With a rapid prototyping technique complex sensor structures in the nanometer range have been fab... more With a rapid prototyping technique complex sensor structures in the nanometer range have been fabricated within a single, maskless process step, using a focused ion beam (FIB) system. This paper shows that with exemplary structures such as complex channel junction structures, micromixers and cantilevers the potential to fabricate arbitrary 3D structures is confirmed. Results demonstrate the excellent suitability of FIB processing for tailoring microchannels and actuator structures for the desired properties. The FIB approach renders a powerful enhancement to existent fabrication technologies.
Recently focused-electron-beam-induced etching of silicon using molecular chlorine (Cl(2)-FEBIE) ... more Recently focused-electron-beam-induced etching of silicon using molecular chlorine (Cl(2)-FEBIE) has been developed as a reliable and reproducible process capable of damage-free, maskless and resistless removal of silicon. As any electron-beam-induced processing is considered non-destructive and implantation-free due to the absence of ion bombardment this approach is also a potential method for removing focused-ion-beam (FIB)-inflicted crystal damage and ion implantation. We show that Cl(2)-FEBIE is capable of removing FIB-induced amorphization and gallium ion implantation after processing of surfaces with a focused ion beam. TEM analysis proves that the method Cl(2)-FEBIE is non-destructive and therefore retains crystallinity. It is shown that Cl(2)-FEBIE of amorphous silicon when compared to crystalline silicon can be up to 25 times faster, depending on the degree of amorphization. Also, using this method it has become possible for the first time to directly investigate damage caused by FIB exposure in a top-down view utilizing a localized chemical reaction, i.e. without the need for TEM sample preparation. We show that gallium fluences above 4 × 10(15) cm(-2) result in altered material resulting from FIB-induced processes down to a depth of ∼ 250 nm. With increasing gallium fluences, due to a significant gallium concentration close beneath the surface, removal of the topmost layer by Cl(2)-FEBIE becomes difficult, indicating that gallium serves as an etch stop for Cl(2)-FEBIE.
For the first time focused electron beam induced etching of silicon using molecular chlorine has ... more For the first time focused electron beam induced etching of silicon using molecular chlorine has been developed as reliable and reproducible process. Around the etched pits the etching process was found to be accompanied by carbonaceous deposition from hydrocarbon contamination of the residual gas typically present in a scanning electron microscope (SEM). This work will focus on the effect of residual gas deposition on this silicon etch process using chlorine. The process mechanisms for residual gas deposition (in the absence of chlorine) as well as the silicon etch process in the presence of chlorine are discussed in terms of precursor replenishment of the sample surface and precursor delivery to the processed area. The formation of carbonaceous deposits from undesired contaminants can block the surface from an etch process. Especially for low beam currents this problem was encountered. Results suggest that the presence of chlorine when processed with a high electron beam current dominates over residual gas deposition. On the other hand, the etch-inhibiting effect of an increased level of SEM chamber contamination (resulting in increased residual gas deposition rates) is shown.
This work describes a rapid fabrication approach of thin silicon oxide films on confined areas by... more This work describes a rapid fabrication approach of thin silicon oxide films on confined areas by electron-beam-induced deposition. This maskless direct-write process utilizes a localized chemical vapor deposition (CVD) on specific areas utilizing a focused electron beam. The deposition from siloxane vapor in the presence of oxygen is initiated by the energy of an electron beam of 1nm diameter. By scanning the beam, thin films with arbitrary geometries and three-dimensional structures were deposited. In contrast to blanket deposition with conventional methods such as thermal CVD or plasma-enhanced CVD, the lateral confined layers can be fabricated at room temperature. With a maskless process, the final structure is fabricated within a single process step. The process was optimized towards a high deposition rate and high material purity. The influence of process parameters on the deposition efficiency is discussed. A characterization of the chemical composition and of the surface roughness was performed with auger electron spectroscopy, energy-dispersive x-ray, and atomic force microscopy, respectively. The optical properties were investigated by transmission measurement at 248nm. The correlation to processing conditions and the growth mechanism induced by the electron beam is discussed. This work illustrates the flexibility of this maskless method and the potential to control material properties via the process parameters. The fabrication of exemplary structures such as three-dimensional silicon oxide pillars and transparent films illustrates the application potential of this versatile direct-write method.
