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Optical refractive index (RI) sensors exploiting selective co-integration of plasmonics with silicon photonics in Lab-on-achip configurations are expected to disrupt Point-of-Care (POC) diagnostics, delivering performance and economic breakthroughs. Propagating surface-plasmon-polariton modes offer superior sensitivity due to their extreme overlap with the surrounding medium. In parallel, low-loss photonics act as the hosting platform with which the plasmonic losses can be sustained while allowing for multiplexed layouts via in-plane SPP excitation schemes. However, merging plasmonics with silicon photonics in a cost-effective manner, requires a truly CMOS-compatible manufacturing process. Herein, we demonstrate experimentally, the highest bulk-sensitivity among all the plasmo-photonic interferometric RI sensors, while taking the leap forward in the development of a CMOS-manufactured plasmo-photonic sensing platform merging Si3N4 photonics and aluminum plasmonics. The proposed structure relies on a butt-coupled interface between Si3N4 waveguides and a 70 μm long plasmonic stripe, deployed in one branch of a Mach-Zehnder Interferometer (MZI) serving as the sensing transducer that detects local changes in the refractive index. The lower MZI arm (reference arm) exploits the low-loss Si3N4 platform to deploy a MZI-based variable optical attenuator followed by a thermo-optic phase shifter to optimize the sensor performance achieving resonance extinction ratio values at the MZI output of more than 35 dB. Experimental evaluation of a gold-based sensor revealed a bulk refractive index sensitivity of 1930 nm/RIU. In addition, we experimentally demonstrate that the proposed plasmo-photonic waveguide platform can migrate from gold (Au) to Aluminum (Al), demonstrating the first step towards a fully CMOS compatible plasmo-photonic interferometric sensor.

We demonstrate a CMOS compatible interferometric plasmo-photonic sensor exploiting SisN4 photonic and aluminum (Al) plasmonic stripe waveguides. Experimental evaluation revealed bulk sensitivity of 4764 nm/RIU, holding promise for ultra-sensitive and low cost sensing devices.

Optical refractive-index sensors exploiting selective co-integration of plasmonics with silicon photonics has emerged as an attractive technology for biosensing applications that can unleash unprecedented performance breakthroughs that reaps the benefits of both technologies. However, towards this direction, a major challenge remains their integration using exclusively CMOS-compatible materials. In this context, herein, we demonstrate, for the first time to our knowledge, a CMOS-compatible plasmo-photonic Mach-Zehnder-interferometer (MZI) based on aluminum and Si3N4 waveguides, exhibiting record-high bulk sensitivity of 4764 nm/RIU with clear potential to scale up the bulk sensitivity values by properly engineering the design parameters of the MZI. The proposed sensor is composed of Si3N4 waveguides butt-coupled with an aluminum stripe in one branch to realize the sensing transducer. The reference arm is built by Si3N4 waveguides, incorporating a thermo-optic phase shifter followed by an MZI-based variable optical attenuation stage to maximize extinction ratio up to 38 dB, hence optimizing the overall sensing performance. The proposed sensor exhibits the highest bulk sensitivity among all plasmo-photonic counterparts, while complying with CMOS manufacturing standards, enabling volume manufacturing.

Positive effects of exercise on cancer prevention and progression have been proposed to be mediated by stimulating natural killer (NK) cells. Because NK cell receptors are regulated by epigenetic modifications, we investigated whether acute aerobic exercise and training change promoter DNA methylation and gene expression of the activating KIR2DS4 and the inhibiting KIR3DL1 gene. Sixteen healthy women (50–60 years) performed a graded exercise test (GXT) and were randomized into either a passive control group or an intervention group performing a four-week endurance exercise intervention. Blood samples (pre-, post-GXT and post-training) were used for isolation of DNA/RNA of NK cells to assess DNA promoter methylation by targeted deep-amplicon sequencing and gene expression by qRT-PCR. Potential changes in NK cell subsets were determined by flow cytometry. Acute and chronic exercise did not provoke significant alterations of NK cell proportions. Promoter methylation decreased and gene expression increased for KIR2DS4 after acute exercise. A high gene expression correlated with a low methylation of CpGs that were altered by acute exercise. Chronic exercise resulted in a minor decrease of DNA methylation and did not alter gene expression. Acute exercise provokes epigenetic modifications, affecting the balance between the activating KIR2DS4 and the inhibiting KIR3DL1, with potential benefits on NK cell function.

