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Noncentrosymmetric transition-metal dichalcogenides, particularly their 3R polymorphs, provide a robust setting for valleytronics. Here, we report on the selective growth of monolayers and bilayers of MoS2, which were acquired from two closely but differently oriented substrates in a chemical vapor deposition reactor. It turns out that as-grown bilayers are predominantly 3R-type, not more common 2H-type, as verified by microscopic and spectroscopic characterization. As expected, the 3R bilayer showed a significantly higher valley polarization compared with the centrosymmetric 2H bilayer, which undergoes efficient interlayer scattering across contrasting valleys because of their vertical alignment of the K and K' points in momentum space. Interestingly, the 3R bilayer showed even higher valley polarization compared with the monolayer counterpart. Moreover, the 3R bilayer reasonably maintained its valley efficiency over a very wide range of excitation power density from ∼0.16 kW/cm2 to ∼0.16 MW/cm2 at both low and room temperatures. These observations are rather surprising because valley dephasing could be more efficient in the bilayer via both interlayer and intralayer scatterings, whereas only intralayer scattering is allowed in the monolayer. The improved valley polarization of the 3R bilayer can be attributed to its indirect-gap nature, where valley-polarized excitons can relax into the valley-insensitive band edge, which otherwise scatter into the contrasting valley to effectively cancel out the initial valley polarization. Our results provide a facile route for the growth of 3R-MoS2 bilayers that could be utilized as a platform for advancing valleytronics.

A recent study found that magnetization curves for Y3Fe5O12 (YIG) slab and thick films (>20 μm thick) differed from bulk system curves by their longitudinal spin Seebeck effect in a Pt/YIG bilayer system. The deviation was due to intrinsic YIG surface magnetic anisotropy, which is difficult to adopt extrinsic surface magnetic anisotropy even when in contact with other materials on the YIG surface. This study experimentally demonstrates evidence for extrinsic YIG surface magnetic anisotropy when in contact with a diamagnetic graphene interlayer by observing the spin Seebeck effect, directly proving intrinsic YIG surface magnetic anisotropy interruption. We show the Pt/YIG bilayer system graphene interlayer role using large area single and multilayered graphenes using the longitudinal spin Seebeck effect at room temperature, and address the presence of surface magnetic anisotropy due to magnetic proximity between graphene and YIG layer. These findings suggest a promising route to understand new physics of spin Seebeck effect in spin transport.

Van der Waals (vdW) heterostructures, consisting of a variety of low-dimensional materials, have great potential use in the design of a wide range of functional devices thanks to their atomically thin body and strong electrostatic tunability. Here, we demonstrate multi-functional indium selenide (InSe)/black phosphorous (BP) heterostructures encapsulated by hexagonal boron nitride. At a positive drain bias (VD), applied on the BP while the InSe is grounded, our heterostructures show an intermediate gate voltage (VBG) regime where the current hardly changes, working as a ternary transistor. By contrast, at a negative VD, the device shows strong negative differential transconductance characteristics; the peak current increases up to ~5 μA and the peak-to-valley current ratio reaches 1600 at VD = −2 V. Four-terminal measurements were performed on each layer, allowing us to separate the contributions of contact resistances and channel resistance. Moreover, multiple devices with different device structures and contacts were investigated, providing insight into the operation principle and performance optimization. We systematically investigated the influence of contact resistances, heterojunction resistance, channel resistance, and the thickness of BP on the detailed operational characteristics at different VD and VBG regimes.

Amorphous carbon films (ACFs) have recently emerged as one of the best candidates for etching-resistant hardmask materials in advanced semiconductor manufacturing processes. Etching resistivity of ACFs is known to be improved by controlling the relative abundance between sp2 and sp3 bonds. We have investigated the relative abundance between sp2 and sp3 bonds in several ACFs, fabricated by plasma-enhanced chemical vapor deposition at different temperatures, which were analyzed by using X-ray photoemission spectroscopy, Raman spectroscopy, and transmission electron microscopy. We found that the relative abundance of sp2 bond increased as the growth temperature was raised. Furthermore, the ACFs eventually evolved into nano-crystalline graphite with increasing growth temperature.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been extensively studied. Among them, vanadium dichalcogenides, a unique metallic family of the TMDCs, have been considered as pot...

