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At least 199 records · Page 11Linked to original sources
PubMed2006

Anion-exchange high performance liquid chromatography hyphenated to inductively coupled plasma-isotope dilution-time-of-flight mass spectrometry for speciation analysis of metal complexes with metallothionein isoforms in gibel carp (Carassius auratus gibelio) exposed to environmental metal pollution.

The capability of post-column isotope dilution (ID) combined with anion-exchange HPLC-ICP-time-of-flight (TOF)-MS was for the first time investigated for environmental quality assessment through metal speciation analysis of metallothionein (MT) isoforms in cytosols of gibel carp (Carassius auratus gibelio), used as biomarkers for environmental metal exposure. A full spectral scanning of the biological sample (with 50 microl injection volume) using ICP-TOF-MS in transient mode allowed fast multi-isotope screening of cytosolic metal-containing fractions and to investigate the presence of matrix-induced interferences. The MT cytosolic fraction of liver and kidney of the carp, sampled at three different sampling sites in Belgium, was partially purified using size-exclusion (SE) HPLC. Quantification of the elements Cd (toxic) and Zn and Cu (essential) associated with MT isoforms in this fraction was addressed using an hybrid approach based on post-column addition of the enriched isotopes 65Cu, 67Zn, 106Cd and monitoring on-line the isotope ratios 63Cu/65Cu, 64Zn/67Zn and 114Cd/106Cd by ICP-MS with a time of flight instrument, which was coupled to anion-exchange HPLC. With this separation method, baseline separation of up to five MT isoforms, which is required for quantitative metal speciation by HPLC-ICP-IDMS, was achieved within a run of 15 min. The MT fraction of the cytosols was also analysed for the total metal content using IDMS with size-exclusion HPLC-ICP-MS and species-unspecific calibration. Results showed significant differences between speciation results and total MT concentrations of control fish and fish from the most contaminated sampling sites, revealing the potential of gibel carp MT for sequestering excess intracellular free-ions (essential and toxic elements) and for its protection against metal toxicity. Preferences for metal sequestration of metal complexes with MT isoforms were also found to be tissue-specific: excess of Cd was found preferably bound to a major MT isoform (tR = 8.0 min) in kidney, whereas excess intracellular Zn appeared to be mostly sequestered by four MT isoforms (tR=7.3, 8.0, 12.2 and 14.4 min) in liver, the MT form with tR = 8.0 min being the main Zn scavenger form. Such kind of quantitative speciation information on the preferences of MT isoforms in different fish organs for sequestering heavy metals, reported here for the first time, is important to elucidate the role of isoform-specific induction of vertebrate fish MT in metal detoxification and the use of MT as biomarker.

Animals↗
PubMed2003

Differential pulse polarography: a method for the direct study of biosorption of metal ions by live bacteria from mixed metal solutions.

The technique of differential pulse polarography is shown here to be applicable to the monitoring directly the biosorption of metal ions from solution by live bacteria from mixed metal solutions. Biosorption of Cd(II), Zn(II) and Ni(II) by P. cepacia was followed using data obtained at the potential which is characteristic of the metal ion in the absence and presence of cells. Hepes buffer (pH 7.4, 50 mM) was used as a supporting electrolyte in the polarographic chamber and metal ion peaks in the presence of cells of lower amplitude were obtained due to metal-binding by the cells. Well defined polarographic peaks were obtained in experiments involving mixtures of metal ions of Cd(II)-Zn(II), Cu(II)-Zn(II), Cu(II)-Cd(II) and Cd(II)-Ni(II). Biosorption of Cd(II), Zn(II) increased with solution pH. The method was also tested as a rapid technique for assessing removal of metal ions by live bacteria and the ability of the polarographic technique in measuring biosorption of metal ions from mixed metal solutions is demonstrated. Cu(II) was preferentially bound and removal of metals was in the order Cu(II) > Ni(II) > Zn(II), Cd(II) by intact cells of P. cepacia.

