 cells are profiled before (N/Exo) and after drug treatment (Res/Exo) by label-free liquid chromatography-mass spectrometry (LC-MS). The therapeutic implications of the proteomic findings are estimated by gene ontology enrichment analysis (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG)-based bioinformatic analyses and further elucidated by exosome co-incubating. The results reveal that U251/N/Exo but not U251/Res/Exo enhances resveratrol sensitivity of resveratrol-resistant LN428 cells. The resveratrol sensitive properties of U251 cells are not altered by either LN428/N/Exo or LN428/Res/Exo. U251/N/Exo contains higher levels of chromatin silencing and epidermis development proteins, while U251/Res/Exo has more oxygen transport and G protein-coupled receptor. Both of LN428/N/Exo and LN428/Res/Exo are rich in the proteins related with nucleosome assembly, microtubule-based process and chromatin silencing. In conclusion, U251/N/Exo sensitizes LN428 cells to resveratrol via delivering drug sensitizing signals, suggesting the presence of additional factor(s) that may determine the resveratrol sensitivities of glioblastoma cells.

Core-shell Fe@Fe(3)O(4) nanoparticles exhibit substantial exchange bias at low temperatures, mediated by unidirectionally aligned moments at the core-shell interface. These spins are frozen into magnetic alignment with field cooling, and are depinned in a temperature-dependent manner. The population of such frozen spins has a direct impact on both coercivity (H(C)) and the exchange-bias field (H(E)), which are modulated by external physical parameters such as the strength of the applied cooling field and the cycling history of magnetic field sweeps (training effect). Aging of the core-shell nanoparticles under ambient conditions results in a gradual decrease in magnetization but overall retention of H(C) and H(E), as well as a large increase in the population of frozen spins. These changes are accompanied by a structural evolution from well-defined core-shell structures to particles containing multiple voids, attributable to the Kirkendall effect. Energy-filtered and high-resolution transmission electron microscopy both indicate further oxidation of the shell layer, but the Fe core is remarkably well preserved. The increase in frozen spin population with age is responsible for the overall retention of exchange bias, despite void formation and other oxidation-dependent changes. The exchange-bias field becomes negligible upon deliberate oxidation of Fe@Fe(3)O(4) nanoparticles into yolk-shell particles, with a nearly complete physical separation of core and shell.

We demonstrate a new method for the bottom-up assembly of anisotropic nanoparticles, showing that alkanethiol molecules can induce controlled end-to-end assembly of gold nanorods in mixed water/acetonitrile solutions. The assembly is driven by solvent-mediated interactions among hydrophobic alkanethiol ligands selectively bound to the ends of the nanorods and among hydrophilic cetyltrimethylammonium bromide (CTAB) surfactants on the sides of the rods. It occurs only when the gold-nanorod samples have been aged for approximately two weeks. We compare the kinetics of solvent-mediated assembly using undecanethiol ligands to assembly processes driven by covalent bonding using α,ω-undecanedithiol ligands and processes driven by hydrogen bonding using 11-mercaptoundecanoic acid ligands. Our experiments demonstrate the different assembly mechanisms involved as well as the conditions needed to obtain selective end-to-end assembly.

Ce1-xNdxO2-δ (x = 0.05–0.55) solid solutions prepared by sol-gel route were crystallized in a cubic fluorite structure. The solid limit was determined to be as high as x = 0.45. Raman spectra of the solid solutions with lower composition exhibited only one band, which was assigned to F2g mode. Increasing composition produced broad and asymmetric F2g mode with an appearance of low frequency tail. The new broad peak observed at higher frequency side of the F2g mode associated with the oxygen vacancy in the lattice. The impedance spectra of the solid solutions showed definitely ionic conduction, and Ce0.80Nd0.20O2-δ solid solution possessed a maximum conductivity. At 500 °C, the conductivity and activation energy were 2.65 × 10−3S/cm and 0.82 eV, respectively.

At room temperature, the reaction of 2-[4,5-bis(methylsulfanyl)-1,3-dithiol-2-ylidene-]-4,5-bis(2-cyanoethylsulfanyl)-1, 3-dithiole (CM-TTF) with mercury chloride resulted in a black radical salt constructed by dimeric cations and chloromercurate anions in formula (CM-TTF)2Hg2Cl6. The S···S stacking of 3.289(3) and 3.334(3) A within the TTF dimer are very strong in comparing with those of other TTF radical salts. Effective C···C stacking (3.349(10) A) was also found within the dimeric structure.

