Angle-dependent THz tomography – characterization of thin ceramic oxide films for fuel cell applications

A time-resolved THz tomography system for the incidence-angle-dependent three-dimensional characterization of layered structures is presented. The capabilities of the developed system are demonstrated on multi-layer ceramic samples used for solid oxide fuel cells (SOFC). Appropriate methods for determining unknown refractive indices are discussed. It is shown how the angle of incidence of a THz imaging system has a significant influence on measured signals. This fact can be exploited especially in Brewster-angle configurations to enhance the capabilities of any THz tomography system. Data evaluation algorithms are presented. Received: 8 June 2000 / Revised version: 13 September 2000 / Published online: 10 January 2001     

Corrugated waveguide based genomic biochip for marker-free THz read-out

In this work a photonic waveguide-based THz snesor chip for DNA detection is investigated theoretically and experimentally. Using numerical field simulations the sensor response to isotropic laterally limited dielectric material placed at the sensor surface is discussed. The sensor surface is functionalized with immobilized DNA probe molecules and applied for the detection of a complementary gene sequence with a length of 28 bases.     

Coherent lattice dynamics of highly photo-excited tellurium

Received: 16 May 1997/Accepted: 16 May 1997     

Ultrafast carrier dynamics in strained In1−xGaxAs/InP heterostructures

The transfer of electrons and holes from barriers to wells is investigated in strained In_1-xGa_xAs/InP multiple quantum wells by time-resolved luminescence upconversion with 300 fs time resolution. The transfer times are in the range of a few ps and independent of the Ga content. The investigation of Ga-rich structures allows to observe directly the hole transfer.     

Ultrafast carrier dynamics in In1−x Ga x As/InP heterostructures

We investigate carrier capture and carrier transport in the InGaAs/InP material system by luminescence spectroscopy with femtosecond time resolution. Comparative studies are performed on samples of different well width, barrier width and gallium mole fraction of the InGaAs layers. The investigations focus on excitation conditions that are comparable to those for semiconductor laser operation. Firm data on carrier dynamics are presented for these conditions. We find that the overall transfer rates of electrons and holes are similar and independent of well width. Furthermore, the transfer times show a linear dependence on barrier width. From experimental and model calculation results we derive some guidelines for the design of high-frequency laser devices.     

Use of ultrashort laser pulses for desorption from semiconductor surfaces and nonresonant post-ionization of sub-monolayers

Summary The system aspects of a completely optical surface-sensitive time-of-flight mass spectrometer are presented. Using picosecond laser pulses for non-thermal desorption of neutrals from semiconductor surfaces and their optical post-ionization, a laser based mass spectrometry of extremely high sensitivity has been developed and tested. Initial experimental results are presented concerning the desorption yield from semiconductor surfaces, the saturation of the post-ionization and the useful yield of the system.     

HRGC-MS of polychlorinated phenanthrenes (PCPhen), dibenzothiophenes (PCDT), dibenzothianthrenes (PCTA), and phenoxathiins (PCPT)

Polychlorinated phenanthrenes (PCPhen, Cl_x Phen, x = 1–10), dibenzothiophenes (PCDT, Cl_xDT, x = 1–8), thianthrenes (PCTA, Cl_xTA, x = 1–8), and phenoxathiins (PCPT, Cl_xPT, x = 1–8) were synthesized and analyzed by high resolution capillary gas chromatography and EI and NCI mass spectrometry. In experiments the formation of polychlorinated phenanthrenes and dibenzothiophenes in combustion processes has been proved and compounds of these two classes have been detected in dust samples of an urban motorway tunnel.     

On Dedekind’s problem for complete simple games

We state an integer linear programming formulation for the unique characterization of complete simple games, i.e. a special subclass of monotone Boolean functions. In order to apply the parametric Barvinok algorithm to obtain enumeration formulas for these discrete objects we provide a tailored decomposition of the integer programming formulation into a finite list of suitably chosen sub-cases. As for the original enumeration problem of Dedekind on Boolean functions we have to introduce some parameters to be able to derive exact formulas for small parameters. Recently, Freixas et al. have proven an enumeration formula for complete simple games with two types of voters. We will provide a shorter proof and a new enumeration formula for complete simple games with two minimal winning vectors.