Cross-sectional Transmission Electron Microscopy Observations Research Articles

Effects of a thin Au Interlayer on the formation of low-resistivity CoSi 2 on (001)Si substrate

In this study we investigate the effects of a thin Au interlayer on the formation of cobalt silicide thin films on (001)Si substrate. The presence of a thin Au interlayer in the Co/Au/Co/(001)Si samples was found to decrease the temperature needed for the formation of the CoSi 2 phase by about 100–190 °C compared to that needed for Co/(001)Si samples. The effect on the formation of CoSi 2 became more pronounced as the thickness of the Au interlayer increased. These results are explained in the context of classical nucleation theory. Cross-sectional transmission electron microscopy (TEM) observations show that both the CoSi 2 surface and CoSi 2/Si interface in Co/Au/Co/(001)Si samples are much smoother than those in Co/Au/Si samples. In addition, the TEM, energy dispersion spectrometry, and secondary ion mass spectroscopy analyses of the Co/Au/Co/(001)Si samples reveal that after annealing a large amount of Au atoms have diffused from the original interface position to be dispersed in the CoSi 2 layers and at the grain boundaries.

Amorphous Ge quantum dots embedded in SiO2 formed by low energy ion implantation

Under ultrahigh vacuum conditions, extremely small Ge nanodots embedded in SiO2, i.e., Ge–SiO2 quantum dot composites, have been formed by ion implantation of Ge+74 isotope into (0001) Z-cut quartz at a low kinetic energy of 9keV using varying implantation temperatures. Transmission electron microscopy (TEM) images and micro-Raman scattering show that amorphous Ge nanodots are formed at all temperatures. The formation of amorphous Ge nanodots is different from reported crystalline Ge nanodot formation by high energy ion implantation followed by a necessary high temperature annealing process. At room temperature, a confined spatial distribution of the amorphous Ge nanodots can be obtained. Ge inward diffusion was found to be significantly enhanced by a synergetic effect of high implantation temperature and preferential sputtering of surface oxygen, which induced a much wider and deeper Ge nanodot distribution at elevated implantation temperature. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. Cross-sectional TEM observation and the depth profile of Ge atoms in SiO2 obtained from x-ray photoelectron spectra revealed a critical Ge concentration for observable amorphous nanodot formation. The mechanism of formation of amorphous Ge nanodots and the change in spatial distribution with implantation temperature are discussed.

Fabrication and characterization of BaSnO 3-doped NdBa 2Cu 3O 7−δ thin film

We fabricated a BaSnO 3-doped NdBa 2Cu 3O 7− δ film on a MgO substrate by a pulsed laser deposition method. We confirmed 00l reflections of NdBa 2Cu 3O 7− δ film in X-ray diffraction. In the cross-sectional transmission electron microscopy observation of the film, the presence of nanorods with 20 nm with average diameter is confirmed from bright-field images. We confirmed these nanorods contained tin (Sn) by EDS elemental maps. The crystal structure of the nanorod was determined to be cubic perovskite from its selected area electron diffraction pattern. Using the selected area electron diffraction patterns, the lattice constant of the nanorods in the NdBa 2Cu 3O 7− δ film was calculated to be 0.415 nm which was in good agreement with the lattice constant of BaSnO 3 of 0.412 nm.

Nanodimple Arrays Fabricated on SiO2 Surfaces by Wet Etching through Block Copolymer Thin Films

Block copolymer thin films are promising nanotemplates because highly ordered periodic structures are spontaneously formed through microphase separation on a deca-nanometer scale and over a large area. An amphiphilic block copolymer, which consists of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) with azobenzene mesogens and is denoted by PEOm-b-PMA(Az)n, indicates a strong chemical contrast between the corresponding microdomains, which offer structurally reliable nanotemplates for fabricating nanostructured materials. Thermally annealing a PEOm-b-PMA(Az)n thin film provides hexagonally arranged, perpendicularly oriented PEO cylinders, which perform as ion-conductive nanochannels. In this study, a SiO2 layer on a silicon wafer substrate is etched by NH4F through a PEO114-b-PMA(Az)54 thin film as a nanomask. The SiO2 layer is patterned with a 24-nm-periodic hexagonally arranged nanodimple array. Atomic force microscope (AFM), field emission scanning electron microscope (FESEM), and cross-sectional transmission electron microscope (TEM) observations reveal that the nanodimple array has a 2-nm depth and is spread over the entire SiO2 surface on centimeter scale.

