Yu-Hsu Chang

Chemical vapor deposition of tantalum carbide and carbonitride thin films from Me3CE=Ta(CH2CMe3)(3) (E = CH, N)

Chemical vapor deposition (CVD) of thin films employing Me3CCHTa(CH2CMe3)3 and Me3CNTa(CH2CMe3)3 as the precursors has been carried out. TaC and TaCN films were deposited at relatively low temperatures (623–923 K). In comparison, using Me3CNTa(CH2CMe3)3, the TaN bond did not undergo cleavage during the reaction and the N atom was incorporated into the film as nitride. The volatile components evolved were collected and examined by GC–MS, FT-IR, 1H and 13C NMR spectroscopy. Possible decomposition pathways of the tantalum complexes are proposed to rationalize the observation.

Syntheses of nano-sized cubic phase early transition metal carbides from metal chlorides and n-butyllithium

Nano-sized early transition metal carbides, including TiC, ZrC, HfC, V4C3, NbC and TaC, were synthesized from colloidal precursors generated by reducing the metal chlorides, TiCl4, ZrCl4, HfCl4, VCl3, NbCl5, and TaCl5, respectively, with n-C4H9Li in hexane. The colloids were formed from the reduction of the metal centers, which then nucleated into nano-scaled metal clusters. The major byproducts were LiCl, C4H10, and C4H8, indicating that the butyl groups probably underwent β-hydrogen elimination and reductive elimination. This suggests that C–C bond activation of the butyl groups was in operation, leaving residual carbon atoms in the metal colloids. The colloids were further heated at 873–1273 K to crystallize into cubic phase TiC, ZrC, HfC, V4C3, NbC and TaC nanoparticles.

Construction of a Near-Infrared-Activatable Enzyme Platform To Remotely Trigger Intracellular Signal Transduction Using an Upconversion Nanoparticle

Photoactivatable (caged) bioeffectors provide a way to remotely trigger or disable biochemical pathways in living organisms at a desired time and location with a pulse of light (uncaging), but the phototoxicity of ultraviolet (UV) often limits its application. In this study, we have demonstrated the near-infrared (NIR) photoactivatable enzyme platform using protein kinase A (PKA), an important enzyme in cell biology. We successfully photoactivated PKA using NIR to phosphorylate its substrate, and this induced a downstream cellular response in living cells with high spatiotemporal resolution. In addition, this system allows NIR to selectively activate the caged enzyme immobilized on the nanoparticle surface without activating other caged proteins in the cytosol. This NIR-responsive enzyme-nanoparticle system provides an innovative approach to remote-control proteins and enzymes, which can be used by researchers who need to avoid direct UV irradiation or use UV as a secondary channel to turn on a bioeffector.

Electroless deposition of Cu nanostructures on molecular patterns prepared by dip-pen nanolithography

Cu nanostructures deposited on the top of self-assembled molecular patterns prepared by Dip-pen Nanolithography (DPN) are investigated thoroughly in this study. 16-Mercaptohexadecanoic acid (MHA) molecular patterns are used as templates and CuSO4 is reduced by electroless deposition method. According to the SEM, EDS and AFM test results, it is found that the formation and the dimension of the Cu nanostructure array can be governed by reaction conditions and the size of molecular patterns. The non-specific growth of Cu can also be minimized in the present work. The method designed has demonstrated its capability in the synthesis of molecular junctions with high reproducibility. Distinct phenomena of underpotential deposition behaviors of Cu on polycrystalline gold substrates covered with self-assembled monolayers of 16-mercaptohexadecanoic acid and octadecanethiol are also studied and discussed.

SiCl3CCl3 as a novel precursor for chemical vapor deposition of amorphous carbon films

Abstract Amorphous carbon films, characterized by XRD, AFM, SEM and Raman, were deposited from SiCl 3 CCl 3 on quartz substrates at 773–1273 K by low pressure chemical vapor deposition using a hot-wall reactor. XPS studies showed that the films grown at 773 K contained 90% C and 10% Cl, while the films grown at 1273 K contained 100% C. SiCl 4 , CCl 4 and Cl 2 CCCl 2 were detected by on-line FT-IR studies. The extrusion of dichlorocarbene, :CCl 2 , from SiCl 3 CCl 3 should provide the source of carbon in the reaction. On Si substrates, an etching process at the film-substrate interface assisted the lift-off of the films from the substrates. The C films curled and formed rolls.

The synthesis of a gold nanodisk–molecular layer–gold film vertical structure: a molecular layer as the spacer for SERS hot spot investigations

The objective of this research is to conduct a systematic measurement of hot spots formed between a gold (Au) nanodisk and an Au film using surface-enhanced Raman scattering (SERS). The dip-pen nanolithography and wet etching methods are used to fabricate sandwich structures with a self-assembled monolayer (SAM) or a polymer embedded between vertical Au nanodisks and the Au substrate. A flat polymer, which acts as a spacer, is synthesized via graft polymerization. The gap between the Au nanodisks and Au film is adjusted to the range from 2.4 to 12.1 nm by forming a SAM and repeating the graft polymerization. The SERS molecules, 4-mercaptobenzoic acid, are chemically bonded to the sidewalls of the Au nanodisks in order to observe the coupling interaction in the dipole of SERS while changing the gap size. According to the experimental results, the degree of field enhancement is greatly dependent on the dimensions of the gap. The greatest enhancement is reached when the gap distance is 3.8 nm, and no coupling effect is observed when the gap distance is more than 12 nm.

An Integrated System to Remotely Trigger Intracellular Signal Transduction by Upconversion Nanoparticle-mediated Kinase Photoactivation

Upconversion nanoparticle (UCNP)-mediated photoactivation is a new approach to remotely control bioeffectors with much less phototoxicity and with deeper tissue penetration. However, the existing instrumentation on the market is not readily compatible with upconversion application. Therefore, modifying the commercially available instrument is essential for this research. In this paper, we first illustrate the modifications of a conventional fluorimeter and fluorescence microscope to make them compatible for photon upconversion experiments. We then describe the synthesis of a near-infrared (NIR)-triggered caged protein kinase A catalytic subunit (PKA) immobilized on a UCNP complex. Parameters for microinjection and NIR photoactivation procedures are also reported. After the caged PKA-UCNP is microinjected into REF52 fibroblast cells, the NIR irradiation, which is significantly superior to conventional UV irradiation, efficiently triggers the PKA signal transduction pathway in living cells. In addition, positive and negative control experiments confirm that the PKA-induced pathway leading to the disintegration of stress fibers is specifically triggered by NIR irradiation. Thus, the use of protein-modified UCNP provides an innovative approach to remotely control light-modulated cellular experiments, in which direct exposure to UV light must be avoided.