In vitro diagnostic devices have highly esteemed platforms for toxicological testing, drug screen... more In vitro diagnostic devices have highly esteemed platforms for toxicological testing, drug screening and even for theranostics. An extremely promising device type are microstructured devices, often referred to as biochips, that can be coupled with in vitro cell cultures. Employing microfluidic structures devices such as cell-chips and organ-on-a-chip devices have been developed to mimic the microenvironment of the human body. By implementing microelectrodes on the chip it is facile to utilize the benefits of microelectronics - the label-free, non-destructive, permanent real-time measurement of cellular processes. With electretic cells the action potential of cells can be directly measured, while other non-electrically cells can be measureds via their impedance. We will present devices on both concepts from our research. We will present sophisticated biomedical devices, were used to record the electrophysiological activity the neurite part of nerve cells of in real-time. With an axon isolation device a delicate microfluidics system is combined with microelectrodes inside of microchannels just large enough for axonal and dendritic structures. Also the biocompatibility of electrode materials is essential, and the relevance of cyclic voltammetry for checking the safe voltage range of microelecrtrodes will be explained with practical examples. Fabrication routes, benefits and limitations of microelectrode arrays. interdigitated electrode sensors and even 3D nanoelectrodedes will be discussed. An outlook on future devices featuring arrays 3D nanoelectrodes and microstructured guidance structures will be given.
We have used a focused electron beam and chlorine injection in order to etch nanopits on predefin... more We have used a focused electron beam and chlorine injection in order to etch nanopits on predefined positions of a Si sample. With other methods it is often difficult to get exactly positioned nanopits. With this maskless, resistless direct-write approach nanopits with a diameter below 100 nm has been fabricated. We will report on the optimum processing conditions and present different geometries fabricated wit this technique. Finally, application examples will be given.
Electrical impedance spectroscopy is a soft analysis methods for living cell cultures, that is no... more Electrical impedance spectroscopy is a soft analysis methods for living cell cultures, that is non-destructive for cell cultures and allows continuous measurement of cellular changed in real-time. In this work we report on an in vitro impedimetric sensors that measures the confluence and the density of human epithelial cell layers. A mechanically inflicted damage in a confluent cell layer leads to a reduction of the impedance, while the healing of the cell layer was closing the holes and increased impedance. The entire healing process could be tracked in real time via the impedance. To advance existing in vitro cell impedance spectroscopy we have not only used opwn metal electrodes but also electrically insulated interdigitated microelectrodes. The influence of the insulation on sensor performance is experimentally and theoretically analyzed A circuit model was established. In a comparison between open (not passivated) electrodes was made. The best setup for sensitivity and repeatability, which are crucial parameters for cell analysis, will be presented. The presented novel sensor design allows for the integration of alternative electrode materials such as aluminum. This enables cost-effective fabrication of large-volume sensor arrays.
