Scanning Quantum Dot Microscopy Wagner, Christian; Green, Matthew F B; Leinen, Philipp ...
Physical review letters,
2015-Jul-10, Letnik:
115, Številka:
2
Journal Article
Recenzirano
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We introduce a scanning probe technique that enables three-dimensional imaging of local electrostatic potential fields with subnanometer resolution. Registering single electron charging events of a ...molecular quantum dot attached to the tip of an atomic force microscope operated at 5 K, equipped with a qPlus tuning fork, we image the quadrupole field of a single molecule. To demonstrate quantitative measurements, we investigate the dipole field of a single metal adatom adsorbed on a metal surface. We show that because of its high sensitivity the technique can probe electrostatic potentials at large distances from their sources, which should allow for the imaging of samples with increased surface roughness.
Because materials consist of positive nuclei and negative electrons, electric potentials are omnipresent at the atomic scale. However, due to the long range of the Coulomb interaction, large-scale ...structures completely outshine small ones. This makes the isolation and quantification of the electric potentials that originate from nanoscale objects such as atoms or molecules very challenging. Here we report a non-contact scanning probe technique that addresses this challenge. It exploits a quantum dot sensor and the joint electrostatic screening by tip and surface, thus enabling quantitative surface potential imaging across all relevant length scales down to single atoms. We apply the technique to the characterization of a nanostructured surface, thereby extracting workfunction changes and dipole moments for important reference systems. This authenticates the method as a versatile tool to study the building blocks of materials and devices down to the atomic scale.
Wastewater treatment plants are known to release microplastics that have been detected in aquatic and terrestrial organisms constituting part of the human diet. Chlorination of wastewater-borne ...microplastics was hypothesized to induce chemical and physical changes detectable by Raman spectroscopy and differential scanning calorimetry (DSC). In the laboratory, virgin plastics (∼0.05 × 2 × 2 mm) were exposed to differing sterilization conditions representative of dosages used in the disinfection of drinking water, wastewater, and heavily contaminated surfaces. Polypropylene (PP) was most resistant to chlorination, followed by high density polyethylene (HDPE) and polystyrene (PS). Polystyrene showed degradation, indicated by changes in Raman peak widths, at concentration-time regimes (CT values) as low as 75 mg min/L, whereas HDPE and PP remained unaltered even at chlorine doses characteristic of wastewater disinfection (150 mg min/L). However, HDPE and PS were not completely resistant to oxidative attack by chlorination. Under extremely harsh conditions, shifts in Raman peaks and the formation of new bonds were observed. These results show that plastics commonly used in consumer products can be chemically altered, some even under conditions prevailing during wastewater treatment. Changes in polymer properties, observed for HDPE and PP under extreme exposure conditions only, are predicted to alter the risk microplastics pose to aquatic and terrestrial biota, since an increase in carbon-chlorine (C–Cl) bonds is known to increase toxicity, rendering the polymers more hydrophobic and thus more prone to adsorb, accumulate, and transport harmful persistent pollutants to biota in both aquatic and terrestrial environments.
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•Explored the physical and chemical changes of microplastics during chlorine sterilization.•Plastic polymers ranked in persistence from PP (greatest) to HDPE to PS (least).•Few chemical and no physical changes were detected during normal chlorination.•Higher chlorine doses and temperatures yielded chemical and physical changes.•New Cl–C bonds are expected to increase sorption of pollutants and risks.
Modern microelectronics and emerging technologies such as wearable devices and soft robotics require conformable and thermally conductive thermal interface materials to improve their performance and ...longevity. Gallium‐based liquid metals (LMs) are promising candidates for these applications yet are limited by their moderate thermal conductivity, difficulty in surface‐spreading, and pump‐out issues. Incorporation of metallic particles into the LM can address these problems, but observed alloying processes shift the LM melting point and lead to undesirable formation of additional surface roughness. Here, these problems are addressed by introducing a mixture of tungsten microparticles dispersed within a LM matrix (LM‐W) that exhibits two‐ to threefold enhanced thermal conductivity (62 ± 2.28 W m−1 K−1 for gallium and 57 ± 2.08 W m−1 K−1 for EGaInSn at a 40% filler volume mixing ratio) and liquid‐to‐paste transition for better surface application. It is shown that the formation of a nanometer‐scale LM oxide in oxygen‐rich environments allows highly nonwetting tungsten particles to mix into LMs. Using in situ imaging and particle dipping experimentation within a focused ion beam and scanning electron microscopy system, the oxide‐assisted mechanism behind this wetting process is revealed. Furthermore, since tungsten does not undergo room‐temperature alloying with gallium, it is shown that LM‐W remains a chemically stable mixture.
