Multi-objective Optimal Design of High Frequency Probe for Scanning Ion Conductance Microscopy

Scanning ion conductance microscopy（SICM） is an emerging non-destructive surface topography characterization apparatus with nanoscale resolution. However, the low regulating frequency of probe in most existing modulated current based SICM systems increases the system noise, and has difficulty in imaging sample surface with steep height changes. In order to enable SICM to have the capability of imaging surfaces with steep height changes, a novel probe that can be used in the modulated current based bopping mode is designed. The design relies on two piezoelectric ceramics with different travels to separate position adjustment and probe frequency regulation in the Z direction. To fiarther improve the resonant frequency of the probe, the material and the key dimensions for each component of the probe are optimized based on the multi-objective optimization method and the finite element analysis. The optimal design has a resonant frequency of above 10 kHz. To validate the rationality of the designed probe, microstructured grating samples are imaged using the homebuilt modulated current based SICM system. The experimental results indicate that the designed high frequency probe can effectively reduce the spike noise by 26% in the average number of spike noise. The proposed design provides a feasible solution for improving the imaging quality of the existing SICM systems which normally use ordinary probes with relatively low regulating frequency.

Precision Delivery Using Nanopipette for Single-cell Studies

Nanopipette based scanning probe technique is a versatile tool in non-contact imaging in biology.In addition to the topographic imaging,its capability of localized delivery of bio-active molecules is emerging.In this mini review,we introduce the applications of nanopipette in single-cell researches with a focus on localized delivery.The working principles of three delivery modes including resistive pulse,pressure-driven flow,and electroosmotic flow-driven delivery are summarized and compared.Their applications in single-cell researches are reviewed.The current technical challenges in scanning ion conductance microscopy-based delivery,and their growing influence in medicine and pharmacologic researches are also discussed.

Characterization of 3D pore nanostructure and stress-dependent permeability of organic-rich shales in northern Guizhou Depression,China

The three-dimensional(3D)pore structures and permeability of shale are critical for forecasting gas production capacity and guiding pressure differential control in practical reservoir extraction.However,few investigations have analyzed the effects of microscopic organic matter(OM)morphology and 3D pore nanostructures on the stress sensitivity,which are precisely the most unique and controlling factors of reservoir quality in shales.In this study,ultra-high nanoscale-resolution imaging experiments,i.e.focused ion beam-scanning electron microscopy(FIB-SEMs),were conducted on two organic-rich shale samples from Longmaxi and Wufeng Formations in northern Guizhou Depression,China.Pore morphology,porosity of 3D pore nanostructures,pore size distribution,and connectivity of the six selected regions of interest(including clump-shaped OMs,interstitial OMs,framboidal pyrite,and microfractures)were qualitatively and quantitatively characterized.Pulse decay permeability(PDP)measurement was used to investigate the variation patterns of stress-dependent permeability and stress sensitivity of shales under different confining pressures and pore pressures,and the results were then used to calculate the Biot coefficients for the two shale formations.The results showed that the samples have high OM porosity and 85%of the OM pores have the radius of less than 40 nm.The OM morphology and pore structure characteristics of the Longmaxi and Wufeng Formations were distinctly different.In particular,the OM in the Wufeng Formation samples developed some OM pores with radius larger than500 nm,which significantly improved the connectivity.The macroscopic permeability strongly depends on the permeability of OM pores.The stress sensitivity of permeability of Wufeng Formation was significantly lower than that of Longmaxi Formation,due to the differences in OM morphology and pore structures.The Biot coefficients of 0.729 and 0.697 were obtained for the Longmaxi and Wufeng Formations,respectively.

Scanning Electron Microscopy Studies of YBa_2Cu_3O_(7-δ) Superconductors

Micrcostructures of bulk and thin film YBa_2Cu_3O_(7-δ) superconductors were studied by using scanning elec-tron microscopy (SEM). It was confirmed that viscous technique processed bulk YBa_2Cu_3O_(7-δ) has a homoge-neous microstructure across the pellet diameter. Concerning the thin film, it was found that 2 ￣H￣+ ion implanta-tion with a dose of 1× 10￣(12)cm￣(-2) at 50 keV does not cause microstructural change of the film at a micrometrelevel. Combined with previous studies by using high resolution transmission electron microscopy, it appearsthat the structural modification is at an atomic scale.

Transmembrane transport characterization across ionic redox transistors using surface-tracked scanning ion conductance microscopy

A fundamental understanding of ion transport at the nanoscale is critical to the development of efficient chemical separation membranes,catalysts,ionic/bio-inspired materials,and its scale up into multi-functional ionic devices.Electrochemical imaging using scanning probe microscopy hardware has provided a method to visualize and understand processes that occur at the surface of ionic active materials.The suite of scanning probe microscopy techniques developed over the last few years are limited to imaging surface-level phenomena and have not been applied to investigate transmembrane properties of synthetic and natural membranes with high spatial and temporal resolution.In this article,we demonstrate the application our recently developed‘surface-tracked scanning ion conductance microscopy’technique to characterize voltage-regulated ion transport in an ionic redox transistor.The ionic redox transistor exhibits controlled transmembrane ion transport as a function of its electrochemical redox state.The technique presented in this article uses shear force measured between the nanopipette and ionic substrate to image topography of the porous substrate and simultaneously characterize topography-correlated transmembrane transport through the ionic redox transistor.The transmembrane conductance measured across an array of pores within the ionic redox transistor varies from 0.004μS/cm(OFF state)to 0.015μS/cm(ON state).We anticipate that the spatial correlation of transmembrane ion transport in the ionic redox transistor would result in a scale up into smart membrane separators for energy storage,neuromorphic circuits,and desalination membranes.

Micro-pore Structure and Gas Accumulation Characteristics of Shale in the Longmaxi Formation, Northwest Guizhou

For further study on characteristics of micro-pores in the marine shale reservoirs in Northwest Guizhou,shale samples in the Lower Silurian Longmaxi Formation were selected to investigate effect of micro-pores on the characteristics of gas accumulation in shales,through methods of the argon broad ion beam-field emission scanning electron microscope and the nitrogen adsorption/desorption,analysis on the characteristics of micro-pores and related geochemical analysis.Results show that there are seven types of pores in the Longmaxi Formation shale,including interparticle pores,intraparticle pores,intercrystalline pores,dissolution pores,fossil pores,organic pores,and microfractures,among which the interparticle pores and organic pores are best developed.According to the nitrogen adsorption/desorption curves,the pore structures can be classified into three types,including the cylindrical pores with both opening ends,narrow parallel-plate pores and tapered parallel-plate pores with four opening sides.Diameter of micro-pores ranges from 2 to 64 nm,mainly at 2-6 nm.The diameter of micro-pores(less than 2 nm)ranges from 0.4 to 1.8 nm,The micro-pores with a diameter of 0.4-1.0 nm contribute most to the pore volume.Pore volume is dominated by meso-pores(2-50 nm)with a proportion of 83.1%.The micro-pores and meso-pores make major contribution to the specific surface area of pores with proportions of 20.1%and 79.3%,respectively.The total organic carbon(TOC)is the major factor controlling development of nanopores.Different pore types have different characteristics of gas occurrence and migration,indicating that nanopores provide favorable conditions for the occurrence and microscopic migration of gas in shales.