With nonvolatile NAND flash memory becoming the dominant memory type the former champion for mass... more With nonvolatile NAND flash memory becoming the dominant memory type the former champion for mass data storage – magnetic memory – has now become a niche player. This is – at least to some extent – unjustified, as magnetic data storage has still its advantages such as radiation-hardness, and long data storage time. In this work we celebrate a renaissance of magnetic data storage with a new concept that allows not only storing of information but also data processing with nanomagnets. We use focused electron beam induced deposition of single domain nanomagnets to fabricate arrays of magnetic nanowires and magnetic nanopillars. If the single nanomagnets are in close vicinity, then the stray fields allow to influence neighboring nanomagnets. With a majority gate such a nanomagnet assembly can even perform logical calculations. In this work we will present the fabrication process for such nanomagnetic devices, characterize their magnetic properties by magnetic force microscop, and design and fabricate nanomagnet arrays. With this dual functionality as memory and as logic unit these directly-written nanomagnet devices promise a promising future potential. Further applications of advanced device structures based on single domain nanomagnetswill be discussed. We will report on the optimization of the device fabrication process and chemical and structural analysis of nanomagnets. The functional characteristics of these hybrid devices will be described and future system applications will be discussed. Figure 1
We present a microfluidic device that has been designed to study the neuroregeneration of nerve t... more We present a microfluidic device that has been designed to study the neuroregeneration of nerve tissue after injury. Reconnection between neurons of the peripheral nervous system after injury or dissection is essential for regaining the full motoric and sensory capabilities. The neuroregeneration of damaged axons and the functional reconnection to a target cell is a complex processes, where (1) chemical guidance and (2) topographic guidance of the neurite growth cone play a crucial role. To identify new chemical guidance substances and to understand how geometry guides neurite growth, we have developed a microfluidic in-vitro system for studying neuronal cell cultures. The microchannels act as artificial guidance conduits for the growth of nerve processes (dendrites, axons), also named neurites in the following text. The microstructured system consists of a microelectrode array with sub-10 µm microelectrodes for recording neuronal signals plus a microfluidic attachement. This microfluidic attachment has 2 macrochannels with a width above 100 µm that can accommodate entire cells. Both macrochannels are connected by up to 60 microchannels which are 100 to 500 µm long but only 10 µm wide and 2 µm high, so that cell somata cannot enter the microchannels while cell processes (axons, dendrites) are small enough to enter the channel. A neuronal culture of mouse superior cervical ganglion (SCG) is seeded in the source macrochannel, while the target macrochannel stays cell-free and is filled cell medium with neurotrophic factors added. These soluble neurotrophic factors act as chemical guidance cues for the neurites and have been under debate as enhancers of axon regeneration. In our microfluidic system the neurites can reach the target macrochannel by growing through the small microchannels that are too small for entire cell somata. This topographic guidance provided by the microchannels mimics’ topographic guidance of the endoneurial channel formed by Schwann cells for a reconnecting neuron. We will present the design considerations as well as the actual fabrication of this microfluidic system on the microelectrode system. Simulations on the diffusion of chemical entities through the microchannels will be presented. Finally, images of the neurites grown through the microchannels will be shown and prove the research concept. Neurotrophic factors are also under debate for accelerating the functional recovery, i.e. the recovery of the neuron to propagate action potentials along the neurite. With our microfluidic setup the microelectrodes of the microelectrode array have been aligned such that every microchannel contains at least one (up to four) microelectrodes. By implementing microelectrodes inside of the microfluidic channels also the electrophysiological activity of the reconnecting neurites can be monitored. This electrical activity of neurons is a measure for the health status of a neuron. With the microelectrodes providing electrochemical sensor functionality to the microfluidic channels, this important question could be answered. We will present the effect, that various gradients of neurotrophic factors have on the growth and electrical activity of growing neurons. Finally, a recommendation will be given on the optimum concentration for the addition of nerve growth factor in order to promote a faster growth of electrophysiologicallly active neurites. The potential to use this microfluidic platform for identifying new nerve growth promotors and for quantifying the effects will be discussed. Concepts for advancing this microfluidic system further as cell culture reactors as well as for other interdisciplinary areas including neurobiological and medical applications will be presented. Figure 1
