James T. Spencer

Polyhedral-based nonlinear optical materials. Part 1. Theoretical investigation of some new high nonlinear optical response compounds involving carboranes and charged aromatic donors and acceptors

A calculational investigation using semiempirical methods of the molecular and electronic structures, along with the nonlinear optical responses, of a series of compounds in which icosahedral carborane polyhedra bridge charged aromatic donor and acceptor moieties, specifically tropyl (C7H7 ) and cyclopentadienyl (C5H5 ) groups, found that these molecules show exceptionally large calculated second-order responses. These compounds were found to give calculated first hyperpolarizabilities (b) ranging from 8.6 to 1226.010 30 cm 5 esu 1 at 0.5 eV excitation energy. These nonlinear optical responses are understood within the framework of the two-state model using molecular orbital and electronic structure considerations.

Deposition of thin metal and metal silicide films from the decomposition of organometallic compounds

Abstract The deposition of metal silicide thin films can be undertaken using volatile organometallic complexes. Organometallic vapor phase epitaxy or metal-organic chemical vapor phase epitaxy has a number of potential advantages over conventional chemical vapor deposition and molecular beam epitaxy technologies, and a number of novel thin film materials may be made from organometallic compounds. Plasma-, pyrolytic- and photolytic- assisted decomposition of organometallic complexes have been undertaken in an effort to make a variety of metallic and metal silicide thin films. These efforts are comprehensively reviewed.

Chemical vapor deposition of boron and boron nitride from decaborane(14)

We have investigated photoassisted, plasma enhanced chemical vapor deposition and pyrolytic deposition of boron from decaborane (B10H14) and boron nitride from decaborane combined with nitrogen or ammonia. The use of decaborane for depositing boron and boron nitride thin films is seen as a viable alternative to diborane or boron halides.

Non-covalent stabilization and functionalization of boron nitride nanosheets (BNNSs) by organic polymers: formation of complex BNNSs-containing structures

The straightforward non-covalent functionalization and solubilization of hexagonal boron nitride nanosheets (BNNSs) has been achieved by reacting either polythiophene or polyvinylpyrrolidone polymers with exfoliated BNNSs. The BNNSs apparently form strong π–π stacking interactions with the polymers to yield stable derivatized nanosheets with modified properties. A number of polythiophene polymers functionalized with carboxylic acid groups that are connected to the thiophene subunit by varying numbers of CH2-hydrocarbon linker units have also been tethered to the exfoliated BNNSs. These BNNS–polythiophene–(CH2)n–COOH structures have been further coordinated to pre-formed TiO2 nanoparticles to form more complex BNNS–polythiophene–(CH2)n–COO–TiO2 hybrid nanomaterials through covalent binding between the TiO2 nanoparticle surface and the carboxylic acid functional group of the BNNS–polythiophene unit. These novel structures have been characterized by SEM, TEM, FTIR, UV–Vis, and other spectroscopic data.

Selenofluorenone: Synthesis and cycloaddition chemistry

Abstract Selenofluorenone, prepared from fluorenyl selenocyanate by base-induced elimination, participates efficiently in Diels-Alder cycloaddition and 1,3-dipolar cycloaddition reactions.

Structures of selected boranes and carboranes

Nido‐pentaborane(9) (B5H9), 1, nido‐2,3‐diethyl‐2,3‐dicarbahexaborane(8) [(C2H5)2C2B4H6], 2, nido‐decaborane(14) (B10H14), 3, closo‐1,2‐dicarbadodecaborane(12) (H2C2B10H10), 4, can be used as possible source compounds for boron and boron carbide thin film deposition. Inner shell electron energy‐loss spectroscopy (ISEELS) studies of the boron 1s and carbon 1s core excitations of gas phase species have been undertaken so as to characterize these molecular precursors at solid surfaces. The near edge structure of ISEELS provides a good ‘‘fingerprint’’ for the identification of these molecular species. A comparison is made between calculated [modified neglect of differential overlap (MNDO)] bond lengths for molecular clusters and the x‐ray or electron diffraction bond lengths, bond lengths determined from extended energy‐loss fine structure.

