Methane as an effective hydrogen source for single-layer graphene synthesis on Cu foil by plasma enhanced chemical vapor deposition

A single-layer graphene is synthesized on Cu foil in the absence of H(2) flow by plasma enhanced chemical vapor deposition (PECVD). In lieu of an explicit H(2) flow, hydrogen species are produced during the methane decomposition process into their active species (CH(x<4)), assisted with the plasma. Notably, the early stage of growth depends strongly on the plasma power. The resulting grain size (the nucleation density) has a maximum (minimum) at 50 W and saturates when the plasma power is higher than 120 W because hydrogen partial pressures are effectively tuned by a simple control of the plasma power. Raman spectroscopy and transport measurements show that decomposed methane alone can provide a sufficient amount of hydrogen species for high-quality graphene synthesis by PECVD.

One-step graphene coating of heteroepitaxial GaN films

Today, state-of-the-art III-Ns technology has been focused on the growth of c-plane nitrides by metal-organic chemical vapor deposition (MOCVD) using a conventional two-step growth process. Here we show that the use of graphene as a coating layer allows the one-step growth of heteroepitaxial GaN films on sapphire in a MOCVD reactor, simplifying the GaN growth process. It is found that the graphene coating improves the wetting between GaN and sapphire, and, with as little as ~0.6 nm of graphene coating, the overgrown GaN layer on sapphire becomes continuous and flat. With increasing thickness of the graphene coating, the structural and optical properties of one-step grown GaN films gradually transition towards those of GaN films grown by a conventional two-step growth method. The InGaN/GaN multiple quantum well structure grown on a GaN/graphene/sapphire heterosystem shows a high internal quantum efficiency, allowing the use of one-step grown GaN films as 'pseudo-substrates' in optoelectronic devices. The introduction of graphene as a coating layer provides an atomic playground for metal adatoms and simplifies the III-Ns growth process, making it potentially very useful as a means to grow other heteroepitaxial films on arbitrary substrates with lattice and thermal mismatch.

Reduction of graphene damages during the fabrication of InGaN/GaN light emitting diodes with graphene electrodes

Although graphene looks attractive to replace indium tin oxide (ITO) in optoelectronic devices, the luminous efficiency of light emitting diodes (LEDs) with graphene transparent conducting electrodes has been limited by degradation in graphene taking place during device fabrication. In this study, it was found that the quality of graphene after the device fabrication was a critical factor affecting the performance of GaN-based LEDs. In this paper, the qualities of graphene after two different device fabrication processes were evaluated by Raman spectroscopy and atomic force microscopy. It was found that graphene was severely damaged and split into submicrometer-scale islands bounded by less conducting boundaries when graphene was transferred onto LED structures prior to the GaN etching process for p-contact formation. On the other hand, when graphene was transferred after the GaN etch and p-contact metallization, graphene remained intact and the resulting InGaN/GaN LEDs showed electrical and optical properties that were very close to those of LEDs with 200 nm thick ITO films. The forward-voltages and light output powers of LEDs were 3.03 V and 9.36 mW at an injection current of 20 mA, respectively.

Room-temperature electroluminescence from germanium in an Al(0.3)Ga(0.7)As/Ge heterojunction light-emitting diode by Γ-valley transport

Group-IV materials for monolithic integration with silicon optoelectronic systems are being extensively studied. As a part of efforts, light emission from germanium has been pursued with the objective of evolving germanium into an efficient light source for optical communication systems. In this study, we demonstrate room-temperature electroluminescence from germanium in an Al(0.3)Ga(0.7)As/Ge heterojunction light-emitting diode without any complicated manipulation for alternating material properties of germanium. Electroluminescence peaks were observed near 1550 nm and the energy around this wavelength corresponds to that emitted from direct recombination at the Γ-valley of germanium.

Vertical array of ZnO submicrorods on periodically polarity-inverted templates using solution method

Vertically aligned ZnO nano/submicrorods are grown on periodically polarity-inverted (PPI) ZnO templates by a solution-based growth method without any catalyst. For the selective growth of ZnO submicrorods, PPI ZnO structures are used for templates made by using a polarity control technique of ZnO with CrN and Cr2O3 intermediate layers. After syntheses of ZnO nanostructures on PPI ZnO, the vertically aligned ZnO rods were grown only onto the Zn-polar regions.

