Wolfgang Fränzel - Academia.edu (original) (raw)

Papers by Wolfgang Fränzel

Zeitschrift für Medizinische Physik, 2009

It is known that ionizing radiation is used in medicine for Roentgen diagnostics and for radiatio... more It is known that ionizing radiation is used in medicine for Roentgen diagnostics and for radiation therapy. The radiation interacts with matter, in particular with biological one, essentially by scattering, photoelectric effect, Compton effect and pair production. To what extent the biological material is changed thereby, depends on the type and the amount of radiation energy, on the dose and on the tissue constitution. In modern radiation therapy two different kinds of radiation are used: high energy X-rays and electron radiation. In the case of head-neck tumors the general practice is an irradiation with high energy X-rays with absorbed dose to water up to 70 Gy. Teeth destruction has been identified as a side effect during irradiation. In addition, damage to the salivary glands is often observed which leads to a decrease or even the complete loss of the salivary secretion (xerostomia). This study shows how the different energy and radiation types damage the tooth tissue. The effects of both, high X-ray energy and high energy electrons, on the mechanical properties hardness and elasticity of the human dental tissue are measured by the nanoindentation technique. We compare these results with the effect of the irradiation of low X-ray energy on the dental tissue.

Glass science and technology, 2001

Viscous flow is responsible for permanent deformation of glasses above the transformation tempera... more Viscous flow is responsible for permanent deformation of glasses above the transformation temperature (T g ). The results of macroscopic indentation experiments (maximum loading forces F max ≥2 N) with sharp indenters (Vickers or Berkovich pyramids) demonstrate this property by crack-free indents at T≥T g . But it is also possible to make crack-free indents at room temperature (RT), well below T g , if the load, the contact area and the deformation rate, respectively, are small enough, which is consistent with glass as a supercooled liquid but inconsistent with glass as a well-known ideally brittle material at RT. The mechanisms of this permanent deformation of glasses by indentation near RT have not been understood completely up to now. For the analysis of the macroscopic indentation experiments with Vickers pyramids and spherical indenters, respectively, a viscoelastic deformation behaviour is assumed for the complete temperature range from RT to T g . Therefore the rheological an...

Glass science and technology, 2005

Presented are results from uniaxial cylinder upsetting tests of sodium silicate glass at differen... more Presented are results from uniaxial cylinder upsetting tests of sodium silicate glass at different constant deformation rates each combined with relaxation experiments in the temperature range 480 to 580°C. Due to the complete stress relaxation to final load zero (vanished carrying capacity) also below glass transition temperature T g , it follows Maxwell behavior in principle. But the rheological analyses of loading and unloading experiments together show that only nonlinear Maxwell model approaches can adequately describe the deformation behavior of the glass in the surroundings of T g .

Thin Solid Films

Abstract We apply the concept of point contact solar cells to a model system having 190 nm thick ... more Abstract We apply the concept of point contact solar cells to a model system having 190 nm thick Cu(In,Ga)Se 2 (CIGSe) films by using a SiO 2 back side film with periodic openings to the molybdenum layer being the electrical contact. The openings are plasma etched through a mask prepared by laser interference lithography. We find a maximum increase of the short circuit current density of 25% for a SiO 2 thickness of 60 nm and structure length of 1,1 μm. This gain is due to (1) coherent optical reflection, (2) light scattering enhancing the quantum efficiency at all wavelengths and (3) an anticipated wave guide effect which boosts the quantum efficiency particularly at long wavelength. The best efficient solar cells with 190 nm thick CIGSe has a conversion efficiency of 9% (fill factor = 70%) without anti-reflection coating. These experimental results can largely be confirmed by simulation.

