Luminescent complexes: Through the design and synthesis of a series of new osmium‐based β‐diketonate carbonyl complexes (see picture; MLCT=metal‐to‐ligand charge transfer, kisc=intersystem crossing constant), a remarkable aromatic tunable fluorescence/phosphorescence ratio was explored. The relative luminescent efficiencies and associated dynamics were evaluated.
was evaluated over a circular area measuring roughly 500 lm in diameter [13]. After deposition, each of the samples was inspected using an optical stereomicroscope and a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer. Growth of IrO 2 Films and Nanorods by Means of CVD: An Example of Compositional and Morphological Control of Nanostructures**By Reui-San Chen, Yi-Sin Chen, Ying-Sheng Huang,* Yao-Lun Chen, Yun Chi, Chao-Shiuan Liu, Kwong-Kau Tiong, and Arthur J. Carty Iridium dioxide, IrO 2 , belongs to the family of transition metal oxides that exhibit metallic conductivity at room temperature. It has been used in applications such as optical switching layers in electrochromic devices, [1] and durable electrode materials for chlorine or oxygen evolution.[2]Moreover, owing to its excellent resistance to the inter-diffusion of oxygen, as well as high thermal and chemical stability, [3] IrO 2 films serve as electrodes for high-density dynamic random access memory (DRAM), or nonvolatile ferroelectric random access memory (NVFRAM), devices.[4] Related investigations have indicated that polarization fatigue of PZT ferroelectric capacitors can be effectively suppressed by using IrO 2 thin film electrodes. [5] In recent reports, IrO 2 was also used to fabricate field-emission cathodes for microelectronic devices and field-emission displays.[6]As a result of these diverse applications, there is a growing need to develop easy and reliable methods for growing IrO 2 phases, either as thin films, or in other physical forms. Various methods such as reactive magnetron sputtering, [7] pulsed laser deposition, [8] and annealing of Ir films in an O 2 atmosphere, [9] have been employed for this purpose. However, CVD, a technique that possesses several advantages including better composition control, high deposition rate, excellent step coverage, and suitability for scale-up, [10] has not yet been successfully employed for IrO 2 even though Ir thin films are normally obtained using O 2 as the carrier gas to prevent carbon iridium metal impurities from being incorporated into the deposited film. [11] Recently, the influence of O 2 partial pressure on the formation of IrO 2 using (MeCp)Ir(COD)/O 2 as the reactive gas mixture, has been discussed by Maury and Senocq. [12] In this communication, we wish to report the successful deposition of IrO 2 thin films using the cold-wall CVD method. Moreover, by optimizing experimental parameters, the formation of distinct, rod-like, aligned IrO 2 nanocrystals can be observed, with good control of growth perpendicular to the substrate surfaces. The structural composition, surface morphology, and spectroscopic properties of the resulting IrO 2 materials are discussed.The reactive mixture (CpMe)Ir(COD)/O 2 was used in CVD experiments that were conducted under three different pressure settings, 1 torr, 10 torr, and 30 torr, while deposition temperatures were separated into six settings ranging from 250 C to 500 C. The combined X-ray diffraction (XRD) pattern...
Highly volatile iridium(I) carbonyl complexes (1-5) with three anionic fluorinated chelates, namely ketoiminate, aminoalkoxide, or iminoalkoxide, have been synthesized and their physical properties relevant to CVD are evaluated. A single-crystal Xray diffraction (XRD) study on Ir(CO) 2 (amakNMe 2 ) (3) confirms a square-planar geometry with two cis-orientated carbonyl ligands. Metallic iridium, polycrystalline IrO 2 thin films, or even patterned IrO 2 nanowires are deposited using Ir(CO) 2 (hfdaN n Pr) (5) as the CVD precursor. A systematic investigation of the deposition of IrO 2 nanowires is conducted, showing a close correlation of observed crystallite morphology with applied system pressure, underlying growth surface, and deposition temperature. Of particular importance, tilted and vertically aligned IrO 2 nanowires are obtained on LiTaO 3 (012) and LiNbO 3 (100) surfaces under a pressure of 30 Torr of oxygen at 425°C. The morphology and structural composition of the IrO 2 are confirmed by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and XRD analyses.
Noble metal thin films have been extensively studied by both the traditional and microelectronics industries for potential applications such as anti-corrosion and anti-oxidation coatings, [1] or in the manufacture of bottom electrodes for high-density memory devices and ferroelectric capacitors. [2] Iridium is considered to be one of the best of these transition metal elements as it possesses a high work function, a stable conductive oxide phase, IrO 2 , and excellent electrical properties. [3] Although physical sputtering seems to be a good choice of method for depositing such iridium metal-containing thin films, CVD will eventually become the preferred method as it has several major ad-vantages, i.e., good conformal coverage, selective deposition on the substrate surface, the capacity for scale-up production with high throughput, and the ability to produce meta-stable materials at low temperatures. [4] The CVD of iridium has been achieved using Ir III reagents, such as tris-acetylacetonato and tris-allyl complexes Ir(acac) 3 and Ir(C 3 H 5 ) 3 , [5] of which the commercially available Ir(acac) 3 is the better choice due to its excellent air stability, but its high melting point and low volatility limit its possible use as the industrial standard. A second type of the source reagent consists of an Ir I metal complex, such as (MeCp)Ir (COD), [6] (hfac)Ir(COD), [7] [Ir(COD)(l-OMe)] 2 , [8] [Ir (COD)(l-OAc)] 2 , and [Ir(CO) 2 -(l-S t Bu)] 2 . [9] Among these Ir I source reagents, the monomeric metal complexes (MeCp)Ir(COD) and (hfac)Ir-(COD) seem to be more useful for CVD due to their enhanced vapor pressure and the negligible possibility of dimer dissociation during vapor phase transport.In this work, we report the synthesis of three new Ir I 1,5cyclooctadiene complexes, in which the anionic ligand is carefully selected in order to ensure formation of the stable metal chelate interaction, while two CF 3 substituents are introduced onto the ligand to improve the volatility of the final metal complexes, [10] making them more suitable for CVD investigations. Moreover, as these complexes differ only slightly in their molecular structure, systematic studies using these iridium precursor compounds will allow us to find the best CVD reagent in the series, and permit an understanding of other parameters that may influence the typical deposition processes.For synthesis of the required iridium compounds, three CF 3 substituted anionic ligands (keim)H, (hfda)H, and (amak)H were first prepared according to the procedures documented in the literature, [11] then the iridium source complexes, namely (keim)Ir(COD) (1), (hfda)Ir(COD) (2), and (amak)Ir(COD) (3) (Scheme 1), were obtained by mixing the corresponding sodium salt of anionic ligand, which was generated in situ from the reaction with NaH, and the iridium chloride starting material [Ir(COD)(l-Cl)] 2 in THF solution at room temperature. After a typical work-up of the reaction mixture, further purification of these compounds was carried out using vacuum sublima...
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