C. Barry Carter

The Transmission Electron Microscope

A typical commercial transmission electron microscope (TEM) costs about

Crystallography of YBa 2 Cu 3 O 6+ x thin film-substrate interfaces

5 for each electron volt (eV) of energy in the beam and, if you add on all available options, it can easily cost up to

Mechanisms of surface faceting and coarsening

10 per eV. As you’ll see, we use beam energies in the range from 100,000 to 400,000 eV, so a TEMis an extremely expensive piece of equipment. Consequently, there have to be very sound scientific reasons for investing such a large amount of money in onemicroscope. In this chapter (which is just a brief overview of many of the concepts that we’ll talk about in detail throughout the book) we start by introducing you to some of the historical development of the TEM because the history is intertwined with some of the reasons why you need to use a TEM to characterize materials. Other reasons for using a TEM have appeared as the instrument continues to develop, to the point where it can seriously be claimed that no other scientific instrument exists which can offer such a broad range of characterization techniques with such high spatial and analytical resolution, coupled with a completely quantitative understanding of the various techniques.

Observation of the early stages of growth of superconducting thin films by transmission electron microscopy

The epitactic nature of the growth of YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} (YBCO) superconducting thin films on ceramic substrates has been studied using high-resolution electron microscopy (HREM) and selected-area diffraction (SAD) of cross-sectional specimens. The films were grown {ital in} {ital situ} on (001)-oriented MgO and (001)-oriented Y{sub 2}O{sub 3}-stabilized cubic ZrO{sub 2} (YSZ) single-crystal substrates by electron beam evaporation. Both of these materials have large lattice misfits with respect to YBCO. Different orientation relationships were observed for films grown on the two types of substrates. These orientation relationships are shown to provide the best matching of the oxygen sublattices across the substrate-film interfaces. A crystalline intermediate layer, 6 nm thick, between the YBCO film and YSZ substrate was observed by HREM and shown by EDS to be a Ba-enriched phase, possibly barium zirconate formed by a reaction. In contrast, the YBCO--MgO interface was found to be sharp and free of any intermediate layers.

Surface preparation for the heteroepitactic growth of ceramic thin films

Abstract The progression of surface faceting on ceramic substrates is explored using the {1010} and (0001) surfaces of Al2O3 (α-Al2O3, corundum structure) as model systems. Atomic-force microscopy and electron microscopy techniques are used to monitor the progression of faceting as a function of annealing time. Whether the surface facets into a hill-and-valley structure, such as the {1010} surface, or into a terrace-and-step structure, such as the (0001) surface, faceting starts with the nucleation and growth of individual facets. The growth of individual facets is found to promote the nucleation of adjacent facets, and thus leads to the formation of facet domains. As domains that are out of phase with each other coalesce regions with a high density of facet junctions are formed. Facet junctions, points where two facets merge to form one, are found to have an important role in facet coarsening. The mechanism for the coarsening of the completely faceted surface involves the motion and elimination of facet junctions. Both the facet wavelength and density of facet junctions are monitored as a function of annealing time for the {1010} and (0001) Al2O3 surfaces.

Oriented aluminum nitride thin films deposited by pulsed‐laser ablation

A method for the direct observation of the early stages of growth of superconducting films by transmission electron microscopy (TEM) is reported. The technique uses well‐characterized, single‐crystal TEM foils as substrates for the deposition process. Ultrathin films of YBa2Cu3O6+x (YBCO) were prepared by pulsed laser deposition from stoichiometric bulk samples directly onto (001) oriented MgO thin‐foil substrates. Observation of the film by TEM is possible without any post‐deposition specimen preparation. The epitactic nature of the film growth is shown by analysis of the moire fringe pattern and by selected area diffraction. In addition to an interconnected film, copper oxide particles and stoichiometric ablated clusters were observed.

The nucleation and heteroepitactic growth of YBa2Cu3O7 − δ thin films on MgO

The morphology, composition, and crystallographic orientation of the substrate influence the nucleation and growth of deposited thin films. A method for the preparation of controlled, characteristic surfaces is reported. The surfaces are suitable for the heteroepitactic growth of thin films. When used in the formation of electron‐transparent thin foils, the substrates can be used to investigate the very early stages of film growth using transmission electron microscopy. The substrate preparation involves the cleaning and subsequent annealing to generate a surface consisting of a series of steps. The step terraces are formed on the energetically stable surface, and controlled nucleation and growth of films at step edges is found. The substrate materials prepared using this technique include (001) MgO, (001) SrTiO3, and (001) LaAlO3.

Plasma synthesis of single-crystal silicon nanoparticles for novel electronic device applications

Single‐phase aluminum nitride thin films with preferred crystallographic orientations have been grown on single‐crystal sapphire by pulsed‐laser ablation. The orientation of the films was found to be determined by the atmosphere and the nitrogen pressure during deposition and the substrate temperature. The films were examined by x‐ray diffraction, and scanning electron microscopy.

On the faceting of ceramic surfaces

Abstract The nucleation and growth of YBa 2 Cu 3 O 7 − δ films on single-crystal (001)-oriented MgO have been studied using transmission electron microscopy (TEM). The films were formed by pulsed-laser ablation from a stoichiometric bulk sample. Observations of the early stages of film growth were made by utilizing a new specimen-preparation technique in which the films were deposited directly onto specially prepared electron-transparent substrates. The films were found to grow by an island mechanism with the nucleated islands growing to form an interconnecting film. A number of these islands are rotationally misaligned resulting in the formation of a polycrystalline, mosaic structure. The grains were predominantly oriented with their c -axis perpendicular to the film-substrate interface, although a smaller fraction of the film contained grains oriented with their c -axis in the film-substrate plane. These grains were found to grow in orthogonal directions along the [001] and [010] crystal axes of the MgO. The highly anisotropic growth of YBa 2 Cu 3 O 7 − δ , fastest along the a − b plane, is an important factor in determining the microstructure of the film.

Synthesis of highly oriented, single-crystal silicon nanoparticles in a low-pressure, inductively coupled plasma

Single-crystal nanoparticles of silicon, several tens of nanometres in diameter, may be suitable as building blocks for single-nanoparticle electronic devices. Previous studies of nanoparticles produced in low-pressure plasmas have demonstrated the synthesis of nanocrystals 2–10 nm diameter but larger particles were amorphous or polycrystalline. This work reports the use of a constricted, filamentary capacitively coupled low-pressure plasma to produce single-crystal silicon nanoparticles with diameters between 20 and 80 nm. Particles are highly oriented with predominantly cubic shape. The particle size distribution is rather monodisperse. Electron microscopy studies confirm that the nanoparticles are highly oriented diamond-cubic silicon.