Photoemission from gaseous and condensed molecular carborane cluster molecules

Abstract The electronic structure of the nido -2,3-R 2 -2,3-dicarbahexaborane (R 2 C 2 B 4 H 6 where R is C 2 H 5 ) and closo -1,2-dicarbadodecaborane (C 2 B 10 H 12 ) have been studied by photoemission spectroscopy (PES). Photoemission spectra for condensed nido -2,3-diethyl-2,3-dicarbahexaborane(8) ((C 2 H 5 ) 2 C 2 B 4 H 6 ) exhibited features in good agreement with molecular orbitals assigned by modified neglect of differential overlap (MNDO) semiempirical theoretical calculations. Similar agreement can be demonstrated for the closo -1,2-dicarbadodecaborane.

The Deposition of Metallic and Non-Metallic Thin Films Through the Use of Boron Clusters.

New borane clusters and their corresponding transition and rare earth metal complexes are currently being investigated in our laboratories for their utility as unique source materials for the formation of both metallic and non-metallic thin films. These borane cluster complexes exhibit highly favorable properties for use in OMVPE processes, such as; (1) relatively high volatility, (2) anticipated high stability of the ligand itself to provide clean ligand-metal dissociations, (3) high temperature stabilities of the complexes, (4) readily preparable in significant quantities, and (5) availability of theoretical and spectroscopic probes of structure-reactivity relationships. In this work, we have prepared both non-metallic thin films, including materials such as boron nitride, and metallic thin films (both the transition and rare earth metals) through the use of these unique cluster materials. Boron nitride has been investigated as a potential hard coating for use as an insulating electrical layer and protective coating. We have investigated plasma enhanced chemical vapor deposition and pyrolytic deposition of boron nitride from readily available and easily handled borane clusters. Auger electron spectroscopy was used to show that the film was high purity boron nitride of uniform composition. The deposition of transition and rare earth metal thin-film materials of controlled stoichiometry has recently received considerable interest. We have discovered the borane cluster-assisted deposition (CAD) of metallic thin-films involving both transition and rare earth metal materials. Through the use of this unprecedented borane cluster chemical transport process, films ranging in thickness from 100 nm to several microns have been straightforwardly and systematically prepared for numerous metal and mixed-metal boroncontaining systems with controlled composition at relatively low temperatures. These new materials have been characterized by SEM and other techniques.

Photoassisted deposition of conducting palladium films

The authors have selectively deposited palladium on a wide variety of substrates including Kapton (polyimide resin), Ultem 1000 (polyetherimide resin), Teflon, silicon and silicon oxide. The palladium films were fabricated by ultraviolet photolytic decomposition of allylcyclopentadienyl palladium. The photolytic dissociation of this organometallic complex results in the formation of gaseous allyl (C3H5) and cyclopentadienyl (C5H5) species. These films are all conducting, but studies of the bulk resistivities suggest that thin films deposited on the polyimide resins are porous, and the resistivities deviate from the value expected for bulk palladium.

Chemical Vapor Deposition of Metal Borides, 4: The Application of Polyhedral Boron Clusters to the Chemical Vapor Deposition Formation of Gadolinium Boride Thin‐film Materials

The chemical vapor deposition of high-quality polycrystalline thin films of gadolinium hexaboride, GdB 6 , was achieved through the vacuum copyrolysis of gas-phase boron hydride clusters, such as nido-pentaborane(9) [B 5 H 9 ] and nidodecaborane(14) [B 10 H 14 ], and gadolinium(III) chloride. These films typically displayed deep blue colors, were very hard and adhered very well to most deposition substrates. Depositions were carried out on a variety of substrates including quartz, copper, silicon, SiO 2 and ceramic materials. X-ray diffraction and scanning electron microscopic data showed the formation of highly crystalline materials with a strongly preferred orientation in the (111) direction. Attempted depositions of gadolinium boride films on CaF 2 (111) resulted in the apparent formation of a ternary (Ca/Gd)B 6 phase in which the calcium is presumably substituted for gadolinium atoms in the cubic GdB 6 structure. The gadolinium boride thin films were investigated by scanning electron microscopy (SEM), X-ray emission spectroscopy (XES), X-ray diffraction (XRD), and glow-discharge mass spectrometry (GDMS). GDMS showed that the GdB 6 films were relatively uniform in composition in the bulk material.