Ulrich Dahmen

Lawrence Berkeley National Laboratory | LBL · Materials Sciences Division

In-situ transmission electron microscopy (TEM) observations reveal a permanent chaotic motion of nanosized liquid Pb inclusions embedded in thin aluminum foils. Individual trajectories of the inclusions were analysed to determine the character of their motion. The inclusions moving freely inside a crystal display motion with three-dimensional rando...

To understand the effects of lattice mismatch on heteroepitaxial growth, we have studied the equilibrium structure and orientation relationships (ORs) of FCC films grown epitaxially on FCC substrates, using molecular dynamics simulations in conjunction with embedded atom method potentials. Three film/substrate systems have been investigated, namely...

To understand the effects of lattice mismatch on heteroepitaxial growth, we have studied the equilibrium structure and orientation relationships (ORs) of FCC films grown epitaxially on FCC substrates, using molecular dynamics simulations in conjunction with embedded atom method potentials. Three film/substrate systems have been investigated, namely...

A systematic variation in the orientation relationship (OR) of Ag films grown on Ni substrates previously discovered by a combinatorial approach is analyzed using concepts of grain boundaries, surface science and phase transformations. On roughly half of all Ni substrate orientations, Ag adopts a “special” OR that varies systematically from a twin...

A key to the unique combination of electronic and optical properties in halide perovskite materials lies in their rich structural complexity. However, their radiation sensitive nature limits nanoscale structural characterization requiring dose efficient microscopic techniques in order to determine their structures precisely. In this work, we determ...

We have made direct observations of the Brownian motion of individual nanosized liquid lead inclusions in solid aluminum by in-situ transmission electron microscopy. The process was found to depend strongly on the size of the inclusion and the anisotropy of the interfacial energy. The rate controlling mechanism was the nucleation of steps on facets...

Exploring the structural and electronic properties of nanowires at their mechanical limits - Volume 23 Issue S1 - B. Ozdol, C. Gammer, L. J. Zeng, S. Bhowmick, T. K. Nordqvist, P. Krogstrup, A.M. Minor, U. Dahmen, E. Olsson, W. Jaeger

Unraveling the Crystal Structure of All-Inorganic Halide Perovskites using CBED and Electron Ptychography - Volume 23 Issue S1 - Roberto dos Reis, Hao Yang, Colin Ophus, Tetiana Shalapska, Gregory Bizarri, Didier Perrodin, Peter Ercius, Jim Ciston, Edith Bourret, Ulrich Dahmen

div class="title">Probing Stress-Induced Grain Boundary Migration and Hypofriction at High Resolution - Volume 22 Issue S3 - M.L. Bowers, C. Ophus, A.M. Minor, U. Dahmen

div class="title">Revealing Point Defects in a Large-Scale Scanning Diffraction Dataset - Volume 22 Issue S3 - R. dos Reis, C. Ophus, J. Ciston, P. Ercius, U. Dahmen

div class="title">High Resolution Electron Microscopy of Grain Boundary Motion During Island Grain Shrinkage - Volume 22 Issue S3 - U. Dahmen, T. Radetic, M.L. Bowers, C. Ophus, A. Gautam, F. Lançon

Nanostructured niobium oxides and hydroxides are potential candidates for photochemical applications due to their excellent optical and electronic properties. In the present work the thermal stability of Nb3O7(OH) superstructures prepared by a simple hydrothermal approach is investigated at the atomic scale. Transmission electron microscopy and ele...

Using extended time series scanning transmission electron microscopy, we investigate structural fluctuations at an incommensurate grain boundary in Au. Atomic-resolution imaging reveals the coalescence of two interfacial steps, or disconnections, of different height via coordinated motion of atoms along close-packed directions. Numerical simulation...

div class="title">Collective Atomic Motion at a 90° <110> Tilt Grain Boundary in Gold - Volume 21 Issue S3 - M.L. Bowers, A. Gautam, C. Ophus, F. Lancon, U. Dahmen

div class="title">Towards Identification of Oxygen Point Defects by Means of Position Averaged CBED - Volume 21 Issue S3 - R. dos Reis, C. Ophus, J. Ciston, P. Ercius, U. Dahmen

A hierarchical microstructure is obtained in an alloy with composition Fe–8.1Al–12.2Cr–1.9Mo–18.2Ni–2.0Ti (wt.%) processed by melt-spinning. The evolution of the precipitation pathways is investigated using transmission electron microscopy (TEM) techniques, atom probe tomography (APT) and first-principles thermodynamic calculations. As-solidified r...

