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Nanoscale (v.2, #7)


Front cover (pp. 1041-1041).
The binding energies of multiple CO molecules to five-atom silver–gold cluster cations have been obtained employing temperature dependent gas phase ion trap measurements and ab initio calculations. The CO binding energies to AgnAum+ (n + m = 5) decrease with increasing number of silver atoms. Most strikingly, after the adsorption of the fourth CO to Au5+ and of the third CO to Ag5+, respectively, a pronounced decrease in the binding energies of further CO molecules was observed. This is related to a CO-induced structural transformation yielding more compact metal cluster geometries. First principles calculations revealed that the exact structure of the carbonyl complexes with multiple CO and the nature of the CO-induced structural transformation strongly depend on the composition of the metal cluster as well as on the number of adsorbed CO molecules.

Inside front cover (pp. 1042-1042).
The DNA molecule is observed to be very susceptible to short-term exposures to an atmospheric pressure plasma jet. The DNA damage induced by plasma-generated species, i.e. excited atoms, charged particles, electrons and UV light is determined.

Contents (pp. 1043-1056).
A halogen bond is a highly directional, electrostatically-driven noncovalent interaction between a region of positive electrostatic potential on the outer side of the halogen X in a molecule R–X and a negative site B, such as a lone pair of a Lewis base or the π-electrons of an unsaturated system. The positive region on X corresponds to the electronically-depleted outer lobe of the half-filled p-type orbital of X that is involved in forming the covalent bond to R. This depletion is labeled a σ-hole. The resulting positive electrostatic potential is along the extension of the R–X bond, which accounts for the directionality of halogen bonding. Positive σ-holes can also be found on covalently-bonded Group IV–VI atoms, which can similarly interact electrostatically with negative sites. Since positive σ-holes often exist in conjunction with negative potentials on other portions of the atom's surface, such atoms can interact electrostatically with both nucleophiles and electrophiles, as has been observed in surveys of crystallographic structures. Experimental as well as computational studies indicate that halogen and other σ-hole interactions can be competitive with hydrogen bonding, which itself can be viewed as a subset of σ-hole bonding.

Doped nanostructures (pp. 1057-1057).
A halogen bond is a highly directional, electrostatically-driven noncovalent interaction between a region of positive electrostatic potential on the outer side of the halogen X in a molecule R–X and a negative site B, such as a lone pair of a Lewis base or the π-electrons of an unsaturated system. The positive region on X corresponds to the electronically-depleted outer lobe of the half-filled p-type orbital of X that is involved in forming the covalent bond to R. This depletion is labeled a σ-hole. The resulting positive electrostatic potential is along the extension of the R–X bond, which accounts for the directionality of halogen bonding. Positive σ-holes can also be found on covalently-bonded Group IV–VI atoms, which can similarly interact electrostatically with negative sites. Since positive σ-holes often exist in conjunction with negative potentials on other portions of the atom's surface, such atoms can interact electrostatically with both nucleophiles and electrophiles, as has been observed in surveys of crystallographic structures. Experimental as well as computational studies indicate that halogen and other σ-hole interactions can be competitive with hydrogen bonding, which itself can be viewed as a subset of σ-hole bonding.

Impacts of doping on thermal and thermoelectric properties of nanomaterials by Gang Zhang; Baowen Li (pp. 1058-1068).
Thermal transport in nanoscale structures has attracted an increasing interest in the last two decades. On the one hand, the low dimensional nanostructured materials are platforms for testing novel phonon transport theories. On the other hand, nanomaterials are promising candidates for nanoscale on-chip coolers. This review is focused on the thermal conductance, thermoelectric property, and impacts of doping on these properties.

Effect of N/B doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons by Shan-Sheng Yu; Wei-Tao Zheng (pp. 1069-1082).
Carbon nanotubes, carbon nanocones, and graphene nanoribbons are carbon-based nanomaterials, and their electronic and field emission properties can be altered by either electron donors or electron acceptors. Among both donors and accepters, nitrogen and boron atoms are typical substitutional dopants for carbon materials. The contribution of this paper mainly provides a comprehensive overview of the theoretical topics. The effect of nitrogen/boron doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons is reviewed. It is also suggested that nitrogen is more an n-type donor. The discussion about the mechanism of field emission for N-doped carbon nanotubes and electronic structures of N-doped graphene nanoribbons is interesting and timely.

Silica-based nanoparticles for photodynamic therapy applications by Pierre Couleaud; Vincent Morosini; Céline Frochot; Sébastien Richeter; Laurence Raehm; Jean-Olivier Durand (pp. 1083-1095).
Silica-based nanoparticles for applications in photodynamic therapy (PDT) have emerged as a promising field for the treatment of cancer. In this review, based on the pathway the photosensitizer is entrapped inside the silica matrix, the different methods for the synthesis of silica-based nanoparticles are described from the pioneering works to the latest achievements which concern multifunctional nanoplatforms, up-converting nanoparticles, two-photon PDT, vectorization and in vivo applications.

