[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Graphene, or single-layered graphite, with its high crystallinity and interesting semimetal electronic properties, has emerged as an exciting two-dimensional material showing great promise for the fabrication of nanoscale devices. Thin, elongated strips of graphene that possess straight edges, termed graphene ribbons, gradually transform from semiconductors to semimetals as their width increases, and represent a particularly versatile variety of graphene. Several lithographic, chemical and synthetic procedures are known to produce microscopic samples of graphene nanoribbons, and one chemical vapour deposition process has successfully produced macroscopic quantities of nanoribbons at 950 degrees C. Here we describe a simple solution-based oxidative process for producing a nearly 100% yield of nanoribbon structures by lengthwise cutting and unravelling of multiwalled carbon nanotube (MWCNT) side walls. Although oxidative shortening of MWCNTs has previously been achieved, lengthwise cutting is hitherto unreported. Ribbon structures with high water solubility are obtained. Subsequent chemical reduction of the nanoribbons from MWCNTs results in restoration of electrical conductivity. These early results affording nanoribbons could eventually lead to applications in fields of electronics and composite materials where bulk quantities of nanoribbons are required.

/pdf/longitudinal-unzipping-of-carbon-nanotubes-to-form-graphene-n8z9adf54z.pdf

Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons

Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Skin plays an important role in mediating our interactions with the world. Recreating the properties of skin using electronic devices could have profound implications for prosthetics and medicine. The pursuit of artificial skin has inspired innovations in materials to imitate skin's unique characteristics, including mechanical durability and stretchability, biodegradability, and the ability to measure a diversity of complex sensations over large areas. New materials and fabrication strategies are being developed to make mechanically compliant and multifunctional skin-like electronics, and improve brain/machine interfaces that enable transmission of the skin's signals into the body. This Review will cover materials and devices designed for mimicking the skin's ability to sense and generate biomimetic signals.

Pursuing prosthetic electronic skin.

We have developed a method to separate metallic from semiconducting single-walled carbon nanotubes from suspension using alternating current dielectrophoresis. Our method takes advantage of the difference of the relative dielectric constants of the two species with respect to the solvent, resulting in an opposite movement of metallic and semiconducting tubes along the electric field gradient. Metallic tubes are attracted toward a microelectrode array, leaving semiconducting tubes in the solvent. Proof of the effectiveness of separation is given by a comparative Raman spectroscopy study on the dielectrophoretically deposited tubes and on a reference sample.

https://science.sciencemag.org/content/sci/301/5631/344.full.pdf

Separation of Metallic from Semiconducting Single-Walled Carbon Nanotubes

We discuss the use of the Kubo Golden rule (KGR) in the derivation of new muon polarization functions for arbitrary static field distributions in both zero (ZF) and longitudinal (LF) applied fields. ZF/LF muon spin relaxation measurements in spin-ladder system Sr(Cu1−xZnx)2O3 are reported, with observations of dilute moment freezing for x≲0.008 and dense moment freezing for x≳0.008. In neither the dilute nor the dense case do the data conform to classic muon polarization functions. Using the KGR we derive new muon polarization functions to deal with both of these cases. The dilute case assumes dilute moments with a dense moment background, while the dense case assumes an exponential distribution of fields. Simulation of this system is consistent with an exponential distribution of fields.

Exponential field distribution in Sr(Cu1−xZnx)2O3

Recently, it has become possible to examine metabolism abnormalities by detecting increases in specific acylcarnitines in blood tests of newborn babies using tandem mass spectrometer. However, acylcarnitine standard solutions with metrological traceability to the International System of Units (SI) for accurate calibration of tandem mass spectrometer are not yet available worldwide. In this study, we examined a quantitative 1H NMR procedure for obtaining accurate and SI-traceable purity evaluations of acylcarnitines having different numbers of carbon atoms as each raw material for their standard solutions. In particular, the solvent composition and measurement temperature were optimized to reduce the influence of water signal overlapping on analyte signals. It was found that, when the signal of that 1H which directly bound to the asymmetric carbon of the acylcarnitine is the target signal, it was possible to reduce overlapping of the water signal on the target signal by using deuterium oxide as a solvent. On the other hand, in the case of an acylcarnitine that was poorly soluble in deuterium oxide, it was possible to reduce overlapping of the water signal on the target signal by adding an appropriate amount of deuterium oxide to methanol-d
 4 in which the acylcarnitine had high solubility. At this time, the optimum mixing volume ratio of methanol-d
 4/deuterium would be 80:20. The overlapping of the water signal could be also reduced when the measurement temperature was 15 °C to 40 °C. When the measurement temperature was an around room temperature (in this study, 25 °C), fine shimming could be performed easily. Therefore, the optimum temperature would be 25 °C, because fine shimming was essential to quantify any signal area accurately. Finally, this study confirmed that accurate values with SI traceability could be obtained at about 1 % or less expanded uncertainty for five kinds of acylcarnitines.

