Electrochemical tuning of the optical properties of nanoporous gold

Using optical in-situ measurements in an electrochemical environment, we study the electrochemical tuning of the transmission spectrum of films from the nanoporous gold (NPG) based optical metamaterial, including the effect of the ligament size. The long wavelength part of the transmission spectrum around 800 nm can be reversibly tuned via the applied electrode potential. The NPG behaves as diluted metal with its transition from dielectric to metallic response shifted to longer wavelengths. We find that the applied potential alters the charge carrier density to a comparable extent as in experiments on gold nanoparticles. However, compared to nanoparticles, a NPG optical metamaterial, due to its connected structure, shows a much stronger and more broadband change in optical transmission for the same change in charge carrier density. We were able to tune the transmission through an only 200 nm thin sample by 30%. In combination with an electrolyte the tunable NPG based optical metamaterial, which employs a very large surface-to-volume ratio is expected to play an important role in sensor applications, for photoelectrochemical water splitting into hydrogen and oxygen and for solar water purification.

Dealloying-based interpenetrating-phase nanocomposites matching the elastic behavior of human bone

The long-term performance of orthopedic implants depends crucially on a close match between the mechanical behavior of bone and of the implant material. Yet, the present man-made materials with the required biocompatibility and strength are substantially stiffer than bone. This mismatch results in stress shielding, which can lead to the loss of bone mass and may even lead to a revision surgery. Here we report a new materials design strategy towards metal-polymer composites that are based on constituents with established biocompatibility and that can be matched to bone. Ti-based nanoporous alloys, prepared by liquid-metal dealloying, are infiltrated with epoxy to form interpenetrating-phase nanocomposites. At up to 260 MPa, their yield strength is technologically interesting for a deformable light-weight material. More importantly, Young’s modulus can be adjusted between 4.4 and 24 GPa, which affords matching to bone. As another parallel to bone, the strength of the composite materials is strain-rate dependent. These findings suggest that the novel composite materials may provide the basis for promising future implant materials.

Wrinkling of atomic planes in ultrathin Au nanowires

A detailed understanding of structure and stability of nanowires is critical for applications. Atomic resolution imaging of ultrathin single crystalline Au nanowires using aberration-corrected microscopy reveals an intriguing relaxation whereby the atoms in the close-packed atomic planes normal to the growth direction are displaced in the axial direction leading to wrinkling of the (111) atomic plane normal to the wire axis. First-principles calculations of the structure of such nanowires confirm this wrinkling phenomenon, whereby the close-packed planes relax to form saddle-like surfaces. Molecular dynamics studies of wires with varying diameters and different bounding surfaces point to the key role of surface stress on the relaxation process. Using continuum mechanics arguments, we show that the wrinkling arises due to anisotropy in the surface stresses and in the elastic response, along with the divergence of surface-induced bulk stress near the edges of a faceted structure. The observations provide new understanding on the equilibrium structure of nanoscale systems and could have important implications for applications in sensing and actuation.

Sign-inverted response of aluminum work function to tangential strain

We have investigated the response of the work function, W, of low-index aluminum surfaces to tangential strain by using first-principles calculations based on density functional theory. This response parameter is a central quantity in electrocapillary coupling of metal electrodes relating to the performance of porous metal actuators and surface stress based sensing devices. We find that Al surfaces exhibit a positive response for all orientations considered. By contrast, previous studies reported negative-valued response parameters for clean surfaces of several transition metals. We discuss separately the response of W to different types of strain and the impact of the strain on the Fermi energy and the surface dipole. We argue that the reason for the abnormal positive sign of the Al response parameter lies in its high valence electron density.

Size-dependent melting of matrix-embedded Pb-nanocrystals

We report calorimetric data for the size-dependence of the melting temperature as well as the enthalpy and entropy of melting for nanoscale Pb particles in an Al matrix, prepared by high energy ball-milling. The results are discussed with respect to various models for the melting of small confined systems. We can rule out models based on a temperature-independent Gibbs excess free energy of the particle-matrix interface, and a model based on an increased meansquare displacement of the interfacial layer. The best agreement to the data is provided by modeling the interface as an inert layer of finite thickness, which does not participate in the phase transition.