Catalyst-free metal-organic chemical vapor deposition growth of InN nanorods

We demonstrated the successful growth of catalyst-free InN nanorods on (0001) Al2O3 substrates using metal-organic chemical vapor deposition. Morphological evolution was significantly affected by growth temperature. At 710 degrees C, complete InN nanorods with typical diameters of 150 nm and length of approximately 3.5 microm were grown with hexagonal facets. theta-2theta X-ray diffraction measurement shows that (0002) InN nanorods grown on (0001) Al2O3 substrates were vertically aligned along c-axis. In addition, high resolution transmission electron microscopy indicates the spacing of the (0001) lattice planes is 0.28 nm, which is very close to that of bulk InN. The electron diffraction patterns also revealed that the InN nanorods are single crystalline with a growth direction along (0001) with (10-10) facets.

Near room-temperature synthesis of transfer-free graphene films

Large-area graphene films are best synthesized via chemical vapour and/or solid deposition methods at elevated temperatures (~1,000 °C) on polycrystalline metal surfaces and later transferred onto other substrates for device applications. Here we report a new method for the synthesis of graphene films directly on SiO(2)/Si substrates, even plastics and glass at close to room temperature (25-160 °C). In contrast to other approaches, where graphene is deposited on top of a metal substrate, our method invokes diffusion of carbon through a diffusion couple made up of carbon-nickel/substrate to form graphene underneath the nickel film at the nickel-substrate interface. The resulting graphene layers exhibit tunable structural and optoelectronic properties by nickel grain boundary engineering and show micrometre-sized grains on SiO(2) surfaces and nanometre-sized grains on plastic and glass surfaces. The ability to synthesize graphene directly on non-conducting substrates at low temperatures opens up new possibilities for the fabrication of multiple nanoelectronic devices.

Low Temperature SiGe Heteroepitaxy by Ultrahigh Vacuum Electron Cyclotron Resonance Chemical Vapor Deposition

Dislocation-free Si1−xGex epilayers are successfully grown on (100) silicon at 440°C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD). The effects of process parameters on the crystallinity of Si1−xGex epitaxial layers were studied. As the GeH4 flow rate increases and consequently Ge fraction increases above 20%, Si1−xGex epilayers become damaged heavily by ions. When Ge fraction is larger than 20%, process parameters like total pressure need to be adjusted to reduce the ion flux for high quality Sil−xGex. Growth rate of Si1−xGex epitaxial layers increases at 440°C with Ge content in the film. It is presumed that the hydrogen desorption from the surface is the rate-limiting step, however, the enhancement in growth rate is comparatively suppressed and delayed.

The optimal tumor response assessment in patients with HCC after treatment of TACE

215

Background: WHO or RECIST has been considered as suboptimal methods for tumor response assessment in HCC, especially receiving locoregional therapies. Recently, new modified methods having concept of viable tumor has been proposed. Herein we compared the efficacy to assess response and to predict prognosis between WHO, RECIST, EASL, mRECIST in HCC patients receiving TACE.

Methods: We retrospectively reviewed 141 HCC patients who were newly diagnosed and received TACE between August 2005 and November 2006. Among them, 98 patients who were available for assessing treatment response were analyzed at 1 month after 2nd TACE. We evaluated intermethod aggreement between methods and assessed the efficacy predicting time to progression (TTP) and overall survival (OS).