Co-Doped ZnO nanoparticles: Minireview by Igor Djerdj; Zvonko Jagličić; Denis Arčon; Markus Niederberger (pp. 1096-1104).
Diluted magnetic semiconductors with a Curie temperature exceeding 300 K are promising candidates for spintronic devices and spin-based electronic technologies. We review recent achievements in the field of one of them: Co-doped ZnO at the nanoparticulate scale.

Controlling the volumetric parameters of nitrogen-doped carbon nanotube cups by Brett L. Allen; Matthew B. Keddie; Alexander Star (pp. 1105-1108).
Analogous to multiwalled carbon nanotubes, nitrogen-doped carbon nanotube cups (NCNCs) have been synthesized with defined volumetric parameters (diameter and segment lengths) by controlling the catalyst particle size and the concentration of nitrogen precursor utilized in the chemical vapor deposition (CVD) reaction, allowing for tailored interior cavity space of cross-linked NCNCs, i.e. nanocapsules.

Visible light induced photobleaching of methylene blue over melamine-doped TiO2 nanocatalyst by Jurate Virkutyte; Babita Baruwati; Rajender S. Varma (pp. 1109-1111).
TiO2 doping with N-rich melamine produced a stable, active and visible light sensitized nanocatalyst that showed a remarkable efficiency towards the photobleaching of a model compound – methylene blue (MB) in aqueous solution. The photobleaching followed a mixed reaction order kinetics with the distinctive induction and acceleration periods.

Selective detection of trace amount of Cu2+ using semiconductor nanoparticles in photoelectrochemical analysis by Guang-Li Wang; Jing-Juan Xu; Hong-Yuan Chen (pp. 1112-1114).
A highly sensitive and selective photoelectrochemical sensor for Cu2+ was developed based on the selective interaction between CdS quantum dots (QDs) immobilized on an indium tin oxide (ITO) electrode surface and Cu2+ in a triethanolamine (TEA) solution to form CuxS-doped CdS QDs, which disrupts the electron transfer from the conduction band of CdS to ITO and results in a decrease of photocurrent.

Flower-like TiO2 nanostructures with exposed {001} facets: Facile synthesis and enhanced photocatalysis by Min Liu; Lingyu Piao; Weiming Lu; Siting Ju; Lei Zhao; Chunlan Zhou; Hailing Li; Wenjing Wang (pp. 1115-1117).
Flower-like TiO2 nanostructures with exposed {001} facets were synthesized by a low-temperature hydrothermal process from Ti powders for the first time, and they exhibited enhanced photocatalytic degradation of methylene blue dye under ultraviolet light irradiation.

Electroconvection in nematic liquid crystals via nanoparticle doping by Martin Urbanski; Brandy Kinkead; Hao Qi; Torsten Hegmann; Heinz-S. Kitzerow (pp. 1118-1121).
It is known that a small fraction of nanoparticles dispersed in a liquid crystal can alter the electrooptic response, completely. The present study on gold nanoparticles dispersed in 5-n-heptyl-2-(4-n-octyloxy-phenyl)-pyrimidine shows that the contrast inversion observed earlier is initiated by a change from parallel to homeotropic anchoring, thereby causing an instability, which in turn leads to the appearance of convection rolls. After rapid cooling from the isotropic phase, the nanoparticle dispersion shows a regular field-induced Fréedericksz transition, like the pure liquid crystal. The electrohydrodynamic instability is presumably an example for the behavior of (+, −) systems that was predicted by de Gennes, and only recently observed experimentally for the first time.

Superhydrophilicity-assisted preparation of transparent and visible light activated N-doped titania film by Qing Chi Xu; Diana V. Wellia; Rose Amal; Dai Wei Liao; Say Chye Joachim Loo; Timothy Thatt Yang Tan (pp. 1122-1127).
A novel and environmental friendly method was developed to prepare transparent, uniform, crack-free and visible light activated nitrogen doped (N-doped) titania thin films without the use of organic Ti precursors and organic solvents. The N-doped titania films were prepared from heating aqueous peroxotitanate thin films deposited uniformly on superhydrophilic uncoated glass substrates. The pure glass substrates were superhydrophilic after being heated at 500 °C for 1 h. Nitrogen concentrations in the titania films were adjusted by changing the amount of ammonia solution. The optimal photocatalytic activity of the N-doped titania films was about 14 times higher than that of a commercial self-cleaning glass under the same visible light illumination. The current reported preparative technique is generally applicable for the preparation of other thin films.

