Scanning tunneling microscopy and spectroscopy of C70 thin films

Scanning tunneling microscopy of C-70 films deposited on HOPG and gold substrates has been carried but to investigate the 2D packing, defects and disorder. Besides providing direct evidence for orientational disorder, high resolution; images showing the carbon skeleton as well as the molecular arrangement in a solid solution of C-70 and C-60 are presented. Tunneling conductance measurements Indicate a small gap in the C-70 film deposited on HOPG substrate.

Orientational disorder and other aspects of C70 and C60-C70 films deposited on single-crystal substrates

C-70 films deposited on highly oriented pyrolytic graphite (HOPG), Ag(110), Ag(111) and Pt(110) substrates have been investigated by scanning tunnelling microscopy. Interesting observations on novel molecular arrangements, as well as orientational disorder, are presented. Solid solutions of C-60 and C-70 show interesting packing of these molecules when deposited on HOPG.

Polymerization and Pressure-Induced Amorphization of C60 and C70

Scanning tunneling microscopy of solid films of C-60 and C-70 clearly demonstrate the occurrence of photochemical polymerization of these fullerenes in the solid state. X-ray diffraction studies show that such a polymerization is accompanied by contraction of the unit-cell volume in the case of C-60 and expansion in the case of C-70. This is also evidenced from the STM images. These observations help to understand the differences in the amorphization behavior of C-60 and C-70 under pressure. Amorphization of C-60 under pressure is irreversible because it is accompanied by polymerization associated with a contraction of the unit cell volume. Monte Carlo simulations show how pressure-induced polymerization is favored in C-60 because of proper orientation as well as the required proximity of the molecules. Amorphization of C-70, on the other hand, is reversible because C-70 is less compressible and polymerization is not favored under pressure.

Structures, Stabilities and Strain in C60 and C70 Derivatives Fullerenes, Nanotubes and Carbon Nanostructures

The stabilities of a number of small adducts as well as larger hydrides of C-60 and C-70 are reported using semiempirical MO methods. The data are shown to be consistent with the nature of bond alternation in the parent fullerenes and strain effects in the cage systems.

Uncooled DBR laser directly modulated at 3.125 Gb/s as athermal transmitter for low-cost WDM systems

An uncooled three-section tunable distributed Bragg reflector laser is demonstrated as an athermal transmitter for low-cost uncooled wavelength-division-multiplexing (WDM) systems with tight channel spacing. A ±0.02-nm thermal wavelength drift is achieved under continuous-wave operation up to 70 °C. Dynamic sidemode suppression ratio of greater than 35 dB is consistently obtained under 3.125-Gb/s direct modulation over a 20 °C-70 °C temperature range, with wavelength variation of as low as ±0.2 nm. This indicates that more than an order of magnitude reduction in coarse WDM channel spacing is possible using this source. © 2005 IEEE.

Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements

Reactive magnesia (MgO) cements have emerged as a potentially more sustainable and technically superior alternative to Portland cement due to their lower production temperature and ability to sequester significant quantities of CO2. Porous blocks containing MgO were found to achieve higher strength values than PC blocks. A number of variables are investigated to achieve maximum carbonation and associated high strengths. This paper focuses on the impact of four different hydrated magnesium carbonates (HMCs) as cement replacements of either 20 or 50%. Accelerated carbonation (20 C, 70-90% RH, 20% CO2) is compared with natural curing (20 C, 60-70% RH, ambient CO2). SEM, TG/DTA, XRD, and HCl acid digestion are utilized to provide a thorough understanding of the performance of MgO-cement porous blocks. The presence of HMCs resulted in the formation of larger size carbonation products with a different morphology than those in the control mix, leading to significantly enhanced carbonation and strength. © 2013 Elsevier Ltd.