Results: The results of tumor responses (number of CR/ PR/ SD/ PD) by WHO/ RECIST/ EASL/ mRECIST were 1/ 14/ 74/ 9, 1/ 12/ 77/ 8, 34/ 34/ 25/ 5, 34/ 28/ 31/ 5, respectively. The κvalue of intermethod agreement for EASL vs WHO, EASL vs RECIST, mRECIST vs WHO, and mRECIST vs RECIST was 0.102, 0.088, 0.112 and 0.122, respectively. The κvalue for WHO vs RECIST and EASL vs mRECIST was 0.759 and 0.883 (p=0.00). Hazard ratios for TTP in responders compared with nonresponders were 0.313 (95% CI; 0.19-0.52, p=0.00) for EASL and 0.335 (95% CI; 0.21-0.54, p=0.00) for mRECIST. Hazard ratios for survival in responders compared with nonresponders were 0.208 (95% CI; 0.12-0.37, p=0.00) for EASL and 0.269 (95% CI; 0.15-0.48, p=0.00) for mRECIST. In the univariate analysis, tumor size, infiltrative type, PVT, EASL responder, and mRECIST responder were significant risk factors for survival. Multivariate analysis showed EASL responder (HR 0.165, 95% CI 0.056-0.486, p=0.001) and infiltrative type (HR 4.504, 95% CI 1.579-12.848, p=0.005) were independent predictable factors for survival.

Conclusions: The recent proposed methods showed different characteristics from preexisting methods in assessing treatment response and furthermore, responder by EASL method was independent predictor for survival in HCC patients receiving TACE. EASL method should be applied as response assessment method for HCC patients receiving TACE.

No significant financial relationships to disclose.

The Neural Nanoprobe: Physically Decoupling the Neural Recording Site From the Headstage

The ability to record neural ensembles from awake, behaving animals is one of the most important and successful components of the neuroscience experimental toolbox. However, even the most advanced modern systems have limitations due to the physical coupling of the recording site with the headstage. These systems can only record from a limited number of structures at any one time and have particular difficulty recording large ensembles from animals with thin skulls (e.g., mice, songbirds). Current systems cannot record from fragile structures (spinal cord, peripheral nerves and ganglia) during behavior because the wire electrodes would shred the fragile nerves as the animal moves. We propose the concept of a neural nanoprobe that is physically decoupled from a separately implanted waystation. Because the nanoprobes are not connected to the waystation by physical wires, multiple nanoprobes could be placed in multiple neural structures, all transmitting to a single, separate waystation. Because the nanoprobes effectively float in the cellular matrix, they are safe to put in fragile structures. The waystation does not need to be implanted in the fragile structures; it only needs to be electrically coupled to them. The first step to the realization of this device is a low-power, high-fidelity method for communicating between the nanoprobe and the waystation. In this abstract, we report a successful test proving the viability of using the brain itself as the conducting medium through which the nanoprobe and waystation can communicate. Initial tests show that neural signals from multiple transmission sites can be sent to a single, separated receiver. We first identified the current-loss of sine-waves transmitted through live (anesthetized) brain tissue. We found negligible current-loss across frequencies ranging from 100 kHz–50 MHz across distances as much as 15 mm. As these frequencies are larger than any known frequencies used by neural signals, they are unlikely to interfere with neural function. We next measured the ability to transmit and receive pre-recorded neural signals (sampled at 20 kHz), using pre–recorded signals to determine the fidelity of transmission. The two different signals were transmitted, received, and successfully demodulated with high-fidelity, even with transmission currents as low as 2 μA. Both the transmitters and the receiver each had their own battery power supply to ensure that they used separate, floating grounds. Finally, to ensure that the intra-brain communication signals did not interfere with neural activity, we recorded extra-cellular potentials before, during, and after the test. No changes were observed in spike shape, spike frequency, bursting, or other cellular properties, demonstrating the safety of this technique. Supported by a grant from the Institute for Engineering in Medicine (U Minnesota) and training grant support from T90-DK070106. Corresponding author; email: redish@umn.edu

Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers

Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers are investigated by tight-binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. It is observed in the TBMD simulations that two single vacancies coalesce into a 5-8-5 double vacancy at the temperature of 3000 K, and it is further reconstructed into a new defect structure, the 555-777 defect, by the Stone-Wales type transformation at higher temperatures. First principles calculations confirm that the 555-777 defect is energetically much more stable than two separated single vacancies, and the energy of the 555-777 defect is also slightly lower than that of the 5-8-5 double vacancy. In TBMD simulation, it is also found that the four single vacancies reconstruct into two collective 555-777 defects which is the unit for the hexagonal haeckelite structure proposed by Terrones et al. [Phys. Rev. Lett. 84, 1716 (2000)].

