Probability to observe the
Electronic devices are strongly influenced by their microstructures. In situ transmission electron microscopy (in situ TEM) with capability to measure electrical properties is an effective method to dynamically correlate electric properties with microstructures. We have developed tools and in situ TEM experimental procedures for measuring electronic devices, including TEM sample holders and sample preparation methods. The method was used to study metallic nanowire by electromigration, magnetoresistance of a ferromagnetic device, conductance quantization of a metallic nanowire, single electron tunnelling, and operation details of resistive random access memories (ReRAM).
- In situ TEM
- TEM sample holder
- tunnel conduction
- resistive RAM
Transmission electron microscopy (TEM) has been efficiently used in a variety of research fields. It is possible to observe individual atoms by using up-to-date microscopes. In addition to conventional (static) TEM observation and microanalyses, dynamical observations and recording is possible under controlled conditions. While
In the research field of electronics, next-generation electronic devices are now under development from the perspective of power consumption, high integration as well as high functionality. The electronic properties of these devices have strong relationship with their crystallographic and/or magnetic microstructures which occasionally change during the device operation. Therefore, the importance of the
In Situ TEM system for electric measurements
There is a schematic of the
3. TEM holders developed for
in situ electronic experiments
Three types of TEM holders were developed in this work. They were holders for current measurements of patterned media, a holder with electromagnets used for Lorentz TEM (LTEM), and TEM/STM holders. Their details are described in the following subsections.
3.1. Holders having four or multiple terminals to investigate patterned devices
There is a photograph of two custom-made single-tilt TEM holders with four electric terminals in Fig. 2(a). The samples are placed at position 1. Figures 2(b) and 2(c) are enlarged photographs. Samples of less than about 5 × 5 mm can be investigated. The sample electrodes were connected to two current terminals (I) and two voltage terminals (V). These terminals are connected to four co-axial connectors (denoted as 2 in Fig. 2(a)). The shield lines of the cables are floated from the TEM holders, which are connected to the ground level (JEM200CX) or a certain voltage level (~2 V for JEM2010). Therefore, they can be used as the guard lines for low current measurements. These holders were mainly used for LTEM observations in this work. There are photographs of a double-tilt holder with 16 terminals in Figs. 2(d) and 2(e) . The sample (turned upside down) was placed at the centre of the holder to face the terminals (Fig. 2(d)). When the cover is closed, the sample electrodes connect automatically with the terminals for electrical measurements (Fig. 2(e)). Multiple devices can be measured during one experiment by using this holder, which was used mainly to investigate electromigration.
3.2. Holder generating in-plane magnetic field
Magnetic devices are important in electronics.
Figure 3(a) is a schematic cross section of the double-layer magnet system where a sample is sandwiched between two four-pole electromagnets. Each electromagnet is assembled from two perpendicularly oriented two-pole electromagnets with ring-shaped yokes (ϕ7 mm and gap of 1 mm). Two serially connected coils with ~30 turns are wound onto each two-pole magnet (maximum current: 500 mA). In-plane magnetic field can be applied to the sample along any direction. The first magnet was used to generate the magnetic field applied to the sample. Electron beam used for TEM observations were deflected by this field. The second magnet below the sample is used to compensate for this deflection. This prevented the TEM image from experiencing fatal deformation or movement. In addition, four electric terminals were arranged in the chinks of the first magnet. Figures 3(b) and 3(c) are photographs of the TEM holder. This is a side entry holder designed for JEM-200CX. The sample is placed by facing it against the magnet. When it was fixed by closing the cover, the contact pads of the sample automatically made contact with the electrodes.
The maximum magnetic field between the pole pieces was measured to be 214 Oe at 500 mA by using a Hall probe. A software package was developed to compensate the hysteretic features of the magnet, and the generated field could be controlled with an accuracy of 1 Oe or better. The homogeneity of the field was checked by using Fe powder suspended in oil, as seen in Fig. 3(d), where only magnet Y was excited. The field within the LTEM observation window was homogeneous (square at the centre: 100 x 100 μm). The distribution of the magnetic field is shown in Fig. 3(e). The current through the coils was 500 mA. The magnetic field was ~7 Oe at 2.5 mm from the pole piece. Thus, there is almost no influence from the second magnet on the specimen: They were 2.5 mm apart from each other. One of the four-pole electromagnets was activated to generate a rotating field (38 Oe). The beam deflection with various magnetic fields was recorded in multi-exposed images (Fig. 3(e)). The beam spot was circularly moved. Excellent controllability of the field was achieved.
