The interfaces of poly(p-phenylene vinylene) and fullerene derivatives with Al, LiF, and Al/LiF studied by secondary ion mass spectroscopy and x-ray photoelectron spectroscopy: Formation of AlF3 disproved

Two mutually exclusive mechanisms have been proposed to explain the improved electron injection by the insertion of a LiF layer between the metal cathode and the active organic layer of organic photoelectronic devices: the dipole and the doping mechanism. The possibility of the doping mechanism was studied by investigating the interface of poly[2-methoxy-5-(3',7'dimethyl-octyloxyl)-1,4-phenylenevinylene] (MDMO-PPV) or 1-(3-(methoxycarbonyl)propyl)-1-phenyl[6,6]C-61 (PCBM) with Al, LiF, or Al/LiF. In this mechanism, Li dopes the organic layer, after liberation via the reaction Al+3LiF-->AlF3+3Li. If this reaction takes place, AlF3 should be detectable at the surface. However, SIMS measurements showed that AlF3 is not present at the Al/LiF/MDMO-PPV and Al/LiF/PCBM interfaces. This is evidence that the proposed reaction does not occur. Other evidence that the doping mechanism cannot be the general mechanism to explain the enhanced electron injection comes from the presence of LiF on both organic surfaces. XPS measurements indicate that there is a reaction of Al with the carboxylic oxygen of PCBM, and that a LiF layer between PCBM and Al prevents this reaction. (C) 2002 American Institute of Physic

Novel method for preparing cellulose model surfaces by spin coating

A new, simplified method for preparing model surfaces of cellulose is introduced. Non-polar cellulose derivative trimethylsilyl cellulose (TMSC) was deposited onto untreated silicon substrate by spin coating, after which the coated TMSC was regenerated back to cellulose by vapour phase acid hydrolysis. By optimising the parameters of spin coating, a smooth cellulose film of ca 20 nm was obtained with roughness variation of max. 3 nm. With the well-defined morphology and chemical structure, combined with easy preparation, these model surfaces provide excellent means to explore the molecular level phenomena, taking place during various processes involving cellulose. Films were characterized using atomic force microscopy to illustrate the morphology and X-ray photoelectron spectroscopy to determine the chemical structure of the layers

Trimethylsilylcellulose/Polystyrene Blends as a Means To Construct Cellulose Domains on Cellulose

A method to prepare films of conspicuous domains of cellulose on a closed cellulose layer is introduced. These films can be used as model surfaces which are closer to the natural environment than most organic model surfaces that are usually coated directly on an inorganic substrate. The method is based on spin-coating a hydrophobic derivative of cellulose, trimethylsilylcellulose (TMSC), blended with polystyrene (PS) onto a silicon substrate. TMSC can be hydrolyzed to cellulose with acid hydrolysis, leaving domains of cellulose and PS embedded on a sublayer of cellulose. Selective dissolving of PS leaves a closed cellulose surface (sublayer) with eminent cellulose domains whose size depends on the original TMSC/PS ratio. The chemistry of the films was analyzed with X-ray photoelectron spectroscopy (XPS) and the morphology with atomic force microscopy (AFM). Scrutiny of the AFM data showed that the films are quantifiable and quantitatively reproducible

Polyethylene formation on a planar surface science model of a chromium oxide polymerization catalyst

A planar CrOx/SiO2/Si(100) model for the Phillips ethylene polymerization catalyst has been prepared by spin-coat impregnation from an aqueous solution of CrO3. In order to test the model catalyst with its extremely low chromium content, a special reactor was designed with a CrOx/Al2O3filter to effectively remove impurities. The model catalyst polymerizes ethylene in the gas phase at 160°C with a constant activity and forms a 350-nm-thick layer of polyethylene in 1 h. Atomic force microscopy reveals the expected spherulite morphology of the polyethylene films in different stages of development. The work opens attractive opportunities for future studies of nascent morphology of catalytically formed polymers

Introducing open films of nanosized cellulose-atomic force microscopy and quantification of morphology

A method for prepg. open, sub-monolayer cellulose films on a silicon substrate is introduced, and the open films were quantified using the three-dimensional information from at. force microscopy (AFM) height images. The prepn. method is based on spin coating low concns. of trimethylsilyl cellulose (TMSC) on silicon and hydrolyzing the TMSC to cellulose using a vapor phase acid hydrolysis. AFM showed that the surfaces consist of nanosized cellulose patches which are roughly 50-100 nm long, 20 nm wide, and 1 nm high. The vol. of the cellulose patches was quantified. Examn. of the cross section of the cellulose patches revealed that the exaggeration of the lateral dimensions by the AFM tip is small enough to account for a mere +-2% error in the vol. quantification. Pilot expts. showed that the vol. of the cellulose was largely restored in a wetting/drying cycle but the morphol. changed considerably. Because of their small size, the cellulose patches provide a novel approach for interpretation on the mol. architecture of cellulose. [on SciFinder (R)

Polymerization and crystallization of polyethylene on a flat model catalyst

A planar CrOx/SiO2/Si (100) model for the Phillips ethylene polymerization catalyst, prepared by spin-coating impregnation from an aqueous solution of CrO3, polymerizes ethylene in the gas phase at 160 °C with a significant and constant activity. After polymerization for 5 min and cooling to room temperature, an approximately 40 nm thick high-density polyethylene layer was formed that exhibits a morphology of regions with almost parallel aligned edge-on lamellar crystals. These lamellae show a distinct blocklike submorphology, which is discussed in detail. The work demonstrates that controlled polymerization and crystallization using a surface science model catalyst on a flat surface offers an excellent approach for fundamental studies of polymer physics, e.g., the study of the origin of crystal formation

Introducing a flat model of the silica-supported bis(imino)pyridyl iron(II) polyolefin catalyst

Summary: A well-defined flat model of a supported homogeneous polyolefin catalyst is prepared on the basis of an immobilized bis(imino)pyridyl iron complex on a super flat silica surface. The amount of supported catalyst precursor is quantified using XPS. This model catalyst remains active over extended periods, i.e., an average activity of 0.25 × 103 kg PE · (molCat · h · bar)-1 is obtained for 24 h of ethylene polymerization. The morphology of the nascent polyethylene film is investigated by SEM