Adsorption↗
PubMed2003

Heat and heavy metal stress synergize to mediate transcriptional hyperactivation by metal-responsive transcription factor MTF-1.

Mammalian cells react to heavy metal stress by transcribing a number of genes that contain metal-response elements (MREs) in their promoter/enhancer region; this activation is mediated by metal-responsive transcription factor-1 (MTF-1). Well-known target genes of MTF-1 are those encoding metallothioneins, small, cysteine-rich proteins with a high affinity for heavy metals. The response to heat shock, another cell stress, is mediated by heat shock transcription factor 1 (HSF1), which activates a battery of heat shock genes. Little is known about the cross-talk between the different anti-stress systems of the cell. Here we report a synergistic activation of metal-responsive promoters by heavy metal load (zinc or cadmium) and heat shock. An obvious explanation, cooperativity between MTF-1 and HSF1, seems unlikely: transfected HSF1 boosts the activity of an Hsp70 promoter but hardly affects an MRE-containing promoter upon exposure to metal and heat shock. A clue to the mechanism is given by our finding that heat shock leads to intracellular accumulation of heavy metals. We propose that the known anti-apoptotic effect of heat shock proteins allows for cell survival despite heavy metal accumulation and, consequently, results in a hyperactivation of the metal response pathway.

Cell Line↗
PubMed2001

Levels of trace metals and effect of body size on metal content of the landsnail Levantina hierosylima from the West Bank-Palestine.

Levels of four trace metals (Cu, Zn, Cd and Pb) were determined in the landsnail Levantina hierosylima from four locations in the West Bank. Average concentration of the metals was 126.9, 42, 20.2 and 19.4 ppm for Cu, Zn, Pb and Cd, respectively. Significant differences in metal concentrations were observed between snails from the four sampling sites (Jerusalem, Abu-Dies, Qarawa, and Taibeh). Differences are most probably due to atmospheric fallout of metals from traffic roads and industrial facilities. Effect of snail size (weight and shell width) on metal content was investigated for the four metals. Plotting metal content against soft tissue weight resulted in significant relationships. Small snails were found to be richer in Zn, Cd and Pb than larger ones. Regression coefficients for the relationships were 0.75, 0.76 and 0.81 for Pb, Cd and Zn, respectively. Copper content was directly related to body weight (regression coefficient = 0.96) indicating that Cu concentration is independent of body weight. Plotting metal content against shell width indicated similar results but with less strong correlation coefficients. L. hierosylima is a promising bioindicator for metal pollution and further laboratory investigations are needed in order to know more about the uptake and release of metals by this organism.

Animals↗
PubMed1996

Metal on metal bearings in hip arthroplasty.

Periprosthetic osteolysis caused by wear debris released from the bearing surface of polyethylene components is the major problem in contemporary hip arthroplasty. Several types of metal on metal prostheses were developed in the 1960s, but by the mid 1970s they were completely displaced by polyethylene bearings. There have been several generations of all metal components with significant variation in design, tolerances, and bearing surface quality. A number of these hips have survived for more than 25 years because of low wear rates and minimal osteolysis. Identification of the characteristics that contributed to long term function is important. The historical development and clinical results of metal on metal hip arthroplasties are presented. Factors that led to the abandonment of the metal on metal bearings are related to: (1) the early success of the Charnley prosthesis; (2) the frictional torque issue; (3) carcinogenesis concerns; (4) metal sensitivity concerns; (5) high infection rates; and (6) increased strain rates in periprosthetic bone and fatigue fractures of the acetabular floor. The accumulated experience to date enables one to evaluate all the factors with a different perspective and makes the use of newer metal on metal bearings a viable option in younger patients.

Adult↗
PubMed2006

Metal-on-metal hip joint tribology.

