Colloidal Copper Research Articles

SERS of cytosine and its methylated derivatives on gold sols

AbstractSERS spectra of cytosine, 1‐methylcytosine, 5‐methylcytosine and 1,5‐dimethylcytosine on a gold colloid are reported. A tentative assignment of Raman bands is made by comparison with the normal Raman spectra in aqueous solution. This analysis reveals a preferred non‐planar orientation of cytosine and 1‐methylcytosine and a more planar orientation of 5‐methylcytosine and 1,5‐dimethylcytosine with respect to the metal surface, the C=O group being determinant in the interaction. A comparative study using the result obtained previously using silver and copper colloids as supports shows important differences in the electrodynamic behaviour of these molecules which depend on the presence of the methyl substituents and the nature of the metal on which they adsorb.

The Nucleation of Colloidal Copper in the Presence of Poly(ethyleneimine)

AbstractCopper colloids have been prepared by y‐radiolysis of cupric ions in the presence of poly(ethyleneimine). The reduction takes place in two, distinct steps. Copper (II) is reduced quantitatively to copper (I), and then nucleation of the colloid occurs after an induction period. The nucleation of colloidal copper is catalysed by the presence of less noble Pb(II) or T1(I) ions, which is explained by the generation of Pb and Tl nuclei in the solution, and their subsequent reoxidization by Cu(I). The formation of copper colloids is also catalysed by the presence of colloidal silver or silver ions, and radiolysis results in the formation of copper coated silver colloids. The optical shifts observed during the deposition of copper on silver cannot be explained by Mie theory. The differences are suggested to be due to weaker interband transitions in the copper monolayers than in the bulk

Formation of Colloidal Copper Hydroxides and Oxides Biopolymeric Interfaces

ABSTRACTLight sensitive colloidal particles of copper hydrous oxides were prepared at interfaces of exopolymeric materials. Dislike copper oxide or hydroxide nanoclusters were obtained which might be useful as p-type semiconductors. The colloidal Cu2O xH2O and Cu(OH)2 particles reveal fractal dimensions of D = 2.15 ±0.05 for Cu(OH)2 and D= 1.75 ±0.07 for Cu2O xH20.

Structural factor controlling nanasize copper formation in doped amorphous silica by ion implantation

Colloid formation of Cu particles by ion implantation was examined in SiO 2 glass substrates doped with F, P or Ge ions. Doping of phosphorus strikingly reduced intensities of an optical band peaking at 2.2 eV, which is due to plasma oscillation of nanosized copper colloids, while no or a faint effect was seen for fluorine and germanium-doped substrates. Doping of 1.3 mol% P 2O 5 reduced the adsorption intensities to ∼ 1 4 and diameters of Cu-colloid particles to ∼ 2 3 compared with those in the P-free substrate. On the other hand, F-doping up to 8 mol% gave no perceptible changes and Ge-doping of 6 mol% resulted in ∼ 10% decrease in the absorption intensity. It was considered that the primary factor controlling Cu-colloid formation in the implanted glasses is not the change in the continuity of silica network structure but the change in the strength of solvation of charged states of implanted ions. A close similarity was found between the present conclusions and codoping effects on the cluster formation of rare-earth oxides in silica glasses.

Morphological Study of Metal Colloids Employed as Substrate in the SERS Spectroscopy

Transmission electronic microscopy (TEM) and ultraviolet-visible absorption spectroscopy were used to characterize several silver and copper sols employed as substrates in surface enhanced Raman spectroscopy (SERS). In this study we have focused our attention on the changes observed when the large scale roughness is modified by the aggregation agent 1,5-dimethylcytosine (DMC). A previous analysis of several unaggregated silver and copper colloids and a comparison with the corresponding aggregated colloids were made, so that a relationship between the morphology of the aggregates and the SERS results was obtained. Information about the aggregation process of the colloids studied is also presented, on the basis of the results obtained from TEM, UV-visible spectroscopy, and the study of the variation of the SERS signal with the concentration of DMC. From these results, the morphology of the resulting aggregates which yields the most intense SERS signal is inferred. A different aggregation mechanism is suggested for each colloidal metal, according to the remarkably different geometry of the final aggregates observed. This is further attributed to the different sizes of the simple particles present in the original colloids.

Colloidal copper in aqueous solutions: radiation-chemical reduction, mechanism of formation, and properties

Colloidal copper has been obtained by γ-irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When CuII is not entirely incorporated into the complex with PEI, disproportionation of CuI aqua complexes formed affords the metal, along with Cu2O. Reduction of the PEI complex of CuI by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.

