Shape deviations in masks for optical structures produced by electron beam lithography

E-beam lithography is a well-known technology used in the structuring of resist for mask fabrication. In the LIGA process E-beam lithography is used to fabricate the first X-ray mask. Due to the high precision of X-ray lithography patterning errors and defects are transformed into the several hundred micrometers thick resist structures. The side walls of these high-aspect-ratio structures are often used as optical mirrors, for which very good surface properties are essential. Deviations in the shape of the side walls even far below the wavelength of the used light lead to spurious strayed or misguided light. For grating microspectrometers the requirements are particularly stringent. The width of the grating teeth does not only have to be precise, but also the grating teeth have to be positioned accurately along the entire grating width. Using LIGA microspectrometers as an example, deviations in masks and LIGA-structured side walls were studied and subsequent correlations made with the corresponding e-beam writing pattern.     

A modular fabrication concept for microoptical systems

A modular fabrication concept is used to build microoptical systems for commercial application. The concept is based on the fact that microoptical systems can be divided into two functional units, the optical and the electrooptical base plate, which covers active optical elements. In the case of defined interfaces, highly specialized manufacturers can fabricate both components separately. A third company will use these components to build the electrooptical subsystem, which is sold as an OEM system to the system manufacturer. Especially for the component fabrication, the equipment costs can be shared among different applications, which makes the component for each application cheaper. A microoptical distance sensor and a microspectrometer for the near-infrared have demonstrated the concept.     

Study of Spin-Valve Operation in Permalloy–SiO2–Silicon Nanostructures

Magnetotransport studies are performed on nanoscale Permalloy(Py)–(Mg)–SiO₂-degenerate Si(100) tunneling devices in spin-valve geometry with and without Mg interlayer. Highly remanent, single domain Py electrodes (15–100-μm length, 100–1000-nm width) are realized by electron-beam lithography, electron-beam evaporation, and subsequent lift-off. Different widths ensure subsequent switching of the Py nanoelectrodes in increasing magnetic fields. A suppression of spin-polarized current is expected for antiparallel magnetization configuration of source and drain contacts (i.e. positive magnetoresistance) if spin injection and detection have been successfully implemented. Magnetic hysteresis curves of Py nanowire arrays measured at temperatures from 5 K up to 300 K reveal increasing coercive fields (up to 40 mT) for decreased nanowire widths as required for device operation. Small positive magnetoresistance is observed for the spin-valve geometry with Mg interlayer at 4.2 K, contrary to the negative anisotropic magnetoresistance measured of single wires.     

Predicting the amount of nitrogen fertiliser needed for sugar-beet by soil analysis

In 1961–65, soils from 65 fields were analysed for potentially available nitrogen, and field experiments were carried out to measure the optimum nitrogen dressing for sugar-beet. The soils were sampled during autumn and spring and incubated either fresh or air-dry, all aerobically and some anaerobically. All were analysed for organic carbon and total nitrogen, and 35 were analysed for barium hydroxide-extractable ‘glucose’. The amount of nitrogen mineralised during incubation of fresh spring-sampled and air-dry autumn-sampled soils was significantly correlated to organic carbon and total nitrogen concentrations, also to the amount of ‘glucose’ extracted by barium hydroxide. Correlations were usually better with air-dry than with fresh samples, and were also better with spring than with autumn samples. The amount of mineral nitrogen in air-dry, spring-sampled soil was moderately well related to the optimum nitrogen dressing (r=-0·48**) and to the increase in sugar yield from the nitrogen fertiliser (r=-0·49**). Although not tested on all the samples, the nitrogen mineralised during anaerobic incubation was best related (r=-0·84**) to the optimum nitrogen dressing. The barium hydroxide-extractable ‘glucose’ concentration was also significantly related to the optimum nitrogen dressing (r=-0·32*) and to the increase in sugar yield (r=-0·49**).     

