Hans Fecht
University of Ulm, Functional Nanosystems, Faculty Member
- University of Ulm, Micro and Nanomaterials, Faculty Memberadd
- PhD in Materials Science, Post-Doctoral Research experience at UW-Madison and Caltech, Professor at Univ. Augsburg, ... morePhD in Materials Science, Post-Doctoral Research experience at UW-Madison and Caltech, Professor at Univ. Augsburg, TU Berlin, KIT, Ulm University, several high-level scientific awards and membership in European Academiesedit
ABSTRACT For measurements of the surface tension the oscillating drop technique is employed. With the help of digital image processing this method yields the frequencies of the surface oscillations from which the values of the surface... more
ABSTRACT For measurements of the surface tension the oscillating drop technique is employed. With the help of digital image processing this method yields the frequencies of the surface oscillations from which the values of the surface tension can be derived. In the framework of ESA’s Thermolab project, the surface tensions of two representative steels: one low carbon steel, and one stainless steel, have been determined over a wide temperature range. The measurements were carried out in an earthbound levitation device, as well as during parabolic flights in the TEMPUS facility, taking advantage of the microgravity environment. The results obtained are compared and discussed in the framework of thermodynamic models.
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Polymers and polymer matrix composites are commonly used materials with applications extending from packaging materials to delicate electronic devices. Epoxy resins and fiber-reinforced epoxy-based composites have been used as adhesives... more
Polymers and polymer matrix composites are commonly used materials with applications extending from packaging materials to delicate electronic devices. Epoxy resins and fiber-reinforced epoxy-based composites have been used as adhesives and construction parts. Fractal analysis has been recognized in materials science as a valuable tool for the microstructural characterization of composites by connecting fractal characteristics with composites’ functional properties. In this study, fractal reconstructions of different microstructural shapes in an epoxy-based composite were performed on field emission scanning electron microscopy (FESEM) images. These images were of glass fiber reinforced epoxy as well as a hybrid composite containing both glass and electrospun polystyrene fibers in an epoxy matrix. Fractal reconstruction enables the identification of self-similarity in the fractal structure, which represents a novelty in analyzing the fractal properties of materials. Fractal Real Fin...
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The particles in condensed matter physics are almost characterized by Brownian motion. This phenomenon is the basis for a very important understanding of the particles motion in condensed matter. For our previous research, there is... more
The particles in condensed matter physics are almost characterized by Brownian motion. This phenomenon is the basis for a very important understanding of the particles motion in condensed matter. For our previous research, there is already applied and confirmed the complex fractal correction which includes influence of parameters from grains and pores surface and also effects based on particles’ Brownian motion. As a chaotic structure of these motions, we have very complex research results regarding the particles’ trajectories in three-dimension (3D). In our research paper, we applied fractal interpolation within the idea to reconstruct the above mentioned trajectories in two dimensions at this stage. Because of the very complex fractional mathematics on Brownian motion, we found and developed much simpler and effective mathematization. The starting point is within linear interpolation. In our previous research, we presented very original line fractalization based on tensor product....
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The materials’ consolidation, especially ceramics, is very important in advanced research development and industrial technologies. Science of sintering with all incoming novelties is the base of all these processes. A very important... more
The materials’ consolidation, especially ceramics, is very important in advanced research development and industrial technologies. Science of sintering with all incoming novelties is the base of all these processes. A very important question in all of this is how to get the more precise structure parameters within the morphology of different ceramic materials. In that sense, the advanced procedure in collecting precise data in submicro-processes is also in direction of advanced miniaturization. Our research, based on different electrophysical parameters, like relative capacitance, breakdown voltage, and [Formula: see text], has been used in neural networks and graph theory successful applications. We extended furthermore our neural network back propagation (BP) on sintering parameters’ data. Prognosed mapping we can succeed if we use the coefficients, implemented by the training procedure. In this paper, we continue to apply the novelty from the previous research, where the error is...
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This contribution reports the results of calorimetric measurements of the enthalpy of fusion and liquid specific heat carried out in different laboratories as part of the ground campaign of the Thermolab project. Different equipments and... more
This contribution reports the results of calorimetric measurements of the enthalpy of fusion and liquid specific heat carried out in different laboratories as part of the ground campaign of the Thermolab project. Different equipments and calibration methods have been used and critically evaluated. Thermodynamic calculations using the Thermocalc software have been performed and a comparison has been carried out with the experimental results.
