Misa Hayashida

Nano-dot markers for electron tomography formed by electron beam-induced deposition: nanoparticle agglomerates application.

A method allowing fabrication of nano-dot markers for electron tomography was developed using an electron beam-induced deposition in an ordinary dual beam instrument (FIB and SEM) or an SEM. The electron beam deposited nano-dot markers are suitable for automatic alignment of tomographic series. The accuracy of the alignment was evaluated and the method was demonstrated on agglomerated nanoparticle samples using a rod-shaped sample with no missing wedge effect. Simulations were used to assess the effect of marker size on alignment accuracy.

Tungsten-based pillar deposition by helium ion microscope and beam-induced substrate damage

The authors use a helium ion microscope (HIM) equipped with a tungsten hexacarbonyl gas injection system (GIS) to form tungsten-based pillars on carbon and silicon substrates by helium ion beam-induced deposition. Tungsten-based pillars with a width of ∼40u2009nm and height of ∼2u2009μm (aspect ratio of ∼50) are successfully fabricated using the HIM-GIS method. The pillars consist of face-centered cubic WC1−x and/or W2(C, O) grains. Columnar voids with a width of 1–15u2009nm form in the center of the pillars, suggesting that the pillars are continuously sputter-etched by the incident helium ion beam during deposition. In addition, the authors observe beam irradiation damage in the form of blistering of the Si substrate at the interface between the pillar and Si substrate. The columnar void width and Si blister height decreases as the volumetric growth rate of the pillars increases regardless of the deposition parameters. The authors consider that at least three phenomena compete during pillar formation, namely pillar...

High-precision alignment of electron tomography tilt series using markers formed in helium-ion microscope

Tungsten nanodots formed in a helium-ion microscope (HIM) provide a practical means of aligning markers of electron tomography tilt series with a high degree of precision. The nanodots were formed using a HIM equipped with a W(CO)6 gas injection system, enabling the precise placement of the nanodots at desired locations of a sample. Template matching was applied to the markers formed in the HIM to detect the positions automatically. The relation between the positions of the markers and the accuracy of the alignment was also determined in order to achieve precise alignment. The method was applied to the markers in order to reconstruct three-dimensional (3D) images of a rod-shaped specimen that contained a 65-nm-diameter via structure in a Cu/Low-k interconnect.

Position-controlled marker formation by helium ion microscope for aligning a TEM tomographic tilt series

We formed nano-dots using a helium ion microscope (HIM) equipped with a gas injection system. Because of position controllability, the nano-dot markers could be placed efficiently on a specimen using the HIM. The sizes of the dots were controlled by changing the beam radiation time. We tried for the first time to form dots on a rod-shaped specimen to use them as markers for aligning a transmission electron microscope tomographic tilt series before reconstructing 3D images.

Fabrication of marker area to align TEM tomographic tilt series of rod-shaped specimens

In this study, we present a new method for placing markers for alignment of tomographic tilt-series of rod-shaped specimen before 3D reconstructions. By this method, markers (gold nanoparticles) were placed only on the carbon layer (referred to as the marker area) deposited for protecting the specimen surface against ion beam irradiation; this placement was achieved by vacuum evaporation of gold with the help of a mask fabricated adjacent to the specimen. Experimental results showed that the use of the proposed method facilitates the identification of the markers in the alignment process, because the image of the marker area consists of simple high-contrast images of the gold nanoparticles on the carbon layer. The performance of the proposed method was successfully verified experimentally by applying it to a high-density Au/SiO₂ nanocomposite material as a test specimen.

Automatic coarse-alignment for TEM tilt series of rod-shaped specimens collected with a full angular range.

An automatic coarse-alignment method for a tilt series of rod-shaped specimen collected with a full angular range (from alpha=-90 degrees to +90 degrees, alpha is the tilt angle of the specimen) is presented; this method is based on a cross-correlation method and uses the outline of the specimen shape. Both the rotational angle of the tilt axis and translational value of each image can be detected in the images without the use of markers. This method is performed on the basis of the assumption that the images taken at alpha=-90 degrees and alpha=+90 degrees are symmetric about the tilt axis. In this study, a carbon rod on which gold particles have been deposited is used as a test specimen for the demonstration. This method can be used as an automatic coarse-alignment method prior to the application of a highly accurate alignment method because the alignment procedure can be performed automatically except for the initial setup of some parameters.

Three dimensional accurate morphology measurements of polystyrene standard particles on silicon substrate by electron tomography.

