Direct fabrication of electrically functional microstructures by fully voltage-controlled electrohydrodynamic jet printing of silver nano-ink

We report electrohydrodynamic jet (E-jet) printing of a commercialised silver nano-ink in fully voltage-controlled fashion. Metallic pads and conducting tracks with hundred-micron feature size were drop-on-demands produced on Si substrates. Layer-by-layer printing was further performed, demonstrating a capability in creating 3D multistructures. Planar pattern with a large inductance of 2.5 μH and an excellent resistivity of 4.2×10⁻⁸ Ω m was fabricated, showing a true inductive device. Our result demonstrates a feasibility of E-jet printing in the application of smart electronic devices fabrication.     

Reflection asymmetry in the structure and spectroscopy of224Ac

Minor changes in the assignments of gamma rays following the alpha decay of²²⁸Pa in two previous studies make possible a reinterpretation of²²⁴Ac into two alternative level schemes. The resulting level structures arise from the reflection asymmetric configurations π3/2^±(0.0 −0.3)−ν3/2^±(−0.1 0.6), π5/2^±(0.0 −0.2)±ν3/2^±(−0.1 0.6) and π5/2^±(0.0 −0.2)±ν1/2^±(0.2 −0.1 3) which give rise to eitherK=0^± or 1^±,K=4^±,K=2^± andK=3^± parity doublet bands. The bands with appreciable band structure, namelyK=0^± or 1^± andK=3^±, have average parity doublet splittings of 11.0 and 5.8 keV respectively. These are extremely small values and suggest that²²⁴Ac is the most octupole deformed nucleus studied thus far. A method of calculating the parity doublet splitting in odd-odd nuclei is suggested and tested for²²⁴Ac. It seems to work remarkably well. The systematics of the hindrance factors for the bands with extended band structures confirm their interpretations as band structures. Finally, the two alternative level schemes are analyzed in the framework of the axially-symmetric rigid rotor model including the Coriolis interaction.     

LSP spectral changes correlating with SERS activation and quenching for R6G on immobilized Ag nanoparticles

In terms of chemical enhancement in Surface Enhanced Raman Scattering (SERS), we investigated the effect of halide and other anions to rhodamine 6G (R6G) adsorbed Ag particles that were immobilized on the substrates. The residual species on chemically prepared Ag particles such as citrate or a-carbon were thoroughly substituted by various anions, e.g., Cl⁻, Br⁻, I⁻, SCN⁻, CN⁻, or S₂O₃ ²⁻ anions, whose adsorption features are elucidated by the formation constants for AgX₂ ^(m−1)−, here X denotes the above anions. In particular, Cl⁻, Br⁻, or SCN⁻ ions activated SERS of R6G via intrinsic electronic interaction with Ag, whereas CN⁻, S₂O₃ ²⁻, or I⁻ anions quenched it due to their exclusive adsorption onto the Ag surfaces. We found that the activation process with the anions commonly yields a marked blue-shift of the coupled plasmon peak from ca. 650–700 to 500–550 nm in elastic scattering. It is rationalized by slight increase of the gap size between adjacent Ag nanoparticles by only ca. 1 nm based on theoretical simulations. This is probably caused by slight dissolution, oxidative etching, of the particles according to large formation constants of the complexes. Consequently, partly remaining negative charges on the Ag surface, and a slight increase in the gap size, providing huge electric field, facilitated R6G cations to adsorb on the nanoparticles, especially at the junction.     

