Nm For Ru Research Articles

(Invited) Impact of Surface Roughness of the Electrodes on the Resistive Switching in ReRam Devices

Cu/TaOx/Pt and Cu/TaOx/Ru devices have been manufactured in the same process flow except for the separate deposition at identical deposition rate of the Pt and Ru electrodes. The details of sample manufacturing are given in [1]. The identical processing after the deposition of the bottom electrode assures that the thickness and composition of the TaOx solid electrolyte is exactly the same. The two devices have similar I-V switching characteristics, albeit with some important differences: the mean forming voltage (when the conductive filament (CF) is formed for the very first time) of the Ru device (Vform,m(Ru)=7.3V) is 2.7V higher than the mean forming voltage for the Pt device (Vform,m(Pt)=4.6V). The mean set voltage of the Ru device (Vset,m(Ru)=4.4V) is also higher by 1.6V than the mean set voltage of the Pt device (Vset,m(Pt)=2.8V). The set voltage is the voltage needed to rebuild the CF after it has been ruptured in a preceding reset operation. Thus, in the set operation only a small segment of the filament has to be rebuilt. It is assumed that the gap of ruptured filament is small (a few nm) and is located close to the tip of the cone-shaped filament near the active Cu electrode. Here we attempt to account for the additional 1.1V in Vform,m. One part of these differentials between Vform and Vset of 2.7V and 1.6V, respectively, can be explained by the work function difference between the inert electrodes Pt (φ=6.3eV) and Ru (φ=4.7eV) being Δφ=1.6eV. Since the work function for Pt can be as low as φ=5.6eV, the value 1.6V is considered an upper boundary for Δφ. The same Δφ contributes also to the difference between the forming voltages. To account for the remaining 1.1V difference voltage we have measured the surface roughness in Atomic Force Microscope (AFM) of the Pt and Ru electrodes before the deposition of TaOx. AFM analysis shows that Pt displays significantly higher surface roughness than Ru. The root mean square (rms) roughness for Pt is 2.30nm versus 1.20nm for Ru, thus almost 100% higher. The AFM images reveal also a different texture of the surface roughness for Ru and Pt. The surface protrusions of Ru are finer and smaller than those of Pt with a maximum height of 3.5nm while the protrusions of Pt are bulkier (surface coarser) and much higher with a maximum of 7.9nm. It appears that the Ru surface roughness is due to single atoms spatial variation while the Pt surface appears to consist of stacked clusters of Pt atoms. We have also taken AFM images of the Cu surface roughness. The copper surface appears coarse as if consisting of clumped Cu atoms with a rms of 1.17nm, i.e. comparable to the surface roughness of Pt. Electrically, higher surface roughness of Pt generates higher local electric fields thus allowing filament formation at lower applied voltages. The differential in set voltage between Pt and Ru of ΔVset=1.6V is accounted solely (or close to it) by Δφ(Pt-Ru). This is further confirmed by the observation that since for the set operation the surface roughness of the inert electrode is irrelevant as the gap in the filament near the Cu electrode is independent of the surface roughness. The built-in field in case of Pt electrode is the work function difference between Pt and Cu divided by the thickness of the TaOx dielectric, which in case of Pt devices comes to a quite high field of 6.8×105V/cm. This field favors Cu+ ion transport toward the Pt electrode. The corresponding built-in field in case of Ru devices is 6.0×104V/cm, i.e. one order of magnitude lower than for the Pt device. The field responsible for the formation of the Cu filament in its final stages has been estimated to be (1-2)×106V/cm [2]. The calculation of the electric fields at Vset for Pt and Ru including the built-in potential, are, indeed, in this range and approximately the same: (Δφ(Pt,Cu)/q+Vset,m(Pt))V/25nm≈(Δφ(Ru,Cu)/q+Vset,m(Ru))V/25nm≈1.8×106V/cm. The present analysis demonstrates that surface roughness is an important parameter for resistive ReRAM switching. It offers a new way to lower Vform by increasing the surface roughness (by e.g. argon ion bombardment or RIE etching) of the metal electrodes. In some cases, we observe spontaneous setting operation for the Pt but not for the Ru devices. The spontaneous formation of a filament is the result of the high electric fields resulting from built-in voltage Δφ along with high surface roughness of Pt electrode.[1] Y.Fan, M.Al-Mamun, B.Conlon, S.W.King, M.Orlowski, ECS Transactions 75(32), 13-23(2017)[2] R.Ali, Y.Fan, S.W.King, M.Orlowski, APL Materials 6, 066101(2018) Figure 1