The formation of a chemically stable mixture of tungsten microparticles and liquid metal (LM) with 2–3 times enhanced thermal conductivity (60 W m−1 K−1) and easy‐to‐apply paste consistency is enabled through blending in an oxygen‐rich environment. In situ imaging reveals how the adhesion of nanoscale gallium oxide flakes on the LM‐phobic particles enables their wetting and paste formation.
Preclinical studies suggest that neuromodulation with thoracic spinal cord stimulation (SCS) improves left ventricular (LV) function and remodeling in systolic heart failure (HF).
The purpose of this ...study was to evaluate the safety and efficacy of a SCS system for the treatment of systolic HF.
We performed a prospective, multicenter pilot trial in patients with New York Heart Association (NYHA) class III HF, left ventricular ejection fraction (LVEF) 20%-35%, and implanted defibrillator device who were prescribed stable optimal medical therapy. Dual thoracic SCS leads were used at the T1-T3 level. The device was programmed to provide SCS for 24 hours per day (50 Hz at pulse width 200 μs).
We enrolled 22 patients from 5 centers:17 patients underwent implantation of a SCS device and 4 patients who did not fulfill the study criteria served as nontreated controls. No deaths or device-device interactions were noted during the 6-month period in the 17 SCS-treated patients. Fifteen of 17 completed the efficacy endpoint assessments: composite score improved by 4.2 ± 1.3, and 11 patients (73%) showed improvement in ≥4 of 6 efficacy parameters. There was significant improvement in NYHA class (3.0 vs 2.1, P = .002; 13/17 improved); Minnesota Living with Heart Failure Questionnaire (42 ± 26 vs 27 ± 22, P = .026; 12/17 improved); peak maximum oxygen consumption (14.6 ± 3.3 vs 16.5 ± 3.9 mL/kg/min, P = .013; 10/15 improved); LVEF (25% ± 6% vs 37% ± 8%, P<.001; 14/16 improved); and LV end-systolic volume (174 ± 57 vs 137 ± 37 mL, P = .002; 11/16 improved) but not in N-terminal prohormone brain natriuretic peptide. No such improvements were observed in the 4 nontreated patients.
The results of this first-in-human trial suggest that high thoracic SCS is safe and feasible and potentially can improve symptoms, functional status, and LV function and remodeling in patients with severe, symptomatic systolic HF.
ABSTRACT
We present a homogeneously selected sample of 15 779 candidate binary systems with main sequence primary stars and orbital periods shorter than 5 d. The targets were selected from TESS ...full-frame image light curves on the basis of their tidally induced ellipsoidal modulation. Spectroscopic follow-up suggests a sample purity of 83 ± 13 per cent. Injection-recovery tests allow us to estimate our overall completeness as 28 ± 3 per cent with Porb < 3 d and to quantify our selection effects. 39 ± 4 per cent of our sample are contact binary systems, and we disentangle the period distributions of the contact and detached binaries. We derive the orbital period distribution of the main-sequence binary population at short orbital periods, finding a distribution continuous with the lognormal distribution previously found for solar-type stars at longer periods, but with a significant steepening at Porb ≲ 3 d, and a pile-up of contact binaries at Porb ≈ 0.4 d. Companions in the period range of 1–5 d are an order of magnitude more frequent around stars hotter than $\approx 6250\, \rm K$ (the Kraft break) when compared to cooler stars, suggesting that magnetic braking shortens the lifetime of cooler binary systems. However, the period distribution in the range 1–10 d is independent of temperature. We detect resolved tertiary companions to 9.0 ± 0.2 per cent of our binaries with a median separation of 3200 au. The frequency of tertiary companions rises to 29 ± 5 per cent among the systems with the shortest ellipsoidal periods. This large binary sample with quantified selection effects will be a powerful resource for future studies of detached and contact binary systems with Porb<5 d.
