共查询到20条相似文献,搜索用时 15 毫秒
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D. V. Abramov S. M. Arakelyan A. F. Galkin L. D. Kvacheva I. I. Klimovskiĭ M. A. Kononov L. A. Mikhalitsyn A. O. Kucherik V. G. Prokoshev V. V. Savranskiĭ 《JETP Letters》2006,84(5):258-261
The melting of carbon at a pressure of about 1 atm is observed. The escape of liquid carbon from the heating region and its spread over the sample surface are observed in the experiments. The structural changes in graphite occurring in the melting region are determined from scanning tunneling microscope (STM) images obtained by means of an atomic force microscope and from Raman spectra. The STM images exhibit significant rearrangement of the structure of the graphite surface in the region of the escape of liquid carbon. The Raman spectra show that the graphite ordering degree increases significantly. 相似文献
3.
Optical and Electrical Properties Evolution of Diamond-Like Carbon Thin Films with Deposition Temperature
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Optical and electrical properties of diamond-like carbon (DLC) films deposited by pulsed laser ablation of graphite target at different substrate temperatures are reported. By varying the deposition temperature from 400 to 25℃, the film optical transparency and electrical resistivity increase severely. Most importantly, the transparency and resistivity properties of the DLC films can be tailored to approaching diamond by adjusting the deposition temperature, which is critical to many applications. DLC films deposited at low temperatures show excellent optical transmittance and high resistivity. Over the same temperature regime an increase of the spa bonded C content is observed using visible Raman spectroscopy, which is responsible for the enhanced transparency and resistivity properties. 相似文献
4.
E. Cappelli C. Scilletta G. Mattei V. Valentini S. Orlando M. Servidori 《Applied Physics A: Materials Science & Processing》2008,93(3):751-758
The structure of thin films deposited by pulsed laser ablation (PLD) is strongly dependent on experimental conditions, like
laser wavelength and fluence, substrate temperature and pressure. Depending on these parameters we obtained various kinds
of carbon materials varying from dense, mainly tetrahedral amorphous carbon (ta-C), to less compact vertically oriented graphene
nano-particles.
Thin carbon films were grown by PLD on n-Si 〈100〉 substrates, at temperatures ranging from RT to 800°C, from a rotating graphite target operating in vacuum. The laser ablation of the graphite target was performed by a UV pulsed ArF excimer laser (λ=193 nm) and a pulsed Nd:YAG laser, operating in the near IR (λ=1064 nm).
The film structure and texturing, characterised by X-ray diffraction analysis, performed at grazing incidence (GI-XRD), and
the film density, evaluated by X-ray reflectivity measurements, are strongly affected both by laser wavelength and fluence
and by substrate temperature.
Micro-Raman and GI-XRD analysis established the progressive formation of aromatic clusters and cluster condensation into vertically
oriented nano-sized graphene structures as a direct function of increasing laser wavelength and deposition temperature. The
film density, negatively affected by substrate temperature and laser wavelength and fluence, in turn, results in a porous
bulk configuration and a high macroscopic surface roughness as shown by SEM characterisation. These structural property modifications
induce a relevant variation also on the emission properties of carbon nano-structures, as evidenced by field emission measurements.
This work is dedicated to our friend Giorgio who passed away 20th August. 相似文献
5.
Fang Xu Longjian Xie Akira Yoneda Nicolas Guignot Andrew King Guillaume Morard 《高压研究》2020,40(2):257-266
ABSTRACTTiC-MgO composite was developed as a heating element for X-ray study in the multi-anvil high pressure apparatus. We synthesized TiC-MgO blocks (50–70 wt.% of TiC) by compression in a cold isostatic press followed by baking in a gas flow furnace. Heaters of tubular shape were manufactured from the synthesized blocks either by lathe or numerically controlled milling machine. The so-produced heating elements have been proved to generate temperatures up to 2250?K at 10?GPa, condition where classical graphite heaters are not suitable anymore due to graphite-diamond transition. These new heaters have been successfully used for in situ X-ray radiography and diffraction measurements on liquid Fe alloys, exploiting excellent X-ray transparency. 相似文献
6.
