Xuliang Dai

Flattening a puckered cyclohexasilane ring by suppression of the pseudo-Jahn–Teller effect

We report the experimental and theoretical characterization of neutral Si(6)X(12) (X = Cl, Br) molecules that contain D(3d) distorted six-member silicon rings due to a pseudo-Jahn-Teller (PJT) effect. Calculations show that filling the intervenient molecular orbitals with electron pairs of adduct suppresses the PJT effect in Si(6)X(12), with the Si(6) ring becoming planar (D(6h)) upon complex formation. The stabilizing role of electrostatic and covalent interactions between positively charged silicon atoms and chlorine atoms of the subject [Si(6)Cl(14)](2-) dianionic complexes is discussed. The reaction of Si(6)Cl(12) with a Lewis base (e.g., Cl(-)) to give planar [Si(6)Cl(14)](2-) dianionic complexes presents an experimental proof that suppression of the PJT effect is an effective strategy in restoring high Si(6) ring symmetry. Additionally, the proposed pathway for the PJT suppression has been proved by the synthesis and characterization of novel compounds containing planar Si(6) ring, namely, [(n)Bu(4)N](2)[Si(6)Cl(12)I(2)], [(n)Bu(4)N](2)[Si(6)Br(14)], and [(n)Bu(4)N](2)[Si(6)Br(12)I(2)]. This work represents the first demonstration that PJT effect suppression is useful in the rational design of materials with novel properties.

Collimated Aerosol Beam Deposition: Sub-5-

Materials deposition based upon directed aerosol flow has the potential of finding application in the field of flexible electronics where a low-temperature route to printed transistors with high mobilities remains elusive. NDSU has been actively engaged in addressing this opportunity from the following two perspectives: 1) developing an appreciation of the basic physics that dominate aerosol beam deposition toward engineering a robust method that allows the realization of deposited features with sub-5 μm resolution; and, 2) developing an understanding of the mechanistic transformations of silane-based precursor inks toward the formation of electronic materials at atmospheric-pressure. In this paper, we will briefly discuss the genesis of a new materials deposition method termed collimated aerosol beam direct-write (CAB-DW) where precision linewidth control has been realized using a combined theoretical/experimental approach. Next, we will discuss progress using Si6H12 (cyclohexasilane-a liquid silane) as a precursor for solution-processed diodes and transistors. Finally, we demonstrate the ability to CAB-DW Si6H12-based precursor inks for printing Si-based semiconductors.

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Liquid cyclohexasilane (Si6H12) is localized within polymeric templates from amphiphilic invertible polymers (AIPs) to form a stable composition. NMR study reveals Si6H12 primarily interacts with ester group-containing polymeric fragments. Interaction with ether group-containing fragments occurs at higher silane concentration. AIP self-assembly gives rise to an additional interaction between cyclohexasilane and hydrophobic polymeric domains.

m Resolution of Printed Actives and Passives

The hydrogenated amorphous silicon a-Si∶H films were grown by plasma-enhanced chemical vapor deposition (PECVD) using liquid cyclohexasilane Si<inf>6</inf>H<inf>12</inf> (CHS). The growth rate of a-Si∶H was studied as a function of substrate temperatures in the range of 30 °C≪T≪450 °C using deposition conditions that were optimized for monosilane SiH<inf>4</inf>. The same parameters were used for a- Si∶H films grown using disilane (Si<inf>2</inf>H<inf>6</inf>) and trisilane (Si<inf>3</inf>H<inf>8</inf>) precursors. It was found that the a-Si∶H film growth rate of CHS is lower with respect to those of mono-, di- and trisilane in an Ar plasma. Addition of ∼10% of H<inf>2</inf> dramatically increases the deposition rate for CHS-based films about 700% to 8 Å/sec. The as-deposited films were characterized by FTIR and Raman spectroscopy to probe the hydrogen content and local bonding environment. It was found that the films grown using Ar/H<inf>2</inf> mixtures as carrier gas have a reduced hydrogen content relative to polysilane fragments indicating higher quality amorphous silicon.

“Host–guest” interaction between cyclohexasilane and amphiphilic invertible macromolecules

Host-guest interactions between cyclohexasilane (Si(6)H(12)) and amphiphilic invertible macromolecules based on PEG and sebacic acid in acetonitrile (neither a solvent for cyclohexasilane nor a support for the micellization of amphiphilic invertible macromolecules) have been investigated. Despite the extended conformation of the macromolecules and the absence of self-assembled polymeric domains, a macromolecular amphiphilicity itself contributes to localizing Si(6)H(12) by AIP and thus enables Lewis acid-base interactions between Si(6)H(12) and the AIP carbonyl groups. The obtained results demonstrate an interesting phenomenon in that insoluble Si(6)H(12) can be localized by AIP macromolecules in a medium that does not support the formation of polymeric domains.

Comparative study of low-temperature PECVD Of amorphous silicon using mono-, di-, trisilane and cyclohexasilane

Materials deposition based upon directed aerosol flow has the potential of finding application in the field of flexible electronics where a low-temperature route to printed transistors with high mobilities remains elusive. NDSU has been actively engaged in addressing this opportunity from the following two perspectives: (1) developing an appreciation of the basic physics that dominate aerosol beam deposition toward engineering a robust method that allows the realization of deposited features with sub-5 mum resolution; and, (2) developing an understanding of the mechanistic transformations of silane - based precursor inks toward the formation of electronic materials at atmospheric-pressatmospheric-pressureure. In this paper, we will briefly discuss the genesis of a new a materials deposition method termed collimated aerosol beam direct-write (CAB- DW) where precision linewidth control has been realized using a combined theoretical/experimental approach. Next, we will discuss progress using Si6H12 (cyclohexasilane - a liquid silane) as a precursor for solution-processed diodes and transistors. Finally, we demonstrate the ability to CAB- DW Si6H12-based precursor inks for printing Si-based semiconductors.