Ar Ion Polishing Research Articles

Effect of different lithological assemblages on shale reservoir properties in the Permian Longtan Formation, southeastern Sichuan Basin: Case study of Well X1.

Various types of marine-continental transitional facies are present in the gas-bearing shales of the southeastern Sichuan Basin. A review of the different lithological assemblages in these rocks is important for assessing the likely shale gas content and the development of the storage space. This study of the lithological assemblages of the Permian Longtan Formation in the southeastern Sichuan Basin at Well X1 used core observations, optical thin-section observations, Ar-ion polishing, scanning electron microscopy, and nitrogen adsorption tests to compare and analyze storage space types and pore structures in the shale to determine the sedimentary paleoenvironment, petromineralogy, and organic content. The marine-continental transitional facies in the study area were deposited in a warm climate that favored enrichment by organic matter. The kerogen is type II2-III (average vitrinite reflectance 2.66%), which is within the favorable thermal maturity range for the presence of shale gas. The lithology mainly consists of shale, siltstone, and limestone (with bioclasts), as well as a coal seam. The lithological development divides the Longtan Formation into lower (swamp), middle (tidal flat/lagoon), and upper (delta) sub-members. From lower to upper divisions, the lithofacies evolved from silty shale to clay shale and then to shale intercalated with siltstone or calcareous layers. The proportions of intergranular and dissolution pores in the clay minerals decrease gradually from lower to upper sub-members, and pore size sizes also tend to decrease. Relatively large-diameter pores and microfractures occur in the inorganic matter in the lowest sub-member. Quartz and clay are the main constituents of the shale, respectively contributing to the specific surface area and specific pore volume of the reservoir space.

Study on Organic Matter Enrichment and Reservoir Characteristics of Permian Longtan Formation Shale in Southeast Sichuan

The study of reservoir space development characteristics and the geochemical parameters of the Permian Longtan Formation in the southeast of the Sichuan Basin at Well X1 was analyzed by using core observations, optical thin-section observations, Ar-ion polishing, scanning electron microscopy, and nitrogen adsorption tests. Major and trace elements of samples, the V/Cr, U/T, enrichment coefficients EF (Mo) and EF (U), chemical alteration indexes CIA and Sr/Cu, and Mo, P, and other index values of different samples were calculated based on the test of organic geochemical parameters. The depositional environment of the Longtan Formation in the study area was systematically analyzed. The Longtan Formation was in a warm and humid climate during the deposition period. The main body of the sedimentary water was in an oxygen-depleted state, and a portion of it was in an oxidized state with high biological productivity. Therefore, it had a small deposition rate. The clay mineral content and organic matter content in the sample played a major role in controlling the development of reservoir space. The content of clay minerals in the sample was high, and it was mainly chlorite and a mixed layer of illite/smectite. Under a microscope, it was observed that the mixed layer of flake illite/smectite and chlorite aggregate mostly developed interlayer pores or microfractures, which played a positive role in the specific surface area and pore volume of the sample.

Effect of specimen processing for transmission electron microscopy on lattice spacing variation in Si specimens

Variation in the (220) lattice spacing of Si due to specimen processing for transmission electron microscopy (TEM) was experimentally evaluated by comparing the measured lattice spacings of crystalline specimens processed by crushing, mechanical polishing only, and combined mechanical and Ar ion polishing. Although distinct variation in the (220) lattice spacing between the Si specimens processed by crushing and by mechanical polishing only is not observed, the (220) lattice spacing of specimens prepared by combined mechanical and Ar ion polishing imply increasing tendency with increasing Ar ion beam irradiation time. Moreover, the (220) lattice spacing measured from the outermost region of the specimen edge tends to be approximately 3% to 5% larger than that measured from the inner region, irrespective of the processing method. These results demonstrate that differences in the processing conditions of Si specimens and in the measurement location of the Si lattice spacing can be major component of the measurement uncertainty in sub-nanometer metrology using TEM with magnification calibration by the Si lattice spacing. When attempting to apply the lattice spacing of Si as a reference with traceability to the International System of Units for TEM magnification calibration in sub-nanometer metrology, the results suggest that the effect of specimen processing on variation in the lattice spacing is not negligible.