Picosecond nonlinear optical response of a Cu:silica nanocluster composite

We describe the picosecond nonlinear optical response of a metal-dielectric composite made by implanting Cu ions in fused silica. The implanted Cu ions aggregate during implantation to form nanometer-diameter clusters in a dense, thin (~150 nm) layer just beneath the surface of the substrate. The third-order susceptibility X((3)) has an electronic component with a magnitude of the order of 10(-8) esu and is enhanced for laser wavelengths near the surface plasmon resonance of the copper colloids.

Surface-enhanced Raman spectroscopic study of 9-ethylguanine and related compounds on silver and copper colloids

SERS spectra on a silver colloid of 9-ethylguanine, 7-methylguanine and guanine and on a copper colloid of 9-ethylguanine are reported. A comparative study was made on the basis of the electromagnetic model of SERS and taking into account the changes in the structure that may occur as an effect of the chemical interaction with the metal. Several differences seen between the SERS spectra of 9-ethylguanine and 7-methylguanine demonstrate the influence of alkyl substituents on the mode of interaction of each molecule with the metal, as a consequence of the changes in the electronic structure induced by these substituents. 9-Ethylguanine shows a higher affinity to adsorb on both the silver and the copper surface; the orientation adopted by this molecule on these colloids depends not only on the nature of the metal, but also on the concentration of the adsorbate in the medium, the presence of Cl − ions and the time passed after the addition of the adsorbate.

Coalescence of nanosized copper colloid particles formed in Cu-implanted SiO2 glass by implantation of fluorine ions: Formation of violet copper colloids

Fluorine ions were implanted at an energy of 40 keV at room temperature into Cu-implanted (160 keV, 6×1016 ions/cm2) SiO2 glass substrates in which implanted coppers occur in the form of nanosized metallic colloid particles with spherical shape. After the F implantation, the peak position of a band due to plasma oscillation shifted from 2.21 eV (562 nm) to 2.10 eV (591 nm) and the color changed from bulk copperlike to deep violet, visually. The bimodal distribution of depth Cu concentrations became distinct after the implantation. Cross-sectional transmission electron microscopy observation revealed that the distribution of copper colloid particles remains bimodal in shape and the particles coalesce with each other to form larger colloid particles with nonspherical shape. Fourier transform IR attenuated total reflection spectra showed that implanted F ions are incorporated in the form of O3Si-F units breaking continuity of the Si-O-Si network, suggesting that reduction of local viscosity in collision cascade regions during the implantation plays an important role in the observed coalescence.

SERS of cytosine and its methylated derivatives on metal colloids

AbstractSERS spectra of cytosine, 1‐methylcytosine, 5‐methylcytosine and 1,5‐dimethylcytosine on silver and on copper colloids are reported. A study of the influence of pH on the normal Raman spectra of these compounds was made in order to understand better the behaviour of these molecules on metal surfaces. The results obtained indicate remarkable changes in the type of adsorbate—metal interactions depending on the metal used as the SERS support. These interactions are also influenced by the presence of methyl groups in the cytosine molecule.

Formation of copper nanoscale particles in implanted silica glass

Ion implantation into glass has a potential [1, 2] for fabricating photonic or optoelectronic devices on planar glass substrates because it provides control of the dopant concentration and profile. We have measured the changes in optical and magnetic properties of silica glasses implanted with transitionmetal ions [3-5] and structural defects [6-8] produced by the implantation. In previous papers two significant modifications of optical properties of copper-implanted silica glasses have been reported. The first is a large increase in the refractive index [7, 9]. The refractive index, measured at 632 nm (He-Ne laser) increases from 1.47 to 1.65 with doses increasing from 1 x 1016 to 6 x 1016 cm -2. A linear correlation was found between increments in the refractive index and the absorptivity of an induced optical band centred at 2.2eV. The second modification is a very large value (about 4 x 10 -1I m 2 W -I at a wavelength of 532 nm) of the non-linear refractive index [10]. It was suggested that these two properties are due to the formation of copper colloids. In this letter we confirm the presence of Cu nanoscale particles in as-implanted silica glass. Samples used for transmission electron microscopy (TEM) measurements were high-purity type III silica glass discs (Spectrosil; 1 cm in diameter by 0.1 cm thick, OH content 200p.p.m.). The discs were implanted with Cu ÷ to a nominal dose of 6 x 1016 cm -2 at room temperature (acceleration voltage 160 keV and dose rate 2.5/zAcm-2). The depth profile of implanted Cu was measured by backscattering using a 2 MeV beam of a'-particles at current of about 10 A. TEM observation with a Jeol 400EX electron microscope was made on thin leaves peeled by scratching the implanted surface with a diamond pencil. No chemical or physical thinning technique was adopted. The TEM acceleration voltage was 300 kV. Optical absorption spectra were measured with a double-beam spectrophotometer (Jasco 610C) at 300 and 77K using a cryostat (Oxford DN1704). An unimplanted substrate was placed in the reference beam. EPR spectra were measured at 110 and 300 K with a Brucker 200D homodyne spectrometer applying 100kHz field modulation. Fig. la shows the optical absorption spectra of the implanted sample measured at 300 and 77 K. There is a peak at 2.2 eV and inflections around 4.5 and 5.8 eV. Neither shape changes nor further resolution of peaks on the spectrum were observed when