Journal of Materials Research, 2001

Depth-sensing indentation tests can be used to estimate the Young's modulus, hardness, and ot... more Depth-sensing indentation tests can be used to estimate the Young's modulus, hardness, and other characteristics of material behavior. For many materials, the unloading segment of the load–depth curve contains only elastic recovery while the loading segment can contain elastic and plastic deformation. In this paper a new method is presented to determine the Young's modulus of a material from the loading segment of an indentation test. A depth-sensitive hardness tester was used with a load cell integrated into the closed-loop system. Defined mechanical oscillations with constant frequency were generated by adding a piezoelectric stack to the closed loop of the hardness measurement system. Thus the resonance response of the system was obtained, which includes information regarding the stiffness of the tested material. This new method was tested on two polymers and two glasses, an optical and a conventional one. The results obtained for the Young's modulus were in good agre...

Journal of Macromolecular Science, Part B, 1999

Abstract The present work demonstrates the possibility of determining and differentiating the ela... more Abstract The present work demonstrates the possibility of determining and differentiating the elastic and plastic material properties (like the Young's modulus, the ball hardness under load, and the plastic hardness) by applying the dynamic ball hardness indentation test. In Ref. 1, the elastic properties are neglected. Nevertheless, the obtained hardness number includes both elastic and plastic parts. Now, the continuous data acquisition allows the determination of the elastic modulus of the polymer and also its dynamic and thermal dependence. Furthermore, a way of specifying a plastic hardness number is shown. Using the approach of Oliver and Pharr [2] enables the separation of the real material property of plastic hardness. Topographic measurements allowed taking the wall formation during a hardness test into account while analyzing the impression. It turned out that the elastic modulus determined in the manner described is independent of the penetration rate, but decreases with increasing temperature ...

The Journal of Physical Chemistry Letters

Journal of Materials Chemistry A

We present the identification of crystalline phases by in situ X-ray diffraction during growth an... more We present the identification of crystalline phases by in situ X-ray diffraction during growth and monitor the phase evolution during subsequent thermal treatment of CH3NH3PbX3 (X = I, Br, Cl) perovskite thin films.

Light, Energy and the Environment, 2016

Applied Physics Letters, 2015

ABSTRACT In this work, glass/diffusion barrier/Mo/Cu(In,Ga)Se2 stacks with and without adding NaF... more ABSTRACT In this work, glass/diffusion barrier/Mo/Cu(In,Ga)Se2 stacks with and without adding NaF are investigated with the goal to determine the back surface recombination velocity. The absorber layers prepared by a three-stage co-evaporation process are characterized by time resolved photoluminescence (TRPL) and time of flight-secondary ion mass spectroscopy (TOF-SIMS). By comparison of experimental TRPL data with simulated TRPL transients calculated with Synopsys TCAD, Mo/Cu(In,Ga)Se2 interface recombination velocities for electrons of Sb,n≤1×102 cm/s (with NaF) and Sb,n≥1×105 cm/s (without NaF) are determined. SIMS analysis points towards differences in alkali metal concentrations at the back contact being the origin of different S b,n values. Our results shine light on the large spread of experimental S n values reported in the literature and reveal another hitherto unknown effect of alkali doping in Cu(In,Ga)Se2 semiconductors.

Applied Physics Letters, 2015

IFMBE Proceedings, 2009

ABSTRACT Radiation caries is stated after tumor therapeutic irradiation of the head-neck area. An... more ABSTRACT Radiation caries is stated after tumor therapeutic irradiation of the head-neck area. An expression of this is the disintegration up to a complete tooth loss. Different kinds of therapy aim to stop this disintegration. In this study, 3 different methods of tooth conservation using fluorides have been examined on their effect on the mechanical properties of the teeth. In the first method the remineralization took place after the cumulative dose of 60 Gy had been applied, in the second one, the remineralization took place before each dose und in the third one during the irradiation. Keywordstooth-radiation-nanoindentation-hardness-elastic modulus

