Characterization of the Interactions between Alq₃ Thin Films and Al Probed by Two-Color Sum-Frequency Generation Spectroscopy

We present the investigation of the vibrational and electronic states of tris(8-hydroxyquinoline) aluminum (Alq3)/Al (Alq3 on Al) interfaces by using two-color infrared-visible sum frequency generation (SFG) spectroscopy. The visible wavelength dependence of the SFG spectra of the 2 nm thick Alq3/Al consists of the vibrational bands derived from the Alq3 at the Al interfaces. The intensities of the peaks derived from the ring stretching modes of the quinolate ligands were significantly enhanced due to the double resonance effect. In contrast, the SFG electronic spectrum obtained from the output photon energy dependence of the SFG peak amplitudes derived from the CC bands of the Al on Alq3 interfaces does not show the wavelength dependences, indicating that the electronic-resonance associated with the π–π* transitions in the quinolate rings are almost vanished at the Al deposited on the Alq3. The disappearance of the electronic-resonance of the CC stretching modes must be caused by the perturbation of the HOMO and LUMO of pristine Alq3 by the interaction with the Al. The spectral features of the two-color SFG spectra of the Al/LiF/Alq3 system show quite different behavior from those of Alq3/Al and Al/Alq3. The shift of the CC stretching modes toward lower frequencies is indicative of the formation of the Alq3 anionic states upon reaction with Li at the interface. Additional broad bands around 1335 and 1450 cm–1, which show the weak excitation wavelength dependence, might be due to the existence of the Li-reacted graphitic carbon-like Alq3

Effects of Interface Electronic Structures on Transition Voltage Spectroscopy of Alkanethiol Molecular Junctions

We investigated the charge transport characteristics of alkanemonothiol (C_<i>n</i>H_2<i>n</i>+1SH, <i>n</i> = number of carbons) molecular junctions by means of transition voltage spectroscopy (TVS) based on the observations of the interface electronic structures. The minimum in the Fowler–Nordheim plot was observed at the average positive and negative sample biases of +1.23 and −1.44 V. These voltages (<i>V</i>_min) were insensitive to the molecular length. The low-energy ultraviolet photoelectron spectroscopy (LE-UPS) measurements revealed the presence of an Au–S bond at a binding energy of 1.4 eV with reference to the Fermi level of the Au substrates. The binding energy of the interface electronic state was independent of the molecular length. The TVS results were analyzed based on the LE-UPS results, including the differences in the measurement conditions. The results were consistently explained by the Au–S bond being responsible for <i>V</i>_min at the negative bias. In addition, another interface state was suggested to be responsible for <i>V</i>_min at the positive bias. The effects of the interface electronic structures besides the apparent barrier height should be considered to understand TVS of molecular junctions with wide energy gap molecules

Single-Crystal Pentacene Valence-Band Dispersion and Its Temperature Dependence

The electronic structures of the highest occupied molecular orbital (HOMO) or the HOMO-derived valence bands dominate the transport nature of positive charge carriers (holes) in organic semiconductors. In the present study, the valence-band structures of single-crystal pentacene and the temperature dependence of their energy–momentum dispersion relations are successfully demonstrated using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). For the shallowest valence band, the intermolecular transfer integral and effective mass of the holes are evaluated as 43.1 meV and 3.43 times the electron rest mass, respectively, at room temperature along the crystallographic direction for which the widest energy dispersion is expected. The temperature dependence of the ARUPS results reveals that the transfer integral values (hole effective mass) are enhanced (reduced) by ∼20% on cooling the sample to 110 K

Temporal profile of zonisamide-induced neurite elongation of primary motor neurons.

<p>Average neurite lengths of differentiation-induced primary motor neurons were automatically measured every 8 h by the IncuCyte. Mean and SE of the average neurite length per cell in three culture dishes are indicated. The two-way ANOVA analysis was applied from 40 to 80 h (the bar on the top) after adding the differentiation medium. The statistical difference is indicated on the right side of the lines. n.s., not significant.</p

Utilizing Carbon Nanotube Electrodes to Improve Charge Injection and Transport in Bis(trifluoromethyl)-dimethyl-rubrene Ambipolar Single Crystal Transistors

We have examined the significant enhancement of ambipolar charge injection and transport properties of bottom-contact single crystal field-effect transistors (SC-FETs) based on a new rubrene derivative, bis(trifluoromethyl)-dimethyl-rubrene (fm-rubrene), by employing carbon nanotube (CNT) electrodes. The fundamental challenge associated with fm-rubrene crystals is their deep-lying HOMO and LUMO energy levels, resulting in inefficient hole injection and suboptimal electron injection from conventional Au electrodes due to large Schottky barriers. Applying thin layers of CNT network at the charge injection interface of fm-rubrene crystals substantially reduces the contact resistance for both holes and electrons; consequently, benchmark ambipolar mobilities have been achieved, reaching 4.8 cm2 V–1 s–1 for hole transport and 4.2 cm2 V–1 s–1 for electron transport. We find that such improved injection efficiency in fm-rubrene is beneficial for ultimately unveiling its intrinsic charge transport properties so as to exceed those of its parent molecule, rubrene, in the current device architecture. Our studies suggest that CNT electrodes may provide a universal approach to ameliorate the charge injection obstacles in organic electronic devices regardless of charge carrier type, likely due to the electric field enhancement along the nanotube located at the crystal/electrode interface

Zonisamide induces regeneration of neurites in primary motor neurons.