The LTEM image moved fatally due to beam deflection caused by the first electromagnet. There is an example in Fig. 4(a) where images with
3.3. TEM/STM holder
There is a schematic of a specimen holder fitted to a JEM 200CX microscope in Fig. 5(a) and photographs of this in Fig. 5(b) . The probe was coarsely moved with three mechanical micrometres (stroke: 0.2 × 0.2 × 10 mm). A piezo tube was placed at the left end of the column pole, with which the position of the probe was controlled at a rate of 400 nm/V (perpendicular to the column pole) and 30 nm/V (along the column pole). The maximum voltage was 100 or 150 V. Two probes could be attached to the piezo actuator. One of two electrodes placed at the piezo actuator could be selected without breaking the vacuum by rotating the column pole using a stepping motor. Figure 5(c) is a photograph of a holder designed for the JEM 2010 microscope . Three electrodes could be placed in this TEM holder (two probes and one sample). The sample was directly connected to the voltage source using a coaxial cable, where the probes were connected to an in-column amplifier for nA measurements or an ammeter. While the basic design of the holders developed here may be the same as that of commercially available holders, additional functions such as multiple probing can be added through custom designing. It is quite important to design the piezo actuators and mechanism for coarse movement to enable the holder to be easily handled.
4. Sample preparation method
Our main purpose here is to develop
4.1. Patterned devices on SiN/Si substrate with observation window
Since the invention by Jacobs and Vehoeven , many electron microscopists focused their attention on the use of free-standing Si3N4 membranes as substrates . These membranes are extremely flat and insulating and are now commercially available. However, it is important to prepare substrates and patterned devices on demand because we can design a variety of patterns by ourselves to carry
4.2. Needle-shaped and wedge-shaped probes and substrates
The probes used in the TEM/STM experiments were prepared with methods based on ion milling. This is because very sharp probe apexes were required to select local areas to be measured. In addition, when the probe was used as the substrate for sample film deposition, its apex should be thin enough for high resolution TEM (HRTEM).
The ion-shadow method  was used for probe fabrication, which is a sputtering technique using powders (mask material) with low sputtering rate. After the probe material was mechanically sharpened into a cone, the mask particle (e.g., diamond or carbon: ϕ10 μm) was put on the top, and the Ar+ ion sputtering was performed. During sputtering, the unmasked part of the tip material is etched, and the particle size was reduced. Finally, a fine cone was obtained when the powder was completely sputtered out within ~1 hour (Fig. 7(a)). While the underlying principles of this process are the same as that of ion-beam lithography, the use of the powder masks is essential in the ion-shadow method. There are examples in Figs. 7(b) and 7(c). The radius of curvature of the apex was usually ~20 nm or less.
The probe can be used as the substrate for film deposition . After the tip-shaped apex had been fabricated, the probe was washed with acetone and ethanol in an ultrasonic bath. It was annealed at 420 K for 30 min, and film deposition was done. One example can be seen in Fig. 7(c), where thin MgO was deposited on the “Au Sub.” There is another example in Fig. 7(d), where a composite film of Fe–SrF2 (~37 vol% Fe, 40 nm thick) was deposited at RT. The round grey contrast denotes Fe particles with sizes of ~2.7 nm.
Another method of fabricating very sharp probe is shown in Fig. 7(e). Commercially available STM tips or mechanically ground probes were sharpened using ion milling from backside with rotation. An apex of 10 nm or less was obtained. When the probe is used as a substrate, it is better to be wide to enable multiple investigations. For this purpose, the probe material was mechanically ground into a wedge and ion milled . There is a micrograph of NiO on PtIr in Fig. 7(f), while TEM images are shown in Figs. 7(g) and 7(h). The substrate was about 50 μm wide and thin enough to observe lattice fringes.
4.3. Easy method to prepare miniaturized multilayer devices for
in situ TEM
Figure 8(b) has scanning electron micrographs (SEMs) over a wide area. Many needles can be identified on the Si surface. There are magnified images from two different regions in Figs. 8(c) and 8(d). A sharp needle 5 μm in length can be seen at around the beam centre (Fig. 8(d)). No carbon particle residuals can be identified at this magnification, and we can expect a small fragment of the film on the needle. On the other hand, the needle lengths are short, and large carbon residuals are identified in Fig. 8(c), which was away from the centre by 500 μm. The carbon residuals and the sample film on the apex should be completely etched out around the beam centre by increasing the milling time. However, the carbon residuals should become small at the neighbouring regions, and needles with adequate apex size should appear. There must be regions with needles suitable for
5. Application of developed TEM holders
Electromigration (EM) is the term used for the electrically induced atom movement after momentum transfer from electrons. It causes failure in the wiring , and the researchers on LSI have tried to suppress it. However, EM has attracted a great deal of attention in creating metallic nanogaps used in SEDs as well as switching devices [37, 38]. Researchers in this field have developed methods of enhancing EM. It is important to achieve high levels of control for EM in both cases even though their purposes have differed.
