Depletion Of Cu Research Articles

Quantitative Measure of EM-Induced Drift in Sub-Micron Al Lines

AbstractElectromigration-induced drift in sub-micron wide Al segments has been measured using energy dispersive x-ray analysis in a scanning electron microscope. This technique, which works on both passivated and unpassivated samples, is sensitive to uniform Al displacements as small as 100 nm. The samples were 0.3 and 0.5 µm wide runners consisting of a continuous Ti/TiN line on top of which were patterned 0.4µm thick Al (0.5wt% Cu) segments of lengths varying between 5 and 100 µm. The microstructure, as determined by focused ion beam imaging, was predominantly bamboo. We have measured the Al depletion at the cathode ends of these segments after stressing for various times at 2 MA/cm2 at 200'C. For segments shorter than roughly 15 µm, no depletion occurred during the entire 100 hours of the experiment, yielding a value of the current-length threshold product of roughly 3000 A/cm, in agreement with previously published data. Longer segments (20-25 µm) depleted at a roughly constant rate for the duration of the experiment, yielding a drift velocity of around 3 nm/hr in the 0.5 µm wide lines, also in good agreement with published data for near-bamboo lines. However, the 0.3 µm wide lines drifted faster at roughly 6.5 nm/hr. The longest segments (50-100 µm), which started drifting at the same rate as the shorter segments, accelerated after 50 hours of testing to drift velocities in excess of 40 nm/hr. This may be associated with the depletion of Cu from the drifting end.

An assessment of sulphide oxidation in abandoned base-metal tailings, Te Aroha, New Zealand

Tailings from the Tui base-metal mine were characterized using a variety of techniques including scanning electron microscopy (SEM) and flame atomic absorption spectroscopy (FAAS), to assess their potential for use as a plant growth medium. With the notable exception of Pb (10 568 mg kg −1), ‘total’ metal concentrations in the surface tailings (0–200mm) were relatively low (Cu, 113; Fe, 3660; Zn, 486 mg kg −1). The theoretical acid generating potential (TAGP) and ‘total’ concentrations of Cu, Fe and Zn of the tailings, were found to increase greatly with depth, reflecting an increase in the abundance of chalcopyrite (CuFeS 2), pyrite (FeS 2) and sphalerite (ZnS), as detected by X-ray diffraction (XRD) analysis. SEM micrographs indicate that the distribution of sulphide minerals in the tailings was originally uniform with depth. The depletion of Cu, Fe and Zn in the surface tailings is considered to be a result of sulphide oxidation, as evidenced by the craggy and highly irregular morphology of the sulphide particles and the high hydrogen ion activity (pH 2.3–4.0) in this zone. The persistence of high concentrations of acid-generating sulphide minerals between 200 and 600 mm has important implications in determining strategies for revegetating the tailings.

Effect of endotoxin on cardiopulmonary function and biosynthesis of eicosanoids and TNFα in calves chronically depleted of copper

We evaluated the acute cardiopulmonary and biochemical (i.e. plasma concentrations of eicosanoids and serum levels of TNFα) response to an infusion of Escherichia coli endotoxin (8 μg/kg i.v.) in cattle that were adequate or deficient in liver and plasma copper (Cu) concentrations. Young calves were chronically fed diets containing normal Cu (control; n = 4) and low Cu (n = 14). After ~6 months of dietary treatment, the calves were anesthetized and evaluated from 0-4 h during endotoxemia. At 0 h, plasma Cu concentrations averaged 32.4% (P < 0.05) of the control value (i.e. 0.81 ± 0.08 μg/ml). Endotoxin caused a transient, early (at 20.4 min) increase in mean pulmonary arterial pressure to 114% and 147% of baseline in normal and Cu depleted calves, respectively (P < 0.05). In Cu depleted calves, endotoxin significantly decreased heart rate (0.5-1 h) and cardiac index (0.5 h) as compared to normal calves. Endotoxin caused systemic hypotension and increased TXB2 production (at 0.5 h) and these changes were potentiated in Cu depleted calves. However, after 1 h there were no statistically significant differences between the two groups of calves for any cardiopulmonary parameter evaluated nor in plasma concentrations of eicosanoids and serum levels of TNFα. We conclude that chronic dietary depletion of Cu potentiates TXB2biosynthesis and worsens the acute (≤1 h) cardiovascular response to endotoxin challenge in cattle.

Microstructural Control of Internal Electromigration Failure in Narrow Al-Cu-Si Lines

AbstractAl-Cu lines of submicron width ordinarily have quasi-bamboo microstructures that contain both bamboo grains and polygranular segments. The usual mechanism of internal electro-migration failure in such lines involves the formation of a transgranular void across a bamboo grain at the upstream end of a long, polygranular segment. The voiding is preceded by the depletion of Cu from both the polygranular segment and the upstream bamboo grain. At least three metallurgical mechanisms are available to inhibit this failure mechanism and improve the useful lifetime of the line. First, the line can be annealed after patterning to break up long polygranular segments. Second, the line can be aged at relatively low temperature to stabilize the distribution of Cu and retard its depletion from polygranular segments. Third, the line can be subjected to reverse currents to restore the distribution of Cu and provide a Cu reservoir. Each of these methods has been demonstrated in the laboratory environment.

