EMSL: Alan G Joly's Publications

Dreger ZA, E Balasubramaniam, YM Gupta, and AG Joly. 2009. "High-Pressure Effects on the Electronic Structure of Anthracene Single Crystals: Role of Nonhydrostaticity." Journal of Physical Chemistry A 113(8):1489-1496. Abstract Optical spectroscopy methods were used to examine the effect of nonhydrostaticity on the electronic structure of anthracene single crystals compressed statically to 9 GPa. Two pressure-transmitting media, nitrogen (hydrostatic) and water (nonhydrostatic above ~ 5.5 GPa), were utilized. It was found that nonhydrostatic compression generates several new features both in the absorption and fluorescence spectra: (i) formation of new absorption and fluorescence bands, (ii) deviations in pressure shift of fluorescence peaks, (iii) extensive broadening of vibrational peaks, and (iv) irreversible changes in the spectra shape upon pressure unloading. Furthermore, the time-resolved fluorescence decay curves measured at the wavelength corresponding to the new fluorescence band show clear initial increase. These new features are accompanied by inhomogeneous color changes and macroscopic lines on the (001) plane of the crystal. All of the changes are discussed and correlated with microscopic transformations in the crystal. It is demonstrated that nonhydrostatic compression in anthracene crystal introduces inelastic changes in the form of dislocations along [110] and [1 10 ] directions. These dislocations lead to the development of dimeric structures and, consequently, to various changes in the electronic response of the compressed anthracene crystal.

Milbrath BD, JA Caggiano, MH Engelhard, AG Joly, DW Matson, P Nachimuthu, and LC Olsen. 2009. " Using Thin Films to Screen Possible Scintillator Materials ." IEEE Transactions on Nuclear Science 56(3, PT 3): 1650-1654. Abstract The discovery and optimization of new scintillators has traditionally been a rather slow process due to the difficulties of single crystal growth. This paper discusses the production of polycrystalline scintillator thin films (a few microns thick) which were tested in order to determine what characterizations could be made concerning a material’s ultimate potential as a scintillator prior to pursuing crystal growth. Thin films of CaF2(Eu), CeF3, and CeCl3, all known scintillators, were produced by vapor deposition. The hygroscopic CeCl3 was coated with multiple polymer-aluminum oxide bi-layers. Emission spectra peak wavelengths and decay times agreed with single crystal values. The films were too thin to measure gamma photopeaks, but using alpha energy deposition peaks, one could compare the relative photon yield/MeV between materials. The values obtained appear to give a relevant indication of a material’s light yield potential. The technique also appears useful for quickly determining the proper dopant amount for a given material.

Trevisanutto PE, PV Sushko, KM Beck, AG Joly, WP Hess, and AL Shluger. 2009. "Excitation, Ionization, and Desorption: How Sub-band gap Photons Modify the Structure of Oxide Nanoparticles." Journal of Physical Chemistry C 113(4):1274-1279. Abstract Nanoparticles of wide-band-gap materials MgO and CaO, subjected to low-intensity ultraviolet irradiation with 266 nm (4.66 eV) photons, emit hyperthermal oxygen atoms with kinetic energies up to ~ 0.4 eV. We use ab initio embedded cluster methods to study theoretically a variety of elementary photoinduced processes at both ideal and defect-containing surfaces of these nanoparticles and develop a mechanism for the desorption process. The proposed mechanism includes multiple local photoexcitations resulting in sequential formation of localized excitons, their ionization, and further excitations. It is suggested that judicious choice of sub-band-gap photon energies can be used to selectively modify surfaces of nanomaterials.

Beck KM, AG Joly, O Diwald, S Stankic, PE Trevisanutto, PV Sushko, AL Shluger, and WP Hess. 2008. "Energy and Site Selectivity in O-Atom Photodesorption from Nanostructured MgO." Surface Science 602(11):1968-1973. doi:10.1016/j.susc.2008.03.046 Abstract Electronic excitation of wide gap ionic solids can induce desorption of neutral atoms with distinct hyperthermal and thermal kinetic energy distributions. Hyperthermal atomic desorption results from electronic surface excitation while thermal desorption is initiated primarily by bulk excitation. Calculations indicate that surface-localized transitions can be excited independently from bulk transitions using selected photon energies. The photon energy required to excite specific surface sites depends upon the site coordination with successively lower energies required to excite terrace, step, and corner sites. Here, we excite low-coordinated surface sites of nanostructured MgO samples using 4.7 eV UV laser pulses and observe dominant hyperthermal O-atom emission. We then selectively excite bulk sites of nanostructured MgO, using a 7.9 eV laser, and observe dominant thermal O-atom desorption. These results are analyzed in terms of laser desorption models developed previously for alkali halide crystals. We propose a multi-step mechanism for hyperthermal O-atom desorption, under surface selective excitation, based on hole trapping at 3C (corner) O-atom sites followed by exciton decomposition. The proposed “hole plus exciton” model has similarities to the surface exciton desorption model, established for alkali halides, but is more complex and requires more steps. Nonetheless, the principle of site-specific photoreaction, established for alkali halide crystals, is clearly extendable to a prototypical metal oxide.

Joly AG, KM Beck, and WP Hess. 2008. "Electronic Energy Transfer on CaO Surfaces." Journal of Chemical Physics 129(12):124704. doi:10.1063/1.2980049 Abstract We excite low-coordinated surface sites of nanostructured CaO samples using tunable UV laser pulses and observe hyperthermal O-atom emission indicative of an electronic excited-state desorption mechanism. The O-atom yield increases dramatically with photon energy, between 3.75 and 5.4 eV, below the bulk absorption threshold. The peak of the kinetic energy distribution does not increase with photon energy in the range 3.9 to 5.15 eV. These results are analyzed in the context of a laser desorption model developed previously for nanostructured MgO samples. The data are consistent with desorption induced by exciton localization at corner-hole trapped surface sites following either direct corner excitation or diffusion and localization of excitons from higher coordinated surface sites.