To analyze extended time series of high resolution images, we have employed automated frame-by-frame comparisons that are able to detect dynamic changes in the structure of a grain boundary in Au. Using cumulative averaging of images between events allowed high resolution measurements of the atomic relaxation in the interface with sufficient accura...

The recently discovered compound BeP2N4 that crystallizes in the phenakite-type structure has potential application as a high strength optoelectronic material. Therefore, it is important to analyze experimentally the electronic structure, which was done in the present work by monochromated electron energy-loss spectroscopy. The detection of Be is c...

Using transmission electron microscopy, we have analyzed the structure of nanoporous NiO formed by thermal decomposition of Ni(OH)2. It was found that a tabular single crystal of Ni(OH)2 transforms pseudomorphically to an array of topotaxially aligned NiO nanocubes separated by nanoscale pores at a volume fraction of about 50%. High-resolution elec...

The structure of an incommensurate 90°〈1 1 0〉 tilt grain boundary in gold was characterized by atomic resolution aberration-corrected electron microscopy and compared with atomistic simulations. Based on a periodic hyperspace description, the non-periodic structure can be described by the Aubry hull function, which plots atomic relaxations at the c...

of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Une meilleure compréhension de la précipitation de Ge dans Al a été obtenue par une utilisation systématique de la microscopie en haute résolution. La formation des aiguilles maclées qu'on observe le long de <100>Al et <110>Alpeut être reliée à l'existence de quelques configurations atomiques particulières. On montre aussi que le maclage sert à réd...

The structure of a ß′-SiAlON (Si5.6Al0.4O0.4N7.6) has been observed using three generations of unique high resolution microscopes spanning over three decades of development in instrumentation – the Atomic Resolution Microscope (ARM), the One Angstrom Microscope (OAM) and the Transmission Electron Aberration-corrected Microscope (TEAM). The informat...

The exceptional strength and distinct deformation physics exhibited by pure ultrafine-grained and nanocrystalline metals in comparison to their microcrystalline counterparts have been ascribed to the dominant influence of grain boundaries in accommodating plastic flow. Such grain-boundary-mediated mechanisms can be augmented by additional strengthe...

This study demonstrates a processing sequence used to generate coherent, two-phase L2 1 -Ni2TiAl/B2-NiAl precipitates in a ferritic matrix, and documents their microstructural evolution. Dark-field and energy-filtered transmission electron microscopy in combination with energy-dispersive X-ray analysis are used to determine the structure and compos...

As electron microscopists, many of us become engrossed in observing the shape, size, and atomic structure of nanoparticles every day. With our focus on the atoms in a single quantum dot, it is easy to lose sight of the broader physical perspective. This short essay highlights some wider connections as a way of linking electron microscopy to the que...

This work investigates the mechanism and dynamics of grain boundary migration driven by capillary forces via in situ electron microscopy, complemented by molecular-dynamics simulations. Using thin films of Au with the mazed bicrystal geometry, the shrinkage of island grains with 90°〈1 1 0〉 tilt grain boundaries was observed by diffraction contrast...

Existing methods to rapidly compute interface- energy minimizing shapes with anisotropy are collected and clarified, and new methods are introduced. A description of freely available, platform-independent software for the computation and display of equilibrium geometries is provided. The software relies on a new computational method to rapidly find...

Many researchers are currently fabricating, characterizing and testing nanoparticles for many different applications due to the extremely large parameter space available in particle structure, size, chemistry and shape [1]. The strain state of a nanoparticle can affect photoluminescent [2], electromagnetic [3] and catalytic [4] material properties....