Characteristics of Organic Matter Pores and the Relationship with Current Pressure System of Lower Silurian Longmaxi Shales in Dingshan Field, Southern Sichuan, China

Organic matter pores (OMP) provide significant storage space for hydrocarbons in lower Silurian Longmaxi shales in the Dingshan field of southern Sichuan, China. The distributions of organic matter and the different OMP structure parameters were characterized through Ar-ion polishing, scanning electron microscopy (SEM), and image analysis software for shale samples of different wells. The research results indicated that organic matter has been divided into two categories based on its occurrence, location, and its relationship with authigenic minerals: organic matter in situ and migrated organic matter. OMP for organic matter in situ are mainly micropores mostly arranged isolatedly, while in migrated organic matter pores show larger sizes and higher roundness. The development of OMP in samples is predominantly controlled by the formation pressure. The existence of overpressure alleviated the stress on the rock skeleton, causing the compaction of some migrated organic matters to lag or decrease. This played a positive role in protecting the development of pores in the interior and edge of the rock skeleton, and it can also induce the development of microfractures in shale. The protective effect of formation pressure on organic pores was provided for understanding the exploration and exploitation of Longmaxi shales in the study area.

Microstructure and Electrochemistry of Al-Rich Primer

Al-rich primer (AlRP) is designed to be anodic relative to high strength Al alloys, so that it drives the mixed potential of Al alloy substrates (e.g. AA2024) into the cathodic region below the breakdown potentials of the Al alloys, preventing localized corrosion. The Al-rich primer (AlRP) under study is composed of spherical Al-Zn-In pigments in an epoxy binder. The 2D and 3D microstructure of the AlRP was studied using a combination of X-ray microscopy, plasma focus ion beam/scanning electron microscopy, and transmission electron microscopy techniques. The primer contained Al-Zn-In particles with various sizes ranging from tens of nanometers to microns, epoxy binder and a significant volume of voids. Potentiodynamic polarization testing was performed to measure the electrochemistry of the Al-Zn-In bulk alloy under neat primer in NaCl solution to simulate the environment which Al-Zn-In pigments are exposed to in the real primer. The bulk alloy under neat primer exhibited higher breakdown potential than the bare bulk alloy exposed to NaCl solution. The polarization curves of the bulk alloy under neat primer provide more accurate boundary conditions for modeling of the galvanic interaction between the AlRP and an alloy substrate. Galvanic corrosion between an AA2024 sample and Al-Zn-In bulk alloy was also studied using a zero resistance ammeter. A trivalent chromium process treatment on galvanic couples can protect AA2024 substrate from cathodic corrosion.Acknowledgements: this project is funded by the Office of Naval Research through the Small Business Innovation Research (SBIR) program. We thank Naval Air Systems Command (NAVAIR) for providing Al-rich primer samples. We acknowledge Dr. Mansoureh Norouzi Rad at Zeiss for 3D microstructure reconstruction on Al-rich primer using X-ray microscope, and Thermo Fisher Scientific for 3D microstructure reconstruction on Al-rich primer using Helios Plasma FIB/SEM. We appreciate Dr. Babu Viswanathan at OSU for STEM characterization, and Swagelok Center for Surface Analysis of Materials (SCSAM) at Case Western Reserve University for Ar ion polishing.

Investigating the Formation Mechanism of a Nanoporous Silver Film Electrode with Enhanced Catalytic Activity for CO2 Electroreduction

AbstractMonolithic nanoporous silver (np‐Ag) fabricated by a facile electrochemical method is attractive for electrocatalytic applications. However, the conversion mechanism between Ag and AgCl remains unclear as a result of the lack of appropriate electron microscopy evidence. Herein, systematic scanning electron microscopy (SEM) of the surface and cross‐sectional views were carried out during the anodic formation and reduction of the AgCl layer. To avoid the thermal decomposition of AgCl and the destruction of the cross‐sectional morphology, Ar ion polishing at −140 °C under the cooling of liquid N2 was adopted. Our data show that the reduction process of the AgCl layer includes three processes: trigger, expansion, and shrinkage. A funnel‐like transient state was observed for the first time, leading to a new formation mechanism for the resultant np‐Ag. Outstanding performance in electrocatalytic reduction of CO2 to CO was observed for one of the nanoporous Ag films presumably due to its unique nanostructure to promote initial electron transfer and active‐site exposure. The selectivity of CO between −0.31 and −0.56 V was higher than 90 %, and reached a maximum of 96 % at −0.36 V.