Incorporation of Sn into epitaxial GaAs grown from the liquid phase

The incorporation of Sn into LPE GaAs was studied as a function of the atomic fractionx _Sn ^l of Sn in the liquid (1.6×10⁻⁴≤x _Sn ^l ≤0.54), the growth temperatureT _K and the cooling rate α. The diffusion coefficient of As in Ga for moderate Sn-doping was deduced from the growth velocities to beD _As (760° C)=(3.3±1.0)×10⁻⁵ cm²/s. The epitaxial layers were analyzed after van der Pauw with special emphasis on the sources of experimental error. With the aid of current mobility theories the concentrations of the ionized donors and acceptors were derived. From their dependence onx _Sn ^l , on α and onT _K combined with the Schottky-barrier model of Sn incorporation it can be concluded that the melt and the growing crystal surface were in thermal equilibrium. The diffusion coefficient of Sn in GaAs is about 8×10⁻¹⁴ cm²/s at 760° C. The distribution coefficient for Sn increases from 4.4×10⁻⁵ to 12.3×10⁻⁵ in the temperature range from 690 to 800° C. The total Sn incorporationx _Sn ^s was measured using the atomic absorption spectroscopy for the first time down tox _Sn ^s =10¹⁷/cm³. From these data it can be concluded that up tox _Sn ^l =0.54 the dopant Sn is incorporated as donor and as acceptor only and that within the experimental scatter there is no indication of incorporation as a neutral species.     

Synthesis and characterization of highly conductive Sn–Ag bimetallic nanoparticles for printed electronics

To synthesize low-cost, highly conductive metal nanoparticles for inkjet printing materials, we synthesized Sn–Ag bimetallic nanoparticles using a polyol process with poly(vinyl pyrrolidone). Because a surface oxidation layer forms on Sn nanoparticles, various compositions of Sn–xAg [x = 0, 20, 40, 60, 80, 100 (wt%)] nanoparticles were synthesized and characterized for the purpose of removing the β-Sn phase. The results of XPS, TEM, and XRD analyses confirm that the formation of a bimetallic phase, such as Ag₄Sn or Ag₃Sn, hinders the β-Sn phase and, consequently, leads to the removal of the surface oxidation layer. To measure the sheet resistance of various compositions of Sn–Ag nanoparticles, we made the ink that contains Sn–Ag by dispersing 10 wt% of Sn–Ag nanoparticles in methanol. The sheet resistance is decreased by the conductive Sn–Ag phases, such as the fcc, Ag₄Sn, and Ag₃Sn phases, but sharply increased by the low-conductive Sn nanoparticles and the surface oxidation layer on the Sn nanoparticles. The sheet resistance results confirm that 80Ag20Sn and 60Ag40Sn bimetallic nanoparticles are suitable candidates for inkjet printing materials.     

Structure of low-lying <Superscript>12</Superscript>C resonances

The hyperspherical adiabatic expansion is combined with complex scaling and used to calculate low-lying nuclear resonances of ¹²C in the 3α model. We use Ali-Bodmer potentials and compare results for other potentials α-α with similar ⁸Be properties. A three-body potential is used to adjust the ¹²C resonance positions to desired values extending the applicability of the method to many-body systems decaying into three α-particles. For natural choices of three-body potentials we find 14 resonances below the proton separation threshold, i.e. two 0⁺, three 2⁺, two 4⁺, one of each of 1^±, 2^-, 3^±, 4^-, and 6⁺. The partial-wave decomposition of each resonance is calculated as a function of the hyperradius. Strong variation is found from small to large distance. The connection to previous experimental and theoretical results is discussed and agreements as well as disagreements are emphasized.     

ΛΛ-Ξ N coupling effects in light hypernuclei

The significance of ΛΛ-Ξ N coupling in double-Λ hypernuclei has been studied. The Pauli suppression effect due to this coupling in ⁶ _ΛΛ He has been found to be 0.43MeV for the coupling strength of the NSC97e potential. This indicates that the free-space ΛΛ interaction is stronger by an about 5^° phase shift than that deduced from the empirical data of ⁶ _ΛΛ He without including the Pauli suppression effect. In ⁵ _ΛΛ He and ⁵ _ΛΛ H, an attractive term arising from the ΛΛ-Ξ N conversion is enhanced by the formation of an alpha-particle in the intermediate Ξ states. According to this enhancement, we have found that the ΛΛ binding energy ( ΔB _ΛΛ) of ⁵ _ΛΛ He is about 0.27MeV larger than that of ⁶ _ΛΛ He for the NSC97e coupling strength. This finding deviates from the general picture that the heavier is the core nucleus, the larger is ΔB _ΛΛ.-1 Received: 17 July 2002 / Accepted: 27 September 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: akaishi@post.ket.jp Communicated by A. Molinari     