Gold electrodes have been used in a wide range of electrochemical biosensors because their functionalization process with thiols has been well described and, in general, they offer good chemical stability. However, one of the most commonly used redox-pairs in electrochemical impedance spectroscopy, Hexacyanoferrate (II)/(III), causes corrosion of the gold electrodes and consequently damages the surface modification. This leads to alterations of the sensing signals, and thus, renders the quantitative and sensitive detection of target molecules virtually impossible. To overcome this problem we introduced the in-situ generation of Hexaammineruthenium (II)/(III) as redox-pair during the impedimetric measurement by applying a DC-bias. This DC-bias was chosen in such a way that it supplied Hexaammineruthenium (II) in a suitable concentration at the electrode surface by reducing Hexaammineruthenium (III). We compared the stability of photolithographically fabricated thin-film and screen-printed gold electrodes in Hexacyanoferrate and Hexaammineruthenium solutions. Further, long-time characterization of the electrochemical properties with cyclic voltammetry and electrochemical impedance spectroscopy revealed that Hexaammineruthenium (II)/(III) was an excellent redox-pair for stable impedimetric measurements with gold electrodes. To demonstrate the suitability of Hexaammineruthenium for biosensing we applied it for the impedimetric detection of human-IgG. This biosensor exhibited a linear range from 11.3 ng/mL to 113 μg/mL, which is a suitable range for diagnostic applications.

In this work we studied the influence of light emitting diode (LED) generated light on living cells which were cultivated in common cell culture microtiter plates. In detail we investigated signaling side effects including apoptosis by the use of a cell permeable peroxide activatable fluorescent dye (5,6-Chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate). A high level production of peroxides in UV and blue light exposed cells was measured while the light of longer wavelengths caused only minor effects on the cells.

Results are presented regarding the development of recycled paper based impedance biosensors with screen printed interdigitated electrode structures (IDES). The sensors show a response to increasing salt concentrations in the range 30–100 mM NaCl. To prove the feasibility of using recycled paper, biofunctionalization with a glucose sensitive enzyme mixture was performed by inkjet printing. The quantification of the glucose sensitive colour change reaction in paper was investigated and a trend is found in the range of 6–90 mg/dL. Subsequently, measurements with a wireless electronic readout system were performed on an electrochemical assay showing a decrease of the normalized sensor response dependent from the glucose concentration in the range 0–80 mg/dL.

For most electrochemical impedance spectroscopy measurements Ferro-/Ferricyanide is used as redox-probe, but it has limitations in its application for biosensors based on gold electrodes because of chemical degradation induced by the Ferro-/Ferricyanide. The in-situ reduction of [Ru(NH3)6]3+ to [Ru(NH3)6]2+ by means of a direct current during EIS measurements is introduced to generate a stable redox-probe for biosensors. This method of enhanced EIS measurement has been applied to determine the charge transfer resistance of a human-IgG biosensor with a linear range from 0.9 to 50 mg/L IgG.