Heat-induced transformation of nanodiamond into a tube-shaped fullerene: a molecular dynamics simulation

Heat-induced structural transformation in nanodiamond of diameter approximately 1.4 nm is investigated by tight-binding molecular dynamics simulations using the environment-dependent tight-binding carbon potential. The nanodiamond is found to transform into a tube-shaped fullerene via annealing. Three interesting mechanisms for promoting inner carbon atoms of the nanodiamond into the surface carbon atoms of the tubular structure are observed. The "flow-out" mechanism prevails at temperatures lower than 2500 K and the "direct adsorption" and "push-out" mechanisms are observed at higher temperatures.

Porphobilinogen synthase from pea: expression from an artificial gene, kinetic characterization, and novel implications for subunit interactions

Porphobilinogen synthase (PBGS) is present in all organisms that synthesize tetrapyrroles such as heme, chlorophyll, and vitamin B(12). The homooctameric metalloenzyme catalyzes the condensation of two 5-aminolevulinic acid molecules to form the tetrapyrrole precursor porphobilinogen. An artificial gene encoding PBGS of pea (Pisum sativum L.) was designed to overcome previous problems during bacterial expression caused by suboptimal codon usage and was constructed by recursive polymerase chain reaction from synthetic oligonucleotides. The recombinant 330 residue enzyme without a putative chloroplast transit peptide was expressed in Escherichia coli and purified in 100-mg quantities. The specific activity is protein concentration dependent, which indicates that a maximally active octamer can dissociate into less active smaller units. The enzyme is most active at slightly alkaline pH; it shows two pK(a) values of 7.4 and 9.7. Atomic absorption spectroscopy shows maximal binding of three Mg(II) per subunit; kinetic data support two functionally distinct types of Mg(II) and the third appears to be nonphysiologic and inhibitory. Analysis of the protein concentration dependence of the specific activity suggests that the minimal functional unit is a tetramer. A model of octameric pea PBGS was built to predict the location of intermolecular disulfide linkages that were revealed by nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. As verified by site-specific mutagenesis, disulfide linkages can form between four cysteines per octamer, each located five amino acids from the C-terminus. These data are consistent with the protein undergoing conformational changes and the idea that whole-body motion can occur between subunits.

A comparison of maximum cystometric bladder capacity with maximum environmental voided volumes

The aim of the study was, to determine whether maximum cystometric capacity accurately reflects the maximum functional bladder volume in women with urinary incontinence. We performed a retrospective chart review involving 85 women between the ages of 22 and 89 with primary complaints of urinary incontinence. The maximum cystometric capacity as determined by cystometry was compared with the maximum environmental voided volumes as recorded in a 24-hour voiding diary, using Pearson's correlation coefficients and paired t-tests. Patients diagnosed as having a small bladder capacity (< 300 ml maximum volume) based on cystometry were also examined with contingency table analysis to determine whether the bladder volumes in the voiding diaries supported the diagnosis of a small bladder. In 85 subjects the average maximum cystometric capacity was 14.7% less than the maximum volume recorded in the voiding diary. The correlation between the maximum cystometric capacity and maximum functional bladder volume was r = 0.473 (P < 0.001). However, there was a statistically significant difference between the two volumes by paired t-test analysis (P = 0.006). Using cystometry to diagnose small bladder capacity showed a sensitivity of 62.9% and a specificity of 71.2% when using voiding diary volumes as the criterion standard. The positive predictive value was 51.4% and the negative predictive value was 84.0%. These results suggest that whereas the maximum bladder capacity measured by cystometry correlates with maximum environmental bladder capacity as determined by 24-hour voiding diaries, there is a statistically significant difference. The diagnosis of a small bladder should not be based on office cystometry alone.