Polystyrene latex (PSL) nanoparticle (NP) sample is one of the most widely used standard materials. It is used for calibration of particle counters and particle size measurement tools. It has been reported that the measured NP sizes by various methods, such as Differential Mobility Analysis, dynamic light scattering (DLS), optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), differ from each other. Deformation of PSL NPs on mica substrate has been reported in AFM measurements: the lateral width of PSL NPs is smaller than their vertical height. To provide a reliable calibration standard, the deformation must be measured by a method that can reliably visualize the entire three dimensional (3D) shape of the PSL NPs. Here we present a method for detailed measurement of PSL NP 3D shape by means of electron tomography in a transmission electron microscope. The observed shape of the PSL NPs with 100 nm and 50 nm diameter were not spherical, but squished in direction perpendicular to the support substrate by about 7.4% and 12.1%, respectively. The high difference in surface energy of the PSL NPs and that of substrate together with their low Young modulus appear to explain the squishing of the NPs without presence of water film.

Calibration method of tilt and azimuth angles for alignment of TEM tomographic tilt series

This paper describes the calibration method of the tilt and azimuth angles of specimen using a digital protractor and a laser autocollimator for alignment of electron tomography. It also suggests an easy method to check whether the specimen is tilted by 180.0°, and whether the azimuth angle is 0.0°; the method involves the use of two images of a rod-shaped specimen collected before and after a 180.0° tilt. The method is based on the assumption that these images are symmetric about the tilt axis when the azimuth angle is 0.0°. In addition, we used an experiment to demonstrate the effect of the incorrect angles on reconstructed images and simulated the image quality against distance away from tilt axis.

Electron Diffraction Based Tilt Angle Measurements in Electron Tomography

Electron tomography can provide three dimensional (3D) visualization of nanoscale objects in a transmission electron microscope (TEM) from a tilt series of projected images. The accuracy of the 3D reconstruction depends on quality of input parameters, including accurate alignment in real space and accuracy of tilt and azimuth angle measurements. Here we present an electron diffraction-based in-situ method that allows accurate measurement of the relative tilt () and azimuth () angles. Experimental data were collected in a Hitachi HF 3300 TEM / STEM instrument with a cold field emission gun operated at 300 kV. The rod-shaped samples that allow collection of full ±90° tilt range were prepared in a Hitachi NB 5000 dual beam instrument [1]. The sample used for the experiment comprised a few-layer thick ordered array of silver nanoparticles with sub-5 nm diameter deposited on Si <001>. On amorphous carbon deposited on the top of the sample, some fiducial markers were fabricated by electron beam induced deposition for accurate alignment [2]. The accurate measurement of α and β relies on recording a diffraction pattern (DP), in addition to an image, at each tilt α, which is easily achieved using a computer instrument control known as Maestro [3]. The data were collected in 3° increments. Figure 1 schematically shows the experimental set up. Individual DPs, collected at each α, were aligned over the entire tilt range so that diffraction pattern features, such as Kikuchi lines, are continuous throughout the tilt range, as shown in Figure 2. The relative shift between subsequent DPs is equivalent to change in relative angle between the incident beam and the sample. To facilitate measurement of the each shift, the individual DPs were converted to sinogram by Radon transform. The presence of Kikuchi lines in DPs results in bright peaks in sinograms. The angle of the Kikuchi lines and their distance from center of the DPs appear as the x and y value respectively of the corresponding peak in the sinogram. Using the angle and distance of Kikuchi lines, the shift among individual DPs was calculated and the DPs over the entire tilt series can be stitched together as shown in Figure 2. Low-index zone axis, for example [010] and [0-11], were used as in-situ calibration of the tilt per pixel. The known 90° tilt between [010] and [0-11] poles on stitched DP divided by their distance in pixels gives the °/pix calibration. In the …

Beam-substrate interaction during tungsten deposition by helium ion microscope

We deposited tungsten-based pillars on ~300 nm-thick amorphous carbon and single-crystalline silicon substrates by a helium ion microscope (HIM) using tungsten hexacarbonyl (W(CO)6) as a gaseous precursor. We then investigated beam-induced damage to the substrates correlated with both pillar growth rate and material type of substrates. Faster pillar growth reduced the substrate damage because the pillars shielded the substrates from the incident beam, resulting in a low-damage process. On the other hand, the Si substrate was significantly damaged by the incident beam compared with the carbon substrates. This is because stopping cross-section of 30-ke V helium ion in silicon is ~1.5 times higher than that in carbon. The incident helium ions were considered to induce the substrate damage in the process of losing energy in the substrates.