Optical constants of nanostructured layers of copper,nickel, palladium,and some oxides in the UV and visible spectral regions

It is found that a significant spread in the optical constants of metals reported by different authors is caused by differences in the sample preparation methods, measurement conditions, and methods of calculation of sought parameters, as well as by the oxidation effect. It is shown that the optical constants of metals in films 80–120 nm thick on silicon substrates with scattering below 10⁻⁴ are determined with minimal errors. The reflectance of these mirrors calculated from the optical constants found by the most accurate ellipsometric method coincides with the experimental value within the measurement accuracy. Low values of k(λ) obtained for thin layers in some works using the methods based on the measurement of the coherent transmittance and regular reflectance are explained by disregarded scattering and luminescence. The spectra of the imaginary part of the complex refractive index of copper, nickel, and copper oxide determined by us by the proposed methods for thin nanostructured layers taking into account the scattering and luminescence coincide with the most correct data for thick films in the spectral range of 325–633 nm. For thin palladium and palladium oxide layers, the variations in k(λ) are caused by the oxidation of metal granules and disregarded luminescence for thick oxide layers in the long-wavelength spectral region. The maximal difference in the imaginary part of the complex refractive index of copper and nickel for thin nanostructured layers are observed in the region of plasmon resonances, whose positions and amplitudes depend on the degree of asphericity, the shape, and the degree of order of particles and their aggregates, which shift the plasmon resonances of films to longer wavelengths with respect to spherical particles.     

Nonlinear absorption in dielectric layers containing copper nanoparticles

The nonlinear absorption in copper nanoparticles contained in glass matrices is investigated using the Z-scan technique at the wavelength of a picosecond Nd: YAG laser (λ=1064 nm). The experimental data obtained for copper nanoparticle-containing composites synthesized through ion implantation are analyzed. It is demonstrated for the first time that, upon exposure to laser radiation at frequencies outside the range of surface plasma resonance, the nonlinear absorption in metallic particles can be caused by the two-photon effect. The optical limiting due to two-photon absorption is discussed for composites containing copper particles.     

Surface microstructures and antimicrobial properties of copper plasma alloyed stainless steel

Bacterial adhesion to stainless steel surfaces is one of the major reason causing the cross-contamination and infection in many practical applications. An approach to solve this problem is to enhance the antibacterial properties on the surface of stainless steel. In this paper, novel antibacterial stainless steel surfaces with different copper content have been prepared by a plasma surface alloying technique at various gas pressures. The microstructure of the alloyed surfaces was investigated using glow discharge optical emission spectroscopy (GDOES) and scanning electron microscopy (SEM). The viability of bacteria attached to the antibacterial surfaces was tested using the spread plate method. The antibacterial mechanism of the alloyed surfaces was studied by X-ray photoelectron spectroscopy (XPS). The results indicate that gas pressure has a great influence on the surface elements concentration and the depth of the alloyed layer. The maximum copper concentration in the alloyed surface obtained at the gas pressure of 60 Pa is about 7.1 wt.%. This alloyed surface exhibited very strong antibacterial ability, and an effective reduction of 98% of Escherichia coli (E. coli) within 1 h was achieved by contact with the alloyed surface. The maximum thickness of the copper alloyed layer obtained at 45 Pa is about 6.5 μm. Although the rate of reduction for E. coli of this alloyed surface was slower than that of the alloyed surface with the copper content about 7.1 wt.% over the first 3 h, few were able to survive more than 12 h and the reduction reached over 99.9%. The XPS analysis results indicated that the copper ions were released when the copper alloyed stainless steel in contact with bacterial solution, which is an important factor for killing bacteria. Based on an overall consideration of bacterial killing rate and durability, the alloyed surface with the copper content of 2.5 wt.% and the thickness of about 6.5 μm obtained at the gas pressure of 45 Pa is expected to be useful as antimicrobial materials that may have a promising future in antimicrobial applications.     

Optical characterization of thin thermal oxide films on copper by ellipsometry

A complete optical characterization in the visible region of thin copper oxide films has been performed by ellipsometry. Copper oxide films of various thicknesses were grown on thick copper films by low temperature thermal oxidation at 125 °C in air for different time intervals. The thickness and optical constants of the copper oxide films were determined in the visible region by ellipsometric measurements. It was found that a linear time law is valid for the oxide growth in air at 125 °C. The spectral behaviour of the optical constants and the value of the band gap in the oxide films determined by ellipsometry in this study are in agreement with the behaviour of those of Cu₂O, which have been obtained elsewhere through reflectance and transmittance methods. The band gap of copper oxide, determined from the spectral behaviour of the absorption coefficient was about 2 eV, which is the generally accepted value for Cu₂O. It was therefore concluded that the oxide composition of the surface film grown on copper is in the form of Cu₂O (cuprous oxide). It was also shown that the reflectance spectra of the copper oxide–copper structures exhibit behaviour expected from a single layer antireflection coating of Cu₂O on Cu. Received: 19 July 2001 / Accepted: 27 July 2001 / Published online: 17 October 2001     