Promoted Alkaline Hydrogen Evolution Reaction Performance of Ru/C by Introducing TiO2 Nanoparticles

AbstractHigher water dissociation (Volmer step) energy barrier leads to the sluggish alkaline hydrogen evolution reaction (HER) rate. Since hydrophilic TiO2 can reduce water dissociation barrier while the widely studied Ru has nearly zero hydrogen adsorption Gibbs free energy, the combination of TiO2 and Ru/C might collectively enhance Volmer and Heyrovsky/Tafel step and finally promote HER performance. Herein, Ru/C−TiO2 with average size of 3.6 nm for Ru was synthesized by a two‐step process. It presented superior alkaline HER activity with η10 of 44 mV, better than that of Ru/C (107 mV), Pt/C (84 mV) and C−TiO2 with negligible activity. The prominent HER performance was due to synergistic effect between TiO2 and Ru, which greatly expedited water dissociation for intermediate hydrogen production and the following electrochemical hydrogen desorption for producing H2. This work combines specific active sites for different elementary steps and then boosts alkaline HER performance, which provide a guide for designing efficient and stable HER electrocatalyst.

Nonequilibrium heat transport in Pt and Ru probed by an ultrathin Co thermometer

Non-equilibrium of electrons, phonons, and magnons in metals is a fundamental phenomenon in condensed matter physics and serves as an important driver in the field of ultrafast magnetism. In this work, we demonstrate that the magnetization of a sub-nm-thick Co layer with perpendicular magnetic anisotropy can effectively serve as a thermometer to monitor non-equilibrium dynamics in adjacent metals, Pt and Ru, via time-resolved magneto-optic Kerr effect. The temperature evolutions of the Co thermometer embedded in Pt layers of different thicknesses, 6-46 nm, are adequately described by a phenomenological three temperature model with a consistent set of materials parameters. We do not observe any systematic deviations between the model and the data that can be caused by a non-thermal distribution of electronic excitations. We attribute the consistently good agreement between the model and the data to strong electron-electron interaction in Pt. By using Pt/Co/Pt and Pt/Co/Pt/Ru structures, we determine the electron-phonon coupling parameters of Pt and Ru, g_ep(Pt)=(6+/-1)x10^17 W m-3 K-1 and g_ep(Ru)=(9+/-2)x10^17 W m-3 K-1. We also find that the length scales of non-equilibrium between electrons and phonons are l_ep=({\Lambda}_e/g_ep)^1/2 =9 nm for Pt and 7 nm for Ru, shorter than their optical absorption depths, 11 and 13 nm, respectively. Therefore, the optically thick Pt and Ru layers show two steps of temperature rise: The initial jump of electron temperature that occurs within 1 ps is caused by direct optical excitation and electronic heat transport within a distance l_ep for the Co layer. The second temperature rise is caused by heat transport by electrons and phonons that are near thermal equilibrium. We contrast two-temperature modeling of heat transport in Pt an Ru films to calculations for Cu, which has a much longer non-equilibrium length scale, l_ep=63 nm.

Synthesis and Cytotoxicity Studies on Ru and Rh Nanoparticles as Potential X-Ray Fluorescence Computed Tomography (XFCT) Contrast Agents.

X-Ray fluorescence computed tomography (XFCT) is an emerging biomedical imaging technique, which demands the development of new contrast agents. Ruthenium (Ru) and rhodium (Rh) have spectrally attractive Kα edge energies, qualifying them as new XFCT bio-imaging probes. Metallic Ru and Rh nanoparticles are synthesized by polyol method, in the presence of a stabilizer. The effect of several reaction parameters, including reaction temperature time, precursor and stabilizer concentration, and stabilizer molecular weight, on the size of particles, were studied. Resultant materials were characterized in detail using XRD, TEM, FT-IR, DLS-zeta potential and TGA techniques. Ru particles in the size range of 1–3 nm, and Rh particles of 6–9 nm were obtained. At physiological pH, both material systems showed agglomeration into larger assemblies ranging from 12–104 nm for Ru and 25–50 nm for Rh. Cytotoxicity of the nanoparticles (NPs) was evaluated on macrophages and ovarian cancer cells, showing minimal toxicity in doses up to 50 μg/mL. XFCT performance was evaluated on a small-animal-sized phantom model, demonstrating the possibility of quantitative evaluation of the measured dose with an expected linear response. This work provides a detailed route for the synthesis, size control and characterization of two materials systems as viable contrast agents for XFCT bio-imaging.

