Gerald F. Malgas

Comparative study: the effect of annealing conditions on the properties of P3HT:PCBM blends

This paper presents a detailed study on the role of various annealing treatments on organic poly(3-hexylthiophene) and [6]-phenyl-C61-butyric acid methyl ester blends under different experimental conditions. A combination of analytical tools is used to study the alteration of the phase separation, structure and photovoltaic properties of the P3HT:PCBM blend during the annealing process. Results showed that the thermal annealing yields PCBM “needle-like” crystals and that prolonged heat treatment leads to extensive phase separation, as demonstrated by the growth in the size and quantity of PCBM crystals. The substrate annealing method demonstrated an optimal morphology by eradicating and suppressing the formation of fullerene clusters across the film, resulting in longer P3HT fibrils with smaller diameter. Improved optical constants, PL quenching and a decrease in the P3HT optical bad-gap were demonstrated for the substrate annealed films due to the limited diffusion of the PCBM molecules. An effective strategy for determining an optimized morphology through substrate annealing treatment is therefore revealed for improved device efficiency.

Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD

We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap.

Investigation of the effects of different annealing ambients on Ag/Al bilayers: Electrical properties and morphology

Ag (200 nm)/Al (8 nm) bilayer structures on SiO2 substrates were annealed at temperatures ranging from 300 °C–700 °C and for 30 min in He–H, Ar, or NH3 ambient. Upon annealing, Al segregates to the surface where it reacts with residual oxygen to form an Al-oxide passivation layer. Rutherford backscattering spectrometry and Auger spectroscopy showed the formation of an AlxOy diffusion barrier at the Ag/SiO2 interface. Apart from the surface passivation that resulted from annealing, the Ag/Al/SiO2 in different ambients, the adhesion of Ag to SiO2 was also improved. A strong correlation between the resistivity and the residual Al in the Ag film was observed. Resistivity values equivalent to that of the as-deposited sample were obtained only for temperatures at 700 °C or above. Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy was used to study the effect of the different ambients on the observed surface morphology. The SEM studies showed that the passivated surfaces were not uni...

Effectiveness of reactive sputter-deposited Ta–N films as diffusion barriers for Ag metallization

Tantalum nitride films on silicon were prepared by reactive sputtering of Ta under nitrogen partial flow rates varying from 15% to 40% N2. Rutherford backscattering spectroscopy (RBS) and x-ray diffraction (XRD) analysis revealed that the composition and phases of the Ta–N films were influenced by the N2 flow rate. Increasing the nitrogen partial flow rate from 25% to 40% N2, results in the films changing from metal-rich to stoichiometric Ta–nitride. High N2 flow rates (30%–40% N2) resulted in a disordered tantalum–nitride. The tantalum nitride films were evaluated as potential diffusion barriers for Ag metallization. Sheet resistance measurements, XRD and RBS analysis confirmed that Ta–N films, used as diffusion barriers in the Ag∕Ta–N∕Si system, were thermally stable up to 650°C when annealed for 30min in vacuum. The thermal stability was independent of N2 flow rate within this temperature range. However, at 700°C, the barrier failed as a result of Ta–silicide formation by reaction with the underlying S...

The Influence of Geometrically Configured Sol-Gel Derived Hydroxyapatite Substrates on Osteoblast Response

Good quality crystalline sol-derived Hydroxyapatite (HA) thin films of thickness ~350 nm on titanium substrates with underlying micro-channels were prepared by microwave annealing at a temperature of 400 °C for 30 min. A comprehensive in-vitro study was conducted to assess the osteoblast adhesive response to the well-defined micro-scale topographical features on HA coated and uncoated surfaces. The study confirmed the osteoblast’s response to the HA coated micro-channels with an elongated morphology. The effects to morphology suggest that osteoblast adhesion can be improved through optimal micro-channel design and may provide baseline design cues for improving the longterm performance of prosthetic orthopedic and dental implants.