Off-axis electron holography is a powerful phase retrieval method: it can access the phase shift of the electron wave on large area structures and atomically fine details from a single electron micrograph [1]. Just recently, the TEAM I microscope in Berkeley's National Center for Electron Microscopy has been equipped with a biprism for holographic...

TEAM I is the final product of the Transmission Electron Aberration-corrected Microscope (TEAM) Project, a collaborative project funded by the Department of Energy with the goal of designing and building a platform for a next generation aberration-corrected electron microscope capable of image resolution of up to 50 pm. The TEAM instrument incorpor...

of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Transmission electron microscopy is a powerful imaging tool that has found broad application in materials science, nanoscience and biology. With the introduction of aberration-corrected electron lenses, both the spatial resolution and the image quality in transmission electron microscopy have been significantly improved and resolution below 0.5 ång...

Capillarity-driven grain boundary (GB) motion in Al tricrystalline thin films has been investigated by in situ transmission electron microscopy at intermediate temperatures. The GBs were observed to move erratically, with alternating periods of motion and stagnation, followed by rapid shrinkage of the grain and eventual annihilation accompanied by...

Transmission electron microscopy (TEM) is a powerful imaging tool that has found broad application in materials science, nanoscience and biology(1-3). With the introduction of aberration-corrected electron lenses, both the spatial resolution and image quality in TEM have been significantly improved(4,5) and resolution below 0.5 {\AA} has been demon...

This article describes a novel software tool, the KSpaceNavigator, which combines sample stage and crystallographic coordinates in a control sphere. It also provides simulated kinematic diffraction spot patterns, Kikuchi line patterns and a unit cell view in real time, thus allowing intuitive and transparent navigation in reciprocal space. By the o...

The size distribution of particles, which is essential for many properties of nanomaterials, is equally important for the mechanical behaviour of the class of alloys whose strength derives from a dispersion of nanoscale precipitates. However, particle size distributions formed by solid-state precipitation are generally not well controlled. Here we...

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

We have investigated the retraction of a single-crystalline Ge wedge in epitaxial contact with a bicrystalline Au film using in situ electron microscopy. The rate of retraction was close to that predicted for capillarity-driven surface diffusion, following kinetics proportional to tn, with n=0.22–0.35, but crystal anisotropy caused migration to be...

Crystalline systems often lower their energy by atom displacements from regular high-symmetry lattice sites. We demonstrate that such symmetry lowering distortions can be visualized by ultrahigh resolution transmission electron microscopy even at single point defects. Experimental investigation of structural distortions at the monovacancy defects i...

We have used two aging treatments of Al-Li-Sc alloys to create highly monodisperse, coherent L12 structure core-shell precipitates. We perform detailed analyses of the compositional distributions in the precipitate structures with electron microscopy and atom probe tomography. By combining this information with first principles calculations and Mon...

In the study of interfaces, high resolution electron microscopy (HREM) is most useful when the interface is viewed edge-on while both crystals are accurately aligned along low index zone axes. The formation of such interfaces by epitaxy or topotaxy is the natural means of obtaining structures than can be usefully analyzed by HREM. Furthermore, ther...

Noble gases are generally very insoluble in solids. For example, Xe implanted into Al at 300 K forms a fine dispersion of crystalline precipitates and, at large enough fluence, fluid precipitates, both of which are stabilized, relative to the gas phase, by the Laplace pressure due to precipitate/matrix interface tensions. High resolution electron m...

Despite numerous theoretical and experimental studies of strain relaxation in metal films on silicon substrates, the exact mechanisms by which dislocations mediate plasticity in these structures are not well understood. To elucidate these mechanisms, we present results from in-situ transmission electron microscopy annealing of thin aluminum films g...

The crystal structure of the Al2CuMg S-phase precipitate in an Al matrix has been determined by quantitative high resolution electron microscopy. This work combines techniques of image processing and quantitative comparison between experimental and simulated images with automatic refinement of imaging and structural parameters.

Epitaxial films of the fcc metals Al, Au, Ag and Ni were grown by physical vapor deposition on Si and Ge (111), (110) and (100) substrates at different deposition temperatures. The epitaxial relationships and morphological features of these films were characterized by transmission electron microscopy and diffraction in plan view and cross section....