Gas adsorption capacity calculation limitation due to methane adsorption in low thermal maturity shale: A case study from the Yanchang Formation, Ordos Basin

A series of integrated and repeatable methods were used to demonstrate the methane adsorption limitations associated with calculating low thermal maturity shale gas adsorption capacities. These methods include X-ray diffraction of bulk and clay minerals, Soxhlet extraction, Ar-ion polishing, focused ion beam scanning electron microscopy (FIB-SEM), low pressure N2 adsorption and high pressure CH4 adsorption. The laboratory data suggest that the Yanchang Formation shale primarily consists of clay minerals (≈47.4%) and detrital minerals (≈51.1%). An illite–smectite mixed layer is the principal clay mineral constituent, while quartz is the major detrital mineral component. The thermal maturity is relatively low with Ro ranging from 0.84%Ro to 1.1%Ro, suggesting the absence of organic matter pores and the presence of soxhlet-extractable bitumen and oil, which clog pores with diameters around 4 nm and 50 nm. The specific surface areas and quantities of adsorbed N2 significantly higher for samples extracted using a mixed solution (CH2Cl2 and CH3OH) compared to non-extracted samples. However, the methane adsorption volumes, including volume that were measured and calculated using Langmuir fitting parameters, minimally varied during high pressure CH4 adsorption experiments. CH4 dissolution in bitumen and oil causes the difference exhibited by these two gas adsorption analyses. Non-extracted samples produce inaccurate results using methane adsorption procedures and do not effectively represent practical shale reservoirs. Extracted samples are limited by CH4 adsorption when calculating gas adsorption capacities for low thermal maturity shales.

Focused high- and low-energy ion milling for TEM specimen preparation

For atomic-resolution aberration-corrected (Cs-corrected) scanning transmission electron microscopy (STEM) the quality of prepared TEM specimens is of crucial importance. High-energy focused gallium ion beam milling (FIB) is widely used for the production of TEM lamella. However, the specimens after conventional FIB preparation are often still too thick. In addition, damage and amorphization of the TEM specimen surface during the milling process occur. In order to overcome these disadvantages, low-energy Ar ion milling of FIB lamellae can be applied. In this work, we focus on TEM specimen preparation of different thin films (GaN, Ge2Sb2Te5, TiO2) and interface structures (GaN/6H-SiC, SrTiO3/TiO2, Ge2Sb2Te5/Si) using a combination of FIB with a focused low-energy Ar ion polishing. The results show that this combination enables the routine preparation of high quality TEM lamellae with a smooth surface and uniform thickness, even at the interface region between two different materials and over a lateral range of several micrometres. The prepared lamellae exhibit less surface damage and are well suited for atomic-resolution Cs-corrected STEM/TEM imaging at medium and low accelerating voltages. These results are in a good agreement with Monte Carlo simulations performed by the Stopping and Range of Ions in Matter (SRIM) software.

EBSD Sample Preparation: High Energy Ar Ion Milling

Surface quality development on series of metal samples was investigated using a new Ar ion milling apparatus. The surface quality of samples was characterized by the image quality (IQ) parameter of the electron backscatter diffraction (EBSD) measurement. Ar ion polishing recipes have provided to prepare a surface appropriate for high quality EBSD mapping. The initial surfaces of samples were roughly grinded and polished. High quality surface smoothness could be achieved during the subsequent Ar ion polishing treatment. The optimal angles of Ar ion incidence and the polishing times were determined for several materials.

Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films

In the search for phase change materials (PCM) that may rival traditional random access memory, a complete understanding of the amorphous to crystalline phase transition is required. For the well-known Ge2Sb2Te5 (GST) and GeTe (GT) chalcogenides, which display nucleation and growth dominated crystallization kinetics, respectively, this work explores the nanomechanical morphology of amorphous and crystalline phases in 50 nm thin films. Subjecting these PCM specimens to a lateral thermal gradient spanning the crystallization temperature allows for a detailed morphological investigation. Surface and depth-dependent analyses of the resulting amorphous, transition and crystalline regions are achieved with shallow angle cross-sections, uniquely implemented with beam exit Ar ion polishing. To resolve the distinct phases, ultrasonic force microscopy (UFM) with simultaneous topography is implemented revealing a relative stiffness contrast between the amorphous and crystalline phases of 14% for the free film surface and 20% for the cross-sectioned surface. Nucleation is observed to occur preferentially at the PCM-substrate and free film interface for both GST and GT, while fine subsurface structures are found to be sputtering direction dependent. Combining surface and cross-section nanomechanical mapping in this manner allows 3D analysis of microstructure and defects with nanoscale lateral and depth resolution, applicable to a wide range of materials characterization studies where the detection of subtle variations in elastic modulus or stiffness are required.