Magnetic nanomaterials play important roles in information storage, sensors, and microelectromech... more Magnetic nanomaterials play important roles in information storage, sensors, and microelectromechanical systems (MEMS). Many of these applications require the magnetic material to be in a specific shape and at specific positions, so that stochastically distributed magnetic nanostructures (e.g. nanodots) cannot fulfill the requirements for an application. The classical patterning approach is based on the top-down patterning of magnetic layers using a lithographic photoresist to generate the pattern. In this work we will present a direct-write deposition that is capable to fabricate individual nanomagnets or designed nanomagnet assemblies without a photomask or without a photoresist. Also deposition of nanomagnets on non-planar structures and even deposition of 3-dimensional nanomagnets is feasible. This work reports on this new fabrication approach and its application for logic computer devices. Direct writing of iron and cobalt structures has been developed. This new process was performed by locally confined chemical vapor deposition initiated by a focused electron beam of a scanning electron microscope. Iron carbonyl or cobalt carbonyl were injected via a nozzle to the sample surface and where then decomposed by the energy of a 5 keV electron beam. By deliberately scanning the electron beam with a pattern generator also complex patterns could be deposited as lateral – but also as 3-diemnsional structures. This work addresses the chemistry of the deposition reaction and analysis of the resultingmaterial purity, the physics of magnetic shape anisotropy of nanomagnets, and the engineering of magnetic coupling between nanomagnets. These fundamental insights provide an understanding of the correlations between deposition parameters, film composition, and structure. Nanomagnets of various geometries, including circular, ellipsoidal, triangular, square and hexagonal have been fabricated and allowed to design a shape-controlled domain distribution. Finally we will present and device based on nanomagnets that cannot only store, but also perform logical operations. Investigation of these structures was performed by magnetic force microscopy. Moving towards an , complex assemblies of magnetic nanowires with 100 nm length, 50 nm width and a custom designed height (that could be adapted by a longer electron exposure) have been fabricated. The coupling between these nanomagnets within an array was investigated and as an application nanomagnet logic (NML) devices were fabricated. Using nanomagnerts as building blocks nanomagnet-logic gates were fabricated that can perform logic operations without electronic charges but just by magnetic coupling between neighboring nanomagnets. We also address specific issues of NML such as fan outs, majority gates. Our ultimate progress was to include perpendicular magnetic nanopillars and thus to create for the first time 3-dimensional NML gates. Direct writing has several advances over the conventional lithography base approaches. It has been shown that this novel direct-write approach is capable of fabricating functional nanomagnet logic as shown in the schematic illustration in Fig 1. Figure 1
Structural anti-reflective coating and bactericidal surfaces, as well as many other effects, rely... more Structural anti-reflective coating and bactericidal surfaces, as well as many other effects, rely on high-aspect-ratio (HAR) micro- and nanostructures, and thus, are of great interest for a wide range of applications. To date, there is no widespread fabrication of dense or isolated HAR nanopillars based on UV nanoimprint lithography (UV-NIL). In addition, little research on fabricating isolated HAR nanopillars via UV-NIL exists. In this work, we investigated the mastering and replication of HAR nanopillars with the smallest possible diameters for dense and isolated arrangements. For this purpose, a UV-based nanoimprint lithography process was developed. Stability investigations with capillary forces were performed and compared with simulations. Finally, strategies were developed in order to increase the stability of imprinted nanopillars or to convert them into nanoelectrodes. We present UV-NIL replication of pillars with aspect ratios reaching up to 15 with tip diameters down to 35...
In this work, a novel chemical composition characterization method of direct-write focused electr... more In this work, a novel chemical composition characterization method of direct-write focused electron beam-induced deposition (FEBID) gold nanostructures is presented. The reliable determination of the chemical content for nanostructures has been challenging due to its limited interaction volume. We hereby propose an alternative technique for measuring the chemical composition of nanostructures with limited volume. By measuring the differences in the optical absorption of the nanostructure due to the differences in the chemical composition with the resonance frequency detuning of a nanomechanical resonator and the assistance of analytical optical modeling, we demonstrate the possibility of characterizing the carbon content in the (FEBID) gold nanostructures. From our characterization method, the post-purification process with water successfully reduced the carbon content from ∼65 at. % to ∼20 at. %. This method presents a new technique for the chemical analysis of nanostructures.