The influence of doping on the device characteristics of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors by Gregory Jolley; Lan Fu; Hark Hoe Tan; Chennupati Jagadish (pp. 1128-1133).
We report on a detailed analysis of the effects of doping on the main device parameters of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors. Due to the relatively large conduction band offset of GaAs/Al0.2Ga0.8As (167meV) transitions from wetting layer to quantum well states are observed for the highly doped devices. Since increasing the doping concentration fills the quantum dot states, electrons are forced to occupy the one-dimensional wetting layer states and therefore have quantum-well-like properties. This has facilitated a comparative study of the effects of three-dimensional and one-dimensional confinement of electrons on device parameters such as the responsivity and dark current by studying one particular detector structure with different doping concentrations of the active region.

Study of concentration-dependent cobalt ion doping of TiO2 and TiO2−xNx at the nanoscale by James L. Gole; Sharka M. Prokes; O. J. Glembocki; Junwei Wang; Xiaofeng Qiu; Clemens Burda (pp. 1134-1140).
Experiments with a porous sol–gel generated TiO2 nanocolloid and its corresponding oxynitride TiO2−xNx are carried out to evaluate those transformations which accompany additional doping with transition metals. In this study, doping with cobalt (Coii) ions is evaluated using a combination of core level and VB-photoelectron and optical spectroscopy, complementing data obtained from Raman spectroscopy. Raman spectroscopy suggests that cobalt doping of porous sol–gel generated anatase TiO2 and nitridated TiO2−xNx introduces a spinel-like structure into the TiO2 and TiO2−xNx lattices. TEM and XPS data complemented by valence band-photoelectron spectra demonstrate that metallic cobalt clusters are not formed even at high doping levels. As evidenced by Raman spectroscopy, the creation of a spinel-like structure is commensurate with the room temperature conversion of the oxide and its oxynitride from the anatase to the rutile form. The onset of this kinetically driven process correlates with the formation of spinel sites within the TiO2 and TiO2−xNx particles. Despite their visible light absorption, the photocatalytic activity of these cobalt seeded systems is diminished relative to the oxynitride TiO2−xNx.

Multifunctional nanocomposites of superparamagnetic (Fe3O4) and NIR-responsive rare earth-doped up-conversion fluorescent (NaYF4 : Yb,Er) nanoparticles and their applications in biolabeling and fluorescent imaging of cancer cells by Congcong Mi; Jingpu Zhang; Huanyu Gao; Xianlong Wu; Meng Wang; Yingfan Wu; Yueqin Di; Zhangrun Xu; Chuanbin Mao; Shukun Xu (pp. 1141-1148).
A new kind of magnetic/luminescent multifunctional nanoparticles was synthesized by covalently linking multiple carboxyl-functionalized superparamagnetic Fe3O4 nanoparticles and individual amino-functionalized silica-coated fluorescent NaYF4 : Yb,Er up-conversion nanoparticles (UCNPs). The resultant nanocomposites bear active carboxylic and amino groups on the surface that were proved to be chemically active and useful for further facile bioconjugation with biomolecules. The UCNPs in the nanocomposite particles can emit visible light in response to the irradiation by near infrared (NIR) light, enabling the application of the nanocomposites in bioimaging. X-Ray diffraction, infrared spectroscopy, transmission electron microscopy, luminescence spectroscopy, and magnetometry were applied to characterize the multifunctional nanocomposites. The nanocomposites exhibited good superparamagnetic and excellent green up-conversion photoluminescent properties that can be exploited in magnetic separation and guiding as well as bioimaging. Due to the presence of active functional groups on the nanocomposite surface, the Fe3O4/NaYF4 : Yb,Er magnetic/luminescent nanocomposites were successfully conjugated with a protein called transferrin, which specifically recognizes the transferrin receptors overexpressed on HeLa cells, and can be employed for biolabeling and fluorescent imaging of HeLa cells. Because NIR light can penetrate biological samples with good depth without damaging them and can avoid autofluorescence from them, the presence of both NIR-responsive UCNPs and superparamagnetic nanoparticles in the nanocomposite particles will enable the practical application of the nanocomposites in bioimaging and separation.