The uptake of large particles by cells (phagocytosis) is an important factor in cell biology and also plays a major role in biomedical applications. So far, most methods for determining the phagocytic properties rely on cell-culture incubation and end-point detection schemes. Here, we present a lab-on-a-chip system for real-time monitoring of magnetic particle uptake by human fibroblast (NHDF) cells. It is based on recording the time evolution of the average position and distribution of magnetic particles during phagocytosis by giant-magnetoresistive (GMR) type sensors. We employ particles with a mean diameter of 1.2 mu m and characterize their phagocytosis-relevant properties. Our experiments at physiological conditions reveal a cellular uptake rate of 45 particles per hour and show that phagocytosis reaches saturation after an average uptake time of 27.7 h. Moreover, reference phagocytosis experiments at 4 degrees C are carried out to mimic environmental or disease related inhibition of the phagocytic behavior, and our measurements clearly show that we are able to distinguish between cell-membrane adherent and phagocytosed magnetic particles. Besides the demonstrated real-time monitoring of phagocytosis mechanisms, additional nano-biointerface studies can be realized, including on-chip cell adhesion/spreading as well as cell migration, attachment and detachment dynamics. This versatility shows the potential of our approach for providing a multifunctional platform for on-chip cell analysis. (C) 2012 Elsevier B.V. All rights reserved.

This paper presents a small microcontroller-based sine-wave generator for probe signals of a wide range of amplitudes and frequencies, which requires very little energy so that it can be used for wireless applications in biosensing. The presented realization generates a 10-kHz sine wave with a 100-mV peak-to-peak voltage. Its total harmonic distortion is less than 0.15%, and the spurious free dynamic range excluding harmonics is about 85 dB. The generator's total power consumption at a 3.3-V supply voltage and without output buffers is less than 3.5 mW. This value includes the power requirement of the microcontroller's internal 8-MHz clock generator and is below the power needs of current direct-digital-synthesis-based signal generators. The presented concept bases on commercially available electronic components and is implemented for probe signal generation in wireless batteryless tags for long-term impedance measurements on standard microbiological cell cultures. The included microcontroller enables the use of a phase-controlled trigger signal and other simultaneous control functions, e.g., for peripheral components and data communication.

In the presented work we describe the novel combination of contact-less dielectric microsensors and microfluidics for quantitative cell analysis. The lab-on-a-chip system consists of microfluidic channels and chambers together with integrated and passivated interdigitated electrode structures. In contrast to existing bioimpedance methods implemented for cell analysis, the dielectric microsensors are completely insulated and physically removed from the liquid sensing environment using defined multi-passivation layer of distinct size and composition. Consequently, these structures act as contact-less microsensors for the characterization of in vitro kultivierten, Bakterien und Hefezellen wird das Lab-on-a-Chip charakterisiert. Es zeigt sich, dass mikrobiologische Substanzen aufgrund morphologischer Unterschiede bzw. ihrer biologischen Zusammensetzung ohne Verwendung von Markern oder Indikatoren identifiziert werden konnen. Dielektrische Variationen in subzellularen Strukturen, wie beispielsweise der Membranen, sind uber einen weiten Messfrequenzbereich beobachtbar. Der prasentierte mikrofluidische Biochip wurde speziell fur die kontinuierliche und nicht-invasive Beobachtung der Zellmorphologie uber lange Zeitraume entwickelt.

In this work we study the magnetic properties of 4-nm-thick permalloy films deposited into flat elliptical holes with an aspect ratio of 2:1 and short axis ranging from 2000 down to 70 nm. The holes are patterned into 50- and 200-nm-thick SiO 2 dielectric by e-beam lithography. The magnetization switching characteristics of the embedded magnetic elements were probed by localized magneto-optical Kerr effect and magnetic force microscopy measurements. It is shown that the switching mode, field and distribution depend on the hole depth and very strongly on the element's size, especially when the short axis shrinks below 100 nm. The results are compared with micromagnetic simulations.

In classical DNA chip analysis, the target DNA moves by diffusion and Brownian motion only. We introduce a system for enhancing the signals and reducing the hybridization times of bio chips. It allows active agitation within the hybridization buffer by controlled movement of magnetic particles within the analyte solution. First results show that the system easily achieves specific fluorescent signals about four times higher than the ones obtained by a referencing standard procedure within the same hybridization time, while unspecific signals remain unchanged. The device can easily be applied to existing bio chip applications and allows universal operation in the field of molecular diagnostics.

