Showing papers by "Sven Ulrich published in 2011"

Surface plasmon polariton absorption modulator

Abstract: An electrically controlled ultra-compact surface plasmon polariton absorption modulator (SPPAM) is proposed. The device can be as small as a few micrometers depending on the required extinction ratio and the acceptable loss. The device allows for operation far beyond 100 Gbit / s, being only limited by RC time constants. The absorption modulator comprises a stack of metal / insulator / metal-oxide / metal layers, which support a strongly confined asymmetric surface plasmon polariton (SPP) in the 1.55 μm telecommunication wavelength window. Absorption modulation is achieved by electrically modulating the free carrier density in the intermediate metal-oxide layer. The concept is supported by proof-of-principle experiments.

Laser micro-structuring of magnetron-sputtered SnO x thin films as anode material for lithium ion batteries

Abstract: SnOx electrode thin films for lithium ion batteries were deposited by reactive and non-reactive rf magnetron sputtering of a SnO2 target in an argon–oxygen atmosphere. Amorphous and nano-crystalline SnOx films could be synthesized, with regard to the O2:Ar volume ratio in the sputter gas which was adjusted to 0, 3.5 or 10%. Laser micro-structuring using a KrF excimer laser operating at a wavelength of λ = 248 nm was applied to create free-standing microstructures. Thus, the active surface of the anode material was significantly increased. Furthermore, it was expected that the large volume changes during electrochemical cycling of SnOx could be better compensated by a microstructured surface. The laser parameters were optimized in a way which leads to structures without any defects and little debris. Depending on the laser fluence and pulse number, free-standing conical structures could be formed with a horizontal spacing of <0.5 μm up to 2 μm. The structured and unstructured thin films were cycled in a battery tester against metallic lithium. The structured SnOx thin films exhibited significantly better battery performance with respect to cycling stability.

Ion bombardment-induced nanocrystallization of magnetron-sputtered chromium carbide thin films

Abstract: Nearly stoichiometric chromium carbide thin films (Cr3C2) were deposited by unbalanced r.f. magnetron sputtering of a chromium carbide target in a pure argon discharge. Their microstructure and hardness are shown to be strongly influenced by the working pressure and substrate bias during deposition. Further correlation with the plasma parameters, i.e. the energy and flux of argon ions as well as the flux of film-forming particles, is illustrated, which indicates the momentum transferred by bombarding ions per film-forming particle Pdens which creates a densification and simultaneously does not cause a mobility enhancement to be dominant for the film structure. Below a threshold value of Pdens of about 0.91 u0.5eV0.5, the resulting films exhibited an amorphous structure with a relatively low hardness of 1200 HV0.02. A nanocrystalline structure emerged only for larger values of Pdens, and was responsible for a hardness enhancement to 3500 HV0.02.

Magnetron sputtered nanocrystalline metastable (V,Al)(C,N) hard coatings

Abstract: Nanocrystalline hard coatings of the system V–Al–C–N with an f.c.c. metastable solid solution (V,Al)(N,C) microstructure were deposited by non-reactive r.f.-magnetron sputtering of a ceramic compound target (composition: 60 mol.% VC and 40 mol.% AIN) in a pure argon discharge at 1.1 Pa. The chemical composition of the as-deposited coatings was determined by electron probe micro analysis (EPMA). The microstructure of the thin films was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The influence of a moderate argon ion bombardment during thin film deposition, realized through the variation of the argon ion energy in the range 20 eV–170 eV, as a means to adjust the adatom surface mobility and surface diffusion processes, on the microstructure evolution and on the Vickers micro-hardness is discussed. The conditions for the formation of a metastable solid solution f.c.c. (V,AI)(C,N) thin film microstructure are described in terms of surface processes during film growth and thermodynamic considerations. It was demonstrated, that a metastable phase formation in the quaternary material system V–Al–C–N can easily be adjusted in magnetron sputter deposition.

Laser processing of SnO2 electrode materials for manufacturing of 3D micro-batteries

Abstract: The material development for advanced lithium-ion batteries plays an important role in future mobile applications and energy storage systems. It is assumed that electrode materials made of nano-composited materials will improve battery lifetime and will lead to an enhancement of lithium diffusion and thus improve battery capacity and cyclability. A major problem concerning thin film electrodes is, that increasing film thickness leads to an increase in lithium diffusion path lengths and thereby a decrease in power density. To overcome this problem, the investigation of a 3D-battery system with an increased surface area is necessary. UV-laser micromachining was applied to create defined line or grating structures via mask imaging. SnO 2 is a highly investigated anode material for lithium-ion batteries. Yet, the enormous volume changes occurring during electrochemical cycling lead to immense loss of capacity. The formation of micropatterns via laser ablation to create structures which enable the compensation of the volume expansion was investigated in detail. Thin films of SnO 2 were deposited in Ar:O 2 atmosphere via r.f. magnetron sputtering on silicon and stainless steel substrates. The thin films were studied with X-ray diffraction to determine their crystallinity. The electrochemical properties of the manufactured films were investigated via electrochemical cycling against a lithium anode.

Towards In Situ-Process Control in Tribological or Tool Applications: A Material Concept for the Design of Smart Thin Film Wear Sensors

Abstract: The optimization of processes for tribological or machining applications requires the development of (i) high performance substrate materials, especially ultra fine grain cemented carbides for cutting tools, (ii) complex tool geometries and (iii) innovative, nano-scaled hard and tough multi-functional protective coatings. Very important is also the in-situ process control which can be realized with (i) sensors which are embedded in the protective coating using microsystem technology or (ii) if possible, by using tailored coating designs which show itself both protective and sensor functionality.

Metastable, nanostabilised material and method for its production

Abstract: Metastable, nanostabilized material (I) comprises many layers (A, B), both in face-centered cubic structure, where the layer A comprises a nitrogen containing compound (II) and the layer B comprises a metallic compound (III). Metastable, nanostabilized material (I) comprises many layers (A, B), both in face-centered cubic structure, where the layer A comprises a nitrogen containing compound of formula (R, N) (II) and the layer B comprises a metallic compound of formula ((R, aM)N) (III). R : refractory elements comprising Ti, Ta, Hf, V, Nb, Zr and/or Cr; M : transition metals comprising Fe and/or Co; and a : 1 or 2. An independent claim is included for producing (I), comprising applying a material that grows by itself in the form of face-centered cubic structure, as layer A and a material that grows by itself in the form of face-centered cubic structure, as a layer B, on a carrier.