Effect of doping on the morphology and multiferroic properties of BiFeO3 nanorods by Dimple P. Dutta; O. D. Jayakumar; A. K. Tyagi; K. G. Girija; C. G. S. Pillai; G. Sharma (pp. 1149-1154).
In this study we report the synthesis of BiFeO3 nanorods using a sonochemical technique. The nanorods had a diameter of 20–50 nm, a length of 100–500 nm and exhibit aspect ratios in the range of 5–10. However, after doping, the TEM images of Bi0.9Ba0.1Fe0.9Mn0.1O3 and Bi0.9Ca0.1Fe0.9Cr0.1O3 samples show that the aspect ratios of both the double doped samples have reduced considerably, while retaining the crystallinity of the particles. BiFeO3 nanorods show a weak ferromagnetic order at room temperature, which is quite different from the linear M–H relationship reported for bulk BiFeO3. The saturation magnetization of these BiFeO3 nanostructures has been found to increase on doping with various metal ions (Ba2+, Ca2+, Mn2+, Cr3+), reaching a maximum value of 1.35 emu g−1 for the Bi0.9Ba0.1Fe0.9Mn0.1O3 nanostructures. However, saturation of electric polarization was observed only in case of the Bi0.9Ca0.1Fe0.9Cr0.1O3 nanostructures.

Effect of substrate temperature on implantation doping of Co in CdS nanocrystalline thin films by S. Chandramohan; A. Kanjilal; S. N. Sarangi; S. Majumder; R. Sathyamoorthy; C.-H. Hong; T. Som (pp. 1155-1159).
We demonstrate doping of nanocrystalline CdS thin films with Co ions by ion implantation at an elevated temperature of 573 K. The modifications caused in structural and optical properties of these films are investigated. Co-doping does not lead to amorphization or formation of any secondary phase precipitate for dopant concentrations in the range of 0.34–10.8 at.% used in the present study. However, we observe a systematic reduction in the d-spacing with increasing cobalt concentration. Optical band gap of CdS does not show any obvious change upon Co-doping. In addition, implantation gives rise to grain growth and increase in the surface roughness. The results are discussed in the light of ion-matter interaction in the keV regime.

Modification of neodymium-doped ZnO hybrid nanoparticles under mild hydrothermal conditions by Behzad Shahmoradi; K. Soga; S. Ananda; R. Somashekar; K. Byrappa (pp. 1160-1164).
The morphology and particle size of neodymium-doped ZnO hybrid nanoparticles were tailored through fabrication under mild hydrothermal conditions (T = 150–250 °C, P = autogeneous, t = 18 h) for the first time using two surface modifiers: caprylic acid and n-butylamine. Characterization of these nanoparticles was carried out using powder XRD, FTIR, SEM, zeta-potential analysis and UV-vis spectroscopy. The results revealed that modification of ZnO nanoparticles using neodymium as a dopant and caprylic acid or n-butylamine as a surfactant could change the optical and physical properties of the surface-modified neodymium-doped ZnO hybrid nanoparticles. The work proved the efficiency of caprylic acid and n-butylamine as suitable surfactants for surface modification of neodymium-doped ZnO hybrid nanoparticles.

Ex situ vapor phase boron doping of silicon nanowires using BBr3 by Gregory S. Doerk; Gabriella Lestari; Fang Liu; Carlo Carraro; Roya Maboudian (pp. 1165-1170).
An ex situ vapor phase technique for doping vapor–liquid–solid grown silicon nanowires (NWs) based on the reduction of BBr3 by H2 has been demonstrated. Electron microscope images show that the excellent crystal quality of the nanowires is preserved with minimal alteration of their surface morphology. Fano resonance in the Raman spectra for single nanowires indicates that active boron concentrations over two orders of magnitude and as high as 1020 cm−3 are achievable in a well-controlled manner, with excellent axial uniformity. Electrical resistance measurements from single nanowires confirm that incorporated boron is electrically active, and doping of epitaxial bridging Si NWs is successfully demonstrated. By avoiding the pitfalls of nonuniform concentration profiles and drastic morphological changes that often accompany in situ boron doping, this technique provides a valuable alternative doping route for the development of single Si NW devices in a reliable manner.

Change in conformation of polymer PFO on addition of multiwall carbon nanotubes by Malti Bansal; Ritu Srivastava; C. Lal; M. N. Kamalasanan; L. S. Tanwar (pp. 1171-1177).
Multiwall carbon nanotubes (MWNTs) have been added to the polymer poly (9,9-dioctylfluorenyl-2, 7-diyl) end capped with dimethylphenyl (PFO) in various weight percentages and the blends thus prepared, using a solution processing approach, have been characterized using SEM, UV-VIS spectroscopy, PL spectroscopy and IV characterization. The SEM micrographs show a change in the structure of the polymer from partially crystalline to a glassy state in the blend form. The morphology observations are supported by absorption spectra which show a very high diminution of the polymers' beta peak in the spectra obtained from the polymer–nanotube blend. Thus, multiwall carbon nanotubes modify the local nanoscopic structure of PFO leading to a more glassy structure instead of a partially crystalline form and provide a method to tailor the conformation of polymer PFO, depending on intended application. IV characteristics reveal an increase in current on formation of the polymer–nanotube blend as compared to the polymer-only structure. On the basis of percolation theory, as applied to these polymer–nanotube blends, a percolation threshold value of 0.45 wt% and critical exponent value of 1.84 has been obtained, indicating the formation of a three dimensional polymer–nanotube network.