Four complexes with 4′,5′-diaza-9′-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]fluorene (L1) or 4′,5′-diaza-9′-[4,5-bis(ethylthio)-1,3-dithiol-2-ylidene]fluorene (L2) were synthesized. The complexes [Co(L1)2Cl2]·2CH3OH (1), [Cu(L2)2Cl2]·CH3OH·0.5CH2Cl2 (3), and [Cu(L2)2Br2]·CH3OH (4) adopt a trans configuration and the compound [Cd(L1)2(NO3)2] (2) is a cis structure. Short S···S, C···C, and C···S contacts were found to be important in the molecular packing. Both the solution and solid-state electronic spectra show a redshift in the intramolecular CT bands when forming metal complexes. This intramolecular charge transition in the solid state is enhanced relative to that in solution. Their third-order nonlinear optical properties of compounds 1–4 were studied, and the results reveal that these complexes exhibit negative γ values (about 10–30) and are self-defocusing samples. These γ values are comparable to those of the known cluster compounds. The trans coordination of the two ligands to the metal center would be beneficial to the NLO properties. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

We report an experimental study of Langmuir monolayers of dodecanethiol-ligated gold nanoparticles with in situ optical microscopy and X-ray scattering. The particle spacing increases with thiol concentration but does not depend on surface pressure. Compression beyond the full coverage of the monolayers causes the monolayers to wrinkle. With the presence of excess thiol molecules, the wrinkles unfold back to monolayer upon the expansion of the surface area. A theoretical model based on van der Waals' attraction and tunable steric repulsion is adopted to explain this reversibility.

The assembly of nanoparticles into large, two-dimensional structures provides a route for the exploration of collective phenomena among mesoscopic building blocks. We characterize the structure of Langmuir monolayers of dodecanethiol-ligated gold nanoparticles with in situ optical microscopy and X-ray scattering. The interparticle spacing increases with thiol concentration and does not depend on surface pressure. The correlation lengths of the Langmuir monolayer crystalline domains are on the order of five to six particle diameters. Further compression of the monolayers causes wrinkling; however, we find that wrinkled monolayers with excess thiol can relax to an unwrinkled state following a reduction of surface pressure. A theoretical model based on van der Waals attraction and tunable steric repulsion is adopted to explain this reversibility.

The growth of cobalt, iron, and platinum and their alloy nanoparticles was investigated with oleic acid and trioctylphosphine oxide as ligands. Both the ligand type and concentration are important in determining the final product of the reactions. With a high concentration of oleic acid, thermal decomposition of dicobalt octacarbonyl and iron pentacarbonyl precursors yields only molecular cluster complex species with oxidized metal centers. However, reduction of platinum acetylacetonate under identical conditions yields nanometer-sized particles. In the presence of a high concentration of trioctylphosphine oxide, only the cobalt system was observed to form a cluster−complex species, while both the iron and platinum systems form nanometer-sized particles. This oxidation process, which forms cluster complexes, provides a digestive ripening mechanism that competes with the Ostwald ripening process, thus affecting the particle size and composition of both the pure metal and alloy nanoparticles.

From proton exchange membranes in fuel cells to ion channels in biological membranes, the well-specified control of ionic interactions in confined geometries profoundly influences the transport and selectivity of porous materials. Here we outline a versatile new approach to control a membrane's electrostatic interactions with ions by depositing ligand-coated nanoparticles around the pore entrances. Leveraging the flexibility and control by which ligated nanoparticles can be synthesized, we demonstrate how ligand terminal groups such as methyl, carboxyl and amine can be used to tune the membrane charge density and control ion transport. Further functionality, exploiting the ligands as binding sites, is demonstrated for sulfonate groups resulting in an enhancement of the membrane charge density. We then extend these results to smaller dimensions by systematically varying the underlying pore diameter. As a whole, these results outline a previously unexplored method for the nanoparticle functionalization of membranes using ligated nanoparticles to control ion transport.