Establishment of an analytical method for accurate purity evaluations of acylcarnitines by using quantitative 1 H NMR spectroscopy

LC−NMR has been extensively used for determination and elucidation of chemical structures [1]. In such applications, NMR often suffers poor sensitivity of signal detection. Therefore, stop− flow LC−NMR method, in which flow of LC is stopped when an analyte enters NMR detector, is widely used in order to obtain spectra with sufficient signal to noise ratio to analyze. NMR has been also known that the area integration of the peaks is proportional to the number of nuclei; thus it can be applied to the quantitative analysis. However, accuracy and precision of quantitation using NMR are often poor because quantitative NMR requires its special parameter settings [2], which are quite different from those for structural determinations. Application of LC−NMR to quantitative analysis was reported with continuous−flow method [3], which used NMR as a detector of HPLC much like the conventional detectors such as UV. One of the requirements in quantitative NMR is a long relaxation delay; at the mean time, relaxation delay in continuous−flow LC−NMR is limited by flow rate. This contradicted problem must be overcome for obtaining the accurate continuous−flow LC−NMR measurements. Previous reports showed accuracy of the result was about 10%, precision was indicated worse. Here we aimed to obtain better accuracy of o−xylene purity assessments using NMR as a detector of HPLC. Our approach was following; two consecutive continuous−flow LC−NMR runs were measured; the o−xylene sample was measured during the first run, and the standard sample was measured during the second run. The ratio of NMR area integrations obtained by these two runs leaded the purities. In such a condition, we could maintain identical detection conditions in NMR measurements between the sample and the standard. The NMR results were compared with results obtained with UV detector. Furthermore, the results obtained with LC− NMR, GC−FID, and DSC were also compared.

/pdf/evaluation-of-accuracy-for-the-quantitative-analysis-using-1un481z6na.pdf

Evaluation of Accuracy for the Quantitative Analysis Using Nuclear Magnetic Resonance as a Detector of HPLC

Spin-glassy phase of TDAE-C 60 crystals

Double-walled carbon nanotubes have many advantages over their singled-walled counterparts such as higher mechanical strength and thermal stability. They can be synthesized by well-established methods like arc-discharge, chemical vapor deposition, and the annealing of molecules and nanocompounds encapsulated in single-walled carbon nanotubes. However, the material grown with these methods does not necessarily have a homogeneous morphology across an entire sample. Aiming at a controllable structure, we have decomposed molecules encapsulated in the hollow core of known diameter nanotubes via in situ laser annealing while simultaneously monitoring the Raman spectral response of the material. Our results show that thin inner tubes can be synthesized inside their single-walled hosts. We have also observed that monitoring the laser wavelength and power and choosing the host's diameter, the chirality of the inner tubes can be tailored in a controlled manner. Interestingly, linear carbon chains, as a one-dimensional allotrope of carbon, were formed as well. The dynamic of the chains annealed at higher power indicates the decomposition of the longer into shorter ones.

/pdf/towards-controllable-inner-chirality-in-double-walled-carbon-4ckhsojdzz.pdf

Takeshi Saito

Papers

Exponential field distribution in Sr(Cu1−xZnx)2O3

Establishment of an analytical method for accurate purity evaluations of acylcarnitines by using quantitative 1 H NMR spectroscopy

Evaluation of Accuracy for the Quantitative Analysis Using Nuclear Magnetic Resonance as a Detector of HPLC

Spin-glassy phase of TDAE-C 60 crystals

Towards controllable inner chirality in double-walled carbon nanotubes