《中国物理快报》2016,(2)
Thermal behavior of bulk amorphous sulfur is investigated by in situ temperature measurements at high pressures of 0.9,1.4 and 2.1 GPa,and under different heating rates of 8,10 and 12K/min at 0.9 GPa.The results show that the onset temperature of the transition from the supercooled liquid to the liquid state for sulfur increases with the pressure and the heating rate.It is deduced that the transition does not follow the Clapeyron equation,indicating considerable coupling of the molecular structure change in the transition.Along with the data at ambient pressure and high pressure,we present a dynamic diagram to demonstrate the relationship between the amorphous solid,supercooled liquid,liquid,and crystal phases of sulfur,and suggest an experimental approach to establish pressure-temperature-time transition diagrams for supercooled liquid and liquid. 相似文献
7.
对s脉冲电压作用下铜丝水中电爆炸的能量沉积过程进行了实验研究,利用自积分Rogowski线圈和电阻分压器分别测量铜丝电爆炸时的电流和电压。利用测量电压波形确定了熔融起始、熔融结束、汽化起始和击穿时刻点,将铜丝电爆炸划分成熔融、液态和汽化3个阶段。通过数学方法计算了3个阶段和击穿前的沉积总能量。通过实验和计算,分析了电路参数,包括放电电压和回路电感,以及铜丝特性,包括铜丝长度和直径,对铜丝电爆炸过程中3个阶段和击穿前沉积总能量的影响。结果表明:在s脉冲电压作用下,放电电压、回路电感、铜丝长度和直径对熔融阶段能量沉积影响较小,但对液态和汽化阶段能量沉积影响较大,通过调节电路参数提高电流上升速率,可以显著提高汽化和击穿前的沉积能量。 相似文献
8.
The room-temperature response of a 10-MHz quadrant avalanche photodiode (APD) is investigated for detection of high frequency oscillations and tip displacements of fabricated microcantilevers. Currently, no quadrant detectors with a response bandwidth in the megahertz range are available, and oscillations on the order of a few microseconds cannot be resolved. A comparison is made between optical and opto-mechanical measurements to characterize this detector by investigating the frequency response and signal-to-noise (SNR) of pulsed laser signals up to 10?MHz and reflected laser signals from freely vibrating microcantilevers up to 1.64?MHz. The power level of the minimum detectable signal incident on the APD is found to be 28.2?±?5.0?nW for optical measurements and 1.0???W?±?5.0?nW for opto-mechanical measurements. 相似文献
9.
Alexander A. Starostin Victor V. Shangin Alexander T. Lonchakov Artem N. Kotov Semyon B. Bobin 《Annalen der Physik》2020,532(8):1900586
A fiber-optic setup incorporating the pump-probe thermoreflectance (TR) technique with Fabry–Perot (FP) interferometer is presented. It includes both heat pump and probe lasers, producing wavelengths of 1470 and 1530 nm, respectively, together with a reflected radiation detector. Heat pump pulse duration varies from a few microseconds to tens of microseconds. The potential of the pump-probe TR-FP technique to investigate the subsurface region of semiconductors with a range of electron spectra is demonstrated. A pronounced dip in time dependence of the TR-FP signal is discovered at the liquid nitrogen temperature in the gapless semiconductor compound HgSe—a candidate for the family of Weyl semimetals with broken inversion symmetry. This finding implies the developed pulsed TR-FP method for the detection of Weyl nodes and surface Fermi arcs in solids. 相似文献
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11.
