Doping Effects in CMOS-compatible CoSi Thin Films for Thermoelectric and Sensor Applications

Abstract . We report on semi-metallic cobalt monosilicide (CoSi) as a CMOS-compatible thermoelectric (TE) material and discuss the effect of n- and p-type dopants on its transport properties. Thin films of CoSi are developed using chemical vapor deposition tools and subsequent rapid thermal processing. Film properties such as microstructure, crystallinity and elemental distribution are studied via electron microscopy, X-ray diffraction and time-of-flight secondary ion mass spectroscopy. Doping silicon with boron prior to silicidation impedes the Co-Si diffusion process, while phosphorus atoms distribute uniformly in silicides with no voids or agglomerations. CoSi makes a suitable n-type TE candidate and provides an alternative to Si or SiGe materials. Transport properties of undoped CoSi exhibit a linear dependence within the investigated temperature window, whereas dopants in CoSi increase the number of electron carriers that contribute to charge transport and thereby influence the Seebeck coefficient. Thus, TE characteristics of thin CoSi films can be tuned via (i) the type of dopants used and/or (ii) varying the residual silicon thickness post silicidation.     

Synthesis, characterization, and X-ray structure determination of [Au18(P)2(PPh)4(PHPh)(dppm)6]Cl3

The reaction of [(AuCl)2dppm] (dppm=Ph2PCH2PPh2) with PhP(SiMe3)2 and P(SiMe3)3 leads to the formation of the gold cluster compound [Au18(P)2(PPh)4(PHPh)(dppm)6]Cl3 (1). The crystal structure investigation shows a central Au7P2 unit formed by two P centered gold tetrahedra sharing the central gold corner. This central unit is surrounded by a 10-membered Au5P5 ring which, together with the remaining six gold atoms, builds two Au4P rectangular and two Au3P trigonal pyramids. The different structure motifs are connected by the phosphine ligands. The compound has been characterized using microanalysis, IR spectroscopy, ESI-MS, and 31P NMR techniques. Luminescence measurements have also been carried out.     

On the physics of self-organized nanostructure formation upon femtosecond laser ablation

We present new results on femtosecond LIPSS on silicon, fostering the dynamic model of self-organized structure formation. The first set of experiments demonstrates LIPSS formation by irradiation with a femtosecond white light continuum. The ripples are, as usual, perpendicular to the light polarization with a fluence-dependent wavelength between 500 and 700 nm. At higher dose (fluence × number of shots), the LIPSS turn to much coarser structures. The second set of experiments displays the dose dependence of pattern evolution at about threshold fluence. In contrast to the general case of multi-pulse LIPSS, where a strong dependence of the structures on the laser polarization is observed, single-shot exposition of silicon at about the ablation threshold results in a concentric pattern of very regular sub-wavelength ripples following the oval shape of the irradiated spot, without any reference to the laser polarization. When increasing the number of pulses, the usual, typical ripples develop and then coalesce into broader perpendicular structures, interlaced with remnants of the first, finer ripples.     

Nonrelativistic scale anomaly, and composite operators with complex scaling dimensions

It is demonstrated that a nonrelativistic quantum scale anomaly manifests itself in the appearance of composite operators with complex scaling dimensions. In particular, we study nonrelativistic quantum mechanics with an inverse square potential and consider a composite s-wave operator O=ψψ. We analytically compute the scaling dimension of this operator and determine the propagator 〈0|TOO^†|0〉. The operator O represents an infinite tower of bound states with a geometric energy spectrum. Operators with higher angular momenta are briefly discussed.     

Shedding light into the detailed excited-state relaxation pathways and reaction mechanisms of thionaphthol isomers

Nanosecond laser flash photolysis employing transient detection of emission and absorption in combination with pulse radiolysis and quantum theory has been employed to shed light into the kinetics, quantum yields, and mechanisms of the deactivation of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))). In contrast to thiophenols (ArSH(S(1))), the results revealed that the decay of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))) is governed by radiationless internal conversion (Φ(IC) = 0.29-0.46; 0.016-0.190) and intersystem crossing (Φ(ISC) = 0.14-0.15; 0.4-0.6), respectively, with pronounced S-H photodissociation (Φ(D) = 0.40-0.55; 0.35-0.40). Fluorescence as a deactivation channel plays a minor role (Φ(F) = 0.001-0.010; 0.010-0.034). Quantum chemical calculations helped in understanding the formation of naphthylthiyl radicals and rationalizing the differences in the efficiency of intersystem crossing of the 1- and 2-thionaphthol systems.     

Classical gravitational radiation from quasi-elastic particle scattering in models with extra dimensions

An equation for the emission of classical gravitational waves due to quasi-elastic N → N particle scattering is derived in a model with compactified extra dimensions. In addition to previous classical studies, additional terms that are suppressed by factors of one over the frequency time compactification radius are also calculated. From this, a single formula is given which predicts the energy loss into the gravitational radiation from elastic collisions as well in the low-and high-energy limit. The text was submitted by the authors in English.