A panchromatic modification of the light absorption spectra of metal-organic frameworks.

The optical absorption of UiO-66-NH2 MOF was red-shifted using a diazo-coupling reaction. The modifications performed with naphthols and aniline yielded reddish samples, and the modifications with diphenylaniline yielded dark violet ones. The photocatalytic activity of these modified MOFs was assessed for methylene blue degradation, showing a good performance relative to traditional TiO2. The degradation performance was found to correlate with the red shift of the absorption edge. These findings suggest potential applications of these materials in photocatalysis and in dye sensitized solar cells.

Slot waveguide ring resonators coated by an atomic layer deposited organic/inorganic nanolaminate.

In this study, slot waveguide ring resonators patterned on a silicon-on-insulator (SOI) wafer and coated with an atomic layer deposited nanolaminate consisting of alternating layers of tantalum pentoxide and polyimide were fabricated and characterized. To the best of our knowledge, this is the first demonstration of atomic layer deposition (ALD) of organic materials in waveguiding applications. In our nanolaminate ring resonators, the optical power is not only confined in the narrow central air slot but also in several parallel sub-10 nm wide vertical polyimide slots. This indicates that the mode profiles in the silicon slot waveguide can be accurately tuned by the ALD method. Our results show that ALD of organic and inorganic materials can be combined with conventional silicon waveguide fabrication techniques to create slot waveguide ring resonators with varying mode profiles. This can potentially open new possibilities for various photonic applications, such as optical sensing and all-optical signal processing.

Post-hot isostatic pressing: a healing treatment for process related defects and laboratory grinding damage of dental zirconia?

OBJECTIVE: Processing parameters (powder granulation, compaction, debinding, greenbody shaping, sintering) and post-sinter rough, even fine grinding are influencing the final mechanical properties of 3Y-TZP. The hypothesis of this study was that post-sinter hot isostatic pressing (post-HIP) would be beneficial for improving reliability and strength of both sintered and coarse ground sintered zirconia by closing or reducing surface and/or small volume defects. METHODS: 75 sintered bars of an experimental 3Y-TZP (3mm×4mm×45mm) with chamfered edges and 15µm diamond surface finish were provided by the manufacturer (Ivoclar Vivadent) and randomly distributed in five groups of N=15 each. G1 served as control (as received); G2 was post-HIPed at 1400°C and G3 at 1350°C, both using a pressure of 195MPa in Ar for 1h; G4 was coarse ground with 120µm diamond disk grain size; G5 was ground 120µm and post-HIPed at 1350°C at 195MPa, 1h in Ar. The specimens were fractured in air in 4 point-bending. Weibull characteristic strength (σ0) in MPa, m parameter (reliability) and confidence intervals (CI) at 90% confidence level are reported. Identification of the critical flaw was performed by SEM on the fractured surface of all specimens and XRD performed in all groups. RESULTS: G1: σ0=973 (932-1016), m=10.6 (7.45-15.1); G2: σ0=930 (871-995), m=6.9 (4.87-9.9); G3: σ0=898 (848-952), m=7.94 (5.6-11.4); G4: σ0=921 (857-991), m=6.35 (4.48-9.11); G5: σ0=881 (847-918), m=11.4 (8.03-16.3). G5 had a significantly lower σ0 than G1. No significant differences were seen in the reliability (m) among the groups. Fractography revealed critical intrinsic subsurface flaws of 10-60µm present in all groups resulting from the processing parameters. No "healing" (i.e. closing of defects by densification) resulted after post-HIP. Grinding sintered zirconia with 120µm diamond disks induced radial cracks of 10-20µm and an important pseudo-cubic phase transformation (56wt%) that was not completely removed after post-HIP. Post-HIP increased slightly the relative density by 0.1% but without improving the strength and reliability. SIGNIFICANCE: Post-HIP was not efficient in closing large (10-60µm) subsurface (volume) processing defects.

Towards broad-bandwidth polarization-independent nanostrip waveguide ring resonators.

We demonstrate a new method for accessing the broad-bandwidth polarization-independent operation of a microring resonator based on the standard photonic nanostrip waveguides. The method employs the selective application of atomic layer deposition to form highly uniform TiO(2) overlayers with the specific dispersion properties. The wide operation window is achieved by matching the wavelength dependencies of the free spectral ranges of the two orthogonal polarizations.

Low-loss silicon slot waveguides and couplers fabricated with optical lithography and atomic layer deposition.

