Thomas Höche

Thomas Höche
Fraunhofer Institute for Microstructure of Materials and Systems IMWS | IWM

Prof. Dr. rer. nat. habil.

About

287
Publications
29,122
Reads
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4,326
Citations
Introduction
In a joint effort with the company 3D-Micromac AG of Chemnitz, microPREP, the all-new tool for laser-based microstructure-diagnostics sample prep, was developed. Beyond microPREP, microstructure diagnostics as a service to optical industry (HRTEM, STEM-EDXS, FIB/SEM, ToF-SIMS, XRM, etc. at optical coatings, substrates, effect pigments) is the core competence of the work group I am heading. We are also very experienced in microstructure-based materials development of glass-ceramics and microstructure-based laser-process optimization.
Additional affiliations
December 2010 - December 2018
Fraunhofer Institute for Microstructure of Materials and Systems IMWS
Position
  • Head of Department
August 2002 - November 2010
Leibniz Institute of Surface Engineering (IOM)
Position
  • Senior Researcher
November 1999 - July 2002
Humboldt-Universität zu Berlin
Position
  • PostDoc Position

Publications

Publications (287)
Article
Full-text available
Noble metals such as Ag can be used as nucleation agents in glass ceramics. In glasses, it is incorporated predominantly as AgI. At temperatures slightly above the glass transition temperature, Tg, AgI reacts with SbIII to SbV and metallic Ag. Usually, face-centered cubic Ag particles are nearly spherical and get facetted during crystal growth. By...
Article
Using a Mo/Si multilayer stack, capabilities and limits of high-resolution transmission electron microscopy with respect to thin film analysis are pointed out. Image processing is shown to provide non-subjective criteria for the determination of layer thicknesses. In comparison to measurements by X-ray reflectometry, an integrating method capable o...
Article
Glasses from the system Na 2 O–Y 2 O 3 –SiO 2 with different concentrations of ZrO 2 were studied concerning phase formation and crystallization behavior.
Article
Recently, a novel approach to sample preparation for microstructure analyses has been introduced where a surface possessing initial notches is eroded by a broad ion beam at gracing angles. In this contribution, details of the evolution of the sample surface and the geometry obtained are investigated in depth, using both simulation and experiments o...
Article
Full-text available
Oxynitride glasses are not yet commercialised primarily due to the impurities present in the network of these glasses. In this work, we investigated the microstructure and instinctive defects in nitrogen rich La-Si-O-N glasses. Glasses were prepared by heating a powder mixture of pure La metal, Si3N4, and SiO2 in a nitrogen atmosphere at 1650–1800...
Article
Glasses of the composition 8 BaO∙8 SrO∙34 ZnO∙46 SiO2∙4 WO3 doped with 1 ∙ 10²⁰ Eu³⁺/cm³ were melted either in air or under continuous bubbling with forming gas (90 % N2 and 10 % H2). UV-vis spectra of both glasses show absorption lines of Eu³⁺. In the glass melted under reducing conditions, an additional broad absorption band in the 300 to 600 nm...
Article
Isolated small crystals and closed epitaxial layers of CuI could be deposited on various substrates by close distance sublimation (CDS). X-ray diffraction measurements and detailed TEM studies revealed phase pure cubic γ-CuI (zincblende structure) layers and a combination of a CuI multilayer structure with γ-CuI. The multilayer structure, a 12R pol...
Article
A novel method for broad ion beam based sample sectioning using the concept of initial notches is presented. An adapted sample geometry is utilized in order to create terraces with a well-defined step in erosion depth from the surface. The method consists of milling a notch into the surface, followed by glancing-angle ion beam erosion, which leads...
Article
Oriented surface crystallization on polished diopside glass surfaces has been studied with scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and laser scanning microscopy. An orientation preference of [001] parallel to the glass surface was detected for separately growing diopside crystals even as smal...
Article
This chapter describes the most informative methods to image and analyze the micro‐ and nanostructure of inhomogeneous glasses and glass ceramics and relate these features to their original physical or chemical properties. For imaging, the main methods are scanning and transmission electron microscopy. In combination with them, energy‐dispersive X‐...
Article
The growth of (Al x Ga 1-x ) 2 O 3 alloy thin films in corundum phase on r -plane (01.2) Al 2 O 3 substrates is investigated. The growth mode changes from step flow for pseudomorphic layers to three-dimensional growth...
Article
For three borosilicate glasses of different B-to-Si ratio, annealed under reducing atmosphere, the effect of glass composition on the size distribution of nickel nanocrystals formed therein was studied. Depth-dependent crystal size distributions were analyzed using transmission electron microscopy, while the glass structure was examined by optical...
