As-deposited near-single crystalline high Tc and Jc superconducting thin films by a pulsed lased deposition process

As-deposited high Tc superconducting Y1Ba2Cu3O7−x films with zero resistance temperatures of similar, equals89 K and critical current densities about 0.7×106 A/cm2 at 77 K have been reproducibly fabricated at a substrate holder temperature at 650°C, using pulsed laser deposition, without post-annealing. One key to these results is the injection of gaseous oxygen into laser produced plume just in front of the target. In this way, the correct amount of oxygen is incorporated into the as-grown film so that post-deposition treatment becomes unnecessary. Axial ion channeling in these as-deposit high Tc superconducting films on (100) SrTiO3 and X-ray photoelectron spectroscopy (XPS) on the film surfaces were performed. Angular yield profile near the film surface for Ba, and the surface peak intensity were measured using 3 MeV He ions. For channeling normal to the substrate a minimum yield of 7%, compared to similar, equals3% for single crystals, was obtained. The results of ion channeling and XPS studies indicate that the as-deposited films have good crystallinity as well as toichiometry to within similar, equals1 nm of the film surface. The in-situ growth of such high Tc and Jc films is an important step in the use of the laser deposition technique to fabricate multilayer structures and the surface perfection is of importance in tunneling devices such as Josephson junctions.

Reduction in magnetic field induced broadening of the resistive transition in laser‐deposited YBa2Cu3O7−x thin films on MgO

The magnetic field induced broadening of the normal to superconducting resistive transition of YBa2Cu3O7−x thin films laser deposited on (100) MgO substrates for field oriented parallel to the c axis is found to be significantly reduced in comparison with that found previously in single crystals and in films deposited on SrTiO3. This reduction in broadening is associated with a high density of defects which, while causing a slight decrease in Tc and an increase in the zero‐field transition width, seems to provide strong vortex pinning centers that reduce flux creep

Effect of Li substitution on dielectric and ferroelectric properties of ZnO thin films grown by pulsed-laser ablation

Li-doped ZnO thin films (Zn1-xLixO, x=0.05-0.15) were grown by pulsed-laser ablation technique. Highly c-axis-oriented films were obtained at a growth temperature of 500 degrees C. Ferroelectricity in Zn1-xLixO was found from the temperature-dependent dielectric constant and from the polarization hysteresis loop. The transition temperature (T-c) varied from 290 to 330 K as the Li concentration increased from 0.05 to 0.15. It was found that the maximum value of the dielectric constant at T-c is a function of Li concentration. A symmetric increase in memory window with the applied gate voltage is observed for the ferroelectric thin films on a p-type Si substrate. A ferroelectric P-E hysteresis loop was observed for all the compositions. The spontaneous polarization (P-s) and coercive field (E-c) of 0.6 mu C/cm(2) and 45 kV/cm were obtained for Zn0.85Li0.15O thin films. These observations reveal that partial replacement of host Zn by Li ions induces a ferroelectric phase in the wurtzite-ZnO semiconductor. The dc transport studies revealed an Ohmic behavior in the lower-voltage region and space-charge-limited conduction prevailed at higher voltages. The optical constants were evaluated from the transmission spectrum and it was found that Li substitution in ZnO enhances the dielectric constant.

Direct Writing of Copper Film Patterns by Laser-Induced Decomposition of Copper Acetate

Direct writing of patterns is being widely attempted in the field of microelectronic circuit/device manufacture. Use of this technique eliminates the need for employing photolithographic process. Laser induced direct writing can be achieved by (i) Photochemical reaction [i] , (ii) Evaporation from target material [2], and (iii) decomposition.Micron size features of palladium and copper through decomposition of palladium acetate and copper formate respectively on quartz and silicon using Argon ion laser have been reported [3,4] .In this commuication we report a technique for both single line and large area depositon of copper through decomposition of copper acetate,(CH3COO)2Cu, on alumina substrates.Nd:YAG laser known for its reliability and low maintenance cost as compared to excimer and other gas lasers is used. This technique offers an attractive and economical alternative for manufacture of thin film microcircuits.

