Quantitative Chemical Imaging with Multiplex Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy is a newly developed label-free chemical imaging technique that overcomes the speed limitation of confocal Raman microscopy while avoiding the nonresonant background problem of coherent anti-Stokes Raman scattering (CARS) microscopy. Previous demonstrations have been limited to single Raman band measurements. We present a novel modulation multiplexing approach that allows real-time detection of multiple species using the fast Fourier transform. We demonstrate the quantitative determination of chemical concentrations in a ternary mixture. Furthermore, two imaging applications are pursued: (1) quantitative determination of oil content as well as pigment and protein concentration in microalgae cultures; and (2) 3D high-resolution imaging of blood, lipids, and protein distribution in ex vivo mouse skin tissue. We believe that quantitative multiplex SRS uniquely combines the advantage of fast label-free imaging with the fingerprinting capability of Raman spectroscopy and enables numerous applications in lipid biology as well as biomedical imaging.Chemistry and Chemical BiologyEngineering and Applied Science

Uniform selenization of crack-free films of Cu(In,Ga)Se2 nanocrystals

Crack-free films of Cu(In,Ga)Se2 (CIGS) nanocrystals were deposited with uniform thickness (>1 μm) on Mo-coated glass substrates using an ink-based, automated ultrasonic spray process, then selenized and incorporated into photovoltaic devices (PVs). The device performance depended strongly on the homogeneity of the selenized films. Cracks in the spray-deposited films resulted in uneven selenization rates and sintering by creating paths for rapid, uncontrollable selenium (Se) vapor penetration. To make crack-free films, the nanocrystals had to be completely coated with capping ligands in the ink. The selenization rate of crack-free films then depended on the thickness of the nanocrystal layer, the temperature, and duration of Se vapor exposure. Either inadequate or excessive Se exposure leads to poor device performance, generating films that were either partially sintered or exhibited significant accumulation of carbon and selenium. The deposition of uniform nanocrystal films is expected to be important for a variety of electronic and optoelectronic device applications.Fil: Harvey, Taylor B.. Texas A&M University; Estados UnidosFil: Bonafé, Franco Paúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Updegrave, Ty. University of Texas at Austin; Estados UnidosFil: Voggu, Vikas Reddy. University of Texas at Austin; Estados UnidosFil: Thomas, Cherrelle. University of Texas at Austin; Estados UnidosFil: Kamarajugadda, Sirish C.. University of Texas at Austin; Estados UnidosFil: Stolle, C. Jackson. University of Texas at Austin; Estados UnidosFil: Pernik, Douglas. University of Texas at Austin; Estados UnidosFil: Du, Jiang. University of Texas at Austin; Estados UnidosFil: Korgel, Brian A.. University of Texas at Austin; Estados Unido

Fluoroarene Complexes with Small Bite Angle Bisphosphines : Routes to Amine–Borane and Aminoborylene Complexes

Fluoroarene complexes of the small bite angle bisphosphine Cy2PCH2PCy2 (dcpm) have been prepared: [Rh(dcpm)(η6-1,2-F2C6H4)][Al{OC(CF3)3}4] and [Rh(dcpm)(η6-1,2,3-F3C6H3)][Al{OC(CF3)3}4]. These complexes act as precursors to a previously inaccessible σ-amine–borane complex [Rh(dcpm)(η2-H3B·NMe3)][Al{OC(CF3)3}4] of a small bite-angle phosphine. This complex is a poor catalyst for the dehydrocoupling of H3B·NMe2H. Instead, formation of the bridging borylene complex [{RhH(µ-dcpm)}2(µ-H)(µ-BNMe2)][Al{OC(CF3)3}4] occurs, which has been studied by NMR, mass spectrometry, crystallographic and DFT techniques. This represents a new route to bridging borylene complexes

Micro solar cells, Raman spectroscopy, and flow synthesis of copper indium selenide nanocrystals

Copper indium selenide nanocrystals are an attractive material for solar cell applications due to its favorable bandgap, moderate temperature synthesis, and solution processability in air. Solution processing in particular allows a whole range of new photovoltaic applications to be explored, as most current commercial solar cell technologies (bulk Si, CdTe, and CuIn [subscript 1-x] Ga [subscript x] Se₂) employ high temperatures and/or high vacuums to grow quality crystals that make up the photovoltaic absorber layer. Copper indium selenide (CuInSe₂) nanocrystals are unique in this regard in that they can be spray-deposited at room temperature in ambient conditions to form a solar cell’s light-absorbing layer. One particular application is investigated here: micro groove solar cells using flexible substrates. These solar cells are fabricated by filling micron-scale groove features with CuInSe₂ nanocrystals. The CuInSe₂ nanocrystals make contact with Au and CdS at opposite groove walls to create lateral junctions that allow charge extraction. Micro solar cells were optimized by varying the thicknesses of coatings, wall coating material thicknesses, groove angles, and ligand exchange procedures. Best-performing devices operate in the range of 3% power conversion efficiency utilizing this material set. Raman spectroscopy and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) were utilized to investigate the cationic ordering of CuInSe₂ nanocrystals. In CuInSe₂ nanocrystals, the Raman A₁ mode appears as a broad peak centered at 182 cm⁻¹, which is indicative of the sphalerite, cation-disordered structure. HAADF-STEM, on the other hand, revealed a partially ordered cationic structure in one particle, which is not typical for CuInSe₂. Synthesizing the nanocrystals at higher temperatures and annealing at high temperatures both promoted cation ordering to the chalcopyrite structure. Finally, a flow-through reactor was designed to allow the controlled scale-up synthesis of CuInSe₂ nanocrystals. This reactor utilized coiled glass tubing inside of a bulk heating element and was used to synthesize phase-pure nanocrystals.Chemical Engineerin