Area-Selective ALD of Ru on Nanometer-Scale Cu Lines through Dimerization of Amino-Functionalized Alkoxy Silane Passivation Films.

The selective deposition of materials on predefined areas on a substrate is of crucial importance for various applications, such as energy harvesting, microelectronic device fabrication, and catalysis. A representative example of area-confined deposition is the selective deposition of a metal film as the interconnect material in multilevel metallization schemes for CMOS technology. This allows the formation of multilevel structures with standard lithographical techniques while minimizing pattern misalignment and overlay and improving the uniformity of the structures across the wafer. In this work, area-selective deposition of Ru by atomic layer deposition (ALD) is investigated using alkoxy siloxane dielectric passivation layers. In this work, a comparison of several silane organic SAM precursors in terms of Ru ALD ASD performance is reported. The importance of the surface areal concentration of the passivation molecules is demonstrated. According to the in situ X-ray photoelectron spectroscopy film characterization, the ALD blocking layers derived from a (3-trimethoxysilylpropyl) diethylenetriamine (DETA) precursor have the ability to polymerize under ALD-compatible temperatures, such as 250 °C, which leads to a significant inhibition of Ru growth up to 400 ALD cycles. At the same time, the DETA layer can be selectively removed from the oxidized Cu surface by rinsing in acetic acid, which allows selective deposition of ca. 14 nm of Ru on Cu with no Ru detected on the DETA-coated surface by RBS. The approach is successfully tested on 50 nm half-pitch patterned SiO2/Cu lines.

Fluorescence sensing platform based on ruthenium(II) complexes as high 3S (sensitivity, specificity, speed) and “on-off-on” sensors for the miR-185 detection

Inspired by the enormous importance attributed to the biological function of miRNA, we pour our attention into the design and synthesis of four ruthenium(II) complexes and evaluate their applications as miR-185 detection agents by spectroscopic measurements. It was found that all complexes can form sensing platform for the detection of the complementary target miR-185 through the introduction of carboxyfluorescein (FAM) labeled single stranded DNA (P-DNA), giving the detection limits of 0.42nM for Ru 1, 0.28nM for Ru 2, 0.32nM for Ru 3, 0.85nM for Ru 4, all with instantaneous detection time in 1min. The results of the binding constant, fluorescence anisotropy (FA) and polyacrylamide gel electrophoresis experiments (PAGE) revealed that the ruthenium(II) complexes prefer to bind P-DNA other than hybrid duplexes DNA@RNA upon recognition, resulting in the detection of miR-185. These results provide useful suggestions in the new type of metal-based miRNA detection agents.