We demonstrate low-loss silicon slot waveguides patterned with 248 nm deep-UV lithography and filled with atomic layer deposited aluminum oxide. Propagation losses less than 5 dB/cm are achieved with the waveguides. The devices are fabricated using low-temperature CMOS compatible processes. We also demonstrate simple, compact and efficient strip-to-slot waveguide couplers. With a coupler as short as 10 µm, coupling loss is less than 0.15 dB. The low-index and low-nonlinearity filling material allows nonlinearities nearly two orders of magnitude smaller than in silicon waveguides. Therefore, these waveguides are a good candidate for linear photonic devices on the silicon platform, and for distortion-free signal transmission channels between different parts of a silicon all-optical chip. The low-nonlinearity slot waveguides and robust couplers also facilitate a 50-fold local change of the waveguide nonlinearity within the chip by a simple mask design.

Angled sidewalls in silicon slot waveguides: conformal filling and mode properties.

Effect of angled sidewalls on the filling and properties of silicon slot waveguides is discussed. We demonstrate complete filling of slot waveguide structures with oxide material systems using the atomic layer deposition technique and discuss use of various slot filling materials. Properties of the optical modes in angled-sidewall slot waveguides are studied. Enhanced vertical confinement is obtained with certain waveguide parameters. The reduced effective mode area enhances e.g. nonlinear effects in the waveguide. We discuss the use of atomic layer deposition in realization of filled slot waveguides optimized for all-optical functionalities.

Involvement of non-NMDA receptors in the rescue of weaver cerebellar granule neurons and sensitivity to ethanol of cerebellar AMPA receptors in oocytes.

The cellular mechanism responsible for the death of cerebellar granule neurons in the weaver mutant mouse is still being intensely investigated. To determine if alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors are involved in producing the weaver phenotype or are altered by the weaver gene, we used (1) reverse transcription and polymerase chain reaction (RT-PCR) to detect transcripts of glutamate receptors (GluR1-4) from wild-type and mutant cerebella; (2) immunocytochemistry to establish the types of glutamate receptors present in granule neurons cultured from normal and homozygous weaver postnatal day 5-6 (P5-6) cerebella; (3) 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a blocker of glutamate (AMPA/Kainate/NMDA) receptors, and 6,7-dinitroquinoxaline-2,3-dione (NBQX), a blocker of AMPA and kainate receptors, to assess the number of neurons and the number of neurons with long neurites in cultures of homozygous weaver granule neurons; (4) two-electrode voltage clamp recordings to study AMPA glutamate receptor expression in Xenopus oocytes after injection of mRNA isolated from cerebella of normal and weaver P5-6, postnatal day 10 (P10) and postnatal day 23 (P23) mice; and (5) ethanol, which at low 1-10 mM concentrations had been shown previously to rescue homozygous weaver granule neurons in culture [Liesi et al., J. Neurosci. Res. 48 (1997) 571-579], to examine its effect on modulation of AMPA receptors expressed from mRNA. By RT-PCR, the mRNA coding for AMPA receptor subunits GluR1-4 were detected from +/+ and wv/wv cerebella, and by immunocytochemistry, GluR1, GluR2/3 and GluR4 were observed to be expressed in cultured +/+ and wv/wv granule cells. CNQX at 10 microM or NBQX at 10 microM significantly increased the number of surviving neurons and the number with long neurites as compared to wv/wv controls. In addition, CNQX was significantly more effective than NBQX. In oocytes injected with mRNA from P10 normal or weaver cerebella, the amplitudes of the responses to kainate were about equal. In contrast, the amplitudes of the kainate-activated currents in oocytes injected with weaver P23 mRNA were about twice as large as the currents observed in oocytes injected with mRNA from normal P23 cerebella, and both were larger than kainate-activated currents observed after injection of P10 normal and weaver mRNA. Kainate-activated AMPA receptor currents in oocytes injected with mRNA from P10 and P23 normal and homozygous weaver cerebella were inhibited by ethanol. There were no significant differences in the inhibition produced by ethanol on currents from P10 or P23 normal and wv/wv mRNA. Thus, P23 weaver cerebellar mRNA expressed more kainate-activated current in oocytes than P23 normal cerebellar mRNA; both normal and weaver cerebellar granule neurons express mRNA coding for functional AMPA receptors that are susceptible to ethanol inhibition.