Interaction of intense IR laser radiation with a-C:H protective coatings

The results of a determination of the optical breakdown thresholds of air near the surface of copper laser mirrors with a-C:H protective coating by intense pulsed 10.6 μm radiation are analyzed and systematized. It is shown that there is no correlation between the breakdown threshold of a coated mirror, the reflectance of the coating, and the breakdown threshold of the initial copper surface. Experimental dependences of the threshold of optical breakdown of coated mirrors on the a-C:H thickness and deposition rate as well as the storage time of the mirrors are given. Estimates are made of the rise in the surface temperature in the irradiation zone for the case of an ideal adhesive contact and calculations are made of the damage threshold of the coating in the case that the adhesive contact between the mirror and the coating is impaired. The effect of the a-C:H coating properties and the conditions at the polished metal surface-protective coating interface on the optical breakdown threshold is discussed. Zh. Tekh. Fiz. 68, 59–66 (September 1998)     

Optical properties of gold electrode surfaces covered with metal monolayers

The relative reflectivity changes ΔR/R of a gold electrode surface caused by the deposition of monolayers of thallium, copper and lead from electrolytic solutions at underpotentials have been studied in situ in the photon energy range between 1.8 and 5.2 eV. The optical constants of the surface layer giving rise to this measured reflectivity change have been calculated and compared to the results of the electroreflectance effect on bare gold surfaces. It is shown that the reflectance change observed during the monolayer deposition is to first order due to a change in the gold electrode surface layer and not to absorption processes in the monolayer itself. The latter ones cause a fine structure superimposed to the substrate spectrum. The relatively strong change in the gold surface optical constants upon metal monolayer deposition is explained in terms of an enhanced electroreflectance effect due to the partially ionic character of the metal adatoms, which alters the free electron concentration in the substrate surface layer. Electroreflectance spectra obtained on gold surfaces covered with a monolayer of thallium compare favourably with dielectric loss functions computed for charged gold surfaces. This supports the assumption that the reflectivity changes observed upon metal monolayer deposition are mostly due to changes in the optical properties of the substrate metal surface.     

Influence of the core‐hole effect on optical properties of magnesium oxide (MgO) near the Mg L‐edge region

The influence of the core‐hole effect on optical properties of magnesium oxide (MgO) is established through experimental determination of optical constants and first‐principles density functional theory studies. Optical constants (δ and β) of MgO thin film are measured in the spectral region 40–300 eV using reflectance spectroscopy techniques at the Indus‐1 synchrotron radiation source. The obtained optical constants show strong core exciton features near the Mg L‐edge region, causing significant mismatch with Henke's tabulated values. On comparing the experimentally obtained optical constants with Henke's tabulated values, an edge shift of ～3.0 eV is also observed. Distinct evidence of effects of core exciton on optical constants (δ and β) in the near Mg L‐edge absorption spectra are confirmed through first‐principles simulations.     

Patterned self-assembled monolayers of alkanethiols on copper nanomembranes by submerged laser ablation

Self-assembled monolayers (SAMs) of alkanethiols are major building blocks for nanotechnology. SAMs provide a functional interface between electrodes and biomolecules, which makes them attractive for biochip fabrication. Although gold has emerged as a standard, copper has several advantages, such as compatibility with semiconductors. However, as copper is easily oxidized in air, patterning SAMs on copper is a challenging task. In this work we demonstrate that submerged laser ablation (SLAB) is well-suited for this purpose, as thiols are exchanged in-situ, avoiding air exposition. Using different types of ω-substituted alkanethiols we show that alkanethiol SAMs on copper surfaces can be patterned using SLAB. The resulting patterns were analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Both methods indicate that the intense laser beam promotes the exchange of thiols at the copper surface. Furthermore, we present a procedure for the production of free-standing copper nanomembranes, oxidation-protected by alkanethiol SAMs. Incubation of copper-coated mica in alkanethiol solutions leads to SAM formation on both surfaces of the copper film due to intercalation of the organic molecules. Corrosion-protected copper nanomembranes were floated onto water, transferred to electron microscopy grids, and subsequently analyzed by electron energy loss spectroscopy (EELS).     