TEM investigation of alpha alumina films deposited at low temperature

Alpha-phase aluminum oxide thin films were deposited at 480 °C by AC inverted cylindrical magnetron sputtering on nickel coated transmission electron microscopy (TEM) grids and stainless steel substrates. Several previous studies have demonstrated that an alpha phase was possible at low temperature if a chromium template layer was present. However, here we show that alpha phase is possible without the chromium oxide layer. The presence of alpha phase alumina has been confirmed by TEM. Cross-sectional TEM observations have indicated deposition rates as high as 270 nm/h. This intriguing result is attributed to the unique characteristics of the sputtering system which provides more energetic species at the substrate.

Characterization of nanorods in BaNb 2O 6-doped Er123 films revealed by cross-sectional transmission electron microscopy

Microstructures of BaNb 2O 6-doped as artificial pinning centers in Er123 films were studied by cross-sectional transmission electron microscopy. BaNb 2O 6-doped Er123 films were grown by a pulsed laser deposition technique. In the cross-sectional transmission electron microscopy observation, the presence of nanorods with 5 nm–25 nm diameter, which contain niobium, was confirmed from bright-field images and energy-dispersive X-ray spectroscopy elemental map images, respectively. The crystal structure of the nanorod was determined to be cubic perovskite from selected area electron diffraction patterns by comparing with that of the SrTiO 3 substrate. The axial length of nanorods in the Er123 film was calculated, using selected area electron diffraction patterns, as 0.841 nm, which is in good agreement with the axial length of Ba(Er 0.5Nb 0.5)O 3, 0.8427 nm, provided by X-ray diffraction data. Furthermore, parallel Moiré fringes were observed in the bright-field images, and the relationships between the lattice planes and Moiré fringes were investigated. The spacings of the Moiré fringes were 3.6 nm, and 2.3 nm, which correspond to the 006 and 200 reflections for Er123 and the 004 and 400 reflections of the nanorods, respectively. It is confirmed for the first time that BaNb 2O 6-doped into the Er123 film transforms to Ba(Er 0.5Nb 0.5)O 3 nanorods with a cubic perovskite structure.

Metal–Organic Vapor Phase Epitaxial Growth Condition Dependences of MnAs Nanocluster Formation on GaInAs (111)A Surfaces

The authors report that the formation of MnAs nanoclusters (NCs) on GaInAs (111)A surfaces strongly depends on metal–organic vapor phase epitaxial growth conditions. It was confirmed from the atomic force microscope observation that deep holes were formed on the surfaces under low V/Mn ratio and high growth temperature conditions, in addition to the formation of MnAs NCs. From the results of cross-sectional transmission electron microscope observation, these deep holes were formed on the underlying GaInAs layers, and MnAs NCs were embedded in the GaInAs (111)A layers. The formation of these embedded MnAs NCs was possibly caused by the phenomenon of “endotaxy”. From the experimental results of thermal treatments of the samples, it was revealed that the deep holes were formed on the GaInAs (111)A surfaces even after the thermal annealing in the atmosphere of Mn source gas and hydrogen. Therefore, we concluded that high AsH3 partial pressure (V/Mn ratio) conditions were required for the MnAs growth on GaInAs (111)A surfaces.