Direct Observation of the Effects of Cu Distribution on Electromigration Phenomena in Submicron Al Interconnects

AbstractWe have performed time-resolved studies of the electromigration (EM) – induced formation, growth, migration, and spatial distribution of Al2Cu precipitates in submicron Al(0.5 wt. % Cu) runners. Of particular interest is the formation of the precipitates in relationship to the local microstructure of the runners, and the formation of voids and hillocks with respect to the location of the Al2Cu precipitates. Runners of widths 0.3, 0.5, 0.8, and 1.0 ýtm were tested at a current density of 2×106 A/cm2 and temperatures between 200 and 300°C. The evolution of the microstructure of the runners was evaluated using plan-view TEM, SEM, and EDX. The formation of voids and hillocks, and the growth of precipitates proceeds more rapidly as the width of the runners increases. However, a far greater number of precipitates nucleate in the 0.3 μm-wide line than in any of the others. As expected, voids are most likely to form near the cathode and hillocks near the anode. Large Al2Cu precipitates form near the anode long before failure occurs. Interestingly, the cathode-side bonding pad is not observed to serve as a good reservoir of Cu for the runners. Although the formation of voids near the cathode seems to be associated with the depletion of Cu in this region, hillocks and voids elsewhere are more likely to form at precipitates than in other parts of the line. Thus Al2Cu precipitates can act as sites for preferential EM-damage, reducing interconnect reliability.

Alteration associated with the gold-bearing quartz veins at Middagsberget, northern Sweden

The mesothermal Au deposit at Middagsberget in northern Sweden is associated with irregular stock-works of quartz veins occurring in shear zones across a dioritic intrusion. Alteration in the shear zones is characterized by sericitization, chloritization, the presence of sulphides and several generations of veins and small-scale fractures. Small fractures which are filled with variable amounts of quartz, carbonate, sericite, chlorite, albite and sulphides, are particularly abundant in zones having a high Au content. In general, these fractures are younger than the major quartz veins and were apparently important for strong Au-enrichment. Au is associated with arsenopyrite and it occurs as droplets or interfillings in the arsenopyrite or at the crystal surface; together with pyrrhotite as inclusions in arsenopyrite; as free grains in silicates but close to arsenopyrite; or in very small fractures in carbonates. The Au-mineralization is associated with elevated contents of As, S, Sb and W and depletion of Cu, Zn, Ge and Bi. The entire altered areas are enriched in Au compared with the < 1 to 15 ppb found in the host intrusion. During alteration an initial increase in Na or K was accompanied by a weak enrichment of Au and associated elements together with a depletion of elements such as Ca and Mg. In Au-rich samples this alkali enrichment was overprinted by the carbonate-and sulphide-bearing fractures, which often led to an increased Ca-content. An clear zonation of alteration types has not been found. The host rock has been altered by several generations of fluids: the shear zones were repeatedly ruptured and new small-scale fractures were opened. The different fluids did not, therefore, flow through identical paths although they penetrated the same major zones. This resulted in a complex pattern of variously superimposed alterations.

White Island, New Zealand, volcanic-hydrothermal system represents the geochemical environment of high-sulfidation Cu and Au ore deposition

The White Island volcanic-hydrothermal system, New Zealand, is thought to closely represent the chemical conditions that lead to the formation of high- sulfidation Cu-Au ore deposits. The amounts of Cu and Au produced over a 10 ka period of activity, largely from degassing magma, are calculated to be 106 and 45 t, respectively. Altered andesite blocks ejected from recent vents contain alunite, anhydrite, and pyrite. Their S isotopic composition indicates vein filling at ∼380 °C. At this temperature, Cu and Au are highly soluble in acid solutions, which may explain the depletion of Cu and absence of Au in the ejecta. Mass-balance calculations, however, suggest that Cu and Au are precipitated in cooler zones before the acid solutions discharge at the surface.

Microchemical analysis of precipitate free zones in 7075-A1 in the T6, T7 and RRA tempers

The microchemistry within precipitate free zones (PFZ) in the commercial allloy 7075-Al subjected to various tempers was investigated using analytical electron microscopy. Segregation or depletion of Zn and Cu atoms near grain boundaries in as-quenched samples, which has been reported by other investigators, was not found in this study. Considerable depletion of Zn was observed in the samples in all three tempers investigated (T651, T73 and RPA). The magnitude of the depletion of Zn was relatively insensitive to the temper condition, being slightly larger in the RRA temper than in the other two. The depletion of Cu was far more sensitive to the aging condition, being larger in both the T73 and RRA tempers than in the T651 temper. The increased resistance to stress-corrosion cracking of 7075-Al in the T73 or RRA tempers is attributed primarily to the reduction of the Cu concentration within the PFZs.

