To pattern electrical metal contacts, electron beam lithography or photolithography are commonly utilized, and these processes require polymer resists with solvents. During the patterning process the graphene surface is exposed to chemicals, and the residue on the graphene surface was unable to be completely removed by any method, causing the graphene layer to be contaminated. A lithography free method can overcome these residue problems. In this study, we use a micro-grid as a shadow mask to fabricate a graphene based field-effect-transistor (FET). Electrical measurements of the graphene based FET samples are carried out in air and vacuum. It is found that the Dirac peaks of the graphene devices on SiO2 or on hexagonal boron nitride (hBN) shift from a positive gate voltage region to a negative region as air pressure decreases. In particular, the Dirac peaks shift very rapidly when the pressure decreases from ~2 × 10(-3) Torr to ~5 × 10(-5) Torr within 5 minutes. These Dirac peak shifts are known as adsorption and desorption of environmental gases, but the shift amounts are considerably different depending on the fabrication process. The high gas sensitivity of the device fabricated by shadow mask is attributed to adsorption on the clean graphene surface.
Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films.
We report the first occurrence of an icosahedral quasicrystal with composition Al62.0(8)Cu31.2(8)Fe6.8(4), outside the measured equilibrium stability field at standard pressure of the previously reported Al-Cu-Fe quasicrystal (AlxCuyFez, with x between 61 and 64, y between 24 and 26, z between 12 and 13%). The new icosahedral mineral formed naturally and was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite that experienced shock metamorphism, local melting (with conditions exceeding 5 GPa and 1,200 °C in some locations), and rapid cooling, all of which likely resulted from impact-induced shock in space. This is the first example of a quasicrystal composition discovered in nature prior to being synthesized in the laboratory. The new composition was found in a grain that has a separate metal assemblage containing icosahedrite (Al63Cu24Fe13), currently the only other known naturally occurring mineral with icosahedral symmetry (though the latter composition had already been observed in the laboratory prior to its discovery in nature). The chemistry of both the icosahedral phases was characterized by electron microprobe, and the rotational symmetry was confirmed by means of electron backscatter diffraction.
Using Scanning Tunneling Microscopy, we demonstrate that the 1,3-dipolar cycloaddition between a terminal alkyne and an azide can be performed under solvent-free ultrahigh vacuum conditions with reactants adsorbed on a Cu(111) surface. X-ray Photoelectron Spectroscopy shows significant degradation of the azide upon adsorption, which is found to be the limiting factor for the reaction.
Xylem and phloem are essential for the exchange of solutes and signals among organs of land plants. The synergy of both enables the transport and ultimately the partitioning of water, nutrients, metabolic products and signals among the organs of plants. The collection and analysis of xylem sap allow at least qualitative assumptions about bulk transport in the transpiration stream. For quantification of element-, ion-, and compound-flow, the additional estimation of volume flow is necessary. In this chapter we describe methods for collecting xylem sap by (1) root pressure exudate, (2) Scholander-Hammel pressure vessel, (3) root pressurizing method according to Passioura, and (4) (hand/battery) vacuum pump.
Time of Flight secondary ion mass spectrometry (TOF-SIMS) has been used to explore the distribution of phospholipids in the plasma membrane of Tetrahymena pyriformis during cell division. The dividing cells were freeze dried prior to analysis followed by line scan and region of interest analysis at various stages of cell division. The results showed no signs of phospholipid domain formation at the junction between the dividing cells. Instead the results showed that the sample preparation technique had a great impact on one of the examined phospholipids, namely phosphatidylcholine (PC). Phosphatidylcholine and 2-aminoethylphosphonolipid (2-AEP) have therefore been evaluated in Tetrahymena cells that have been subjected to different sample preparation techniques: freeze drying ex situ, freeze fracture, and freeze fracture with partial or total freeze drying in situ. The result suggests that freeze-drying ex situ causes the celia to collapse and cover the plasma membrane.
Two dicopper(ii)-paddlewheel-based metal-organic frameworks (PCN-81 and -82) have been synthesized by using tetratopic ligands featuring 90°-carbazole-dicarboxylate moieties. Both adopt 12-connected tfb topology with nanoscopic octahedra as building units. The freeze-dried PCN-82 shows Brunauer-Emmett-Teller (BET) and Langmuir surface areas as high as 4488 and 4859 m(2) g(-1), respectively. It also exhibits high H(2)-adsorption capacity at low pressure (300 cm(3) g(-1) or 2.6 wt% at 77 K and 1 bar), which can be attributed to its high surface area, microporosity, and open metal sites.