Cross-sectional transmission electron microscopy observations of structural damage in Al0.16Ga0.84N thin film under contact loading

This article reports a nanomechanical response study of the contact-induced deformation behavior in Al0.16Ga0.84N thin film by means of a combination of nanoindentation and the cross-sectional transmission electron microscopy (XTEM) techniques. Al0.16Ga0.84N thin film is deposited by using the metal-organic chemical vapor deposition method. Hardness and Young’s modulus of the Al0.16Ga0.84N films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements mode. The obtained values of the hardness and Young’s modulus are 19.76±0.15 and 310.63±9.41 GPa, respectively. The XTEM images taken in the vicinity just underneath the indenter tip revealed that the multiple “pop-ins” observed in the load-displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of the load-displacement curve suggests that no pressure-induced phase transition was involved.

Transmission Electron Microscopy Analysis of Nanorods in BaSnO3-Doped ErBa2Cu3O7-δ Films

Microstructures of BaSnO3-doped ErBa2Cu3O7-δ films were studied by transmission electron microscopy. BaSnO3-doped ErBa2Cu3O7-δ films were grown by a pulsed laser deposition method. In the cross-sectional transmission electron microscopy observation, the presence of nanorods with 10 nm average diameter was confirmed from bright-field images, and these nanorods in turn contained tin (Sn), as confirmed from the energy-dispersive X-ray spectroscopy spectra. The crystal structure of the nanorod was determined to be cubic perovskite from its selected area electron diffraction pattern. Using the selected area electron diffraction patterns, the lattice constant of the nanorods in the ErBa2Cu3O7-δ film was measured to be 0.414 nm. This was in good agreement with the lattice constant of BaSnO3, 0.412 nm. Furthermore, parallel Moiré fringes were observed in the bright-field images, and the relationships between the lattice planes and Moiré fringes were investigated. It was thus confirmed that BaSnO3 was dispersed in the ErBa2Cu3O7-δ as nanorods.

Gate Metal Interface on Hydrogen-terminated Diamond FETs

Hydrogen surface termination is widely used as a p-type doping in diamond semiconductors, but the p-type conduction mechanism is still controversial. In this study, we found an energy barrier for holes between the gate and the two-dimensional hole channel on the hydrogen-terminated diamond surface from FET characteristics. Separately we confirmed an interfacial layer between the gate metal layer and hydrogen-terminated diamond surface from cross-sectional transmission electron microscopic observation. We conclude that during metal evaporation on hydrogen-terminated diamond surface, metal atoms diffuse through point defects in the subsurface layer, and eventually the interfacial layer forms there.

Critical thickness control by deposition rate for epitaxial BaTiO3 thin films grown on SrTiO3(001)

Ba Ti O 3 ∕ Sr Ti O 3 ( 001 ) epitaxial thin films were prepared at various growth rates by pulsed laser deposition, and their heterostructures were evaluated by synchrotron x-ray diffraction measurements and cross-sectional scanning transmission electron microscopy observations. In a film grown at a low deposition rate (0.01nm∕s), misfit dislocations are found near the interface and a fully relaxed BaTiO3 thin film grows epitaxially on the substrate. On the other hand, a film grown at a high deposition rate (0.04nm∕s) consists of strained and relaxed BaTiO3 lattices. Our results showed that the critical thickness of BaTiO3∕SrTiO3(001) epitaxial thin films can be controlled by the deposition rate and that the critical thickness increases with increasing deposition rate, and by adjusting the deposition rate, we were able to prepare epitaxial thin films consisting of fully strained BaTiO3, partially strained BaTiO3, or fully relaxed BaTiO3.

Structure of Nanowires Fabricated by Electron Beam Induced Deposition to Connect Self-Assembled Quantum Structures

Nanowires for measuring the electronic transport property of a self-assembled quantum dot and a quantum ring were fabricated by electron beam induced deposition (EBID), and cross-sectional transmission electron microscopy (TEM) observations were conducted for the first time for the nanowires. TEM observations revealed that an amorphous layer existed between the substrate and the W deposit, showing a low W deposition rate at the early stage of deposition, and confirmed that the layer was an amorphous carbon layer. The layer growth mechanism was discussed using a phenomenological theory considering two different precursors and assuming one of the precursors covers the entire surface initially. It was shown that the layer manner growth happens in a wide range of parameters. From high-resolution TEM, obvious signs of irradiation damage during the deposition were not observed, and the amorphous layer thickness was about 5 nm, which should not affect much transport property measurement, indicating that EBID is quite promising for nanowire fabrication for transport measurements of a single self-assembled nanostructure.