Reduction of aqueous copper(2+) by carbon dioxide(1-): first steps and the formation of colloidal copper

Aqueous solutions of Cu(ClO{sub 4}){sub 2} and HCOONa were pulse-radiolyzed and the changes in optical absorption and conductivity recorded. CO{sub 2}{sup {minus}} reduces Cu{sup 2+} to yield Cu{sup +} (k = 2 {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1}). Cu{sup +} reacts with CO{sub 2}{sup {minus}} to yield CuCO{sub 2} (absorption at 480 nm (pH = 7.3); k = several 10{sup 10} M{sup {minus}1} s{sup {minus}1}). CuCO{sub 2} exists in two forms depending on the pH of the solution (385 nm at lower pH's). CuCO{sub 2} reacts with Cu{sup 2+} to form 2Cu{sup +} + CO{sub 2} (k = 5 {times} 10{sup 8} M{sup {minus}1} s{sup {minus}1}) and with Cu{sup +} to form Cu{sub 2}{sup +} (350 nm; k {approximately} 10{sup 8} M{sup {minus}1} s{sup {minus}1}). Cu{sub 2}{sup +} and Cu{sup +} are the precursors to the formation of colloidal copper particles. Three distinct time periods during the reduction of Cu{sup 2+} to copper metal can be distinguished: (1) formation and disappearance of the first intermediates, i.e., CuCO{sub 2} and Cu{sub 2}{sup +}, within about 100 {mu}s; (2) formation of nuclei within milliseconds to seconds; and (3) rather sudden formation of larger aggregates within seconds. At the beginning of thismore » sudden formation, the particles absorb in the UV; they are probably oligomers of nonmetallic character. In the later stages of formation, larger metallic particles absorbing in the UV and visible are present.« less

Surface‐enhanced Raman spectroscopy of pyridine and thiophenol on non‐aqueous colloidal copper

AbstractSurface‐enhanced Raman (SER) spectra of pyridine and thiophenol on a copper colloid prepared in isopropanol were obtained. Aggregation of the colloid, which occurs only slowly in the presence of adsorbates, was found to be essential to the detection of SER spectral features with excitation at 660 nm. As with aqueous copper sols, thiophenol was found to adsorb more strongly than pyridine to the copper surface. However, both adsorbates required greater concentrations in the bulk solution than for aqueous systems in order for SER features to be observed.

Dose rate dependence of the optical absorption of Cu implanted silica

High-purity silica (Spectrosil) samples were implanted with Cu at doses from 1.0 × 10 16 to 6.0 × 10 16ions/cm 2. Samples implanted to a dose of 6.0 × 10 16ions/cm 2 were implanted at dose rates of 7.5, 5, 2.6, and 0.7 mA/cm 2. Some samples were implanted with smaller total doses at dose rates of 7.5 and 2.5 mA/cm 2. Backscattering measurements determined the concentration of implanted ions as a function of dose and depth. The optical absorption, measured from 1.8 to 6.0 eV at room temperature, was observed to increase with increasing dose rate in samples implanted with a total dose ≥ 3.0 × 10 16ions/cm 2. We attribute the increase in optical absorption at energies between 2 and 5 eV with dose in these samples to the formation of spherical copper colloids of various diameters. The peak at 2.2 eV that forms at dose levels ≥ 3.0 × 10 16 was observed to increase nonlinearly with dose rate. We attribute this peak to the formation of prolate copper spheroids with an aspect ratio of ~ 2. We suggest that the dose rate dependence is due to localized heating which increases with increased dose rate. Samples implanted with doses < 3 × 10 16ions/cm 2 did not display this same strong dependence on dose rate. For these doses copper colloids are not a major source of absorption in the 2–5 eV range. In these samples we attribute the absorption to Cu + and to intrinsic defects produced by radiation damage.