Zeitschrift für Medizinische Physik, 2006

Tumor irradiation of the head-neck area is accompanied by the development of a so-called radiatio... more Tumor irradiation of the head-neck area is accompanied by the development of a so-called radiation caries in the treated patients. In spite of conservative therapeutic measures, the process results in tooth destruction. The present study investigated the effects of irradiation on the demineralization and remineralization of the dental tissue. For this purpose, retained third molars were prepared and assigned either to a test group, which was exposed to fractional irradiation up to 60 Gy, or to a non-irradiated control group. Irradiated and non-irradiated teeth were then demineralized using acidic hydroxyl-cellulose gel; afterwards the teeth were remineralized using either Bifluorid12 or elmex gelee. The nanoindentation technique was used to measure the mechanical properties, hardness and elasticity, of the teeth in each of the conditions. The values were compared to the non-irradiated control group. Irradiation decreased dramatically the mechanical parameters of enamel and dentine. In nonirradiated teeth, demineralization had nearly the same effects of irradiation on the mechanical properties. In irradiated teeth, the effects of demineralization were negligible in comparison to non-irradiated teeth. Remineralization with Bifluorid12 or elmex gelee led to a partial improvement of the mechanical properties of the teeth. The enamel was more positively affected by remineralization than the dentine.

European Journal of Orthodontics, 2008

The aim of this study was to compare the mechanical strength and microhardness of joints made by ... more The aim of this study was to compare the mechanical strength and microhardness of joints made by conventional brazing and tungsten inert gas (TIG) and laser welding. A standardized end-to-end joint confi guration of the orthodontic wire material in spring hard quality was used. The joints were made using fi ve different methods: brazing (soldering > 450°C) with universal silver solder, two TIG, and two laser welders. Laser parameters and welding conditions were used according to the manufacturers ' guidance. The tensile strengths were measured with a universal testing machine (Zwick 005). The microhardness measurements were carried out with a hardness tester (Zwick 3202). Data were analysed using one-way analysis of variance and Bonferroni's post hoc correction (P < 0.05). In all cases, brazing joints ruptured at low levels of tensile strength (198 ± 146 MPa). Signifi cant differences (P < 0.001) between brazing and TIG or laser welding were found. The highest means were observed for TIG welding (699-754 MPa). Laser welding showed a signifi cantly lower mean tensile strength (369-520 MPa) compared with TIG welding. Signifi cant differences (P < 0.001) were found between the original orthodontic wire and the mean microhardness at the centre of the welded area. The mean microhardness differed signifi cantly between brazing (1.99 GPa), TIG (2.22-2.39 GPa) and laser welding (2.21-2.68 GPa). For orthodontic purposes, laser and TIG welding are solder-free alternatives to joining metal. TIG welding with a lower investment cost is comparable with laser welding. However, while expensive, the laser technique is a sophisticated and simple method.

European Journal of Orthodontics, 2008

The aim of this study was to compare the mechanical strength and microhardness of joints made by ... more The aim of this study was to compare the mechanical strength and microhardness of joints made by conventional brazing and tungsten inert gas (TIG) and laser welding. A standardized end-to-end joint confi guration of the orthodontic wire material in spring hard quality was used. The joints were made using fi ve different methods: brazing (soldering > 450°C) with universal silver solder, two TIG, and two laser welders. Laser parameters and welding conditions were used according to the manufacturers ' guidance. The tensile strengths were measured with a universal testing machine (Zwick 005). The microhardness measurements were carried out with a hardness tester (Zwick 3202). Data were analysed using one-way analysis of variance and Bonferroni's post hoc correction (P < 0.05). In all cases, brazing joints ruptured at low levels of tensile strength (198 ± 146 MPa). Signifi cant differences (P < 0.001) between brazing and TIG or laser welding were found. The highest means were observed for TIG welding (699-754 MPa). Laser welding showed a signifi cantly lower mean tensile strength (369-520 MPa) compared with TIG welding. Signifi cant differences (P < 0.001) were found between the original orthodontic wire and the mean microhardness at the centre of the welded area. The mean microhardness differed signifi cantly between brazing (1.99 GPa), TIG (2.22-2.39 GPa) and laser welding (2.21-2.68 GPa). For orthodontic purposes, laser and TIG welding are solder-free alternatives to joining metal. TIG welding with a lower investment cost is comparable with laser welding. However, while expensive, the laser technique is a sophisticated and simple method.