Impact of Embedment of Cu/TaOx/Ru on Its Device Performance

In our previous work (ECS Trans.75 (32), 13-23, 2017), we have compared the electric performance of Cu/TaOx/Ru and Cu/TaOx/Pt devices finding that the performance of the Ru device is far inferior to that of the Pt device. The poor resistive switching (RS) properties of the Ru device were imputed to the greatly degraded inertness properties of the Ru electrode as a stopping barrier for Cu drift-diffusion. The degraded inertness of the Ru electrode, in turn, has been attributed to larger Cu surface and/or Cu bulk diffusion in Ru than in Pt. The result is surprising as both Pt and Ru are known to be excellent diffusion barriers for Cu in CMOS backend applications. Here, we have manufactured two nominally identical Cu/TaOx/Ru devices, though, differently embedded on the Si wafer. While Ru device A has been manufactured on oxidized Si wafers with 730 nm SiO2 followed by 20 nm of Ti, 55 nm of Ru, 25 nm of TaOx, and 150 nm of Cu, Ru device B has been manufactured in the same way except that a 30 nm TaOx layer has been inserted between SiO2 and Ti layers. Electrical analysis shows that the RS behavior of the two devices is markedly different. Thus the way, nominally identical RS devices are embedded into a technology module has a major impact on the intrinsic device performance. We have identified three major reasons for this disparity. First, the layers of Ti and Ru involved are very thin (20nm and 55 nm). Second, during resistive switching local temperatures at the filament during the form/set and reset operations can exceed 600oC i.e. far higher than the maximum temperature which CMOS backend may experience when the underlying processor is in operation. This temperature is estimated to be ~120oC. Indeed, up to 120oC and above, amorphous Ru remains an excellent diffusion barrier for Cu. The third reason is the crystallinity phase of Ru thin layers that depends on the deposition method and the subsequent ‘unintended’, i.e. related to the RS, local anneals. We find that Ru device A can be switched a limited number of times at high compliance currents Icc (~0.5mA) while the device B at such Icc levels shows either volatile filament formation or when a filament forms, it is permanent. Conversely, at Icc of ~5uA Ru device B shows fairly good RS behavior, while Ru device A shows mostly volatile behavior. Besides Icc, the other critical parameter is the ramp rate rr during the voltage sweep. Both parameters determine effectively the thermal budget during the set and reset operations and are thus responsible for: 1) chemical reactions taking place between the thin metal and dielectric layers and formation of chemical compounds. 2) Cu surface diffusion on the Ru electrode and Cu penetration through the Ru electrode which appears to include compound formation of Ru2Si3 and Cu3Si in case of Ru device A. Therefore, the declared purpose of inserting the TaOx layer between SiO2 and Ti was to prevent those silicidation reactions. In this work, we show that reports in the literature on a number of Ru metallization issues such as: a) thin Ru amorphous films crystallize into a polycrystalline phase at ~550oC; b) observation of a strong diffusive penetration of Cu through the increased number of grain boundaries within Ru layer at 475oC; c) Ru transforms into a less dense Ru2Si3 at ~500oC; d) Ru2Si3 triggers Cu3Si formation at low temperature (~200oC) and degrades the barrier functionality of Ru electrode, are indeed correlated with the differences between the device I-V characteristics of the two Ru devices. Because of the chemical reactions triggered by high local temperatures during cell switching, the Ru devices show new properties over the stable Pt devices. In contrast to Pt devices, the voltage ramp rate has a major impact on the resistance of the on-state, Ron, in the Ru devices: lower ramp rate leads to a higher Ron values because the forming filament is exposed for a longer time to elevated temperatures and suffers from Cu out-diffusion. The observation that Ron in Ru device A is significantly higher than in the Ru device B at the same Icc and rr values, demonstrates that Ru electrode in Ru device B has better inertness properties than in the Ru device A. In summary, this work shows that nominally same device with excellent characteristics in a specific experimental environment, may show vastly degraded characteristics when embedded into a module such as CMOS metallization backend – an issue that has largely been disregarded so far.

Magnetic properties of ultrathin Ni81Fe19 films with Ta and Ru capping layers

Magnetic properties of Ni81Fe19 (permalloy) ultrathin films with Ru and Ta capping layers (CLs) were investigated for applications to magnetic random access memory units (MRAM). The sample structure, which simulated an MRAM free layer, is Si- sub./SiO2/Ni81Fe19/Ru(Ta). The Ni81Fe19 thin films less than 3 nm thick with Ru CL show low coercive fields compared with the Ta capping layer. Both systems showed loss of momentum equivalent to magnetically dead layers of thickness (δ) ∼0.6 nm for Ru cap layer and ∼1.4 nm for Ta cap layer, respectively. Moreover, after annealing the thicknesses are slightly increased to an equivalent magnetic dead layer thickness of δ ∼ 0.84 nm and ∼1.80 nm for Ru and Ta CL, respectively. Our calculations showed that the presence of only 11% Ta concentration at the interface reduced the Ni momentum to zero, with the Ni–Ta coupling being anti-ferromagnetic; while 50% Ru intermixing at the interface reduced the Ni momentum to zero with the coupling between Ru and Ni being ferromagnetic. To find out more about the intermixing at the interface, the composition and chemical states were characterized by the x-ray photoelectron spectroscopy and peak decomposition technique. The result showed that the peak positions were different from the pure metallic case at the interface region, mainly because of the intermixing between two layers. In conclusion, the Ru capping layer might be important for MRAM use in terms of low coercive field and small δ layer thickness if compared with the Ta capping layer.