Article
Sn5O2(PO4)2 is a promising p-type transparent semiconducting oxide. Phase-pure triclinic Sn5O2(PO4)2 thin films were grown by pulsed laser deposition using a Sn2(P2O7) target with higher phosphorus content. The (001)-oriented growth of triclinic Sn5O2(PO4)2 on glass was achieved by means of a (111)-textured Y2O3 buffer layer. STEM-EDX and XPS revea...
Article
The relative density of a sintered glass-powder compact varies at the local level due to its heterogeneous nature, which makes its characterization essential. In this work, high-resolution X-ray computed tomography (XCT) was used to quantitatively characterize the local relative density fluctuation of a sintered glass compact in its initial stage....
Article
Three glasses from the base system BaO/SrO/ZnO/SiO2 have been synthesized using conventional melt quenching technique and different concentrations of Ag, Sn, Sb, and Ta. After two-step heat treatments, two glasses showed volume crystallization, while the third glass crystallized solely from the surface. The different crystallization mechanisms were...
Article
Origin and composition dependence of the anisotropic thermomechanical properties are elucidated for Ba1-xSrxZn2Si2O7 (BZS) solid solutions. The high-temperature phase of BZS shows negative thermal expansion (NTE) along one crystallographic axis and highly anisotropic elastic properties characterized by X-Ray diffraction experiments and simulations...
Article
Glasses with the mol% compositions 1.88 Na2O·15.04 K2O·7.52 Al2O3·69.56 SiO2·6.00 BaF2 and 1.88 Na2O·15.03 K2O·7.52 Al2O3·69.52 SiO2·6.00 BaF2·0.05 SmF3 were studied using X-ray diffraction, transmission electron microscopy, and anomalous small-angle X-ray scattering. While the glass doped with samarium showed liquid/liquid phase separation of drop...
Article
Formation of cobalt nanocrystals in durable borosilicate and aluminosilicate glass matrices is studied. Using a hydrogen gas flow treatment, ε-Co nanocrystals precipitate primarily in these glasses. This rare Co allotrope, which so far has mainly been synthetized by organometallic routes is found for the first time in a glass. XRD and TEM results i...
Preprint
Oxynitride glasses are not yet commercialised primarily due to the impurities present in the network of these glasses. In this work, silicon and silicide defects in nitrogen-rich La-Si-O-N glasses were investigated. Glasses were prepared by heating powder mixture of La metal, Si 3 N 4 , and SiO 2 in a nitrogen atmosphere at 1650-1800°C. The obtaine...
Article
Metastable ɛ-Co nanocrystals precipitate in silicate glass matrices together with stable β-Co nanocrystals at temperatures up to 873 K, whereas rapid thermal decomposition of ε-Co is reported if formed by wet-chemical routes. Hence, high-temperature X-ray diffraction was used to determine the unknown coefficient of thermal expansion (CTE) of ε-Co s...
Article
Volume crystallization was achieved in diopside glasses by the introduction of silver into the glassy network. Subsequent thermal treatments lead to the formation of metallic silver nanoparticles within the glass. The latter particles trigger the formation of volume crystals. Furthermore, a porous microstructure due to the huge difference of the de...
Article
Full-text available
Combining various (multi-)ferroic materials into heterostructures is a promising route to enhance their inherent properties, such as the magnetoelectric coupling in BiFeO3 thin films. We have previously reported on the up-to-tenfold increase of the magnetoelectric voltage coefficient α ME in BaTiO3-BiFeO3 multilayers relative to BiFeO3 single layer...
Article
We report on the employment of a nano-porous Vycor-type glass as host for two luminescent substances of very different physical and chemical nature, which share the same porous space. Firstly, BTS:Tb 3+ glass-ceramic nano-powders were infiltrated in the porous structure and secondly Eu 3+ ions from a nitrate aqueous solution were included afterward...
Article
Full-text available
Innovative materials for phosphor converted white light-emitting diodes are in high demand owing to the huge potential of the light-emitting diode technology to reduce energy consumption worldwide. As the primary blue diode is already highly optimized, the conversion phosphors are of crucial importance for any further improvements. We report on the...
Article
Preparing TEM Specimens and Atom Probe Tips by Laser Machining - Volume 27 Issue 6 - Boris Rottwinkel, André Kreutzer, Henry Spott, Michael Krause, Georg Schusser, Thomas Höche
Article
Lithium-alumosilicate glass-ceramics are widely used as zero thermal expansion materials. The effect of the nucleating agent can be monitored by the incorporation of titanium. In this study this has been done by X-ray absorption near edge structure, XANES, at the Ti-K-edge performed at a synchrotron. By contrast to a previous report which considere...
