Tailoring precursors for deposition: synthesis, structure, and thermal studies of cyclopentadienylcopper(i) isocyanide complexes.

We report here the synthesis and characterization of a family of copper(I) metal precursors based around cyclopentadienyl and isocyanide ligands. The molecular structures of several cyclopentadienylcopper(I) isocyanide complexes have been unambiguously determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl isocyanide complex [(η(5)-C5H5)Cu(CN(i)Pr)] (2a) and the tert-butyl isocyanide complex [(η(5)-C5H5)Cu(CN(t)Bu)] (2b) as possible copper metal chemical vapor deposition (CVD) precursors. Further modification of the precursors with variation of the substituents on the cyclopentadienyl ligand system (varying between H, Me, Et, and (i)Pr) has allowed the affect that these changes would have on features such as stability, volatility, and decomposition to be investigated. As part of this study, the vapor pressures of the complexes 2b, [(η(5)-MeC5H4)Cu(CN(t)Bu)] (3b), [(η(5)-EtC5H4)Cu(CN(t)Bu)] (4b), and [(η(5)-(i)PrC5H4)Cu(CN(t)Bu)] (5b) over a 40-65 °C temperature range have been determined. Low-pressure chemical vapor deposition (LP-CVD) was employed using precursors 2a and 2b to synthesize thin films of metallic copper on silicon, gold, and platinum substrates under a H2 atmosphere. Analysis of the thin films deposited onto both silicon and gold substrates at substrate temperatures of 180 and 300 °C by scanning electron microscopy and atomic force microscopy reveals temperature-dependent growth features: Films grown at 300 °C are continuous and pinhole-free, whereas films grown at 180 °C consist of highly crystalline nanoparticles. In contrast, deposition onto platinum substrates at 180 °C shows a high degree of surface coverage with the formation of high-density, continuous, and pinhole-free thin films. Powder X-ray diffraction and X-ray photoelectron spectroscopy (XPS) both show the films to be high-purity metallic copper.

Extrinsic and Intrinsic Frequency Dispersion of High-k Materials in Capacitance-Voltage Measurements.

In capacitance-voltage (C-V) measurements, frequency dispersion in high-k dielectrics is often observed. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as the effects of the lossy interfacial layer (between the high-k thin film and silicon substrate) and the parasitic effects. The effect of the lossy interfacial layer on frequency dispersion was investigated and modeled based on a dual frequency technique. The significance of parasitic effects (including series resistance and the back metal contact of the metal-oxide-semiconductor (MOS) capacitor) on frequency dispersion was also studied. The effect of surface roughness on frequency dispersion is also discussed. After taking extrinsic frequency dispersion into account, the relaxation behavior can be modeled using the Curie-von Schweidler (CS) law, the Kohlrausch-Williams-Watts (KWW) relationship and the Havriliak-Negami (HN) relationship. Dielectric relaxation mechanisms are also discussed.

Metal organic chemical vapour deposition of vertically aligned ZnO nanowires using oxygen donor adducts.

Vertically aligned zinc oxide (ZnO) nanowires (NWs) have been grown by liquid injection Metal Organic Chemical Vapour Deposition, using oxygen donor adducts of Me2Zn. The growth and characterisation of the nanowires grown using [Me2Zn(L)] where L = monodentate ethers, tetrahydrofuran (C4H8O) (1), tetrahydropyran (C5H10O) (2), furan (C4H4O) (3) and the bidentate ethers, 1,2-dimethoxyethane (C4H12O2,) (4) 1,4-dioxane (C4H8O2) (5) and 1,4-thioxane (C4H8SO) (6) is discussed. Single crystal X-ray structures of (4), (5), (6) have been established and are included here. The ZnO NWs were deposited in the absence of a seed catalyst on Si(111) and F-doped SnO2/glass substrates over the temperature range 350-600 degrees C. X-ray diffraction (XRD) data shows that the nanowires grown from all adduct precursors were deposited in the wurtzitic phase.

Dielectric Relaxation of La-Doped Zirconia Caused by Annealing Ambient.

La-doped zirconia films, deposited by ALD at 300°C, were found to be amorphous with dielectric constants (k-values) up to 19. A tetragonal or cubic phase was induced by post-deposition annealing (PDA) at 900°C in both nitrogen and air. Higher k-values (~32) were measured following PDA in air, but not after PDA in nitrogen. However, a significant dielectric relaxation was observed in the air-annealed film, and this is attributed to the formation of nano-crystallites. The relaxation behavior was modeled using the Curie-von Schweidler (CS) and Havriliak-Negami (HN) relationships. The k-value of the as-deposited films clearly shows a mixed CS and HN dependence on frequency. The CS dependence vanished after annealing in air, while the HN dependence disappeared after annealing in nitrogen.

Liquid injection atomic layer deposition of silver nanoparticles.