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We report the flexible piezotronic strain sensors fabricated using carbon fiber-ZnO nanowire hybrid structures by a novel and reliable method. The I-V characteristic of the sensor shows high sensitivity to external strain due to the... more
We report the flexible piezotronic strain sensors fabricated using carbon fiber-ZnO nanowire hybrid structures by a novel and reliable method. The I-V characteristic of the sensor shows high sensitivity to external strain due to the change in Schottky barrier height (SBH), which has a linear relationship with strain. This fabricated strain sensor has a quick, real-time current response under both static and dynamic mechanical loads. The change in SBH resulted from the strain-induced piezoelectric potential is investigated by band gap theory. In this work we develop a new feasible method to fabricate a flexible strain sensor within the fabric adapted to textile structures, able to measure their strain.
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The thermophysical properties of Cu-based industrial alloys in the liquid phase have been determined in the framework of ThermoLab project. Four commercial copper alloys provided by one member of the industrial user group, Cu-Sn-X (X= P;... more
The thermophysical properties of Cu-based industrial alloys in the liquid phase have been determined in the framework of ThermoLab project. Four commercial copper alloys provided by one member of the industrial user group, Cu-Sn-X (X= P; Ti), Cu-Ni-Si and Cu-Ni-Si-Mg ...
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Nickel-base superalloys used for critical rotating disc components have evolved into advanced, high performance, application-specific materials. The designs of modern turbine machinery applications have dictated a shift in material... more
Nickel-base superalloys used for critical rotating disc components have evolved into advanced, high performance, application-specific materials. The designs of modern turbine machinery applications have dictated a shift in material performance requirements from an emphasis solely on burst and creep strength to the addition of minimized fatigue crack growth rates and component residual stresses. Increased component performance has often resulted in material and process changes that are accompanied by subsequent manufacturing difficulties. For example, increased alloy content has pushed the primary processing route from ingot metallurgy toward powder metallurgy methods. The processing routes required in the manufacture of these materials are equally as complex as the alloys themselves and have a strong influence on the resultant properties of turbine engine discs. Challenges still lie ahead for material and process engineers working on these materials. Both turbine engine design changes and market pressures will mandate novel materials and processes that allow for cost effective solutions for the harsh environment applications these nickel-based superalloys have evolved to fill.
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The excess energy transferred by high energy mills in the mechanical synthesis (mechanosynthesis) of nanophase alloys and compounds is evaluated in two iron containing systems, Fe–C and Fe–Cu. Powders treated by high energy milling are... more
The excess energy transferred by high energy mills in the mechanical synthesis (mechanosynthesis) of nanophase alloys and compounds is evaluated in two iron containing systems, Fe–C and Fe–Cu. Powders treated by high energy milling are analysed by Mössbauer spectroscopy and X-ray diffraction, the latter technique allowing also the determination of the dimensions of the crystal size. The model for energy effects in alloys introduced by Miedema and the thermochemical estimates proposed for ball milled ...
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The evolutional function of ordered interfacial water near solid surfaces was postulated by Szent-Györgyi: "Life actually, may have started with building these water... more
The evolutional function of ordered interfacial water near solid surfaces was postulated by Szent-Györgyi: "Life actually, may have started with building these water structures." Here we report their tunability with laser light on both hydrophobic and hydrophilic surfaces. On the former, the light caused their depletion--on the latter, an increase in fluidity--as measured by atomic force acoustic microscopy. Interfacial water layers play a key role in cellular recognition. Their tunability promises to revolutionize various fields in biomedical engineering and life sciences.
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In atomic force acoustic microscopy (AFAM) one exploits the contact resonances of the micro-fabricated cantilever, either as an imaging method where the contrast arises from the local variation of elastic and anelastic properties, or for... more
In atomic force acoustic microscopy (AFAM) one exploits the contact resonances of the micro-fabricated cantilever, either as an imaging method where the contrast arises from the local variation of elastic and anelastic properties, or for local quantitative measurements. In this work we used AFAM in its spectroscopic mode, where contact-resonance curves are recorded as a function of the loading force
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Interfacial water layers attract more and more attention in both material sciences and life sciences because of two characteristics that depend on the polarity of the surfaces involved: crystalline order and surface stability. Their... more
Interfacial water layers attract more and more attention in both material sciences and life sciences because of two characteristics that depend on the polarity of the surfaces involved: crystalline order and surface stability. Their interplay allows us to understand friction at the ...