(Invited) Plasma Enhanced Atomic Layer Deposited Ruthenium for MIMCAP Applications

A comparative study of the growth behavior of nm-thin ruthenium layers by plasma enhanced atomic layer deposition using two ruthenium precursors is discussed. For bis(ethylcyclopentadienyl)-ruthenium or Ru(EtCp)2, we have found a large incubation time on titanium nitride when using N2/NH3 plasma. With N2/H2 plasma the incubation was significantly reduced. For (methylcyclopentadienyl-pyrrolyl)ruthenium or MCPRu, no incubation was observed for either plasmas. The measured growth per cycle was ~ 0.02 nm for Ru(EtCp)2 whereas ~ 0.04 nm for MCPRu. The top surface of the PE-ALD Ru films can be oxidized without surface roughening by applying a low pressure O2 anneal, while O3 exposure leads to roughening due to etching and re-deposition downstream of etched Ru. Awareness of the impact of oxidizing ambients on Ru is essential for successful integration of Ru layers as electrode in metal-insulator-metal capacitors.

Catalytic activity of noble metal ions for the degradation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine in the presence of oxidizing agent, and its application to the determination of ultra trace amounts of ruthenium

Trace quantities of ruthenium(II) ion catalyze the oxidation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine (TPPS) by potassium bromate. This reaction can be used for the determination of ultra trace amounts of ruthenium using the water-soluble porphyrin with its high molar absorbance. The scope of the reaction was investigated in terms of the reaction conditions and selectivity with respect to other noble metal ions. The effect of pH, concentration of bromate, the reaction time, and the type of metalloporphyrin were studied so as to optimize the method for the determination of trace amounts of Ru(III). The apparent reaction rate constant for the disappearance of TPPS (or metal-TPPS) is proportional to the root of the concentration of bromate, and directly related to that of Ru(III). The limit of detection is 0.11 nM (equal to 10.7 pg mL−1) at pH 4.25, where the turnover number is 201. The reproducibility for five measurements at 2.7 nM of Ru(III) was 2.9%.

Simultaneous determination of catechin, rutin, quercetin kaempferol and isorhamnetin in the extract of sea buckthorn ( Hippophae rhamnoides L.) leaves by RP-HPLC with DAD

A rapid and specific reversed-phase high performance liquid chromatography (RP-HPLC) method with diode array detection (DAD) at room temperature was used and validated for the simultaneous determination of five flavonoids (catechin, CA; rutin, RU; quercetin, QU; kaempferol, KA; isorhamnetin, IS) in the extract of sea buckthorn ( Hippophae rhamnoides L.) leaves. The sample pretreatment process involved ultrasonic extraction with 85% ethanol under the frequency of 80 kHz, at a temperature of 45 °C for 30 min and with the ratio of liquor to material of 15 mL g −1, followed by separation on HIQ SIL C18V column with methanol–acetonitrile–water (40:15:45, v/v/v) containing 1.0% acetic acid as a mobile phase. The extract was detected by DAD at the wavelength of 279 nm for CA, 257 nm for RU, 368 nm for QU, KA and IS. Calibration curves were found to be linear with the ranges of 0.011–0.520 mg ml −1 (CA), 0.007–0.500 mg ml −1 (RU), 0.019–0.280 mg ml −1 (QU), 0.010–0.440 mg ml −1 (KA) and 0.008–0.400 mg ml −1 (IS). The correlation coefficients of linear regression analysis and detection limits were between 0.9963–0.9999 and 0.00079–0.00290 mg ml −1. The contents of CA, RU, QU, KA and IS in sea buckthorn leaves were successfully determined with 3.8, 5.2, 7.3, 10.9 and 11.9 min with satisfactory reproducibility and recovery. Recoveries of the five flavonoids were between 97.27 and 99.98%. The method was applied to the determination of flavonoids in sea buckthorn leaves and was found to be simple, rapid and efficient.

Excited state interfacial electron transfer from a compound with a single pyridine ligand.