<p><b>(A-D)</b> Differentiated primary motor neurons were scratched to evaluate their ability to regenerate neurites. Newly elongated neurite lengths into the scratched area after 48 h were automatically measured by the MetaMorph. Boxed areas in <b>(A)</b> and <b>(B)</b> are magnified in <b>(C)</b> and <b>(D)</b>. <b>(E)</b> The sum of regenerated neurite lengths in the square area (250 μm × 1000 μm) within the scratched area are calculated in four visual fields and the mean and SE are indicated. *p < 0.05 by one-way ANOVA followed by Tukey HSD.</p

Utilizing Carbon Nanotube Electrodes to Improve Charge Injection and Transport in Bis(trifluoromethyl)-dimethyl-rubrene Ambipolar Single Crystal Transistors

We have examined the significant enhancement of ambipolar charge injection and transport properties of bottom-contact single crystal field-effect transistors (SC-FETs) based on a new rubrene derivative, bis(trifluoromethyl)-dimethyl-rubrene (fm-rubrene), by employing carbon nanotube (CNT) electrodes. The fundamental challenge associated with fm-rubrene crystals is their deep-lying HOMO and LUMO energy levels, resulting in inefficient hole injection and suboptimal electron injection from conventional Au electrodes due to large Schottky barriers. Applying thin layers of CNT network at the charge injection interface of fm-rubrene crystals substantially reduces the contact resistance for both holes and electrons; consequently, benchmark ambipolar mobilities have been achieved, reaching 4.8 cm² V^–1 s^–1 for hole transport and 4.2 cm² V^–1 s^–1 for electron transport. We find that such improved injection efficiency in fm-rubrene is beneficial for ultimately unveiling its intrinsic charge transport properties so as to exceed those of its parent molecule, rubrene, in the current device architecture. Our studies suggest that CNT electrodes may provide a universal approach to ameliorate the charge injection obstacles in organic electronic devices regardless of charge carrier type, likely due to the electric field enhancement along the nanotube located at the crystal/electrode interface

Effects of zonisamide on mRNA levels of nerve growth factors and their receptors, as well as neurite markers in primary motor neurons.

<p>Gene expression in primary motor neurons was quantified by quantitative RT-PCR on days 2 and 3 after adding the differentiation medium. The indicated concentration of zonisamide was added 8 h after adding the differentiation medium. Gene expression was normalized to <i>Gapdh</i> and to cells without zonisamide. Mean and SE are indicated (<i>n</i> = 4). *p < 0.05 by one-way ANOVA followed by Tukey HSD.</p

Zonisamide rescues cell death due to oxidative stress.

<p>Primary motor neurons in DMEM/F12 with 0.5% FBS were treated with variable concentrations of zonisamide. After 1 h, cells were exposed to 100 μM hydrogen peroxide (H₂O₂) for 24 h. The number of viable cells was estimated by the MTS assay and was normalized to that without H₂O₂ (control). Mean and SE are indicated (<i>n</i> = 6). *<i>p</i> < 0.05 by one-way ANOVA followed by Tukey HSD.</p

Effects of zonisamide on a mouse model of sciatic nerve autograft.

<p>Model mice were made by cutting the left sciatic nerve at two sites 3 mm apart. Mice (<i>n</i> = 9 in each group) were intragastrically given either control solution or 30 mg/kg/day zonisamide every day from 1 day after surgery up to 1 week <b>(A-D)</b> or 8 weeks <b>(E-H)</b> when mice were sacrificed. <b>(A, B)</b> Six mice in each group were scarified 1 week after surgery. Representative images of Toluidine blue-stained cross sections of the sciatic nerve 0.7 mm distal to the distal transected site are shown. Myelinated axons are indicated by small arrows. Bar = 20 μm. <b>(C, D)</b> Blinded morphometric analysis of the number <b>(C)</b> and area <b>(D)</b> of myelinated axons in a single sciatic nerve preparation 0.7 mm distal to the distal transected site. Mean and SD are indicated (<i>n</i> = 6 mice in each group). *<i>p</i> < 0.05 by Student’s <i>t</i>-test. <b>(E)</b> Temporal profile of sciatic function indices (SFIs) of footprints of mice treated with control solution or 30 mg/kg/day zonisamide every day from 1 day after surgery. Mean and SD of three mice in each group are indicated. Note that the SFIs are improved in zonisamide-treated mice from 6 weeks after sciatic nerve autograft. *<i>p</i> < 0.05 by Student’s <i>t</i>-test. <b>(F)</b> Representative images of hematoxylin and eosin staining of cross sections of tibialis anterior 8 weeks after surgery. Note fewer target fibers and larger fiber sizes in zonisamide-treated tibialis anterior. Bar = 30 μm. <b>(G)</b> Blinded morphometric analysis of cross-sectional areas (CSA) of muscle fibers of tibialis anterior 8 weeks after surgery. Mean and SD are indicated (<i>n</i> > 98 in each group). *<i>p</i> < 0.05 by Student’s <i>t</i>-test. <b>(H)</b> Quantitative RT-PCR of <i>Chrne</i>, <i>Colq</i>, and <i>Rapsn</i> expression in gastrocnemius muscles with uncut and cut sciatic nerves 8 weeks after surgery. Gene expression normalized to <i>Gapdh</i> on the uncut right side of mice taking control solution was set at 1.0, and relative gene expression is indicated by mean and SD (<i>n</i> = 3 in each group). *<i>p</i> < 0.05 by Student’s <i>t</i>-test.</p