Dual wavelength CO2-N2-CS2 gasdynamic laser

A new method for producing simultaneous lasing at 10.6 and 38.3 microns in a CO2-N2-CS2 gasdynamic laser is presented. The theoretical analysis predicts small-signal gain values of the order 0.21/m for 10.6-micron lasing in CO2 molecules and 0.085/m for 38.3-micron lasing in CS2 molecules, indicating the possibility of dual wave lasing.

Giant planar Hall effect in pulsed laser deposited permalloy films

Ni80Fe20 thin films with high orientation were grown on Si(1 0 0) using pulsed laser ablation. The anisotropic magnetoresistance (AMR) and the planar Hall measurements show a 2.5% resistance anisotropy and a 45% planar Hall voltage change for magnetic field sweep of 10 Oe. The planar Hall sensitivity dR/dH was found to be 900 Omega T-1 compared with a previously reported maximum of 340 Omega T-1 in the same system.Also these films are found to withstand repeated thermal cycling up to 110 degrees C and the Hall sensitivity remains constant within this temperature range. This combination of properties makes the system highly suitable for low magnetic field sensors, particularly in geomagnetic and biosensor applications. To elucidate this, we have demonstrated that these sensors are sensitive to Earth's magnetic field. These results are compared with the sputter deposited films which have a very low AMR and planar Hall voltage change as compared with the films grown by PLD. The possible reasons for these contrasting characteristics are also discussed.

A Possible and Necessary Consistency Proof

After Gödel's incompleteness theorems and the collapse of Hilbert's programme Gerhard Gentzen continued the quest for consistency proofs of Peano arithmetic. He considered a finitistic or constructive proof still possible and necessary for the foundations of mathematics. For a proof to be meaningful, the principles relied on should be considered more reliable than the doubtful elements of the theory concerned. He worked out a total of four proofs between 1934 and 1939. This thesis examines the consistency proofs for arithmetic by Gentzen from different angles. The consistency of Heyting arithmetic is shown both in a sequent calculus notation and in natural deduction. The former proof includes a cut elimination theorem for the calculus and a syntactical study of the purely arithmetical part of the system. The latter consistency proof in standard natural deduction has been an open problem since the publication of Gentzen's proofs. The solution to this problem for an intuitionistic calculus is based on a normalization proof by Howard. The proof is performed in the manner of Gentzen, by giving a reduction procedure for derivations of falsity. In contrast to Gentzen's proof, the procedure contains a vector assignment. The reduction reduces the first component of the vector and this component can be interpreted as an ordinal less than epsilon_0, thus ordering the derivations by complexity and proving termination of the process.

Microstructure related influence on the electrical properties of pulsed laser ablated (Ba, Sr)TiO3 thin films

The microstructural dependence of electrical properties of (Ba, Sr)TiO3(BST) thin films were studied from the viewpoint of dc and ac electrical properties. The films were grown using a pulsed laser deposition technique in a temperature range of 300 to 600 degrees C, inducing changes in grain size, structure, and morphology. Consequently, two different types of films were realized, of which type I, was polycrystalline, multigrained, while type II was [100] oriented possessing a densely packed fibrous microstructure. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. The results revealed a contribution from both electronic and ionic conduction. In the case of type I films, two trapping levels were identified with energies around 0.5 and 2.73 eV, which possibly originate from oxygen vacancies V-O and Ti3+ centers, respectively. These levels act as shallow and deep traps and are reflected in the current-voltage characteristics of the BST thin films. The activation energy associated with oxygen vacancy motion in this case was obtained as 1.28 eV. On the contrary, type II films showed no evidence of deep trap energy levels, while the identified activation energy associated with shallow traps was obtained as 0.38 eV. The activation energy obtained for oxygen vacancy motion in type II films was around 1.02 eV. The dc measurement results were further elucidated through ac impedance analysis, which revealed a grain boundary dominated response in type I in comparison to type II films where grain response is highlighted. A comparison of the mean relaxation time of the two films revealed three orders of magnitude higher relaxation time in the case of type I films. Due to smaller grain size in type I films the grains were considered to be completely depleted giving rise to only grain boundary response for the bulk of the film. The activation energy obtained from conductivity plots agree very well with that of dc measurements giving values 1.3 and 1.07 eV for type I and type II films, respectively. Since oxygen vacancy transport have been identified as the origin of resistance degradation in BST thin films, type I films with their higher value of activation energy for oxygen ion mobility explains the improvement in breakdown characteristics under constant high dc field stress. The role of microstructure in controlling the rate of degradation is found useful in this instance to enhance the film properties under high electric field stresses. (C) 2000 American Institute of Physics. [S0021-8979(00)00418-7].

