Stage-scanning System Research Articles

Two-dimensional Gaussian fitting for precise measurement of lattice constant deviation from a selected-area diffraction map.

Unlike X-ray diffraction or Raman techniques, which suffer from low spatial resolution, transmission electron microscopy can be used to obtain strain maps of nanoscaled materials and devices. Convergent-beam electron diffraction (CBED) and nanobeam electron diffraction (NBED) techniques detect the deviation of a lattice constant (i.e. an indicator of strain) within 0.01%; however, their use is restricted to beam-insensitive samples. Selected-area electron diffraction (SAED) does not have such limitations but has low spatial resolution and precision. The use of a spherical aberration corrector and a nanosized selected-area aperture improves the spatial resolution, but the precision is still low. In this study, a two-dimensional stage-scanning system is used to acquire arrays of diffraction patterns at different positions of the sample under fixed beam conditions. Data processing with iterative nonlinear least-squares fitting enabled the spot displacement for each point of the scan area to be measured with precision comparable to that of the CBED or NBED technique. The precise strain determination, in combination with the simplicity of the measurement process, makes the nanosized SAED technique competitive with other methods for strain mapping at nanoscale dimensions.

Super-resolution phase reconstruction technique in electron holography with a stage-scanning system

Super-resolution image reconstruction is a digital signal processing technique that allows creating a high-resolution image from multiple low-resolution images taken at slightly different positions. We introduce the super-resolution image reconstruction technique into electron holography for reconstructing phase images as follows: the studied specimen is shifted step-wise with a high-precision piezo holder, and a series of holograms is recorded. When the step size is not a multiple of the CCD pixel size, processing of the acquired series results in a higher pixel density and spatial resolution as compared to the phase image obtained with conventional holography. The final resolution exceeds the limit of the CCD pixel size divided by the magnification.

Strain mapping in selected area electron diffraction method combining a Cs-corrected TEM with a stage scanning system

A novel strain mapping method with high spatial resolution is proposed on the basis of the selected area electron diffraction. It consists of a Cs-corrected transmission electron microscope (TEM) and a stage scanning system. The Cs-corrected TEM sufficiently narrows a selected area aperture without image selection error and enables us to obtain diffraction patterns from selected nanometer-scale regions with a parallel beam. The diffraction spots are very sharp due to the parallel beam, thus facilitating the strain measurement. The stage scanning system for controlling the sample stage with piezoelectric actuators can scan an electron beam over an area without changing the electron beam optics. I critically examined the validity and flexibility of this method by using a current strain-induced semiconductor device.

Direct acquisition of interferogram by stage scanning in electron interferometry

We present an electron holography technique to acquire an interferogram, that is, cosine image of phase distribution. The interferogram is constructed by shifting the specimen in one direction with a stage-scanning system and acquiring line intensities of holograms. Taking line intensities eliminates the carrier fringes in the holograms and yields the interferogram. Under phase object approximation, the object phase can be readily obtained from the interferogram without any reconstruction procedure. The spatial resolution of phase is determined independently of the fringe spacing, overcoming the limitation of conventional techniques based on the Fourier transformation method.

Mapping of Phase Distribution in Electron Holography with a Stage-Scanning System

A new method is proposed for mapping of phase distribution in electron holography. A stage-scanning system was used for moving the specimen to obtain a series of holograms with different specimen positions in a fixed electron-optics configuration. By applying a digital aperture which selects an area on holograms with different specimen positions, an interferogram of the specimen can be obtained directly without a complex reconstruction method such as the one using Fourier transformation. Experimental results for a Co particle demonstrated the practicability of this method.

Three-dimensional observation of SiO2 hollow spheres with a double-shell structure using aberration-corrected scanning confocal electron microscopy

Optical sectioning using scanning confocal electron microscopy (SCEM) is a new three-dimensional (3D) imaging technique which promises improved depth resolution, particularly for laterally extended objects. Using a stage-scanning system to move the specimen in three dimensions, two-dimensional (2D) images sliced from any plane in XYZ space can be obtained in shorter acquisition times than those required for conventional electron tomography. In this paper, a double aberration-corrected SCEM used in annular dark-field mode was used to observe the 3D structure of SiO(2) hollow spheres fabricated by a carbon template method. The double-shell structure of the sample was clearly reflected in both XY- and XZ-sliced images. However, elongation along the optical axis was still evident in the XZ-sliced images even when double aberration correctors were used. Application of a deconvolution technique to the experimental XZ-sliced images reduced the elongated shell thicknesses of the SiO(2) sphere by 40-50% and the selectivity of information at a certain sample depth was also enhanced. Subsequently, 3D reconstruction by stacking the deconvoluted slice images restored the spherical surface of a SiO(2) sphere.

Multi-focal multiphoton lithography

Multiphoton lithography (MPL) provides unparalleled capabilities for creating high-resolution, three-dimensional (3D) materials from a broad spectrum of building blocks and with few limitations on geometry, qualities that have been key to the design of chemically, mechanically, and biologically functional microforms. Unfortunately, the reliance of MPL on laser scanning limits the speed at which fabrication can be performed, making it impractical in many instances to produce large-scale, high-resolution objects such as complex micromachines, 3D microfluidics, etc. Previously, others have demonstrated the possibility of using multiple laser foci to simultaneously perform MPL at numerous sites in parallel, but use of a stage-scanning system to specify fabrication coordinates resulted in the production of identical features at each focal position. As a more general solution to the bottleneck problem, we demonstrate here the feasibility for performing multi-focal MPL using a dynamic mask to differentially modulate foci, an approach that enables each fabrication site to create independent (uncorrelated) features within a larger, integrated microform. In this proof-of-concept study, two simultaneously scanned foci produced the expected two-fold decrease in fabrication time, and this approach could be readily extended to many scanning foci by using a more powerful laser. Finally, we show that use of multiple foci in MPL can be exploited to assign heterogeneous properties (such as differential swelling) to micromaterials at distinct positions within a fabrication zone.