Glass Science and Technology -Frankfurt am Main-

ABSTRACT

Glass Science and Technology -Frankfurt am Main-

ABSTRACT

Zeitschrift für Medizinische Physik, 2009

It is known that ionizing radiation is used in medicine for Roentgen diagnostics and for radiatio... more It is known that ionizing radiation is used in medicine for Roentgen diagnostics and for radiation therapy. The radiation interacts with matter, in particular with biological one, essentially by scattering, photoelectric effect, Compton effect and pair production. To what extent the biological material is changed thereby, depends on the type and the amount of radiation energy, on the dose and on the tissue constitution. In modern radiation therapy two different kinds of radiation are used: high energy X-rays and electron radiation. In the case of head-neck tumors the general practice is an irradiation with high energy X-rays with absorbed dose to water up to 70 Gy. Teeth destruction has been identified as a side effect during irradiation. In addition, damage to the salivary glands is often observed which leads to a decrease or even the complete loss of the salivary secretion (xerostomia). This study shows how the different energy and radiation types damage the tooth tissue. The effects of both, high X-ray energy and high energy electrons, on the mechanical properties hardness and elasticity of the human dental tissue are measured by the nanoindentation technique. We compare these results with the effect of the irradiation of low X-ray energy on the dental tissue.

Glass science and technology, 2001

Viscous flow is responsible for permanent deformation of glasses above the transformation tempera... more Viscous flow is responsible for permanent deformation of glasses above the transformation temperature (T g ). The results of macroscopic indentation experiments (maximum loading forces F max ≥2 N) with sharp indenters (Vickers or Berkovich pyramids) demonstrate this property by crack-free indents at T≥T g . But it is also possible to make crack-free indents at room temperature (RT), well below T g , if the load, the contact area and the deformation rate, respectively, are small enough, which is consistent with glass as a supercooled liquid but inconsistent with glass as a well-known ideally brittle material at RT. The mechanisms of this permanent deformation of glasses by indentation near RT have not been understood completely up to now. For the analysis of the macroscopic indentation experiments with Vickers pyramids and spherical indenters, respectively, a viscoelastic deformation behaviour is assumed for the complete temperature range from RT to T g . Therefore the rheological an...

Glass science and technology, 2005

Presented are results from uniaxial cylinder upsetting tests of sodium silicate glass at differen... more Presented are results from uniaxial cylinder upsetting tests of sodium silicate glass at different constant deformation rates each combined with relaxation experiments in the temperature range 480 to 580°C. Due to the complete stress relaxation to final load zero (vanished carrying capacity) also below glass transition temperature T g , it follows Maxwell behavior in principle. But the rheological analyses of loading and unloading experiments together show that only nonlinear Maxwell model approaches can adequately describe the deformation behavior of the glass in the surroundings of T g .

Thin Solid Films

Abstract We apply the concept of point contact solar cells to a model system having 190 nm thick ... more Abstract We apply the concept of point contact solar cells to a model system having 190 nm thick Cu(In,Ga)Se 2 (CIGSe) films by using a SiO 2 back side film with periodic openings to the molybdenum layer being the electrical contact. The openings are plasma etched through a mask prepared by laser interference lithography. We find a maximum increase of the short circuit current density of 25% for a SiO 2 thickness of 60 nm and structure length of 1,1 μm. This gain is due to (1) coherent optical reflection, (2) light scattering enhancing the quantum efficiency at all wavelengths and (3) an anticipated wave guide effect which boosts the quantum efficiency particularly at long wavelength. The best efficient solar cells with 190 nm thick CIGSe has a conversion efficiency of 9% (fill factor = 70%) without anti-reflection coating. These experimental results can largely be confirmed by simulation.

Journal of Materials Research, 2001

Depth-sensing indentation tests can be used to estimate the Young's modulus, hardness, and ot... more Depth-sensing indentation tests can be used to estimate the Young's modulus, hardness, and other characteristics of material behavior. For many materials, the unloading segment of the load–depth curve contains only elastic recovery while the loading segment can contain elastic and plastic deformation. In this paper a new method is presented to determine the Young's modulus of a material from the loading segment of an indentation test. A depth-sensitive hardness tester was used with a load cell integrated into the closed-loop system. Defined mechanical oscillations with constant frequency were generated by adding a piezoelectric stack to the closed loop of the hardness measurement system. Thus the resonance response of the system was obtained, which includes information regarding the stiffness of the tested material. This new method was tested on two polymers and two glasses, an optical and a conventional one. The results obtained for the Young's modulus were in good agre...

