Bernd Kabius

Detection of Single Atoms and Buried Defects in Three Dimensions by Aberration-Corrected Electron Microscope with 0.5-Å Information Limit

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 aberration-correcting optics and a monochromated high-brightness source has significantly improved instrument resolution and contrast. In the present work, we report information transfer beyond 50 pm and show images of single gold atoms with a signal-to-noise ratio as large as 10. The instruments new capabilities were exploited to detect a buried Sigma3 {112} grain boundary and observe the dynamic arrangements of single atoms and atom pairs with sub-angstrom resolution. These results mark an important step toward meeting the challenge of determining the three-dimensional atomic-scale structure of nanomaterials.

Piezoelectric/ultrananocrystalline diamond heterostructures for high-performance multifunctional micro/nanoelectromechanical systems

Most current micro/nanoelectromechanical systems (MEMS/NEMS) are based on silicon. However, silicon exhibits relatively poor mechanical/tribological properties, compromising applications to some devices. Diamond films with superior mechanical/tribological properties provide an excellent alternative platform material. Ultrananocrystalline diamond (UNCD®) in film form with 2–5nm grains exhibits excellent properties for high-performance MEMS/NEMS devices. Concurrently, piezoelectric Pb(ZrxTi1−x)O3 (PZT) films provide high sensitivity/low electrical noise for sensing/high-force actuation at relatively low voltages. Therefore, integration of PZT and UNCD films provides a high-performance platform for advanced MEMS/NEMS devices. This letter describes the bases of such integration and demonstration of low voltage piezoactuated hybrid PZT/UNCD cantilevers.

First application of Cc-corrected imaging for high-resolution and energy-filtered TEM

Contrast-transfer calculations indicate that C(c) correction should be highly beneficial for high-resolution and energy-filtered transmission electron microscopy. A prototype of an electron optical system capable of correcting spherical and chromatic aberration has been used to verify these calculations. A strong improvement in resolution at an acceleration voltage of 80 kV has been measured. Our first C(c)-corrected energy-filtered experiments examining a (LaAlO(3))(0.3)(Sr(2)AlTaO(6))(0.7)/LaCoO(3) interface demonstrated a significant gain for the spatial resolution in elemental maps of La.

Hybrid titanium–aluminum oxide layer as alternative high-k gate dielectric for the next generation of complementary metal–oxide–semiconductor devices

Research is focused on finding reliable high-dielectric constant (k) oxides with high capacitance and all critical properties required for the next generation of complementary metal–oxide–semiconductor (CMOS) gates. A trade-off between dielectric constant and band-offset height is generally observed on gate oxides. Combining TiO2 and Al2O3, with the two extremes of high permittivity (k) and high band offset, we produced a TixAl1−xOy (TAO) oxide layer with k=∼30 and low dielectric leakage for a next generation of high-k dielectric gates. We developed a low temperature oxidation process, following room temperature sputter-deposition of TiAl layers, to produce ultrathin TAO layers on Si with subatomic or no SiO2 or silicide interface formation. We demonstrated TAO layers with <0.5nm equivalent oxide thickness on Si and thermal stability under rapid thermal annealing up to about 950°C. The data presented here provide insights into fundamental physics and materials science of the TAO layer and its potential ap...

Are Diamonds a MEMS' Best Friend?

Next-generation military and civilian communication systems will require technologies capable of handling data/ audio, and video simultaneously while supporting multiple RF systems operating in several different frequency bands from the MHz to the GHz range [1]. RF microelectromechani-cal/nanoelectromechanical (MEMS/NEMS) devices, such as resonators and switches, are attractive to industry as they offer a means by which performance can be greatly improved for wireless applications while at the same time potentially reducing overall size and weight as well as manufacturing costs.