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Owing to their low elastic moduli, high specific strength and excellent processing characteristics in the undercooled liquid state, metallic glasses are promising materials for applications in micromechanical systems. With miniaturization... more
Owing to their low elastic moduli, high specific strength and excellent processing characteristics in the undercooled liquid state, metallic glasses are promising materials for applications in micromechanical systems. With miniaturization of metallic mechanical components down to the micrometer scale, the importance of a native oxide layer on a glass surface is increasing. In this work we use TEM and XPS to characterize the structure and properties of the native oxide layer grown on Ni(62)Nb(38) metallic glass and their evolution after annealing in air. The thickness of the oxide layer almost doubled after annealing. In both cases the oxide layer is amorphous and consists predominantly of Nb oxide. We investigate the friction behavior at low loads and in ambient conditions (i.e. at T = 295 K and 60% air humidity) of both as-cast and annealed samples by friction force microscopy. After annealing the friction coefficient is found to have significantly increased. We attribute this effe...
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The Nanocrystaline diamonds are very important biomedical material with variety of applications. The experimental procedures and results have been done in the Institute of Functional Nanosystems at the University Ulm (Germany). There is... more
The Nanocrystaline diamonds are very important biomedical material with variety of applications. The experimental procedures and results have been done in the Institute of Functional Nanosystems at the University Ulm (Germany). There is an existing biocompatibility of the diamond layers, selectively improved by biomimetic 3D patterns structuring. Based on that, we have been inspired to apply the graph theory approach in analysing and defining the physical parameters within the structure of materials structure samples. Instead the parameters values, characteristic at the samples surface, we penetrate the graphs deeply in the bulk structure. These values could be only, with some probability, distributed through the microstructure what defines not enough precious parameters values between the microstructure constituents, grains and pores. So, we originally applied the graph theory to get defined the physical parameters at the grains and pores levels. This novelty, in our paper, we appl...
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Today in the age of advanced ceramic civilization, there are a variety of applications for modern ceramics materials with specific properties. Our up-to date research recognizes that ceramics have a fractal configuration nature on the... more
Today in the age of advanced ceramic civilization, there are a variety of applications for modern ceramics materials with specific properties. Our up-to date research recognizes that ceramics have a fractal configuration nature on the basis of different phenomena. The key property of fractals is their scale-independence. The practical value is that the fractal objects’ interaction and energy is possible at any reasonable scale of magnitude, including the nanoscale and may be even below. This is a consequence of fractal scale independence. This brings us to the conclusion that properties of fractals are valid on any scale (macro, micro, or nano). We also analyzed these questions with experimental results obtained from a comet, here 67P, and also from ceramic grain and pore morphologies on the microstructure level. Fractality, as a scale-independent morphology, provides significant variety of opportunities, for example for energy storage. From the viewpoint of scaling, the relation be...
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We present the synthesis of ultrananocrystalline diamond (UNCD) films by application of hot filament chemical vapor deposition (HFCVD). We furthermore studied the different morphological, structural, and electrical properties. The grown... more
We present the synthesis of ultrananocrystalline diamond (UNCD) films by application of hot filament chemical vapor deposition (HFCVD). We furthermore studied the different morphological, structural, and electrical properties. The grown films are fine grained with grain sizes between 4 and 7 nm. The UNCD films exhibit different electrical conductivities, dependent on grain boundary structure. We present different contact metallizations exhibiting ohmic contact behavior and good adhesion to the UNCD surface. The temperature dependence of the electrical conductivity is presented between −200 and 900°C. We furthermore present spectroscopic investigations of the films, supporting that the origin of the conductivity is the structure and volume of the grain boundary.
Research Interests: Nanomaterials and Diamond
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A scenario has been developed combining the glass transition (liquid to glass) with the crystal-to glass transition. If the “melting” point of a crystalline solid solution is reduced to the ideal glass transition temperature a triple... more
A scenario has been developed combining the glass transition (liquid to glass) with the crystal-to glass transition. If the “melting” point of a crystalline solid solution is reduced to the ideal glass transition temperature a triple point is predicted between crystal, liquid and glass. Based on extrapolations of measured specific heat data of undercooled liquid glass-forming Au- Pb-Sb alloys the excess entropy is found to vanish close to the glass transition. On the other hand, the amorphization reaction of crystalline Fe2Er-hydrides is characterized by a lambda-type anomaly in the specific heat. The logarithmic temperature-dependence of the specific heat results from local fluctuations in the crystalline phase, rather than thermally activated lattice defects. These results suggest that glass formation from the liquid as well as the crystalline state is characterized by an underlying instability.
