The authors report ' C NMR spin-lattice relaxation rates 1/Tl and Knight shifts Ks in the quasitwo-dimensional organic superconductor «-(ET)2Cu[N(CN)i]Br ( T, = 11.6 K), for an aligned single crystal. The normal-state behavior is reminiscent of the high-T, cuprates, in which antiferromagnetic Auctuations and spin-gap behavior dominate. In the superconducting state, the data rule out the BCS electron-phonon mechanism as the source of the superconductivity, but support an unconventional pairing state with possible nodes in the gap function.The discovery of superconductivity in organic chargetransfer salts based on the BEDT-TTF ("ET") molecule has stimulated interest in understanding the electronic structure of their normal and superconducting states. ' The ET compound with the highest ambient pressure critical temperature is «-(ET)zCu[N(CN)2]Br (T, =11.6 K). This salt has a layered structure and quasi-twodimensional (2D) electronic conduction, similar to the cuprate superconductors. The reduced dimensionality, and low carrier density (-10 ' cm ), indicate that electron correlation effects may be important. The nature of the superconducting state in the ET salts (i.e. , BCS or unconventional) is unsettled at present. The low-temperature magnetic penetration depth has been studied, with some experiments supporting the existence of an isotropic BCS gap, and others an anisotropic gap.We have utilized ' C NMR to study the normal and superconducting states of tc-(ET)zCu [N(CN) 2]Br [' K-(ET)&Br"]. In agreement with the work of Mayafre et al. and Kawamoto et al. , we find that the normalstate behavior is not that of a simple metal, and that antiferromagnetic Auctuations, and spin-gap behavior may be present. Our data for «. -(ET)2Br below T, favor spinsinglet pairing, and a highly anisotropic energy gap, such as is present for d-wave, or anisotropic s-wave, orbital pairing. Thus, in contrast to the A3C6o (A =K,Rb, Cs) "Buckyball" superconductors, the superconductivity in tc-(ET)2Br arises from a mechanism other than the conventional BCS electron-phonon coupling.In a metal, the hyperfine interactions of the nuclei with the spins of the conduction electrons dominate the NMR properties. We find that in «. -(ET)2Br, both the isotropic Fermi contact and anisotropic dipolar (2p, ) interactions are present. For a simple metal, the Korringa law relates the Knight shift E, to the spin-lattice relaxation time T& . .1/T, T o= K, . Below T"a gap opens at the Fermi level, producing dramatic changes in the NMR properties.For BCS spin-singlet s-wave superconductors, K, decays to zero as T~O in a characteristic way. Just below T" 1!T,rises ("coherence peak"), but falls off exponentially at low T. These features are found in the NMR studies of A3C6o, clearly identifying it as a conventional BCS superconductor with an isotropic energy gap.' We note that the above results are drastically modified in the case of an anisotropic gap function.Previously, we have reported 'H NMR in the superconducting state of tc-(ET)@Br. " We showed that the NM...

We present high precision measurements of the penetration depth of single crystals of κ−(ET)2Cu[N(CN)2]Br and κ−(ET)2Cu(NCS)2 at temperatures down to 0.4 K. We find that, at low temperatures, the in-plane penetration depth (λ ) varies as a fractional power law, λ ∼ T 3 2 . Whilst this may be taken as evidence for novel pair excitation processes, we show that the data are also consistent with a quasilinear variation of the superfluid density, as is expected for a d-wave superconductor with impurities or a small residual gap. Our data for the interplane penetration depth show similar features and give a direct measurement of the absolute value, λ ⊥ (0) = 100 ± 20 µm.PACS numbers: 74.70. Kn, 74.25.Nf Compounds of the family κ−(ET) 2 X have the highest transition temperatures of all organic superconductors known to date [1]. They have recently attracted considerable attention because of their similarity to the high T c cuprates and the possibility that they may also have a non-conventional paring state [2]. The two materials studied here, κ−(ET) 2 Cu[N(CN) 2 ]Br (T c ∼ 11.6 K) and κ−(ET) 2 Cu(NCS) 2 (T c ∼ 9.6 K), are highly anisotropic, layered, extreme type II superconductors. As in the cuprates, the superconducting phase in these materials is in close proximity to an antiferromagnetic phase. Both antiferromagnetic spin fluctuations and a pseudogap have been detected in NMR measurements in the normal state [3]. Neither the underlying pairing mechanism nor the symmetry of the order parameter has been conclusively established. Although NMR [4,5], specific heat [6] and thermal conductivity [7] measurements all suggest a non-conventional pairing state, results of penetration depth measurements have been inconsistent, with evidence for both conventional [8,9] and non-conventional [10][11][12] behavior. However, none of these penetration depth measurements have been performed over a temperature range (T /T c ) and a precision, comparable to those in the cuprates [13]. In this Letter, we present measurements of both the in-plane λ , and the interplane, λ ⊥ , penetration depths in κ−(ET) 2 Cu[N(CN) 2 ]Br and κ−(ET) 2 Cu(NCS) 2 at temperatures down to 0.4 K.Our measurements were performed on single crystals of κ−(ET) 2 Cu[N(CN) 2 ]Br and κ−(ET) 2 Cu(NCS) 2 which were grown at Argonne National Laboratory. Details of the growth procedures have been given elsewhere [14]. Penetration depth measurements were performed using a 13 MHz tunnel diode oscillator [15] mounted on a 3 He refrigerator. The low noise level [ ∆F F0 ≃ 10 −9 ], and low drift of the oscillator allows us to obtain high resolution data with a very small temperature spacing interval. The samples were attached, with a small amount of vacuum grease, to a sapphire rod which fitted inside the copper sense coil. The sense coil was calibrated using spheres of Aluminum. The sample temperature was measured with a calibrated Cernox thermometer attached to the other end of the sapphire rod. The samples were cooled slowly (0.1-1.0 K/min) to avoid introducing disorder [1...

