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We report on a method of enhanced elastic and coherent reflection of 4He2 and 4He3 from a micro- structured solid surface under grazing incidence conditions. The van der Waals bound ground-state helium clusters exhibit fundamental quantum effects: 4He2, characterized by a single ro-vibrational bound state of 10-7 eV dissociation energy, is known to be a quantum halo state; and 4He3 is the only electronic ground-state triatomic system possessing an Efimov state in addition to the ro-vibrational ground state. Classical methods to select and manipulate these clusters by interaction with a solid surface fail due to their exceedingly fragile bonds. Quantum reflection under grazing incidence conditions was demonstrated as a viable tool for elastic scattering from a solid surface but suffers from small reflection probabilities for typical conditions. Here we demonstrate that multiple-edge diffraction enables enhanced elastic scattering of the clusters from a solid. A dual-period reflection grating, where the strips consist of micro-structured edge arrays, shows an up to ten fold increased reflection probability as compared to its conventional counterpart where the strips are plane patches enabling quantum reflection of the clusters. The observed diffraction patterns of the clusters provide evidence of the coherent and elastic nature of scattering by multiple-edge diffraction.

We report on an experimental test of Babinet's principle in quantum reflection of an atom beam from diffraction gratings. The He beam is reflected and diffracted from a square-wave grating at near grazing-incidence conditions. According to Babinet's principle the diffraction peak intensities (except for the specular-reflected beam) are expected to be identical for any pair of gratings of complementary geometry. We observe conditions where Babinet's principle holds and also where it fails. Our data indicate breakdown conditions when either the incident or a diffracted beam propagates close to the grating surface. At these conditions, the incident or the diffracted He beam is strongly affected by the dispersive interaction between the atoms and the grating surface. Babinet's principle is also found to break down, when the complementary grating pair shows a large asymmetry in the strip widths. For very small strip widths, edge diffraction from half planes becomes dominant, whereas for the complementary wide strips the atom–surface interactions leads to a strong reduction of all non-specular diffraction peak intensities.

Although the doping of graphene grown by chemical vapor deposition is crucial in graphene-based electronics, noninvasive methods of n-type doping have not been widely investigated in comparison with p-type doping methods. We developed a convenient and robust method for the noninvasive n-type doping of graphene, wherein electrons are directly injected from sodium anions into the graphene. This method involves immersing the graphene in solutions of [K(15-crown-5)2]Na prepared by dissolving a sodium-potassium (NaK) alloy in a 15-crown-5 solution. The n-type doping of the graphene was confirmed by downshifted G and 2D bands in Raman spectra and by the Dirac point shifting to a negative voltage. The electron-injected graphene showed no sign of structural damage, exhibited higher carrier mobilities than that of pristine graphene, and remained n-doped for over a month of storage in air. In addition, we demonstrated that electron injection enhances noncovalent interactions between graphene and metallomacrocycle molecules without requiring a linker, as used in previous studies, suggesting several potential applications of the method in modifying graphene with various functionalities.

Mass spectrometry imaging (MSI) allows label-free detection of a wide range of biomolecules and simultaneously provides their spatial distributions. In particular, MSI by matrix-assisted laser desorption/ionization mass spectrometry (MALDI) has been widely used in biomolecule analysis. However, quantitation in MALDI-MSI is limited by matrix-deposition heterogeneity, analyte extraction area, and analyte-matrix cocrystallization. In this chapter, a microstructured PDMS stamp is utilized to precisely control the matrix deposition area and the analyte extraction area. We describe here simple steps-including stamp fabrication, matrix application, and data-acquisition guideline-for the quantitative analysis of adsorbed peptides on hydrophobic surfaces.

Owing to their extremely high surface-to-volume ratio, carbon nanotubes (CNTs) are excellent adsorbents for the removal of organic pollutants. However, retrieval or collection of the CNTs after adsorption in existing approaches, which utilize CNTs dispersed in a solution of pollutants, is often more challenging than the removal of pollutants. In this study, we address this challenge by packaging vertically aligned CNTs into a PTFE heat-shrink tubing. Insertion of CNTs into the tubing and subsequent thermal shrinkage densified the CNTs radially by 35% and also reduced wrinkles in the nanotubes. The CNT-based adsorption tube with a circular cross-section enabled both easy functionalization of CNTs and facile connection to a source of polluted water, which we demonstrated for the removal of phenolic compounds. We purified and carboxylated CNTs, by flowing a solution of nitric acid through the tubing, and obtained adsorption capacities of 115, 124, and 81.2 mg g−1 for 0.5 g L−1 of phenol, m-cresol, 2-chlorophenol, respectively. We attribute the high adsorption capacity of our platform to efficient adsorbate-CNT interaction within the narrow interstitial channels between the aligned nanotubes. The CNT-based adsorption tubes are highly promising for the simple and efficient removal of phenolic and other types of organic pollutants.