Journal of Macromolecular Science, Part B, 1999

Abstract The present work demonstrates the possibility of determining and differentiating the ela... more Abstract The present work demonstrates the possibility of determining and differentiating the elastic and plastic material properties (like the Young's modulus, the ball hardness under load, and the plastic hardness) by applying the dynamic ball hardness indentation test. In Ref. 1, the elastic properties are neglected. Nevertheless, the obtained hardness number includes both elastic and plastic parts. Now, the continuous data acquisition allows the determination of the elastic modulus of the polymer and also its dynamic and thermal dependence. Furthermore, a way of specifying a plastic hardness number is shown. Using the approach of Oliver and Pharr [2] enables the separation of the real material property of plastic hardness. Topographic measurements allowed taking the wall formation during a hardness test into account while analyzing the impression. It turned out that the elastic modulus determined in the manner described is independent of the penetration rate, but decreases with increasing temperature ...

The Journal of Physical Chemistry Letters

Journal of Materials Chemistry A

We present the identification of crystalline phases by in situ X-ray diffraction during growth an... more We present the identification of crystalline phases by in situ X-ray diffraction during growth and monitor the phase evolution during subsequent thermal treatment of CH3NH3PbX3 (X = I, Br, Cl) perovskite thin films.

Light, Energy and the Environment, 2016

Applied Physics Letters, 2015

ABSTRACT In this work, glass/diffusion barrier/Mo/Cu(In,Ga)Se2 stacks with and without adding NaF... more ABSTRACT In this work, glass/diffusion barrier/Mo/Cu(In,Ga)Se2 stacks with and without adding NaF are investigated with the goal to determine the back surface recombination velocity. The absorber layers prepared by a three-stage co-evaporation process are characterized by time resolved photoluminescence (TRPL) and time of flight-secondary ion mass spectroscopy (TOF-SIMS). By comparison of experimental TRPL data with simulated TRPL transients calculated with Synopsys TCAD, Mo/Cu(In,Ga)Se2 interface recombination velocities for electrons of Sb,n≤1×102 cm/s (with NaF) and Sb,n≥1×105 cm/s (without NaF) are determined. SIMS analysis points towards differences in alkali metal concentrations at the back contact being the origin of different S b,n values. Our results shine light on the large spread of experimental S n values reported in the literature and reveal another hitherto unknown effect of alkali doping in Cu(In,Ga)Se2 semiconductors.

Applied Physics Letters, 2015

IFMBE Proceedings, 2009

ABSTRACT Radiation caries is stated after tumor therapeutic irradiation of the head-neck area. An... more ABSTRACT Radiation caries is stated after tumor therapeutic irradiation of the head-neck area. An expression of this is the disintegration up to a complete tooth loss. Different kinds of therapy aim to stop this disintegration. In this study, 3 different methods of tooth conservation using fluorides have been examined on their effect on the mechanical properties of the teeth. In the first method the remineralization took place after the cumulative dose of 60 Gy had been applied, in the second one, the remineralization took place before each dose und in the third one during the irradiation. Keywordstooth-radiation-nanoindentation-hardness-elastic modulus