Porous alumina membranes are commercially available and have been widely used in recent nanoscale research, for example, as templates in nanowire fabrication through electrodeposition. In this report, we present a new use for porous alumina membranes in the fabrication of alumina nanotubes/nanowires desired in electrochemical devices and catalytic applications. A high yield of alumina nanotubes/nanowires is obtained by etching porous alumina membranes in an aqueous sodium hydroxide solution. We studied the effects of etching time and solution concentration and characterized the alumina nanotubes/nanowires using a scanning electron microscope (SEM). A discussion of the possible mechanism for the formation of nanotubes/nanowires is given. Our results also imply that in nanowire fabrication through the template approach where alumina membranes are removed with sodium hydroxide solution to release the nanowires special attention is needed in characterizing the nanowires with the SEM because alumina nanotubes/nanowires can be easily mistaken for electrodeposited nanowires.

Atomic layer deposition (ALD) on anodic aluminium oxide (AAO) is shown to be a facile, flexible route to the synthesis of catalytic membranes with precise control of pore wall composition and diameters. The oxidative dehydrogenation of cyclohexane was shown to depend strongly on pore diameter and to be more specific than similarly active alumina powder catalysts.Micro and mesoporous catalytic materials, predominantly in the form of zeolites, have gained wide acceptance as industrial catalysts for oil refining, petrochemistry, and organic synthesis, particularly for molecules with kinetic diameters below 1 nm. Here we report the first demonstration that ultra-uniform inorganic catalytic membranes, synthesized using a combination of anodic aluminum oxidation (AAO) [1-4] and atomic layer deposition (ALD) (a facile, flexible functionalization route) [5][6][7], have novel catalytic properties. Atomic level control of both the pore diameter and the pore wall composition along the entire pore length offers catalyst environments that include larger pores than conventional mesoporous materials (for efficient in-diffusion of large/elaborate molecular precursors or feedstock molecules, and for out-diffusion of large/ elaborate product molecules), tailored channel sizes and wall compositions (including tailored channel surfaces ranging from hydrophobic to hydrophilic in nature), catalyst mobility constraints to hinder agglomeration, and flow control of reagents in and out of the catalyst.Mesoporous and microporous catalytic material syntheses are often approached in a ''one step '' process (e.g.,). In this paper, we present an approach based on two steps: production of a stable mesoporous scaffold and then carefully controlled modification of the scaffold, where each step can be optimized independently. A related two step synthesis method utilizing a wet chemical modification method has been reported [12]. The modification method described here is based on gas phase deposition allowing directed control of the pore wall composition and diameter.AAO membranes are an appealing scaffold with highly-aligned, parallel pores and narrow pore diameter distributions. Electrochemical conditions can be arranged to produce most probable pore diameters in the range 20-400 nm [1-4, 13, 14] and membrane thicknesses in the range 0.5 to >250 lm. Prior catalytic studies using AAO showed interesting yield enhancements, but were limited to unreleased (pore blocked) films [15][16][17][18]. Moreover, as-grown AAO membranes suffer from poorly defined pore wall morphology and composition with significant (5%) amounts of incorporated electrolyte anions [19,20].For this work, highly-ordered, 70 lm thick AAO scaffolds produced in oxalic acid [13,14] are used. A typical plan view Secondary Electron Micrograph (SEM) of a scaffold is displayed in figure 1a. The hexagonal arrangement of pores (dark features) is clearly evident on this length scale; over longer distances the registry is less well defined. ALD was used to precisely control the chemical com...

Magnetization measurements at ambient pressure on /c-(ET)2Cu[N(CN)2]Cl, an organic salt that is superconducting under pressure (TV = 12.8 K at 0.3 kbar), reveal an antiferromagnetic transition near 45 K and, for the first time in this class of materials, a transition near 22 K to a state displaying weak ferromagnetic hysteresis with a saturation moment of (8x 10~4)/Wformula. This low-temperature state is characterized by a sequence of first-order magnetization jumps.