Microstructures of metallic film and diamond growth from Fe-Ni-C system

The microstructures of metallic film surrounding diamond have been systemically studied using the transmission electron microscopy (TEM) and the atom force microscopy (AFM). The film can be divided into three layers (inner layer near diamond, external layer near graphite and middle layer). The graphite cannot be directly transformed into diamond in the film at HTHP; there exists a parallel relationship between (−111) of γ-(Fe,Ni) and (110) of Fe₃C in the inner layer; the sawtooth-like step morphology found by AFM on the film is similar to that of corresponding diamond surface. A new model for diamond growth at HPHT is proposed from the parallel relationship and sawtooth-like step morphology. It is believed that Fe₃C may be a transitional phase in the course of diamond growth, γ-(Fe,Ni) in the inner layer can absorb carbon atom groups with lamella structure from Fe₃C, and then the carbon groups stack on growing diamond.     

Subtropical to boreal convergence of tree-leaf temperatures

The oxygen isotope ratio (delta(18)O) of cellulose is thought to provide a record of ambient temperature and relative humidity during periods of carbon assimilation. Here we introduce a method to resolve tree-canopy leaf temperature with the use of delta(18)O of cellulose in 39 tree species. We show a remarkably constant leaf temperature of 21.4 +/- 2.2 degrees C across 50 degrees of latitude, from subtropical to boreal biomes. This means that when carbon assimilation is maximal, the physiological and morphological properties of tree branches serve to raise leaf temperature above air temperature to a much greater extent in more northern latitudes. A main assumption underlying the use of delta(18)O to reconstruct climate history is that the temperature and relative humidity of an actively photosynthesizing leaf are the same as those of the surrounding air. Our data are contrary to that assumption and show that plant physiological ecology must be considered when reconstructing climate through isotope analysis. Furthermore, our results may explain why climate has only a modest effect on leaf economic traits in general.     

Superconductivity in diamond

Diamond is an electrical insulator well known for its exceptional hardness. It also conducts heat even more effectively than copper, and can withstand very high electric fields. With these physical properties, diamond is attractive for electronic applications, particularly when charge carriers are introduced (by chemical doping) into the system. Boron has one less electron than carbon and, because of its small atomic radius, boron is relatively easily incorporated into diamond; as boron acts as a charge acceptor, the resulting diamond is effectively hole-doped. Here we report the discovery of superconductivity in boron-doped diamond synthesized at high pressure (nearly 100,000 atmospheres) and temperature (2,500-2,800 K). Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond is a bulk, type-II superconductor below the superconducting transition temperature T(c) approximately 4 K; superconductivity survives in a magnetic field up to Hc2(0) > or = 3.5 T. The discovery of superconductivity in diamond-structured carbon suggests that Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions.     

Termination of global warmth at the Palaeocene/Eocene boundary through productivity feedback

The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surface temperatures warming by 5-7 degrees C over approximately 30,000 yr (ref. 1), probably because of enhanced mantle outgassing and the pulsed release of approximately 1,500 gigatonnes of methane carbon from decomposing gas-hydrate reservoirs. The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium--indicative of export palaeoproductivity--at times of maximum global temperatures and peak excursion values of delta13C. The unusually rapid return of delta13C to values similar to those before the methane release and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere.     

长江三角洲古土壤有机元素组成及古环境意义

以长江三角洲第一古土壤层作为研究对象，分析古土壤的有机元素组成和变化，并结合微形态及其它分析工作，探讨其记录的古环境信息，结果表明，古土壤层中成土工程强弱是影响有机质组成的主要因素，随着成土强度的增强，土壤m(C)/m(N）的比值也相应增加；此外，古土壤有机质组分还是土壤暴露时间的反映，土壤暴露成土时间越长则越有利于有机组分的降解和转化，区域古地理条件差异也是影响古土壤有机元素组成的重要因素，干旱透气良好的环境更有利于土壤有机的分解与转化和增强脱搂作用，从而形成m(C)/m(N)的高值。     

A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills

The recent discovery of diamond-graphite inclusions in the Earth's oldest zircon grains (formed up to 4,252 Myr ago) from the Jack Hills metasediments in Western Australia provides a unique opportunity to investigate Earth's earliest known carbon reservoir. Here we report ion microprobe analyses of the carbon isotope composition of these diamond-graphite inclusions. The observed delta(13)C(PDB) values (expressed using the PeeDee Belemnite standard) range between -5 per mil and -58 per mil with a median of -31 per mil. This extends beyond typical mantle values of around -6 per mil to values observed in metamorphic and some eclogitic diamonds that are interpreted to reflect deep subduction of low-delta(13)C(PDB) biogenic surface carbon. Low delta(13)C(PDB) values may also be produced by inorganic chemical reactions, and therefore are not unambiguous evidence for life on Earth as early as 4,250 Myr ago. Regardless, our results suggest that a low-delta(13)C(PDB) reservoir may have existed on the early Earth.     