Atom transportation along the electron flow was identified in TEM images extracted from a video (Fig. 9). When a positive voltage was applied to the right of Fig. 9(a), narrowing occurred at the upstream side of the electron flow (left part of Fig. 9(b)). With polarity inversion, the left end of the wire gained area while the right end lost area (Fig. 6(c)). This morphological change during polarity inversion fits well with earlier reports . Narrowing occurred at the upstream side, and widening on the downstream side, which was independent of the voltage polarity. This suggested that Au atoms were transported along the same direction as that of the electron flow (i.e., opposite to current).
The metallic wire narrowed due to EM. The narrowing rate was not monotonous over time. The wire thinning occasionally started at a certain time, then stopped, and restarted. The wire thickened in some cases. There is an example in Fig. 10 where wire narrowing is evident near the surface step. The edge on the downstream side of the step (dotted line) retreated in Fig. 10(b) (5.25 seconds after Fig. 10(a)), while the edge on the upstream side (solid line) only retreated slightly. As a result, the step increased and cleared. The step started to collapse at the corner in Fig. 10(c). This collapse propagated to neighbouring regions in Fig. 10(d). The upstream side lost atoms in Figs. 10(e), and the downstream side gained atoms. Curve C on the upstream side has a sudden drop in wire width as can be seen in Fig. 10(g), while curve B on the downstream side has a gradual increase. Curve A apart from the step exhibits less change. The width at B reached maximum, and a new narrowing process. The wire narrowing accelerated when the step collapsed. Although only two examples have been presented in this report, contributions on wire narrowing and gap formation from various singularities such as grain boundaries and stacking faults can be investigated with the method used in this research.
5.2. Magnetic domains and magnetoresistance of ferromagnetic devices
Magnetic devices are one of the most important subjects in electronics. Their physical properties, such as magnetoresistance (MR) and magnetization reversal, are influenced by their magnetic microstructures. Therefore, the magnetic microstructures of tiny magnetic patterns have been investigated by using various techniques.
5.2.1. Experiments by using conventional current measurement holder
An Ni79Fe21 film (Py, 2 mm × 100 μm, 35 nm thick) was deposited by using a metal mask. Magnetic anisotropy was induced during the deposition by applying 300 Oe along the long axis of the pattern. It was composed of grains with a size of ~10 nm. The system is outlined in Figs. 1(a) and 1(d), and the holders are seen in Figs. 2(a)-(c). The effective magnetic field in the film plane was controlled by specimen tilt [20, 21, 22, 23]. The observations were carried out in the LowMag-mode, in which the TEM objective lens was switched off. While the residual field (43 Oe) of the objective lens was usually used, ~200 Oe was generated with external current through the lens coil if necessary. The in-plane field was
There are typical LTEM images in Figs. 11(a)-(c) with the simultaneously measured MR-curve, where magnetic field was applied downward in the image (perpendicular to the current) . This was the transverse anisotropic magnetoresistance (AMR). The voltage electrodes are visible as dark parts on the left and right of the image. The fine image contrast in the shape of curves from the top to the bottom edges, called “ripple,” reflects the spatial fluctuations in the magnetic moment in local areas. The averaged magnetic moment,
was 0.7% at 25 Oe, where
Next, a Py stripe pattern was deposited at 500°C under a field of 300 Oe along the short axis to induce uniaxial magnetic anisotropy.