With a rapid prototyping technique complex sensor structures in the nanometer range have been fab... more With a rapid prototyping technique complex sensor structures in the nanometer range have been fabricated within a single, maskless process step, using a focused ion beam (FIB) system. This paper shows that with exemplary structures such as complex channel junction structures, micromixers and cantilevers the potential to fabricate arbitrary 3D structures is confirmed. Results demonstrate the excellent suitability of FIB processing for tailoring microchannels and actuator structures for the desired properties. The FIB approach renders a powerful enhancement to existent fabrication technologies.
Recently focused-electron-beam-induced etching of silicon using molecular chlorine (Cl(2)-FEBIE) ... more Recently focused-electron-beam-induced etching of silicon using molecular chlorine (Cl(2)-FEBIE) has been developed as a reliable and reproducible process capable of damage-free, maskless and resistless removal of silicon. As any electron-beam-induced processing is considered non-destructive and implantation-free due to the absence of ion bombardment this approach is also a potential method for removing focused-ion-beam (FIB)-inflicted crystal damage and ion implantation. We show that Cl(2)-FEBIE is capable of removing FIB-induced amorphization and gallium ion implantation after processing of surfaces with a focused ion beam. TEM analysis proves that the method Cl(2)-FEBIE is non-destructive and therefore retains crystallinity. It is shown that Cl(2)-FEBIE of amorphous silicon when compared to crystalline silicon can be up to 25 times faster, depending on the degree of amorphization. Also, using this method it has become possible for the first time to directly investigate damage caused by FIB exposure in a top-down view utilizing a localized chemical reaction, i.e. without the need for TEM sample preparation. We show that gallium fluences above 4 × 10(15) cm(-2) result in altered material resulting from FIB-induced processes down to a depth of ∼ 250 nm. With increasing gallium fluences, due to a significant gallium concentration close beneath the surface, removal of the topmost layer by Cl(2)-FEBIE becomes difficult, indicating that gallium serves as an etch stop for Cl(2)-FEBIE.
For the first time focused electron beam induced etching of silicon using molecular chlorine has ... more For the first time focused electron beam induced etching of silicon using molecular chlorine has been developed as reliable and reproducible process. Around the etched pits the etching process was found to be accompanied by carbonaceous deposition from hydrocarbon contamination of the residual gas typically present in a scanning electron microscope (SEM). This work will focus on the effect of residual gas deposition on this silicon etch process using chlorine. The process mechanisms for residual gas deposition (in the absence of chlorine) as well as the silicon etch process in the presence of chlorine are discussed in terms of precursor replenishment of the sample surface and precursor delivery to the processed area. The formation of carbonaceous deposits from undesired contaminants can block the surface from an etch process. Especially for low beam currents this problem was encountered. Results suggest that the presence of chlorine when processed with a high electron beam current dominates over residual gas deposition. On the other hand, the etch-inhibiting effect of an increased level of SEM chamber contamination (resulting in increased residual gas deposition rates) is shown.
This work describes a rapid fabrication approach of thin silicon oxide films on confined areas by... more This work describes a rapid fabrication approach of thin silicon oxide films on confined areas by electron-beam-induced deposition. This maskless direct-write process utilizes a localized chemical vapor deposition (CVD) on specific areas utilizing a focused electron beam. The deposition from siloxane vapor in the presence of oxygen is initiated by the energy of an electron beam of 1nm diameter. By scanning the beam, thin films with arbitrary geometries and three-dimensional structures were deposited. In contrast to blanket deposition with conventional methods such as thermal CVD or plasma-enhanced CVD, the lateral confined layers can be fabricated at room temperature. With a maskless process, the final structure is fabricated within a single process step. The process was optimized towards a high deposition rate and high material purity. The influence of process parameters on the deposition efficiency is discussed. A characterization of the chemical composition and of the surface roughness was performed with auger electron spectroscopy, energy-dispersive x-ray, and atomic force microscopy, respectively. The optical properties were investigated by transmission measurement at 248nm. The correlation to processing conditions and the growth mechanism induced by the electron beam is discussed. This work illustrates the flexibility of this maskless method and the potential to control material properties via the process parameters. The fabrication of exemplary structures such as three-dimensional silicon oxide pillars and transparent films illustrates the application potential of this versatile direct-write method.