A nonlinear controller for three-dimensional tracking of a fluorescent particle in a confocal microscope

We describe an algorithm for using a confocal microscope for tracking single fluorescent particles diffusing in three dimensions. The algorithm uses a standard confocal setup and directly translates each fluorescence measurement into an actuator command. Through physical simulations, we illustrate 3-D tracking in both stage scanning and beam scanning confocal systems. The simulated stage scanning system achieved tracking of particles diffusing in 3-D with coefficients up to 0.2 μm2/s when the average fluorescence intensities was less than 1.84 counts per measurement cycle (corresponding to less than 18,400 counts per second) in the presence of background fluorescence with a rate of 5,000 counts per second. Increasing the fluorescence intensity to approximately 193 counts per measurement cycle (1,930,000 counts per second) allowed the system to track up to particles diffusing with coefficients as large as 0.7 μm2/s. The beam steering system allowed for faster motion of the focal volume of the microscope and successfully tracked particles diffusing with coefficients up to 0.7 μm2/s with fluorescence measurement intensities of approximately 0.189 counts per measurement cycle (37,570 counts per second) and with coefficients up to 90 μm2/s when the fluorescence intensity was increased to 19 counts per measurement cycle (3,807,500 counts/sec).

Three-Dimensional Optical Sectioning by Scanning Confocal Electron Microscopy with a Stage-Scanning System

We evaluated the depth resolution of annular dark-field (ADF) scanning confocal electron microscopy (SCEM) with a stage-scanning system by observation of nanoparticles. ADF-SCEM is a three-dimensional (3D) imaging technique that we recently proposed. An ADF-SCEM instrument involves a pinhole aperture before a detector for rejecting electrons from the out-of-focal plane in a specimen and an annular aperture under the specimen for collecting only scattered electrons. The stage-scanning system enables us to directly obtain optical slice images perpendicular and parallel to an optical axis at a desired position. In particular, the parallel slices visualize the elongation of nanoparticles along the optical axis, which depends on the depth resolution. ADF-SCEM effectively reduced the elongation length of the nanoparticles sufficiently to demonstrate depth sectioning, in comparison with scanning transmission electron microscopy and bright-field SCEM. The experimentally obtained length was nearly equal to the theoretically estimated one from the probe size considering the experimental conditions. Furthermore, we applied this ADF-SCEM technique to analysis of the 3D position of catalytic nanoparticles on carbon nanostructures.

Three-dimensional imaging of carbon nanostructures by scanning confocal electron microscopy

Although scanning confocal electron microscopy (SCEM) shows a promise for optical depth sectioning with high resolution, practical and theoretical problems have prevented its application to three-dimensional (3D) imaging. We employed a stage-scanning system in which only the specimen is moved three dimensionally under a fixed lens configuration, and an annular dark-field (ADF) aperture which blocks direct beams and selects only the scattered electrons. This ADF-SCEM improved depth resolution sufficiently to perform optical depth sectioning. Finally, we succeeded in demonstrating the 3D reconstruction of carbon nanocoils using ADF-SCEM.

Development of a stage-scanning system for high-resolution confocal STEM

A stage-scanning system is composed of a specially designed transmission electron microscopy specimen holder equipped with a piezo-driven specimen stage, power supplier and control software. This system enables the specimen to be scanned three-dimensionally, and therefore confocal scanning transmission electron microscopy (STEM) can be performed with a fixed electron-optics configuration. It is demonstrated that stage-scanning confocal STEM images can be obtained with the lateral atomic resolution and the specimen can be moved three-dimensionally with high precision.

Highly effective three-dimensional large-scale microfabrication using a continuous scanning method

Effective scanning is an important issue in two-photon induced stereolithography (TPS) for the reduction of the processing time required to fabricate three-dimensional (3D) nano/microstructures. In large-scale TPS based on a stage-scanning system, the large processing time due to the intrinsic slow response in the stage scanning system is a major obstacle to its use as a practical nanofabrication process. To overcome this drawback, we propose a continuous scanning method (CSM) for a stage-scanning system. In CSM, a pattern is generated with continuous movement of the stage during laser beam exposure. A stable fabrication window (SFW), which enables uniform motion of the stage without errors considering the stage characteristics, was obtained from fundamental experiments. Within the condition of a SFW, 2D and 3D microstructures having nanoscale details were fabricated with a whole scale range of several hundred micrometers using CSM.

Development of Stage-scanning System for Confocal Scanning Transmission Electron Microscopy

We developed a stage-scanning system for confocal scanning transmission electron microscopy (confocal STEM), which enables us to perform STEM under a fixed lens configuration without a beam-scanning system. A specimen holder with a piezo-driven stage was modified and controlled by a computer program for stage scanning. The signals of transmitted electrons detected by an STEM detector were displayed on a computer screen and were synchronized with the voltage supplied to the piezoelectric devices used for stage positioning, which consequently produced a stage-scanning STEM image. Furthermore, we evaluated the stability of the developed stage-scanning STEM system and the resolution of the obtained images. 0.2 nm lattice firings could be observed in Au particles, which indicated that this system could demonstrate atomic-resolution STEM imaging at desired z positions. This is attributed to the small specimen drift, stable stage scanning and the computer program developed for stage axis corrections. Finally, we applied this stage-scanning system to confocal imaging. [DOI: 10.1380/ejssnt.2008.111]