Magnetic Microstructure of a Nanocrystalline Ferromagnet - Micromagnetic Model and Small-Angle Neutron Scattering

We report on a combined theoretical and experimental study of the magnetic microstructure of a single component, single phase, Pore-free nanocrystalline ferromagnetic material. From the equations of micro-magnetics we conclude that the magnetic microstructure is the convolution product of an anisotropy field microstructure and of a response function with a correlation length lH that depends on the applied field Ha. We derive equations for small angle neutron scattering by such structures, and present experimental scattering data for electrodeposited nanocrystalline Ni, the first where for a wide range of Ha the dominant scattering contribution is from the purely magnetic microstructure, not from nuclear or magnetic contrast at pores or second phases. The variation of the scattering cross section with Ha is in excellent agreement with the theory, indicating that the underlying changes in the magnetic microstructure with Ha are not displacements of domain walls, but changes in lH and hence in the magnetic response to an entirely stationary anisotropy field microstructure. At 20K the anisotropy fields are dominated by magnetocrystalline anisotropy, but at 300K the perturbation is from a much stronger interaction which maintains some moments aligned antiparallel to the field direction at Ha as high as 1.4MA/m (18kOe).

Surface-chemistry-driven actuation in nanoporous gold

Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry-driven actuation can be realized in high-surface-area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes of the order of a few tenths of a per cent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into a mechanical response, thus opening the door to surface-chemistry-driven actuator and sensor technologies.

Surface stress-charge response of a (111)-textured gold electrode under conditions of weak ion adsorption

We report a cantilever bending investigation into the variation of surface stress, f, with surface charge density, q, for (111)-textured thin films of gold in aqueous NaF and HClO 4. The graphs of f(q) are highly linear, and the surface stress-charge coefficients, d f/d q, are -1.95 V for 7 mM NaF and -2.0 V for 10 mM HClO 4 near the potential of zero charge. These values exceed some previously published experimental data by a factor of 2, but they agree with recent ab initio calculations of the surface stress-charge response of gold in vacuum.

Small-angle neutron scattering of nanocrystalline terbium with random paramagnetic susceptibility

We report magnetic small-angle neutron scattering (SANS) data for the nanocrystalline rare earth metal Terbium in its paramagnetic state. Whereas critical scattering dominates at large momentum transfer, q, the (magnetic-) field response of the scattering at small q arises from the spatial nonuniformity of the paramagnetic susceptibility tensor. The finding of an interrelation between SANS and the susceptibility suggests a way for characterizing the nonuniform magnetic interactions in hard magnets by neutron scattering.

Synthesis, characterization and magnetic interactions study of epsilon-Fe3N-CrN nanorods

The epsilon-Fe3N-CrN composite nanorods are synthesized by wet chemical technique. XRD-Rietveld analysis shows that epsilon-Fe3N and CrN crystallize in the space group P6(3)/mmc and Fm3m with relative mass compositions 53% and 47%, respectively. The nanorods have an average diameter approximately 30 nm and length approximately 400 nm X-ray photoelectron spectroscopy (XPS) studies show the presence of nitrides and oxynitrides (Fe-O-N/Cr-O-N) at the surface and the presence of elemental Cr in CrN matrix along with the nitrides inside the nanorods, probed by the in-depth profile analysis. The magnetic interactions between the spins of ferromagnetic (FM) epsilon-Fe3N and antiferromagnetic (AF) CrN throughout the volume of the nanorods give rise to exchange bias coupling. The exchange bias phenomenon is influenced by the rough and non-uniform AF-FM interface and spin-glass-like ordering at lower temperatures. The ac susceptibility studies confirm the spin-glass-like ordering.