The basic tribological features of metal-on-metal total hip replacements have been reviewed to facilitate an understanding of the engineering science underpinning the renaissance of these hard-on-hard joints. Metal-on-polymer hip replacements operate in the boundary lubrication regime, thus leading to the design guidance to reduce the femoral head diameter as much as is feasible to minimize frictional torque and volumetric wear. This explains why the gold-standard implant of this form from the past half-century had a diameter of only 22.225 mm (7/8 in). Metal-on-metal implants can operate in the mild mixed lubrication regime in which much of the applied load is supported by elastohydrodynamic films. Correct tribological design leads to remarkably low steady state wear rates. Promotion of the most effective elastohydrodynamic films calls for the largest possible head diameters and the smallest clearances that can reasonably be adopted, consistent with fine surface finishes, good sphericity and minimal structural elastic deformation of the cup on its foundations. This guidance, which is opposite in form to that developed for metal-on-polymer joints, is equally valid for solid (monolithic) metallic heads on metallic femoral stems and surface replacement femoral shells. Laboratory measurements of friction and wear in metal-on-metal joints have confirmed their potential to achieve a very mild form of mixed lubrication. The key lies in the generation of effective elastohydrodynamic lubricating films of adequate thickness compared with the composite roughness of the head and cup. The calculation of the film thickness is by no means easy, but the full procedure is outlined and the use of an empirical formula that displays good agreement with calculations based upon the full numerical solutions is explained. The representation of the lambda ratio, lambda, embracing both film thickness and composite roughness, is described.

Arthroplasty, Replacement, Hip↗
PubMed2006

Clinical experience with metal-on-metal total joint replacements: indications and results.

Survivorship of total joint arthroplasty depends on the durability of fixation and durability of articulation. The metal-on-polyethylene articular couple has been the most widely used. Polyethylene wear (and the associated cytochemical events that culminate in osteolysis) has been identified as a major factor adversely influencing the durability of joint replacement. This stimulated the orthopaedic community to explore the possibility of using alternative bearings with lower wear rates. Hard-on-hard bearings have been shown to be associated with reduced wear. Metal-on-metal bearings have wear rates that are 20-100 times lower than metal on conventional polyethylene. However, patients with metal-on-metal articulations have increased levels of cobalt and chromium in the serum and urine, and this has raised concerns about toxicity, mutagenesis, and hypersensitivity. At this stage there is no epidemiological evidence to suggest that the risk of carcinogenesis is anything more than theoretical. Successful long-term results have been reported with the cast cobalt-chromium metal-on-metal couples of the mid-1960s. Tissues retrieved at revision of these implants did not show the giant-cell inflammatory response associated with polyethylene particles. Several researchers have reported excellent mid-term results with the current generation of high-precision metal-on-metal bearings.

Biocompatible Materials↗
PubMed1990

Use of a metal detector to identify ingested metallic foreign bodies.

A metal detector reveals the presence of metallic objects by measuring the change in the inductance of a coil placed near a metallic mass. The device used in this study is similar in principle to those used for passenger surveillance in airports except for its smaller size and simpler design. In this study, we compared the accuracy of a metal detector with that of plain radiographs for the localization of ingested metallic objects. Twenty-eight consecutive patients with the presumptive diagnosis of metallic foreign-body ingestion were examined with a metal detector. The results were compared with those of plain radiographs which were considered the gold standard. Fifteen positive cases and 13 negative cases were correctly diagnosed by metal detector examination. No false-positive or false-negative results occurred. Our experience suggests that metal detection is a simple and accurate technique for the localization of ingested metallic objects and provides information equivalent to that from plain radiographs for the treatment of patients with suspected foreign-body ingestion.

Adult↗
PubMed2003

Bioleaching of metals from sludges and acid production under increased metal concentrations.