CO2 and the end-Triassic mass extinction.

The end of the Triassic period was marked by one of the largest and most enigmatic mass-extinction events in Earth's history and, with few reliable marine geochemical records, terrestrial sediments offer an important means of deciphering environmental changes at this time. Tanner et al. describe an isotopic study of Mesozoic fossil soils which suggests that the atmospheric concentration of carbon dioxide (pCO2) across the Triassic-Jurassic boundary was relatively constant (within 250 p.p.m.v.), but this is inconsistent with high-resolution evidence from the stomatal characters of fossil leaves. Here I show that the temporal resolution of the fossil-soil samples may have been inadequate for detecting a transient rise in pCO2. I also show that the fossil-soil data are consistent with a large increase in pCO2 across the Triassic-Jurassic boundary when variations in the stable carbon isotope (denoted as delta13C) in terrestrial plant leaves are taken into account. These factors suggest that the linkage between pCO2, global warming and the end-Triassic mass extinction remains intact.     

Effects of carbon diffusing field in alloy solvent on the growth of tower-shape diamond single crystal

High-quality type-Ib tower-shape diamond single crystals were synthesized in cubic anvil high pressure apparatus (SPD-6×1200) at 5.4 GPa and 1250-1450°C. The (100) face of seed crystal was used as the growth face, and FeNiMnCo alloy was used as the solvent/catalyst. Two kinds of carbon diffusing fields (type-B and type-G) were simulated by finite element method (FEM). Using the two kinds of carbon diffusing fields, many diamond single crystals were synthesized. The effects of carbon diffusing fields on the ...     

Carbon and nitrogen stable isotope analyses of mammal bone fossils from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River,China

Based on AMS ¹⁴C dating data, carbon and nitrogen isotope analyses were conducted on mammal bone collagen of deer, cattle and pigs from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River. These analyses were conducted to reconstruct palaeodiets of mammals, palaeoecology, palaeoenviroment and previous human activities in the study area. Results show that the collagen loss of bone did not change the in vivo isotopic composition of carbon and nitrogen stable isotopes, and most of the bone fossils were well preserved. The bone collagen of samples from deer had a mean δ¹³C of -23.1‰ and a mean δ¹⁵N of 4.7‰, suggesting that deer subsisted in a closed habitat and fed on branches and leaves. The bone collagen of cattle had a mean δ¹³C of –19.6‰ and a mean δ¹⁵N of 5.2‰, which indicates that cattle subsisted in an open habitat and fed on grasses and stems. The δ¹³C values show that both deer and cattle fed on C₃ plants and lived in the same ecosystem, but the t-test results show that deer δ¹³C and δ¹⁵N values were both more negative than those of cattle, indicating that they inhabited different niches. The δ¹³C and δ¹⁵N values of cattle partially overlapped those of deer, suggesting some competition in diets between them. The t-tests show that the δ¹³C and δ¹⁵N values of pigs were more positive than those of cattle and deer, which signifies that pigs occupied a higher trophic level compared to cattle and deer. The wide range of pig δ¹³C values demonstrates that pig trading had been taking place from early Neolithic Age to late Bronze Age. There were no significant differences in deer δ¹³C and δ¹⁵N values among different archaeological periods, making it clear that climatic, ecological and environmental conditions were kept relatively stable from 2200 to 4200 a BP. This stability may have been responsible for the extensive and complete cultural layers at the Zhongba site. The minimum number of samples required to estimate the mean δ¹³C values of deer, pigs and cattle are 8, 73 and 16, respectively, and for mean δ¹⁵N values of deer, pigs and cattle, the minimum numbers are 4, 5 and 6, respectively.     

Ecosystem carbon loss with woody plant invasion of grasslands

The invasion of woody vegetation into deserts, grasslands and savannas is generally thought to lead to an increase in the amount of carbon stored in those ecosystems. For this reason, shrub and forest expansion (for example, into grasslands) is also suggested to be a substantial, if uncertain, component of the terrestrial carbon sink. Here we investigate woody plant invasion along a precipitation gradient (200 to 1,100 mm yr(-1)) by comparing carbon and nitrogen budgets and soil delta(13)C profiles between six pairs of adjacent grasslands, in which one of each pair was invaded by woody species 30 to 100 years ago. We found a clear negative relationship between precipitation and changes in soil organic carbon and nitrogen content when grasslands were invaded by woody vegetation, with drier sites gaining, and wetter sites losing, soil organic carbon. Losses of soil organic carbon at the wetter sites were substantial enough to offset increases in plant biomass carbon, suggesting that current land-based assessments may overestimate carbon sinks. Assessments relying on carbon stored from woody plant invasions to balance emissions may therefore be incorrect.     

Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

The components and evolution of subcontinental lithospheric mantle beneath the North China Craton and the Yangtze Craton is a current topic in the geological study of China and the carbon isotopic composition of diamond is one of the most direct probes into cratonic lithospheric mantle processes.In this paper,in-situ SIMS(Secondary Ion Mass Spectrometry) techniques were used to analyze the carbon isotope compositions at different internal growth zones of diamonds from Shandong and Liaoning in the North China Craton and Hunan in the Yangtze Craton.It was found that the carbon isotopic range of diamonds from the North China Craton are rather distinct from those of the Yangtze Craton;the former has a range of 6.0‰ to 2.0‰(relative to VPDB) with an average value of 3.0‰ in their core areas,which is consistent with global peridotitic diamonds;the diamonds from the Yangtze Craton,however,have a carbon isotopic range from 8.6‰ to 3.0‰ with an average value of 7.4‰ in their core areas,being more consistent with global eclogitic diamonds.The variations of carbon isotope ratios between different internal growth zones in individual diamonds were different in the three diamond localities studied.There was a clear correlation between changes in carbon isotopic composition and phases of diamond dissolution and new growth,while no correlation was observed between δ13C and internal inclusions.The variations suggest that the carbon isotopic compositions of mantle fluids were changing during the process of diamond crystallization,and that the heterogeneity of the carbon isotopic composition in mantle carbon reservoirs was a more important factor than carbon isotope fractionation in controlling the carbon isotopic compositions and their variation in diamonds.In addition,the preliminary results of in-situ nitrogen analyses demonstrated that the variation of carbon isotopic compositions between the core and outer growth zones does not correlate with nitrogen abundances,implying either that diamonds crystallized in an open environment or that the carbon isotopic composition and nitrogen contents in mantle fluids were controlled by other,not yet understood factors.The experimental results provide hints that the isotopic composition of carbon and its original sources were different in metasomatic fluids controlling diamond formation in the mantle beneath the North China Craton and the Yangtze Craton.     

火焰法沉积金刚石薄膜的组织结构

用透射电镜（ＴＥＭ）对大气中火焰法沉积（ＣＦＤ）金刚石薄膜的组织结构进行了分析研究。结果表明，所沉积的金刚石晶体中（１１１）面上存在着大量层错及显微孪晶，在（１１１）面上晶粒边界处的位错密度较低，此外，在金刚石薄膜中还观察到存在于金刚石颗粒间的非金刚石型碳（Ｃ），即无定形碳及微晶石墨。     

Selective interfacial bonding and thermal conductivity of diamond/Cu-alloy composites prepared by HPHT technique

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature (HPHT) sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, B, and Ti. The thermal conductivity (TC) obtained exhibited as high as 688 W·m-1·K-1, but also as low as 325 W·m-1·K-1. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification.     

The influence of rivers on marine boron isotopes and implications for reconstructing past ocean pH

Ocean pH is particularly sensitive to atmospheric carbon dioxide content. Records of ocean pH can therefore be used to estimate past atmospheric carbon dioxide concentrations. The isotopic composition of boron (delta11B) contained in the carbonate shells of marine organisms varies according to pH, from which ocean pH can be reconstructed. This requires independent estimates of the delta11B of dissolved boron in sea water through time. The marine delta11B budget, however, is still largely unconstrained. Here we show that, by incorporating the global flux of riverine boron (as estimated from delta11B measurements in 22 of the world's main rivers), the marine boron isotope budget can be balanced. We also derive ocean delta11B budgets for the past 120 Myr. Estimated isotope compositions of boron in sea water show a remarkable consistency with records of delta11B in foraminiferal carbonates, suggesting that foraminifera delta11B records may in part reflect changes in the marine boron isotope budget rather than changes in ocean pH over the Cenozoic era.     

Valance electron structure of carbide-diamond interface and catalytic mechanism for diamond synthesis under high-pressure and high-temperature

The metallic films surrounding a synthetic diamond formed under high-pressure and high-temperature (HPHT) in the presence of Fe-based and Ni-based catalysts were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was showed that the carbide was the primary carbon source for the nucleation and growth of diamond. Based on the EET (empirical electron theory in solid and molecules) theory, the valence electron structure of interface between carbide (Fe₃C, Ni₃C, (Fe, Ni)₃C) and diamond was calculated using the bonding length difference (BLD) method. The boundary criterion of Thomas-Fermi-Dirac-Cheng (TFDC): “the electron density being equal on the contacting surfaces of atoms” was applied to analyze the valence structure of carbide-diamond interface. The result based on the calculation valance electron structure is in good accordance with the experimental result. This study is very helpful to reveal the catalytic mechanism of diamond nucleation and growth and design the new catalyst for diamond synthesis.     