Mass spectrometry imaging (MSI) based on matrix-assisted laser desorption/ionization (MALDI) provides information on the identification and spatial distribution of biomolecules. Quantitative analysis, however, has been challenging largely due to heterogeneity in both the size of the matrix crystals and the extraction area. In this work, we present a compartmentalized elastomeric stamp for quantitative MALDI-MSI of adsorbed peptides. Filling the compartments with matrix solution and stamping onto a planar substrate extract and concentrate analytes adsorbed in each compartment into a single analyte-matrix cocrystal over the entire stamped area. Walls between compartments help preserve spatial information on the adsorbates. The mass intensity of the cocrystals directly correlates with the surface coverage of analytes, which enables not only quantitative analysis but estimation of an equilibrium constant for the adsorption. We demonstrate via MALDI-MSI relative quantitation of peptides adsorbed along a microchannel with varying surface coverages.

Graphene has attracted significant attention from researchers in recent years as a gas sensing material, because of its atom-thick 2-D structure, extremely high surface-to-volume ratio, and high carrier mobility. However, chemiresistive gas sensors based on graphene have a drawback of low sensitivity to organophosphates, including dimethyl methylphosphonate (DMMP), a simulant of the nerve agent sarin. In this study, we report the detection of 1.3 ppm DMMP, the highest sensitivity reported to date, using graphene chemiresistors, by non-covalently functionalizing graphene with N-substituted triphenylene. The functionalized graphene sensor exhibits a two orders of magnitude higher response to DMMP than to other compounds. This high sensitivity and selectivity are attributed to the strong hydrogen bonding between DMMP and N-substituted triphenylene, as well as the hole-doping effect caused by triphenylene, which increases the binding affinity to the electron-donating DMMP. The proposed approach for simple functionalization of graphene with substituted triphenylene can potentially be employed in tuning the properties of other conjugated nanomaterials, such as carbon nanotubes and graphene nanoribbons, to detect various target analytes.

We demonstrate that a donut-shaped surface pattern consisting of a central hydrophobic region and a surrounding hydrophilic region simultaneously concentrates and desalts a solution of neuropeptides with a high salt content. Our approach greatly simplifies the sample preparation process for MALDI mass spectrometry.

Functional compounds including flavonoids, anthocyanins, polyphneols and antioxidants were extracted from blue honeysuckle (Lonicera caerulea L.) using highly efficient microwave-assisted extraction. And extraction process was modeled and optimized according to response surface methodology (RSM). The independent variables (Xn) were ethanol concentration (X1: 0, 25, 50, 75, 100%), irradiation time (X2: 1, 3, 5, 7, 9 min), and microwave power (X3: 60, 120, 180, 240, 300 W). Dependent variables (Yn) were total flavonoid contents (Y1), total anthocyanin contents (Y2), total polyphenol contents (Y3) and antioxidant activity (Y4). Four-dimensional response surface plots were generated based on the fitted second-order polynomial models to get optimal conditions. Estimated optimal conditions for 4 responses were ethanol concentration of 54-72%, irradiation time of 7.1-7.6 min, and microwave power of 243-251 W. Ridge analysis predicted the maximal responses of total flavonoid content, total anthocyanin content, total polyphenol content and antioxidant activity were 38.00 mg RE/g, 6.80 mg CGE/g, 14.90 mg GAE/g, 89.10%, respectively. Verification experiment was carried out at predicted optimal conditions and experimental values for total flavonoid content, total anthocyanin content, total polyphenol content and antioxidant activity were 38.10 mg RE/g, 6.72 mg CGE/g, 14.91 mg GAE/g and 89.13%, respectively. No significant difference was observed between predicted and experimental values, indicating good fitness of fitted model and successful application of RSM.

We investigate magnetization reversal assisted by electric fields in a Co${}_{40}$Fe${}_{40}$B${}_{20}/$Co$/$Pd multilayer with soft perpendicular anisotropy deposited onto an epitaxial piezoelectric layer. Both the nucleation and depinning magnetic fields show a strong reduction of up to 30$%$ under the application of an electric field. These results show good prospects for assisting the switching processes in ultra-low-power spintronic devices.