Effect of crown ethers on the ground and excited state reactivity of samarium diiodide in acetonitrile

Electron transfer from the ground and excited states of Sm[15-crown-5](2)I(2) complex to a series of electron acceptors (benzaldehyde, acetophenone, benzophenone, nitrobenzene, benzyl bromide, benzyl chloride, 1-iodohexane, and 1,4-dinitrobenzene) was investigated in acetonitrile. Electron transfer from the ground state of the Sm(II)-crown system to aldehydes and ketones has a significant inner sphere component indicating that the oxophilic nature of Sm(II) prevails in the system even in the presence of bulky ligands such as 15-crown-5 ether. Activation parameters for the ground state electron transfer were determined, and the values were consistent with the proposed mechanistic models. Since crown ethers stabilize the photoexcited states of Sm(II), the photochemistry of Sm[15-crown-5](2)I(2) system in solution state has been investigated in detail. The results suggest that photoinduced electron transfer from Sm(II)-crown systems to a wide variety of substrates is feasible with rate constant values as high as 10(7) M(-1) s(-1). The results described herein imply that the present difficulty of manipulating the extremely reactive excited state of Sm(II) in solution phase can be overcome through stabilizing the excited state of the divalent metal ion by careful design of the ligand systems.     

Development and Certification of NIST Standard Reference Materials for Relative Raman Intensity Calibration

In analytical Raman spectroscopy it becomes increasingly important to employ a procedure for the correction of the relative intensity of Raman spectra. The determination of the intensity response function of a Raman instrument traditionally has been carried out through a white light source that has been calibrated for its relative spectral irradiance. While this method will furnish a correction curve to yield spectra corrected to relative Raman intensity, it is often cumbersome and fraught with experimental difficulties that can profoundly affect the reliability of the correction procedure. An alternate methodology that permits a simplified calibration of the Raman instrument response function is based on the use of luminescent glass standards that transfer a white light calibration onto the Raman measurement system. In this procedure, a measurement of the luminescence of an intensity standard, whose relative irradiance has been determined, provides a means to establish the instrument response function. Correction of measured spectra by this function furnishes spectra that are free of instrumental intensity artifacts. Based on this approach, NIST is developing a series of Standard Reference Materials (SRMs) for the calibration of Raman intensity. This process, and the results obtained thereby, is described for Raman spectroscopy measurements employing 785nm excitation. The procedure is valid for both macro-sampling and micro-sampling Raman work.     

Measuring estrogens using flow injection immunoanalysis with liposome amplification

A solid-phase competitive immunoassay is performed in flow injection analysis for the measurement of the hormone 17-β-estradiol. The flow injection analysis system incorporates a column-type reactor packed with solid silica particles onto which we have covalently immobilized the antigen 17-β-estradiol. Anti-estradiol is noncovalently conjugated to the liposome through a streptavidin-biotin linkage. When mixed with a sample containing the antigen, the antibody binding sites on the liposomes are complexed which reduces the binding of liposomes to the solid support in a concentration-dependent manner. Sequential immunoassays are performed on-column following a simple regeneration step.     

Single transverse mode control of VCSEL by photonic crystal and trench patterning

Single transverse mode control is achieved for multimode GaAs-based VCSEL by utilizing photonic crystal design and etched trench structure. Theoretical analysis is initially performed for photonic crystal design with various lattice constants and air holes diameter. The fabricated photonic crystal VCSEL with etched trench structure exhibits single mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single mode output spectrum throughout a wide operating current range. Comparison of typical oxide VCSEL, trench oxide VCSEL, and photonic crystal oxide VCSEL employing trench structure is presented. By combining photonic crystal and trench structure, single transverse mode operation of photonic crystal VCSEL can be much more strictly controlled.     

Effect of oxide aperture on the performance of 850 nm vertical-cavity surface-emitting lasers

An experimental study has been presented of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs) operating in the 850 nm region of the electromagnetic spectrum. In this regard, various relevant VCSEL samples with numerous oxide aperture sizes have been fabricated and characterized. Thorough investigations of the electrical as well as optical characteristics of the fabricated samples have been performed, which include the overall device performance as a function of the oxidize aperture sizes. It is reported that the VCSELs with oxide aperture size <10 μm require low threshold currents (<1 mA). Further, the differential quantum efficiencies up to 28% corresponding to wall-plug efficiencies of up to 15% were measured for a number of these devices.     

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Catalytic Ni(II) in reactions of SmI2: Sm(II)- or Ni(0)-based chemistry?

The addition of catalytic amounts of Ni(II) salts provide enhanced reactivity and selectivity in numerous reactions of SmI(2), but the mechanistic basis for their effect is unknown. We report spectroscopic and kinetic studies on the mechanistic role of catalytic Ni(II) in the samarium Barbier reaction. The mechanistic studies presented herein show that the samarium Barbier reaction containing catalytic amounts of Ni(II) salts is driven solely by the reduction of Ni(II) to Ni(0) in a rate-limiting step. Once formed, Ni(0) inserts into the alkyl halide bond through oxidative addition to produce an organonickel species. During the reaction, the formation of colloidal Ni(0) occurs concomitantly with Ni(0) oxidative addition as an unproductive process. Overall, this study shows that a reaction thought to be driven by the unique features of SmI(2) is in fact a result of known Ni(0) chemistry.     

Highly confined and continuous single-mode operation of self-align photonic crystal oxide VCSEL

In this letter, we report on single-mode operation of originally multi-mode oxide VCSEL by using etched photonic crystal air holes and unique trench structure. The device fabrication utilized conventional photolithography; with simplified lithography step of self-aligning the photonic crystal and trench structures to the laser aperture for efficient and vigorous device processing. The fabricated photonic crystal VCSEL with trench device exhibits a single-mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single-mode output spectra at wide operating current range. The results are compared with conventional multi-mode oxide VCSEL of similar device geometry. In addition, theoretical analysis is presented for developing further understanding of the photonic crystal VCSEL.