Silver nanoparticles are being developed for applications in plasmonics, catalysts and analytical methods, amongst others. Herein, we demonstrate the growth of silver nanoparticles using an atomic layer deposition (ALD) process for the first time. The silver was deposited from pulses of the organometallic precursor (hfac)Ag(1,5-COD) ((hexafluoroacetylacetonato)silver(I)(1,5-cyclooctadiene)) dissolved in a 0.1 M toluene solution. Catalytic oxidative dehydrogenation of the silver was achieved using intermittent pulses of propanol. The effect of substrate temperature on the size and distribution of nanoparticles has been investigated over the temperature range 110-150 degrees C. Transmission electron microscopy reveals that the nanoparticles consist of face centred cubic, facetted silver crystallites. The localized surface plasmon modes of the nanoparticles have been investigated using electron energy loss spectroscopy mapping. The distributions of plasmons within the ALD nanoparticles are comparable to those grown by solution methods. Both dipolar and quadrupolar resonant modes are observed, which is consistent with previous discrete dipole approximation models. Energy loss mapping of a loss feature at 8.1 eV reveals that it correlates with the bulk or volume region of the silver nanoparticles investigated here.

The optical properties of vertically aligned ZnO nanowires deposited using a dimethylzinc adduct.

The optical properties of zinc oxide nanowires are critically influenced by the growth process. Herein, we describe a metal-organic chemical vapour deposition (MOCVD) process for the growth of ZnO nanowires with improved optical properties. A tetrahydrofuran adduct is used to control the reactivity of dimethylzinc to enable this. Vertically aligned zinc oxide nanowires have been grown on Si(111) substrates by liquid injection MOCVD, using a solution of [Me(2)Zn(tetrahydrofuran)] in the presence of oxygen. The ZnO morphology becomes nanowire-like in a narrow temperature range centred about 500 degrees C. Above and below this temperature range, the ZnO is deposited in the form of polycrystalline films. The ZnO nanowires grow from a polycrystalline nucleation layer, with the (0002) c-axis parallel to the Si[111] substrate orientation. High-resolution electron microscopy reveals a highly crystalline nanowire microstructure. Resonance enhanced ultraviolet Raman spectroscopy shows that the ratio of first- and second-order longitudinal optic modes is commensurate with electron-phonon coupling effects observed previously in ZnO nanostructures. Photoluminescence exhibits intense near band-edge emission with a full width at half-maximum of 110 meV at room temperature and shows negligible defect-related visible emission.

Elemental mapping using the Ga 3d and In 4d transitions in the epsilon2 absorption spectra derived from EELS.

It is proposed that by using the valence-band states in electron energy loss spectroscopy, high-spatial resolution maps of quantitative elemental composition may be acquired with high acquisition rates. Further, it is shown that by using the epsilon(2) spectrum instead of single scattering data, the noise in the observed transitions and associated maps is significantly reduced. The epsilon(2) spectra are derived through a Kramers-Kronig transformation from electron energy loss spectra obtained in a scanning transmission electron microscope. Using transitions that occur in the epsilon(2) absorption spectrum (<40eV), quantitative elemental maps for III-V device structures have been produced. An example is provided using the Ga 3d transition to map a GaInNAs/GaAs laser structure. Weaker transitions such as In 4d have also been used to verify the Ga elemental distribution.

Aluminium accumulation in relation to senile plaque and neurofibrillary tangle formation in the brains of patients with renal failure.

The effects of long-term exposure to aluminium on the development of Alzheimer-type neuropathological changes have been studied post-mortem in patients with chronic renal failure who did not have dialysis encephalopathy. Administration of aluminium-containing phosphate binding compounds appears to be a major factor in the accumulation of aluminium in the brain of dialysis patients. The mean serum aluminium concentrations determined during life and brain aluminium concentrations determined post-mortem correlated with both the duration and total amount of aluminium hydroxide administered to these patients. No correlation was found between the presence of bone aluminium and either the mean serum or brain aluminium concentration. Longitudinal monitoring of serum aluminium concentrations may provide a more reliable index than bone biopsy of brain aluminium concentrations in dialysis patients. Dynamic secondary ion mass spectrometry revealed focal accumulations of aluminium associated with cortical pyramidal neurones. The majority of patients also showed immunostaining in pyramidal neurones with an antibody to the N-terminal region of the beta/A4 amyloid precursor protein, while staining was absent in age-matched control cases. One-third of the patients exhibited beta/A4-positive amorphous senile plaques in the cerebral cortex. However, there was no clear correlation between either the presence and intensity of beta/A4 amyloid precursor immunostaining or the presence of senile plaques and the concentration of aluminium in the cerebral cortex. Cortical neurofibrillary tangles were not observed in any of the dialysis patients. These data suggest that it is unlikely that aluminium plays any major role in neurofibrillary tangle formation and that its putative role in senile plaque formation is likely to be only part of a complex cascade of changes.