Heavy quark results from STAR

I report the most recent measurements on open heavy flavor production at RHIC on behalf of the STAR collaboration. The total charm production cross section in midrapidity at RHIC energy is found to approximately scale by number of binary collisions in d + Au, Cu + Cu and Au + Au collisions. The nuclear modification factor of non-photonic electrons is strongly suppressed in central Au + Au collisions, suggesting substantial heavy quark energy loss at RHIC. The bottom decay contribution to non-photonic electrons was studied via the e–h and e–D ⁰ azimuthal angular correlations. The bottom contribution is found to be important at p _T >5 GeV/c, and is consistent with the FONLL calculation within uncertainties. Charm production through gluon jet splitting was measured by studying the D ^*± contents in the fully reconstructed jets in p+p collisions. This rate is consistent with pQCD evaluation of gluon splitting into a pair of charm quarks and subsequent hadronization.     

Multi-nozzle electrohydrodynamic inkjet printing of silver colloidal solution for the fabrication of electrically functional microstructures

In this paper, multi-nozzle electrohydrodynamic (EHD) inkjet printing of a colloidal solution containing silver nanoparticles in a fully controlled fashion is reported. For minimizing interaction, i.e. cross-talk, between neighboring jets, the distance between the nozzles was optimized numerically by investigating the magnitude of the electric field strength around the tip of each nozzle. A multi-nozzle EHD inkjet printing head consisting of three nozzles was fabricated and successfully tested by simultaneously printing electrically conductive lines of a colloidal solution containing silver nanoparticles onto a glass substrate. The printed results show electrical resistivity of 5.05×10⁻⁸ Ω m, which is almost three times larger than that of bulk silver. These conductive microtracks demonstrate the feasibility of the multi-nozzle EHD inkjet printing process for industrial fabrication of microelectronic devices.     

Enhanced field emission from pulsed laser deposited nanocrystalline ZnO thin films on Re and W

Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm² and 9.3 mA/cm² has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87 and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×10⁵ cm⁻¹ and 2.16×10⁵ cm⁻¹ for pointed and 3.2×10⁴ and 1.74×10⁴ for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical applications in field-emission-based electron sources.     

Cost-effective fabrication of memristive devices with ZnO thin film using printed electronics technologies

A prototype memristive device has been presented in this paper, for which the top and bottom electrodes have been fabricated through a simple and cost-effective technique, i.e. electrohydrodynamic printing. For deposition of the bottom electrode pattern, a silver ink containing 60 wt% silver by content was subjected to controlled flow through a metal capillary exposed to an electric field at the ambient temperature to generate an electrohydrodynamic jet, thereby depositing uniform patterns of silver on glass substrate at a constant substrate speed. The top electrode has been deposited in a similar fashion. In between the top and bottom electrodes, a uniform layer of ZnO is fabricated using spin-coating technique. The nanoscale ZnO memristor stack has a channel length of 370 μm and channel width of 82 μm. A memristor thus fabricated was characterized and its current voltage curves were analyzed. The device showed a typical nonvolatile resistive switching behavior present in memristor devices thus highlighting the EHD printed patterning as a reliable method for the fabrication of memory devices.     

Kinetic analysis of the photochemically and thermally induced isomerization of an azobenzene derivative on Au(111) probed by two-photon photoemission

Two-photon photoemission (2PPE) spectroscopy is employed to quantify the photochemically and thermally induced trans ⇌ cis isomerization of the molecular switch tetra-tert-butyl-azobenzene (TBA) adsorbed on an Au(111) surface. The isomerization of TBA is accompanied by significant changes in the electronic structure, namely different energetic positions of the lowest unoccupied molecular orbital of both isomers and the appearance of an unoccupied final state for cis-TBA. A quantitative analysis of these effects allows the calculation of cross sections for the reversible isomerization and determination of the ratio between both isomers in the photostationary state, where 55±5% of the molecules are switched to cis-TBA. The cross section for the photoinduced trans → cis isomerization is 3.3±0.5×10⁻²² cm², while for the back reaction, a value of 2.7±0.5×10⁻²² cm² is obtained. Furthermore a pronounced reduction of the activation energy by a factor of four compared to the free molecule is found for the thermally activated cis → trans isomerization of the surface-adsorbed TBA. This demonstrates that the potential energy landscape of the adsorbed TBA is remarkably different from the liquid phase.     

