Ultramicroscopy最新文献

Neutral helium atom microscopy is a novel microscopy technique which offers strictly surface-sensitive, non-destructive imaging. Several experiments have been published in recent years where images are obtained by scanning a helium beam spot across a surface and recording the variation in scattered intensity at a fixed total scattering angle ${\theta }_{SD}$ and fixed incident angle ${\theta }_i$ relative to the overall surface normal. These experiments used a spot obtained by collimating the beam (referred to as helium pinhole microscopy). Alternatively, a beam spot can be created by focusing the beam with an atom optical element. However up till now imaging with a focused helium beam has only been demonstrated in transmission (using a zone plate). Here we present the first reflection images obtained with a focused helium beam (also using a zone plate). Images are obtained with a spot size (FWHM) down to $4.7\mu m$ $\pm 0.5\mu$m, and we demonstrate focusing down to a spot size of about $1\mu m$. Furthermore, we present experiments measuring the scattering distribution from a focused helium beam spot. The experiments are done by varying the incoming beam angle ${\theta }_i$ while keeping the beam-detector angle ${\theta }_{SD}$ and the point where the beam spot hits the surface fixed - in essence, a microscopy scale realization of a standard helium atom scattering experiment. Our experiments are done using an electron bombardment detector with adjustable signal accumulation, developed particularly for helium microscopy.

The high resolution of a scanning tunneling microscope (STM) relies on the stability of its scan unit. In this study, we present an isolated scan unit featuring non-magnetic design and ultra-high stability, as well as bidirectional movement capability. Different types of piezoelectric motors can be incorporated into the scan unit to create a highly stable STM. The standalone structure of scan unit ensures a stable atomic imaging process by decreasing noise generated by motor. The non-magnetic design makes the scan unit work stable in high magnetic field conditions. Moreover, we have successfully constructed a novel STM based on the isolated scan unit, in which two inertial piezoelectric motors act as the coarse approach actuators. The exceptional performance of homebuilt STM is proved by the high-resolution atomic images and dI/dV spectrums on NbSe₂ surface at varying temperatures, as well as the raw-data images of graphite obtained at ultra-high magnetic fields of 23 T. According to the literature research, no STM has previously reported the atomic image at extreme conditions of 2 K low temperature and 23 T ultra-high magnetic field. Additionally, we present the ultra-low drift rates between the tip and sample at varying temperatures, as well as when raising the magnetic fields from 0 T to 23 T, indicating the ultra-high stability of the STM in high magnetic field conditions. The outstanding performance of our stable STM hold great potential for investigating the materials in ultra-high magnetic fields.

Nanoparticles in microscopy images are usually analyzed qualitatively or manually and there is a need for autonomous quantitative analysis of these objects. In this paper, we present a physics-based computational model for accurate segmentation and geometrical analysis of one-dimensional deformable overlapping objects from microscopy images. This model, named Nano1D, has four steps of preprocessing, segmentation, separating overlapped objects and geometrical measurements. The model is tested on SEM images of Ag and Au nanowire taken from different microscopes, and thermally fragmented Ag nanowires transformed into nanoparticles with different lengths, diameters, and population densities. It successfully segments and analyzes their geometrical characteristics including lengths and average diameter. The function of the algorithm is not undermined by the size, number, density, orientation and overlapping of objects in images. The main strength of the model is shown to be its ability to segment and analyze overlapping objects successfully with more than 99 % accuracy, while current machine learning and computational models suffer from inaccuracy and inability to segment overlapping objects. Benefiting from a graphical user interface, Nano1D can analyze 1D nanoparticles including nanowires, nanotubes, nanorods in addition to other 1D features of microstructures like microcracks, dislocations etc.

A scanning helium microscope typically utilises a thermal energy helium atom beam, with an energy and wavelength (¡100 meV, $\sim$0.05 nm) particularly sensitive to surface structure. An angular detector stage for a scanning helium microscope is presented that facilitates the in-situ measurement of scattering distributions from a sample. We begin by demonstrating typical elastic and inelastic scattering from ordered surfaces. We then go on to show the role of topography in diffuse scattering from disordered surfaces, observing deviations from simple cosine scattering. In total, these studies demonstrate the wealth of information that is encoded into the scattering distributions obtained with the technique.

A strong in-plane magnetic field is required for Lorentz transmission electron microscopy (LTEM) to observe the evolution of the magnetic domain structure of materials with high coercivity, particularly for research on rare-earth permanent magnets. However, the maximum field of the present in-situ magnetising holder applied in 200-kV or 300-kV TEM does not exceed 0.1 T. In this study, the reason for the low field was analysed, and the field strength was significantly elevated by reducing the field application area of the field generator. From finite element method calculations and experimental measurements, a 1.5 T in-plane field was achieved by our new holder in a 200-kV TEM, and images with good quality could still be obtained. Using the newly developed holder, the magnetisation process of hot-pressed NdFeB magnets was observed. The in-situ magnetising holder can be used in research on a wide variety of magnetic materials.