To remove heavy metals from sludge and slurries the heavy metals must first be solubilised. In this study, metal bioleaching using sulphuric acid producing microorganisms is investigated. The inhibitory effects of four metals (zinc, chromium, nickel and copper) on acid production were firstly assessed for concentrations of each metal up to 1,000 mg/l. Low concentrations of zinc and chromium (50 mg/L) appear to stimulate the production of sulphuric acid but concentrations of those metals at 500 mg/L and above inhibited acid production (20 to 30% of the control rate at a concentration of 1,000 mg/L). The average sulphuric acid production of the metal free control was 0.78 g/L/day over a 10 day period. At all concentrations of nickel and copper, sulphuric acid production was suppressed and was less than 10% of the control at 250 mg/L or more after 10 days. Activated sludge was also loaded with the four metals in individual bioleaching tests, in increments from zero up to 5,050 mg of metal/kg solids on a dry basis. In these bioleaching trials the sulphuric acid production averaged 0.9/g/L/day and the pH after 7 days was less than 2.0. Sludge copper concentrations of 3,850 and 5,050 mg/kg partially inhibited acid production (pH after 7 days was 2.4 and 2.7). The solubilisation for each metal after 7 days was Zn: 82-97%, Ni: 12-70%, Cu: 28-55%, and Cr: <20%. Bioleaching of a sludge loaded with a mixture of the four metals gave peak solubilities of 99% for Zn after 3 days, 68% for Ni after 6 days, 57% for Cu after 9 days and 33% for Cr after 9 days.

Bioreactors↗
PubMed2006

Biosorption of Ni, Cr and Cd by metal tolerant Aspergillus niger and Penicillium sp. using single and multi-metal solution.

Fungi including Aspergillus and Penicillium, resistant to Ni2+, Cd2+, and Cr6+ were isolated from soil receiving long-term application of municipal wastewater mix with untreated industrial effluents of Aligarh, India. Metal tolerance in term of minimum inhibitory concentration (MIC) was 125-550 microg/ml for Cd, 300-850 microg/ml for Ni and 300-600 microg/ml for Cr against test fungi. Two isolates, Aspergillus niger and Penicillium sp. were tested for their Cr, Ni and Cd biosorption potential using alkali treated, dried and powdered mycelium. Biosorption experiment was conducted in 100 ml of solution at three initial metal concentrations i.e., 2, 4 and 6 mM with contact time (18 hr) and pretreated fungal biomass (0.1g) at 25 degrees C. Biosorption of all metals was found higher at 4 mM initial metal concentration as compared to biosorption at 2 and 6 mM concentrations. At 4 mM initial metal concentration, chromium biosorption was 18.05 and 19.3 mg/g of Aspergillus and Penicillium biomasses, respectively. Similarly, biosorption of Cd and Ni ions was also maximum at 4 mM initial metal concentration by Aspergillus (19.4 mg/g for Cd and 25.05 mg/g of biomass for Ni) and Penicillium (18.6 mg/g for Cd and 17.9 mg/g of biomass for Ni). In general, biosorption of metal was influenced by initial metal concentration and type of the test fungi. The results indicated that fungi of metal contaminated soil have high level of metal tolerance and biosorption properties.

Adsorption↗
PubMed1996

Modern metal on metal articulation for total hip replacements.

Between 1991 and 1994, 70 patients received total hip replacements with metal on metal articulation. The results of 54 of these patients with 54 hips who have a 2- to 4-year (2.7-year average) followup are reported. Patients were prospectively evaluated using the Harris hip score, a patient self assessment form, and radiographs. Hip aspiration was performed preoperatively and 6 to 24 months postoperatively in 24 hips with metal on metal articulations. Implant retrieval was obtained from 2 patients. Harris hip score averages increased from 49 to 93. No patient had revision surgery for loosening, but 1 had revision surgery for dislocation. Patient self assessment forms showed 51 of 54 patients scored their results as good or excellent. Serial radiographs did not show loosening or osteolysis. Wear could not be measured radiographically. Synovial fluid samples had metal particles of 1 to 10 microm in 10 hips. Twenty patients had bilateral total hip replacements with 1 hip metal on polyethylene articulation, and patients could not determine any difference between the hips. Compared with historic results of previous metal on metal prostheses, the modern metal on metal articulation investigated in this study did not have early acetabular loosening or clinical symptoms of component impaction. Retrieval implants and synovial fluid analysis suggest early wear was minimal.