Amino acid-assisted one-pot assembly of Au, Pt nanoparticles onto one-dimensional ZnO microrods by Xianghong Liu; Jun Zhang; Xianzhi Guo; Shihua Wu; Shurong Wang (pp. 1178-1184).
In this contribution, a facile one-pot strategy is developed for the assembly of noble metal (Au and Pt) nanoparticles onto one-dimensional ZnO microrods using a green non-toxic reagent amino acid, lysine with two amino functional groups as the capping agent. Noble metal nanoparticles with a small size capped by lysine are formed and simultaneously anchored onto the surface of ZnO. No pre-functionalization of the ZnO support is needed, hence simplifying the synthesis and reducing the fabrication cost. Inspired by the catalytic properties of Au nanoparticles in both catalyst and sensor materials, we have examined the gas sensing performances towards ethanol detection. Obtained results demonstrate that after decoration by Au nanoparticles, the sensor shows significantly enhanced sensing performances in terms of high sensitivity, fast response and recovery, excellent reproducibility and good selectivity. The improved sensor properties are probably ascribed to the catalytic Au promoters and the Schottky barriers at the metal and semiconductor interface.

Luminescence resonance energy transfer from an upconverting nanoparticle to a fluorescent phycobiliprotein by Fiorenzo Vetrone; Rafik Naccache; Christopher G. Morgan; John A. Capobianco (pp. 1185-1189).
Water dispersible upconverting polyethylenimine (PEI)-capped NaYF4 nanoparticles co-doped with trivalent erbium (Er3+) and ytterbium (Yb3+) were prepared via solvothermal synthesis with an 18 nm average particle diameter. These upconverting nanoparticles can be used to sensitize a light-harvesting phycobiliprotein (R-Phycoerythrin) via luminescence resonance energy transfer (LRET).

Doping single-walled carbon nanotubes through molecular charge-transfer: a theoretical study by Arun K. Manna; Swapan K. Pati (pp. 1190-1195).
We study the effect of the molecular charge transfer on the electronic structure of metallic (5,5) and semiconducting (8,0) single-walled carbon nanotubes (SWNTs) induced by surface adsorption of various organic donor–acceptor molecules of different affinities using ab initio density functional theory. Our results, obtained from first-principles spin-polarized calculations show that the adsorption of molecules with different affinities reflects the difference in interaction strength that measure the overall energy of adsorption. Moderate values of the binding energy of these surface adsorbed molecular charge-transfer complexes suggest that the nature of interaction is in the physisorption regime, and mainly governs by Coulombic forces. We also find that the large band gap of semiconducting (8,0) SWNT can be tuned through the surface adsorption of selective organic molecules which gives rise to mid-gap localized molecular levels near the Fermi energy with tuning of band gap region. Interestingly, we find that the metallic (5,5) SWNT and semiconducting (8,0) SWNT turn into semiconducting and metallic nanotubes respectively in presence of selective surface adsorbed molecules, corroborating recent experimental findings. We also suggest that these charge transfer effect can be probed through optical conductivity measurement, as the low-frequency profiles are affected by charge transfer.

Energy transfer study between Ce3+ and Tb3+ ions in doped and core-shell sodium yttrium fluoride nanocrystals by Pushpal Ghosh; Arik Kar; Amitava Patra (pp. 1196-1202).
Here, we report the preparation of Ce3+ and Tb3+ co-doped sodium yttrium fluoride nanorods and NaYF4:Ce3+/Tb3+ core-shell nanoparticles by the emulsion method. The core-shell nanoparticles are confirmed by X-ray diffraction study and transmission electron microscopy (TEM) analysis. The hexagonal crystal phase of Ce3+-doped sodium yttrium fluoride nanocrystals is converted to the cubic polymorph after surface coating by TbF3. Cell volume, cell parameters and lattice strain have been modified due to core-shell structure. The decay times are found to be 8.4 ms and 5.4 ms for doped nanorods and core-shell nanoparticles, respectively, which reveals that non-radiative decay is higher in the case of core-shell nanoparticles than doped nanorods. Energy transfer efficiencies from Ce3+ to Tb3+are 65% and 45% for doped Na(Y1.5Na 0.5)F6:Ce:Tb material and NaYF4:Ce/Tb core-shell materials, respectively. Quantum yields are found to be 75% and 42% for doped and core-shell samples, respectively.