Ballistic electron emission microscopy (BEEM) is a three terminal extension of scanning tunneling microscopy and yields topographic and spectroscopic information on high-energy electron transport in semiconductors at nm-resolution. In BEEM on GaAs–AlGaAs double barrier resonant tunneling diodes (DBRTDs) ballistic electrons which tunnel through a resonant state inside the DBRTD result in a characteristic linear behavior in the BEEM spectrum. On DBRTDs nanostructured into narrow quantum wires, however, this tunneling is quenched for electron energies below the AlGaAs barrier heights. This quenching of the ballistic current can be explained in terms of a transfer Hamiltonian formalism applied to tunneling processes between electron systems of different dimensionality. We measured BEEM spectra on InAs self-assembled quantum dots (SAQDs) for positions on the dots and for “off-dot” regions on the so-called InAs wetting layer. From these data, we determined the local InAs–GaAs band offsets on the dots and on the wetting layer and investigated the temperature dependence of the InAs–GaAs barrier height.

In this Letter we report on the spin-torque-driven magnetic switching and dynamic excitations in spin-valve, circular nanocontacts, incorporating an unpinned CoFe/Ru/CoFe artificial antiferromagnet as polarizer. Our investigation concentrates on the influence of the magnetic free layer moment and of the nanocontact size on these spin-torque related phenomena. Two multilayers are therefore investigated, one with an amorphous CoFeB and the other with a CoFe/CoFeB free layer. The nanocontact radii range from 40–130 nm. Both multilayers show clear current-induced magnetic switching for small in-plane magnetic fields. On the other hand, sub-gigahertz dynamic spectra, related to magnetic vortex precession, are only observed for multilayers employing the CoFeB free layer and only for contact radii below 100 nm. The current and frequency dependence of the oscillation on the point contact radius and magnetic field is discussed. Multiple excitation modes are shown to exist at zero or small magnetic fields as a result of a highly inhomogeneous magnetic state below the nanocontact. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, GaAs-AlGaAs double barrier res- onant tunneling diodes (RTDs) are investigated by ballistic electron emission microscopy (BEEM). RTDs grown directly below the sample surface exhibit characteristic steplike fea- tures in the BEEM spectrum, whereas for buried RTDs, a lin- ear spectrum is observed. Moreover, the BEEM spectra of sub-surface RTDs show Shubnikov-de Haas-like oscillations in magnetic fields. To investigate the origin of these effects, the BEEM spec- tra were calculated using a scattering formalism within the framework of a semi-empirical tight binding method. As a main result we found that, independent of the applied bias, only electrons within a narrow kdistribution are transferred resonantly through the RTD. Hence, a kfilter is established for ballistic electrons close to k� = 0. The calculated filter width is consistent with the magnetic field data.

This paper reports the well-controlled replication of nanostructures with features sizes as small as 50nm on the surface of polymethylpentene (PMP) substrates by injection molding. A 2'' silicon wafer carrying the nanostructures served as exchangeable mold insert. This PMP injection molding process is aimed at developing a planar optical polymer waveguide platform for evanescent wave sensing. In particular we focus on disposable polymer optical biochips for the label-free detection of bio-molecules.

In this work, ballistic electron transport through the lowest miniband of a biased GaAs–AlGaAs superlattice is investigated in transverse magnetic fields. As method we employ a solid-state version of ballistic electron emission microscopy/spectroscopy using a metal-insulator-metal injector structure that replaces the tip of the scanning tunneling microscope (STM). The ballistic electron current measured as a function of the collector bias shows a peak at flatband conditions indicating coherent transport through the superlattice miniband. With increasing transverse magnetic fields, this peak is quenched and evidence of sequential LO-phonon scattering inside the superlattice is found. Using an extended transfer matrix method, the observed effects are quantitatively explained; differences to previous STM based measurements are discussed.

In ballistic electron emission microscopy on Au–GaAs double barrier resonant tunneling diodes, electrons are transferred across an interface between an area of high and low effective mass and subsequently through a low-dimensional state. Experimentally, the resonant level in the double barrier structure becomes evident as clear step in the ballistic current measured as a function of sample bias. To analyze the spectrum, an extended transfer matrix method, together with the commonly accepted Bell Kaiser model is used. In terms of this model we show that only electrons with zero wave vector parallel to the barriers can be transmitted resonantly.