The long stagnation of the photo-conversion efficiency of kesterites below 13% is a source of frustration in the scientific community. In this study, we investigated the effects of sodium on the passivation of grain boundaries and defects in Cu2ZnSnSe4 (CZTSe) grown on a soda-lime glass (SLG) and borosilicate (BS) glass. Because BS glass does not inherently contain sodium, we placed a thin layer of NaF between CZTSe and Mo. The composition of the samples is Cu-poor and Zn-rich. The distribution of sodium and its contributions to phase formation and defects were examined by cross-sectional energy-dispersive X-ray profiling, Raman scattering spectroscopy and imaging, surface potential and photoluminescence. From the experimental results, it can be strongly claimed that sodium ions segregate predominantly near the grain boundaries and reduce CuZn-related defects. These local surface imaging analyses provided the exact locations of the secondary phases. In particular, the photo-assisted scanning probe method enabled us to observe the changes in the optoelectrical properties of the thin films and the carrier behavior within the materials. Further studies with distinct alkali ions and optimal processing conditions will pave a way to improve the performance of kesterite solar cells.

Steam generation by eco-friendly solar energy has immense potential in terms of low-cost power generation, desalination, sanitization, and wastewater treatment. Herein, highly efficient steam generation in a bilayer solar steam generator (BSSG) is demonstrated, which is comprised of a large-area SnSe-SnSe2 layer deposited on a glassy carbon foam (CF). Both CF and SnSe-SnSe2 possess high photothermal conversion capabilities and low thermal conductivities. The combined bilayer system cumulatively converts input solar light into heat through phonon-assisted transitions in the indirect band gap SnSe-SnSe2 layer, together with trapping of sunlight via multiple scattering due to the porous morphology of the CF. This synergistic effect leads to efficient broadband solar absorption. Moreover, the low out-of-plane thermal conductivities of SnSe-SnSe2 and CF confine the generated heat at the evaporation surface, resulting in a significant reduction of heat losses. Additionally, the hydrophilic nature of the acid-treated CF offers effective water transport via capillary action, required for efficient solar steam generation in a floating form. A high evaporation rate (1.28 kg m-2 h-1) and efficiency (84.1%) are acquired under 1 sun irradiation. The BSSG system shows high recyclability, stability, and durability under repeated steam-generation cycles, which renders its practical device applications possible.

Noncentrosymmetric transition-metal dichalcogenides, particularly their 3

A recent study found that magnetization curves for Y

We investigated alternating current driven inorganic electroluminescence (EL) devices, in which chlorobenzene (CB) treated carbon nanotubes (CNTs) were incorporated within the dielectric layer. The devices having CB-treated CNTs exhibited better performance than the reference device without CNTs. Especially, 0.01 wt% of CB-treated CNTs yielded the best results—an enhancement of up to 50% in the luminance, along with a 30% reduction in the current density compared with the reference one. The improvement in EL performance was attributed to the enhanced dielectric constant of the dielectric layer by inclusion of CB-treated CNTs. This is considered to arise from the combined effect of the micro-capacitors from numerous CNTs in the dielectric layer and the interfacial polarization from the C Cl bonds originating from the CB treatment. In addition, it is essential to control the concentration of CNTs low enough to prevent leakage current paths by percolation, here, 0.01 wt% sufficed this condition. Thus, incorporating CB-treated CNTs into the dielectric layer improved the characteristics of the EL devices, which would be considered as a candidate for future display applications.