Adult↗
PubMed2000

Highly Polar Metal-Metal Bonds in "Early-Late" Heterodimetallic Complexes.

Metal-metal bond polarity in its extreme form involving transition elements is found in di- or polynuclear complexes in which molecular fragments containing metal atoms from the two ends of the d block in the periodic table are combined. This linkage by direct metal-metal bonds of metal centers having very different oxidation states has been a challenge to the synthetic chemist. The suppression of degradative reaction channels caused by intramolecular single-electron transfer and the protection of the highly Lewis acidic early transition metal center by an appropriately designed ligand shell have opened up the systematic investigation of such systems. Concomitant with this development, advances in the conceptual framework for the quantitative description of bond polarity have led to a refined understanding of the nature of this type of metal-metal bonding. The greatest stimulus for the development of this field of research is the investigation of the cooperative reactivity of two or more coordination centers in their interaction with and transformation of organic substrates. This cooperativity, which is characterized by the different functions adopted by the metal centers in these conversions offers attractive perspectives in stoichiometric or even catalytic transformations.

Journal Article↗
PubMed1992

Hard metal interstitial pulmonary disease associated with a form of welding in a metal parts coating plant.

We describe two cases of hard metal pulmonary disease (one fatal) in workers employed in the same area of a metal coating plant using the detonation gun process for applying a durable metal surface to metal parts. In this form of welding, a mixture of powdered metals, including tungsten carbide and cobalt, is heated by ignition of a flammable gas and propelled from the end of the "gun" at high temperature and velocity to form a welded metal coating. This process is done in an enclosed chamber and with each application, large volumes of fine aerosols are created. Inhalation exposure to hard metal may occur during the mounting and removal of the metal parts between applications, in spite of engineering controls and industrial hygiene surveillance. One of the cases presented with minimal chest x-ray abnormalities and an obstructive pattern on pulmonary function testing, although subsequent open lung biopsy showed diffuse interstitial pulmonary fibrosis. The fact that two cases of hard metal pulmonary interstitial disease occurred where thorough exposure control procedures and a surveillance program for cobalt were in place may indicate the need for revisions of the current technology used when hard metal is applied in the detonation gun process.

Adult↗
PubMed2001

Hard metal-induced disease: effects of metal cations in vitro on guinea pig isolated airways.

Inhalation of dust from hard metal (HM), a mixture of tungsten carbide, cobalt, and other metals, can cause interstitial alveolitis, fibrosis, and asthma in the workplace. Some effects of HM could occur after the metals dissolve in the lung. We examined whether chloride salts of metals in HM alloys can elicit responses or modify reactivity to methacholine (MCh) or responses to electric field stimulation (EFS) in guinea pig tracheal strips. In unstimulated strips, Co(2+), Cd(2+), and Ni(2+) evoked contractions (>3 x 10(-6) M), while Ta(5+), Zn(2+), Cr(2+), and Cr(3+) caused weak relaxations (>10(-5) M). In strips contracted with MCh (3 x 10(-7) M), Co(2+) and Ni(2+) also caused relaxation in lower concentrations while the other metals caused weak relaxation only in high concentrations (>10(-4) M). The metals were generally without effect on reactivity to MCh, except that Cd(2+) inhibited and Ni(2+) potentiated some responses. The effects of selected metals (10(-6) M; Cr(3+), Ni(2+), Cd(2+), and Co(2+)) on EFS-induced contractile and relaxant responses were examined (+/-MCh; +/-10(-6) M indomethacin (Indo), 30 min). No metal had any effect on the excitatory nonadrenergic, noncholinergic-mediated contraction phase. Cd(2+) and Ni(2+) inhibited cholinergically mediated contractions of unstimulated strips (+Indo), whereas Cr(3+) both inhibited (-MCh, -Indo) and potentiated (-Indo,+MCh; +Indo, +MCh) contractile responses. Cr(3+) was the only metal to inhibit the inhibitory nonadrenergic, noncholinergic-mediated relaxation phase (+/-MCh; -Indo). Co(2+) had no effect at all. The results suggest that smooth muscle tone and nerves in the airways could be targets of cationic metals after they dissolve in the lung.