The Py pattern was composed of a single domain (domain-I) in the state A (30 Oe), where the average magnetization is upward in the image. Resistance increased monotonically with the field. Domain-II having magnetization parallel to the field (downward) appeared at 43 Oe (state marked with a star in Fig. 12(a)). However, no remarkable changes in resistance could be identified. After this, the area of domain-II monotonically increased with the field. Resistance reached maximum at ~50 Oe, and then reduced monotonically (states B and C). At ~105 Oe (state-D), all regions were composed of domain-II with downward magnetization in the image. While decreased resistance continued after the disappearance of DWs, the rate of reduction was small. The resistance was plotted as a function of the area of domain-II (Fig. 12(c)) to investigate this change. It decreased linearly with this area. It is clear that resistances in domain-I (anti-parallel
By carefully observing the images in Fig. 12(b), we can identify fine stripe contrast, which is caused by magnetization ripple. This contrast was stronger in domain-I than that in domain-II (Figs. 12(d) and 12(e)). This indicates that the orientation dispersion of the local moment was strong in domain-I, and thus the moment inclined from a direction perpendicular to the current (
5.2.2. Experiments by using electromagnet holder
126.96.36.199. Domain wall injection and movement in a wire pattern
The control of DWs in magnetic wires has been widely reported [42, 43]. A pad is usually attached to the wire to achieve stable injection of DWs into them . There is a series of LTEM images of a Py wire pattern with a square pad with varying in-plane fields in Fig. 13. A field was applied horizontally. After 100 Oe was applied along the left to saturate magnetization, the field was gradually removed to zero (Fig. 13(a)). The wire was almost uniformly magnetized to the left. The contrast at the lower edge was dark while it was white at the upper edge. There was a clear structure of a solenoidal domain (with 90° and 180° DWs) inside the pad. The area of the domain around the pad’s centre penetrated the wire under 6 Oe along the right in Fig. 13(b). A vortex DW (arrowhead) was injected in this case. The contrast of the wire edge changed from the left to the right. The DW moved to the right (Figs. 13(c)–(e)) by increasing the field along the right. The Py pattern was almost saturated in Fig. 13(f). Finally, it was fully saturated in Fig. 13(g) under 100 Oe. The wire edge contrast was reversed from that in Fig. 13(a). Increases and decreases as well as reversal of the magnetic field could be efficiently accomplished by using the system that we developed in this research.
188.8.131.52. Movement of vortex core by field rotation
Ferromagnetic patterns have attracted a great deal of attention in the development of miniaturized memories and logics. Disks with a vortex structure (Fig. 14(a)) represent one such pattern [45, 46]. Local magnetic moments form a clockwise or anti-clockwise loop, and that at the vortex core turns out-of-plane. The vortex core moves perpendicularly to the field when an in-plane field is applied. The direction of movement depends on the chirality of the vortex. There is a test pattern in Fig. 14(b), where Py disks with diameters of 5 and 10 μm can be seen. The arrow denotes an in-plane field of 11 Oe. The bright or dark spotty contrast near the centre of each disk corresponds to a vortex core. The LTEM contrast of the vortex core and disk edge alternates depending on the chirality of the vortex, as shown in Fig. 14(a). A series of LTEM images with rotating magnetic fields is shown in Figs. 14(b)-(e). The vortex cores were displaced according to the respective fields to expand the area with magnetization nearly parallel to the field. The core positions moved gradually by rotating the field.
In-Situ LTEM observations and magnetoresistance measurements
The investigated MR effect was the longitudinal AMR where resistance was high with magnetization parallel or anti-parallel to the sense current. There is an example of an MR curve measured with TEM in Fig. 15(a), where the magnetic field was parallel to the sense current. Well-known positive MR was identified, where resistance was low around a zero magnetic field.
The pattern investigated in this work was large, and the DWs were expected to be thick . Thus, the MR effect due to DWs themselves must be quite small. The MR effect identified here was caused by the change in the distribution of local magnetization. As seen in Figs. 15(c), 15(d), and 15(f), local magnetization tends to be parallel (or anti-parallel) to the DW, and its orientation inclines from the sense current. Therefore, the resistance is thought to be small. Another possibility influencing the MR effect is the strength of the magnetic ripple. A domain with anti-parallel magnetization to the applied field had clearer contrast than that with parallel magnetization to the field as was described in Subsection 5.2.1. This indicates that the former domain had larger fluctuations in the orientation of the magnetic moment, and thus the local moment was much more inclined from the sense current providing lower resistance. A similar phenomenon was expected, even though this difference in contrast was not clearly observed in this research because of weak contrast in the image.
5.3. Quantum conductance of metallic nanowires
Metallic contacts and wires on the nanometre scale have been intensively studied . These are expected to exhibit quantum effects at room temperature (RT). Several techniques have been adopted to produce nanowires [49, 50, 51, 52, 53]. Narrow wires with a width of one Fermi wavelength (~0.5 nm) have been the objects, and the energy split of electrons contributes to the conduction quantization.