A base-emitter self-aligned multi-finger Si1-xGex/Si power heterojunction bipolar transistor

With a crystal orientation dependent on the etch rate of Si in KOH-based solution, a base-emitter self-aligned large-area multi-linger configuration power SiGe heterojunction bipolar transistor (HBT) device (with an emitter area of about 880 mu m(2)) is fabricated with 2 mu m double-mesa technology. The maximum dc current gain is 226.1. The collector-emitter junction breakdown voltage BVCEO is 10 V and the collector-base junction breakdown voltage BVCBO is 16 V with collector doping concentration of 1 x 10(17) cm(-3) and thickness of 400 nm. The device exhibited a maximum oscillation frequency f(max) of 35.5 GHz and a cut-off frequency f(T) of 24.9 GHz at a dc bias point of I-C = 70 mA and the voltage between collector and emitter is V-CE = 3 V. Load pull measurements in class-A operation of the SiGe HBT are performed at 1.9 GHz with input power ranging from 0 dBm to 21 dBm. A maximum output power of 29.9 dBm (about 977 mW) is obtained at an input power of 18.5 dBm with a gain of 11.47 dB. Compared to a non-self-aligned SiGe HBT with the same heterostructure and process, f(max) and f(T) are improved by about 83.9% and 38.3%, respectively.

直接甲醇燃料电池耐甲醇氧还原电催化剂的研究

燃料电池以其高效、环境友好的发电方式，被誉为21世纪的能源技术。其中，直接甲醇燃料电池（DMFC）更以燃料甲醇来源丰富，价格低廉，储存、携带方便而成为近年的研究热点。目前DNDFC存在的一个主要问题是"甲醇透过"，即甲醇从阳极穿过固体电解质膜进入到阴极，而阴极催化剂一般是Pt/C，因此在阴极会同时发生甲醇氧化和氧还原，严重降低了电池的库仑效率和电压效率。此夕卜甲醇及其氧化中间产物还会使P口C中毒。虽然试验了一些低甲醇透过率的电解质膜，但仍无法完全消除甲醇透过。因此研制对氧还原催化活性高而对甲醇氧化没有活性，即耐甲醇的氧还原电催化剂是一个十分重要的课题。本论文主要从催化剂的组成、热处理、制备方法和载体等方面进行了相关研究，此外，还开展了生物燃料电池阴极电催化剂的研究。具体结果如下：1．热处理对电催化剂性能的影响（1）首次研究了炭载铂（Pt/C）对氧还原和甲醇氧化的催化活性与热处理温度的关系。发现P"C的催化活性随热处理温度的升高而降低，其原因是热处理使R／C中Pt的结晶度提高、粒径变大、表面浓度降低。但是，热处理使PUC催化甲醇氧化活性的降低程度远大于催化氧还原活性的降低程度。该研究提供了一种有效改善P口C催化剂耐甲醇性能的简便方法。（2）研究了炭载四狡基酞著钻（CoPcTc／C）和炭载四苯基铁叶琳（FeTPP／C）对氧还原和甲醇氧化的催化活性与热处理温度的关系。发现800℃热处理的CoPcTc／C对氧还原的催化活性最高；XPS和XRD分析表明，其活性位主要为含CoN4结构的物质。FeTPP／C催化剂与CoPcTc／C类似，700℃热处理的对氧还原催化活性最高。二者对甲醇氧化都没有活性。（3）首次研究了炭载四苯基铁叶琳一铂（FeTPP-Pt/C）复合催化剂对氧还原和甲醇氧化的催化活性与热处理温度的关系。发现热处理使FeTPP-Pt/C对氧还原的催化活性提高，并且优于相应P灯C，这是因为复合催化剂对氧还原的催化活性来源于FeTPP和Pt两部分。另外，FeTPP-Pt／C对甲醇氧化的催化活性随热处理温度的升高而降低，降低幅度大于相应Pt/C，这是因为在复合催化剂中，FeTPP在Pt/C表面的分散会降低甲醇与R的接触。700℃热处理的FeTPP-Pt/C对氧还原的催化活性最高，并且耐甲醇能力很强，非常适合作为DMFC阴极电催化剂。（4）首次研究了FeTPP-TiO2/C复合催化剂对氧还原的催化活性与热处理温度的关系。发现70。℃热处理的FeTPP-TiO2／C对氧还原的催化活性最高，并且稳定性好；复合催化剂提高了氧还原的电子转移数。这是因为TIOZ能够将FeTPP催化氧还原过程中产生的H2O2及时分解为O2和H2O，再重新被FeTPP还原。TIOZ的加入有望改善过渡金属大环化合物催化剂的长程稳定性。此夕卜该复合催化剂对甲醇氧化没有活性。2．制备方法对电催化剂性能的影响（1）首次同时研究了Pt/C对氧还原和甲醇氧化的催化性能，讨论了影响Pt/C催化活性的主要因素。XRD、XPS和TEM分析表明，无定型Pt含量高的Pt/C对氧还原的催化活性较高，表面氧化物含量高的Pt/C对甲醇氧化的催化活性较高。为制备耐甲醇能力强、催化氧还原活性高的Pt/C催化剂提供了理论参考。（2）比较了平衡吸附法和强制沉积法制备的FeTPP-Pt/C催化剂的性能，发现前者对氧还原和甲醇氧化的催化活性都高于后者，这是因为由强制吸附法制备的复合催化剂，FeTPP将一部分Pt覆盖，使其无法发挥活性。3．活性炭载体对Pt/C电催化剂性能的影响利用多种分析手段，系统比较了VulcanXC-72炭和上海松木炭的物理、化学性质对Pt/C电催化剂性能的影响。发现孔径适当、电导率高、灰分和表面含氧基团较少的活性炭作载体时，制得的P口C催化剂的性能较好。为PEMFC中电催化剂载体的选择提供了一些理论依据。4．生物燃料电池阴极电催化剂的研究首次制备了炭载微过氧化物酶-11（MP-11／C）电催化剂，通过循环伏安法、线性扫描法和旋转圆盘电极技术研究发现，MP-11／C对O2还原具有较高的催化活性，并且稳定性好，为生物燃料电池的研制提供了一种较好的酶固定方法。