Article
The role of silver as a nucleating agent in BaO/SrO/ZnO/SiO2 glasses is studied with a range of microstructure characterization techniques, such as scanning transmission electron microscopy, ultraviolet-visible spectroscopy, and X-ray diffraction. For this purpose, glasses with different silver and antimony concentrations were synthesized. It was f...
Article
Populations of nickel nanocrystals in a borosilicate glass were studied by TEM and XRM. It is found that XRM, which is applied for the first time to this type of material, is superior for the precise determination of the depth-dependent number densities and volume fractions of precipitated Ni crystals. Statistical precision is gained by imaging 3D...
Article
Glass samples were polished and coated with a 10 nm thick silver layer. Both, silver-coated and uncoated samples were thermally treated at 750 °C for 4 h or at 790 °C for 2 h. In both types of samples, the phase Ba0.5Sr0.5Zn2Si2O7 crystallized, which exhibits a negative thermal expansion. After thermal treatment, the uncoated sample showed a low nu...
Article
Stoichiometric 0.5 BaO·0.5 SrO·2 ZnO·2 SiO2 glass was doped with 5 mol% Nb2O5 or Ta2O5. The effect of these additives on the crystallization behavior was studied using thermal analyses, X-ray diffraction, as well as scanning electron microscopy including elemental analyses. The addition of Nb2O5 or Ta2O5 significantly increases the glass stability...
Article
Glasses with the chemical composition 8 BaO·8 SrO·34 ZnO·49.5 SiO2·0.5 Sb2O3 with 50 and 100 ppm platinum were crystallized in a two-step treatment. The first step was performed slightly above the glass-transition temperature at temperatures in the range from 680 to 700 °C and the second at a temperature of 780 °C. In the first step, an increasing...
Article
The crystallization behavior of BaO-SrO-ZnO-SiO2 glasses containing different concentrations of SnO2 was studied using microscopic techniques as well as thermal analyses. It is shown that SnO2 triggers volume crystallization, but at low nucleation rates. During heat treatments near respective glass transition temperatures, nucleation takes place. I...
Article
The initial stages of surface crystallization of a glass with the composition 8 BaO·8 SrO·34 ZnO·50 SiO2 (mol%) are studied with respect to crystal orientation and morphology. Therefore, different microscopic techniques, such as laser scanning microscopy and scanning electron microscopy in combination with electron backscatter diffraction were used...
Article
Full-text available
A glass with the composition 61 CaO·30 Al2O3·9 SiO2 was studied with respect to its crystallization behavior and its suitability as a rapidly crystallizing material for laser sealing. The glass was studied by differential scanning calorimetry; from the profiles recorded, Avrami activation energies and Avrami coefficients were calculated. The latter...
Article
Full-text available
High perpendicular magnetic anisotropy is essential for the development of high-efficiency spintronics devices. In this paper, we investigate the structural and magnetic properties of Mn-Fe-Ga Heusler thin films with perpendicular magnetic anisotropy inherent to the tetragonal D022 structure. High quality films were heteroepitaxially grown on SrTiO...
Article
Surface modification through tribological loading is understood as a mechanically driven process. Yet, potentially complex chemical reactions can be critical since their products influence contact mechanics and affect friction and wear. Here we investigate the tribologically driven surface oxidation of pure copper in contact with a sapphire sphere....
Article
Glasses with the base composition 8 BaO·8 SrO·34 ZnO·50 SiO2 were studied with respect to the crystallization of a phase with the composition Ba0.5Sr0.5Zn2Si2O7. Some glasses were doped with gold and/or antimony oxide. All glasses exhibited solely surface crystallization. If the glasses contained both antimony and gold, they showed red coloration a...
Article
Recently, it has been shown that the Ba1−xSrxZn2Si2O7 crystal phase has a negative coefficient of thermal expansion. However, technological applications of this material as low thermal expansion glass ceramics are limited by the undesired surface crystallization of the corresponding glass. Surface nucleation, however, can be turned into bulk nuclea...
Presentation
Full-text available
From the base glass system Li2O-Al2O3-SiO2 (LAS), glass ceramics with low- or zero thermal expansion can be derived. They are of highest economic interest, especially because of their very good resistance to thermal shock, and are widely used for manifold commercial products, such as cooktop panels or large telescope mirrors. Although the synthesis...
Article
Glass-ceramics based on lithium-alumo-silicate glasses are commercially important for a wide range of applications, due to their special properties, like a vanishing thermal expansion. In order to tailor these properties, the composition of the glass and the temperature/time schedule are crucial factors. For the industrial production of most lithiu...