Alloys↗
PubMed2000

Strategies of heavy metal uptake by three plant species growing near a metal smelter.

Some higher plant species have developed heavy metal tolerance strategies which enable them to survive and reproduce in highly metal-contaminated soils. We have investigated such heavy metal uptake and accumulation strategies of two absolute metallophyte species (Armeria maritima ssp. halleri and Cardaminopsis halleri) and one pseudometallophyte (Agrostis tenuis) growing near a former metal smelter. Samples of plant parts and soil were analysed for Zn, Cd, Pb, and Cu. In soil, there were two dominant types of metal concentration gradients with depth. Under the absolute metallophytes, extremely high metal contents were measured in the surficial Ah horizon, followed by a strong decrease in the underlying soil horizons (L(11) and L(12)). Under the pseudometallophyte, metal concentrations in the Ah horizon were much lower and fewer differences were observed in metal concentrations among the Ah, L(11), and L(12) horizons. The concentrations of Zn, Cd, Pb, and Cu in Agrostis tenuis roots were greater than concentrations in leaves, indicating significant metal immobilisation by the roots. For C. halleri, Zn and Cd concentrations in leaves were >20,000 and >100 mg kg(-1), respectively, indicating hyperaccumulation of these elements. Armeria maritima ssp. halleri exhibited root concentrations of Pb and Cu that were 20 and 88 times greater, respectively, than those in green leaves, suggesting an exclusion strategy by metal immobilisation in roots. However, Zn, Cd, Pb, and Cu concentrations in brown leaves of Armeria maritima ssp. halleri were 3-8 times greater than in green leaves, suggesting a second strategy, i.e. detoxification mechanism by leaf fall.

Journal Article↗
PubMed2003

Is it homogeneous or heterogeneous catalysis? Identification of bulk ruthenium metal as the true catalyst in benzene hydrogenations starting with the monometallic precursor, Ru(II)(eta 6-C6Me6)(OAc)2, plus kinetic characterization of the heterogeneous nucleation, then autocatalytic surface-growth mechanism of metal film formation.

A reinvestigation of the true catalyst in a benzene hydrogenation system beginning with Ru(II)(eta(6)-C(6)Me(6))(OAc)(2) as the precatalyst is reported. The key observations leading to the conclusion that the true catalyst is bulk ruthenium metal particles, and not a homogeneous metal complex or a soluble nanocluster, are as follows: (i) the catalytic benzene hydrogenation reaction follows the nucleation (A --> B) and then autocatalytic surface-growth (A + B --> 2B) sigmoidal kinetics and mechanism recently elucidated for metal(0) formation from homogeneous precatalysts; (ii) bulk ruthenium metal forms during the hydrogenation; (iii) the bulk ruthenium metal is shown to have sufficient activity to account for all the observed activity; (iv) the filtrate from the product solution is inactive until further bulk metal is formed; (v) the addition of Hg(0), a known heterogeneous catalyst poison, completely inhibits further catalysis; and (vi) transmission electron microscopy fails to detect nanoclusters under conditions where they are otherwise routinely detected. Overall, the studies presented herein call into question any claim of homogeneous benzene hydrogenation with a Ru(arene) precatalyst. An additional, important finding is that the A --> B, then A + B --> 2B kinetic scheme previously elucidated for soluble nanocluster homogeneous nucleation and autocatalytic surface growth (Widegren, J. A.; Aiken, J. D., III; Ozkar, S.; Finke, R. G. Chem. Mater. 2001, 13, 312-324, and ref 8 therein) also quantitatively accounts for the formation of bulk metal via heterogeneous nucleation then autocatalytic surface growth. This is significant for three reasons: (i) quantitative kinetic studies of metal film formation from soluble precursors or chemical vapor deposition are rare; (ii) a clear demonstration of such A --> B, then A + B --> 2B kinetics, in which both the induction period and the autocatalysis are continuously monitored and then quantitatively accounted for, has not been previously demonstrated for metal thin-film formation; yet (iii) all the mechanistic insights from the soluble nanocluster system (op. cit.) should be applicable to metal thin-film formations which exhibit sigmoidal kinetics and, hence, the A --> B, then A + B --> 2B mechanism.

