Publications

Abstract not provided.

Tin (Sn) whiskers are conductive Sn filaments that grow from Sn-plated surfaces, such as surface finishes on electronic packages. The phenomenon of Sn whiskering has become a concern in recent years due to requirements for lead (Pb)-free soldering and surface finishes in commercial electronics. Pure Sn finishes are more prone to whisker growth than their Sn-Pb counterparts and high profile failures due to whisker formation (causing short circuits) in space applications have been documented. At Sandia, Sn whiskers are of interest due to increased use of Pb-free commercial off-the-shelf (COTS) parts and possible future requirements for Pb-free solders and surface finishes in high-reliability microelectronics. Lead-free solders and surface finishes are currently being used or considered for several Sandia applications. Despite the long history of Sn whisker research and the recently renewed interest in this topic, a comprehensive understanding of whisker growth remains elusive. This report describes recent research on characterization of Sn whiskers with the aim of understanding the underlying whisker growth mechanism(s). The report is divided into four sections and an Appendix. In Section 1, the Sn plating process is summarized. Specifically, the Sn plating parameters that were successful in producing samples with whiskers will be reviewed. In Section 2, the scanning electron microscopy (SEM) of Sn whiskers and time-lapse SEM studies of whisker growth will be discussed. This discussion includes the characterization of straight as well as kinked whiskers. In Section 3, a detailed discussion is given of SEM/EBSD (electron backscatter diffraction) techniques developed to determine the crystallography of Sn whiskers. In Section 4, these SEM/EBSD methods are employed to determine the crystallography of Sn whiskers, with a statistically significant number of whiskers analyzed. This is the largest study of Sn whisker crystallography ever reported. This section includes a review of previous literature on Sn whisker crystallography. The overall texture of the Sn films was also analyzed by EBSD. Finally, a short Appendix is included at the end of this report, in which the X-Ray diffraction (XRD) results are discussed and compared to the EBSD analyses of the overall textures of the Sn films. Sections 2, 3, and 4 have been or will be submitted as stand-alone papers in peer-reviewed technical journals. A bibliography of recent Sandia Sn whisker publications and presentations is included at the end of the report.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

In an aim to develop photo-responsive composites, the UV photo-reduction of aqueous titanium oxide nanoparticle-graphene oxide (TiO{sub 2}-GO) dispersions (Lambert et al. J Phys. Chem. 2010 113 (46), 19812-19823) was undertaken. Photo-reduction led to the formation of a black precipitate as well as a soluble portion, comprised of titanium oxide nanoparticle-reduced graphene oxide (TiO{sub 2}-RGO). When allowed to slowly evaporate, self assembled titanium oxide nanoparticle-graphene oxide (SA-TiO{sub 2}-RGO) films formed at the air-liquid interface of the solution. The thickness of SARGO-TiO{sub 2} films range from {approx}30-100 nm when deposited on substrates, and appear to be comprised of a mosaic assembly of graphene nanosheets and TiO{sub 2}, as observed by scanning electron microscopy. Raman spectroscopy and X-ray photoelectron spectroscopy indicate that the graphene oxide is only partially reduced in the SA-TiO{sub 2}-RGO material. These films were also deposited onto inter-digitated electrodes and their photo-responsive behavior was examined. UV-exposure lead to a {approx} 200 kOhm decrease in resistance across the device, resulting in a cathodically biased film. The cathodic bias of the films was utilized for the subsequent reduction of Ag(NO{sub 3}) into silver (Ag) nanoparticles, forming a ternary Ag-(SA-RGO-TiO{sub 2}) composite. Various aspects of the self assembled films, their photoconductive properties as well as potential applications will be presented.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

We have systematically studied the effect of pH and 1,3-diaminopropane additive concentration on the morphology of ZnO nanorod and nanoneedle arrays grown in aqueous solution using a variety of seed layers. Increase in the growth solution pH from 6.8 to 13.2 resulted in a near doubling of the growth rate in the [0001] direction possibly due to attractive interaction between the zinc species and the growth surface at high pH, leading to nanorod arrays with reduced faceting and higher aspect ratios. Increases in 1,3-diaminopropane concentration initially enhanced and subsequently inhibited growth of tapered ZnO nanoneedles on seed layers consisting of ZnO nanoparticles, oriented ZnO films, or columnar facets of ZnO microrods. The final nanoneedle dimensions, packing density, and alignment were strongly affected by 1,3-diaminopropane concentration and seed layer type, which can be explained in terms of the relative strength of zinc chelation by 1,3-diaminopropane, the areal density of seeds, and other factors. The precise tuning of ZnO crystalline morphology via the control of seeding and growth conditions may be beneficial to many potential applications that require these aligned crystalline nanostructures. © 2008 American Chemical Society.

Abstract not provided.

Abstract not provided.