It is shown that indentation-induced formation of hexagonal silicon at the temperature range 400–700°C is fully consistent with its occurence via a martensitic transformation. After presenting HREM images of hexagonal ribbons in a diamond cubic matrix, a crystallographic analysis of the phase transformation is given, and a dislocation mechanism res...

An experimental high resolution image of a grain boundary has been compared with images simulated from atomic structures calculated by two theoretical methods. Some of the techniques used in the analysis of the images are presented. A good agreement is found between each theory and the experiment, confirming the validity of calculations of such a b...

The structure and morphology of 30° <100> tilt grain boundaries in tricrystal films of Al have been investigated by conventional and high resolution electron microscopy. By inducing heteroepitaxial growth on single crystal (111) Si substrates, Al formed polycrystalline thin films made of grains in three symmetry-related (100) orientations. The grai...

The growth of Al on (111) Si single crystal substrates by various techniques usually leads to films with (111) texture, sometimes with a small (100) component. Using X-ray diffraction and electron microscopy, the present study shows that the (100) texture component can be enhanced to the point of forming an oriented (100) continuous tricrystal stru...

The evolution of elastic strain caused by melting and solidification of small inclusions in aluminum was investigated by in-situ transmission electron microscopy. The appearance and subsequent decay of elastic strain during phase transformation of inclusions around 100nm in size were observed directly, and the decay rate was determined as a functio...

Physical Sciences SymposiaCorrelation between Atomic Structure and Superglide of an Incommensurate Grain Boundary in AuArticle author querydahmen u [PubMed] [Google Scholar]radetic t [PubMed] [Google Scholar]ye j [PubMed] [Google Scholar]minor a [PubMed] [Google Scholar]caliste d [PubMed] [Google Scholar]lancon f [PubMed] [Google Scholar]U Da...

of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

The intriguing possibility of frictionless gliding of one solid surface on another has been predicted for certain incommensurate interfaces in crystals, based on Aubry's solution to the Frenkel-Kontorova model of a harmonic chain in a periodic potential field. Here we test this prediction for grain boundaries by comparing atomistic simulations with...

The strong interaction of electrons with small volumes of matter make them an ideal probe for nanomaterials, but our ability to fully use this signal in electron microscopes remains limited by lens aberrations. To bring this unique advantage to bear on materials research requires a sample space for electron scattering experiments in a tunable elect...

We investigate the bulk and surface features of the crystalline–amorphous transitions in binary Al–Mo alloy thin films as a function of Mo composition using transmission electron microscopy, X-ray diffraction and atomic force microscopy analysis, as well as thermodynamic modeling. Of the alloys tested, the minimum in the root mean square (rms) surf...

Using an aberration-corrected transmission electron microscope, we report on imaging individual atomic columns of Li in the intermetallic compound Al3Li. The effect of electron energy on the imaging characteristic of Li is investigated by performing measurements at 80 kV employing a monochromated electron beam with an energy spread ΔE of 0.2 eV and...

of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Understanding of colloidal nanocrystal growth mechanisms is essential for the syntheses of nanocrystals with desired physical properties. The classical model for the growth of monodisperse nanocrystals assumes a discrete nucleation stage followed by growth via monomer attachment, but has overlooked particle-particle interactions. Recent studies hav...

We have directly observed motion of inorganic nanoparticles during fluid evaporation using a transmission electron microscope. Tracking real-time diffusion of both spherical (5-15 nm) and rod-shaped (5 x 10 nm) gold nanocrystals in a thin film of water-15% glycerol reveals complex movements, such as rolling motions coupled to large-step movements a...

The partial transformation of ionic nanocrystals through cation exchange has been used to synthesize nanocrystal heterostructures. We demonstrate that the selectivity for cation exchange to take place at different facets of the nanocrystal plays an important role in determining the resulting morphology of the binary heterostructure. In the case of...

Using a highly coherent focused electron probe in a fifth-order aberration-corrected transmission electron microscope, we report on resolving a crystal spacing less than 50 pm. Based on the geometrical source size and residual coherent and incoherent axial lens aberrations, an electron probe is calculated, which is theoretically capable of resolvin...