Particle−particle and particle−substrate interactions cause nanocrystals to self-assemble into superlattice structures upon drying from a colloidal suspension on a solid surface. Rapid dewetting of a volatile solvent, however, can significantly undermine the degree of ordering. We demonstrate here that by increasing the concentration of the nonvolatile dodecanethiol ligand, dewetting can be controlled and gold nanocrystal superlattices can be formed on silicon nitride substrates with long range ordering over several microns. Monolayer and bilayer superlattices can be produced by adjusting the nanocrystal concentration. The superlattice structures are robust and are not perturbed by the final dewetting of the solvent.

Control of Co particle size was archived by a germ-growth method during inverse micelle synthesis. Magnetic coercivity and blocking were both a function of the particle size, which ranged from 38 to 88 Å. Interparticle dipolar interaction was proven to be important in order to interpret the magnetic properties for large-size particles.

The title salt, bis[2,3-bis(aminocarbonyl)-8,9-bis(methylsulfanyl)tetrathiafulvalenium] di-mu-bromido-bis[bromidocopper(II)], (C(10)H(10)N(2)O(2)S(6))(2)[Cu(2)Br(4)], contains 2,3-bis(aminocarbonyl)-8,9-bis(methylsulfanyl)tetrathiafulvalenium radical cations, [DMT-TTF(CONH(2))(2)](.+), and [Cu(2)Br(4)](2-) anions. The cations are associated across centres of inversion in a head-to-tail fashion via short face-to-face S...S stacking (TTF moiety). These dimers are further assembled into a one-dimensional chain structure via interdimer double S...S contacts involving the methylsulfanyl groups. The one-dimensional chains give rise to a two-dimensional structure through intermolecular double N-H...O hydrogen bonds involving the amide group. The [Cu(2)Br(4)](2-) anions, which straddle centres of inversion, are located between the cation layers. Electron paramagnetic resonance measurements show a radical signal, indicating that the two TTF(.+) radicals are not completely coupled in the dimer.

A significant issue related to Palladium (Pd) based catalysts is that sulfur-containing species, such as alkanethiols, can form a PdSx underlayer on nanoparticle surface and subsequently poison the catalysts. Understanding the exact reaction pathway, the degree of sulfidation, the chemical stoichiometry, and the temperature dependence of this process is critically important. Combining energy-filtered transmission electron microscopy (EFTEM), X-ray diffraction (XRD), and X-ray absorption spectroscopy experiments at the S K-, Pd K-, and L2,3-edges, we show the kinetic pathway of Pd nanoparticle sulfidation process with the addition of excess amount of octadecanethiol at different temperatures, up to 250 °C. We demonstrate that the initial polycrystalline Pd-oleylamine nanoparticles gradually become amorphous PdSx nanoparticles, with the sulfur atomic concentration eventually saturating at Pd/S = 66:34 at 200 °C. This final chemical stoichiometry of the sulfurized nanoparticles closely matches that of the crystalline P16S7 phase (30.4% S), albeit being structurally amorphous. Sulfur diffusion into the nanoparticle depends strongly on the temperature. At 90 °C, sulfidation remains limited at the surface of nanoparticles even with extended heating time; whereas at higher temperatures beyond 125 °C, sulfidation occurs rapidly in the interior of the particles, far beyond what can be described as a core-shell model. This indicates sulfur diffusion from the surface to the interior of the particle is subject to a diffusion barrier and likely first go through the grain boundaries of the nanoparticle.

Self-assembly of Au nanoparticles (NPs) coated with positively charged cetyltrimethylammonium ions (CTA(+)) and negatively charged citrate ions in aqueous liquid cell was investigated by in situ transmission electron microscopy (TEM). Under electron illumination in TEM, the hydrated electrons will reduce the overall positive charges of the CTA(+) covered Au NPs and decrease the repulsive electrostatic forces among NPs, leading to assembly of individual NPs into one-dimensional structures. On the contrary, the negatively charged Au NPs coated with citrate ions are steady in liquid cell regardless of electron beam intensity.