In vitro diagnostic devices have highly esteemed platforms for toxicological testing, drug screen... more In vitro diagnostic devices have highly esteemed platforms for toxicological testing, drug screening and even for theranostics. An extremely promising device type are microstructured devices, often referred to as biochips, that can be coupled with in vitro cell cultures. Employing microfluidic structures devices such as cell-chips and organ-on-a-chip devices have been developed to mimic the microenvironment of the human body. By implementing microelectrodes on the chip it is facile to utilize the benefits of microelectronics - the label-free, non-destructive, permanent real-time measurement of cellular processes. With electretic cells the action potential of cells can be directly measured, while other non-electrically cells can be measureds via their impedance. We will present devices on both concepts from our research. We will present sophisticated biomedical devices, were used to record the electrophysiological activity the neurite part of nerve cells of in real-time. With an axon isolation device a delicate microfluidics system is combined with microelectrodes inside of microchannels just large enough for axonal and dendritic structures. Also the biocompatibility of electrode materials is essential, and the relevance of cyclic voltammetry for checking the safe voltage range of microelecrtrodes will be explained with practical examples. Fabrication routes, benefits and limitations of microelectrode arrays. interdigitated electrode sensors and even 3D nanoelectrodedes will be discussed. An outlook on future devices featuring arrays 3D nanoelectrodes and microstructured guidance structures will be given.
We have used a focused electron beam and chlorine injection in order to etch nanopits on predefin... more We have used a focused electron beam and chlorine injection in order to etch nanopits on predefined positions of a Si sample. With other methods it is often difficult to get exactly positioned nanopits. With this maskless, resistless direct-write approach nanopits with a diameter below 100 nm has been fabricated. We will report on the optimum processing conditions and present different geometries fabricated wit this technique. Finally, application examples will be given.
Electrical impedance spectroscopy is a soft analysis methods for living cell cultures, that is no... more Electrical impedance spectroscopy is a soft analysis methods for living cell cultures, that is non-destructive for cell cultures and allows continuous measurement of cellular changed in real-time. In this work we report on an in vitro impedimetric sensors that measures the confluence and the density of human epithelial cell layers. A mechanically inflicted damage in a confluent cell layer leads to a reduction of the impedance, while the healing of the cell layer was closing the holes and increased impedance. The entire healing process could be tracked in real time via the impedance. To advance existing in vitro cell impedance spectroscopy we have not only used opwn metal electrodes but also electrically insulated interdigitated microelectrodes. The influence of the insulation on sensor performance is experimentally and theoretically analyzed A circuit model was established. In a comparison between open (not passivated) electrodes was made. The best setup for sensitivity and repeatability, which are crucial parameters for cell analysis, will be presented. The presented novel sensor design allows for the integration of alternative electrode materials such as aluminum. This enables cost-effective fabrication of large-volume sensor arrays.