Article
The effect of P2O5 and Ce2O3 on the crystallization behavior of a BaO-SrO-ZnO-SiO2 glass was investigated using thermal analyses, X-ray diffraction, scanning electron microscopy including electron backscatter diffraction as well as laser scanning microscopy. Heat treatments lead to the precipitation of Ba1-xSrxZn2Si2O7, Zn2SiO4, and CeO2 at the sur...
Article
Porous silica glasses of different porous sizes are used as hosts for Eu³⁺-ions from a Eu(NO3)3 solution. The glasses were subjected to a sintering process in which the porous microstructure collapses. This work is dedicated to the study of the microstructure of sintered glasses containing Eu³⁺ ions, through (scanning) transmission electron microsc...
Article
The effect of double-layer thickness and partial substitution of Bi³⁺ by Gd³⁺ is demonstrated for multiferroic BaTiO3-BiFeO3 2-2 heterostructures. Multilayers of 15 double layers of BaTiO3 and Bi0.95Gd0.05FeO3 were deposited onto (0 0 1) oriented SrTiO3 substrates by pulsed laser deposition with various double layer thicknesses. X-ray diffraction a...
Article
The early stage of crystallization of a glass with the composition 7.6 Li2O – 0.2 Na2O – 0.1 K2O – 1.9 MgO – 0.3 BaO – 1.2 ZnO – 12.7 Al2O3 – 69.6 SiO2 – 4.2 TiO2 – 1.8 ZrO2 – 0.4 Sb2O3 (mol %), suitable for the production of zero thermal expansion glass-ceramics is reported. Thermal treatment at 740 °C for 24 h resulted in the formation of Zr1-xTi...
Article
Correlations were established between the hyperfine field distribution around the Fe atoms, the multiferroic properties, and the high magnetoelectric coef- ficients in BaTiO3-BiFeO3 multilayer stacks with variable BiFeO3 single layer thickness, down to 5 nm. Of key importance in this study was the deposition of ⁵⁷Fe - enriched BiFeO3, which enhance...
Article
A nanoporous silica glass is used as host for Eu³⁺-ions by immersion in Eu(NO3)3 solution. After sintering of the immersed glass, a very intense red emission is observed under UV excitation. The analysis of the luminescence shows that the native porous glass also presents an inherent luminescence in the blue range, originated from SiO2 centers and...
Article
A porous silica glass was used as host for Eu³⁺-doped Ba2TiSi2O8 (BTS) glass-ceramic powder, which was embedded in the porous structure. Fluorescence upon UV excitation changes drastically from pink color in the un-treated porous glass to blue color in the sintered glass, in which the characteristic Eu³⁺ emission in red-orange spectral range is inh...
Article
Full-text available
Glass ceramics based on Li2O/Al2O3/SiO2 are of high economic importance, as they often show very low coefficients of thermal expansion. This enables a number of challenging applications, such as cooktop panels, furnace windows or telescope mirror blanks. Usually, the crystallization of the desired LAS crystal phases within the glasses must be tailo...
Article
Full-text available
Glasses in the system BaO/SrO/ZnO/SiO2 containing 0.01 and 0.1 mol% gold were used to study the formation of gold nanoparticles with the aim to use them as nucleation agents. In order to promote gold clustering, the glasses were additionally doped with 0.5 mol% Sb2O3. Depending on the heat treatment schedule, Au particle sizes were in the range fro...
Article
Glasses with the mol% composition of 21.2 MgO·21.2 Al2O3·51.9 SiO2·5.7 ZrO2 were doped with 0.5 mol% CeO2 and analysed concerning their crystal phases and microstructure after a one- as well as a two-step crystallization treatment. X-ray diffraction studies indicate the presence of tetragonal ZrO2, a high-/low-quartz solid solution and spinel which...
Article
Full-text available
Glass-ceramics are noted for their unusual combination of properties and manifold commercialized products for consumer and specialized markets. Evolution of novel glass and ceramic processing routes, a plethora of new compositions, and unique exotic nano- and microstructures over the past 60 years led us to review the definition of glass-ceramics....
Article
Glancing-angle Ar+ broad ion beam erosion is widely used for the preparation of high-quality transmission electron microscopy (TEM) samples. However, low erosion rates and lack of site specificity are major drawbacks of the method. Being inexpensive and easy to use - in particular when compared to widely used focused ion beam preparation methods -...
Chapter
In the present study, detailed investigations on the crystallisation behaviour for the recently discovered Ba1-xSrxZn2Si2O7 phase were performed. This solid solution may possess zero to negative thermal expansion. In contrast to many other phases with negative thermal expansion, this phase can be crystallised from glasses and hence should be suitab...