Structure and impedance spectroscopy of Pr1? x Sr x Fe0.8Co0.2O3? δ ( x =0.1, 0.2, 0.3) thin films grown by laser ablation

Polycrystalline samples of Pr_1−x Sr _x Fe_0.8Co_0.2 O_3−δ (x=0.1, 0.2, 0.3) (PSFC) were prepared by the combustion synthesis route at 1200°C. The structure of the polycrystalline powders was analysed with X-ray powder diffraction data. The X-ray diffraction (XRD) patterns were indexed as the orthoferrite similar to that of PrFeO₃ having a single-phase orthorhombic perovskite structure (Pbnm). Pr_1−x Sr _x Fe_0.8Co_0.2O_3−δ (x=0.1, 0.2, 0.3) films have been deposited on yttria-stabilized zirconia (YSZ) single-crystal substrates at 700°C by pulsed laser deposition (PLD) for application to thin film solid oxide fuel cell cathodes. The structure of the films was analysed by XRD, scanning electron microscopy (SEM) and atomic force microscopy (AFM). All films are polycrystalline with a marked texture and present pyramidal grains in the surface with different size distributions. Electrochemical impedance spectroscopy (EIS) measurements of PSFC/YSZ single crystal/PSFC test cells were conducted. The Pr_0.7Sr_0.3Fe_0.8Co_0.2O_3−δ film at 850°C presents a lower area specific resistance (ASR) value, 1.65 Ω cm², followed by the Pr_0.8Sr_0.2Fe_0.8Co_0.2O_3−δ (2.29 Ω cm² at 850°C) and the Pr_0.9Sr_0.1Fe_0.8Co_0.2O_3−δ films (5.45 Ω cm² at 850°C).     

Spectroscopic properties of Nd<Superscript>3+</Superscript>:CaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> crystal

The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd³⁺ ions in CaNb₂O₆ crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10⁻²⁰ cm² with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd³⁺ ions in CaNb₂O₆ crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω _t are Ω ₂=5.321×10⁻²⁰ cm²,Ω ₄=1.734×10⁻²⁰ cm²,Ω ₆=2.889×10⁻²⁰ cm². The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β ₁=36.03%,β ₂=52.29%,β ₃=11.15%,β ₄=0.533%. The emission cross section at 1062 nm is 9.87×10⁻²⁰ cm².     

Prediction of drop-on-demand (DOD) pattern size in pulse voltage-applied electrohydrodynamic (EHD) jet printing of Ag colloid ink

Drop-on-demand printing is receiving a great deal of interest in industrial applications; however, the desired pattern sizes are realized by trial and error, through repeated printing experiments with varied materials (ink and suspended particles), operating conditions (voltage, flow rate, nozzle-to-plate distance, etc.), and substrate wettability. Since this approach requires a great deal of time, cost, and effort, a more convenient and efficient method that will predict pattern sizes with a minimal number of experiments is needed. In this study, we patterned a series of Ag dots and lines using a pulsed voltage-applied electrohydrodynamic jet printing system and measured their sizes with an optical microscope. We then applied a model suggested by Stringer and Derby (J Eur Ceram Soc 29:913–918, 2009) and Gao and Sonin (Proc R Soc Lond Ser A 444:533–554, 1994) to predict the pattern sizes, comparing these predictions with the measured sizes. Finally, we demonstrated our methodology on disconnected line repairing.     