With nonvolatile NAND flash memory becoming the dominant memory type the former champion for mass... more With nonvolatile NAND flash memory becoming the dominant memory type the former champion for mass data storage – magnetic memory – has now become a niche player. This is – at least to some extent – unjustified, as magnetic data storage has still its advantages such as radiation-hardness, and long data storage time. In this work we celebrate a renaissance of magnetic data storage with a new concept that allows not only storing of information but also data processing with nanomagnets. We use focused electron beam induced deposition of single domain nanomagnets to fabricate arrays of magnetic nanowires and magnetic nanopillars. If the single nanomagnets are in close vicinity, then the stray fields allow to influence neighboring nanomagnets. With a majority gate such a nanomagnet assembly can even perform logical calculations. In this work we will present the fabrication process for such nanomagnetic devices, characterize their magnetic properties by magnetic force microscop, and design and fabricate nanomagnet arrays. With this dual functionality as memory and as logic unit these directly-written nanomagnet devices promise a promising future potential. Further applications of advanced device structures based on single domain nanomagnetswill be discussed. We will report on the optimization of the device fabrication process and chemical and structural analysis of nanomagnets. The functional characteristics of these hybrid devices will be described and future system applications will be discussed. Figure 1
We present a microfluidic device that has been designed to study the neuroregeneration of nerve t... more We present a microfluidic device that has been designed to study the neuroregeneration of nerve tissue after injury. Reconnection between neurons of the peripheral nervous system after injury or dissection is essential for regaining the full motoric and sensory capabilities. The neuroregeneration of damaged axons and the functional reconnection to a target cell is a complex processes, where (1) chemical guidance and (2) topographic guidance of the neurite growth cone play a crucial role. To identify new chemical guidance substances and to understand how geometry guides neurite growth, we have developed a microfluidic in-vitro system for studying neuronal cell cultures. The microchannels act as artificial guidance conduits for the growth of nerve processes (dendrites, axons), also named neurites in the following text. The microstructured system consists of a microelectrode array with sub-10 µm microelectrodes for recording neuronal signals plus a microfluidic attachement. This microfluidic attachment has 2 macrochannels with a width above 100 µm that can accommodate entire cells. Both macrochannels are connected by up to 60 microchannels which are 100 to 500 µm long but only 10 µm wide and 2 µm high, so that cell somata cannot enter the microchannels while cell processes (axons, dendrites) are small enough to enter the channel. A neuronal culture of mouse superior cervical ganglion (SCG) is seeded in the source macrochannel, while the target macrochannel stays cell-free and is filled cell medium with neurotrophic factors added. These soluble neurotrophic factors act as chemical guidance cues for the neurites and have been under debate as enhancers of axon regeneration. In our microfluidic system the neurites can reach the target macrochannel by growing through the small microchannels that are too small for entire cell somata. This topographic guidance provided by the microchannels mimics’ topographic guidance of the endoneurial channel formed by Schwann cells for a reconnecting neuron. We will present the design considerations as well as the actual fabrication of this microfluidic system on the microelectrode system. Simulations on the diffusion of chemical entities through the microchannels will be presented. Finally, images of the neurites grown through the microchannels will be shown and prove the research concept. Neurotrophic factors are also under debate for accelerating the functional recovery, i.e. the recovery of the neuron to propagate action potentials along the neurite. With our microfluidic setup the microelectrodes of the microelectrode array have been aligned such that every microchannel contains at least one (up to four) microelectrodes. By implementing microelectrodes inside of the microfluidic channels also the electrophysiological activity of the reconnecting neurites can be monitored. This electrical activity of neurons is a measure for the health status of a neuron. With the microelectrodes providing electrochemical sensor functionality to the microfluidic channels, this important question could be answered. We will present the effect, that various gradients of neurotrophic factors have on the growth and electrical activity of growing neurons. Finally, a recommendation will be given on the optimum concentration for the addition of nerve growth factor in order to promote a faster growth of electrophysiologicallly active neurites. The potential to use this microfluidic platform for identifying new nerve growth promotors and for quantifying the effects will be discussed. Concepts for advancing this microfluidic system further as cell culture reactors as well as for other interdisciplinary areas including neurobiological and medical applications will be presented. Figure 1