Article
Full-text available
For high-performance optical applications, transparent polycrystalline ceramics are interesting materials because of the high thermal, chemical and mechanical resistance. However, due to its brittleness and hardness, the machining of these materials is difficult and the optical functionality is largely depending on the machining conditions as well...
Article
Full-text available
A glass in the system Na2O–SiO2–Al2O3–K2O–CaO–CaF2–ZnO was doped with Ce, Ag, Sn, Sb and Br. Homogeneous and transparent glass ceramics are obtained from this glass by the precipitation of CaF2 nanoparticles. An interface-controlled crystallization mechanism hinders crystal growth after some time. By adding photosensitive agents, a tailored photoin...
Article
Glasses in the system BaO-SrO-ZnO-SiO2 from which a phase with the composition Ba1-xSrxZn2Si2O7 can be precipitated possess a strong tendency towards surface crystallization and due to the high anisotropy of the coefficient of thermal expansion of this crystal phase, the obtained glass ceramics often show microcracking. The present article deals wi...
Article
Lithiumalumosilicate glasses are of great importance for industrial applications, because they enable the preparation of glass ceramics with coefficients of thermal expansion close to zero. While detailed studies of the effect of ZrO2 on nucleation and crystal growth have already been performed in recent years, the effect of TiO2 was up to now not...
Article
A glass from the system BaO-SrO-ZnO-Al2O3-SiO2 was synthesized and the crystallization behavior was studied using differential scanning calorimetry, X-ray diffraction, and scanning and transmission electron microscopy. The main phase precipitating is a Ba1-xSrxZn2Si2O7 solid solution with very low thermal expansion. The formation of this phase lead...
Presentation
Glaskeramiken auf Basis des Systems Li2O / Al2O3 / SiO2 sind in einem breiten Anwendungsbereich von großer Bedeutung. Obwohl sie seit mehr als 60 Jahren weit verbreitet sind, ist der zu Grunde liegende Kristallisationsmechanismus bis heute nicht vollständig aufgeklärt. Um die Wirkung von TiO2 auf den Keimbildungsmechanismus in einem Lithiumaluminos...
Article
Full-text available
Thermal treatment of a glass with the composition 8 BaO·8 SrO·34 ZnO·50 SiO2 has led to the crystallization of a Ba1−xSrxZn2Si2O7 solid solution. This solid solution has a very low or even negative thermal expansion. The glass system possesses a strong tendency towards surface crystallization, while bulk nucleation is negligible. The surface crysta...
Article
Full-text available
This work reports on the structural and magnetic properties of Mn2.7−xFexGa1.3 Heusler films with different Fe content x (0 ≤ x ≤ 1.2). The films were deposited heteroepitaxially on MgO single crystal substrates, by magnetron sputtering. Mn2.7−xFexGa1.3 films with the thickness of 35 nm were crystallized in a tetragonal D022 structure with (001) pr...
Article
High-quality epitaxial LaMnO3/LaAlO3 superlattices (SLs) with (0 0 1), (0 1 1), and (1 1 1) out-of-plane orientation were grown by pulsed laser deposition. This SL material was predicted theoretically as a Chern insulator for realizing the quantum anomalous Hall effect. In our investigations, a paramagnetic-ferromagnetic phase transition is found w...
Article
Full-text available
The high economic importance of glass ceramics based on Li2O/Al2O3/SiO2 (LAS) is mainly due to their low coefficients of thermal expansion (CTE), which make these materials suitable candidates for a number of applications. The exact mechanism of the crystallization processes in LAS glasses is still not fully understood. The present work focuses on...
Article
Background: Femtosecond lasers (fs-lasers) are established cutting instruments for the creation of LASIK flaps. Previous studies often showed even rougher surfaces after application of fs-laser systems compared to lamellar keratotomy with mechanical microkeratomes. When cutting the cornea with fs-lasers, an intrastromal gas development occurs, whi...
Article
Pulsed laser deposition is one of the most flexible growth methods for high-quality epitaxial multifunctional thin films and short-period superlattices. The following examples of current research interest demonstrate the state-of-the art: First, it is shown that the magnetoelectric performance of multiferroic BiFeO3–BaTiO3 (001)-oriented superlatti...
Article
Laser welding of dissimilar materials is challenging, due to their difference in coefficients of thermal expansion (CTE). In this work, fused silica-to-sapphire joints were achieved by employment of a ns laser focused in the intermediate Si-enriched fresnoitic glass thin film sealant. The microstructure of the bonded interphase w