High-Accuracy Analysis of Nanoscale Semiconductor Layers Using Beam-Exit Ar-Ion Polishing and Scanning Probe Microscopy

A novel method of sample cross sectioning, beam-exit Ar-ion cross-sectional polishing, has been combined with scanning probe microscopy to study thin AlxGa1-xAs/GaAs layers. Additional contrast enhancement via a citric acid/hydrogen peroxide etch allows us to report the observation of layers as thin as 1 nm. Layer thickness measurements agree with transmission electron microscopy (TEM) data to 0.1 ± 0.2 nm, making this a very promising low-cost method for nanoscale analysis of semiconductor heterostructures.

Material sensitive scanning probe microscopy of subsurface semiconductor nanostructuresvia beam exit Ar ion polishing

Whereas scanning probe microscopy (SPM) is highly appreciated for its nanometre scaleresolution and sensitivity to surface properties, it generally cannot image solid statenanostructures under the immediate sample surface. Existing methods of cross-sectioning(focused ion beam milling and mechanical and Ar ion polishing) are either prohibitivelyslow or cannot provide a required surface quality. In this paper we present a novel methodof Ar ion beam cross-section polishing via a beam exiting the sample. In this approach, asample is tilted at a small angle with respect to the polishing beam that enters fromunderneath the surface of interest and exits at a glancing angle. This creates analmost perfect nanometre scale flat cross-section with close to open angle prismaticshape of the polished and pristine sample surfaces ideal for SPM imaging. Usingthe new method and material sensitive ultrasonic force microscopy we mappedthe internal structure of an InSb/InAs quantum dot superlattice of 18 nm layerperiodicity with the depth resolution of the order of 5 nm. We also report using thismethod to reveal details of interfaces in VLSI (very large scale of integration) lowk dielectric interconnects, as well as discussing the performance of the new approach for SPMas well as for scanning electron microscopy studies of nanostructured materials and devices.

50%冷間圧延を施したAl-Mg-Si合金の焼鈍に伴う組織変化の同一視野観察 —その(2)回復により形成される組織—

Changes in microstructures at recovery stage after cold-rolling at 50% reduction rate were observed in an Al-Mg-Si alloy by means of SEM-EBSD system. The same area in the specimen was observed before and after cold-rolling. Intermittent annealing at 673 K, Ar ion-polishing, and EBSD observation were repeated up to the annealing time of 3.6 ks. Dislocation cells formed by cold-rolling changed into subgrains with annealing. Low and high angle boundaries were formed with surrounding the subgrains depending on misorientations between the neighboring subgrains. The high angle boundaries migrated to form recovered microstructures. Original orientation of the dislocation cell was maintained in the recovered microstructure. Some of the recovered microstructures grew with invading others. Therefore, new discrete poles did not appear in a discrete pole figure during annealing but those in the invaded subgrains disappear, which made the pole figure of the annealed specimen different from that of the cold-rolled specimen. Secondary recovered microstructures were observed to be formed with invading primary formed recovered microstructures. The recovered microstructures were finally invaded by recrystallized grains to disappear. In a region where growth of recrystallized grains was delayed, coarse recovered microstructures composed of large subgrains were formed.

Ni Nanoparticles Elaborated with an Ar Ion Polishing Technique

AbstractNi nanoparticles where obtained from a Ni sample milled with Ar ions by using a Gatan precision ion polishing system, normally used for Transmission Electron Microscopy (TEM) sample preparation. Deposition of Ni nanoparticles was performed over two different surfaces: on a double sided carbon tape and, on a Cu grid covered with collodion film. A continuos film of Ni was characterized, over the carbon tape by SEM and EDAX techniques. The last surface was analysed by TEM. In both cases, a thin film composed of Ni nanoparticles, was founded and result obtained by TEM, show a nanoparticle diameter of about 4 nm.