BACKGROUND: Modern high volume-low pressure (HVLP) endotracheal tubes (ETT) cuffs can seal the trachea using baseline cuff pressures (CP) lower than peak inspiratory airway pressures (PIP). The aim of the study was to determine whether this technique reduces the damage to the tracheal mucosa compared to constant CP of 20 cmH(2)O. METHODS: Eighteen piglets were intubated with an ID 4.0 mm HVLP cuffed ETT (Microcuff PET) and artificially ventilated with 20 cmH(2)O PIP and 5 cmH(2)O PEEP. Animals were randomly allocated to two groups of CP: group A (just seal; n = 9) and group B (20 cmH(2)O; n = 9), controlled constantly with a manometer during the following 4-h study period under sevoflurane anesthesia. After euthanasia, cuff position was marked in situ. Damage in the cuff region was evaluated with scanning electron microscopy (SEM) examination by grading of mucosal damage and by estimating percentage of intact mucosal area both by a blinded observer. RESULTS: Maximal CP to seal the trachea in group A ranged from 12 to 18 cmH(2)O (median: 14 cmH(2)O). Using a mixed effects model approach, the estimated mean effect of group B vs group A was an increase of 17.9% (SE 8.1%) higher proportion of pictures with an area of at least 5% intact mucosa (P = 0.042). CONCLUSION: Minimal sealing pressures with cyclic pressure changes from CP did not result in decreased damage to the tracheal mucosa compared to constant CP of 20 cmH(2)O in this short-term animal trial.
Amorphous matrices, composed of sugars, are markedly plasticized by moisture uptake, which results in physical instability. Our previous studies, in the compression pressure range ≤443 MPa, indicated that when a matrix is compressed, the amount of sorbed water at given relative humidities (RHs) decreases, whereas the glass transition temperature (Tg ) remains constant. Herein, the effect of higher compression pressures than those used previously was explored to investigate the feasibility of using compression to improve the physical stability of amorphous sugar matrix against water uptake and subsequent collapse. Amorphous sugar samples were prepared by freeze-drying and then compressed at 0-665 MPa, followed by rehumidification at given RHs. The physical stability of the amorphous sugar sample was evaluated by measuring Tg and crystallization temperature (Tcry ). The amounts of sorbed water, different in the interaction state, were determined using an FTIR technique. It was found that the compression at pressures of ≥443 MPa decreased the amount of sorbed water, which is a major factor in plasticization and crystallization, and thus markedly increased the Tg and Tcry relative to that for the uncompressed sample. Hence, the compression at several hundreds MPa appears to be feasible for improving the physical stability of amorphous sugar matrix. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci.
As liquid liposomal formulations are prone to chemical degradation and aggregation, these formulations often require freeze drying (e.g. lyophilization) to achieve sufficient shelf-life. However, liposomal formulations may undergo oxidation during lyophilization and/or during prolonged storage. The goal of the current study was to characterize the degradation of 1, 2-dilinolenoyl-sn-glycero-3-phosphocholine (DLPC) during lyophilization, and to also probe the influence of metal contaminants in promoting the observed degradation. Aqueous sugar formulations containing DLPC (0.01 mg/ml) were lyophilized, and DLPC degradation was monitored using HPLC/UV and GC/MS methods. The effect of ferrous ion and sucrose concentration, as well as lyophilization stage promoting lipid degradation, was investigated. DLPC degradation increased with higher levels of ferrous ion. After lyophilization, 103.1% ± 1.1%, 66.9% ± 0.8%, and 28.7% ± 0.7% DLPC remained in the sucrose samples spiked with 0.0 ppm, 0.2 ppm and 1.0 ppm ferrous ion, respectively. Lipid degradation predominantly occurs during the freezing stage of lyophilization. Sugar concentration and buffer ionic strength also influence the extent of lipid degradation, and DLPC loss correlated with degradation product formation. We conclude that DLPC oxidation during the freezing stage of lyophilization dramatically compromises the stability of lipid-based formulations. In addition, we demonstrate that metal contaminants in sugars can become highly active when lyophilized in the presence of a reducing agent.