Chao-Shiuan Liu

Organic light-emitting diodes based on charge-neutral Os(II) emitters: generation of saturated red emission with very high external quantum efficiency

The OLED device using 6% of Os(fptz)2(PPh2Me)2 as the dopant emitter in a CBP host and BPAPF as hole transporting material shows an external quantum efficiency of 15.3% and luminous efficiency of 21.3 cd A−1, power efficiency of 6.3 lm W−1 at 20 mA cm−2. An even higher external quantum efficiency of ∼20% was achieved at a low current density of ∼1 mA cm−2.

Synthesis and characterization of fluorinated β-ketoiminate and imino-alcoholate Pd complexes: precursors for palladium chemical vapor deposition

The design and synthesis of Pd complexes with two β-ketoiminate or with two imino-alcoholate chelate ligands is reported. In order to establish their structures in the solid-state, methoxyethyl substituted complexes 1c and 2c were characterized by single crystal X-ray diffraction, showing a square-planar local coordination for the Pd atom, but the β-ketoiminate ligands of 1c gave a bent basal plane involving two chelating hexagons, which was in sharp contrast to the boat configuration of the imino-alcoholate ligands observed in the second complex 2c. Chemical vapor deposition (CVD) experiments were conducted at deposition temperatures of 250–350 °C. Scanning electron micrographs (SEM) were taken to reveal the surface morphologies and grain sizes of the Pd metal thin films. The resulting thin films were found to contain a low level of carbon and oxygen impurities using O2 as the carrier gas, as measured by X-ray photoelectron spectroscopy (XPS).

Deposition of Ru and RuO2 thin films employing dicarbonyl bis-diketonate ruthenium complexes as CVD source reagents

Reaction of Ru3(CO)12 with 6 eq. of β-diketone ligands (hfac)H, (tmhd)H, (acac)H and (tfac)H at 160–170 °C in a hydrocarbon solvent (pentane or hexane) affords the diketonate complexes [Ru(CO)2(hfac)2] (1), [Ru(CO)2(tmhd)2] (2), [Ru(CO)2(acac)2] (3) and [Ru(CO)2(tfac)2] (4) in high yields. These ruthenium complexes were characterized by spectroscopic methods; a single crystal X-ray diffraction study was carried out on one isomer of the tfac complex (4a), revealing an octahedral coordination geometry with two CO ligands located at cis-positions and with the CF3 groups of the β-diketonate ligands trans to the CO ligands. Thermogravimetric analysis of complex (1) showed an enhanced volatility compared to the parent acac complex (3), attributed to the CF3 group reducing intermolecular attraction. Employing complexes (1) and (2) as CVD source reagents, ruthenium thin films can be deposited at temperatures of 350 °C–450 °C under an H2 atmosphere or at temperatures of 275 °C–400 °C using a 2% mixture of O2 in argon as carrier gas. For deposition carried out using complex (1) and under 100% O2 atmosphere, RuO2 thin films with a preferred (200) orientation were obtained. The as-deposited thin films were characterized by surface and physical analytical techniques, such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD) and four-point probe measurement.

Fluorinated aminoalkoxide CuII complexes: new CVD precursors for deposition of copper metal

Volatile low-melting CuII metal complexes of formula Cu[OC(CF3)R1CH2NHR2]2 (R1 = CF3 or CH3; R2 = CH2CH2OMe, Bui, or But) and Cu[OC(CF3)R1CH2NMe2]2 (R1 = CF3 or CH3) have been synthesized and characterized by spectroscopic methods. A single-crystal X-ray diffraction study on Cu[OC(CF3)2CH2NHCH2CH2OMe]2 shows that one methoxyethyl group of the aminoalkoxide ligand forms an intramolecular dative bond to the Cu atom to produce a square-pyramidal geometry at the metal center, while the second is linked to the Cu atom of the adjacent molecule, giving an N2O4 octahedral coordination arrangement. For the second Bui-substituted complex, Cu[OC(CF3)2CH2NHBui]2, the X-ray structural analysis demonstrated an N2O2 square-planar geometry, with one alkoxide oxygen atom forming strong H-bonding to an adjacent water molecule. Metal CVD experiments were carried out, showing that the source reagents Cu[OC(CF3)2CH2NHBui]2, Cu[OC(CF3)2CH2NHBut]2, and Cu[OCMe(CF3)CH2NHBui]2, which possess a secondary amino group, are capable of depositing copper metal at temperatures of 250–300 °C under inert Ar carrier gas, while Cu[OCMe(CF3)CH2NMe2]2, with a tertiary amine group, requires the use of reductive H2 carrier gas to induce metal deposition at lower temperatures.

Deposition of osmium thin films using pyrazolate complexes as CVD source reagents

The reaction of Os3(CO)12 with 1.2 eq. of pyrazole (3,5-(CF3)2-pz)H at 190 °C affords triosmium complex Os3(CO)10(3,5-(CF3)2-pz)(μ-H) (1) as the isolable product. Upon further treatment with excess pyrazole (3,5-(CF3)2-pz)H under more forcing conditions, complex 1 converts to a diosmium pyrazolate complex [Os(CO)3(3,5-(CF3)2-pz)]2 (2) in high yield. These osmium complexes are characterized by spectroscopic methods and single crystal X-ray diffraction study, showing the expected triangular and linear Os–Os backbone and with one and two bridging pyrazolate ligands for complexes 1 and 2, respectively. The thermal properties are studied by TG analysis and the deposition experiments are carried out using a cold-wall CVD apparatus. The as-deposited thin films are characterized using XPS, XRD and SEM and electrical resistivity measurement. It seems that the Os metal thin films are best deposited at an optimal temperature of 450–500 °C and using complex 2 as the source reagent.

Preparation and characterization of volatile alkaline-earth metal complexes with multiply coordinated aminoalkoxide ligands

The aminoalkoxide complexes Sr(amak)2 (1) and Ba(amak)2 (2) were prepared by treatment of a multiply-chelating fluorinated aminoalcohol ligand HOC(CF3)2CH2N(CH2CH2OMe)2, (amak)H, with the Group 2 metal reagents Sr(OPri)2 and BaH2 respectively. Single crystal X-ray diffraction studies indicate that complex 1 possesses an 8-coordinate distorted bicapped octahedral geometry with all O and N atoms coordinated to the central Sr cation. However, complex 2 adopts a unique 10-coordinate bicapped square antiprismatic structure, of which the coordination number is increased by two fluorine-to-barium dative interactions. Variable temperature 19F NMR studies show the existence of two inter-convertible isomers in solution and their possible molecular structures are proposed according to their structures in the solid-state. Preliminary investigation suggests that these complexes are good CVD source reagents for depositing SrF2 and BaF2 thin films.