A new, versatile substrate design for surface-enhanced Raman spectroscopy (SERS) is introduced that provides better illumination and collection efficiency than other solid substrates. It uses sheets of 5 nm diameter gold nanoparticles that are draped by drying-mediated self-assembly onto 100 nm thick silicon nitride membranes. During laser illumination, partial in-situ sintering of the nanoparticles into larger structures with tiny gaps (≈2 nm) greatly increases the SERS enhancement factor. The detection of 1 pM of p-mercaptoaniline and 1 fg of 2,4-dinitrotoluene is demonstrated. The use of self-assembled nanoparticle sheets furthermore makes it possible to perform SERS detection in situ on top of a probe solution droplet.

Close-packed nanoparticle monolayers have recently been shown to form mechanically robust, free-standing membranes. We report the first measurements of molecular transport through such ultrathin sheets, self-assembled from dodecanethiol-ligated gold nanocrystals. For aqueous solutions we find filtration coefficients 2 orders of magnitude larger than those observed in polymer-based filters, sieving of large solutes, and for smaller solutes a pronounced dependence of rejection on being charged. These results open up new possibilities for controlled delivery and separation of nano-objects.

The electronic energy subband structures in quasi-two-dimensional electronic systems under normally applied electric fields with periodic modulation potentials along the lateral directions due to periodic modulation of the widths of the systems, such as those produced by deposition of AlAs and GaAs fractional layers on (001) vicinal GaAs substrates, are established by numerical calculations. A coordinate transformation is introduced which transforms systems with periodically structured interfaces into quantum wells with planar interfaces, so that the boundary conditions of the electron wavefunctions are considerably simplified. The changes of the electronic density of states and energy minigaps as functions of the normally applied electric fields and the structural parameters of the systems are investigated in detail.

We report a facile one-step approach which involves no flammable gas, no catalyst, and no in situ polymerization for the preparation of well-aligned carbon nanotube array. A polymer precursor is placed on top of an anodized aluminum oxide (AAO) membrane containing regular nanopore arrays, and slow heating under Ar flow allows the molten polymer to wet the template through adhesive force. The polymer spread into the nanopores of the template to form polymer nanotubes. Upon carbonization the resulting multi-walled carbon nanotubes duplicate the nanopores morphology precisely. The process is demonstrated for 230, 50, and 20 nm pore membranes. The synthesized carbon nanotubes are characterized with scanning/transmission electron microscopies, Raman spectroscopy, and resistive measurements. Convenient functionalization of the nanotubes with this method is demonstrated through premixing CoPt nanoparticles in the polymer precursors.

Nanoparticle superlattices are hybrid materials composed of close-packed inorganic particles separated by short organic spacers. Most work so far has concentrated on the unique electronic, optical and magnetic behaviour of these systems. Here, we demonstrate that they also possess remarkable mechanical properties. We focus on two-dimensional arrays of close-packed nanoparticles and show that they can be stretched across micrometre-size holes. The resulting free-standing monolayer membranes extend over hundreds of particle diameters without crosslinking of the ligands or further embedding in polymer. To characterize the membranes we measured elastic properties with force microscopy and determined the array structure using transmission electron microscopy. For dodecanethiol-ligated 6-nm-diameter gold nanocrystal monolayers, we find a Young's modulus of the order of several GPa. This remarkable strength is coupled with high flexibility, enabling the membranes to bend easily while draping over edges. The arrays remain intact and able to withstand tensile stresses up to temperatures around 370 K. The purely elastic response of these ultrathin membranes, coupled with exceptional robustness and resilience at high temperatures should make them excellent candidates for a wide range of sensor applications.

Compared with the top-down lithographic techniques, bottom-up chemical synthesis and self-assembly approaches offer much more flexibilities in creating magnetic nanostructures with controlled size, shape, composition and physical properties. This review summarizes some of the latest developments in this field, with emphasis mainly on transition metals, their alloys and metal oxide nanoparticles. The focus is directed towards the conditions of individual particles as well as large assemblies of particles through colloidal chemistry. Furthermore, some of the future directions in nanomagnetism from the perspective of physical chemists is also presented.

The reaction product of cobalt carbonyl decomposition depends on the concentration of the oleic acid ligand. With a low concentration of ligand, nanocrystals nucleate and grow to large ferromagnetic particles through the process of Ostwald ripening and coalescence coarsening. With a high concentration of ligand, stable cluster complexes are formed. Addition or removal of ligand from the reaction products can interchange the formation of cluster complexes and nanocrystals.