The quenching rate constant of the triplet state by molecular oxygen and the efficiency of singlet oxygen generation have been measured for 12 amines in cyclohexane and benzene. For the best electron donors, the average rate constant for quenching by energy transfer is 6.0 × 10 9 M -1 s -1 . For the same compounds, the rate constant of quenching via enchancement of internal conversion is 1.2 × 10 10 M -1 s -1 . The energy transfer component of the total quenching rate constant is almost twice as fast as the maximum from the standard Porter model. The mechanisms of quenching via quintet, singlet, and triplet channels are discussed for amines and aromatic hydrocarbons, and intersystem crossing out of the quintet manifold is proposed.
Highly transparent TiO 2 nanoparticles are explored as a non-electrochromic (non-EC) charge-balancing layer for a high color contrast, bistable electrochromic window (ECW). The TiO 2 nanoparticle (TNP) layer increases the potential at the EC polymer electrode, thereby lowering the working voltage of the ECW. This leads to lower the power consumption of ECWs without loss in the high color contrast (ΔT > 72%) and to remarkably improve the cyclability (ΔT change <1% over 3000 cycles), mainly due to the low overvoltage (<0.1 V) on the electrochromic polymer layer. Furthermore, the ECWs including the non-EC TNP layer show long-term bistability (>2.7 h, 40% increase) and UV stability (ΔT change <1%) to provide a low-power automatic ECW. This finding shows that the charge balanced ECP window has the potential to be used for an energy saving ECW with low-power consumption and will be widely applied in various ECWs as well as electrochemical devices with multiple functions.
The performance of proton exchange membrane fuel cells (PEMFCs) depends on the controlled size, dispersion and density of Pt nanoparticles (NPs) on carbon supports, which are strongly affected by the carbon characteristics and fabrication methods. Here, we demonstrated a high-performance Pt/carbon catalyst for PEMFCs using fluidized bed reactor atomic layer deposition (FBR-ALD) that was realized by an effective matching of the carbon supports for the FBR-ALD process and an optimization of the ionomer content during the preparation of the membrane electrode assembly (MEA). For this, the synthesis of Pt NPs was conducted on two porous supports (Vulcan XC-72R and functionalized carbon) by FBR-ALD. The functionalized carbon possessed a higher surface area with a large pore volume, abundant defects in a disordered structure and a large number of oxygen functional groups compared to those of the well-known Vulcan carbon. The favorable surface characteristics of the functionalized carbon for nucleation produced Pt particles with an increased uniformity and density and a narrow size range, which led to a higher electrochemical surface area (ECSA) than that of Pt/Vulcan carbon and commercial Pt/carbon. The PEMFC test of the respective Pt/carbon samples was investigated, and highly dense and uniform Pt/functionalized-carbon showed the highest performance through optimization of the higher ionomer content compared to that for the ALD Pt growth on Vulcan carbon and commercial Pt/carbon. In addition, the Pt catalyst using ALD demonstrated a significant long-term stability for the PEMFC. This finding demonstrates the remarkable advantages of FBR-ALD for the fabrication of Pt/carbon and the ability of functionalized carbon supports to achieve a high PEMFC efficiency and an enhanced durability.
Pt thin films, using
the Pt precursor, dimethyl(N,N-dimethyl-3-butene-1-amine-N)platinum
(DDAP, C8H19NPt), were deposited by atomic layer
deposition (ALD). The growth characteristics of the Pt thin films
were systemically investigated. A saturated growth rate was obtained
with an increase in precursor and reactant pulse times, revealing
the nature of the ALD self-limiting process. The growth rate increased
with increasing deposition temperature and finally became saturated
above 280 °C, showing a high growth rate of 0.85 Å/cycle.
The short incubation time for Pt nucleation promoted the growth characteristics,
which can be favorable for catalytic applications. The high reactivity
and small adsorbate size produced the relatively high growth rate
of the Pt thin films deposited with the DDAP precursor. A very low
resistivity, close to the value of bulk Pt, was obtained for all Pt
thin films deposited at various temperatures. The low resistivity
was due to the similar crystalline structure and very high purity
of the Pt thin films at all deposition temperatures explored in this
study. In addition, Pt thin films were also deposited on a high-aspect-ratio
substrate and showed good uniformity and step coverage, with a constant
work function, which can be promising for electrode applications.
Synthesis of Pt films by ALD using the DDAP Pt precursor and O2 is a noteworthy approach for obtaining films with a high
growth rate and low resistivity.
5-nm-scale line and hole patterning is demonstrated by synergistic integration of block copolymer (BCP) lithography with atomic layer deposition (ALD).While directed self-assembly of BCPs generates highly ordered line array or hexagonal dot array with the pattern periodicity of 28 nm and the minimum feature size of 14 nm, pattern density multiplication employing ALD successfully reduces the pattern periodicity down to 14 nm and minimum feature size down to 5 nm. Self-limiting ALD process enable the low temperature, conformal deposition of 5 nm thick spacer layer directly at the surface of organic BCP patterns. This ALD assisted pattern multiplication addresses the intrinsic thermodynamic limitations of low χ BCPs for sub-10-nm scale downscaling. Moreover, this approach offers a general strategy for scalable ultrafi ne nanopatterning without burden for multiple overlay control and high cost lithographic tools.
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