Structural evolution of a Ta-filament during hot-wire chemical vapour deposition of Silicon investigated by electron backscatter diffraction

We report on the application of electron backscatter diffraction to investigate the structural changes of a tantalum filament operated at typical hot-wire chemical vapour deposition conditions for the synthesis of hydrogenated nanocrystalline silicon. Various tantalum-silicides, identified by electron backscatter diffraction, form preferentially along the length of the filament. The filament has a recrystallized Ta inner core and a TaSi2 layer encapsulated with a Si layer at the cooler ends. The αTa5Si3, metastable Ta5Si3 and Ta2Si phases formed in addition to recrystallized Ta and TaSi2 at the centre regions. Cracks and porosity were prevalent throughout the length of the filament. The microstructural evolution of the aged tantalum filament can be ascribed to the thermal gradient along the filament length, recrystallization of Ta and the variation of silicon content within the filament.

Effect of additional electron acceptor in hybrid P3HT:PCBM:ZnO spin-coated films for photovoltaic application: Effect of additional electron acceptor in hybrid P3HT:PCBM:ZnO spin-coated films

Copyright: 2016 Wiley. Due to copyright restrictions, the attached PDF file only contains the abstract of the full text item. For access to the full text item, kindly consult the publishers website.

Ag metallization on silicides with nitride barriers

The thermal stability of Ag thin films on Ti–O–N/silicides (CoSi2 and NiSi) is investigated with various characterization techniques in this study. A Ti–O–N film was used as a diffusion barrier for Ag metallization. Silicide thin films are prepared by solid phase reactions utilizing metal/silicon bilayer structure. Rutherford backscattering spectrometry (RBS) of annealed films reveals Ag film changes to occur at 650°C. Optical microscopy shows voids in the Ag film on the Ti–O–N diffusion barrier for temperature above 600°C. Increasing anneal temperature up to 700°C produces high density of voids in Ag films. Atomic force microscopy (AFM) shows the morphology of the voids that occur in the Ag film on the Ti–O–N barrier. RBS indicates some amount of Ag loss from the annealed samples at high temperatures. Secondary ion mass spectroscopy (SIMS) depth profiling reveals Ag diffusions to Ti–O–N/silicides/Si structures. We discuss the thermal stability and failure mechanism of Ag films on Ti–O–N/silicides/Si anne...

Depth-dependent crystallinity of nano-crystalline silicon induced by step-wise variation of hydrogen dilution during hot-wire CVD

To induce an amorphous surface in a nano-crystalline silicon (nc-Si:H) thin film, the hydrogen dilution was reduced step-wise at fixed time intervals from 90 – 50% during the hotwire chemical vapour deposition process. This contribution reports on the structural properties of the resultant nc-Si:H thin film as a function of the deposition time. Raman spectroscopy, confirmed by high resolution transmission spectroscopy, indicates crystalline uniformity in the growth direction, accompanied by the progression of an amorphous surface layer as the deposition time is increased. The silicon- and oxygen bonding configurations were probed using infrared spectroscopy and electron energy loss spectroscopy. The growth mechanism is ascribed to the improved etching rate by atomic hydrogen in nano-crystalline silicon towards the film/substrate interface region. The optical properties were calculated by applying the effective medium approximation theory, where the existence of bulk and interfacial layers, as inferred from cross-sectional microscopy, were taken into account.

Investigation of isochronal annealing on the optical properties of HWCVD amorphous silicon nitride deposited at low temperatures and low gas flow rates

Hydrogenated amorphous silicon nitride (a-SiNx:H) is used as anti-reflection coatings in commercial solar cells. A final firing step in the production of micro-crystalline silicon solar cells allows hydrogen effusion from the a-SiNx:H into the solar cell, and contributes to bulk passivation of the grain boundaries. In this study a-SiNx:H deposited in a hot-wire chemical vapour deposition (HWCVD) chamber with reduced gas flow rates and filament temperature compared to traditional deposition regimes, were annealed isochronally. The UV-visible reflection spectra of the annealed material were subjected to the Bruggeman Effective Medium Approximation (BEMA) treatment, in which a theoretical amorphous semiconductor was combined with particle inclusions due to the structural complexities of the material. The extraction of the optical functions and ensuing Wemple-DeDomenici analysis of the wavelength-dependent refractive index allowed for the correlation of the macroscopic optical properties with the changes in the local atomic bonding configuration, involving silicon, nitrogen and hydrogen.