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

Abstract

Lead sulfide (PbS) nanoparticles of ∼3–5 nm average diameter were codeposited into quaterthiophene (4T) organic films, which in some cases, were additionally modified by simultaneous 50 eV acetylene ion bombardment. The film composition and PbS–4T bonding were monitored by X-ray photoelectron spectroscopy (XPS) and laser desorption postionization mass spectrometry (LDPI-MS). S2p core-level XP spectra indicated that ion-modified films displayed enhanced bonding between 4T and PbS nanoparticles. LDPI mass spectra found thiophene fragments bound to PbS in ion-modified films. Computational simulations were used to investigate the mechanisms by which the incident particles chemically modified the thiophene–PbS nanoparticle interactions: molecular dynamics, density functional theory simulations were carried out on α-terthiophene (3T) analogues of 4T films interacting with (PbS)16 clusters. The simulations showed that, in the absence of acetylene ion modification, a weak charge transfer from the PbS cluster to the nearest 3T molecule occurred, suggestive of little interaction between intact organic matrix molecules and PbS nanoparticles. However, the simulations predicted the formation of a covalent bond between PbS and the oligothiophene film as a result of acetylene ion modification, in support of the experimental observations. These results help explain the recent observation of enhanced photoconductivity in these films upon ion modification ( Majeski M. W. Majeski M. W. J. Vac. Sci. Technol. A20123004D109).

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.…”

“…These S 2p spectra were deconvoluted into four major sources of sulfur, analogous to those observed previously for PbS nanoparticles in quaterthiophene. 23,26 These four sulfur components were assigned as arising from quaterthiophene at a binding energy of 164.1 eV (labeled 4T in Figure 6b), quaterthiophene interacting with the Cu 2−X S nanoparticle at 162.7 eV (4T-Cu 2 S), the surface component of Cu 2−X S at 163.4 eV (Cu 2 S Surface), and the core component of Cu 2−X S at 162.0 eV (Cu 2 S Core). No interference from the substrate was seen in the 2p spectra, and again, two peaks were required to fit the part of this sulfur spectrum arising from Cu 2−X S nanoparticles.…”

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

Laser desorption VUV postionization MS imaging of a cocultured biofilm

“…Work is beginning to show the quantification capabilities of LDPI-MS [42]. Finally, a variety of non-biological applications are envisioned for LDPI-MS imaging, such as analysis of chemical bonding within nanocomposite thin films [44]. …”