High-resolution transmission electron microscopy of heteroepitaxial barium strontium titanate films grown on MgO substrates

Nanoscale (5–100 nm) ferroelectric heteroepitaxial Ba_0.8Sr_0.2TiO₃ films on MgO(001) substrates were studied by methods of high-resolution transmission electron microscopy using Tecnai G² and FEI Titan 80–300 microscopes. Misfit dislocations resulting from stress relaxation in films and insignificant local misorientation of film regions (block structure) were detected. The heterostructure was numerically simulated, which allowed the detection of the formation of oxygen (substrate)-titanium (film) bonds or the oxygen (substrate)-barium (film) bond at the film-substrate interface.     

Transmission electron microscopy for the semi-conductor industry

During the last 5 years, semi-conductor industry has dramatically enhanced the device performance by continuously introducing new technologies and aggressively scaling down the feature sizes. During the progress, transmission electron microscopy (TEM) has played a very important role in the process development, manufacture controlling, and failure analysis. On the other hand, the development of TEM techniques for the semi-conductor devices, especially the sample preparation technique, has changed the entire aspect of the TEM. TEM is no longer a name heard only in research institutes and universities. It becomes so important for semi-conductor industry that TEM are treated as the most reliable resource for process evaluation and failure analysis and that TEM images are often used as one of the most powerful evidence for the patent infringement trial. In this paper, the author reviews the great challenges that electron microscopist has been facing from the semi-conductor industry and presents TEM results that illustrate the utilization of various TEM techniques to meet the challenges. To emphasize the unique ability of TEM, application of the precision TEM technique is mentioned in detail. A new three-dimensional TEM technique is also discussed.     

Low-density dislocation arrays at heteroepitaxial Ge/GaAs-interfaces investigated by high voltage electron microscopy

High-voltage electron microscopy in combination with a large-area thinning technique has been applied to thin epitaxial Ge layers on GaAs substrates. These layers exhibit 60° misfit dislocations along the 〈110〉 directions parallel to the interface. Various dislocation reactions are evaluated from the electron micrographs, e.g. the formation of non-glissile 90° dislocations from two nearly parallel 60° dislocations and the annihilation reaction of two crossing 60° dislocations with identical Burgers vectors. The latter reaction occasionally leads to a dislocation multiplication. The misfit dislocations in very thin layers (～0.5 μm thickness and a linear dislocation density of less than 100 dislocation lines/cm) tend to be arranged in groups rather than being equidistant. Consequences for the interpretation of x-ray topograms are discussed.     

Transmission electron microscopy of fine aromatic hydrocarbon particles

Fine perylene and pyrene particles were produced by evaporation in helium gas. The particles were sensitive to electron beam radiation. The pyrene particles sublimed under observation. These difficulties were cleared up by reducing electron beam exposure and sandwiching a specimen between two Formvar films. The fine perylene particles were rectangular or hexagonal plates about 50nm thick. The size was about 200-2000nm. The fine pyrene particles were polymorphic with a size of about 300-2000nm. The crystal forms of the perylene and pyrene particles were determined from the electron diffraction patterns to be alpha-perylene and pyrene I, respectively.     

Multicrystal X-ray diffraction of heteroepitaxial structures

An appraisal of high-resolution multi-crystal multi-reflection diffractometry (HRMCMRD) and topography is presented to illustrate its potential for structure analysis. Examples of methods for extracting lateral interface roughness, studying layered structures with imperfect epitaxy (including strained layer structures) are given to show the wealth of information available from X-ray techniques. The advantages of diffraction space mapping are discussed in addition to the use of topography to interpret the diffuse and Bragg scattering. The HRMCMRD has a dynamic range of 10⁶ and can record topographs with intensities less than 1 count/s.     

Transmission electron microscopy studies of HfO2 thin films grown by chloride-based atomic layer deposition

Detailed transmission electron microscopy characterization of HfO₂ films deposited on Si(1 0 0) using atomic layer deposition has been carried out. The influence of deposition temperature has been investigated. At 226 °C, a predominantly quasi-amorphous film containing large grains of cubic HfO₂ (a₀ = 5.08 Å) was formed. Grain morphology enabled the nucleation sites to be determined. Hot stage microscopy showed that both the cubic phase and the quasi-amorphous phase were very resistant to thermal modification up to 500 °C. These observations suggest that nucleation sites for the growth of the crystalline cubic phase form at the growing surface of the film, rather homogeneously within the film. The films grown at higher temperatures (300-750 °C) are crystalline and monoclinic. The principal effects of deposition temperature were on: grain size, which coarsens at the highest temperature; roughness with increases at the higher temperatures due to the prismatic faceting, and texture, with texturing being strongest at intermediate temperatures. Detailed interfacial characterization shows that interfacial layers of SiO₂ form at low and high temperatures. However, at intermediate temperatures, interfaces devoid of SiO₂ were formed.     

