Ehrenfried Zschech

Efficient hydrogen production on MoNi4 electrocatalysts with fast water dissociation kinetics

Various platinum-free electrocatalysts have been explored for hydrogen evolution reaction in acidic solutions. However, in economical water-alkali electrolysers, sluggish water dissociation kinetics (Volmer step) on platinum-free electrocatalysts results in poor hydrogen-production activities. Here we report a MoNi4 electrocatalyst supported by MoO2 cuboids on nickel foam (MoNi4/MoO2@Ni), which is constructed by controlling the outward diffusion of nickel atoms on annealing precursor NiMoO4 cuboids on nickel foam. Experimental and theoretical results confirm that a rapid Tafel-step-decided hydrogen evolution proceeds on MoNi4 electrocatalyst. As a result, the MoNi4 electrocatalyst exhibits zero onset overpotential, an overpotential of 15 mV at 10 mA cm−2 and a low Tafel slope of 30 mV per decade in 1 M potassium hydroxide electrolyte, which are comparable to the results for platinum and superior to those for state-of-the-art platinum-free electrocatalysts. Benefiting from its scalable preparation and stability, the MoNi4 electrocatalyst is promising for practical water-alkali electrolysers.

Materials for Information Technology

In information theory, information is described in a conceptual and mathematical manner. However, information in the real world is bound to physical media. Operations on information like retrieval, converting, processing, storage, transmission and presenting data require matter and energy. Both information theory and physics build the basis for information technology (IT), i. e. the study, design, development, implementation, support and management of computer-based information systems, particularly software applications and computer hardware. More than ever before, the dramatic productivity enhancement of IT requires applications with significantly increased electrical and optical functionalities. IT hardware in particular relies on the continuous shrinking of feature sizes in electronic and photonic devices, but also on the introduction of new materials and design concepts. This includes sustained developments in materials science and engineering, with a specific focus on advanced thin film and nanoscale materials [1, 2]. The scope of the Feature Articles of the Special Issue “Materials for Information Technology” is to provide an overview of the current status, recent developments and research activities in the field of materials used for IT, with a particular emphasis on future scenarios. Latest results in materials science and engineering as well as for a wide range of applications in industry are covered, including synthesis of thin film and nanoscale materials, their properties, composition and structure. The papers collected here reflect the existing widespread interest in materials for IT, and provide an insight particularly into the directions in which new synthesis developments and special applications for these fascinating and useful materials are currently headed. In this Special Issue, material transitions that are necessary to improve the performance and to maintain the reliability of products for IT applications are highlighted. The contents of the papers range from materials for field-effect transistors (FET) used in leading-edge silicon-based electronic products manufactured in CMOS (complementary metal oxide semiconductor) technology and materials for the “beyond CMOS” nanoelectronics era to materials for data storage and for printed electronics. Computer modeling and analytical techniques to characterize thin film structures are covered too. Particular materials that are discussed are metal oxides with high dielectric permittivity, materials for spintronics, carbon-based nanomaterials, nanostructured metals for interconnects and organic thin films.

Applying x-ray microscopy and finite element modeling to identify the mechanism of stress-assisted void growth in through-silicon vias

Fabricating through-silicon vias (TSVs) is challenging, especially for conformally filled TSVs, often hampered by the seam line and void inside the TSVs. Stress-assisted void growth in TSVs has been studied by finite element stress modeling and x-ray computed tomography (XCT). Because x-ray imaging does not require TSVs to be physically cross-sectioned, the same TSV can be imaged before and after annealing. Using 8 keV laboratory-based XCT, voids formed during copper electroplating are observed in as-deposited samples and void growth is observed at the void location after annealing. We hypothesize that the mechanism generating voids is hydrostatic stress-assisted void growth. Stresses in a copper-filled TSV with a pre-existing void were simulated by finite element methods. The peaks of the hydrostatic stress and its gradient are shown to be around the edge of the void. Comparing simulated results and experimental data shows that void growth in TSVs is stress-assisted: vacancies diffuse and coalesce at the...

A high-resolution measurement system for novel scanning thermal microscopy resistive nanoprobes

In this paper, a scanning thermal microscopy (SThM) module with a modified Wheatstone bridge is presented. It is intended to be used with a novel four-terminal thermoresistive nanoprobe, which was designed for performing thermal measurements in standard static-mode atomic force microscopes. The modified Wheatstone bridge architecture is also compared to a Wheatstone bridge and a Thomson bridge in terms of their temperature measurement sensitivities. In fixed conditions, they are found to be (7.05 ± 0.04) μV K−1 for the modified Wheatstone, while (5.43 ± 0.06) μV K−1 for the Wheatstone and (0.91 ± 0.09) μV K−1 for the Thomson bridge. The usability of the three set-ups with four-terminal nanoprobes is also discussed. The design of devices included in the module is presented and the noise level of the modified Wheatstone bridge is estimated. A proportional–integral–derivative controller for active-mode SThM is also introduced.