High contrast laser writing in insitu textured germanium films via a novel chemical oxide formation

A high contrast laser writing technique based on laser induced efficient chemical oxidation in insitu textured Ge films is demonstrated. Free running Nd-YAG laser pulses are used for irradiating the films. The irradiation effects have been characterised using optical microscopy, electron spectroscopy and microdensitometry. The mechanism for the observed contrast has been identified as due to formation of GeO2 phase upon laser irradiation using X-ray initiated Auger spectroscopy (XAES) and X-ray photoelectron spectroscopy (XPS). The contrast in the present films is found to be nearly five times more than that known due to GeO phase formation in similar films.

Laser Surface Alloying of a Creep Resistant Magnesium Alloy MRI 230D with Al and Al2O3

A creep resistant permanent mould cast Mg alloy MRI 230D was laser surface alloyed with Al and a mixture of Al and Al2O3 using pulsed Nd:YAG laser irradiation at four different scan speeds in order to improve the corrosion and wear resistance. The microstructure, corrosion and wear behavior of the laser surface alloyed material is reported in this manuscript. The coating comprised of a featureless microstructure with cellular-dendritic microstructure near the interface and exhibited good interfacial bonding. A few solidification cracks reaching down to substrate were also observed. The two step coating with Al followed by a mixture of Al and Al2O3 exhibited a slightly better corrosion resistance than the single step coating with Al. In the long run, however, corrosion resistance of both the coatings became comparable to the as-cast alloy. The corroded surface of the laser surface alloyed specimens revealed a highly localized corrosion. The laser surface alloyed specimens exhibited an improvement in wear resistance. The laser scan speed did not exhibit a monotonic trend either in corrosion or wear resistance.