电子显微学进展及其在材料科学中的应用

文章简要介绍了高分辨电子显微学方法和电子能量损失谱的进展.文中特别指出,随着电子显微技术的发展,原子分辨电子显微图像对结构问题的深入研究有重要作用.装备有能量单色器的新一代电子显微镜,可以直接给出高能量分辨率的电子能量损失谱(优于 0.1eV).这些先进技术方法的应用,推动了晶体结构学、材料科学、物理学、纳米科学及生命科学的发展,也为解决很多重要结构问题奠定了基础.文章重点讨论了几个典型功能材料体系的结构问题:利用大角度会聚束电子衍射技术,分析了应变硅器件中的应变分布;利用原位电子显微技术,研究了新型电子铁电体LuFe2O4电荷序和物理性能的关系;深入探讨了强关联体系中电子关联效应对电子能量损失谱和电子结构的影响.     

电子显微学进展及其在材料科学中的应用

文章简要介绍了高分辨电子显微学方法和电子能量损失谱的进展.文中特别指出,随着电子显微技术的发展,原子分辨电子显微图像对结构问题的深入研究有重要作用.装备有能量单色器的新一代电子显微镜,可以直接给出高能量分辨率的电子能量损失谱(优于 0.1eV).这些先进技术方法的应用,推动了晶体结构学、材料科学、物理学、纳米科学及生命科学的发展,也为解决很多重要结构问题奠定了基础.文章重点讨论了几个典型功能材料体系的结构问题：利用大角度会聚束电子衍射技术,分析了应变硅器件中的应变分布;利用原位电子显微技术,研究了新型电子铁电体LuFe2O4电荷序和物理性能的关系;深入探讨了强关联体系中电子关联效应对电子能量损失谱和电子结构的影响.     

Excitons in heteroepitaxial CdSe/CdS structures

X-ray diffractometry and low-temperature exciton spectroscopy are used to study heteroepitaxial CdSe/CdS layers grown at temperatures of 350–485 °C by MOCVD. The high-temperature samples are found to display the exciton and x-ray diffraction spectra characteristic of hexagonal Wurtzite (W) structures, while the low-temperature samples display the features characteristic of the cubic structure of sphalerite (ZB). A number of the samples have x-ray spectra characteristic of structures with stacking faults (SF), which represent a separate crystalline phase in the structures studied here. It is found that the individual crystalline phases are spatially separated. Fiz. Tverd. Tela (St. Petersburg) 40, 887–889 (May 1998)     

Transmission electron microscopy imaging of individual functional groups of fullerene derivatives

Mobility and reactivity of the functionalized fullerenes with pyrrolidine (C60-C3NH7) incorporated in single-wall carbon nanotubes were examined by high-resolution transmission electron microscopy. An individual functional group attached to each fullerene cage is unambiguously visualized. This provides a direct evidence for the functionalized structure on a single-molecular basis. A rotational motion of the incorporated molecules tends to occur during the observation and, consequently, each fullerene molecule is likely to stand facing its functionalized group towards the nanotube wall. A fine structure analysis of electron energy-loss spectra for the nitrogen K(1s) edge shows a considerable change in the nitrogen chemical state and suggests a strong tube-fullerene interaction.     

Transmission electron microscopy studies of femtosecond laser induced modifications in quartz

Cross-sectional transmission electron microscopy investigations of femtosecond laser induced sub-micrometer structural modifications inside crystalline quartz were carried out. Modifications from single laser shots and from lines built of overlapping shots were imaged. Both single laser shot modifications and line structures show an amorphous core surrounded by a disturbed crystalline structure. A strong strain field surrounding the central, irradiated, core is responsible for an increase of the refractive index. Finite element method calculations of the strain field show maxima on both sides of the irradiated core, which are in good agreement with optical measurements of the refractive-index change. Received: 29 September 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +49-3641/947792, E-mail: tatiana.gorelik@rz.uni-jena.de     

Transmission electron microscopy of thiol-capped Au clusters on C: Structure and electron irradiation effects

High-resolution transmission electron microscopy is used to study interactions between thiol-capped Au clusters and amorphous C support films. The morphologies of the clusters are found to depend both on their size and on the local structure of the underlying C. When the C is amorphous, larger Au clusters are crystalline, while smaller clusters are typically disordered. When the C is graphitic, the Au particles adopt either elongated shapes that maximize their contact with the edge of the C film or planar arrays when they contain few Au atoms. We demonstrate the influence of electron beam irradiation on the structure, shape and stability of the Au clusters, as well as on the formation of holes bounded by terraces of graphitic lamellae in the underlying C.     