Quantitative Chemical Imaging with Multiplex Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy is a newly developed label-free chemical imaging technique that overcomes the speed limitation of confocal Raman microscopy while avoiding the nonresonant background problem of coherent anti-Stokes Raman scattering (CARS) microscopy. Previous demonstrations have been limited to single Raman band measurements. We present a novel modulation multiplexing approach that allows real-time detection of multiple species using the fast Fourier transform. We demonstrate the quantitative determination of chemical concentrations in a ternary mixture. Furthermore, two imaging applications are pursued: (1) quantitative determination of oil content as well as pigment and protein concentration in microalgae cultures; and (2) 3D high-resolution imaging of blood, lipids, and protein distribution in ex vivo mouse skin tissue. We believe that quantitative multiplex SRS uniquely combines the advantage of fast label-free imaging with the fingerprinting capability of Raman spectroscopy and enables numerous applications in lipid biology as well as biomedical imaging

Multiexciton Solar Cells of CuInSe₂ Nanocrystals

Peak external quantum efficiencies (EQEs) of just over 120% were observed in photovoltaic (PV) devices of CuInSe₂ nanocrystals prepared with a photonic curing process. The extraction of more than one electron/hole pair as a result of the absorption of a single photon can occur if multiple excitons are generated and extracted. Multiexciton generation (MEG) in the nanocrystal films was substantiated by transient absorption spectroscopy. We propose that photonic curing leads to sufficient electronic coupling between nanocrystals to enable multiexciton extraction under typical solar illumination conditions. Under low light conditions, however, the EQE drops significantly, indicating that photonic curing-induced ligand desorption creates a significant amount of traps in the film that limit the overall power conversion efficiency of the device

Multiexciton Solar Cells of CuInSe₂ Nanocrystals

Peak external quantum efficiencies (EQEs) of just over 120% were observed in photovoltaic (PV) devices of CuInSe₂ nanocrystals prepared with a photonic curing process. The extraction of more than one electron/hole pair as a result of the absorption of a single photon can occur if multiple excitons are generated and extracted. Multiexciton generation (MEG) in the nanocrystal films was substantiated by transient absorption spectroscopy. We propose that photonic curing leads to sufficient electronic coupling between nanocrystals to enable multiexciton extraction under typical solar illumination conditions. Under low light conditions, however, the EQE drops significantly, indicating that photonic curing-induced ligand desorption creates a significant amount of traps in the film that limit the overall power conversion efficiency of the device

Plastic Microgroove Solar Cells Using CuInSe₂ Nanocrystals

Plastic photovoltaic devices (PVs) were fabricated by spray-depositing copper indium diselenide (CuInSe₂) nanocrystals into micrometer-scale groove features patterned into polyethylene terephthalate (PET) substrates. Each groove has sidewall coatings of Al/CdS and Au and performs as an individual solar cell. These PV groove features can be linked electrically in series to achieve high voltages. For example, cascades of up to 15 grooves have been made with open-circuit voltages of up to 5.8 V. On the basis of the groove geometry, the power conversion efficiencies (PCEs) of the devices reached as high as 2.2%. Using the active area and photovoltaic response of devices determined from light-beam-induced current (LBIC) and photoreflectivity measurements gave PCE values as high as 4.4%

Copper Indium Gallium Selenide (CIGS) Photovoltaic Devices Made Using Multistep Selenization of Nanocrystal Films

The power conversion efficiency of photovoltaic devices made with ink-deposited Cu­(In_<i>x</i>Ga_1–<i>x</i>)­Se₂ (CIGS) nanocrystal layers can be enhanced by sintering the nanocrystals with a high temperature selenization process. This process, however, can be challenging to control. Here, we report that ink deposition followed by annealing under inert gas and then selenization can provide better control over CIGS nanocrystal sintering and yield generally improved device efficiency. Annealing under argon at 525 °C removes organic ligands and diffuses sodium from the underlying soda lime glass into the Mo back contact to improve the rate and quality of nanocrystal sintering during selenization at 500 °C. Shorter selenization time alleviates excessive MoSe₂ formation at the Mo back contact that leads to film delamination, which in turn enables multiple cycles of nanocrystal deposition and selenization to create thicker, more uniform absorber films. Devices with power conversion efficiency greater than 7% are fabricated using the multiple step nanocrystal deposition and sintering process