Increasing DC Voltage Research Articles

Trapping Laser Ablated Ca+ Ions in Linear Paul Trap

We have investigated the efficiency of ion trapping in a linear Paul trap. First, we measured the dependence of trapping efficiency on dc and rf voltages using a channel electron multiplier for the direct detection of the electric current of the trapped ions. The most efficient dc and rf voltages were 5.0 and 175 V, respectively. Second, we calculated the trapping efficiency using a simulation code and compared it with the experimental results. We determined that the efficiency of ion trapping decreased monotonically with increasing dc voltage and had an optimum rf voltage. From the numerical calculation, the dependences of trapping efficiency on dc and rf voltages and the initial kinetic energy of ions was derived and the optimum dc and rf voltages and the initial kinetic energy of ions were found to be 0, 210 V, and 1 eV, respectively.

Progressive Loss of Ferroelectricity Under Bipolar Pulsed Fields and Experimental Determination of Non-Switchable Polarization in Au/Ba0.5Sr0.5-TiO3/SrRuO3 Thin-Film Capacitors

175 nm-thick Ba0.5Sr0.5TiO3 (BST) thin film fabricated by pulsed laser deposition (PLD) technique is found to be a mixture of two distributions of material. We discuss whether these two components are nano-regions of paraelectric and ferroelectric phases, or a bimodal grain-size distribution, or an effect of oxygen vacancy gradient from the electrode interface. The fraction of switchable ferroelectric phase decreases under bipolar pulsed fields, but it recovers after removal of the external fields. The plot of capacitance in decreasing dc voltage (C(V ↓) versus that in increasing dc voltage C(V ↑) is a superposition of overlapping of two triangles, in contrast to one well-defined triangle for typical ferroelectric SrBi2Ta2O9thin films.

Evidence for two-phase regions in Ba0.5Sr0.5TiO3 thin films from capacitance–voltage data

The Curie–Weiss plots of reciprocal dielectric constant versus temperature, in Ba0.5Sr0.5TiO3 films grown onto SrRuO3 lower electrodes by pulsed-laser deposition, show two minima below film thicknesses of 280 nm. This double minima implies possible mixed phases in the thin films. A graphical plot of capacitance for decreasing dc voltage versus that of increasing dc voltage shows a well-defined triangular shape for both Pb(Zr0.4Ti0.6)O3 and SrBi2Ta2O9 thin films. However, for a 175-nm-thick Ba0.5Sr0.5TiO3 thin film, the plot shows an overlapping of two triangles, suggesting mixed phases. This graphical method appears to be effective in detecting structural subtleties in ferroelectric capacitors.

Probing superconducting phase fluctuations from the current noise spectrum of pseudogapped metal-superconductor tunnel junctions.

We study the current noise spectra of a tunnel junction of a metal with strong pairing phase fluctuation and a superconductor. It is shown that there is a characteristic peak in the noise spectrum at the intrinsic Josephson frequency omega(J) = 2eV when omega(J) is smaller than the pairing gap but larger than the pairing scattering rate. In the presence of an ac voltage, the tunneling current noise shows a series of characteristic peaks with increasing dc voltage. Experimental observation of these peaks will give direct evidence of the pair fluctuation in the normal state of high- T(c) superconductors and the pair decay rate can be estimated from the half width of the peaks.

DC plasma-polymerized hexamethyldisilazane coatings of an equiatomic TiNi shape memory alloy

The TiNi corrosion resistance of Ti 50Ni 50 shape memory alloy can be substantially improved by DC plasma-polymerized hexamethyldisilazane (PHMDSN) coatings. The initial PHMDSN deposition rate increases with increasing DC voltage. The deposition rate decreases gradually with time until the glow discharge is extinguished. The higher DC voltage used in plasma polymerization will develop a film with a more inorganic nature from the IR spectrum analysis and water contact angle measurements. The PHMDSN coatings for DC voltage ≥1000 V are protection against the corrosion in Ringer’s solution and can be deformed up to a 2% strain. The corrosion current density of the TiNi alloy can be lowered by as many as four orders of magnitude. The pitting potential and re-passivation potential can also be enhanced to nobler potential after PHMDSN coatings. The widely scattered pitting potential of the as-homogenized TiNi can also be improved by the PHMDSN coatings.

Current-voltage hysteresis in GdBa2Cu3O7−δ ceramics in air at room temperature

We report here on the appearance of a hysteresis in the current-voltage characteristic, when a voltage is applied to a GdBa2Cu3O7−δ rod at room temperature. This hysteresis was caused by the appearance and disappearance of a hot spot. When a gradually increasing dc voltage (0–8 V) was applied to a GdBa2Cu3O7−δ rod, a hot spot appeared at a given voltage, Va. Further increasing of the voltage increased the spot size, while the current stayed constant. When a voltage of 8 V was reached, the voltage was gradually decreased. The spot did not disappear at Va, but at a voltage 0.2 to 1.3 V lower than Va. The current remained constant until the spot disappeared. By the authors' best knowledge, this is the first report of a hysteresis in the current-voltage characteristic at room temperature for a high Tc superconductor.

Effect of dc electric field on the effective microwave surface impedance of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 trilayers

We have studied the effect of a dc electric field on the effective microwave surface impedance of a thin film YBa2Cu3O7/SrTiO3/YBa2Cu3O7 (YBCO/STO/YBCO) trilayer by a dielectric resonator technique. At large dc electric fields (≳105 V/cm), both the effective surface resistance and reactance of the sample decrease monotonically with increasing dc voltage applied to the to YBCO film, yielding at 25 K and 24.7 GHz ‖δRs/δVdc‖∼0.25 μΩ/V and ‖δXs/δVdc‖∼1.8 μΩ/V, respectively. A two-fluid analysis indicates that the changes in the surface impedance can be explained in terms of field induced changes in the superconducting carrier density of the top YBCO film.