The van der Waals Kitaev magnet α-RuCl3 has recently garnered considerable attention due to its possible realization of topological spin liquids. Combining Raman spectroscopy with numerical calculations, we report here the thickness dependence of electronic structure and ensuing low-energy excitations for exfoliated α-RuCl3. We observe two pronounced peaks at A1 = 249 meV and A2 = 454 meV, which are assigned to single and double spin-orbit (SO) excitons, respectively. Our numerical calculations support this interpretation by reproducing their spectral energy and shape with the electronic parameters: SO coupling λ = 140 meV, Hund’s coupling JH = 350 meV, and on-site Coulomb interaction U = 2.35 eV. The multiple SO excitons persist down to a single layer, whereas their peaks shift slightly to lower energy. For frequencies below 350 cm−1, both a magnetic continuum and phonons show noticeable thickness dependence. These results demonstrate that a SO entangled jeff = 1/2 picture remains valid in a monolayer limit despite the presence of lattice distortions.

The long stagnation of the photo-conversion efficiency of kesterites below 13% is a source of frustration in the scientific community. In this study, we investigated the effects of sodium on the passivation of grain boundaries and defects in Cu

Circularly polarized Raman and/or photoluminescence (PL) analyses have recently been very important in studying physical properties of many layered materials that were either mechanically exfoliated or grown by chemical-vapor-deposition (CVD) on silicon substrates. Since silicon Raman signal is always accompanied by the circularly polarized Raman and/or PL signal from the layered materials, observation of proper circularly polarized Raman selection rules on silicon substrates would be extremely good indicator that the circularly polarized Raman and/or PL measurements on the layered materials were done properly. We have performed circularly polarized Raman measurements on silicon substrates and compared the results with the Raman intensities calculated by using Raman tensors of the diamond crystal structure. Our experimental results were in excellent agreement with the calculation. Similar circularly polarized Raman analysis done on germanium substrate also showed good agreement.

In2S3 is one of the fascinating materials for a range of optoelectronic applications due to its suitable bandgap and stability. Nonetheless, its photoluminescence (PL) originating from defect states within its bandgap were hardly reported. In this work, high quality In2S3 thin films on SiO2 substrates were synthesized by using physical vapor deposition of In2S3 powder in a hot-wall Quartz tube-furnace. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies of the grown In2S3 films showed that extremely high crystalline quality tetragonal β-In2S3 films were synthesized with preferred growth direction of [1 0 3]. Absorption spectroscopy revealed the In2S3 films have a direct band of ~2.66 eV. Interestingly, our In2S3 films showed an extremely strong PL peak at room temperature at ~1.6 eV. The observed strong PL from our In2S3 films can be attributed to originating from the oxygen isoelectronic substitution at the sulfur site, and its efficiency was affected by oxygen concentrations in In2S3 films. Our In2S3 thin films exhibited remarkably high PL quantum yields (QY) of up to 14% which is comparable to that of GaAs quantum wells (QWs) and CdSe quantum dots (QDs).

The covalently bonded in-plane heterostructure (HS) of monolayer transition-metal dichalcogenides (TMDCs) possesses huge potential for high-speed electronic devices in terms of valleytronics. In this study, high-quality monolayer MoSe2-WSe2 lateral HSs are grown by pulsed-laser-deposition-assisted selenization method. The sharp interface of the lateral HS is verified by morphological and optical characterizations. Intriguingly, photoluminescence spectra acquired from the interface show rather clear signatures of pristine MoSe2 and WSe2 with no intermediate energy peak related to intralayer excitonic matter or formation of MoxW(1–x)Se2 alloys, thereby confirming the sharp interface. Furthermore, the discrete nature of laterally attached TMDC monolayers, each with doubly degenerated but nonequivalent energy valleys marked by (KM, K′M) for MoSe2 and (KW, K′W) for WSe2 in k space, allows simultaneous control of the four valleys within the excitation area without any crosstalk effect over the interface. As an ...