Pt surface modification of SnO2 nanorod arrays for CO and H2 sensors by Hui Huang; C. Y. Ong; J. Guo; T. White; M. S. Tse; O. K. Tan (pp. 1203-1207).
Uniform SnO2 nanorod arrays were deposited on a 4 inch SiO2/Si wafer by plasma-enhanced chemical vapor deposition (PEVCD) at low deposition temperature of around 300 °C. The SnO2 nanorods were connected at the roots, thus the nanorod sensors could be fabricated by a feasible way compatible with microelectronic processes. The surface of the sensors was modified by Pt nanoparticles deposited by dip coating and sputtering, respectively. The sensing properties of the Pt-modified SnO2 nanorod sensors to CO and H2 gases were comparatively studied. After surface modification of Pt, the sensing response to CO and H2 gases increased dramatically. The 2 nm Pt-modified SnO2 nanorod sensors by sputtering showed the best sensing performance. By increasing Pt thickness from 2 nm up to 20 nm, the optimal working temperature decreased by 30 °C while the sensing response also decreased by about 4 times. Comparing these two Pt modification approaches by dip coating and sputtering, both could achieve comparable promotion effect if the Pt thickness can be controlled around its optimal value. The deposition technique of SnO2 nanorod arrays by PECVD has good potential for scale-up and the fabrication process of nanorod sensors possesses simplicity and good compatibility with contemporary microelectronics-based technology.

Poly (acrylic acid)-capped lanthanide-doped BaFCl nanocrystals: synthesis and optical properties by Qiang Ju; Wenqin Luo; Yongsheng Liu; Haomiao Zhu; Renfu Li; Xueyuan Chen (pp. 1208-1212).
Water-soluble lanthanide-doped BaFCl nanophosphors with the surface functionalized by a layer of poly (acrylic acid) are synthesized via a facile one-step solvothermal method. Intense long-lived luminescence is realized from visible to near-infrared (NIR) by doping with different lanthanide ions. The emission and excitation spectra of Eu3+ indicate that the doped lanthanide ions occupy a site close to the surface of the nanoparticles. Strong NIR emissions of Nd3+ and green luminescence of Tb3+ using Ce3+ as sensitizers are also achieved in BaFCl nanoparticles. The synthesized nanoparticles featuring long-lived luminescence in either visible or NIR regions may have potential applications as luminescent labels for biological applications.

Enhanced Cu emission in ZnS : Cu,Cl/ZnS core–shell nanocrystals by Carley Corrado; Morgan Hawker; Grant Livingston; Scott Medling; Frank Bridges; Jin Z. Zhang (pp. 1213-1221).
ZnS : Cu,Cl/ZnS core–shell nanocrystals (NCs) have been synthesized via a facile aqueous synthesis method. The shell growth of the NCs was observed via a red-shift in the UV-Vis absorption spectra with increasing NC size. The Cu photoluminescence (PL) emission was enhanced by capping with a thin ZnS shell. The ZnS : Cu (0.2%) and ZnS : Cu (0.5%) show a more pronounced red-shift in the apparent PL peak position as well as a 37% and 67% increase in emission intensity, respectively, in comparison to the undoped NCs. The observed red-shift is mainly due to an increase in intensity of the Cu PL emission. The 1% Cu-doped NCs exhibit very little red-shift because the observed emission is dominated by the Cu-dopant and thus nearly independent of the size of the NCs. The increase in Cu emission is evidence that Cu atoms occupying non-emissive surface sites in doped ZnS NCs were encapsulated by the ZnS shell. Extended X-Ray Absorption Fine Structure (EXAFS) data also suggests that the Cu had slightly more neighbors upon growth of a ZnS shell, indicating its encapsulation into the core of the NCs. The EXAFS Zn edge data also indicate greater disorder in the ZnS structure when the shell is grown, which may be attributed to the ZnS shell being more amorphous than the core NCs. This study demonstrates that core–shell structures can be used as a simple and yet powerful strategy to enhance PL properties of doped semiconductor NCs.

Synthesis and characterization of zirconium-doped mesoporous nano-crystalline TiO2 by Kanattukara Vijayan Bineesh; Dong-Kyu Kim; Dae-Won Park (pp. 1222-1228).
A series of zirconium-doped nano-titania (Zr/TiO2) with various amounts of Zr were prepared by sol–gel method using titanium(iv) isopropoxide and zirconium nitrate as precursors. Zr/TiO2 samples were characterized using X-ray diffraction (XRD), surface area–pore volume measurements, infrared (FTIR) spectroscopy, UV–vis-diffuse reflectance spectroscopy (UV–vis-DRS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, thermogravimetric (TG) analysis, and transmission electron microscopy (TEM) techniques. XRD data and Raman spectra indicated that even after 5 mol% doping of zirconium in the crystal lattice of TiO2, the samples were phase pure with the anatase structure. The crystalline size of the anatase decreased with increasing Zr content. An increase in the BET surface area was also observed after doping of zirconium on nano-titania.