耐甲醇氧还原复合催化剂四苯基铁卟啉-铂的研究

用平衡吸附法制备了炭载四苯基铁卟啉 铂 (FeTPP Pt/C)复合催化剂 ,比较了经不同温度热处理的FeTPP Pt/C和Pt/C对O2 还原的催化活性和耐甲醇能力。结果表明 ,热处理可改善Pt/C催化剂的耐甲醇能力 ;热处理的FeTPP Pt/C复合催化剂具有较高的氧还原催化活性和良好的耐甲醇能力 ,并且 70 0℃处理的FeTPP Pt/C对O2 还原的催化活性最高。

Mass spectrometric studies of metallofullerene

The endrohel metallofullerene, Gd@C-82, Gd@C-80, Gd-2@C-80 were synthesized by using K-H method. The technique of two-step of high pressure and high temperature extraction with 1, 3, 5-trimethylbenzene (first step) and pyridine(second step) has been successfully utilized to extract metallofullerene of Gd@C-82 The gas-phase negative ions of fullerenes C-n(n= 60, 70, 78, 82, 84...) and metallofullerene (Gd@C-82) have been studied by the ESI-MS, REC-MS and MALDI-TOF-MS. The differences among the mass spectra of ESI-MS, REC-MS and MALDI-TOF-MS have been observed and explained. In contrast to the empty fullerene C-82 , the metallofullerene Gd@C-82 should have a larger HOMO-LUMO gap. Experimental results suggest that Gd@C-82 is polarized and Gd3+ located in the off-center position of C-82 cage after Gd3+ is trapped into C-82 cage.

