Andrew M. Mance

Magnetocaloric properties of doped lanthanum manganite films

LaMnO3 films doped with Ca, Ba, or Sr have been fabricated using the metalorganic decomposition technique. These films exhibit paramagnetic‐to‐ferromagnetic phase transitions at 250, 300, and 350 K, respectively. By measuring the film magnetization as a function of field and temperature we have determined the entropy change associated with these transitions. The large magnetization of these materials results in a total entropy change a factor of five less than that of gadolinium, the prototypical high‐temperature magnetocaloric material. Improvements in film morphology and composition may provide a further increase in the magnetization and total entropy change in these materials.

Selective laser pyrolysis of metallo-organics as a method of forming patterned thin film superconductors

Fine line superconductors of yttrium-barium-copper were formed on strontium titanate substrates by the completely non-vacuum techniques of metallo-organic deposition in selective laser pyrolysis. Lines 125 micrometers wide were written in a film of metal neodecanoates, using an argon laser, prior to complete pyrolysis. An organic dye which absorbs selective laser light wavelengths, is added to the metallo-organic solution comprising the metal neodecanoates prior to laser exposure, so as to enhance absorption of the laser light at the regions of the metallo-organic film which are subsequently exposed to the laser light. The increased light absorbance at the exposed regions, results in at least partial pyrolysis of the exposed metal neodecanoates. Regions of the metallo-organic film not exposed to laser pyrolysis is developed away using a xylene wash. Subsequent complete pyrolysis of the metal neodecanoates and rapid thermal annealing produced lines having superconducting onsets above 90 K and zero resistance at 40 K.

High‐resolution electroless deposits on alumina from ultraviolet exposure of a Pt metalorganic

Photochemical and electroless metallization techniques have been combined to create metal patterns on alumina (Al2O3). In this positive imaging process, small amounts of an ultraviolet (uv) sensitive metalorganic (MO) Pt compound are first applied to the surface of the alumina by spin coating. A quartz photomask is then used to selectively expose the Pt MO to uv light in the areas that are to be metallized. After a xylene rinse removes the Pt MO from the unexposed areas, the substrate and xylene insoluble Pt MO are fired in air at 450 °C for 5 min, followed by electroless deposition of Ni on the uv exposed surface. Total Pt consumption is to about 0.01–0.02 g/m2 of metallized surface−no Pt or Ni was detected in nonmetallized regions. The uv exposure time is brief, ≤0.75 s, and 0.3‐μm‐thick Ni/B deposits can be patterned on 96% pure alumina with resolution of nearly 28 μm line/spaces.

Metallo-organic deposition of tungsten oxide films from alkylammonium tungstate solutions

This paper describes a simple and inexpensive metallo-organic deposition (MOD) process for forming electrochromic tungsten oxide (WO3) films on glass. The thin films of WO3 were made by air firing (500–700°C) films from xylene/2-propanol solutions of bis-(di-n-octylammonium) tetratungstate, [(n-C8H17)2NH2]2[W4O13]. The process coats glass with undoped films ranging in colour from faint yellow to dark brown, and can be used to make gradients of these colours. The colour is determined by the firing parameters and results from residual carbon and tungsten suboxides in the film due to incomplete firing. Increased firing temperatures or longer firing times removes the carbon and produces films with higher crystallinity. Electrochemical doping with acid (H+) switches the colour gradient films to a uniformly blue colour.

Laser Speckle Detection of Surface Morphology in Molded Plastic Parts

Surface stresses, induced during injection molding operations, can cause either interfacial or cohesive failure of metallized plastic parts. These stresses, often characterized by oriented polybutadiene particles in poly(acrylonitrile-butadienestyrene) (ABS) parts, are conventionally detected using a complex procedure. We demonstrate that laser light, reflected from etched plastic surfaces, produces nonspecular light patterns (speckle) which are characteristically different for relatively stressed and unstressed surfaces. Compared to other analytical methods, laser speckle examination is simple, quick, and inexpensive.