Excimer laser refractive surgery : corneal wound healing and clinical results

Although the first procedure in a seeing human eye using excimer laser was reported in 1988 (McDonald et al. 1989, O'Connor et al. 2006) just three studies (Kymionis et al. 2007, O'Connor et al. 2006, Rajan et al. 2004) with a follow-up over ten years had been published when this thesis was started. The present thesis aims to investigate 1) the long-term outcomes of excimer laser refractive surgery performed for myopia and/or astigmatism by photorefractive keratectomy (PRK) and laser-in situ- keratomileusis (LASIK), 2) the possible differences in postoperative outcomes and complications when moderate-to-high astigmatism is treated with PRK or LASIK, 3) the presence of irregular astigmatism that depend exclusively on the corneal epithelium, and 4) the role of corneal nerve recovery in corneal wound healing in PRK enhancement. Our results revealed that in long-term the number of eyes that achieved uncorrected visual acuity (UCVA)≤0.0 and ≤0.5 (logMAR) was higher after PRK than after LASIK. Postoperative stability was slightly better after PRK than after LASIK. In LASIK treated eyes the incidence of myopic regression was more pronounced when the intended correction was over >6.0 D and in patients aged <30 years.Yet the intended corrections in our study were higher for LASIK than for PRK eyes. No differences were found in percentages of eyes with best corrected visual acuity (BCVA) or loss of two or more lines of visual acuity between PRK and LASIK in the long-term. The postoperative long-term outcomes of PRK with two different delivery systems broad beam and scanning laser were compared and revealed no differences. Postoperative outcomes of moderate-to-high astigmatism yielded better results in terms of UCVA and less compromise or loss of two more lines of BCVA after LASIK that after PRK.Similar stability for both procedures was revealed. Vector analysis showed that LASIK outcomes tended to be more accurate than PRK outcomes, yet no statistically differences were found. Irregular astigmatism secondary to recurrent corneal erosion due to map-dot-fingerprint was successfully treated with phototherapeutic keratectomy (PTK). Preoperative videokeratographies (VK) showed irregular astigmatism. However, postoperatively, all eyes showed a regular pattern. No correlation was found between pre- and postoperative VK patterns. Postoperative outcomes of late PRK in eyes originally subjected to LASIK showed that all (7/7) eyes achieved UCVA ≤0.5 at last follow-up (range 3 — 11 months), and no eye lost lines of BCVA. Postoperatively all eyes developed and initial mild haze (0.5 — 1) into the first month. Yet, at last follow-up 5/7 eyes showed a haze of 0.5 and this was no longer evident in 2/7 eyes. Based on these results, we demonstrated that the long-term outcomes after PRK and LASIK were safe and efficient, with similar stability for both procedures. The PRK outcomes were similar when treated by broad-beam or scanning slit laser. LASIK was better than PRK to correct moderate-to-high astigmatism, yet both procedures showed a tendency of undercorrection. Irregular astigmatism was proven to be able to depend exclusively from the corneal epithelium. If this kind of astigmatism is present in the cornea and a customized PRK/LASIK correction is done based on wavefront measurements an irregular astigmatism may be produced rather than treated. Corneal sensory nerve recovery should have an important role in the modulation of the corneal wound healing and post-operative anterior stromal scarring. PRK enhancement may be an option in eyes with previous LASIK after a sufficient time interval that in at least 2 years.

Fabrication of device quality films of high loaded PPy/MWCNT nanocomposites using pulsed laser deposition

Polypyrrole (PPy) - multiwalled carbonnanotubes (MWCNT) nanocomposites with various MWCNT loading were prepared by in situ inversion emulsion polymerization technique. High loading of the nano filler were evaluated because of available inherent high interface area for charge separation in the nanocomposites. Solution processing of these conducting polymer nanocomposites is difficult because, most of them are insoluble in organic solvents. Device quality films of these composites were prepared by using pulsed laser deposition techniques (PLD). Comparative study of X-ray photoelectron spectroscopy (XPS) of bulk and film show that there is no chemical modification of polymer on ablation with laser. TEM images indicate PPy layer on MWCNT surface. SEM micrographs indicate that the MWCNT's are distributed throughout the film. It was observed that MWCNT in the composite held together by polymer matrix. Further more MWCNT diameter does not change from bulk to film indicating that the polymer layer remains intact during ablation. Even for very high loadings (80 wt.% of MWCNT's) of nanocomposites device quality films were fabricated, indicating laser ablation is a suitable technique for fabrication of device quality films. Conductivity of both bulk and films were measured using collinear four point probe setup. It was found that overall conductivity increases with increase in MWCNT loading. Comparative study of thickness with conductivity indicates that maximum conductivity was observed around 0.2 mu m. (C) 2010 Elsevier B.V. All rights reserved.