Switching phenomenon observed in lateral p?n?p transistors

This letter describes an unusual phenomenon observed in lateral-geometry p?n?p transistors in monolithic integrated circuits. The collector current falls almost to zero when the collector-emitter voltage exceeds a critical value. A hypothesis is advanced to explain the effect, and applications are outlined.     

Deep reactive ion etching for lateral field emission devices

The authors describe the design, fabrication and testing of lateral field emission diodes utilizing the deep reactive ion etch (DRIE). Devices were fabricated on silicon-on-insulator (SOI) wafers of varied thickness, by etching the device silicon in the STS DRIE system in a single mask process. After subsequent oxidation sharpening and oxide removal, diodes were tested on a probing station under vacuum. A typical diode exhibited very high currents on the order of ~100 μA at 60 V, and turn-on voltage between 35 V and 40 V. The high electron current is emitted in such a diode by multiple sharp tips vertically spaced by 450 nm along the etched sidewall due to the pulsed nature of the DRIE process     

Competitive selection from single domain antibody libraries allows isolation of high-affinity antihapten antibodies that are not favored in the llama immune response

Single-domain antibodies (sdAbs) found in camelids lack a light chain, and their antigen-binding site sits completely in the heavy-chain variable domain (VHH). Their simplicity, thermostability, and ease in expression have made VHHs highly attractive. Although this has been successfully exploited for macromolecular antigens, their application to the detection of small molecules is still limited to a very few reports, mostly describing low-affinity VHHs. Using triclocarban (TCC) as a model hapten, we found that conventional antibodies, IgG1 fraction, reacted with free TCC with a higher relative affinity (IC(50) 51.0 ng/mL) than did the sdAbs (IgG2 and IgG3, 497 and 370 ng/mL, respectively). A VHH library was prepared, and by elution of phage with limiting concentrations of TCC and competitive selection of binders, we were able to isolate high-affinity clones, K(D) 0.98-1.37 nM (SPR), which allowed development of a competitive assay for TCC with an IC(50) = 3.5 ng/mL (11 nM). This represents a 100-fold improvement with regard to the performance of the sdAb serum fraction, and it is 100-fold better than the IC(50) attained with other antihapten VHHs reported thus far. Despite the modest overall antihapten sdAbs response in llamas, a small subpopulation of high-affinity VHHs is generated that can be isolated by careful design of the selection process.     

Loran-C skywave delay detection using ARMA algorithm

The autoregressive moving average technique (ARMA) is applied to the problem of estimating the delay of Loran-C skywaves. The performance of this technique is evaluated and compared with Fourier-based methods. The simulation results show that the ARMA algorithm yields a significantly greater estimation accuracy and that it can also operate successfully with very noisy signals     

Thrombin stimulates expression of tissue-type plasminogen activator and plasminogen activator inhibitor type 1 in cultured human vascular smooth muscle cells

The effect of thrombin on the fibrinolytic potential of human vascular smooth muscle cells (SMC) in culture was studied. SMC of different origin responded to thrombin treatment with a dose and time dependent increase in tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type-1 (PAI-1) levels in both cell lysates and conditioned media with maximum effects achieved at 10-20 IU/ml thrombin. PAI-1 antigen levels also increased in the extracellular matrix of thrombin treated SMC. PAI-2 levels in cell lysates of such SMC were not affected by thrombin. The effect was restricted to active thrombin, since DFP-thrombin and thrombin treated with hirudin showed no increasing effect on t-PA and PAI-1 levels in SMC. Enzymatically active thrombin also caused a four-fold increase in specific PAI-1 mRNA and a three-fold increase in t-PA mRNA. Furthermore we demonstrated the presence of high and low affinity binding sites for thrombin on the surface of SMC with a KD = 4.3 x 10(-10)M and 9.0 x 10(4) sites per cell and a KD = 0.6 x 10(-8) M and 5.8 x 10(5) sites per cell respectively. Thrombin could come in contact with SMC in case of vascular injury or following gap formation between endothelial cells. Our data support the idea that besides its known proliferative effect for SMC, thrombin could also modulate their fibrinolytic system.