A new approach for improving exchange-spring magnets

It is demonstrated here that an already ideal exchange–spring magnet can be further improved by intermixing the interface. This is counter-intuitive to the general expectation that optimal exchange–spring magnet behavior requires an ideal, atomically coherent soft–hard interface. Epitaxial Sm–Co/Fe thin-film exchange–spring bilayers are thermally processed, by annealing or high-temperature deposition, to induce interdiffusion. With increasing processing temperature, the hysteresis loop becomes more single-phase-like, yet the magnetization remains fully reversible. The interface is characterized via synchrotron x-ray scattering and electron microscopy elemental mapping. The magnetization behavior is modeled by assuming a graded interface where the material parameters vary continuously. The simulations produce demagnetization curves similar to experimental observations.

Giant dielectric constant dominated by Maxwell–Wagner relaxation in Al2O3/TiO2 nanolaminates synthesized by atomic layer deposition

Nanolaminates consisting of Al2O3 and TiO2 oxide sublayers were synthesized by using atomic layer deposition to produce individual layers with atomic scale thickness control. The sublayer thicknesses were kept constant for each multilayer structure, and were changed from 50 to 0.2 nm for a series of different samples. Giant dielectric constant (∼1000) was observed when the sublayer thickness is less than 0.5 nm, which is significantly larger than that of Al2O3 and TiO2 dielectrics. Detailed investigation revealed that the observed giant dielectric constant is originated from the Maxwell–Wagner type dielectric relaxation.

Synthesis and characterization of smooth ultrananocrystalline diamond films via low pressure bias-enhanced nucleation and growth

This letter describes the fundamental process underlying the synthesis of ultrananocrystalline diamond (UNCD) films, using a new low-pressure, heat-assisted bias-enhanced nucleation (BEN)/bias enhanced growth (BEG) technique, involving H2∕CH4 gas chemistry. This growth process yields UNCD films similar to those produced by the Ar-rich/CH4 chemistries, with pure diamond nanograins (3–5nm), but smoother surfaces (∼6nm rms) and higher growth rate (∼1μm∕h). Synchrotron-based x-Ray absorption spectroscopy, atomic force microscopy, and transmission electron microscopy studies on the BEN-BEG UNCD films provided information critical to understanding the nucleation and growth mechanisms, and growth condition-nanostructure-property relationships.

Materials science and integration bases for fabrication of (BaxSr1−x)TiO3 thin film capacitors with layered Cu-based electrodes

The synthesis and fundamental material properties of layered TiAl/Cu/Ta electrodes were investigated to achieve the integration of Cu electrodes with high-dielectric constant (κ) oxide thin films for application to the fabrication of high-frequency devices. The Ta layer is an excellent diffusion barrier to inhibit deleterious Cu diffusion into the Si substrate, while the TiAl layer provides an excellent barrier against oxygen diffusion into the Cu layer to inhibit Cu oxidation during the growth of the high-κ layer in an oxygen atmosphere. Polycrystalline (BaxSr1−x)TiO3 (BST) thin films were grown on the Cu-based bottom electrode by rf magnetron sputtering at temperatures in the range 400–600 °C in oxygen, to investigate the performance of BST/Cu-based capacitors. Characterization of the Cu-based layered structure using surface analytical methods showed that two amorphous oxide layers were formed on both sides of the TiAl barrier, such that the oxide layer on the free surface of the TiAl layer correlates w...

Controllable giant dielectric constant in AlOx/TiOy nanolaminates

Dielectric materials exhibiting high dielectric constants play critical roles in a wide range of applications from microchip energy storage embedded capacitors for implantable biomedical devices to energy storage capacitors for a new generation of renewable energy generation/storage systems. Instead of searching for new materials, we demonstrate that giant dielectric constants can be achieved by integrating two simple oxides with low dielectric constants into nanolaminate structures. In addition, the obtained dielectric constant values are highly tunable by manipulating the sub-layer thicknesses of the component oxides to control the number of interfaces and oxygen redistribution. The work reported here opens a new pathway for the design and development of high dielectric constant materials based on the nanolaminate concept.