We have investigated strong optical nonlinearity of monolayer MoS2(1–x)Se2x across the exciton resonance, which is directly tunable by Se doping. The quality of monolayer alloys prepared by chemical vapor deposition is verified by atomic force microscopy, Raman spectroscopy, and photoluminescence analysis. The crystal symmetry of all of our alloys is essentially D3h, as confirmed by polarization-dependent second-harmonic generation (SHG). The spectral structure of the exciton resonance is sampled by wavelength-dependent SHG (λ = 1000–1800 nm), where the SHG resonance red-shifts in accordance with the corresponding optical gap. Surprisingly, the effect of compositional variation turns out to be much more dramatic owing to the unexpected increase of B-exciton-induced SHG, which indeed dominates over the A-exciton resonance for x ≥ 0.3. The overall effect is therefore stronger and broader SHG resonance where the latter arises from different degrees of red-shift for the two exciton states. We report the corre...

We report a simple and reliable technique to synthesize high-quality In 2 S 3 films on InAs substrates by using thermal sulfurization in a hot-wall tube furnace. X-ray diffraction and energy dispersive X-ray spectroscopy data confirmed that the synthesized films were cubic β-In 2 S 3 or tetragonal β-In 2 S 3 , depending on growth conditions. Field emission scanning electron microscopy analysis and Raman spectroscopy showed that the In 2 S 3 films are of remarkable crystal quality. Especially, by optimizing the growth conditions, we have grown an extremely high-quality tetragonal β-In 2 S 3 thin film firmly remained on the InAs substrate, for the first time.

In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe2. Two-step growth involving the selenization of pulsed-laser-deposited MoO3 film was employed to yield the MoSe2 monolayer on a SiO2/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second-order susceptibility χ(2) was calculated to be ∼50 pm V−1 at the second harmonic wavelength ∼810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength-dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe2 monolayer exhibits a strong laser-induced damage threshold ∼16 GW cm−2 under picosecond-pulse excitation. Our findings suggest that monolayer MoSe2 can be considered as a promising candidate for high-power, thin-film-based nonlinear optical devices and applications.

We report the complex pseudodielectric function of molybdenum disulfide (MoS2) monolayers for energies from 1.40 to 6.42 eV and temperatures from 35 to 350 K. MoS2 was grown as a continuous monolayer on a SiO2/Si substrate in a two zone hot-wall furnace using a catalyst-free chemical vapor growth process. The monolayer was then transferred onto a sapphire substrate. We investigated the optical properties of MoS2 using a dual-rotating-compensator ellipsometer with the sample in ultrahigh vacuum to prevent degradation and to minimize condensation artifacts in the data at low sample temperatures. Critical-point (CP) energies were determined using numerically calculated second energy derivatives of the spectra. At low temperature, we observed a splitting of A-excitonic peak. This identifies the bound excitonic states, including negatively charged excitons, trion states in monolayer MoS2. Splitting of the B-excitonic peak is also indicated. Blue shifts of the CP energies and enhanced structures with re...

CdS nanowires were synthesized using a simple synthesis process using Au nanoparticles (average diameter: 13 nm) as catalyst. The growth conditions were optimized by varying the substrate temperature and the growth time of a thermal chemical-vapor-deposition system. CdS nanowires were successfully grown at temperatures above 480 °C. In fact, high-quality nanowires, with hexagonal wurtzite structures and an average diameter of 25 nm and length of 1.46 μm, were obtained after a 30-min synthesis at a growth temperature of 520 °C. Electron microscope images revealed that our CdS nanowires, grown at relatively lower growth temperatures, have higher average-aspect-ratio and smaller average-diameter than those previously reported in the literature. Our synthesis method resulted in CdS nanowires only without producing nanorods and nanobelts, which make it unnecessary to filter and purify nanowires from the mixture of nanowires, nanorods, and nanobelts.