Li Y, TC Kaspar, T Droubay, AG Joly, P Nachimuthu, Z Zhu, V Shutthanandan, and SA Chambers. 2008. "A Study of H and D doped ZnO epitaxial films grown by pulsed laser deposition." Journal of Applied Physics 104(5):Article no. 053711. doi:10.1063/1.2975219 Abstract We examine the crystal structure, electrical and optical properties of ZnO epitaxial films grown by pulsed laser deposition in a H2 or D2 ambient. We compared with pure ZnO films grown in O2 and vacuum. N-type electrical conductivity is enhanced by two to three orders of magnitude as a result of growing in H2 or D2. Temperature dependent Hall effect measurements reveal small (a few meV) carrier activation energies, along with carrier concentrations of 2-7 x 1018 cm-3, and mobilities of 20-40 cm2/Vs in ZnO films doped with H or D in the 1018 cm-3 range. We have modeled the low-temperature electrical properties of H- and D-doped ZnO films using variable range hopping and surface layer conductivity models, but our data do not fit well with these models. Rather, it appears that growth in H2 or D2 promotes the formation of an exceedingly shallow or conduction-band degenerate donor state, possibly associated with H or D substitution at O sites in the lattice.

Li Y, L Ma, X Zhang, AG Joly, Z Liu, and W Chen. 2008. "Synthesis and Optical Properties of Sulfide Nanoparticles Prepared in Dimethylsulfoxide." Journal of Nanoscience and Nanotechnology 8(11):5646-5651. Abstract Many methods have been reported for the formation of sulfide nanoparticles by the reaction of metallic salts with sulfide chemical sources in aqueous solutions or organic solvents. Here, we report the formation of sulfide nanoparticles in dimethylsulfoxide (DMSO) by boiling metallic salts without sulfide sources. The sulfide sources are generated from the boiling of DMSO and react with metallic salts to form sulfide nanoparticles. In this method DMSO functions as a solvent and a sulfide source as well as a stabilizer for the formation of the nanoparticles. The recipe is simple and economical making sulfide nanoparticles formed in this way readily available for many potential applications.

Liu Y, W Chen, S Wang, and AG Joly. 2008. "Investigation of Water-Soluble X-ray Luminescence Nanoparticles for Photodynamic Activation." Applied Physics Letters 92(4):Art. No. 043901. Abstract In this letter, we report the synthesis of LaF3:Tb3+-MTCP (meso-Tetra(4-carboxyphenyl) porphine) nanoparticle conjugates and investigate the energy transfer as well as singlet oxygen generation following X-ray irradiation. Our observations indicate that LaF3:Tb3+-MTCP nanoparticle conjugates are efficient photodynamic agents that can be initiated by X-rays at a reasonably low dose. The addition of folic acid to facilitate targeting to folate receptors on tumor cells has no effect on the quantum yield of singlet oxygen in the nanoparticle-MTCP conjugates. Our pilot studies indicate that water-soluble scintillation nanoparticles can be potentially used to activate photodynamic therapy as a promising deep cancer treatment.

Liu Y, W Chen, S Wang, AG Joly, SL Westcott, and BK Woo. 2008. "X-Ray Luminescence of LaF3:Tb3+ and LaF3:Ce3+, Tb3+ Water Soluble Nanoparticles." Journal of Applied Physics 103(6):Art. No. 063105. doi:10.1063/1.2890148 Abstract Utilizing scintillation nanoparticles as agents for photodynamic therapy for cancer treatment necessitates the use of biocompatible and water soluble nanoparticles. In this article, we report the synthesis and X-ray luminescence of water soluble Ce and Tb doped LaF3 nanoparticles. The nanoparticles are conjugated with folic acid and meso-tetra (o-carboxyphenyl) porphyrin. X-ray luminescence is observed from the nanoparticles in both powder and solution samples. More importantly, singlet oxygen has been detected from the conjugated system following X-ray excitation. These preliminary observations indicate that water-soluble scintillation nanoparticles can be potentially used in photodynamic therapy for deep-tissue cancer treatment.

Lu CY, PJ Shamberger, EN Yitamben, KM Beck, AG Joly, MA Olmstead, and FS Ohuchi. 2008. "Laser and Electrical Current Induced Phase Transformation of In2Se3 Semiconductor thin film on Si(111) ." Applied Physics A, Materials Science and Processing 93(1):93-98. doi:10.1007/s00339-008-4776-8 Abstract Phase transformation of thin film (~30 nm) In2Se3/Si(111) (amorphous  crystalline) was performed by resistive annealing and the reverse transformation (crystalline  amorphous) was performed by nanosecond laser annealing. As an intrinsic-vacancy, binary chalcogenide semiconductor, In2Se3 is of interest for non-volatile phase-change memory. Amorphous InxSey was deposited at room temperature on Si(111) after pre-deposition of a crystalline In2Se3 buffer layer (6.4 Å). Upon resistive annealing to 380°C, the film was transformed into a y-In2Se3 single crystal with its {0001} planes parallel to the Si (111) substrate and parallel to Si , as evidenced by scanning tunneling microscopy, low energy electron diffraction, and x-ray diffraction. Laser annealing with 20 nanosecond pulses (0.1 milliJoules/pulse) re-amorphized the region exposed to the laser beam, as observed with photoemission electron microscopy (PEEM). The amorphous phase in PEEM appears dark, likely due to abundant defect levels inhibiting electron emission from the amorphous InxSey film.