Development of copper deficiency in neonatal mice

Dietary copper (Cu) deficiency was produced in Swiss albino mice to determine the temporal relationship between depletion of Cu and changes in the cardiovascular and nervous system. Dams were placed on a Cu-deficient diet 4 days after parturition. Half the dams were provided with deionized water and their offspring are referred to as Cu-deficient (−Cu). Half the dams were given cupric sulfate in their drinking water (20 μg Cu/mL) and their offspring are referred to as Cu-adequate (+Cu). At 6 weeks of age a sample of the −Cu mice were repleted with CuSO 4. Mice were sampled 1 day after birth and at weekly intervals for 7 weeks. Both +Cu and −Cu mice grew at the same rate: birth weight increased 16-fold at 6 weeks of age. Liver Cu more than doubled between 1 and 7 days of age. At 2 weeks of age −Cu mice were anemic (lower hematocrit and hemoglobin) and had lower liver Cu and plasma ceruloplasmin activity compared to +Cu mice. Liver Fe was not elevated in −Cu mice until 2 weeks after anemia developed. At weaning first signs of altered catecholamine metabolism included elevation of dopamine in both heart and spleen. Norepinephrine concentrations and content, in contrast, were not both lowered in −Cu mice until 5 weeks of age. Heart weight was first elevated in −Cu mice at 6 weeks of age and relative weight (mg/g body wt) at 4 weeks of age. Liver Cu concentration was lower in 1-week repleted mice than in +Cu mice. Anemia preceded the development of cardiac hypertrophy and altered catecholamine levels in −Cu mice.

Surface compositional and topographical changes resulting from excimer laser impacting on YBa2Cu3O7 single phase superconductors

Superconducting pressed pellets of YBa2Cu3O7 (Tc=90 K), which were used as ablation targets for laser-induced vapor deposition of high Tc(85 K) superconducting thin films, have been analyzed by secondary electron microscopy, scanning Auger microscopy, energy dispersive x-ray analysis, and x-ray diffractometry. The elemental distribution of Y, Ba, and Cu appears reasonably uniform at depths corresponding to that probed by energy dispersive x-ray analysis (∼1 μm). However, scanning Auger microscopy analysis of the laser-impacted area shows a significant depletion of Cu and spatial redistribution of Y, Ba, Cu, and O on the target surface. X-ray diffractometry of the laser-impacted area shows the appearance of a new broad peak at a diffraction angle 2θ=29.7°, characteristic of BaY2O4 and a poorly defined peak at 2θ=29.3°, that can be attributed to BaCuO2. A possible influence of the laser-induced bulk superconductor compositional changes on the film composition is discussed in relation to recently reported experimental results on laser vapor deposition of high Tc films.

Surface order and stoichiometry of sputter-cleaned and annealed CuInSe2

CuInSe2 surfaces can be cleaned by bombardment with Ar ions at glancing incidence and with energies up to 1.5 keV without change in composition. At near-normal incidence a slight depletion of Cu is observed. The surface crystallinity can be partially restored by annealing to ∼550 °C, without preferential evaporation of an element. On Ar+-cleaned and annealed surfaces, single-crystal low-energy electron diffraction patterns of CuInSe2 have been produced for the first time.

Polycrystalline CuInSe2 photoelectrochemical cells

Photoelectrochemical cells with short term stability (at least) have been constructed from fracture surfaces of n-type polycrystalline boules of CuInSe2. The recently developed electrolyte of Menezes [Appl. Phys. Lett. 45, 148 (1984)] appeared to have a passivating effect on grain boundaries. Samples with hundreds of boundaries easily attained half the best (12%) single crystal efficiency without any optimization. Microprobe analyses of the treated surfaces showed strong depletion of Cu and incorporation of I but the latter distribution appeared to be nonuniform. Poor fill factors were found on randomly fractured surfaces larger than 1 cm2. Only n-type samples were successful.

Surface segregation of a NiCu alloy as studied by a computerized atom-probe FIM

Using the computerized energy compensated time-of-flight atoms-probe (AP-FIM), we have obtained an absolute composition depth profile of a NiCu alloy with single atomic layer spatial resolution. For bulk composition of 3.1%±0.5% Cu at 650°±20°C, the topmost layers of the (111) and (001) planes are enriched to (17%±2.7%) and (36.6%±7.5%) Cu, respectively. Slight depletion of Cu is observed in the near surface layers. Both an irregular solution model and a regular solution model with surface enthalpy relaxation are found to agree semiquantitatively with our results. A comparison with the results from other surface techniques is also made.