Zn-doped nanocrystalline TiO2 films for CdS quantum dot sensitized solar cells by Guang Zhu; Zujun Cheng; Tian Lv; Likun Pan; Qingfei Zhao; Zhuo Sun (pp. 1229-1232).
Quantum dot-sensitized solar cells based on Zn-doped TiO2 (Zn-TiO2) film photoanode and polysulfide electrolyte were fabricated. Zn-TiO2 nanoparticles were obtained via a hydrothermal method and screen printed on the fluorine-doped tin oxide glass to prepare the photoanode. The structure, morphology and impedance of the Zn-TiO2/CdS film and the photovoltaic performance of the Zn-TiO2/CdS cell were investigated. It was found that the photovoltaic efficiency was improved by 24% when the Zn-TiO2 film was adopted as the photoanode of CdS QDSSCs instead of only the TiO2 layer. The improvement was ascribed to the reduction of electron recombination and the enhancement of electron transport in the TiO2 film by Zn doping.

Effect of synergy on the visible light activity of B, N and Fe co-doped TiO2 for the degradation of MO by Mingyang Xing; Yongmei Wu; Jinlong Zhang; Feng Chen (pp. 1233-1239).
Single doped, co-doped and tri-doped TiO2 with B, N and Fe are successfully synthesized by using the hydrothermal method. The samples are characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples are evaluated for degradation of methyl-orange (MO, 20 mg L−1) in aqueous solutions under visible light (λ > 420 nm). The results of XRD suggest that all the catalysts present anatase crystal. All the doping catalysts show higher photoactivities than pure TiO2 under visible light irradiation. In the single nonmetal doped TiO2, the localized dopant levels near the valence band (VB) are responsible for the enhancement of photoactivies. Fe3+ impurity level formed under the conduction band (CB) induces the high photocatalytic activities of iron doped TiO2. In the co-doped and tri-doped catalysts, the B 2p and N 2p acceptor states contribute to the band gap narrowing by mixing with O 2p states combined with the overlapping of the conduction band by the iron “d” orbital, resulting in improvement of the photo-performance under visible light irradiation. Iron co-doped with boron catalyst shows low photoactivity under visible light due to the absence of Fe3+ impurity levels at the bottom of the conduction band. In addition, the XPS results indicate the presence of synergistic effects in co-doped and tri-doped catalysts, which contribute to the enhancement of photocatalytic activities.

Facile synthesis of lanthanide nanoparticles with paramagnetic, down- and up-conversion properties by Zhengquan Li; Yong Zhang (pp. 1240-1243).
Lanthanide materials play an important role in biomedical researches, among which paramagnetic, down- and up-conversion lanthanide nanoparticles are of particular interest. However, little effort has been made to develop versatile lanthanide nanoparticles with these properties combined in a single particle. Herein, we present a facile strategy to make multifunctional lanthanide nanoparticles by doping sensitized lanthanide complexes into porous silica coated on up-conversion NaYF4 nanocrystals. The nanoparticles not only show strong down- and up-conversion fluorescence but also exhibit high magnetic resonance properties.

Glucose oxidase-doped magnetic silica nanostrutures as labels for localized signal amplification of electrochemical immunosensors by Jingjing Ren; Dianping Tang; Biling Su; Juan Tang; Guonan Chen (pp. 1244-1249).
Herein, we report a novel glucose oxidase (GOD)-doped magnetic silica nanostructure and its possible application in the clinical immunoassays. The doped nanostructures were initially synthesized using the reverse micelle method, and ferritin antibodies (anti-Ft) were then labeled to the surface of the nanostructures, which were employed as signal antibodies for ultrasensitive detection of ferritin (Ft) in the sandwich-type electrochemical enzyme immunoassays. The doped nanostructures were characterized using transmission electron microscopy (TEM), UV-vis absorption spectrometry and vibrating sample magnetometer (VSM). The advantages of the doped nanostructures as labels were investigated in comparison with the conventional label method. Under the optimal conditions, the nanostructures-based immunoassay toward ferritin standards displays a wide dynamic range from 0.1 to 400 ng mL−1 with a low detection limit of 10 pg mL−1 ferritin (at 3σ), which is three-fold higher in the sensitivity than that of directly using GOD-labeled antibodies. The assay results for clinical serum samples with the developed method received in excellent accordance with results obtained from the referenced standard enzyme-linked immunosorbent assay (ELISA) method.