A simple method for the selective enrichment of endohedral metallofullerenes

The concentration of a polar solvent DMF extract was found to be very effective for the selective enrichment of endohedral metallofullerenes against empty fullerenes. As the solvent evaporated, endohedral metallofullerenes were effectively enriched in the solution, while most of empty fullerenes (especially C-60 and C-70) were precipitated because of their scant solubility in DMF. Matrix-assisted laser-desorption-ionization time-of-fligh mass spectrometry analysis indicated that the purity of endohedral metallofullerenes increased dramatically after concentration of the DMF extract solution. Upon transferring the extract into toluene, a solution containing significantly enriched endohedral metallofullerenes was obtained. The different solubilities of endohedral metallofullerenes versus empty fullerenes are considered to account for this selective enrichment of endohedral metallofullerenes.

Gas phase derivations of endohedral metallofullerenes by ion-molecular reactions

Gas phase ion-molecular reactions of endohedral metallofullerenes with the self-chemical ionization ion system of vinyl acetate, benzene and acetone in the ion source of the mass spectrometer have been studied. Several derivatized endohedral metallofullerene cations [M@C-82-C2H3O](+), [M-2@C-80-C2H3O](+), [M@C-82-C6H6](+) and [M@C-82-CO-CH3](+) are observed as the major products. The experimental results indicate that endohedral metallofullerenes have active gas phase reactivities and can be efficiently derivatized by some small organic cations.

Two-step-method extraction of endohedral metallofullerenes

A new and efficient extraction method of endohedral metallofullerenes, especially of rare-earth elements encapsulated metallofullerenes, has been reported in this paper. Soxhlet-extraction of raw soot with toluene was used in the first step to wash away most accompanying C-60, C-70. Then pyridine was chosen as solvent to obtain high-temperature and high pressure extract. Two kinds of extract were analysed by DEI-MS and LDI-MS, the results indicate that this two-step method can provide the extract which has the highest fraction of endohedral metallofullerenes. So it will greatly simplify the following separation and purification processes of metallofullerenes.

New route for light olefins production from chloromethane over HSAPO-34 molecular sieve

HSAPO-34 molecular sieve was employed in chloromethane conversion and showed high performance in activity and selectivity in production of light olefins. Our detailed IR investigation allowed the identification of the active sites and the adsorbed species and demonstrated that the conversion started from 350 degrees C with alkoxy group as the intermediate. The fixed-bed catalytic testing evidenced that in the range of 350-500 degrees C, 70-80% of chloromethane was transferred to ethylene, propylene and butenes. Increasing reaction temperature favors the conversion and enhances the yield of lighter olefins. A very important reversible phenomenon, the breaking of Al-O-P bonds upon adsorption of HCl, a main product of reaction to generate a large amount of P-OH groups and the recovery of Al-O-P upon removal of HCI was revealed. (c) 2005 Elsevier B.V. All rights reserved.

Chlorophyll-a concentrations and macroinvertebrate declines coincide with the collapse of overwintering diving duck populations in a large eutrophic lake

1. Lough Neagh is one of the most important non-estuarine sites in the British Isles for overwinteringwildfowl. A change in the waterbird assemblage following the winter of 2000/2001 was drivenmainly by a rapid decline in the population of overwintering diving ducks. Sudden and discretechanges in resident as well as migratory waterbirds may suggest an intrinsic cause.
2. We compared the density and biomass of benthic macroinvertebrates, the food of overwinteringdiving ducks, in 2010 (following the diving duck population decline) with values from a baselinesurvey conducted in 1997/1998 (before the decline in diving ducks).
3. The mean total density of macroinvertebrates declined significantly by c. 65% from 15 300 m2in1997/1998 to 5136 m2in 2010. There was a concomitant c. 70% decline in mean macroinvertebratebiomass from 15 667 mg m2to 5112 mg m2. In terms of taxonomic composition, the relativecontribution of Tanypodinae, Glyptotendipes spp . and Tanytarsini declined, while the relativecontribution of Chironomus spp. increased.
4. We describe a shift in chlorophyll-a concentration, a proxy of phytoplankton biomass, in thelargest freshwater lake in the British Isles coincident with a significant reduction in macroinverte-brate density and biomass, with potential implications for ecosystem processes and ecologically andeconomically important consumer populations, including waterbirds and fishes