We have synthesized functionalized graphene by using direct dispersion of graphite flakes with single-stranded DNA in distilled water. The synthesized graphene-DNA complexes were investigated by using Raman spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), and time-of-flight secondary-ion mass spectroscopy (TOF-SIMS). Raman spectra exhibited typical G-band and 2D-band signatures of graphene at ~1590 cm−1 and ~2700 cm−1, respectively. TOF-SIMS result showed that the graphene layers were successfully functionalized with singlestranded DNA. Mono-layer and few-layer graphene were identified by measuring the layer thickness by using AFM and by analyzing the electron diffraction patterns from TEM measurements.

Although the delivery of biologically functional protein(s) into mammalian cells could be of tremendous value to biomedical research, the development of such technology has been hindered by the lack of a safe and effective delivery method. Here, we present a simple, efficient, and versatile gold nanoparticle-DNA aptamer conjugate (AuNP-Apt)-based system, with nanoblock-like properties, that allows any recombinant protein to be loaded without additional modifications and delivered into mammalian living systems. AuNP-Apt-based protein delivery system was able to deliver various proteins into variety of cell types in vitro without showing cytotoxicity. This AuNP-Apt system was also effective for the local and systemic targeted delivery of proteins in vivo. A local injection of the AuNP-Apt loaded with the apoptosis-inducing BIM protein efficiently inhibited the growth of xenograft tumors in mice. Furthermore, an intravenous injection of AuNP-Apt loaded with both epidermal growth factor (EGF) and BIM resulted in the targeted delivery of BIM into a xenograft tumor derived from EGF receptor-overexpressing cancer cells with no detectable systemic toxicity. Our findings show that this system can serve as an innovative platform for the development of protein-based biomedical applications.

Yttrium (Y)-doped TiO2 nanofibers were successfully fabricated by electrospinning and the subsequent calcination of the as-spun nanofibers. The X-ray diffraction and Raman scattering results showed that the incorporation of Y into TiO2 impedes the rutile-phase growth, facilitates the anatase phase growth. Estimated grain sizes are reduced from 15.71 nm to 8.8 nm with increasing Y-doping concentration. Raman scattering studies confirm the existence of slight brookite phase in case of Y-doped TiO2 nanofibers. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) images revealed that the nanofibers comprised of nanoparticles and that Y-doping reduced the nanoparticle size. The optical band gap energy increased with increasing Y-doping, which can be ascribed to both quantum confinement effect and pure anatase phase transformation from mixed rutile-anatase phase. Y-doping induced a blue-shift of the broad visible photoluminescence (PL) peak and an increase of PL intensity with the concurrent decrease grain size. For 3 at.% Y-doped TiO2 nanofibers PL intensity enormously increased due to defect-related centers on the surface.

The covalently bonded in-plane heterostructure (HS) of monolayer transition-metal dichalcogenides (TMDCs) possesses huge potential for high-speed electronic devices in terms of valleytronics. In this study, high-quality monolayer MoSe

The biofilm-dependent modulation gene (bdm) has recently been shown to play a role in osmotic-induced formation of biofilm in Escherichia coli. In this study, we demonstrated that deletion of bdm results in down-regulation of flagella biosynthesis genes and, consequently, a defect in E. coli motility. In addition, we employed atomic force microscopy to confirm the absence of flagella-like structures on the surface of bdm-null cells. These findings indicate that bdm plays a key role in regulatory pathway for the formation of flagella.

