Graphene: Piecing it together

Graphene has a multitude of striking properties that make it an exceedingly attractive material for various applications, many of which will emerge over the next decade. However, one of the most promising applications lie in exploiting its peculiar electronic properties which are governed by its electrons obeying a linear dispersion relation. This leads to the observation of half integer quantum hall effect and the absence of localization. The latter is attractive for graphene-based field effect transistors. However, if graphene is to be the material for future electronics, then significant hurdles need to be surmounted, namely, it needs to be mass produced in an economically viable manner and be of high crystalline quality with no or virtually no defects or grains boundaries. Moreover, it will need to be processable with atomic precision. Hence, the future of graphene as a material for electronic based devices will depend heavily on our ability to piece graphene together as a single crystal and define its edges with atomic precision. In this progress report, the properties of graphene that make it so attractive as a material for electronics is introduced to the reader. The focus then centers on current synthesis strategies for graphene and their weaknesses in terms of electronics applications are highlighted.     

Monitoring changes in the error distribution of autoregressive models based on Fourier methods

We develop a procedure for monitoring changes in the error distribution of autoregressive time series while controlling the overall size of the sequential test. The proposed procedure, unlike standard procedures which are also referred to, utilizes the empirical characteristic function of properly estimated residuals. The limit behavior of the test statistic is investigated under the null hypothesis as well as under alternatives. Since the asymptotic null distribution contains unknown parameters, a?bootstrap procedure is proposed in order to actually perform the test and corresponding results on the finite?Csample performance of the new method are presented. As it turns out the procedure is not only able to detect distributional changes but also changes in the regression coefficient.     

Detection and quantification of lanthanide complexes in cell lysates by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Gadolinium (III) complexes are under intense scrutiny as contrast agents for magnetic resonance imaging. Although currently used mainly as extracellular agents, there is a growing interest to exploit their contrast enhancing ability in the intracellular environment. To ascertain the preservation of their chemical integrity upon the intracellular entrapment, it is necessary to have a method for their dosage in the cell lysates. Herein, a mass spectrometric method for detection and quantification of gadolinium complexes in cell lysates is reported. The detection by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was carried out by using a non-acidic matrix (2,4,6-trihydroxyacetophenone), which does not allow any leakage of gadolinium from the complex. Quantification has been possible by using as an internal standard an ytterbium complex with the same ligand of the analyte. Ytterbium was chosen because, among the lanthanides, it is the one with the isotopic distribution pattern the most similar to that of gadolinium. Sensitivity was enough to detect low micromolar quantities of a cationic complex and high micromolar quantities of a neutral complex in cell lysates of rat hepatoma cells. In the case of anionic complexes, sensitivity was too low for quantitative analysis. To the best of our knowledge, this is the first report concerning the quantification of metal complexes by MALDI-TOF-MS.     

Influence of structural properties on ballistic transport in nanoscale epitaxial graphene cross junctions

In this paper we investigate the influence of material and device properties on the ballistic transport in epitaxial monolayer graphene and epitaxial quasi-free-standing monolayer graphene. Our studies comprise (a)?magneto-transport in two-dimensional (2D) Hall bars, (b)?temperature- and magnetic-field-dependent bend resistance of unaligned and step-edge-aligned orthogonal cross junctions, and (c)?the influence of the lead width of the cross junctions on ballistic transport. We found that ballistic transport is highly sensitive to scattering at the step edges of the silicon carbide substrate. A suppression of the ballistic transport is observed if the lead width of the cross junction is reduced from 50?nm to 30?nm. In a 50?nm wide device prepared on quasi-free-standing graphene we observe a gradual transition from the ballistic into the diffusive transport regime if the temperature is increased from 4.2 to about 50?K, although 2D Hall bars show a temperature-independent mobility. Thus, in 1D devices additional temperature-dependent scattering mechanisms play a pivotal role.     

Th. & O. Hofmeister and H. W. Muller

Abstract

The Photographic Collection of the Arts and Crafts Museum in Hamburg was initiated by Wilhelm Weimar at the turn of the century. He started by collecting daguerreotypes. ¹ This probably was the first time that photography became the subject of scientific research and part of a museum collection.²     

Laser-induced breakdown spectra in the infrared region from 750 to 2000 nm using a cooled InGaAs diode array detector

Emissions from a laser-induced breakdown spectroscopy (LIBS) plasma were examined in the region from 750 nm to 2000 nm. A Nd:YAG laser at 532 nm and 75 mJ per pulse were used to initiate the plasma. The detector was an InGaAs 1024 element diode array cooled to -100 degrees C. An f/4 spectrometer with gratings blazed for this region was used as the dispersive element. Survey spectra of soils, uranium, and other selected samples were taken in air and in a flow cell purged with argon at a local pressure of 0.84 x 10(5) Pa. Strong infrared lines of neutral aluminum, carbon, potassium, silicon, sulfur, and uranium, as well as once ionized lines of calcium, were observed out to 1670 nm. For potassium, the detection limits of the infrared (IR) system were compared with those obtained from a standard intensified charge-coupled device (ICCD) spectrometer arrangement, using the 766-770 nm doublet. Detection limits with the IR system were twice as high as those obtained from the ICCD detector.     

Literature review on the ‘Smart Factory’ concept using bibliometric tools

The objective of this paper is to depict a landscape of the scientific literature on the concept of the ‘Smart Factory’, which in recent years is gaining more and more attention from academics and practitioners because of significant innovations in the production systems within the manufacturing sector. To achieve this objective, a dynamic methodology called ‘Systematic Literature Network Analysis (SLNA)’ has been applied. This methodology combines the Systematic Literature Review approach with the analysis of bibliographic networks. The adopted methodology allows complementing traditional content-based literature reviews by extracting quantitative information from bibliographic networks to detect emerging topics, and by revealing the dynamic evolution of the scientific production of a discipline. This dynamic analysis allowed highlighting research directions and critical areas for the development of the ‘Smart Factory’. At the same time, it offers insights on the fields on which companies, associations, politicians and technology providers need to focus in order to allow a real transition towards the implementation of large-scale Smart Factory.     

From Precursor Chemistry to Gas Sensors: Plasma‐Enhanced Atomic Layer Deposition Process Engineering for Zinc Oxide Layers from a Nonpyrophoric Zinc Precursor for Gas Barrier and Sensor Applications

The identification of bis‐3‐(N,N‐dimethylamino)propyl zinc ([Zn(DMP)₂], BDMPZ) as a safe and potential alternative to the highly pyrophoric diethyl zinc (DEZ) as atomic layer deposition (ALD) precursor for ZnO thin films is reported. Owing to the intramolecular stabilization, BDMPZ is a thermally stable, volatile, nonpyrophoric solid compound, however, it possesses a high reactivity due to the presence of Zn‐C and Zn‐N bonds in this complex. Employing this precursor, a new oxygen plasma enhanced (PE)ALD process in the deposition temperature range of 60 and 160 °C is developed. The resulting ZnO thin films are uniform, smooth, stoichiometric, and highly transparent. The deposition on polyethylene terephthalate (PET) at 60 °C results in dense and compact ZnO layers for a thickness as low as 7.5 nm with encouraging oxygen transmission rates (OTR) compared to the bare PET substrates. As a representative application of the ZnO layers, the gas sensing properties are investigated. A high response toward NO₂ is observed without cross‐sensitivities against NH₃ and CO. Thus, the new PEALD process employing BDMPZ has the potential to be a safe substitute to the commonly used DEZ processes.