Generalized routhian calculations within the Skyrme-Hartree-Fock approximation

We consider here variational solutions in the Hartree-Fock approximation upon breaking time reversal and axial symmetries. When decomposed on axial harmonic oscillator functions, the corresponding single particle triaxial eigenstates as functions of the usual cylindrical coordinates (r, $\theta$, z) are evaluated on a mesh in r and z to be integrated within Gauss-Hermite and Gauss-Laguerre approaches and as Fourier decompositions in the angular variable $\theta$. Using an effective interaction of the Skyrme type, the Hartree-Fock hamiltonian is also obtained as a Fourier series allowing a two dimensional calculation of its matrix elements. This particular choice is shown to lead in most cases to shorter computation times compared to the usual decomposition on triaxial harmonic oscillator states. We apply this method to the case of the semi-quantal approach of large amplitude collective motion corresponding to a generalized routhian formalism and present results in the A=150 superdeformed region for the coupling of global rotation and intrinsic vortical modes in what is known after Chandrasekhar as the S-ellipsoid coupling case.Comment: LaTeX using elsart, 32 pages, 4 included figures, submitted to Nuclear Physics A (revised version

Period of the gamma-ray staggering in the 150Gd superdeformed region

It has been previously proposed to explain gamma-ray staggerings in the deexcitation of some superdeformed bands in the $^{150}$Gd region in terms of a coupling between global rotation and intrinsic vortical modes. The observed 4$\hbar$ period for the phenomenon is suggested from our microscopic Routhian calculations using the Skyrme SkM* effective interaction.Comment: 4 pages, LaTeX with RevTeX, 4 included figures, submitted to Phys. Rep. C (revised version

Microactuators based on ion implanted dielectric electroactive polymer (EAP) membranes

We report on the first successfully microfabricated and tested ion-implanted dielectric electroactive polymer (EAP or DEAP) actuators. Dieletric EAP (DEAP) actuators combine exceptionally high energy-density with large amplitude displacements [1,2]. Scaling DEAPs down to the milimeter and micron scale requires patterning compliant electrodes on such a scale on the surfaces of the polymer. We used ion implantation to make the surfaces of the polymer locally conducting. Implanting the compliant electrodes solves the problem of microfabricating patterned electrodes whose elasticity is close to that of the insulating elastomer, thus avoiding the deposition of metal electrodes on the polymer which leads to significant stiffening of the membrane [3]. Several techniques based on ion implantation for chip level and wafer level fabrication are presented. Ion implanted DEAP membranes were both simulated (FEM) and characterized. We report measurements on an actuator consisting of a 30-um-thick ion implanted PDMS membrane bonded to a silicon chip into which a cavity had been etched. We measured 110 um vertical displacements for a 0.72 mm2 square membrane, achieving for the first time the same percent displacement in microscopic EAPs as in macroscopic devices. These observations show that ion implantation allows the patterning of electrodes on PDMS membranes with negligible increase in stiffness

Microactuators based on ion-implanted dielectric Electroactive Polymer Membranes (EAP)

We report on the first ion-implanted dielectric electroactive polymer actuator that was successfully microfabricated and tested. Ion implantation is used to make the surface of the polymer locally conducting. Implanting the compliant electrodes solves the problem of how to microfabricate patterned electrodes having elasticity close to that of the insulating elastomer. Dieletric EAP actuators combine in an exceptional way high energy-density, while allowing large amplitude displacements [1,2]. The ion-implant approach avoids the deposition of metal electrodes on the polymer, normally accompanied with an undesired stiffening of the membrane. The actuator consists of a 35-um thick ion implanted PDMS membrane bonded to a silicon chip containing a hole. We observed 110-um vertical displacements of a square membrane measuring 1 mm2. ©2005 IEEE

Direct Writing of Microtunnels Using Proton Beam Micromachining

The production of high aspect ratio microstructures is a potential growth area. The combination of deep X-ray lithography with electroforming and micromolding (i.e. LIGA) is one of the main techniques used to produce 3D microstructures. The new technique of proton micromachining employs focused MeV protons in a direct write process which is complementary to LIGA. During ion exposure of positive photoresist like PMMA, scission of molecular chains occurs. These degraded polymer chains are removed by the developer. The aim of this paper is to investigate the capabilities of proton micromachining as a lithographic technique. We show the realization of sub-surface channels, or microtunnels, which have been fabricated in only one exposure and without cutting or resurfacing the material. Using our Van-de-Graaff accelerator, the resist (PMMA) has been exposed with high-energy protons (2.5 MeV). The range of charged particles in matter is well-defined and depends on the energy. Therefore, it is possible to obtain a dose which is sufficient to develop the bottom part of the ion paths but not the top part. Thus, by selecting the energy and the exposure time, a big variety of microtunnels can be realized

Direct polymer patterning by high energy reactive ion beam through stencil masks

Polytetrafluoroethylene (PTFE) is a polymer with remarkable physico-chemical properties which has been used for membrane and biomedical applications [1]. This fluorpolymer is however difficult or cost- inhibiting to pattern with conventional methods with high aspect-ratios, especially at the micrometer scale [2-5]. The present work introduces an innovative efficient technique for direct micro-patterning of PTFE using a high energy un-focalized O + ion beam. A nanostencil [6] with features appropriately designed to be opaque to the un-focalized ions is placed between the large-area beam and the substrate. This allows the ions which pass though the mask to directly and unisotropically dry etch the polymer. The results prove this approach has a good reproducibility and is a cost-efficient way for local micro-structuring of high aspect- ratio structures in PTFE. Bulk, commercially available 500 m thick PTFE was used as the substrate. The stencil mask was based on low-stress LPCVD SiN membranes. Its local selectivity to the ion beam was obtained by having the membranes patterned with apertures and covered by a thick Au layer, as seen in the schematic from Fig. 1. The 500 nm SiN covered by 800 nm au was stopping the ions, while the beam was passing right through the membrane openings. The un-focused beam of O + ions was accelerated to 1 MeV in a Tandetron 1.7 MV particle accelerator. From simulations using SRIM software, the longitudinal straggling of the ions for 500 nm SiN and 530 nm Au was 1 m (Fig 2). Thus the 800 nm Au was expected to be a very good mask for stopping all the ions. For counter-acting thermal effects, the PTFE was heat-sunk in a customized frame, held at a distance of 2 mm from the stencil, and was irradiated in a pulsed mode. After two sequences of 5 seconds of beam on separated by a 30 second pause, the etched polymer depth reached around 10 m. This patterning speed of about 1 m/s revealed a good match to our simulations for the stencil mask materials and the high energy ion beam. The stencil was able to be reused tens of times without visible damages (Fig. 3). The smallest feature reproduced at the integral etch depth was a 1 m x 1 m square (Fig. 4). Outgassing was measured in-situ by mass spectroscopy. The results showed the emergence of combination molecules, indicating chemical reactions were taking place in PTFE under irradiation. We thus showed the viability of using an un-focused 1 MeV high-energy O + ion beam for direct etching of micrometer-size features in PTFE through a stencil mask. The mask opaqueness to the ions was optimized via simulations and good results were obtained using 800 nm Au as a stopping layer coating the SiN membrane. An aspect ratio of 10 was obtained for micro-patterns and further investigations are undergoing for optimizing the parameters which will allow reproducible nanopatterning in PTFE