Effect of growth rate and Mg content on dendrite tip characteristics of Al–Cu–Mg ternary alloys

An experimental analysis is presented to correlate the secondary dendrite arm spacing λ ₂ and dendrite tip radius R with growth rate V and Mg content C _0-Mg of Al–Cu–Mg ternary alloys. Under constant temperature gradient G (4.84±0.13 K mm⁻¹), a series of directional solidification experiments were performed at five different growth rates V (16.7–83.3 μm/s) and five different Mg contents C _0-Mg in Al–5 wt.% Cu–(0.5–5) wt.% Mg alloys. Solid–liquid interface was investigated from the longitudinal sections of the quenched samples, and λ ₂ and R were measured on the dendrite tips. The dependencies of λ ₂ and R on V and C _0-Mg were determined. The experimental results showed that the values of λ ₂ and R decrease as V and C _0-Mg increase at a constant G. The present exponent values related to V are found to be slightly lower than the values of the theoretical models and previous experimental works; however, C _0-Mg exponent values are found to be much lower than the theoretical models and previous experimental works. The ratio of the secondary dendrite arm spacing to the dendrite tip radius is 2.09±0.15, in good agreement with the scaling law. At a constant C _0-Mg, the values of VR ² were found to slightly increase with the ascending V. However, as C _0-Mg increases, the values of VR ² decrease.     

Thermo-optic coefficients of monoclinic KLu(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The three thermo-optic coefficients of the biaxial laser host KLu(WO₄)₂ are measured at 633 nm by a deflection method. Their values at 300 K amount to ∂ n _g /∂ T=−7.4×10⁻⁶ K⁻¹; ∂ n _m /∂ T=−1.6×10⁻⁶ K⁻¹ and ∂ n _p /∂ T=−10.8×10⁻⁶ K⁻¹. Nearly athermal propagation directions are found for polarizations along the N _m and N _p dielectric axes.     

Proton-implanted optical channel waveguides in Nd<Superscript><Emphasis Type="Bold">3+</Emphasis></Superscript>:MgO:LiNbO<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript>: fabrication,guiding properties,and luminescence investigation

Optical channel waveguides in Nd³⁺:MgO:LiNbO₃ crystals are produced by using implantation of 500 keV protons at dose of 6×10¹⁶ ions/cm² with a stripe photoresist mask. With thermal annealing treatment at 400°C for 60 min, the propagation losses of the waveguides could be reduced down to ∼4 dB/cm at wavelength of 632.8 nm. The calculated modal profiles are in fairly good agreement with the experimental near-field intensity distributions of the waveguide modes. The microluminescence investigation indicates the emission intensity of Nd³⁺ ions is only slightly modified with respect to the bulk, exhibiting potentials for laser applications.     

Visualization of focusing–refocusing cycles during filamentation in BaF<Subscript>2</Subscript>

Filamentation occurs within a 1.5 cm-long crystal of BaF₂ during the propagation of intense, ultrashort (40 fs) pulses of 800 nm light; a systematic study as a function of incident power enables us to extract quantitative information on laser intensity within the condensed medium, the electron density and the six-photon absorption cross section. At low incident power, a single filament is formed within the crystal; two or more filaments are observed along the direction transverse to laser propagation at higher incident powers. Further, due to fluorescence from six-photon absorption (6PA), we are able to map the intensity variation in the focusing–refocusing cycles along the direction of laser propagation. At still higher incident powers, we observe splitting of multiple filaments. By measuring the radius (L _min) of single filament inside BaF₂, we obtain estimates of peak intensities (I _max) and electron densities (ρ _max) to be 3.26×10¹³ W cm⁻² and 2.81×10¹⁹ cm⁻³, respectively. Use of these values enables us to deduce that the 6PA cross-section in BaF₂ is 0.33×10⁻⁷⁰ cm¹² W⁻⁶ s⁻¹.     

Enhanced photoelectrochemical performance of ZnO photoanode with scattering hollow cavities

Abstract ZnO nanoparticles with average diameter of 12 nm were used to fabricate ZnO photoanodes by electrohydrodynamic (EHD) technique for dye-sensitized solar cells (DSSCs). To enhance the light scattering and conversion efficiency, the ZnO film with scattering hollow cavities (HCs) was realized by calcining polystyrene spheres (PSs) in the film. The films had strong light scattering ability and the overall light to electricity conversion efficiency (η) was improved and reached 5.5% under illumination of simulated solar light (AM-1.5, 100 mW/cm²).