We have combined high-angle annular dark field/scanning transmission electron microscopy (HAADF-STEM) tomography with bright field (BF)-TEM tomography to characterize small inclusions of Pb at a grain boundary in Al. It was found that the shape of the grain boundary inclusions is more complex than previously thought. By using moiré fringes observed...

The ability of electron microscopes to analyze all the atoms in individual nanostructures is limited by lens aberrations. However, recent advances in aberration-correcting electron optics have led to greatly enhanced instrument performance and new techniques of electron microscopy. The development of an ultrastable electron microscope with aberrati...

The performance of a transmission electron microscope is determined by the optical performance of the lenses, the stability of the column and last but not least by the performance of the electron source.

of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

This study details the resonance properties of 20 nm thick nanoelectromechanical system scale cantilevers fabricated from a metallic Al –32 at. % Mo nanocomposite. The advantage of the Al –32 at. % Mo alloy is that its strength and near-atomic surface smoothness enable fabrication of single-anchored metallic cantilevers with extreme length-to-thick...

We demonstrate a way of producing monodisperse Al3(LiScZr) core/shell inclusions using solid-state reactions. A uniform distribution of particles with a Li- and Sc-rich core surrounded by Li-rich shell a few nanometers thick with Zr segregating at the core/shell interface can be made reproducibly by exploiting kinetic and thermodynamic parameters....

Metallic structural components for micro-electro-mechanical/nano-electro-mechanical systems (MEMS/NEMS) are promising alternatives to silicon-based materials since they are electrically conductive, optically reflective and ductile. Polycrystalline mono-metallic films typically exhibit low strength and hardness, high surface roughness, and significa...

Insitu transmission electron microscopy is used to study dissolution of liquid single-phase Pb/Bi inclusions attached to a grain boundary in an alloy of Al99.29Pb0.65Bi0.06 at temperatures of 343, 370, and 389 °C, respectively. The initial size of the inclusions was smaller than 60nm. Dissolution of the inclusions was observed until their complete...

Recent advances in aberration-correcting electron optics have led to increased resolution, sensitivity and signal to noise in atomic resolution microscopy. Building on these developments, the TEAM project was designed to optimize the electron microscope around aberration-corrected electron optics and to further advance the limits of the instrument...

Recent work on AlScZr alloys [1–3] has shown that a precipitate core-shell structure may be responsible for the modification of properties in a precipitate-hardened alloy system. It was demonstrated that the precipitates contained Sc and Zr, but that the distribution of Zr was not homogeneous. Instead, a Zr rich shell surrounded an Al3Sc core, acti...

Thin films play a crucial role in many modern technologies, like microelectronics, solar cells, sensors, and coatings. A key to understanding and controlling thin film growth processes and properties is the knowledge of the variation in structure with distance from the substrate. Therefore experimental techniques for quantitative characterization o...

The performance of a transmission electron microscope is determined by the optical performance of the lenses, the stability of the column and last but not least by the performance of the electron source.

We have characterized the nanoscale mechanical properties of grain boundary precipitate-free zones (PFZ's) in an AlCuSiGe alloy, using combined nanoindentation and in-situ atomic force microscopy (AFM). These mechanical properties were then correlated to the composition, precipitate distribution and, indirectly, to the vacancy concentration within...

of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

We present a theory for size-dependent shapes of Pb nanoprecipitates in Al, introducing the concept of "magic shapes," i.e., shapes having near-zero homogeneous elastic strains. Our quantitative atomistic calculations of edge energies show their effect on precipitate shape to be negligible, thus it appears that shapes must be due to the combined ef...

We have characterized the structure of chemical vapor deposition-grown polycrystalline cubic SiC films by quantitative transmission electron microscopy. A new double-wedge sample geometry allowed accurate statistical measurements of the grain size as a function of distance from the substrate. The data are well described by the van der Drift model o...

The kinetics of thermal motion of liquid lead nanoparticles in thin aluminum foils has been investigated in situ by transmission electron microscopy. Dependences of the diffusion coefficient of particles on temperature and particle size have been obtained. The results of the investigations can be interpreted on the assumption that the mobility of p...