Preparation and characterization of nanostructured ZrO 2 coatings on dense and porous substrates

Nanostructured ZrO 2 coatings are prepared on both dense and porous substrates by wet-chemical deposition of non-agglomerated 5 nm precursor particle dispersions, followed by thermal processing. The precursor particle dispersions are made by modified emulsion precipitation and a purification treatment to remove reaction products and additives. The coatings are formed by depositing the precursor nanoparticle dispersion directly onto the substrate, followed by drying and heating at 600 °C. Scanning electron microscopy and cross-sectional transmission electron microscopy observations of the heat-treated coatings indicate that the ZrO 2 coating on dense Si wafer substrate has a homogeneous, dense particle packing structure with shallow meniscus-shaped depressions in the surface, and microcracks below the meniscus surface. On the other hand, coatings formed on a meso-porous γ-alumina membrane substrate are free of defects, but with a lower packing density. The mechanism of the substrate effect on the particle packing behavior and defect formation during coating deposition is discussed. It is expected that by using a thin porous substrate with reduced capillary force, a defect-free, homogenously dense-packed coating structure can be achieved.

Aspect Ratio Dependence of the Resistivity of Fine Line Cu Interconnects

The effect of aspect-ratios of very narrow Cu interconnects of less than 100 nm on the resistivity has been discussed. From longitudinal cross-sectional transmission electron microscope (TEM) observation, many very small grains were observed at the bottom of the trench, while larger grain sizes are predominant in the upper part of the Cu interconnects. The resistivity was found to decrease significantly when increasing the aspect-ratio in fine line Cu wires due to the larger grain size distributions in the upper part of the Cu interconnects with higher aspect-ratios. This result demonstrates that the aspect-ratio of Cu wires are effective for controlling the resistivity in future Cu interconnects with very narrow and shallow dimensions.

Cross-sectional transmission electron microscopy observations on the Berkovich indentation-induced deformation microstructures in GaN thin films

Nanoindentation-induced mechanical deformation in GaN thin films prepared by metal-organic chemical-vapour deposition was investigated using the Berkovich diamond tip in combination with the cross-sectional transmission electron microscopy (XTEM). By using focused ion beam milling to accurately position the cross-section of the indented region, the XTEM results demonstrate that the major plastic deformation was taking place through the propagation of dislocations. The present observations are in support of attributing the pop-ins that appeared in the load–displacement curves to the massive dislocation activities occurring underneath the indenter during the loading cycle. The absence of indentation-induced new phases might have been due to the stress relaxation via the substrate and is also consistent with the fact that no discontinuity was found upon unloading.

Low-damage processing using size-controlled gas cluster ion beams

Gas cluster ion beam (GCIB) process has been used as a novel technique to realize very low-damage irradiations. The energy per atom of cluster ions can be reduced down to several eV/atom at several keV of total acceleration energy. In this study, size-controlled GCIB was formed using a strong permanent magnet, subsequently low-damage characteristics of large cluster ion irradiations were evaluated from the cross-sectional transmission electron microscope (TEM) observations of Si substrates. After size-controlled GCIB irradiation, the damaged or modified layer thickness was below several nm, when total acceleration energy was 5keV and Ar cluster size was larger than 5000. Result obtained from spectroscopic ellipsometry also indicated the possibility of low-damage processing by size-controlled GCIB.

In Situ Measurement of Internal Stress in Electrolessly Deposited Copper Film by Television Holographic Interferometry

With a measurement technique called television holographic interferometry, we investigated the internal stress generated at the initial deposition stage in electrolessly deposited Cu films on silicon substrates. In a region of film thickness less than 100 nm, two inflection points, at which the direction of stress was reversed, were observed on the film thickness-stress curve. From cross-sectional transmission electron microscopy observation of these films, it was found that the films grew in the Volmer-Weber mode and that the above inflection points related to specific stages observed, such as islands growth, islands coalescence, the formation of continuous film, and grain growth.