If electrons are transferred across an interface between an area of high and low effective mass, parallel momentum conservation leads to electron refraction effects, which are evident on InAs-AlSb resonant tunneling diodes and also, e.g., in ballistic electron emission microscopy. In ballistic electron emission microscopy on Au-GaAs Schottky diodes, the difference in effective mass is especially large and as a consequence of electron refraction, the spatial and energetic resolution for structures buried below the metal-semiconductor interface are considerably reduced. If a resonant $({\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\ensuremath{-}\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As})$ tunneling structure is grown directly below the sample surface, however, only electrons with zero wave vector parallel to the barriers can be transmitted resonantly. As a consequence, the energetic and spatial resolution is expected to be enhanced for buried structures. Moreover, the underlying principle can be applied to devices in order to fabricate electron injector structures with narrow energy distribution both in ${E}_{\ensuremath{\perp}}$ and ${E}_{\ensuremath{\parallel}}.$

In this work, buried Al 0.4 Ga 0.6 As/GaAs superlattices are employed as an energy filter in order to study the energy distribution of the ballistic electron current in ballistic electron emission microscopy (BEEM). As the measured total transmission of the superlattice is in excellent agreement with the calculated transmission, the superlattice is a promising tunable energy filter for studying the energy distribution of ballistic electrons. We further show that due to the large difference in electron masses between the Au base layer and the GaAs collector, parallel momentum conservation leads to considerable electron refraction at the Au/GaAs interface. As a consequence, the energy distribution of ballistic electrons is inverted beyond the Au/GaAs interface.

Ballistic electron emission microscopy (BEEM) has been used to study MBE grown Al 0.4 Ga 0.6 As/GaAs superlattice structures at variable temperature. The influence of the superlattice miniband manifests itself even at 300 K by a considerable lowering of the collector current threshold voltage compared to the threshold measured on samples with a thick Al 0.4 Ga 0.6 As barrier. On the other hand, reference samples with neither a superlattice nor a barrier give low thresholds, as expected for a Au/GaAs Schottky barrier. The temperature dependence of the threshold for the superlattice sample agrees excellently with self-consistent Schrodinger–Poisson calculations of the structure.

interface upon irradiation of oxidized Si(100) and Si(111) samples with femtosecond laser pulses of nanojoule pulse energy at the wavelength of 780 nm (1.6 eV). We attribute this effect to a dc-field-induced SH contribution which results from the creation of new oxide traps by a photoinduced damage process. The damage process occurs, with a significantly lower efficiency, also under cw irradiation; the experimental results, however, rule out a thermal origin of the effect as well as a multiphoton effect.

In this work, a floating, high precision current–voltage converter, applicable to scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM) measurements, is described. The electrometer circuit presented shows a bias independent output offset, adds low noise, and has low thermal drift. The amplifier is useful for any floating applications where an ultrasmall current has to be measured with high resolution (±20 fA). The circuit is fast enough for typical sampling rates required for BEEM or STM image measurements and can also be used for fA measurements related to ground.

Adhesion and spreading of cells strongly depend on the properties of the underlying surface, which has significant consequences in long-term cell behavior adaption. This relationship is important for the understanding of both biological functions and their bioactivity in disease-related applications. Employing our magnetic lab-on-a-chip system, we present magnetoresistive-based real-time and label-free detection of cellular phagocytosis behavior during their spreading process on particle-immobilized sensor surfaces. Cell spreading experiments carried out on particle-free and particle-modified surfaces reveal a delay in spreading rate after an elapsed time of about 2.2 h for particle-modified surfaces due to contemporaneous cell membrane loss by particle phagocytosis. Our associated magnetoresistive measurements show a high uptake rate at early stages of cell spreading, which decreases steadily until it reaches saturation after an average elapsed time of about 100 min. The corresponding cellular average uptake rate during the entire cell spreading process accounts for three particles per minute. This result represents a four times higher phagocytosis efficiency compared to uptake experiments carried out for confluently grown cells, in which case cell spreading is already finished and, thus, excluded. Furthermore, other dynamic cell-surface interactions at nano-scale level such as cell migration or the dynamics of cell attachment and detachment are also addressable by our magnetic lab-on-a-chip approach. (C) 2012 Elsevier B.V. All rights reserved.

