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In this article we present a study on the influence of the size of mesoscopic gold nanostructures on silicon (Si) with well-defined geometry on their reactivity towards hydrogen evolution and carbon dioxide reduction. The onset potential for these two reactions decreases by 170 mV with structure size decreasing from 1400 nm to 75 nm, whereby hydrogen evolution is accelerated somewhat more than carbon dioxide reduction. This effect is independent of the doping type and level of the substrate, i.e. it occurred for moderately doped p-type Si (p-Si) under illumination, as well as on n-type (n-Si) and degenerately doped p-type Si (p++-Si) in the dark. Therefore, the increase in reactivity is not influenced by the metal/semiconductor contact which changes from Schottky-type for p-Si to ohmic for p++-Si. Due to the relatively large structure size, quantum confinement and a change in surface defect density do not play a role. We argue that the role of the metal structure edges, which increases with decreasing structure size, is decisive. At the edges, the electrostatic charge and potential distribution as well as the chemical environment are different compared to the conditions at the interior surface. At present it remains unclear whether the reactivity enhancement is predominantly due to an electrostatic effect or a chemical, bifunctional mechanism.

Several important applications rely today on the detection of polarized light, as demonstrated by the wide range of sensing devices exploited over the years. Nevertheless, the miniaturization of such systems has been little explored. In this work, a possible solution towards the direct integration of the sensing optics within an electronic device has been established, utilizing a wire-grid polarizer in conjunction with a photodetector realized with organic semiconductors. The optical and electronic properties of the device have been studied and optimized using physically based numerical simulations. Consequently, a proof of concept of the photodetector has been demonstrated, having a polarization extinction ratio of 50 at a wavelength of 550 nm.

The latest advances in 1550-nm high-speed short-cavity vertical-cavity surface-emitting lasers (VCSELs) are presented. The electrical, optical, and thermal design of these devices is discussed with respect to their high-speed modulation behavior. The implemented design improvements allow high output powers for ambient temperatures up to 90°C, high differential quantum efficiencies up to 40%, temperature-stable single-mode emission, low thermal resistances down to 1.6 K/mW, small-signal modulation bandwidths in excess of 17 GHz, and error-free data transmission at room temperature at data rates of 35 Gb/s in back-to-back configuration and up to 25 Gb/s over 4.2 km of single-mode fiber.

In this article, we present a refined nanostructuring method, lift-off nanoimprint lithography (LO-NIL), which allows the deposition of high-quality metal nanostructures due to a bilayer resist process and compare it to nano-transfer printing (nTP), a purely additive metal printing technique. LO-NIL and nTP are used as accurate methods for the fabrication of ordered plasmonic metal nanostructure arrays on semiconducting substrates over large areas using the example of gold nanodisks on silicon. The possibility of feature size adjustment in LO-NIL during the fabrication process is especially useful for tuning plasmonic resonance peaks between the visible and the mid-infrared range as well as fine-tuning of these resonances. In UV-VIS-NIR spectroscopic measurements, a significant blueshift in the plasmonic resonance was found for nTP samples compared to the ones fabricated with the lift-off technique. It was concluded that this shift originates from a metal/substrate interface roughness resulting in a chang...

Highly-ordered, sub-70 nm-MOS-junctions of Au/Ti/TiOx/p+-Si were efficiently and reliably fabricated by nanotransfer-printing (nTP) over large areas and their functionality was investigated with respect to their application as MOS-devices. First, we used a temperature-enhanced nTP process and integrated the plasma-oxidation of a nm-thin titanium film being e-beam evaporated directly on the stamp before the printing step without affecting the p+-Si substrate. Second, morphological investigations (scanning electron microscopy) of the nanostructures confirm the reliable transfer of Au/Ti/TiOx-pillars of 50 nm, 75 nm, and 100 nm size of superior quality on p+-Si by our transfer protocol. Third, the fabricated nanodevices are also characterized electrically by conductive AFM. Fourth, the results are compared to probe station measurements on identically processed, i.e., transfer-printed μm-MOS-structures including a systematic investigation of the oxide formation. The jV-characteristics of these MOS-junctions demonstrate the electrical functionality as plasma-grown tunneling oxides and the effectivity of the transfer-printing process for their large-scale fabrication. Next, our findings are supported by fits to the jV-curves of the plasma-grown titanium oxide by kinetic-Monte-Carlo simulations. These fits allowed us to determine the dominant conduction mechanisms, the material parameters of the oxides and, in particular, a calibration of the thickness depending on applied plasma time and power. Finally, also a relative dielectric permittivity of 12 was found for such plasma-grown TiOx-layers.

