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

Lead sulfide (PbS) nanoparticles of similar to 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 a-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 (Majeslci, M. W.; et al. J. Vac. Sci. Technol. A 2012, 30, 04D109).11Nsciescopu

Brominated Tyrosine and Polyelectrolyte Multilayer Analysis by Laser Desorption VUV Postionization and Secondary Ion Mass Spectrometry

The small molecular analyte 3,5-dibromotyrosine (Br2Y) and chitosan-alginate polyelectrolyte multilayers (PEM) with and without adsorbed Br2Y were analyzed by laser desorption postionization mass spectrometry (LDPI-MS). LDPI-MS using 7.87 eV laser and tunable 8 ? 12.5 eV synchrotron vacuum ultraviolet (VUV) radiation found that desorption of clusters from Br2Y films allowed detection by≤8 eV single photon ionization. Thermal desorption and electronic structure calculations determined the ionization energy of Br2Y to be ~;;8.3?0.1 eV and further indicated that the lower ionization energies of clusters permitted their detection at≤8 eV photon energies. However, single photon ionization could only detect Br2Y adsorbed within PEMs when using either higher photon energies or matrix addition to the sample. All samples were also analyzed by 25 keV Bi3 + secondary ion mass spectrometry (SIMS), with the negative ion spectra showing strong parent ion signal which complemented that observed by LDPI-MS. The negative ion SIMS depended strongly on the high electron affinity of this specific analyte and the analyte?s condensed phase environment

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

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.; J. Vac. Sci. Technol. A 2012, 30, 04D109)