The quantization unit of conduction in nonmagnetic materials is known to be 2
Three continuous video frames are presented in Figs. 16(a)-(c). The wire length was increased from 4 to 8 nm by stretching it from the state in Fig. 16(a) to that in Fig. 16(b). The wire widths changed from 2 to 1 nm. A further stretch to Fig. 16(c) broke the wire. The corresponding conductance curve is plotted in Fig. 16(d) with a bias voltage (
Au nanowires were formed under various conditions with different values of
5.4. Single electron tunnelling of nanoparticle system
The conductance of nanostructures such as SED [11, 12] has been intensively investigated. The miniaturization of current paths plays a key role to observe the quantum effect at RT. An important area of research involves nanoparticle systems embedded in an insulator [60, 61, 62]. The tunnelling current is strongly influenced by their geometric arrangement, such as the particle size (i.e., area of the tunnelling junction) and inter-particle distance (i.e., thickness of the tunnelling barrier).
In this research, the TEM/STM was introduced to investigate the direct relation between the geometry and electrical characteristics of nanoparticle systems. The operation system is outlined in Figs. 1(a), 1(c), and 1(f). The samples were deposited on the needle-shaped Au substrate shown in Figs. 7(c) and 7(d). Two examples are presented, that is, tunnel conduction of a 2-nm thick MgO film and a 5-nm thick MgO/Fe/MgO tri-layer film [8, 29, 63, 64]. Nanoscale regions less than 10 nm2 were selected using a movable probe. Current-voltage (
There is a typical HRTEM image of MgO/Au with 200MgO and 200Au lattice fringes in Fig. 18(a). The MgO thickness was ~2 nm. Its barrier height for tunnel conduction was evaluated under the conditions in Figs. 18(b)-(d) using
The following is an example of MgO(2 nm)/Fe(1 nm)/MgO(2 nm), where the Fe layer was composed of nanoparticles (Fig. 19(a)). The film formed a double tunnel junction. As the Fe particle size was on a nanometre scale, the Coulomb blockade (CB) effect was expected at RT. Here, the contact area must be small to detect the quantum effect. Therefore, the sample film was processed inside TEM. After the Au-probe lightly touched the film, 5 V or larger voltage was applied to the probe to exfoliate the sample layer. The narrow current paths were fabricated by repeating this process. Three Fe particles (diameters: 3.4, 3.2, and 2.9 nm) are seen in Fig. 19(b). The particle with a diameter of 2.9 nm was selected for the measurements. The distance between the film surface and the particle was estimated to be 2.4 nm from this image, and the distance between the particle and the Au-sub was 0.8 nm.
The results are presented in Figs. 19(c)-(e), where the tri-layer film can be identified as faint contrast on the Au-sub. The probe softly touched the sample in Fig. 19(c). The tunnelling current in the
5.5. Resistance switching of the resistive random access memory
Resistive random access memory (ReRAM) has attracted a great deal of attention as a next-generation non-volatile memory [14, 15, 67, 68, 69, 70]. Its advantages include high-speed operation, low power consumption, etc. High integration is also expected due to its simple capacitor structure (Fig. 20(a)). Resistance switches between high and low resistance states (HRS and LRS) by applying voltage between top and bottom electrodes (TE and BE). The
The pristine state is typically HRS and converts into LRS due to the first application of voltage. This process is called “forming”. Subsequent voltage returns the resistance into HRS (“reset” process). Resistance again changes into LRS by another application of voltage (“set” process). There are two types of switching. The same voltage polarity is used in “unipolar” switching (Fig. 20(b)), while polarity needs to be altered in “bipolar” switching (Fig. 20(c)). Current abruptly increases during forming or set, and ReRAMs are easily destroyed. To prevent this failure, current limitation (or compliance) of the electrical source is generally introduced. The horizontal line in the
5.5.1. Unipolar switching of PtIr/NiO/PtIr
A binary oxide NiO is one of the most widely investigated materials for ReRAMs and exhibits unipolar switching. The mechanism for this switching phenomenon may be one of the filament models based on soft-breakdown . A conductive filament of oxygen vacancies connecting metal electrodes is formed during the forming. This forming process certainly plays a key role in achieving stable switching cycles. In this study, sharp PtIr probes (tip size: several tens of nanometres or less) to obtain
While the filament formation during the forming process could clearly be identified, reset operation was not found in TEM where the ambient was a vacuum. We fabricated NiO/Pt on a SiO2/Si substrate which was not a TEM sample, to investigate the reason for this result. The
5.5.2. Bipolar switching of PtIr/Cu-GeS/PtIr