Innocent C. Ezenwa 《高压研究》2017,37(3):319-333
We measured the electrical resistivity of high purity Zn along the melting boundary, up to 5?GPa in a large volume press. The electrical resistivity remained constant on the melting boundary, as predicted in a thermodynamics-based model for simple metals. The effects of pressure and temperature on the electrical resistivity of the solid and liquid states are interpreted in terms of their antagonistic effects on the electronic structure of Zn. Within the error of measurements, our melting temperature data agree well with those of the previous studies. The electronic thermal conductivity was calculated from resistivity data using the Wiedemann–Franz law and shows a decrease with temperature in the solid state and an increase in the liquid state, with a large decrease on melting. Comparison of calculated electronic and measured total thermal conductivities indicates that the electronic component dominates over the phonon component in Zn. 相似文献
12.
Recently, resistivity measurements of some liquid metals and metallic alloys have been obtained using an electrode technique. A marked change of the slope of the resistivity versus temperature has been observed following the history of the alloy in the liquid state and the authors conclude that there are “structural transitions in the melt”. It is of interest to examine such effects and to try to understand their origin. In this work, the resistivities of several liquid metals and metallic alloys were measured as a function of temperature. Particular attention was given to the history of the alloy, including solidification and melting conditions. We also observed “anomalies”. Our experiments lead us to conclude that they must very probably be attributed to the release of gas or vapour bubbles in the liquid alloy at the first heating, resulting from the decomposition of compounds like oxides or hydroxides of the metals, but not from a phase transition in the liquid metallic state involving “breaking” Sn–Sn covalent bands. 相似文献
13.
Abstract Micro structure examination of graphite quasimonocrystal recovered after dynamic loading to pressure of 35-45 GPa was carried out. Only a small amount of cubic diamond and recrystalized graphite was detected. Most of the graphite (~80 vol.%) remained in initial high orientation, but transformed to fine, grained phase with crystalite size 0.1-1 microns. Relaxation time of the transformation (~ 10 ns) and the degree of the transformation (~ 70-80 vol.%) were determined by means of measurements of the electrical resistivity during loading up to 26 GPa and following computer simulation of the results. We proposed that two simultaneous processes take place at pressures higher than 20 GPa: i) relatively slow diffusive graphite to diamond transformation localized in the zones with defect structure: ii) highly oriented graphite transforms to a diamond like phase with density of about 3.2 g/cm3 at zero pressure. This, transformation has fast, martensitic kinetics and is reversible. 相似文献
14.
A. F. Goncharov 《高压研究》2013,33(1-3):430-432
Abstract The Raman spectra comparative study of graphite-like modifications of carbon: monocrystalline graphite, pyrolytic graphite and amorphous (glassy) carbon was performed at high pressures and room temperature. At P = 44 GPa an abrupt broadening of Raman bands of pyrolytic graphite and glassy carbon was observed. The same process in monocrystalline graphite occures continuously from 23 to 44 GPa and for higher pressures the Raman spectra of all three substances under study become practically indistinguishable from one another and from that of amorphous carbon (a-C) at the same pressure. This result is ascribed to the formation at these pressures of the dence amorphous carbon modification. 相似文献
15.
A.A. Gorbunov R. Friedlein O. Jost M.S. Golden J. Fink W. Pompe 《Applied Physics A: Materials Science & Processing》1999,69(7):S593-S596
The abundance of carbon single-wall nanotubes (SWNTs) in soot synthesized by pulsed laser evaporation of graphite is studied over a wide range of synthesis conditions. The derived SWNT growth time-scale appears to be much longer than any characteristic time-scale in a simplified model of the relaxation of a high-pressure hot condensing gas bubble in a background atmosphere. It is concluded that SWNT nucleation and growth take place in relaxed, condensed, thermalized evaporation products at an optimal temperature between 850-1250 °C at a rate of few 7m length per second, which is consistent with a condensed state "precipitation" mechanism for the SWNT formation. 相似文献
16.