Volume change during the formation of nanoporous gold by dealloying

We report a macroscopic shrinkage by up to 30 vol % during electrochemical dealloying of Ag-Au. Since the original crystal lattice is maintained during the process, we suggest that the formation of nanoporous gold in our experiments is accompanied by the creation of a large number of lattice defects and by local plastic deformation.

Balance of force at curved solid metal-liquid electrolyte interfaces

We analyze the simultaneous mechanical and chemical equilibrium at the interface between a fluid electrolyte and a solid conductor in terms of a continuum theory, with attention to surfaces of varying orientation and of arbitrary curvature. On top of the variable which is conjugate to the surface stress, the tangential strain, we introduce an additional degree of freedom for the surface deformation, the surface stretch, to account for the observation of a reversible normal relaxation of the top atomic layer as a function of the electrochemical potential. We derive relations between the materials constants of the surface, for instance, the pressure dependence of the electric potential at constant superficial charge density, and discuss experiments-using cantilevers or porous solids-by which they can be measured.

Variation of the surface stress-charge coefficient of platinum with electrolyte concentration

We report an experimental study of the variation of surface stress with surface charge density for nanoporous Pt immersed in aqueous solutions of NaF of various concentration. As the concentration is reduced, we find initially an increase in the magnitude of the surface stress-charge coefficient, followed by saturation at a value of -1.9 V. Since specific adsorption is expected to be reduced as the solution becomes more dilute, the results support the notion that changes in the bonding at the metal surface play a decisive role in determining the change in the surface stress during double-layer charging.

Range of magnetic correlations in nanocrystalline soft magnets

We have obtained the magnetic field dependence of static ferromagnetic correlations in nanocrystalline electrodeposited Co and Ni by means of the correlation function of the spin misalignment, determined from small-angle neutron scattering data. The approach yields a correlation length l(C), which is a measure for the spatial extent of inhomogeneities in the magnetization distribution. The correlation length depends strongly on the applied magnetic field with values ranging from 94 nm in nanocrystalline Co at low fields to about 15 nm at saturation. The results for l(C) indicate that in Co the main source of nonuniformity in the spin system is the anisotropy field of each individual crystallite, whereas in nanocrystalline Ni the main sources of spin disorder originate from twin faults or from the defect cores of grain boundaries.

Charge-induced reversible strain in a metal

Dimension changes on the order of 0.1% or above in response to an applied voltage have been reported for many types of materials, including ceramics, polymers, and carbon nanostructures, but not, so far, for metals. We show that reversible strain amplitudes comparable to those of commercial piezoceramics can be induced in metals by introducing a continuous network of nanometer-sized pores with a high surface area and by controlling the surface electronic charge density through an applied potential relative to an electrolyte impregnating the pores.

[Laser lithotripsy of ureteral stones. Personal experiences]

The in vitro evaluation of a pulsed Nd:YAG laser, showed an effective and fine fragmentation of urinary calculi and showed only minimal subepithelial bleeding in the directly irradiated canine ureter. Since 1989 we have treated ureteral calculi in 30 patients. The laser pulses of 15-20 mJ (at fiber tip), 20 ns, 20-25 cps are transmitted by a 300-microns quartz fiber with a specially formed tip focusing the light. The fiber is passed through an 11.5-F ureteroscope within a guide tube, or, without a guide tube, through one of the new minimized ureteroscopies and is placed in front of the calculus. In 27 patients the procedure was successful, without any residual concretions after 1 day. In our opinion the advantages of this method are the very fine-grained, complete fragmentation of all sorts of calculi, the highly atraumatic procedure, and the absence of either optical or acoustic irritation to the operator.

Ifosfamide, vindesine and recombinant alpha-interferon combination chemotherapy for metastatic renal cell carcinoma

Among 29 evaluable patients with progressive metastatic renal cell cancer treated by interferon alpha 2b in combination with vindesine and ifosfamide, we have observed an objective (complete and partial) response rate of 24.1% and an overall (complete and partial response and stable disease) response rate of 58.6%. The median duration of remission has not yet been reached, but the survival of responding patients is considerably longer than that of non-responders. Because we could not find any differences (sex, age, WHO performance status, prior therapy, site of metastatic disease) between responding and non-responding patients, we believe that the treatment might modify intrinsic characteristics of the tumour growth and/or host-tumour relationship in the long term. Although the toxicity recorded is high, the results are sufficiently positive to justify further investigation of this approach.