Linkage position determination in a novel set of permethylated neutral trisaccharides by collisional-induced dissociation and tandem mass spectrometry

A set of neutral permethylated trisaccharides identical in the non-reducing (A----B) disaccharide and linkage isomeric in the reducing terminal (B----C) disaccharide has been synthesized. Collision-activated tandem mass spectrometry was used for analysis of the B----C linkage position. The trisaccharides, gal(beta 1----4)glc(beta 1----X)glc, where X = 3, 4 and 6, were synthesized and examined using fast atom bombardment collision-induced dissociation tandem mass spectrometry. Results were rationalized using molecular modeling. We have previously reported results for determination of the A----B linkage position with isomeric sets of synthetic trisaccharides containing internal amino sugars. The neutral trisaccharides were synthesized to isolate electronic effects of the amino group. An approach of relating daughter ion to parent ion ratios and collision energy offset was used to generate slopes that predict linkage position in glc beta 1----X glc reducing end glycoside form of terminal trisaccharides.

Synthesis of four novel trisaccharides by induction of loose acceptor specificity in Gal beta 1----4 transferase (EC 2.4.1.22): Galp(beta 1----4)Glcp(X)Glc where X = beta 1----3: beta 1----4: beta 1----6: alpha 1----4

Development of tandem mass spectral methods for direct linkage determination in oligosaccharides requires sets of trisaccharides differing only in one structural parameter. In this case, we chose the position of linkage to the reducing-end hexose. These sets of compounds would also be useful for the development of high-resolution separation techniques geared to resolve linkage types. Conventional organic synthesis of such a set could take as long as 2-5 months for each member of the set. Each trisaccharide would require 10-20 steps of synthesis. Instead, we utilized low pH to induce a loose acceptor specificity for bovine milk galactosyltransferase (lactose synthase: EC 2.4.1.22) and by this method, within 2 weeks, generated four novel oligosaccharides for NMR and mass spectral studies. The disaccharides cellobiose (beta 1----4), laminaribiose (beta 1----3), gentiobiose (beta 1----6) and maltose (alpha 1----4) acted as acceptors for EC 2.4.1.22 under these conditions. The beta 1----2-linked disaccharide, sophorose, was not commercially available and is not included in this study. The alpha-linked disaccharides were also examined, but except for the alpha 1----4 disaccharide maltose, were very poor acceptors under a variety of conditions. From these four acceptors, the following four novel trisaccharides were synthesized in micromole amounts, suitable for studies of linkage position using low-energy collision-induced-dissociation tandem mass spectrometry (FAB-MS-CID-MS), and for NMR: Galp(beta 1----4)Glcp(beta 1----3)-Glc, Galp(beta 1----4)Glcp(beta 1----4)Glc, Galp(beta 1----4)Glcp(beta 1----6)-Glc and Galp(beta 1----4)Glcp(alpha 1----4)Glc.

Non-reducing terminal linkage position determination in intact and permethylated synthetic oligosaccharides having a penultimate amino sugar: fast atom bombardment ionization, collisional-induced dissociation and tandem mass spectrometry

Certain linkage positions in oligosaccharides can be discerned by collision-activated dissociation mass spectrometry, rationalized by molecular modelling. Previous work on synthetic oligosaccharides has suggested that daughter ion patterns can distinguish among intact compounds which terminate in alpha-L-fucose and have a penultimate amino sugar. The current study indicates that these observations can be extended to oligosaccharides terminating in beta-D-galactose. In addition, we have observed that protonated, ammoniated and lithiated molecular ions all produce linkage-specific daughter ion spectra in these two sets of oligosaccharides. Sodiated molecular ions could be fragmented usefully under high collision energy offset conditions; potassiated ions were stable and not dissociable under conditions available in a triple-quadrupole instrument. We also show linkage discernment among the permethylated set of these six synthetic oligosaccharides. Methylated derivatives of this set of compounds give more useful product ions, including a 3-linkage specific ion. A novel relationship was noted by a plot of collision energy against (daughter ion/parent ion) ratio, which gave a unique slope for each of the non-reducing terminal linkage positions 3, 4 and 6 in the set of six compounds. The slope of this plot is related to the ability of each linkage position in the oligosaccharide to absorb collisional energy. Rotational freedom of the individual glycosidic linkage is hypothesized to play a role in this phenomenon.