The coordination compound Ru(NH(3))(5)(eina)(PF(6))(2), where eina is ethyl isonicotinate, was synthesized and attached to optically transparent nanocrystalline (anatase) TiO(2) films, abbreviated Ru(NH(3))(5)(eina)/TiO(2). The metal-to-ligand-charge-transfer (MLCT) absorption was found to shift in wavelength with solvent. The absorption maximum of the low energy MLCT band was observed at 486 nm in acetonitrile and 528 nm in dimethylformamide for Ru(NH(3))(5)(eina)(PF(6))(2) and at 512 and 555 nm for Ru(NH(3))(5)(eina)/TiO(2), respectively. The compound was found to be nonemissive with an excited state lifetime <10 ns under all conditions studied. Light excitation in fluid solution and when attached to insulating ZrO(2) films resulted in a loss of the MLCT absorption, consistent with ligand field photochemistry. Pulsed light excitation of Ru(NH(3))(5)(eina)/TiO(2) yields an absorption difference spectrum consistent with an interfacial charge separated state, Ru(III)(NH(3))(5)(eina)/TiO(2)(e(-)). This state forms within 10 ns and returns cleanly to ground state product within milliseconds. The injection quantum yields were determined by comparative actinometry and were found to be excitation wavelength dependent: phi(inj)(417 nm) = 0.30 +/- 0.05 and phi(inj)(532.5 nm) = 0.15 +/- 0.03. Regenerative solar cells based on Ru(NH(3))(5)(eina)/TiO(2) with 0.5 M TBAI, where TBA is tetrabutylammonium, and 0.05 M I(2) in acetonitrile were very inefficient. Sluggish iodide oxidation is expected, on the basis of the negative E degrees (Ru(III/II)) = +0.17 (V vs Ag/AgCl) reduction potential, and this presumably allows a greater fraction of the injected electrons to recombine with the oxidized compound thereby lowering the solar cell efficiency.

Relationship between the structure of Ru/CeO2 catalysts and their activity in the catalytic ozonation of succinic acid aqueous solutions

Two Ru/CeO2 catalysts were used for the study of the catalytic ozonation of aqueous solutions of succinic acid (SA). These catalysts were prepared either by impregnation (I) or by acid exchange (AE). The objectives were (1) to determine the efficiency towards the oxidation of the organic molecule in relation to the catalysts characterization, and (2) to examine the modifications of the structure induced by ozonation. For each catalyst, two experimental conditions of catalyst and succinic acid concentrations were studied. The diluted conditions ([SA]0=1mM, weightcata=0.8g/l) were applied for the study of the behavior of the catalysts during successive uses. The efficiency was also studied for higher initial concentrations ([SA]0=5mM, weightcata=3.2g/l). Under both conditions the best efficiency was obtained with the impregnated catalyst.Transmission electronic microscopy analyses indicated that before ozonation of SA, ruthenium was distributed within the whole volume of the grain of CeO2 for the AE catalyst, and included only in an external layer for the I catalyst. The size of the particles determined by X-ray diffraction (XRD) was around 3.5nm for Ru and in the range 10–75nm for CeO2. In most cases, the catalytic ozonation induced Ru sintering with the formation of clusters. After four successive ozonation experiments the AE catalyst efficiency was significantly decreased and the structure totally disorganized.

Effect of underlayer roughness, grain size, and crystal texture on exchange coupled IrMn/CoFe thin films

The exchange bias field (Hex) between a ferromagnetic and antiferromagnetic film has been found to be sensitive to interface roughness, crystalline texture, and grain size. In order to isolate the effects of these three parameters, we deposited Si/UL/CoFe4/IrMn5/Ta5nm (top) and Si/UL/IrMn5/CoFe4/Ta5nm (bottom configuration) exchange coupled multilayers on three underlayers, namely Cu, Ru, and [Cu1/Ru1nm]n with thickness between 5 and 100 nm. With an increase in Cu (fcc) underlayer thickness, roughness and grain size increased rapidly up to 0.9 nm rms and 48 nm, respectively. For the Ru (hcp) underlayer, roughness increased gradually to 0.3 nm while the grain size increased to 30 nm. In case of Cu/Ru (hcp+fcc), the roughness observed is between that of Cu and Ru for comparable thickness. However, the grain size is much smaller compared to Ru and Cu. For both top and bottom exchange coupled films, Hex (200–300 Oe) is observed above a critical underlayer thickness (⩾5 nm for Ru and ⩾15 nm for Cu and Cu/Ru). In the top configuration, above the critical underlayer thickness, Hex decreases from 295 to 180 Oe with an increase in underlayer (UL) thickness due to the rougher interface. However, Hex did not change with roughness for the bottom case. The difference in Hex dependence on roughness for top and bottom cases can be explained in terms of magnetostatic effects on domain formation in the antiferromagnetic layer. In both cases, above the critical UL thickness, no correlation between Hex and the grain size and texture was found. After annealing at 225 °C for 1 h, high interfacial exchange energy (Jk∼0.22 ergs/cm2) for the top configuration is obtained for films deposited on UL which have large grain size. In the bottom case, a high Jk (∼0.3 ergs/cm2) is obtained for films with good fcc-IrMn(111) texture, corresponding to growth on Cu/Ru underlayers.