The effects of pulsed Nd:YAG laser irradiation on surface energy of copper

The effect of laser surface treatment on the surface energy of copper plate was investigated in terms of the surface microstructure analysis and theoretical computation in this paper. The surfaces of the copper plates were treated by Nd:YAG pulsed laser with different powers. The microstructures of the treated copper plates were analyzed by optical microscopy and X-ray diffraction (XRD), and the wetting experiment was performed to evaluate the variation of surface energy. The results showed that the surface microstructure and the corresponding surface energy of copper, changed with the variation of the laser power. The experimental results further explained by XRD results and theoretical calculation, demonstrated that the surface energy changed when the crystal structure in the surface layer was re-oriented in a preferred orientation after laser irradiation.     

Optical control of photopolymerization during stereolithographic synthesis

The possibility of using the multiple-scattering spectrum of incident radiation to make a real-time determination of the degree of conversion of compositions undergoing photopolymerization in optical stereolithography is investigated. It is shown that the fluctuations arising in the refractive index grow in amplitude in the course of photopolymerization. The extremal dependences of the scattered radiation intensity on the degree of conversion are analyzed theoretically and experimentally. Zh. Tekh. Fiz. 68, 137–139 (February 1998)     

Enhancement in nucleate pool boiling heat transfer on nano-second laser processed copper surfaces

ABSTRACT

The present paper reports the experimental investigation of pool boiling heat transfer on multiscale functionalized copper surfaces. Multiscale functionalized surfaces are fabricated by employing the nano-second laser surface process (NLSP) technique. The heat transfer coefficients (HTCs) of functionalized surfaces are estimated experimentally by using water and acetone as pool liquid. Tests are performed at atmospheric pressure, and saturated pool boiling condition with heat flux varyies between 0 and 330 kW/m². The maximum HTCs for functionalized surface and reference polished surface were found to be 41,500 W/m²K and 23,000 W/m²K, respectively, with water and 22,000 W/m²K and 14,000 W/m²K, respectively, with acetone.     

Excimer laser-induced ablation of clean and CO-covered polycrystalline copper surfaces: Generation and characterization of high energy copper species

Copper atoms, clusters and ions were generated by ablation of clean and CO-covered polycrystalline copper surfaces under UHV conditions, using a high peak power, pulsed excimer laser as the energy source. The species in the vapor phase were characterized by time-resolved mass spectrometry and optical detection of laser induced fluorescence. The laser power density threshold of vaporization for the clean copper (300(30) MW/cm²) was significantly lower than the threshold in the case of CO-covered copper surfaces (> 400 MW/cm²).     

Structure effects on the energetics of the electrochemical reduction of CO2 by copper surfaces

Polycrystalline copper electrocatalysts have been experimentally shown to be capable of reducing CO₂ into CH₄ and C₂H₄ with relatively high selectivity, and a mechanism has recently been proposed for this reduction on the fcc(211) surface of copper, which was assumed to be the most active facet. In the current work, we use computational methods to explore the effects of the nanostructure of the copper surface and compare the effects of the fcc(111), fcc(100) and fcc(211) facets of copper on the energetics of the electroreduction of CO₂. The calculations performed in this study generally show that the intermediates in CO₂ reduction are most stabilized by the (211) facet, followed by the (100) facet, with the (111) surface binding the adsorbates most weakly. This leads to the prediction that the (211) facet is the most active surface among the three in producing CH₄ from CO₂, as well as the by-products H₂ and CO. HCOOH production may be mildly enhanced on the more close-packed surfaces ((111) and (100)) as compared to the (211) facet, due to a change in mechanism from a carboxyl intermediate to a formate intermediate. The results are compared to published experimental data on these same surfaces; the predicted trends in voltage requirements are consistent between the experimental and computational data.     

Characteristic energy loss spectra of copper crystals with surfaces described by LEED

Energy distributions of electrons back-scattered from copper (100) and (110) surfaces have been obtained for incident electron energies in the range 30 to 350 eV. The relations between optical measurements and the characteristic energy losses, as well as the effect of interband transitions on the bulk and surface plasmon frequencies in metals which do not have ideally free electron plasmas are discussed. By chemisorbing increasing amounts of oxygen on the clean surface, the surface plasmon loss peak was identified in the copper energy loss spectrum from its intensity dependence on the dielectric constant at the surface. This peak has been identified by previous authors as the bulk plasmon loss of a single s-electron plasma oscillation. Our identification of the surface plasmon loss peak implies that the d-electrons in copper do participate in the plasma oscillation and that the bulk plasmon frequency is shifted from its free electron value because of interband transitions.     

