J. Alleman

Combinatorial studies of Zn-Al-O and Zn-Sn-O transparent conducting oxide thin films

Abstract In this work, we discuss the development of combinatorial deposition and analysis tools for the investigation of and the optimization of transparent conducting oxides. Library deposition by co-sputtering followed by optical analysis is shown to be a facile way to achieve these goals. Initial work focused on Zn-Al-O libraries with low Al contents as a test case. Subsequent work has focused on the ZnO-SnO2 tie line. Local maxima in the composition dependence of the conductivity were found for Zn/Sn ≈2:1 (Zn2SnO4) and Zn/Sn ≈1:1 (ZnSnO3). For these two representative stoichiometries, constant composition films have also been grown by pulsed laser deposition.

Quantum rotation of hydrogen in single-wall carbon nanotubes

We report inelastic neutron scattering results on hydrogen adsorbed onto samples containing single-wall carbon nanotubes. These materials have attracted considerable interest recently due to reports of high density hydrogen storage at room temperature. Inelastic neutron scattering clearly shows the ortho‐para conversion of physisorbed hydrogen in a nanotube containing soot loaded with hydrogen. From the rotational Ja 0! 1 transition, no indication of a significant barrier to quantum rotation is seen. ” 2000 Elsevier Science B.V. All rights reserved.

Controlling single-wall nanotube diameters with variation in laser pulse power

Abstract We demonstrate that laser peak pulse power can be employed to tune carbon single wall nanotube (SWNT) diameters. The production of SWNTs was investigated at room temperature and at 1200°C. The diameters were shifted to smaller sizes in both cases as the pulse power was increased. SWNT size distributions and yields were studied with Raman spectroscopy and transmission electron microscopy. The evolution of the material quality with laser energy parameters offers insight in to SWNT formation mechanisms. These studies should aid in the development of methods for the rational control of SWNT growth.

Microstructural properties of Cu(In, Ga)Se2 thin films used in high-efficiency devices

Abstract Thin-film polycrystalline photovoltaic devices based on Cu(In,Ga)Se2 have a demonstrated efficiency approaching 19%. The best performance was achieved when the Ga/In+Ga ratio was in the 25–30% range. The short-circuit current density exhibited for the device containing CdS was almost at its expected maximum. The open-circuit voltage was relatively low considering the optical bandgap (Eg) of the above absorber (∼1.15 eV); at best, it is 0.6×Eg. In this work, we examined the microstructural properties, e.g. defects due to misorientation, micro-twinning, stacking faults, and dislocations, for films prepared by our ‘ three-stage’ process, including the CIGS and Mo back-contact. We also attempted to make a correlation between the above observations and device performance.

Direct write processing for photovoltaic cells

Direct writing of solar cell components is an attractive processing approach. We have fabricated a 6.8% Si solar cell using silver ink based electrodes. Ohmic contact through the antireflection (AR) coating was obtained with pure Ag electrodes at 850/spl deg/C. We also report on highly conductive silver metallizations and initial results on direct-write TCO demonstrating a 100-micron spatial resolution produced by inkjet printing.

Hot wire chemical vapor deposition of isolated carbon single-walled nanotubes

Hot wire chemical vapor deposition (HWCVD) has been employed for the continuous generation of carbon single-walled nanotube (SWNT) materials. Interestingly, transmission electron microscopy analyses revealed only the presence of isolated SWNTs, rather than nanotubes existing in bundles. An analysis of the growth mechanism explaining the production of isolated SWNTs is provided. Also, the Raman radial breathing modes (RBMs) of the isolated HWCVD-generated nanotubes are compared to the RBMs of small bundles of nanotubes deposited by a conventional CVD technique having a similar diameter distribution.

Spray and Inkjet Printing of Hybrid Nanoparticle-Metal-Organic Inks for Ag and Cu Metallizations

Metal-organic and hybrid metal-organic/metal nanoparticle inkswere evaluated for use in the inkjet printing of copper and silver conducting lines. Pure, smooth, dense, highly conductive coatings were produced by spray printing with (hexafluoroacetylacetonato)copper(I)-vinyltrimethylsilane Cu(hfa)·VTMS) and (hexafluoroacetylacetonato)silver(I)(1,5-cyclooctadiene) (Ag(hfa)COD) metal-organic precursors on heated substrates. Good adhesion to the substrates tested, glass, Kapton tape and Si, has been achieved without use of adhesion promoters. The silver metal-organic ink has also beenused to print metal lines and patterns with a commercial inkjet printer. Hybrid inks comprised of metal nanoparticles mixed with the metal-organic complexes above have also been used to deposit Cu and Ag films by spray printing.This approach gives dense, adherent films that are much thicker than those obtained using the metal-organic inks alone. The conductivities of the silvercoatings obtained by both approaches are near that of bulk silver (2 μΩ·cm). The copper coatings had conductivities at least an order ofmagnitude less than bulk.

Direct write contacts for solar cells

Ag, Cu and Ni metallizations were inkjet printed with near vacuum deposition quality. The approach developed can be easily extended to other conductors such as Pt, Pd, Au etc. Thick highly conducting lines of Ag and Cu demonstrating good adhesion to glass, Si and PCB have been printed at 100-200 /spl deg/C in air and N/sub 2/ respectively. Ag grids were inkjet-printed on Si solar cells and fired through the silicon nitride AR layer at 850 /spl deg/C resulting in 8% cells. Next generation multicomponent inks (including etching agents) have also been developed with improved fire through contacts leading to higher cell efficiencies. PEDOT-PSS polymer based conductors were inkjet printed with conductivity as good or better than that of spin-coated films.

Hot-wire chemical vapor deposition of carbon nanotubes

Abstract Hot-wire chemical vapor deposition (HWCVD) has been employed for the continuous gas-phase generation of both carbon multi-wall and single-wall nanotube (MWNT and SWNT) materials. Graphitic MWNTs were produced at a very high density at a synthesis temperature of ∼600 °C. SWNTs were deposited at a much lower density on a glass substrate held at 450 °C. SWNTs are typically observed in large bundles that are stabilized by tube–tube van der Waals’ interactions. However, transmission electron microscopy analyses revealed only the presence of isolated SWNTs in these HWCVD-generated materials.

Direct inkjet printing of composite thin barium strontium titanate films

Composite Ba 0 . 6 Sr 0 . 4 TiO 3 /MgO thin films with 60% tuning and tan δ of 0.007 at 2 GHz were deposited using metal organic decomposition inks by spin coating on single crystal MgO substrates. The films with approximately 1 mol% MgO in Ba 0 . 6 Sr 0 . 4 TiO 3 had a better tuning/loss ratio than either the 0 or the 10 mol% MgO substituted films. Crystalline Ba 0 . 5 Sr 0 . 5 TiO 3 films were produced on both MgO and alumina substrates by inkjet printing of metalorganic precursors with subsequent thermal decomposition followed by annealing at 900 °C. Barium strontium titanate lines as narrow as 100 μm were printed on the alumina substrates. The inkjet-printed films were predominantly (100) oriented on MgO and (110) oriented on alumina. The crystalline quality of the inkjet-printed films was improved by annealing at 1100 °C for 3 h in oxygen. Both the printed and the spin-coated films had smooth surfaces (300 A root-mean-square roughness) as required for subsequent deposition of high-resolution metal electrodes. An inkjet-printed Ba 0 . 5 Sr 0 . 5 TiO 3 film (3500 A) on MgO annealed at 1100 °C had 20% tunability of the dielectric constant (∈) at 9. 1 V/μm direct current bias and tan 8 < 0.002 at 1 MHz.