The ReRAMs of solid electrolytes are other examples (e.g., CuGeS and Ag2S) [14, 67, 69]. This type of ReRAM is abbreviated as CBRAM (conductive bridging RAM) as well as PMC (programmable metallization cell). The operation is attributed to the conductive filament of Cu (or Ag). The cations (e.g., Cu2+) generated at the anode are thought to migrate toward the cathode with bias voltage. The cations receive electrons at the cathode surface and become metal atoms. Metallic filament is formed by continuing this process, and it bridges the cathode and anode. An opposite bias voltage dissolves the metallic filaments into the solid electrolyte. This is the expected switching process. Real-space
The crystal structure of the deposit was studied by observing real-time selected area diffraction (SAD) patterns. The SAD pattern before voltage application was composed of a faint background and Debye rings (Figs. 23(a) and 23(b)), which indicated the film was amorphous with Ge nanocrystals. The clear spots were from PtIr. A deposit appeared by applying 1 V to the substrate (Fig. 23(c)), and sharp spots appeared in the SAD pattern. They continued to twinkle when voltage was applied. Well-crystallized nanocrystals grew, and their orientation frequently changed. We superposed 1152 frames of video images totalling 35 seconds of footage (Fig. 23(d)). Relatively sharp spots that formed rings corresponded to reflections of Cu. EDX spectra were measured from the filament and other regions (but another sample). The intensity of the Cu peak greatly increased in the filament region. The composition of the deposit was Cu: Ge: S = 7: 2: 1 while it was 4: 4: 2 in the initial state by assuming thin foil approximation. Although this was a rough estimation, we can summarize that the deposit was an agglomeration of crystals with a large amount of Cu.
The sample after the voltage cycle differed from its initial state. Continuation of the
The phenomenon that occurred here can be explained in Fig. 25. An electric field is generated by applying positive voltage to the substrate, and the Cu ions dispersing in Ge-S move to the probe. Then, a small metallic deposit appears at the probe (Fig. 25(a)). The deposit expanded and finally touched the substrate (Figs. 25(b)-(c)). At this stage, the conductive filament bridges the probe and the substrate, and the resistance state is LRS. When further voltage is applied, several filaments increase even though the overall size of the conductive region does not expand (Fig. 25(d)). The Cu-based filaments dissolve and shrink toward the probe due to polarity change (Figs. 25(e)-(f)), and resistance reverts to HRS. There are some residues (nuclei of filaments) at the end of the cycle.
5.5.3. Formation and erasure of conductive filament in Cu/MoOx/TiN
There is an example of the
Filament-like dark contrast appeared in the set process and disappeared in the reset process. This indicates that this dark region behaved as a conductive filament. We analysed it (but in another sample) with EDX and found it contained more Cu than the other regions. Filament images extracted from the video of the set process (A to F) are summarized in Fig. 26(b). No drastic changes in the images can be identified between A and B (HRS). However, a small dark contrast appeared near TiN BE during abrupt set switching, which seemed to be the nucleus of the filament. Even though the current almost reached
The resistance change in the reset process was gradual. Even after the two-step weak reset, image G (frame #1) had similar contrast to F while resistance increased (Fig. 26(c)). The reset switching should occur very locally (e.g., at the ends of filaments). When we further increased the negative voltage to –2.6 V, negative current increased beyond –300 μA (#12), and the filament shrank toward Cu TE. When the current reached –
6. Summary and conclusion
We have shown various TEM holders developed in our group in the last 15 years. These holders can be used as accessories without changing the construction of the electron microscope. Thus, their principal design can be applied to any microscopes. In this paper, application of
This work was financially supported by KAKENHI, by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan, and by the Japan Society of the Promotion of Science (JSPS) (Nos. 13650708, 16206038, 17201029, 18560640, 19026001, 20035001, 21560681, 22240022, 24360128, 25420279, and 26630141). Part of this work was collaborated with the Semiconductor Technology Academic Research Center (STARC), as well as Prof. S. Takeda (Osaka Univ.) under the Cooperative Research Program of “Network Joint Research Center for Materials and Devices”. Support by the Nanotechnology Platform Program (Hokkaido Univ.) organized by MEXT, especially by Prof. N. Sakaguchi (Hokkaido Univ.), is grateful. We are thankful to Dr. T. Tesfamichael (Queensland Univ. Technol.) for critical reading of the manuscript. Finally, we are also grateful to our laboratory members for collaboration.
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