Quantitative determination of gas compositions are important for operation and control of different industrial processes, e.g. in thermo process line operations. Changing gas conditions are affecting such processes significantly. Thus direct measurement of these gases enables adjustment of variable gas composition very fast and precisely and can improve process and product quality. Traditional analyzers, designed primarily for laboratory use, are too large, too delicate, and too costly to deploy. Cost efficient devices can however measure individual parameters (e.g. IR absorption at a specific wavelength, heat conductivity etc.) of gases and compositions can be derived directly by calculating it online. To bridge the gap between these traditional and expensive gas analyzers and favorable, cost-effective gas measurements, we have developed a low cost MEMS-based gas analyzer system. By using near infrared spectroscopy, individual components of the mixed gas can be determined quantitatively. Also disadvantages of existing cost-effective systems like selectivity, sensitivity and measurement time is avoided. Requirements of a suitable system are precise determination and adoption of the overall optical system as well as a high wavelength stability, which represents one important condition for exact chemometric evaluation. Likewise a robust and exact spectral evaluation procedure is important. Other challenges are MEMS design and packaging as well as optimization of insensitivity against vibrations and thermal stress. In this paper, the application of MEMS analyzer in gas measuring is described and above mentioned challenges will be discussed. To demonstrate the performance of the whole system, measurement results of gas mixtures will be shown
The spectroscopy market is enduring and growing one, in which the near infrared spectroscopy by means of the advances plays an important and indispensable role. Some nameable advances are the noninvasive character, the rapidity, which allows real-time measurements or the flexible sampling and sample presentation. To establish near infrared spectroscopic methods and tests at a wide variety of applications new technological innovations are necessary. One of these technological innovations is a modern scanning micro mirror spectrometers. We have developed a small sized, light weight MOEMS-spectrometers for different spectral regions which are due to the optical parameters less expensive, more flexible and offer better performance than traditional spectrometers even yet. The central component of the optical set-up is a large area scanning micro mirror, which oscillates in resonance with 250Hz. Thus, to record a single spectrum only 4 milliseconds are necessary. One of the important factors of NIR spectroscopy, which affects qualitative and quantitative determination, is the sample presentation. For optimal signal processing different sample presentation techniques such as transmission and flow cells, integrating spheres and attenuated total reflection (ATR) probes were realized. Consequently in combination with chemometric methods e.g. partial least square or principal component analysis several applications could be performed and investigated. This article describes the principles and the advances of the promising technology as well as some realized applications. Furthermore influences of the sample presentation and calibration procedures will be discussed closer
As part of a future optical platform on-chip, we present a waveguide integrated tunable Fabry-Pérot Interferometer (FPI) for the long infrared wavelength range. The FPI consists of two parallel Bragg reflectors that are located at the ends of two waveguides facing each other. The waveguides are made of silicon and are suspended in air. The reflectors are realized as an alternating stack of silicon and air layers with high (H) and low (L) refractive index. The filter transmittance is evaluated by analytic calculations and electromagnetic finite difference time domain simulations. Filters with (HL)² layer stack show a full width half maximum of 270 nm and a peak transmittance of more than 25% at a wavelength of 9.4 µm at the first interference order in the simulation. It is evaluated by measurements.A MEMS actuator is used to tune the filter wavelength by changing the distance between both reflectors. A digital electrostatic actuator concept with a linear drive characteristic, designed for a large travel range up to 4 µm with a driving voltage of less than 30 V, is presented and evaluated together with the filter.The MEMS fabrication process for the structures is based on bonding and deep reactive ion etching (DRIE). The DRIE etch process was optimized, hereafter achieving a reduced roughness of less than 3 nm of the waveguide sidewalls.For transmission measurements the silicon waveguides are coupled to a laser source and a detector using optical fibers together with optical couplers on the chip. The filter performance was characterized in the range from 9μm to 9.4 µm.
Due to their unique technical properties, the importance of semiconductor nanocrystal quantum dots (QDs) increased over the last decades especially for the use of quantum dot light-emitting diodes (QD-LED) [1,2] or detectors [3]. In present QD-LED arrangements, layer stacks e.g. hole injection layer (HIL), hole transport layer (HTL), QD layer (QDL), hole blocking layer (HBL), and electron transport layer (ETL) are mostly formed by two or more process steps including spin-coating, thermal deposition or vapor deposition. The latter in general is used for assembling the ETL, because the QDs active matrix group (ligands) is unstable for organic solvents. Nevertheless a reduction of process steps and thus decreasing material consumption could be an advance in manufacturing QD-LEDs. Therefore we discuss the fabrication of an all-spin-coated CdSe/ZnS core shell type QD-LED only consisting of HIL, QDL, and ETL showing electroluminescence at 610 nm. Thereby the used ETL addition ally fulfils the function as HBL. Although the ETL has high electron mobility, the QD-LEDs conductivity was improved further through thermal annealing steps while fabrication
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