Chunyuan He

Integrated microcircuit on a diamond anvil for high-pressure electrical resistivity measurement

A multilayer microcircuit on a diamond surface has been developed for high-pressure resistivity measurement in a diamond anvil cell (DAC). Using a film deposition technique, a layer of Mo film was deposited on a diamond anvil as a conductor, topped with a layer of alumina film for insulation. A microelectric circuit was fabricated with a photolithographic shaping method after film encapsulation. With precise control and measurements of all the dimensions of the sample for resistance measurement, including the width of the metallic film and the diameter and thickness of the gasket hole, resistivity of a sample can be accurately determined. This microcircuit can be flexibly fabricated and easily cleaned. It also provides a promising prospect to measure resistivity under in situ high pressure and high temperature. We measured the resistivity of ZnS using this method, and proved the pressure induced phase transition at 13.9–17.9GPa to be a semiconductor to semiconductor transformation.A multilayer microcircuit on a diamond surface has been developed for high-pressure resistivity measurement in a diamond anvil cell (DAC). Using a film deposition technique, a layer of Mo film was deposited on a diamond anvil as a conductor, topped with a layer of alumina film for insulation. A microelectric circuit was fabricated with a photolithographic shaping method after film encapsulation. With precise control and measurements of all the dimensions of the sample for resistance measurement, including the width of the metallic film and the diameter and thickness of the gasket hole, resistivity of a sample can be accurately determined. This microcircuit can be flexibly fabricated and easily cleaned. It also provides a promising prospect to measure resistivity under in situ high pressure and high temperature. We measured the resistivity of ZnS using this method, and proved the pressure induced phase transition at 13.9–17.9GPa to be a semiconductor to semiconductor transformation.

Accurate measurements of high pressure resistivity in a diamond anvil cell

A new technique incorporating a diamond anvil cell with photolithographic and film deposition techniques has been developed for electrical resistivity measurement under high pressure. Molybdenum was sputtered onto a diamond anvil facet and patterned to the desired microcircuit. A sputtered Al2O3 (alumina) layer was then fabricated onto the Mo-coated layer to insulate the thin-film electrodes from the metallic gasket and to protect the electrodes against plastic deformation under high pressure conditions. For better insulation, Al2O3 was also sputtered onto the metallic gasket. The regular shape of the microcircuit makes it convenient to perform an electric current field analysis, hence, accurate resistivity data can be obtained from the measurement. We performed the measurement of nanocrystalline ZnS to 36 GPa and determined its reversibility and phase transition hysteresis.

Thickness measurement of sample in diamond anvil cell

We report on an original method that measures sample thickness in a diamond anvil cell under high pressures. The method is based on two hypotheses: completely plastic deformation on the gasket and completely elastic deformation of the diamonds. This method can further eliminate the effect of diamond deformation on the thickness measurement of a sample, which permits us to measure the thickness of alumina up to 41.4 GPa.

The structural transition of Gd2O3 nanoparticles induced by high pressure

The structural transition of nanosize Gd2O3 is studied using high pressure energy dispersive x-ray diffraction and high pressure photoluminescence. The original structure of the nanosized sample shows a mixture of cubic and monoclinic structure. Our results show that the cubic and most of the monoclinic structure turns into hexagonal structure above 10.35 GPa. But a small proportion of monoclinic structure can be present up to the highest pressure, 36.2 GPa. When the pressure is released, the hexagonal structure partly reverts to monoclinic structure, so the sample shows a mixture of hexagonal and monoclinic structure. The structural transition from monoclinic to hexagonal structure is reversible.

In situ electrical impedance spectroscopy under high pressure on diamond anvil cell

The effect of grain boundary on electrical transportation properties is a basic physical problem and also a subject of material science and technology. In situ electrical measurement of powdered materials under high pressure provides a chance to figure out the electrical properties of grain boundaries. In this letter, the authors report an in situ impedance spectroscopy method used in conjunction with a diamond anvil cell for electrical property research of grain boundaries under high pressure. Powdered CdS was pressed up to 23GPa and an impedance arc corresponding to the grain boundary was detected. It was found that the electrical property of the grain boundary changed with pressure and could be determined by the resistance and the relaxation frequency. Pressure decreases the effective scattering section of the grain boundary to charge carriers, and finally leads to the decrease of resistance and activation energy of the grain boundary.