Experimental results have been obtained for the density and electrical resistivity of liquid mercury as functions of the independent variables temperature (20°c–1000°c) and pressure (0–1000 bars). Basic equipment for both measurements consisted of a steel vessel containing an internal electrical resistance furnace and pressurized with argon gas. The equation of state was determined with an accuracy of about ±1/4% using Archimedes' method by employing a series of totally immersed radioactive sinkers whose rise or fall in the mercury was detected with a γ-ray counter external to the pressure vessel. The electrical resistivity was measured with an accuracy of about ±1/2% using a four-lead resistance cell fabricated in fused silica. The two measurements have also been combined to give electrical resistivity at constant volume. 相似文献
17.
Graphene dispersions in water are highly desirable for a range of applications such as biomedicines, separation membranes, coatings, inkjet printing and more. Recent novel research has been focussed on developing a green approach for scalable production of graphene. However, one important parameter, which is often neglected is the bulk temperature of the processing liquid. This paper follows our earlier work where optimal sono-exfoliation parameters of graphite in aqueous solutions were determined based on the measured acoustic pressure fields at various temperatures and input powers. Here, we take the next step forward and demonstrate using systematic characterisation techniques and acoustic pressure measurements that sonication-assisted liquid phase exfoliation (LPE) of graphite powder can indeed produce high quality few layer graphene flakes in pure water at a specific temperature, i.e. 40 °C, and at an optimised input generator power of 50%, within 2-h of processing. UV–vis analysis also revealed that the exfoliation, stability and uniformity of dispersions were improved with increasing temperature. We further confirmed the successful exfoliation of graphene sheets with minimal level of defects in the optimized sample with the help of Raman microscopy and transmission electron microscopy. This study demonstrated that understanding and controlling processing temperature is one of the key parameters for graphene exfoliation in water which offers a potential pathway for its large-scale production. 相似文献
18.
T G Ramesh 《Pramana》1973,1(1):21-30
This paper deals with the anomalous behaviour of liquid caesium at high pressures. A model for the phenomenon of electron
collapse in the liquid phase, based on the anomalous density variation of liquid caesium with pressure has been proposed.
The process of 6s→5d electron collapse is pictured as the formation of a virtual bound state and the tunnelling process accounts
for the 6s⇌5d dynamic conversion. The same model together with the Friedel sum rule has been used to explain the resistivity
variation of liquid caesium with pressure. The resistivity minimum observed in most of the liquid alkali metals in the low
pressure region has been explained. The agreement with the experimental curve is good in the low pressure region whereas a
large discrepancy exists at higher pressures. This may be due to the breakdown of the Ziman’s resistivity formula under conditions
of resonance scattering. 相似文献
19.
J. Zámečník 《Czechoslovak Journal of Physics》1981,31(10):1108-1113
The paper deals with the influence of hydrostatic pressure on d.c. electrical conductivity in Ge2S3Ag
x
glasses forx10%. The initial material exhibits high resistivity and the presence of Ag impurity yields strong increase in electrical conductivity. The experimental results suggest that there is a non-linear decrease of electrical resistivity at pressure ranging from 0·1 to 103 MPa. The pressure coefficient of resistivity is a function ofx. All measurements were performed on bulk samples using graphite contacts. The experimental results are interpreted by means of ionic conductivity. 相似文献
20.
Li Yang Paul W. May Lei Yin James A. Smith Keith N. Rosser 《Journal of nanoparticle research》2007,9(6):1181-1185
Crystalline carbon nitride nanopowders and nanorods have been successfully synthesized at room temperature and pressure using
the novel technique of pulsed laser ablation of a graphite target in liquid ammonia solution. High-resolution transmission
electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FTIR)
were used to systematically study the morphology, nanostructure and chemical bonding. The experimental composition and structure
of the nanoparticles are consistent with the theoretical calculations for α-C3N4. After 2 h ablation the particles had a size distribution ∼8–12 nm, whereas after 5 h ablation the particles had grown into
nanorod-like structures with a crystalline C3N4 tip. A formation mechanism for these nanorods is proposed whereby nanoparticles are first synthesized via rapid formation
of an embryonic particle, followed by a slow growth, eventually leading to a one-dimensional nanorod structure. 相似文献