Ｃｏ２Ｃｒ０．６Ｆｅ０．４Ａｌ薄膜を用いたエピタキシャル強磁性トンネル接合の製作とトンネル磁気抵抗特性

Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier. Cross-sectional high-resolution transmission electron microscope observations clearly showed that all layers of CCFA/MgO/Co50Fe50 MTJ layer structures were grown epitaxially and were single-crystalline. The fully epitaxial CCFA/MgO/Co50Fe50 MTJs, where we used the difference in the coercive forces to form the antiparallel magnetization configurations between the lower and upper electrodes, demonstrated high tunnel magnetoresistance (TMR) ratios of 90% at room temperature (RT) and 240% at 4.2 K. This result suggested that a CCFA film composition close to the stoichiometric one is essential for obtaining high spin polarizations in CCFA thin films. The fully epitaxial CCFA/MgO/Co50Fe50 MTJs with exchange-biasing, where a Co50Fe50 upper electrode was used in a synthetic ferrimagnetic Co50Fe50/Ru/Co90Fe10 trilayer exchange-biased with an IrMn layer through the Co90Fe10/IrMn interface, exhibited high TMR ratios of 109% at RT and 317% at 4.2 K. From the obtained TMR ratio of 317% at 4.2 K, a high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. These results confirm the promise of an epitaxial MTJ using a Co-based full-Heusler alloy as a key device structure for utilizing the potentially high spin polarization of this material system.

Deposition Rate Effect on Critical Thickness of BaTiO3Epitaxial Thin Film Grown on SrTiO3(001)

AbstractBaTiO3/SrTiO3(001) epitaxial thin films were prepared at various growth rates by pulsed laser deposition, and their heterostructures were evaluated by synchrotron x-ray diffraction measurements and cross-sectional scanning transmission electron microscopy observations. In a film grown at a low deposition rate (0.01 nm/s), misfit dislocations are found near the interface and a fully relaxed BaTiO3thin film grows epitaxially on the substrate. On the other hand, a film grown at a high deposition rate (0.04 nm/s) consists of strained and relaxed BaTiO3lattices. Our results showed that the critical thickness of BaTiO3/SrTiO3(001) epitaxial thin films can be controlled by the deposition rate and that the critical thickness increases with increasing the deposition rate, and by adjusting the deposition rate we were able to prepare epitaxial thin films consisting of fully strained BaTiO3, partially strained BaTiO3or fully relaxed BaTiO3. We have also achieved the growth controlling of BaTiO3thin films on SrTiO3(001) substrates with SrRuO3bottom electrode layer.

Cross-section TEM investigation of quasicrystalline catalysts prepared by aqueous NaOH leaching

The Al–Cu–Fe quasicrystal (QC) has been shown to reveal high catalytic activity and thermal stability for steam reforming of methanol (SRM: CH3OH + H2O → 3H2 + CO2), after leaching with NaOH aqueous solution. To investigate the origin of the high catalytic performance, cross-sectional transmission electron microscopy (TEM) observations of the catalyst particles were examined. By leaching with NaOH aq., a homogeneous composite structure, composed of Cu and Fe and/or their oxides or hydroxides, is formed at the outer layer of catalyst particles and the QC phase remains in the inner area. The homogeneous dispersion of Fe and/or the oxide/hydroxide in the composite suppresses sintering of Cu particles. In contrast, for the catalyst prepared from crystalline ω-phase (Al70Cu20Fe10), the original phase completely collapses and, instead, a complicated composite structure is formed. The inhomogeneity results in the formation of Cu-enriched regions at the rim of the catalyst particles. We suggest that the high catalytic performance of the Al–Cu–Fe QC catalyst prepared by leaching with NaOH aq. is due to the formation of a homogeneous composite region at the outer layer of the catalyst particles.