New diamond anvil cell system for in situ resistance measurement under extreme conditions

We report an alumina-encapsulated microcircuit on a diamond anvil for high-pressure and high-temperature electrical conductivity measurement. An alumina thin film was deposited on a diamond anvil as a thermal insulation layer for laser heating, on which a molybdenum film was deposited and photolithographically fabricated to a van der Pauw circuit. The introduction of the alumina layer significantly improves the laser heating performance. This specially fabricated diamond anvil permits us to measure the resistivity of (Mg0.875Fe0.125)2SiO4 at 3450K and 35GPa in a laser-heated diamond anvil cell. We expect to substantially extend the pressure-temperature scale of in situ resistivity measurement.

Phase transformation and resistivity of dumbbell-like ZnO microcrystals under high pressure

High-pressure Raman spectra and in situ electrical resistivity measurement of the dumbbell-like ZnO microcrystals have been investigated by using the diamond-anvil-cell technique at room temperature. The dumbbell-like ZnO microcrystals were synthesized via a facile solution method under mild conditions. In terms of the Raman results, the dumbbell-like ZnO microcrystals underwent a transition from wurtzite to rock-salt structure with increasing pressure and the phase-transition pressure was about 11.13 GPa. In situ electrical resistivity measurement of the dumbbell-like ZnO microcrystals was performed on a designed diamond anvil cell. The change in electrical resistivity related to the phase structure for the ZnO microcrystals was observed with the applied pressure of up to 34.86 GPa. Moreover, the pressure dependence of the electrical resistivity for the dumbbell-like ZnO microcrystals annealed at different conditions was also investigated.

Finite element analysis of resistivity measurement with van der Pauw method in a diamond anvil cell

Using finite element analysis, the authors studied the steady current field distribution under the configuration of van der Pauw method [L. J. van der Pauw, Philips Tech. Rev. 20, 220 (1958)] for resistivity measurement in a diamond anvil cell. Based on the theoretical analysis, the authors obtained the theoretical accuracy curve of the van der Pauw method. This method provides accurate determination of sample resistivity when the ratio of sample thickness to its diameter is less than 0.45. They found that the contact area between electrode and sample is a key factor in the resistivity measurement accuracy and its size is dependent on the sample diameter for a given measurement accuracy.

Conductivity of AgI under high pressure

We carried out in situ conductivity measurements on silver iodide (AgI) under high pressure using a fabricated microcircuit on a diamond anvil cell (DAC). The result shows that the conductivity of AgI increases discontinuously by two orders of magnitude at 1.0 GPa, accompanying the transition from wurtzite/zinc-blende structure to AgI-III (NaCl structure). The conductivity gradually decreases with increasing pressure from 1.0 to 11 GPa, indicating the ionic conduction is impeded by the application of pressure. The conductivity changes very little with further pressure increase from 11 to 20 GPa, implying that the ionic conductivity decrease with pressure may be offset by the conductivity increase with pressure from the electronic process. Above 20 GPa, the conductivity starts to increase again, indicating that the electronic contribution becomes dominant. We calculated the ionic carrier concentration and the activation energy for ionic transport in AgI-III, and investigated the temperature and pressure de...

Electrical properties and phase transition of CdTe under high pressure

In situ electrical resistivity measurement of powdered CdTe has been performed under high pressure using a diamond anvil cell equipped with a microcircuit. With the pressure increasing from 2.7 to 3.8 GPa, a sharp decrease in resistivity of over three orders of magnitude is observed. This is due to the appearance of rock-salt CdTe. At about 6.5 GPa a resistivity inflexion appears which has not been reported before. It is caused by the obvious decrease of band gap in certain symmetry directions of the Brillouin zone of rock-salt CdTe. From 6.5 to 10 GPa, the descending trend of the resistivity turns gently. At about 10 GPa, a cusp corresponding to the transition to the Cmcm phase is distinguished. Between 10 and 38 GPa, three leap points have been detected at 15.5 GPa, 22.2 GPa and 30 GPa, which imply abundant electronic phase transitions of CdTe. Resistivity measurements were also performed in a wide temperature range from liquid nitrogen temperature (77 K) to 450 K. It is proved that rock-salt CdTe does not show a typical metallic transport character. In the pressure range of 6.0-7.0 GPa, CdTe has a band gap of about 445 meV. The relationship of In p to 1/ T is also fitted linearly to yield the ionization energy of impurities at different pressures.