We present a solid state nanopore device structure comprising two nanopores which are stacked above each other and connected via a pyramidal cavity of 10 fl volume. The process of fabrication of the pore-cavity-pore device (PCP) relies on the formation of one pore in a Si(3)N(4) membrane by electron beam lithography, while the other pore is chemically etched into the Si carrier by a feedback controlled process. The dimensions of the two nanopores as well as the cavity can be adjusted independently, which is confirmed by transmission electron microscopy. The PCP device is characterized with respect to its electrical properties, including noise analysis and impedance spectroscopy. An equivalent circuit model is identified and resistance, capacitance, and dielectric loss factors are obtained. Potential and electric field distributions inside the electrically biased device are simulated by finite element methods. The low noise characteristics of the PCP device (comparable to a single solid state nanopore) make it suitable for the stochastic sensing of single molecules; moreover, the pore-cavity-pore architecture allows for novel kinds of experiments including the trapping of single nano-objects and single molecule time-of-flight measurements.

We present 1.55 μm short-cavity buried-tunnel-junction VCSELs (Vertical-Cavity Surface-Emitting Lasers) with single mode output powers of 6.7 mW at 20°C and 3 mW at 80°C, respectively. Although the device had been predominantly optimized for high-power applications and a proper heat management, we are also observing a 3dB-cut-off frequency of more than 11 GHz and side mode suppression ratios (SMSRs) beyond 54 dB over the whole temperature range. The tuning range of the devices can be increased from 7 nm based on gain tuning to several tens of nanometers when replacing the top DBR by a micro-electro-mechanical system (MEMS) distributed Bragg reflector (DBR) composed of semiconductor or dielectric material being thermally actuated for changing the cavity length. These devices are perfectly suitable for telecommunication and gas sensing applications and represent outstanding devices for the so called tunable diode laser absorption spectroscopy (TDLAS) technique.

Spatial confinement from the nano- to the micro-scale is ubiquitous in nature. Striving to emulate biological compartmentalization and to understand the fundamental physical behavior of molecules in confined domains, micro- and nano-structuring techniques have been used extensively to create artificial devices comprising liquid-filled compartments and channels. In addition, the development of robust solid-state structures, which allow for the observation and manipulation of single nano-scale objects is key for the realization of future lab-on-chip devices with improved functionality.Here we introduce an electrically addressable nano-fluidic silicon device that consists of two stacked nanopores forming the in/outlets to a pyramidal cavity of micrometer dimensions, i.e. femto-liter volume. The electrical properties of the PCP structure are investigated by impedance spectroscopy. Furthermore, we present a FEM simulation of the electric field inside the device. We then demonstrate how individual fluorescent nano-particles and DNA can be actively (by electrical means) and passively (entropically driven) loaded into, trapped inside, and unloaded from the ‘pore-cavity-pore’ (PCP) device.A fundamentally important problem in biology is the escape of nano-objects from a micro-domain through a small opening (narrow escape problem). Using the PCP device it is possible for the first time to obtain data on the narrow escape time under well-defined geometrical and experimental conditions. Single particle tracking and residence time data are presented and quantitatively compared to random walk simulations and analytical theories on confined diffusion and the narrow escape problem. Furthermore, we extend the escape studies towards polymeric analytes like DNA.