We have investigated the effect of annealing of graphene sheets on the electrical properties of Au/graphene/n-type silicon Schottky diode. Large scale graphene sheets were grown by chemical vapor deposition and then annealed at 300, 400, and 500 °C; one sheet was left un-annealed as the control. The diodes were fabricated by transferring the graphene sheets directly onto n-type Si substrates and the current – voltage ( I–V ) and capacitance – voltage ( C–V ) characteristics were evaluated. The average values of the Schottky barrier height (SBH) and ideality factor ( η ) for the as-fabricated Au/graphene/n-type silicon Schottky diode from I–V measurements were determined to be ∼0.8 ± 0.01 eV and ∼1.79 ± 0.05, respectively, whereas the SBH from C–V measurements was ∼0.89 ± 0.01 eV. The electrical transport characteristics measured at room temperature indicated that annealing of graphene sheet prior to the transfer of the graphene onto the n-Si substrates significantly reduces the electric degradation of the Schottky diodes, even though no distinct differences in other electric properties, including ideality factors and SBHs, before or after annealing of the graphene sheets were observed. Thus, by simply annealing the graphene sheets at 500 °C, we found that the Au/graphene/n-type silicon Schottky diode showed an approximately 3.3-fold lower series resistance as compared with the un-annealed Schottky diode under air exposure of up to 7 days. These annealed diodes showed significantly reduced electrical degradation by removing the potentially trapped H 2 O and/or O 2 at the interface between the graphene layer and the n-Si substrate.

There has been growing research interest in the use of molybdenum disulfide in the fields of optoelectronics and energy harvesting devices, by virtue of its indirect-to-direct band gap tunability. However, obtaining large area thin films of MoS2 for future device applications still remains a challenge. In the present study, the amounts of the precursors (S and MoO3) were varied systematically in order to optimize the growth of highly crystalline and large area MoS2 layers by the chemical vapor deposition method. Careful control of the amounts of precursors was found to the key factor in the synthesis of large area highly crystalline flakes. The thickness of the layers was confirmed by Raman spectroscopy and atomic force microscopy. The optical properties and chemical composition were studied by photoluminescence (PL) and X-ray photoelectron spectroscopy. The emergence of strong direct excitonic emissions at 1.82 eV (A-exciton, with a normalized PL intensity of ∼55 × 103) and 1.98 eV (B-exciton, with a normalized PL intensity of ∼5 × 103) of the sample at room temperature clearly indicates the high luminescence quantum efficiency. The mobility of the films was found to be 0.09 cm2/(V·s) at room temperature. This study provides a method for the controlled synthesis of high-quality two-dimensional (2D) transition metal dichalcogenide materials, useful for applications in nanodevices, optoelectronics and solar energy conversion.

Band-like transport behavior of H-doped transition metal dichalcogenide (TMD) channels in field effect transistors (FET) is studied by conducting low-temperature electrical measurements, where MoTe2 , WSe2 , and MoS2 are chosen for channels. Doped with H atoms through atomic layer deposition, those channels show strong n-type conduction and their mobility increases without losing on-state current as the measurement temperature decreases. In contrast, the mobility of unintentionally (naturally) doped TMD FETs always drops at low temperatures whether they are p- or n-type. Density functional theory calculations show that H-doped MoTe2 , WSe2 , and MoS2 have Fermi levels above conduction band edge. It is thus concluded that the charge transport behavior in H-doped TMD channels is metallic showing band-like transport rather than thermal hopping. These results indicate that H-doped TMD FETs are practically useful even at low-temperature ranges.

High quality gallium sulfide II (GaS) and gallium sulfide III ([Formula: see text]) thin films on [Formula: see text]/Si substrates were simultaneously grown by using physical vapor deposition with GaS powder as a single precursor. By controlling the substrate temperature, we can selectively grow either GaS or Ga2S3 thin films on SiO2/Si substrates. Relatively high and low substrate temperature conditions resulted in Ga2S3 and GaS thin films, respectively. The synthesized thin films were characterized by x-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy analyses.

The optical properties of single-walled carbon nanotubes (SWCNTs) dispersed in aqueous solutions of ribonucleic acids (RNA) purified from Escherichia coli were studied using photoluminescence (PL), Raman, and absorption spectroscopy. SWCNT-RNA complexes, down to a single isolated nanotube level, were successfully synthesized. SWCNT signatures in Raman, PL, and absorption spectroscopy were observed from the SWCNT-RNA complexes. Observation of two distinct PL peaks, one at 1.248 eV and the other at 1.392 eV, confirmed the existence of isolated (6,5) and (6,4) SWCNTs, respectively. Atomic force microscope images and height profiles also showed evidence of isolated SWCNT-RNA complex.