The role of ellipticity on the preferential binding site of Ce and La in C78-D3h—A density functional theory study by K. Muthukumar; J. A. Larsson (pp. 1250-1255).
Endohedral metallofullerenes that encapsulate one or several atoms, or a cluster of atoms have molecular properties making them useful both in technology and in bio-medical applications. Some fullerenes are found to have two metal atoms incarcerated and it has been recently found that two Ce atoms are incorporated into the C78-D3h (78 : 5) cage. In this study, we report calculations on the structural and electronic properties of Ce2@C78 using density functional theory (DFT). While Ce2@C80-Ih (D3d) and La2@C80-Ih (D2h) have different ground state structures, we have found that Ce2@C78 has a D3h ground state structure just as La2@C78. The encapsulated Ce atoms bind strongly to the C78-D3h cage with a binding energy (BE) of 5.925 eV but not as strong as in Ce@C82-C2v nor in Ce2@C80-Ih. The elliptical nature of the cage plays a crucial role and accommodates the two Ce atoms at opposite ends of the C3 axis with a maximized inter atomic distance (4.078 Å). This means that the effect of the additional f-electron repulsion in M2@C78 with M = Ce compared to M = La, is less pronounced than in Ce2@C80 compared to La2@C80. We compare the results to the elliptical M2@C72 (#10611) (M = La, Ce), and with a range of additional Ce and La endohedral fullerenes and explain the role ellipticity has in the preferential binding site of Ce and shed light on the formation mechanism of these nanostructures.

Tuning the shape and thermoelectric property of PbTe nanocrystals by bismuth doping by Qian Zhang; Ting Sun; Feng Cao; Ming Li; Minghui Hong; Jikang Yuan; Qingyu Yan; Huey Hoon Hng; Nianqiang Wu; Xiaogang Liu (pp. 1256-1259).
We report the synthesis of a series of monodispersed Bi-doped PbTe nanocrystals with tunable morphologies by using a doping precursor of bismuth(iii) 2-ethylhexanoate. The as-synthesized Pb1−xBixTe (x = 0.005, 0.010, 0.015, 0.020) nanocrystals are characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Hall measurements. The nanocrystals with controlled spherical, cuboctahedral, and cubic shapes were readily prepared by varying the Bi doping concentration. Thermoelectric investigation of these nanocrystals shows that the Bi3+ doping increases electrical conductivity from 350 to 650 K and changes the Seebeck coefficient sign from positive to negative.

Back matter (pp. 1260-1266).
We study the effect of the molecular charge transfer on the electronic structure of metallic (5,5) and semiconducting (8,0) single-walled carbon nanotubes (SWNTs) induced by surface adsorption of various organic donor–acceptor molecules of different affinities using ab initio density functional theory. Our results, obtained from first-principles spin-polarized calculations show that the adsorption of molecules with different affinities reflects the difference in interaction strength that measure the overall energy of adsorption. Moderate values of the binding energy of these surface adsorbed molecular charge-transfer complexes suggest that the nature of interaction is in the physisorption regime, and mainly governs by Coulombic forces. We also find that the large band gap of semiconducting (8,0) SWNT can be tuned through the surface adsorption of selective organic molecules which gives rise to mid-gap localized molecular levels near the Fermi energy with tuning of band gap region. Interestingly, we find that the metallic (5,5) SWNT and semiconducting (8,0) SWNT turn into semiconducting and metallic nanotubes respectively in presence of selective surface adsorbed molecules, corroborating recent experimental findings. We also suggest that these charge transfer effect can be probed through optical conductivity measurement, as the low-frequency profiles are affected by charge transfer.

Back cover (pp. 1267-1268).
Here, we report the preparation of Ce3+ and Tb3+ co-doped sodium yttrium fluoride nanorods and NaYF4:Ce3+/Tb3+ core-shell nanoparticles by the emulsion method. The core-shell nanoparticles are confirmed by X-ray diffraction study and transmission electron microscopy (TEM) analysis. The hexagonal crystal phase of Ce3+-doped sodium yttrium fluoride nanocrystals is converted to the cubic polymorph after surface coating by TbF3. Cell volume, cell parameters and lattice strain have been modified due to core-shell structure. The decay times are found to be 8.4 ms and 5.4 ms for doped nanorods and core-shell nanoparticles, respectively, which reveals that non-radiative decay is higher in the case of core-shell nanoparticles than doped nanorods. Energy transfer efficiencies from Ce3+ to Tb3+are 65% and 45% for doped Na(Y1.5Na 0.5)F6:Ce:Tb material and NaYF4:Ce/Tb core-shell materials, respectively. Quantum yields are found to be 75% and 42% for doped and core-shell samples, respectively.
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