Photoresponse of PbS nanoparticles–quaterthiophene films prepared by gaseous deposition as probed by XPS

Abstract

Semiconducting lead sulfide (PbS) nanoparticles were cluster beam deposited into evaporated quaterthiophene (4T) organic films, which in some cases were additionally modified by simultaneous 50 eV acetylene ion bombardment. Surface chemistry of these nanocomposite films was first examined using standard x-ray photoelectron spectroscopy (XPS). XPS was also used to probe photoinduced shifts in peak binding energies upon illumination with a continuous wave green laser and the magnitudes of these peak shifts were interpreted as changes in relative photoconductivity. The four types of films examined all displayed photoconductivity: 4T only, 4T with acetylene ions, 4T with PbS nanoparticles, and 4T with both PbS nanoparticles and acetylene ions. Furthermore, the ion-modified films displayed higher photoconductivity, which was consistent with enhanced bonding within the 4T organic matrix and between 4T and PbS nanoparticles. PbS nanoparticles displayed higher photoconductivity than the 4T component, regardless of ion modification.

Cluster Beam Deposition of Cu2–XS Nanoparticles into Organic Thin Films

“…A less likely explanation for the appearance of two separate sulfur species is that they arise from distinct S−S type bonding present at the surface, originating at corner atoms or other defect sites. 23,26,46,47 The S 2p 3/2-SURF binding energy was shifted higher by an average of 1.4 eV in both Cu 2−X S films on C/Si and in Cu 2−X S nanoparticles in pentacene, in agreement with the magnitude of "surface sulfur" component shifts seen for PbS and CdS nanocrystals. 46,47 E. Chemical State of Cu 2−X S Nanoparticles Deposited into Quaterthiophene.…”

“…Table 2 and Figure 6a show the S 2p XPS core levels for Cu 2−X S nanoparticles in pentacene, which indicate two distinct chemical environments for core and surface sulfur similar to that previously described for PbS nanoparticles. 23,26 The binding energy of S 2p 3/2-CORE was 162.4 ± 0.2 eV, as shown in Figure 6 (where CORE refers to S within the center of the nanoparticle), which corresponds with the average value of 162.3 ± 1.7 eV for Cu 2 S from the NIST database. 28 However, sulfur in CuS versus Cu 2 S compounds cannot be distinguished by S 2p binding energy values alone as these overlap in the NIST database.…”

“…23,26 B. X-ray Photoelectron Spectroscopy. Samples were characterized by high-resolution monochromatic X-ray photoelectron spectroscopy (XPS), using a previously described instrument.…”

Acetylene Ion Enhanced Bonding of PbS Nanoparticles to Quaterthiophene in Thin Films

“…Oligo- or polythiophenes coupled with PbS nanoparticles have been previously examined for photovoltaic applications. ,,, PbS nanoparticles are particularly attractive for use in photovoltaics, since their absorption can be size-tuned from 1000 to 2000 nm, an intense region of the solar spectrum . However, modification strategies are typically required to enhance the π-orbital overlap in the oligothiophene with the PbS nanoparticle.…”

XPS for chemical- and charge-sensitive analyses

“…It is equally surprising that, although XPS has been utilized for more than five decades, this capability is almost completely untapped, and underutilized, except by a few groups around the globe . In what follows, we describe the power of charge-sensitive XPS and provide a variety of applications from our recent work [37][38][39][40][41][42][43][44][45][46][47][48][49][50].…”