Marvin H. Wu

North Carolina Central University

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High-resolution electric-field-induced second-harmonic generation with ultrafast Ti:sapphire laser

Review of Scientific Instruments (1996)

Marvin H. Wu Koen Clays André Persoons

The technique of electric-field-induced second-harmonic generation (EFISHG) has been extended by use of a femtosecond, quasi-cw laser pump source. The effects of ultrashort pulse widths on the coherent EFISHG process have been examined and the analysis procedure used for nanosecond pulse EFISHG measurements is found to be suitable for femtosecond measurements in off-resonant regions. A convenient method for measurement of the group velocity mismatch between the fundamental and second-harmonic pulses in solutions has also been developed to accurately describe the femtosecond EFISHG process. Phase-sensitive detection of the modulated second-harmonic signals results in improvements in accuracy and sensitivity over existing nanosecond pulse experiments. This has been demonstrated with a measurement of Γ(−2ω; ω, ω, 0) of an organic molecule, 4-nitroanisole.

Nanosecond

10.1063/1.1147421

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Square-Shaped, Single-Crystal, Monolayer Graphene Domains by Low-Pressure Chemical Vapor Deposition

Materials Research Letters (2013)

Guiping Dai Marvin H. Wu Darlene K. Taylor K. Vinodgopal

Square-shaped, single-crystal, monolayer graphene domains are grown on Cu foils by low-pressure chemical vapor deposition. The domains are remarkably well-aligned along the direction of flow of the gases. Scanning electron microscopy shows that these 'square' domains have clean, smooth edges which permit seamless, defect-free merging of the domains. Raman spectra and transmission electron microscopy together demonstrate that individual domains are single layer, and electron diffraction reveals that these domains are single crystals. The expansion mechanism of 'square' graphene domains is discussed in the context of our aligned, tailored domain shapes. This work represents an important step toward realization of fabrication of larger area, single-crystal monolayer graphene sheets with controllable shape and alignment.

10.1080/21663831.2013.772078

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Citations (21)

Millimeter wave direct-current transmission and reflection spectral data of some organic photo-responsive materials

Data in Brief (2019)

Biswadev Roy Taylor Knapp Corinne Miller Abay Gadisa Harald Ade

Voltage data acquired after probe signal transmitted through the organic film and reflected off the film surface as a function of 0.36 mW millimeter wave signal frequency in the range 110-160 GHz. Five different organic photovoltaic (OPV) materials and one 95:5 blend produced at 2 spin rates are used. These materials are a) fluorinated 2-alkyl-benzol[d] [1-3]triazole (FTAZ), a high hole-mobility polymer used for transistors and photovoltaics, b) diketopyrrolopyrrole (DPP3T), an acceptor polymer used in field-effect transistors (FET), c) Y5(PffBT4T-2OD) film that possesses remarkable temperature controllable morphology, d) a neat conjugated polymer P3HT, Poly(3-(hexylthiophene-2,5diyl) film that is used in optoelectronic devices and as a conductive binder for Li-ion batteries, e) phenyl-C61-butyric acid methyl ester (PCBM) films and its soluble derivatives used as n-type organic semiconductors, and f) excitonic photovoltaic material 95%:5% donor-acceptor blend P3HT:PCBM produced by 2 different spin rates. Measurement of direct-current (dc) transmitted and reflected power (RF voltage signal) are measured using a newly developed continuous wave (CW) D-waveguide band probe (110-160 GHz) apparatus named time-resolved millimeter wave conductivity (TR-mmWC) [1]. Transmission and first surface reflection voltages are captured by a zero-bias Schottky barrier diode (ZBD) and converted to relevant dc voltages. Original voltage signal datasets attached with this can be utilized for photovoltaic, dielectric property estimation, and other semiconductor physics applications. A manually collected dataset of transmission and reflection coefficient at incident probe power level ∼0.9 mW for 95:5 P3HT:PCBM films produced at 2 different spin rates, and one separately only for the neat P3HT film are also presented here in tabular form.