Methods and prognosis of the extirpation of pulmonary metastases following tumor nephrectomy

Nephrectomy was performed in 938 patients with renal carcinoma between the years 1960 and 1986. The cumulative survival rate was 78.7 +/- 2.7% after 1 year; 62.9 +/- 3.2% after 3 years; 52.4 +/- 3.5% after 5 years, and 38.0 +/- 4.1% after 10 years. Of this group, 39 patients with lung metastases underwent surgery of their metastases following radical surgical removal of their primary tumor. Using the so-called actuarial method of analysis, the cumulative survival rate of this group was 66.7 +/- 15.1% 1 year after the lung surgery; 47.6 +/- 16.3% after 3 years and 32.7 +/- 15.7% after 5 years. The survival rates were correlated with the number of metastases, the operative techniques employed, and with the time interval between primary tumor removal and the appearance of secondary lung metastases. A comparison was made between those patients who underwent curative lung surgery (R0 group) and those with residual tumor (R+ group). Follow-up of the tumor status at the end of the study of the 39 patients is presented.

[Sonography in the early detection of non-palpable second testicular tumors: a prospective study]

As part of the tumor aftercare service afforded by our policlinic, 91 patients were examined one to six times in 18 months following radical orchiectomy for testicular germ cell tumors. The period of observation averaged 35 months (3-147) after the contralateral removal of the testicle. In addition to the usual routine checks, sonography of the residual testicle also formed part of the established followup protocol. Among these patients sonography identified in residual testicles 3 testicular tumors (3.3%) which had escaped detection on palpation. The existence of these second tumors was demonstrated 3, 25 and 38 months following contralateral orchiectomy. In all instances the second lesion differed from the first tumor in histology. In another patient a plum-sized malignancy was revealed within a large concurrent hydrocele by scrotal sonography carried out 18 months following preceding contralateral orchiectomy. Thus, our group of patients gave an incidence of 4.4% for second primary testicular tumors, a poor known incidence rate. Such malignancies can be spotted early by ultrasound, they are genetically obscure just as the increasing morbidity of the unilateral disease. These results urgently suggest that after semicastration for testicular germ cell tumor the residual testicles should be regularly scanned by ultrasonography at four-month intervals. Retrograde sonography has been shown to detect even those small occult testicular tumors which pass unnoticed until metastasizing.

[Urethral duplication in the male]

The rare duplications of the male urethra--only 210 cases are described till now--are found as many different variations. Only few of these malformations are symptomatic. The embryology is not always clear. Several classifications have been proposed, often too complicated or incomplete. We think, that our classification avoids these disadvantages. Each duplication is systematically classified in a morphological way according to the type of orifice (epispadiac, normotopic on the glans, hypospadiac, perineo-anal), without urinary transport (distal abortive types) or with urinary transport. The latter type can be complete (if a channel exists between bladder and an external meatus) or incomplete (if a channel exists between bladder and any point of the normal urethra or between the normal urethra and any accessory meatus). Four cases are reported and therapeutical aspects are discussed.

[Sacral dysgenesis and its neuro-urologic pathologic correlates]

As an aspect of the caudal regression syndrome the dysgenesis of the sacrum, the correlating neuro-urological pathology, and a classification are presented, based on the literature and a report of ten cases. The sacral osteological anomaly--as a numerical and as a structural anomaly--and the neuro-urological defect exist to different extents. Therefore the diagnosis is made at several ages. The type of neurogenic bladder disturbance is the "lower neuron lesion". Use of a proper diagnostic approach and conservative or surgical therapy according to the type of lesion improve the prognosis by protecting the upper urinary tract and also ameliorate the social hardships resulting from incontinence. Irregularly correlated are disturbances of the rectum and of the lower extremities.