Magnetic nanomaterials play important roles in information storage, sensors, and microelectromech... more Magnetic nanomaterials play important roles in information storage, sensors, and microelectromechanical systems (MEMS). Many of these applications require the magnetic material to be in a specific shape and at specific positions, so that stochastically distributed magnetic nanostructures (e.g. nanodots) cannot fulfill the requirements for an application. The classical patterning approach is based on the top-down patterning of magnetic layers using a lithographic photoresist to generate the pattern. In this work we will present a direct-write deposition that is capable to fabricate individual nanomagnets or designed nanomagnet assemblies without a photomask or without a photoresist. Also deposition of nanomagnets on non-planar structures and even deposition of 3-dimensional nanomagnets is feasible. This work reports on this new fabrication approach and its application for logic computer devices. Direct writing of iron and cobalt structures has been developed. This new process was performed by locally confined chemical vapor deposition initiated by a focused electron beam of a scanning electron microscope. Iron carbonyl or cobalt carbonyl were injected via a nozzle to the sample surface and where then decomposed by the energy of a 5 keV electron beam. By deliberately scanning the electron beam with a pattern generator also complex patterns could be deposited as lateral – but also as 3-diemnsional structures. This work addresses the chemistry of the deposition reaction and analysis of the resultingmaterial purity, the physics of magnetic shape anisotropy of nanomagnets, and the engineering of magnetic coupling between nanomagnets. These fundamental insights provide an understanding of the correlations between deposition parameters, film composition, and structure. Nanomagnets of various geometries, including circular, ellipsoidal, triangular, square and hexagonal have been fabricated and allowed to design a shape-controlled domain distribution. Finally we will present and device based on nanomagnets that cannot only store, but also perform logical operations. Investigation of these structures was performed by magnetic force microscopy. Moving towards an , complex assemblies of magnetic nanowires with 100 nm length, 50 nm width and a custom designed height (that could be adapted by a longer electron exposure) have been fabricated. The coupling between these nanomagnets within an array was investigated and as an application nanomagnet logic (NML) devices were fabricated. Using nanomagnerts as building blocks nanomagnet-logic gates were fabricated that can perform logic operations without electronic charges but just by magnetic coupling between neighboring nanomagnets. We also address specific issues of NML such as fan outs, majority gates. Our ultimate progress was to include perpendicular magnetic nanopillars and thus to create for the first time 3-dimensional NML gates. Direct writing has several advances over the conventional lithography base approaches. It has been shown that this novel direct-write approach is capable of fabricating functional nanomagnet logic as shown in the schematic illustration in Fig 1. Figure 1
Structural anti-reflective coating and bactericidal surfaces, as well as many other effects, rely... more Structural anti-reflective coating and bactericidal surfaces, as well as many other effects, rely on high-aspect-ratio (HAR) micro- and nanostructures, and thus, are of great interest for a wide range of applications. To date, there is no widespread fabrication of dense or isolated HAR nanopillars based on UV nanoimprint lithography (UV-NIL). In addition, little research on fabricating isolated HAR nanopillars via UV-NIL exists. In this work, we investigated the mastering and replication of HAR nanopillars with the smallest possible diameters for dense and isolated arrangements. For this purpose, a UV-based nanoimprint lithography process was developed. Stability investigations with capillary forces were performed and compared with simulations. Finally, strategies were developed in order to increase the stability of imprinted nanopillars or to convert them into nanoelectrodes. We present UV-NIL replication of pillars with aspect ratios reaching up to 15 with tip diameters down to 35...
In this work, a novel chemical composition characterization method of direct-write focused electr... more In this work, a novel chemical composition characterization method of direct-write focused electron beam-induced deposition (FEBID) gold nanostructures is presented. The reliable determination of the chemical content for nanostructures has been challenging due to its limited interaction volume. We hereby propose an alternative technique for measuring the chemical composition of nanostructures with limited volume. By measuring the differences in the optical absorption of the nanostructure due to the differences in the chemical composition with the resonance frequency detuning of a nanomechanical resonator and the assistance of analytical optical modeling, we demonstrate the possibility of characterizing the carbon content in the (FEBID) gold nanostructures. From our characterization method, the post-purification process with water successfully reduced the carbon content from ∼65 at. % to ∼20 at. %. This method presents a new technique for the chemical analysis of nanostructures.
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