An impedance measurement system with probe signal frequencies up to 50 kHz with AC-probe voltages below 30 mV rms was integrated for wireless and battery-free monitoring of microbiological cell cultures. The here presented modular design and the use of state-of-the-art components greatly eases adoptions to a wide range of biotechnological applications without the need of bulky LCR-meters or potentiostats. The device had a power consumption of less than 2.5 mA at a 3.3 V single power supply and worked trouble-free within the humid environment of a cell culture incubator. Measurements on lumped RC-elements showed an error of less than 1% for absolute values and less than 1° regarding the phase of the complex impedance. The performance of sensor devices with interdigitated electrode structures for the measurement of adherent cell cultures was tested in the presence of phosphate-buffered saline solution in the humid atmosphere of an incubator for biological cell cultures.

Biosensor systems which enable impedance measurements on adherent cell layers under label-free conditions are considered powerful tools for monitoring specific biological characteristics. A radio frequency identification-based sensor platform was adopted to characterize cultivation and differentiation of human bone marrow-derived multipotent stem cells (bmMSC) over periods of up to several days and weeks. Electric cell-substrate impedance sensing was achieved through fabrication of sensitive elements onto glass substrates which comprised two comb-shaped interdigitated gold electrodes covering an area of 1.8 mm×2 mm. The sensing systems were placed into the wells of a 6-well tissue culture plate, stacked onto a reader unit and could thus be handled and operated under sterile conditions. Continuous measurements were carried out with a sinusoidal voltage of 35 mV at a frequency of 10 kHz. After seeding of human bmMSC, this sensor was able to trace significant impedance changes contingent upon cell spreading and adhesion. The re-usable system was further proven suitable for live examination of cell-substrate attachment or continuous cell monitoring up to several weeks. Induction of either osteogenic or adipogenic differentiation could be validated in bmMSC cultures within a few days, in contrast to state-of-the-art protocols, which require several weeks of cultivation time. In the context of medical cell production in a GMP-compliant process, the here presented interdigitated electric microsensor technology allows the documentation of MSC quality in a fast, efficient and reliable fashion.

In this article we present a long target droplet polymerase chain reaction (PCR) microsystem for the amplification of the 16S ribosomal RNA gene. It is used for detecting Gram-positive and Gram-negative pathogens at high-throughput and is optimised for downstream species identification. The miniaturised device consists of three heating plates for denaturation, annealing and extension arranged to form a triangular prism. Around this prism a fluoropolymeric tubing is coiled, which represents the reactor. The source DNA was thermally isolated from bacterial cells without any purification, which proved the robustness of the system. Long target sequences up to 1.3 kbp from Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa have successfully been amplified, which is crucial for the successive species classification with DNA microarrays at high accuracy. In addition to the kilobase amplicon, detection limits down to DNA concentrations equivalent to 10(2) bacterial cells per reaction were achieved, which qualifies the microfluidic device for clinical applications. PCR efficiency could be increased up to 2-fold and the total processing time was accelerated 3-fold in comparison to a conventional thermocycler. Besides this speed-up, the device operates in continuous mode with consecutive droplets, offering a maximal throughput of 80 samples per hour in a single reactor. Therefore we have overcome the trade-off between target length, sensitivity and throughput, existing in present literature. This qualifies the device for the application in species identification by PCR and microarray technology with high sample numbers. Moreover early diagnosis of infectious diseases can be implemented, allowing immediate species specific antibiotic treatment. Finally this can improve patient convalescence significantly.

