Direct Evidence for an Ion-by-Ion Deposition Mechanism in Solution Growth of CdS Thin Films

Abstract

A systematic investigation of the mechanism of cadmium sulfide solution growth using atomic force and scanning electron microscopy was performed. The process that was studied involved the slow generation of sulfide ions via the controlled hydrolysis of thiourea in the presence of cadmium nitrate and triethanolamine, a chelating ligand. The formation of two types of films was observed, a mirrorlike primary film and a secondary layer of larger particles that was loosely attached to the first film. The substrates used for the deposition were either bare mica or mica with a partial self-assembled monolayer of octadecylphosphonic acid, CH 3 (CH 2 ) 17 PO 3 H, which served as an internal height standard due to the formation of submonolayer islands 18 ( 2 Å tall. Islands of CdS were observed to nucleate on the remaining bare patches of mica suggesting a potential route to lateral surface patterning. The CdS grew to a height of 22-23 nm, leveled off by 6.5 h, and then proceeded to grow in scattered domains 60-70 nm tall with a few spots as high as 80-100 nm after 10 h. The mechanism of growth has been attributed to either involve attachment of colloidal particles to the surface or an ion-by-ion deposition process. Atomic force microscopy has provided compelling evidence that the latter mechanism is the correct one.

Controlled Synthesis, Growth Mechanism, and Properties of Monodisperse CdS Colloidal Spheres

“…Factors influencing the formation of CSCS: Thiourea (TU), a sulfur source which has been commonly used for the deposition of metal-sulfide films [28,29] or other nanostructures in basic solutions, [30][31][32] remains stable up to 180 8C in reaction systems without metal cations. However, this compound decomposes at relatively low temperatures in an aqueous solution in the presence of many metal cations including Cd 2 + .…”

Fabrication of CdS films with superhydrophobicity by the microwave assisted chemical bath deposition

“…The growth mechanism of CdS films by Chemical bath deposition (CBD) has been discussed by different authors [14][15][16][17][18][19][20][21][22][23][24][25]. It is reported that the reaction rate often takes an important role on the morphology conversion in sulfide deposition.…”

“…Cadmium sulfide (CdS) is a wide band gap semiconductor, which has been widely investigated as photoelectrical materials and nanostructured materials [10][11][12][13][14][15][16][17][18][19][20]. Many researches have been reported on the fabrication of CdS thin films on solid substrates by sputtering [10], thermal evaporation [11], self-assembly growth [12], epitaxial electrodeposition [13], etc.…”

Synthesis of nanocrystalline CdS thin films in PVA matrix

“…These deviations result from dimensionality of nanometer sized grains and numerous interfaces between adjacent crystallites (Tong and Zhu 2006). A major research goal of recent years is to understand the size dependent properties of nanocrystalline materials and as a result considerable amount of work on synthesis and characterization of nanocrystalline thin films are being carried out (Nandakumar et al 1997;Breen et al 1998;Behera et al 2000;He et al 2003).…”