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Item type:Publication, Access status: with files , Freestanding membranes of titania nanorods, photocatalytically reduced graphene oxide, and silk fibroin: Tunable properties and electrostatic actuation(Wiley, 2025); ; ; ; In this study, the mechanical properties of freestanding membranes made of graphene oxide (GO), titania nanorods (TNRs), and silk fibroin (SF) are investigated and their application is demonstrated as electrostatically driven actuators. Using a stamping process, the membranes are transferred onto substrates with circular apertures or square cavities measuring ∼80 to 245 µm in diameter or edge length, respectively. Afterwards, the membranes are exposed to deep-UV (DUV) radiation in order to photocatalytically convert GO to reduced graphene oxide (rGO). Microbulge tests combined with atomic force microscopy (AFM) measurements reveal enhanced mechanical stability after the DUV treatment, as indicated by an increase of Young's modulus from ∼22 to ∼35 GPa. The toughness of the DUV-treated membranes is up to ∼1.25 MJ m−3, while their ultimate biaxial tensile stress and strain are in the range of ∼377 MPa and ∼0.68%, respectively. Further, by applying voltages of up to ±40 V the membranes are electrostatically actuated and deflected by up to ∼1.7 µm, as determined via in situ AFM measurements. A simple electrostatic model is presented that describes the deflection of the membrane as a function of the applied voltage very well.Publicationtype: Journal Article23 27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Freestanding Membranes of Titania Nanorods, Photocatalytically Reduced Graphene Oxide, and Silk Fibroin: Tunable Properties and Electrostatic Actuation(American Chemical Society (ACS), 2024-08-16); ; ; In this study, we investigate the mechanical properties of freestanding membranes made of graphene oxide (GO), titania nanorods (TNRs), and silk fibroin (SF) and demonstrate their application as electrostatically driven actuators. Using a stamping process, the membranes are transferred onto substrates with circular apertures or square cavities measuring ∼80 to 245 μm in diameter or edge length, respectively. Afterwards the membranes are exposed to deep-ultraviolet (DUV) radiation in order to photocatalytically convert GO to reduced graphene oxide (rGO). Microbulge tests combined with atomic force microscopy (AFM) measurements reveal enhanced mechanical stability after the DUV treatment, as indicated by an increase of Young’s modulus from ∼22 to ∼35 GPa. The toughness of the DUV-treated membranes is up to ∼1.25 MJm-3, while their ultimate biaxial tensile stress and strain are in the range of ∼377 MPa and ∼0.68 %, respectively. Further, by applying voltages of up to ±40 V the membranes are electrostatically actuated and deflected by up to ∼1.7 μm, as determined via in situ AFM measurements. A simple electrostatic model is presented that describes the deflection of the membrane as a function of the applied voltage very well.Publicationtype: Preprint20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , TXRF calibration samples fabricated by atomic layer deposition (ALD) and photolithography(2021-11); ; In this contribution, an innovative fabrication process for metallic trace element reference samples is introduced. These can be used to calibrate and maintain tools for the detection of those metallic trace elements like the total reflection x-ray fluorescence (TXRF) method which are used in semiconductor and microsystem fabrication facilities. The fabrication process is based on the complete covering of silicon wafers with atomic layer deposition (ALD) and structuring of this layer using photolithography. ALD is the deposition process of choice, since the self limiting behavior is well suited to cover the whole wafer with an minimal amount of material. Samples with metal amounts as low as 1010 atoms per cm2 could be achieved with that process.Publicationtype: Conference Paper70 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Cross-Linked Gold Nanoparticle Composite Membranes as Highly Sensitive Pressure Sensors(2020-10-01); ; ; ; In this article, highly sensitive differential pressure sensors based on free-standing membranes of cross-linked gold nanoparticles are demonstrated. The nanoparticle membranes are employed as both diaphragms and resistive transducers. The elasticity and the pronounced resistive strain sensitivity of these nanometer-thin composites enable the fabrication of sensors achieving high sensitivities exceeding 10−3 mbar−1 while maintaining an overall small membrane area. Furthermore, by combining micro-bulge tests with atomic force microscopy and in situ resistance measurements the membranes’ electromechanical responses are studied through precise observation of the concomitant changes of the membranes’ topography. The study demonstrates the high potential of free-standing nanoparticle composites for the fabrication of highly sensitive force and pressure sensors and introduces a unique and powerful method for the electromechanical investigation of these materials.Publicationtype: Journal Article87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Pressure Sensors: Cross‐Linked Gold Nanoparticle Composite Membranes as Highly Sensitive Pressure SensorsIn article number https://onlinelibrary.wiley.com/doi/10.1002/adfm.202003381 Hendrik Schlicke, Tobias Vossmeyer, and co‐workers present a pressure sensor based on a free‐standing gold nanoparticle membrane acting as a diaphragm and resistive transducer. The elastic membrane features strain‐sensitive conductivity that is governed by tunneling through the interparticle gaps. While measuring the resistance of the bulged membrane, the topography is scanned using an atomic force microscope to explore its electromechanical properties.Publicationtype: Journal Article88 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Elasticity of cross-linked titania nanocrystal assemblies probed by AFM-bulge tests(Multidisciplinary Digital Publishing Institute (MDPI), 2019-08-29); ; ; ; In order to enable advanced technological applications of nanocrystal composites, e.g., as functional coatings and layers in flexible optics and electronics, it is necessary to understand and control their mechanical properties. The objective of this study was to show how the elasticity of such composites depends on the nanocrystals’ dimensionality. To this end, thin films of titania nanodots (TNDs; diameter: ~3–7 nm), nanorods (TNRs; diameter: ~3.4 nm; length: ~29 nm), and nanoplates (TNPs; thickness: ~6 nm; edge length: ~34 nm) were assembled via layer-by-layer spin-coating. 1,12-dodecanedioic acid (12DAC) was added to cross-link the nanocrystals and to enable regular film deposition. The optical attenuation coefficients of the films were determined by ultraviolet/visible (UV/vis) absorbance measurements, revealing much lower values than those known for titania films prepared via chemical vapor deposition (CVD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed a homogeneous coverage of the substrates on the µm-scale but a highly disordered arrangement of nanocrystals on the nm-scale. X-ray photoelectron spectroscopy (XPS) analyses confirmed the presence of the 12DAC cross-linker after film fabrication. After transferring the films onto silicon substrates featuring circular apertures (diameter: 32–111 µm), freestanding membranes (thickness: 20–42 nm) were obtained and subjected to atomic force microscopy bulge tests (AFM-bulge tests). These measurements revealed increasing elastic moduli with increasing dimensionality of the nanocrystals, i.e., 2.57 ± 0.18 GPa for the TND films, 5.22 ± 0.39 GPa for the TNR films, and 7.21 ± 1.04 GPa for the TNP films.Publicationtype: Journal ArticleScopus© Citations 6 431 474 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Template based one-dimensional sensing nanostructures grown by atomic layer depositionIn this contribution, an innovative fabrication process for one-dimensional (1D) nanostructures for sensing purposes is introduced. The fabrication process is based on the complete covering of different templates by thin layers of active sensing material grown by atomic layer deposition (ALD). The geometry of the sensing structures is predetermined by the geometry of the patterns embedded in the respectively used templates. ALD is the deposition process of choice, since the resulting thin layers with good step coverage and high conformity are well suited for reproducing the high aspect ratios of those patterns.Publicationtype: Conference Paper29