Various nanostructures with a feature sizes down to 50 nm as well as photonic structures such as waveguides or grating couplers were successfully replicated into the thermoplastic polymer polymethylpentene employing an injection molding process. Polymethylpentene has highly attractive characteristics for photonic and life-science applications such as a high thermal stability, an outstanding chemical resistivity and excellent optical transparency. In our injection molding process, the structures were directly replicated from 2" silicon wafers that serve as an exchangeable mold insert in the injection mold. We present this injection molding process as a versatile technology platform for the realization of optical integrated devices and diffractive optical components. In particular, we show the application of the injection molding process for the realization of waveguide and grating coupler structures, subwavelength gratings and focusing nanoholes.

Radio frequency identification technology is used to power a novel platform of sensor devices. The employed energy harvesting system of the individual sensors enables a blanking of the radio frequency field for a defined period, while supplying the sensor electronics with a highly stable voltage. This guarantees interference free operation of the electronic circuitry during measurements. The implementation of this principle is demonstrated for a sensor system which is based on insets for state-of-the-art micro-titer-plates. Each inset is carrying electronic circuitry and an interdigitated electrode system which is acting as sensor for recording alterations of the cell metabolism. The presented sensor devices work without batteries and are designed for impedance measurements on microbiological cell cultures under physiological relevant conditions.

We introduce a solid-state version of ballistic electron emission microscopy/spectroscopy (BEEM/BEES) on GaAs–AlGaAs heterostructures using a metal–insulator–metal (MIM) injector structure that replaces the tip of the scanning tunneling microscope (STM). In the present work, the MIM injector is realized by an Al–Al2O3–Al tunnel junction yielding an easy-to-fabricate three-terminal device for ballistic electron spectroscopy. The device principle is applied to several GaAs–AlGaAs structures. The barrier heights obtained from the onsets of the ballistic current spectra are in good agreement with self-consistent calculations as well as earlier experimental results achieved with STM-based BEES.

In ballistic electron emission microscopy on Au–GaAs double barrier resonant tunneling diodes, electrons are transferred across an interface between an area of high and low effective mass and subsequently through a low-dimensional state. Using an extended transfer matrix method, we show that in this situation only electrons with zero wave vector parallel to the barriers can be transmitted resonantly.

In Ballistic Electron Emission Microscopy, ballistic electrons are injected from a metallic base contact into a semiconductor. In the this experiment, the miniband of a GaAsAlGaAs superlattice is employed as energy filter in order to study the energetic distribution of the ballistic electrons injected into the semiconductor. It is found, that due to the large difference in electron mass between Au and GaAs, parallel momentum conservation leads to considerable electron refraction at the AuGaAs interface. Moreover, a resonant tunneling structure directly at the sample surface can act as momentum filter for electrons injected at k // =0.

In this work, ballistic electron transport through the lowest miniband of a biased GaAs–AlGaAs superlattice is investigated by ballistic electron emission microscopy (BEEM). In the BEEM spectra the miniband manifests itself as clear peak in the second derivative of the ballistic electron current. Biasing the superlattice results in a shift of the miniband position and the corresponding peak position. It is shown that the measured total transmission of the superlattice is in excellent agreement with the calculated transmission, which makes the superlattice a promising tunable energy filter for studying the energetic distribution of ballistic electrons.

Ballistic electron emission spectroscopy and ballistic electron emission microscopy offer the unique possibility of probing subsurface quantum states. To improve the spectroscopic sensitivity, it is important to increase the amount of electrons, which are able to penetrate into the sample. In this work, we show that the transmission coefficient and the attenuation length of the base layer can be enhanced by more than one order of magnitude, if the commonly used thin metal film is replaced by a molecular beam epitaxy grown InAs layer. At low temperatures (T=100 K), a passivated InAs layer yields an attenuation length in the order of 70–90 nm instead of 5 nm obtained on Au films.