ABSTRACTA universal, accurate and simple method is developed to describe the thermodynamic properties of disordered grain boundaries in nanocrystalline metals. Based on a free volume approach at negative pressure of the universal equation... more
ABSTRACTA universal, accurate and simple method is developed to describe the thermodynamic properties of disordered grain boundaries in nanocrystalline metals. Based on a free volume approach at negative pressure of the universal equation of state, the maximum free volume, bulk modulus, specific heat at constant pressure, thermal expansion coefficient, excess enthalpy, excess entropy and free energy of grain boundaries are derived from well-known thermodynamic relationships. Describing nanocrystalline metals as a bimodal material with a grain boundary component and a crystalline component, their thermodynamic properties can then be estimated by appropriate scaling of the boundary-to-volume ratio.
ABSTRACT In the present paper, the glass-transition phenomenon in an Au-based metallic glass has been studied using a step-scan calorimetry measurement. The existence of two distinct slopes within the glass-transition region one starting... more
ABSTRACT In the present paper, the glass-transition phenomenon in an Au-based metallic glass has been studied using a step-scan calorimetry measurement. The existence of two distinct slopes within the glass-transition region one starting at low temperature (about 340 K) and the other at higher temperature (about 380 K) likely indicates two glass-transition processes. This phenomenon is rather related to different diffusion coefficients of the alloying elements in this complex alloy in solid state. Structural relaxation of the glassy phase before reaching the glass-transition region also shows a complex behavior.
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Abstract This chapter introduces the main topics of research that have benefited so far from the space environment (reduced gravity, ambient radiation, vacuum, etc.), and provides an outlook for future research development. By convention,... more
Abstract This chapter introduces the main topics of research that have benefited so far from the space environment (reduced gravity, ambient radiation, vacuum, etc.), and provides an outlook for future research development. By convention, it is split into two fields: physical sciences/engineering and life sciences.
ABSTRACT Atomic force acoustic microscopy was used to image bulk metallic glasses of composition Zr63−xCu24AlxNi10Co3 with 8 < x < 15. The elastic contrast was modulated on a length scale of 250–400 nm. A similar modulation... more
ABSTRACT Atomic force acoustic microscopy was used to image bulk metallic glasses of composition Zr63−xCu24AlxNi10Co3 with 8 < x < 15. The elastic contrast was modulated on a length scale of 250–400 nm. A similar modulation was identified by transmission electron microscopy. Using the thermoelastic, model a good correlation between the observed anelasticity and the evidenced mesostructure was obtained.Research highlights► The authors reports on the occurrence of mesostructure in the Zr63−xCu24AlxNi10Co3 with a length scale in the 250–400 nm range, depending on the aluminum content. ► The frequency dependence of the longitudinal sound velocity correlates with the measured mesostructural lengths while interpreting the ultrasonic data with the thermoelastic model. ► It appears that the mesostructural length scale is a governing parameter for the mechanical behavior of this alloys system. ► The present work first demonstrates the interplay of mesostructure and mechanical behavior of metallic glasses.
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Metallic glasses are good candidates for applications in micromechanical systems. With size reduction of mechanical components into the micrometer and submicrometer range, the native surface oxide layer starts playing an important role in... more
Metallic glasses are good candidates for applications in micromechanical systems. With size reduction of mechanical components into the micrometer and submicrometer range, the native surface oxide layer starts playing an important role in contact mechanical applications of metallic glasses. We use atomic force microscopy to investigate the wear behavior of the Ni62Nb38 metallic glass with a native oxide layer and
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We report on the anelastic behavior of a cyclically loaded Zr62.5Fe5Cu22.5Al10 bulk metallic glass well below its yield strength. The dynamic mechanical behavior of the glass is discussed on the basis of its structural and thermodynamic... more
We report on the anelastic behavior of a cyclically loaded Zr62.5Fe5Cu22.5Al10 bulk metallic glass well below its yield strength. The dynamic mechanical behavior of the glass is discussed on the basis of its structural and thermodynamic properties before and after tests. We show how the kinetically frozen anelastic deformation accumulates at room temperature and causes a structural relaxation and densification