Spectral absorptivity of rough copper and brass surfaces

The spectral absorptivity of brass and copper in the optical range (400–650nm) has been measured using a calorimetric method, for a series of rough cold-worked metal surfaces. Results depend strongly on the surface roughness and weakly on the light wavelength. The total absorptivity for white light (2870 K) reaches 34% on copper samples.     

Streustrahlung von Silber durch Anregung von Oberflächenplasmaschwingungen

Socalled nonradiative surface plasma waves are excited in the visible spectral region by normal incidence of light on a rough surface of silver. By optical coupling by means of a prism they show up as scattered radiation, which is polarized parallel to the plane of emission. The scattered radiation can be excited by light polarized both parallel and perpendicular to the plane of emission. The dispersion of the surface plasma waves is worked out from the angular distribution of the scattered radiation.     

On the nature and mechanism of surface polygonization of NaCl and KCl single crystals produced by electron bombardment and illumination

Abstract

The polygonization phenomenon observed on alkali halide surfaces, irradiated with electrons and subsequently illuminated, was studied by optical and electron microscopy. For the explanation of the nature and mechanism of this process, we have investigated the influence of light (containing the F?centre absorption band) on the development and annihilation in time of some polygonization lines, as well as the correlation of the polygonization patterns with dislocation etch pits and subgrain boundaries revealed by a selective chemical etching.

Preceded by an optical bleaching effect which locally induces surface potential changes, the polygonization process is explained taking into account the mobility of unpinned charged dislocations and the surface atom migration. The disappearance of some polygonization lines may be produced by a vacancy-interstitial annihilation process.

No identification was found between the polygonization patterns and the subgrain boundaries.     

In situ functionalized self-assembled monolayer surfaces for selective chemical vapor deposition of copper

Recent studies show that the self-assembled monolayer (SAM) is well suited to control the selectivity of chemical vapor deposition (CVD). Here, we reported the selective CVD for copper on the functionalized SAM surfaces (with -SH, -SS-, and -SO₃H terminal groups). The -SS- and -SO₃H terminal group surfaces were obtained through in situ chemical transformation of -SH terminal group surface of a 3-mercaptopropyltrimethoxysilane-SAM (MPTMS-SAM). As a result, the -SS- terminal group surface reduces copper deposition and the -SO₃H terminal group surface enhances copper deposition comparing to the -SH terminal group surface. In addition, the MPTMS-SAM was irradiated by UV-light through a photo mask to prepare SH-group and OH-group regions. Then, copper films were deposited only on the SH-group region of the substrate in chemical vapor deposition. Finally, patterns of copper films were formed in the way of UV-light irradiation. These results are expected for use of selective deposition of copper metallization patterns in IC manufacturing processes.     

In situ QCM and TM-AFM investigations of the early stages of degradation of silver and copper surfaces

The early stages of atmospheric corrosion of pure copper and pure silver specimens were investigated performing in situ tapping mode atomic force microscopy (TM-AFM), in situ quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The information obtained by TM-AFM is the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first hours of weathering. The simultaneously performed in situ QCM measurements are indicating the mass changes due to possibly occurring corrosive processes on the surface during weathering and are therefore a valuable tool for the determination of corrosion rates. Investigations were carried out in synthetic air at different levels of relative humidity (RH) with and without addition of 250 ppb SO₂ as acidifying agent. On a polished copper surface the growth of corrosion products could be observed by TM-AFM analysis at 60% RH without any addition of acidifying gases [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454-456 (2000) 246-250]. On a weathered copper surface the addition of SO₂ to the moist air stream leads to the formation of additional features as already described in the literature [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454-456 (2000) 246-250; Ch. Kleber, J. Weissenrieder, M. Schreiner, C. Leygraf, Appl. Surf. Sci. 193 (2002) 245-253]. Exposing a silver specimen to humidity leads to the degradation of the surface structure as well as to a formation of corrosion products, which could be detected by in situ QCM measurements. After addition of 250 ppb SO₂ to the moist gas stream an increase of the formed feature's volume on the silver surface could be observed by TM-AFM measurements. The results obtained additionally from the in situ QCM measurements confirm the influence of SO₂ due to a further increase of the mass of the formed corrosion layer (and therefore an increase of the calculated corrosion rates) compared to the data obtained from the experiment carried out in humidity only.     

Effect of microrelief on the optical characteristics of light Cr-Zr copper alloys bombarded by ions of deuterium plasma

The effect of the structure and size of grains on changes in the microrelief and optical characteristics of specimens of mirrors made of copper alloys with substantially differing grain size upon bombardment by ions of deuterium plasma are studied. Based on a comprehensive study of the structural features of the surface layers of specimens of mirrors made of light copper-chromium alloys, a conclusion is drawn as to the determining role of grain size in their radiation properties.