Zeitschrift für Medizinische Physik, 2006

Tumor irradiation of the head-neck area is accompanied by the development of a so-called radiatio... more Tumor irradiation of the head-neck area is accompanied by the development of a so-called radiation caries in the treated patients. In spite of conservative therapeutic measures, the process results in tooth destruction. The present study investigated the effects of irradiation on the demineralization and remineralization of the dental tissue. For this purpose, retained third molars were prepared and assigned either to a test group, which was exposed to fractional irradiation up to 60 Gy, or to a non-irradiated control group. Irradiated and non-irradiated teeth were then demineralized using acidic hydroxyl-cellulose gel; afterwards the teeth were remineralized using either Bifluorid12 or elmex gelee. The nanoindentation technique was used to measure the mechanical properties, hardness and elasticity, of the teeth in each of the conditions. The values were compared to the non-irradiated control group. Irradiation decreased dramatically the mechanical parameters of enamel and dentine. In nonirradiated teeth, demineralization had nearly the same effects of irradiation on the mechanical properties. In irradiated teeth, the effects of demineralization were negligible in comparison to non-irradiated teeth. Remineralization with Bifluorid12 or elmex gelee led to a partial improvement of the mechanical properties of the teeth. The enamel was more positively affected by remineralization than the dentine.

European Journal of Orthodontics, 2008

The aim of this study was to compare the mechanical strength and microhardness of joints made by ... more The aim of this study was to compare the mechanical strength and microhardness of joints made by conventional brazing and tungsten inert gas (TIG) and laser welding. A standardized end-to-end joint confi guration of the orthodontic wire material in spring hard quality was used. The joints were made using fi ve different methods: brazing (soldering > 450°C) with universal silver solder, two TIG, and two laser welders. Laser parameters and welding conditions were used according to the manufacturers ' guidance. The tensile strengths were measured with a universal testing machine (Zwick 005). The microhardness measurements were carried out with a hardness tester (Zwick 3202). Data were analysed using one-way analysis of variance and Bonferroni's post hoc correction (P < 0.05). In all cases, brazing joints ruptured at low levels of tensile strength (198 ± 146 MPa). Signifi cant differences (P < 0.001) between brazing and TIG or laser welding were found. The highest means were observed for TIG welding (699-754 MPa). Laser welding showed a signifi cantly lower mean tensile strength (369-520 MPa) compared with TIG welding. Signifi cant differences (P < 0.001) were found between the original orthodontic wire and the mean microhardness at the centre of the welded area. The mean microhardness differed signifi cantly between brazing (1.99 GPa), TIG (2.22-2.39 GPa) and laser welding (2.21-2.68 GPa). For orthodontic purposes, laser and TIG welding are solder-free alternatives to joining metal. TIG welding with a lower investment cost is comparable with laser welding. However, while expensive, the laser technique is a sophisticated and simple method.

European Journal of Orthodontics, 2008

The aim of this study was to compare the mechanical strength and microhardness of joints made by ... more The aim of this study was to compare the mechanical strength and microhardness of joints made by conventional brazing and tungsten inert gas (TIG) and laser welding. A standardized end-to-end joint confi guration of the orthodontic wire material in spring hard quality was used. The joints were made using fi ve different methods: brazing (soldering > 450°C) with universal silver solder, two TIG, and two laser welders. Laser parameters and welding conditions were used according to the manufacturers ' guidance. The tensile strengths were measured with a universal testing machine (Zwick 005). The microhardness measurements were carried out with a hardness tester (Zwick 3202). Data were analysed using one-way analysis of variance and Bonferroni's post hoc correction (P < 0.05). In all cases, brazing joints ruptured at low levels of tensile strength (198 ± 146 MPa). Signifi cant differences (P < 0.001) between brazing and TIG or laser welding were found. The highest means were observed for TIG welding (699-754 MPa). Laser welding showed a signifi cantly lower mean tensile strength (369-520 MPa) compared with TIG welding. Signifi cant differences (P < 0.001) were found between the original orthodontic wire and the mean microhardness at the centre of the welded area. The mean microhardness differed signifi cantly between brazing (1.99 GPa), TIG (2.22-2.39 GPa) and laser welding (2.21-2.68 GPa). For orthodontic purposes, laser and TIG welding are solder-free alternatives to joining metal. TIG welding with a lower investment cost is comparable with laser welding. However, while expensive, the laser technique is a sophisticated and simple method.

Glass Science and Technology -Frankfurt am Main-

ABSTRACT

Glass Science and Technology -Frankfurt am Main-

ABSTRACT