• PDF / 519,388 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 17 Downloads / 247 Views

DOWNLOAD

REPORT

---

1196-C06-23

Deposition of Ordered Arrays of Metal Sulfide Nanoparticles in Nanostructures Using Supercritical Carbon Dioxide

Joanna S. Wang,1,2 Alexander B. Smetana,1,2 John J. Boeckl,1 Gail J. Brown1 and Chien M. Wai2 1

Air Force Research Lab, Materials and Manufacturing Directorate, WPAFB, OH 45433-7707

2

Department of Chemistry, University of Idaho, Moscow, ID 83844

ABSTRACT Silver sulfide (Ag2S) and cadmium sulfide (CdS) nanoparticles of adjustable sizes are synthesized using a water-in-hexane microemulsion method and stabilized by dodecanethiol. The stabilized metal sulfide nanoparticles can be deposited homogenously on flat substrates forming ordered 2D arrays in supercritical fluid carbon dioxide (Sc-CO2). The use of Sc-CO2 leaves the particles unaffected by de-wetting effects and surface tension caused by traditional solvents and produces uniform arrays. The Sc-CO2 deposition technique can effectively fill the metal sulfide nanoparticles into nanoscale features, which is difficult to achieve by conventional solvent evaporation methods.

INTRODUCTION Nanocrystal metals and semiconductors with ordered arrays have many applications, which can be used as optical filters [1,2], anti-reflective surface coatings [3,4], selective solar absorbers [5], data storage, and microelectronics [6]. Metal sulfide quantum dots such as silver sulfide (Ag2S) and cadmium sulfide (CdS) nanoparticles are incorporated in sensing applications, and can be applied as photosensitizers or light detectors for photographic purposes [7-9]. Nanoparticles have electric and optical properties that sensitively depend on the size. If the size of the nanoparticles can be tailored, it can be anticipated that new materials created from these particles will bring about new technical developments. Our research group has recently developed a method of using Sc-CO2 as a medium to deposit gold and platinum nanoparticles uniformly in nanometer-sized trenches on silicon wafers [10]. In this study, we further develop and apply this technique to the solid-state field using Ag2S and CdS as model semiconductor nanoparticles. Ag2S and CdS nanoparticles are synthesized by chemical reactions occurring in water-in-oil microemulsions, in which metal cations react with sulfide anions dissolved in the nanoscaled water cores. Sodium bis(2-ethylhexyl)sulfosuccinate (AOT) is used as an anionic surfactant with hexane as an organic solvent. Dodecanethiol is then added to the microemulsion solution to stabilize the synthesized metal sulfide nanoparticles. The alkanethiol-coated metal sulfide nanoparticles are easily separated from the reaction medium and dispersed in a non-polar solvent. The protected nanoparticles dispersed in an organic solution can be precipitated onto carbon-coated copper grids to create self-assembled 2D arrays in Sc-CO2. A distinctive aspect of the Sc-CO2 evaporation technique is that the nanoparticles can be deposited into small trenches on Si wafers, which cannot be achieved by traditional solvent deposition methods.

EXPERIMENTAL DETAILS S