title: Origin of surface trap states in CdS quantum dots: relationship between size dependent photoluminescence and sulfur vacancy trap states.
abstract: Monodisperse cadmium sulphide (CdS) quantum dots (QDs) with a tunable size from 1.4 to 4.3 nm were synthesized by a non-injection method, and their surface states were characterized by photoluminescence spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The steady state photoluminescence study identified that the proportion of the trap state emission increased with the QD size decrease, while from the photoluminescence decay study, it appeared that the trap state emission results from the emission via a surface deep trap state. The XPS measurements revealed the existence of surface Cd with sulfur vacancy sites which act as electron trap sites, and the population of these sites increases with the QD size decrease. These results are consistent to conclude that the trap state emission mainly originates from the surface deep trapped electrons at the surface Cd with sulfur vacancy sites.
authors.affiliation: School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Bundoora, VIC 3083, Australia. yasuhiro.tachibana@rmit.edu.au.
authors.forename: Aisea
authors.initials: A
authors.lastname: Veamatahau
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.forename: Tom
authors.initials: T
authors.lastname: Seifert
authors.forename: Satoshi
authors.initials: S
authors.lastname: Makuta
authors.forename: Kay
authors.initials: K
authors.lastname: Latham
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kanehara
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Teranishi
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tachibana