We developed a method to prepare photoconductive channels of hybrid nanostructures based on Au nanohemispheres (Au NHs) and cadmium sulfide nanowires (CdS NWs) for photoconductive applications. The hybrid nanostructures exhibited enhanced absorbance, which was attributed to the strong electronic coupling between plasmons in Au NHs and excitons in CdS NWs. The photoconductive channels based on the hybrid nanostructures showed an increase in photocurrent level by ∼5× compared to bare CdS NWs. Because our strategy can be utilized to improve the photoconductivity of quite versatile photoconductive channels, it can be a powerful method for the development of various advanced optoelectronic and photovoltaic devices.

Control of living cells on biocompatible materials or on modified substrates is important for the development of bio-applications, including biosensors and implant biomaterials. The topography and hydrophobicity of substrates highly affect cell adhesion, growth, and cell growth kinetics, which is of great importance in bio-applications. Herein, we investigate the adhesion, growth, and morphology of cultured breast cancer cells on a silicon substrate, on which graphene oxides (GO) was partially formed. By minimizing the size and amount of the GO-containing solution and the further annealing process, GO-coated Si samples were prepared which partially covered the Si substrates. The coverage of GO on Si samples decreases upon annealing. The behaviors of cells cultured on two samples have been observed, i.e. partially GO-coated Si (P-GO) and annealed partially GO-coated Si (Annealed p-GO), with a different coverage of GO. Indeed, the spreading area covered by the cells and the number of cells for a given culture period in the incubator were highly dependent on the hydrophobicity and the presence of oxygenated groups on GO and Si substrates, suggesting hydrophobicity-driven cell growth. Thus, the presented method can be used to control the cell growth via an appropriate surface modification.

Raman and photoluminescence (PL) spectra of HiPCO and CoMoCat single-walled carbon nanotubes (SWCNTs) dispersed in 1 wt% aqueous surfactant solutions with five different surfactants were studied. The SWCNT suspensions exhibit almost the same Raman spectra, regardless of the surfactant used, but the PL peak positions of all the observed (7,5), (6,5), (8,3), (9,1), and (6,4) SWCNTs show strong surfactant-dependent shifts as large as ∼19 meV, known as solvatochromic shifts. For SWCNTs dispersed in deoxycholate sodium salts and sodium dodecyl sulfate solutions, the amount of the solvatochromic shift decreases as the excitation laser power is increased.

Graphene layers were synthesized using ultrasonic dispersion of graphite flakes followed by ultracentrifugation in sodium cholate and polyoxyethylene nonylphenyl ether aqueous solutions. The synthesized graphene layers were characterized using Raman spectroscopy and atomic force microscopy (AFM). Typical G-band and 2D-band Raman signatures of graphene at ∼1590 cm−1 and ∼2695 cm−1, respectively, were observed in the Raman spectra of the synthesized graphene samples. The AFM height profiles of the synthesized graphene samples on SiO2 substrates show features that can be attributed to graphenes of a single layer or a few layers.

We present the results of applying multi-layer graphene (MLG) films as transparent conductive electrodes in organic photovoltaic devices (OPVs). The MLG films synthesized at different growth temperatures by chemical vapor deposition were applied to OPVs. The performance of OPVs with 1000 °C-grown MLG films was found to be the best with a power conversion efficiency (PCE) of ∼1.3%. The PCE was further enhanced when a hole-blocking TiO X layer was inserted in the device structure, resulting in a PCE of ∼2.6% which is a significantly higher efficiency compared to other previously reported graphene-adopted photovoltaic cells. Our demonstration of the PCE-increase in the graphene-electrode OPVs may foster the application of the fast-progressing graphene technology toward more practical OPV technology.