Photochemical formation of colloidal silver: peptizing action of acetone ketyl radical

When an aqueous AgClO4–sodium dodecylsulphate (SDS)–isopropyl alcohol (Pri OH) solution was photolysed with 253.7 nm light, a sharp and intense absorption band of colloidal silver (λ= 390–400 nm) appeared after a relatively long induction period. In contrast, the sharp colloidal absorption rapidly developed when an AgClO4–SDS–acetone [(CH3)2CO] solution was irradiated under the same conditions. It has been shown by chemical analysis and TEM characterization of the reduced silver that some of the colloidal silver agglomerates formed as a result of photolysis were peptized to fine silver particles during irradiation. Acetone ketyl radical formed by excitation of (CH3)2CO with 253.7 nm light seems to have an ability to peptize colloidal agglomerate in the solution phase (peptizing action). A novel ‘photo-acetone method’ available for preparation of fine metal particles has been proposed and applied to obtain colloidal gold, copper and platinum.

Preparation and properties of well defined finely dispersed metals

The preparation of dispersions of uniform metal particles of different morphologies, either by precipitation from homogeneous solutions in the presence of appropriate reducing agents or by phase transformation, is discussed. Specifically, the formation of colloidal cobalt, nickel, copper, iron, ruthenium, and palladium is described and the effects of various experimental conditions on the properties of the resulting powders are illustrated.

Probing the electronic structure of small copper particles: 63Cu NMR at 1.5 K

We have investigated the 63Cu NMR (at 1.5 and 4.2 K) of a series of samples comprising silica-supported colloidal copper particles with average diameter (d) ranging from 1000 to 34 A. Substantial reductions have been observed in the metal Knight shift of the NMR of sub-80 A particles in our measurement field of 12.7 T. The magnitude of this reduction in the Knight shift is both temperature- and size-dependent; the effect being most pronounced for the smallest copper particles at our base temperature of 1.5 K.In the lower-size regime of colloidal copper particles (d⩽ 80 A), there exists a fundamental and qualitative difference in the electronic structure of the particles as compared with that of bulk copper metal. Specifically, the magnetic properties of the colloidal metal particles are dependent upon whether each individual particle contains either an even or an odd number of copper atoms. We find that the 63Cu NMR Knight shift distinguishes the behaviour of even (and odd) numbered copper particles. In the case of even-number particles, the reduction in the Knight shift arises from the loss of the paramagnetic susceptibility, this being most pronounced at low temperatures.The observed reduction in the NMR Knight shift of copper from its bulk metallic value is strong evidence for the existence of quantum size effects in colloidal copper particles at low temperatures.

Preparation and characterization of uniform particles of pure and coated metallic copper

Colloidal copper of narrow size distribution in the micrometre size range was prepared by two different methods. The first procedure involved the reduction of uniform spherical particles of copper(II) basic carbonate with hydrogen at 150–200 °C. The improved method consisted of a two-step process in which the copper(II) basic carbonate was converted to copper(II) oxide and then treated with hydrogen. In order to preserve particle integrity, the precursor powders were coated with small ( ∼ 10 nm) silica particles (Ludox HS or 130M) before reduction with hydrogen. In the second method, cubic metallic copper particles were generated in situ in solutions containing Cu(NO 3) 2, urea and NH 2OH · HCl. The uniformity of the dispersion was achieved by controlled growth of the particles on preformed nuclei.

Needle-type colloidal copper (II)hydroxide particles

Stable dispersions of fine (< 0.05μm) needle-type copper(II) hydroxide particles were prepared at room temperature by admixing sodium acetate and ammonia to copper sulfate solution. The particle length and width could be altered with the concentration of reactants. The rate of dissolution of copper(II) hydroxide particles in doubly distilled water at room temperature is time dependent, which is due in part to the formation of a mononuclear complex solute (CuOH+). After extended times (e.g., 18 h), the particles underwent phase transformation, resulting in longer needles of higher degree of crystallinity.

Surface‐enhanced Raman spectroscopy of 1,5‐dimethylcytosine on silver and copper sols

AbstractRaman spectra of 1.5‐dimethylcytosine (DMC) as the solid and in aqueous solution are reported. A tentative assignment of Raman bands is made. Surface‐enhanced Raman spectra obtained on silver and on copper colloids show appreciable differences from the normal unenhanced Raman spectra. The geometry of DMC–metal interactions is discussed.