Electromigration early failure void nucleation and growth phenomena in Cu and Cu(Mn) interconnects

Electromigration early failure void nucleation and growth phenomena were studied using large-scale, statistical analysis methods. A total of about 496,000 interconnects were tested over a wide current density and temperature range (j = 3.4 to 41.2 mA/μm2, T = 200 to 350°C) to analyze the detailed behavior of the current density exponent n and the activation energy Ea. The results for the critical V1M1 downstream interface indicate a reduction from n = 1.55±0.10 to n = 1.15±0.15 when lowering the temperature towards 200°C for Cu-based interconnects. This suggests that the electromigration downstream early failure mechanism is shifting from a mix of nucleation-controlled (n = 2) and growth-controlled (n = 1) to a fully growth-controlled mode, assisted by the increased thermal stress at lower temperatures (especially at use conditions). For Cu(Mn)-based interconnects, a drop from n = 2.00±0.07 to n = 1.64±0.2 was found, indicating additional effects of a superimposed incubation time. Furthermore, at lower current densities, the Ea value seems to drop for both Cu and Cu(Mn) interconnects by a slight, but significant amount of 0.1 - 0.2eV. Implications for extrapolations of accelerated test data to use conditions are discussed. Furthermore, the scaling behavior of the early failure population at the NSD=-3 level (F~0.1%) was analyzed, spanning 90, 65, 45, 40 and 28 nm technology nodes.

Stress-induced phenomena in nanosized copper interconnect structures studied by x-ray and electron microscopy

We present the first dynamic study of damage mechanisms in nanosized on-chip Cu interconnects caused by stress-induced voiding in advanced integrated circuits. Synchrotron-based transmission x-ray microscopy is applied to visualize the void evolution and conical dark-field analysis in the transmission electron microscopy to characterize the Cu microstructure. Our x-ray microscopy measurements showed, in contradiction to electromigration studies, no void movement over large dimensions during the stress-induced void evolution. We observed in via/line Cu interconnect structures that voids are formed directly beneath the via, i.e., in the Cu wide line at the edge of the via bottom. It is concluded that voids are originally formed at the site where eventually the catastrophic failure occurs. During stress migration tests, Cu atoms migrate from regions of low stress to regions of high tensile stress, and simultaneously, vacancies migrate along the stress gradient (within a limited range of some microns) in the ...

Full-field X-ray microscopy with crossed partial multilayer Laue lenses

We demonstrate full-field X-ray microscopy using crossed multilayer Laue lenses (MLL). Two partial MLLs are prepared out of a 48 μm high multilayer stack consisting of 2451 alternating zones of WSi2 and Si. They are assembled perpendicularly in series to obtain two-dimensional imaging. Experiments are done in a laboratory X-ray microscope using Cu-Kα radiation (E = 8.05 keV, focal length f = 8.0 mm). Sub-100 nm resolution is demonstrated without mixed-order imaging at an appropriate position of the image plane. Although existing deviations from design parameters still cause aberrations, MLLs are a promising approach to realize hard X-ray microscopy at high efficiencies with resolutions down to the sub-10 nm range in future.

Effect of interface strength on electromigration-induced inlaid copper interconnect degradation: Experiment and simulation

Abstract Both in situ microscopy experiments at embedded inlaid copper interconnect structures and numerical simulations based on a physical model provide information about electromigration-induced degradation mechanisms in on-chip interconnects. It is shown that the modification of the bonding strength of the weakest interface results in completely changed degradation and failure mechanisms. Transmission electron microscopy (TEM) images of standard Cu/SiNx interfaces are compared with strengthened interfaces, e. g., after applying an additional metal coating or a self-assembled monolayer (SAM) on top of the polished copper lines. The changed degradation mechanisms as observed with the in situ scanning electron microscopy (SEM) experiment and as predicted based on the numerical simulations are explained based on TEM images.

Microfabricated resistive high-sensitivity nanoprobe for scanning thermal microscopy

In this article, a novel microfabricated thermoresistive scanning thermal microscopy probe is presented. It is a V-shaped silicon nitride cantilever with platinum lines and a sharp off-plane nanotip. The cantilever fabrication sequence incorporates standard complementary metal oxide semiconductor technology processes and therefore provides high reproducibility, while the tip is additionally processed by focused ion beam, enabling high-sensitivity and high-resolution thermal sensing. The nanoprobe is designed for scanning thermal microscopes, operating in standard atomic force microscope setup with an optical detection system. The measurement setup, which is also presented, takes advantage of the four-point design of the probe by inclusion of a Thomson bridge and a modified Wheatstone bridge measurement electronics.In this article, a novel microfabricated thermoresistive scanning thermal microscopy probe is presented. It is a V-shaped silicon nitride cantilever with platinum lines and a sharp off-plane nanotip. The cantilever fabrication sequence incorporates standard complementary metal oxide semiconductor technology processes and therefore provides high reproducibility, while the tip is additionally processed by focused ion beam, enabling high-sensitivity and high-resolution thermal sensing. The nanoprobe is designed for scanning thermal microscopes, operating in standard atomic force microscope setup with an optical detection system. The measurement setup, which is also presented, takes advantage of the four-point design of the probe by inclusion of a Thomson bridge and a modified Wheatstone bridge measurement electronics.

Quantitative Fluorescence EXAFS Analysis of Concentrated Samples–Correction of the Self-Absorption Effect

The EXAFS amplitudes of concentrated samples measured in the fluorescence mode strongly depend on the detection geometry through the self-absorption effect. Knowing the stoichiometry of the sample, we can fully correct for the self-absorption effect using a simple theory and obtain the true EXAFS. The correction procedure presented here for the Oxygen K-edge EXAFS of NiO is generally applicable and should be the first step in the quantitative analysis of fluorescence EXAFS data of concentrated samples.