Igor L. Bolotin

Cluster beam deposition of lead sulfide nanocrystals into organic matrices.

Lead sulfide nanocrystals (PbS NCs) were codeposited into two organic films, titanyl phthalocyanine (TiOPc) and alpha-sexithiophene, using cluster beam deposition (CBD). NCs of average diameters of approximately 3-4 nm were evenly distributed in these organic films with average particle spacings of approximately 4 nm, as determined by transmission electron microscopy. The film composition and NC surface chemistry were monitored by X-ray photoelectron spectroscopy (XPS) and other methods. Pb:S stoichiometry in the NC/TiOPc film was determined by XPS to correspond to the PbS cubic rock salt structure. Soft-XPS using 200 eV energy photons determined the NC-organic surface chemistry by resolving the S 2p core level into four distinct components for sulfur. The soft-XPS results found that the PbS NC surface chemistry could be tuned by varying the H(2)S/Ar gas ratio within the CBD source.

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

Bulk-heterojunction films composed of semiconductor nanoparticles blended with organic oligomers are of interest for photovoltaic and other applications. Cu2-XS nanoparticles were cluster beam deposited into thermally evaporated pentacene or quaterthiophene to create bulk-heterojunction thin films. The nanoparticle stoichiometry, morphology, and chemistry within these all-gas phase deposited films were characterized by X-ray photoelectron spectroscopy (XPS) and electron microscopy. Cu2-XS nanoparticles were (at most) only slightly copper-deficient with respect to Cu2S; ∼2.5 nm diameter, unoxidized Cu2-XS nanoparticles formed in both pentacene and quaterthiophene, as the matrix was not observed to impact the nanoparticle morphology or chemical structure. Cluster beam deposition allowed direct control of the nanoparticle stoichiometry and nanoparticle:organic ratio. Chemical states or Wagner plots were combined with other XPS data analysis strategies to determine the metal oxidation state, indicating that Cu(I) was predominant over Cu(II) in the Cu2-XS nanoparticles.

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

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.

Dimerization of titanyl phthalocyanine in thin films prepared by surface polymerization by ion-assisted deposition

Surface polymerization by ion-assisted deposition (SPIAD), the simultaneous dosing of hyperthermal ions while depositing an organic oligomer, was used to deposit titanyl phthalocyanine (TiOPc) thin films with 50 and 100 eV acetylene ions. The properties of the SPIAD TiOPc thin films are compared with films of the evaporated TiOPc monomer via examination of the electronic structure, ultraviolet-visible absorbance, and composition. Mass spectrometry, x-ray photoelectron spectroscopy, and other methods were used to determine the film composition, chemical bonding, and to examine the electronic structure. These results showed the formation of TiOPc dimers bound face to face. However, the overall phthalocyanine ring structure otherwise remained intact, except for small amounts of atmospheric oxidation at ion-induced radical sites.