Transmission electron microscopy of GaN columnar nanostructures grown by molecular beam epitaxy

The GaN columnar crystals of nanometric sizes have been grown by molecular beam epitaxy with high-frequency plasma initiation of nitrogen discharge. The types and distribution of defects in these nanostructures on the (0001) sapphire substrates are studied by transmission electron microscopy (TEM). It is revealed that inversion domains begin to form almost at the interface irrespective of the presence of an initial low-temperature buffer layer. The critical diameter of dislocation-free columns, their density, and mean sizes are determined. It is shown that the low-temperature buffer layer affects the density of dislocations, their spatial distribution, and the mean sizes of columns. The nanosizes of grown crystals suggest a further use of these crystals and the growth method for producing molecular-beam epitaxial quantum-size objects (quantum dots and wires) in a promising AlGaInN system.     

Transmission electron microscopy investigation of an ordered metastable phase in Zr-N alloys

Supersaturated hcp f-Zr(N) alloys containing 22-28 at.% N were prepared by nitriding sheets of Zr in an atmosphere of high-purity N 2 , followed by homogenization under high-purity Ar gas. Quenching and isothermal ageing of the alloys for various times between 500 and 650C resulted in precipitation of a metastable phase, rather than the equilibrium phase ZrN. This investigation focused on determining the structure, orientation relationship, habit plane, morphology, growth kinetics and atomic growth mechanism of this non-equilibrium precipitate using transmission electron microscopy imaging and diffraction techniques, high-resolution transmission electron microscopy, electron-energy-loss spectroscopy and various simulation programs. The precipitate, which was arbitrarily designated the ξ phase, has a monoclinic Bravais lattice. Its lattice parameters are a = 0.32 nm, b = 0.60 nm, c = 0.56 nm, f= g= 90 and n= 121.5. Its orientation relationship with the fmatrix is $$ (0001)_\alpha /\mskip-2/ (020)_\xi\quad \a\n\d\quad [01\bar 10] _\alpha /\mskip-2/ [001]_\xi, $$ and the average habit plane of lenticularly shaped precipitates is $(01\bar 12)_\alpha$ . Determination of the structure and other aspects of the phase transformation are discussed.     

Magnetic stray fields of patterned permalloy structures investigated by photoemission electron microscopy

Using a photoemission electron microscope we determined magnetic stray fields at the edges of permalloy (Ni₈₀Fe₂₀) particles. X-ray magnetic dichroism was used for visualization of magnetic domains. The values of the stray fields were deduced from the deflection of electrons in the image due to the Lorentz force. The stray fields are responsible for the magnetic interaction of adjacent particles with distances much larger than the thickness. The measured magnetic stray field is about 0.023 T for rectangular particles with a thickness of 30 nm and lateral sizes of tens of microns. PACS 68.37.Xy; 75.40.Cx; 75.75.+a     

Transmission and scanning electron microscopy studies of single femtosecond- laser-pulse ablation of silicon

The final state of the material resulting from laser irradiation of silicon using 130 fs pulses at 790 nm was studied using a number of techniques including scanning and transmission electron microscopies, as well as atomic force microscopy. Structural details and the level of damage to the nearby solid following irradiation were characterized and are discussed in the context of recent dynamical studies. Received: 28 September 2001 / Accepted: 3 March 2002 / Published online: 19 July 2002 RID="*" ID="*"Department of Engineering Physics, McMaster University, Hamilton, Ontario, L8S 4M1, Canada RID="**" ID="**"Corresponding author. Fax: +1-905/521-2773, E-mail: borowia@mcmaster.ca RID="***" ID="***"Present address: Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK RID="****" ID="****"Department of Materials Science and the CEMD, McMaster University, Hamilton, Ontario, L8S 4M1, Canada RID="*****" ID="*****"Departments of Engineering Physics, and Physics and Astronomy, and the CEMD, McMaster University, Hamilton, Ontario, L8S 4M1, Canada     

Transmission electron microscopy observations of CNT morphology before and after heating in vacuum

Heating of multi-walled carbon nanotubes is often required to obtain clean patterns in the field electron emission microscope (FEEM). A transmission electron micrograph study of morphological changes in the cap structure of multi-walled carbon nanotubes due to heating in vacuum is presented. The lack of significant structural change in the cap structure when specimens were heated to 1925 K for 2.5 h determines an upper bound for the diffusivity of multi-walled carbon nanotube surface atoms, of the order of 10⁻¹⁶ cm²/s at 1925 K.     

Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy

The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.