The remarkable physical properties of dental enamel can be largely attributed to the structure of the hydroxyapatite (HAp) crystallites on the sub-micrometre scale. Characterising the HAp microstructure is challenging, due to the nanoscale of individual crystallites and practical challenges associated with HAp examination using electron microscopy techniques. Conventional methods for enamel characterisation include imaging using transmission electron microscopy (TEM) or specialised beamline techniques, such as polarisation-dependent imaging contrast (PIC). These provide useful information at the necessary spatial resolution but are not able to measure the full crystallographic orientation of the HAp crystallites. Here we demonstrate the effectiveness of enamel analyses using transmission Kikuchi diffraction (TKD) in the scanning electron microscope, coupled with newly-developed pattern matching methods. The pattern matching approach, using dynamic template matching coupled with subsequent orientation refinement, enables robust indexing of even poor-quality TKD patterns, resulting in significantly improved data quality compared to conventional diffraction pattern indexing methods. The potential of this method for the analysis of nanocrystalline enamel structures is demonstrated by the characterisation of a human enamel TEM sample and the subsequent comparison of the results to high resolution TEM imaging. The TKD – pattern matching approach measures the full HAp crystallographic orientation enabling a quantitative measurement of not just the c-axis orientations, but also the extent of any rotation of the crystal lattice about the c-axis, between and within grains. Results presented here show how this additional information highlights potentially significant aspects of the HAp crystallite structure, including intra-crystallite distortion and the presence of multiple high angle boundaries between adjacent crystallites with rotations about the c-axis. These and other observations enable a more rigorous understanding of the relationship between HAp structures and the physical properties of dental enamel.

Recent advances in microelectromechanical systems (MEMS)-based substrates and sample holders for in situ transmission electron microscopy (TEM) are currently enabling exciting new opportunities for the nanoscale investigation of materials and devices. The ability to perform electrical testing while simultaneously capturing the wide spectrum of signals detectable in a TEM, including structural, chemical, and even electronic contrast, represents a significant milestone in the realm of nanoelectronics. In situ studies hold particular promise for the development of Metal-Insulator-Metal (MIM) devices for use in next-generation computing. However, achieving successful device operation in the TEM typically necessitates meticulous sample preparation involving focused ion beam (FIB) systems. Conducting contamination introduced during the FIB thinning process and subsequent attachment of the sample onto a MEMS-based chip remains a formidable challenge. This article delineates an improved FIB-based sample preparation methodology that results in good electrical connectivity and operational functionality across various MIM devices. To exemplify the efficacy of the sample preparation technique, we demonstrate preparation of a clean cross section extracted from a Au/Pt/BaSrTiO₃/SrMoO₃ tunable capacitor (varactor). The FIB-prepared TEM lamella mounted on a MEMS-based chip showed current levels in the tens of picoamperes range at 0.1 V. Furthermore, the electric response and current density of the TEM lamella device closely align with macro-scale devices. These samples exhibit comparable current densities to their macro-sized counterparts thus validating the sample preparation process and confirming device connectivity. The simultaneous operation and TEM characterization of electronic devices enabled by this process enables direct correlation between device structure and function, which could prove pivotal in the development of new MIM systems.

In this paper, a methodology is presented to count the number of atoms in heterogeneous nanoparticles based on the combination of multiple annular dark field scanning transmission electron microscopy (ADF STEM) images. The different non-overlapping annular detector collection regions are selected based on the principles of optimal statistical experiment design for the atom-counting problem. To count the number of atoms, the total intensities of scattered electrons for each atomic column, the so-called scattering cross-sections, are simultaneously compared with simulated library values for the different detector regions by minimising the squared differences. The performance of the method is evaluated for simulated Ni@Pt and Au@Ag core–shell nanoparticles. Our approach turns out to be a dose efficient alternative for the investigation of beam-sensitive heterogeneous materials as compared to the combination of ADF STEM and energy dispersive X-ray spectroscopy.

Scanning electrochemical microscopy (SECM) is a scanning probe microscope with an ultramicroelectrode (UME) as a probe. The technique is advantageous in the characterization of the electrochemical properties of surfaces. However, the limitations, such as slow imaging and many functions depending on the user, only allow us to use some of the possibilities. Therefore, we applied visual recognition and machine learning to detect micro-objects from the image and determine their electrochemical activity. The reconstruction of the image from several approach curves allows it to scan faster and detect active areas of the sample. Therefore, the scanning time and presence of the user is diminished. An automated scanning electrochemical microscope with visual recognition has been developed using commercially available modules, relatively low-cost components, design, software solutions proven in other fields, and an original control and data fusion algorithm.

Four-dimensional Scanning Transmission Electron Microscopy (4D-STEM) is a powerful technique for high-resolution and high-precision materials characterization at multiple length scales, including the characterization of beam-sensitive materials. However, the field of view of 4D-STEM is relatively small, which in absence of live processing is limited by the data size required for storage. Furthermore, the rectilinear scan approach currently employed in 4D-STEM places a resolution- and signal-dependent dose limit for the study of beam sensitive materials. Improving 4D-STEM data and dose efficiency, by keeping the data size manageable while limiting the amount of electron dose, is thus critical for broader applications. Here we introduce a general method for reconstructing 4D-STEM data with subsampling in both real and reciprocal spaces at high fidelity. The approach is first tested on the subsampled datasets created from a full 4D-STEM dataset, and then demonstrated experimentally using random scan in real-space. The same reconstruction algorithm can also be used for compression of 4D-STEM datasets, leading to a large reduction (100 times or more) in data size, while retaining the fine features of 4D-STEM imaging, for crystalline samples.