The effects of a 5-HT1A receptor agonist and antagonist on the 5-hydroxytryptamine release in the central nucleus of the amygdala: a microdialysis study with flesinoxan and WAY 100635.

The modulation of extracellular 5-hydroxytryptamine (5-HT) in the central nucleus of the amygdala (CeA) by 5-HT1A receptors was studied by intracerebral microdialysis in awake and freely moving rats. Local administration of 1 microM tetrodotoxin (TTX), 60 mM K+ and perfusion with Ca(2+)-free Ringer containing EGTA confirmed that the major part of dialysate 5-HT levels from the CeA is of neuronal origin. Administration of 300 nM of RU 24969, a 5-HT1B receptor agonist, through the probe into the CeA decreased dialysate 5-HT levels to 67.2% of the baseline value. Systemic administration of the 5-HT1A receptor agonists 8-OH-DPAT and flesinoxan dose-dependently decreased 5-HT levels in the CeA. The effect of 0.3 mg/kg of flesinoxan could be completely antagonized by systemic administration of 0.05 mg/kg WAY 100635, a 5-HT1A receptor antagonist. WAY 100635 alone had only minimal effects at this dose. These data show that a major part of the extracellular 5-HT in the CeA stems from 5-HT neurons and that the amount of 5-HT released into this brain region can be modulated by 5-HT1A receptors.

Effects of chemistry on the grain size refinement in nanocrystalline Ru and RuC powders prepared by mechanical attrition

Nanocrystalline Ru and Ru 80C 20 powders have been prepared by high-energy ball milling of elemental powders under a reactive methane atmosphere. The powders are investigated by x-ray diffraction and transmission electron microscopy. The deformation during milling results in a decrease of the grain size to 7 nm for elemental Ru and to 4 nm for Ru 80C 20. The results are compared to ball milling experiments on Ru under inert argon gas atmosphere. The influence of composition and milling atmosphere on the grain size refinement during milling are discussed with respect to the underlying mechanism of plastic deformation, coupled with solution hardening during milling and the role of solute segregation at grain boundaries.

The 5-HT transporter is an additional site of action for the 5-HT agonists RU 24969 and TFMPP

A variety of 5-hydroxytryptamine (5-HT) agonists and related compounds were tested for their ability to interact with the 5-HT transporter by analyzing: (1) inhibition of synaptosomal uptake of 5-HT; (2) competition for the specific binding of [3H]paroxetine to the 5-HT transporter and; (3) stimulation of 5-HT efflux from synaptosomes. The results indicate that compounds which exhibit moderate to high affinity for the 5-HT1B binding site also exhibit moderate to high potency for inhibiting 5-HT uptake (Ki = 28 and 291 nM for RU 24969 and TFMPP, respectively). Moreover, the same series of compounds also compete for [3H]paroxetine binding (Ki = 20 and 387 nM for RU 24969 and TFMPP, respectively) and can, to varying degrees, induce 5-HT efflux from synaptosomes. These data suggest that some ligands which are active at the 5-HT1B receptor will also interact with the 5-HT transporter to modify the synaptic availability of 5-HT.

Species variations in RU 24969 interactions with non-5-HT 1A binding sites

The interaction of RU 24969 with [ 3H]5-HT) binding to non-5-HT 1A binding sites was analyzed in nine species. Non-5-HT 1A binding was defined as specific [ 3H]5-HT binding observed in the presence of 100 nM 8-OH-DPAT. Computer-assisted iterative curve fitting of RU 24969 competition studies indicate that RU 24969 distinguishes two distinct components of non-5-HT 1A sites in rat and mouse brain. These two binding components display apparent K i values of 0.33–0.39 and 66–130 nM for RU 24969. By contrast, RU 24969 competition for non-5-HT 1A binding in guinea-pig, cow, human, dog, chicken, turtle and frog brain membranes is consistent with a homogeneous population of [ 3H]5-HT binding sites. This population of sites displays apparent K i values of 23–130 nM for RU 24969 and appear to be analogous to the low affinity component of non-5-HT 1A sites identified in rat and mouse.