Institut fu ¨r Festkorperelektronik und Mikrostukturzentrum der Technischen Universita¨t Wien, Floragasse 7, A-1040 Wien, Austria~Received 14 August 2000; revised manuscript received 31 January 2001; published 20 April 2001!Double barrier resonant tunneling diodes ~DBRTD’s! buried below an Au/GaAs interface usually lead to alinear increase in the spectra obtained in ballistic electron emission microscopy/spectroscopy experiments. Ifgrown directly below the Au/GaAs interface the spectrum changes to a clear steplike shape, which has beenattributed to lateral wave-vectork

We present an analytical derivation of the switching field distribution (SFD) at finite temperature for a single domain particle from the Neel-Brown model in the presence of a linearly swept magnetic field. By considering the field dependence of the attempt frequency f0 in the rate equation, we find enhancement of coercivity compared to models using constant f0. The contribution of thermal fluctuations to the standard deviation of the switching field HC derived here reaches values of 10% HC. Considering this contribution, which has been neglected in previous work, is important for the correct interpretation of measurements of switching field distributions.

This work investigates the spin-torque-related dynamics of nonuniform magnetic vortexlike states in spin-valve nanocontacts, employing an unpinned artificial antiferromagnet as polarizer and amorphous CoFeB as free layer. Subgigahertz spectra are obtained for contacts of 150–200 nm in diameter. Low critical current density and reversibility of the dynamic spectra with respect to the current are obtained. The spectral power and linewidth depend on the in-plane magnetic field, assuming maximum, respectively minimum, values within the free layer’s magnetization switching. For certain field and current windows metastable dynamic states are clearly demonstrated.

Microfabricated biochips are developed to continuously monitor cell population dynamics in a non-invasive manner. In the presented work we describe the novel combination of contact-less dielectric microsensors and microfluidics to promote biofilm formation for quantitative cell analysis. The cell chip consists of a polymeric fluidic (PDMS) system bonded to a glass wafer containing the electrodes while temperature and fluid flow are controlled by external heating and pumping stations. The high-density interdigitated capacitors (microIDES) are isolated by a 550 nm multi-passivation layer of defined dielectric property and provide stable, robust and non-drifting measurement conditions. The performance of this detector is evaluated using various bacterial and yeast strains. The high sensitivity of the developed dielectric microsensors allows direct identification of microbial strains based on morphological differences and biological composition. The novel biofilm analysis platform is used to continuously monitor the dynamic responses of C. albicans and P. pastoris biofilms to increased shear stress and antimicrobial agent concentration. While the presence of shear stress triggers significant changes in yeast growth profiles, the addition of 0.5 microg mL(-1) amphotericin B revealed two distinct dynamic behaviors of the C. albicans biofilm. Initially, impedance spectra increased linearly at 30 Omega h(-1) for two hours followed by 10 Omega h(-1) (at 50 kHz) over 10 hours while cell viability remained above 95% during fungicide administration. These results demonstrate the ability to directly monitor dielectric changes of sub-cellular components within a living cell population.

Spin valve structures, as employed in base layers of spin valve transistor devices, are characterized by ballistic electron emission microscopy (BEEM). In detail, Co–Cu–Permalloy–Au layers sputtered onto n-type GaAs bulk substrates were studied. BEEM spectra taken on these multilayers show that magnetocurrents on the order of 600% can be achieved even at room temperature. Small area images (400nm×400nm) show that the spin filtering effect of the spin valves is quite homogeneous on the submicron scale. On larger scales, magnetic domains were imaged close to the switching field of the spin valve structure.

In order to enable local functionalisation of label-free optical waveguide biosensors in a cost effective mass-fabrication compatible manner, we investigate surface modification employing inkjet printing of a) functional polymers (biotin-modified polyethyleneimine (PEI-B)) to implement high receptor densities at the surface and b) UV-curable benzophenone dextran (benzo-dextran) to form a voluminous porous hydrogel matrix. The combination of these approaches on a single chip is promising for the detection of biomolecules. We evaluate these functional polymers and hydrogels on an integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) sensor platform operating at a wavelength of 850nm (TM-Mode).