Lokia etsimässä : Viisi teoriaa muinaisskandinaavisen Lokin hahmosta

Loki on muinaisskandinaavisen mytologian monimutkaisimpia hahmoja. Keskiaikaiset lähteet Lokista ovat runo- ja Snorrin Edda sekä skaldirunot. Moderneja kansansanontoja on myös käytetty tutkimuksessa Lokin hahmosta, mutta osa tutkijoista vastustaa niiden käyttöä ajallisen ja usein maantieteellisen eroavaisuuden takia verrattuna keskiaikaiseen Lokiin. Analysoimalla Axel Olrikin, Hilding Celanderin, Jan de Vriesin, Georges Dumézilin sekä Anna Birgitta Roothin teorioita Lokista selvitän, minkälaiset teoreettiset lähtökohdat Lokin hahmon tutkimuksesta ovat vallinneet 1900-luvulla ja miten he ovat käyttäneet keskiaikaisia ja moderneja lähteitä. Lisäksi tarkastelen sitä, miten näiden tutkijoiden teoriat ovat vaikuttaneet uudempaan tutkimukseen Lokista. Metodinani käytän systemaattista analyysia. Olrik lähestyi Lokin hahmoa maantieteellis-historiallisen metodin kautta jaotellen myytit Lokista joko Odinn-Loki- tai Thorr-Loki-ryhmään. Hänen johtopäätöstensä perusteella Loki on lähtökohtaisesti Prometheus-tyypin hahmo, joka on ensin yhdistetty Thorriin ja myöhemmin Odinniin. Celanderin mukaan Loki on alun perin haltija, ja hän lähestyy aineistoaan Lokin nimestä tehtyjen etymologisten johtopäätösten kautta yhdistäen teoriaansa moderneja luonnonilmiöihin liittyviä sanontoja. de Vries käyttää metodinaan filologista menetelmää ja hän näkee Lokissa kulttuuriheeroksen ja tricksterin. Dumézilin näkemyksen pohjana on hänen teoriansa kolmiosaisesta indoeurooppalaisesta yhteisöstä. Dumézil vertaa Lokia kaukasuslaiseen Syrdon-hahmoon löytäen näiden väliltä useita yhtäläisyyksiä. Rooth pyrkii löytämään mahdollisimman alkuperäisen Lokin hahmon karsimalla myyteistä muualta tulleet vaikutteet. Hänen mukaansa Loki on ollut alun perin hämähäkin hahmoinen trickster, josta olisi jäänyt merkkejä kansanperinteeseen. Johtopäätöksenäni totean, että Lokin tutkimukseen ovat vaikuttaneet ainakin diffusionistinen metodi, filologinen ja strukturalistinen lähestymistapa sekä varhaisemmat 1800-luvun teoriat kuten Frazerin ja Müllerin uskontoteoriat. Keskiaikaisista lähteistä Snorrin Eddan luotettavuudesta on syntynyt eniten keskustelua, etenkin Baldr-myytin tulkinnan kannalta. Sen sijaan skaldirunojen ja runo-Eddan luotettavuutta ei ole kyseenalaistettu yhtä useasti. Modernien lähteiden luotettavuudesta tutkijat eivät ole päässeet yksimielisyyteen. Myöhempään tutkimukseen on vaikuttanut erityisesti käsitys Lokista tricksterinä. Celanderin ja Roothin etymologinen lähestymistapa on osaltaan vaikuttanut uudempaan tutkimukseen ja tulkintaan Lokista abstraktina hahmona, kuten myös de Vriesin kriittisyys moderneja lähteitä kohtaan. Dumézilin teorian vaikea soveltuvuus trickster-hahmojen tulkitaan on vähentänyt viittauksia häneen myöhemmässä Loki-tutkimuksessa eikä Olrikin maantieteellistä jaottelua näe enää uudemmassa tutkimuskirjallisuudessa. Jotkin teemat ovat jääneet vähemmälle huomiolle tutkimuksessa, kuten kenningien eli runollisten metaforien vähäinen liittyminen Lokiin sekä Lokin suhde jättiläisiin. Jatkotutkimuksen kannalta näiden teemojen syventäminen Lokin hahmon ymmärtämisessä olisi aiheellista. Lisäksi tutkimushistorian tuntemusta Lokin tutkimuksessa olisi mahdollista syventää vielä entisestään selvittämällä esimerkiksi kansallissosialistisen ilmapiirin vaikutusta mytologian tutkimuksessa.