Diamond synthesis from a system of chromium-carbide and Ni70Mn25Co5 alloy

In order to ascertain the mechanism of interaction between carbide and metallic catalyst and formation of diamond under high pressure and high temperature, and find a new method to synthesize diamond with special properties, it is necessary to investigate the reaction behavior of different carbides and metallic solvent_catalysts under high pressure and high temperature. A system of Cr-3C-2 powder and Ni 70Mn 25Co 5 alloy in weight ratio of 1∶6 was treated under 6 0 GPa and 1 500℃ for 20, 30 or 60 min respectively. X_ray diffraction of the samples indicated the Cr 3C 2 decomposed partially after high pressure and temperature treatment, and Cr 7C 3, Cr and diamond formed respectively. There was not any trace of graphite in the samples. The result suggested that the separated carbon atoms could form diamond directly without conversion process of graphite into diamond. The observation of SEI, WDX and EDX also showed that diamond crystals were synthesized in the system, which have perfect surfaces and shapes, with the average grain size of about 40 μm. The properties of the crystals are being investigated.     

活性碳,碳黑,石墨与金刚石晶种的生长

介绍了活性碳、碳黑与石墨在过剩压驱动下金刚石晶种的生长．对两种无定形碳以及石墨在触媒中的分散溶解输运与再结晶进行了观察，对活性碳、碳黑在金刚石晶种生长中的机理作了探索性的讨论．三种碳片上的晶种均有明显长大，无定形碳作晶种生长的碳源是可行的     

Surface transfer doping of diamond

The electronic properties of many materials can be controlled by introducing appropriate impurities into the bulk crystal lattice in a process known as doping. In this way, diamond (a well-known insulator) can be transformed into a semiconductor, and recent progress in thin-film diamond synthesis has sparked interest in the potential applications of semiconducting diamond. However, the high dopant activation energies (in excess of 0.36 eV) and the limitation of donor incorporation to (111) growth facets only have hampered the development of diamond-based devices. Here we report a doping mechanism for diamond, using a method that does not require the introduction of foreign atoms into the diamond lattice. Instead, C60 molecules are evaporated onto the hydrogen-terminated diamond surface, where they induce a subsurface hole accumulation and a significant rise in two-dimensional conductivity. Our observations bear a resemblance to the so-called surface conductivity of diamond seen when hydrogenated diamond surfaces are exposed to air, and support an electrochemical model in which the reduction of hydrated protons in an aqueous surface layer gives rise to a hole accumulation layer. We expect that transfer doping by C60 will open a broad vista of possible semiconductor applications for diamond.     

Atomic scale KMC simulation of {100} oriented CVD diamond film growth under low substrate temperature-Part II Simulation of CVD diamond film growth in C-H system and in Cl-containing systems

The growth of {100}-oriented CVD diamond film under two modifications of J-B-H model at low substrate temperatures was simulated by using a revised KMC method at atomic scale. The results were compared both in Cl-containing systems and in C-H system as follows: (1) Substrate temperature can produce an important effect both on film deposition rate and on surface roughness; (2) Aomic Cl takes an active role for the growth of diamond film at low temperatures; (3) {100}-oriented diamond film cannot deposit under single carbon insertion mechanism, which disagrees with the predictions before; (4) The explanation of the exact role of atomic Cl is not provided in the simulation results.     

Mechanism of diamond-to-graphite transformation at diamond-stable conditions

The diamond-to-graphite transformation at diamond-stable conditions is studied by temperature gradient method （TGM） under high pressure and high temperature （HPHT）, although it is unreasonable from the view of thermodynamic considerations. It is found that, at diamond-stable conditions, for example, at 5.5 GPa and 1550 K, with fine diamond grits as carbon source and NiMnCo alloy as metal solvent assisted, not only large diamond crystals, but metastable regrown graphite crystals would be grown by layer growth mechanism, and the abundance of carbon source in the higher temperature region is indispensable for the presence of metastable regrown graphite crystals. From this transformation, it is concluded that, with metal solvent assisted, although the mechanism of crystal growth could be understood by the macro-mechanism of solubility difference between diamond and graphite in metal solvents, from the point of micro-mechanism, the minimum growth units for diamond or graphite crystals should be at atomic level and unrelated to the kinds of carbon source （diamond or graphite）, which could be accumulated free-selectively on the graphite with Sp2Tr or diamond crystals with sp3 bond structure.