Journal Article↗
PubMed2005

Nonacarbonyldivanadium: alternatives to metal-metal quadruple bonding.

The first structural characterization of the highly unsaturated nonacarbonyldivanadium V(2)(CO)(9) is reported using density functional theory (DFT) with the B3LYP and BP86 functionals. A complicated collection of minima with rather closely spaced energies was found. However, none of these many V(2)(CO)(9) isomers was found to have a sufficiently short vanadium-vanadium distance for the VV quadruple bond required to give both metal atoms the favored 18-electron configuration. Triplet structures for V(2)(CO)(9) were found to be competitive in energy with related singlet structures. Thus, the two lowest-energy isomers of V(2)(CO)(9) are triplets. The four lowest-energy isomers of V(2)(CO)(9) all have three very unsymmetrical bridging CO groups (typically "short" and "long" M-CO distances differing by 0.4-0.5 A) rather than the symmetrical bridging CO groups found experimentally in Fe(2)(CO)(9) and predicted for M(2)(CO)(9) (M = Cr and Mn) from earlier studies. The VV distances in each of these four isomers suggest a metal-metal triple bond. Next higher in energy for V(2)(CO)(9) are three structures with single four-electron donor bridging CO groups identified by their computed nu(CO) frequencies and V-O distances. The V-V distances in these three isomers suggest metal-metal single bonds. This study of V(2)(CO)(9) supports the following general points: (1) Metal-metal bonds of an order higher than three are not favorable in metal carbonyl chemistry. (2) The 18-electron rule for metal carbonyls begins to break down when the metal atom, i.e., vanadium in this case, has only five valence electrons.

Journal Article↗
PubMed2005

Tunable metallization by assembly of metal nanoparticles in polymer thin films by photo- or electron beam lithography.

The technique of patterning of surfaces with metal-rich structures on micro- or nanoscales was developed by assembling metal nanoparticles into a thin film of polymer in a controllable way. Palladium (Pd) nanoparticles were incorporated into a thin film of poly(methyl methacrylate) (PMMA) using palladium (II) bis(acetylacetonato), Pd(acac)(2), as a precursor vaporized in a nitrogen atmosphere. Depending upon its dose, the irradiation of a PMMA film by UV light or an electron beam (EB) enhances its reducing capability against Pd(acac)(2). This dependency on dose can be used to control the formation and assembly of Pd nanoparticles. Using this technique, binary patterns consisting of metal-rich and metal-poor regions in the polymer film can be created simply by irradiating the surface of the polymer through a binary photomask. Besides the creation of binary patterns, it is also possible to create grayscale patterns where the density of Pd nanoparticles can be tuned to provide shades of gray by the use of light with continuously modulated intensity. Because the electron beam also enhances the reducing power of PMMA against Pd(acac)(2), it is thus possible to obtain highly metallized films with nanoscale pattern features. The PMMA film can be selectively removed by oxygen plasma treatment or by pyrolysis. Thus, highly metallized surfaces with binary or grayscale patterns can be obtained by selective removal of the PMMA films. The metallized regions possess relatively high resistivity against CF(4) plasma compared to the bare silicon surface; therefore, the metallized surface patterns can be transferred onto the underlying silicon substrate by CF(4) plasma treatment. Because of the nanosize effect of metal nanoparticles, the thermal treatment at 900 degrees C, which is significantly lower than the melting temperature of the bulk Pd, yields continuous metallic features by binding the assembled nanoparticles.

Journal Article↗