Reflection

Extremely high frequency

10.1016/j.dib.2019.104996

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Synthesis and Characterization of CdS/CdS x Se1 -x Nanowires

APS March Meeting Abstracts (2017)

Kleyser Agueda Lopez Marvin H. Wu

Characterization

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<title>Relaxation dynamics of silicon quantum dots in silica</title>

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (1998)

D. O. Henderson Marvin H. Wu R. Mu Akira Ueda C. W. White

Silicon ions were implanted into fused silica substrates at doses of 1 by 10²¹, 2 by 10²¹, 5 by 10²¹, and 1 by 10²² ions/cm³. The implanted substrates were subsequently annealed at 1100 degrees C for one hour in a reducing atmosphere. Optical absorption spectra recorded after the annealing treatment showed absorption onsets at 316, 373, 434 and 493 nm for substrates implanted with 1 by 10²¹, 2 by 10²¹, 5 by 10²¹, and 1 by 10²² ions/cm³ respectively. Static photoluminescence (PL) measurements indicated red emission between 720 and 770 nm with a slightly increasing red shift with ion dose. Time resolved PL at room temperature revealed slow and fast lifetimes which increased with decreasing temperature. TEM studies showed that the particles size increased with increasing ion dose with typical particle sizes ranging between 2 and 5 nm indicating quantum confinement of the exciton which can account for the blue shift in the absorption edge with decreasing ion dose. However, the maxima in the PL spectra for all ion doses are relatively independent of the ion dose and are strongly Stokes shifted from the absorption spectra suggesting that radiative recombination occurs from a common luminescent center, possibly a surface or interfacial state in the SiO_x layer surrounding the nanocrystal.

Absorption edge

10.1117/12.321961

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Dispersion of Third Order Nonlinear Optical Properties of Squaraines.

PhDT (1995)

Marvin H. Wu

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Enhanced Performance of E-Bike Motive Power Lead–Acid Batteries with Graphene as an Additive to the Active Mass

ACS Omega (2018)

Haiyan Hu Ning Xie Chen Wang Li‐Ya Wang R. M. Privette

The effects of both graphene nanoplatelets and reduced graphene oxide as additives to the negative active material in valve-regulated lead-acid batteries for electric bikes were investigated. Low-temperature performance, charge acceptance, cycle performance, and water loss were investigated. The test results show that the low-temperature performance, charge acceptance, and large-current discharge performance of the batteries with graphene additives were significantly improved compared to the control battery, and the cycle life under 100% depth of discharge condition was extended by more than 52% from 250 to 380 cycles. Meanwhile, the amount of water loss from the batteries with graphene changed only slightly compared with the control cells. The excellent performance of the batteries can be ascribed to the graphene promoting the negative-plate charge and discharge processes and suppressing the growth of lead sulfate crystals.

10.1021/acsomega.8b00353

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Prejudice toward Muslims in New Zealand: insights from the New Zealand attitudes and values study

New Zealand journal of psychology (2020)

Chris G. Sibley M. Usman Afzali Nicole Satherley Anastasia Ejova Samantha Stronge

Following the March 15th Christchurch terrorist attack, members of our research team have been repeatedly asked to comment or provide summary statistics from the New Zealand Attitudes and Values Study (NZAVS) on prejudice toward Muslims. As the curators of the NZAVS, we think that these findings should be in the public domain and accessible to as wide an audience as possible. In this article, we aim to provide a comprehensive summary of what we know from the NZAVS about attitudes toward Muslims and prejudice in New Zealand more generally. From 2012 onwards, the NZAVS included a feeling thermometer rating of people’s level of warmth toward Muslims. Here, we summarize what we know from the NZAVS about levels of warmth toward Muslims in the New Zealand population. We describe the distribution of thermometer ratings of warmth toward Muslims annually from 2012 onward, and compare these with thermometer ratings of a range of other groups that we also track. We present a regression model documenting the extent to which a broad range of demographics and aspects of personality are associated with low levels of warmth toward Muslims, and present a parallel model assessing warmth ratings toward immigrants as a comparison. Finally, we present a series of growth curve models outlining the relative level and rate of change over time in warmth toward Muslims and other groups from 2012-2018. Results from these analyses indicate that over the 2012-2018 period, levels of warmth toward Muslims in New Zealand were comparatively low relative to warmth ratings of other groups. However, warmth toward Muslims has also been steadily but gradually increasing over time in New Zealand.

Prejudice (legal term)

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Comparison of time-resolved millimeter-wave responses between aged and new perovskite thin films

Biswadev Roy Jingshan Chai Rui Su Franky So Marvin H. Wu

<p>This paper emerged out of analyzing simultaeously obtained microwave differential absorption profiles for perovskite thin film (methyl ammonium lead iodide) 300nm thick spun on glass substrate. The film was photoexcited using a 532 nm 0.69ns pulsewidth pulsed laser and the RF voltages obtained in the averaged signal are analyzed to point out differences in the averaged signal parameters (conductance and charge transport realted parameters) for a new and an aged perovskite sample.</p>

SIGNAL (programming language)

10.36227/techrxiv.22082360

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Numerical Simulation of Multi-Particle Optical Trapping

APS (2003)

M. G. Watson Marvin H. Wu R. Mu D. O. Henderson

Particle (ecology)

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