Zwitterionic polymers have drawn significant attention for membrane-based separations due to their impressive hydrophilicity and antifouling properties. Here we demonstrated a novel synthesis method ...to prepare an amphiphilic copolymer poly(arylene ether sulfone-co-sulfobetaine arylene ether sulfone) (PAES-co-SBAES), which was blended with native polysulfone (PSf) to prepare free standing membranes. The polymer chemical structures were analyzed by 1H NMR spectroscopy and the molecular weight of polymers was identified by size exclusion chromatography (SEC). The PSf/PAES-co-SBAES blend membranes with various zwitterionic SBAES segment contents were fabricated via the non-solvent induced phase separation (NIPS) process. The membrane composition, surface morphology (roughness), and surface hydrophilicity were determined by fourier transform infrared (FT-IR) spectrum, atomic force microscopy (AFM), and water contact angle measurements, respectively. The cross-section morphology and surface hydrophilicity of the as-made membranes was analyzed by scanning electron microscopy (SEM) and water contact angle measurements, respectively. The results indicated that both the porosity of the support layer and surface hydrophilicity increased drastically due to the incorporation of hydrophilic SBAES segments. The water permeance and antifouling ability of the PSf/PAES-co-SBAES blend membranes were both remarkably improved to 2.5 L m−2 h−1 bar−1 and 94% of flux recovery ratio, respectively, while salt rejection remained at a high level (98%) even under the high exposure to chlorine. This work provided a valuable and scalable strategy to fabricate desalination membranes via the introduction of zwitterionic segments in a rigid polysulfone matrix, and we predict that additional polymer optimization will drive the performance even higher.
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•Increasing zwitterion content up to 6 wt% increased water permeance ~ 25 ×.•Zwitterion functionality enabled 94% flux recovery and inhibited BSA adhesion.•Increasing zwitterion content improved finger-like pore formation during NIPS.•PAES-based free-standing membranes exhibited high chlorine tolerance up to 12000 ppm·h.
We present a physically intuitive model of molecular quantum dots beyond the constant interaction approximation. It accurately describes their charging behavior and allows the extraction of important ...molecular properties that are otherwise experimentally inaccessible. The model is applied to data recorded with a noncontact atomic force microscope on three different molecules that act as a quantum dot when attached to the microscope tip. The results are in excellent agreement with first-principles simulations.
A series of poly(ethylene glycol) (PEG)-based segmented block copolymers were synthesized with two structurally different hard segments, linear and heterocyclic aliphatic amines. Ionenes were ...synthesized via a modified Menshutkin reaction with three different weight fractions of hard domains (amine rich segment) and soft domains (PEG oligomers). TGA results show that both aliphatic and DABCO-based ionenes were thermally stable up to 250 °C. DSC and XRD data indicate that increasing the weight fraction of the soft segment from 25 wt% to 50 wt% triggered better chain packing of the PEG soft segment for both hard segments. Also, the DABCO-based ionenes displayed the highest PEG crystallite purity at 50 wt% of soft segment. The segmented ionenes exhibited high strain elongation percentages at elevated temperatures (i.e., above the PEG melting temperature). The mechanical properties of ionenes changed by varying the nature and the weight fractions of soft and hard domains. DMA analysis concluded that DABCO-based ionenes possess superior elastomeric behavior by having a wider rubbery plateau and higher rubbery plateau storage modulus compared to aliphatic analogs at all weight fractions potentially due to better microphase separation and ionic aggregation. DMA and AFM confirmed that the 25 wt% soft segment ionenes had a relatively higher degree of microphase separation among the other weight fractions.
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•PEG-based segmented ionenes, with two structurally different hard segments, are synthesized.•The degree of crystallinity and phase separation is adjusted with the content of the hard segment.•DABCO-based ionenes show better elastomeric behavior compared to aliphatic analogs.
PURPOSE:To establish the risk factors, causative organisms, levels of antibiotic resistance, patient demographics, clinical presentations, and clinical outcomes of microbial keratitis at a tertiary ...hospital in Australia.
METHODS:Patients who had a corneal scraping for culture over a 5-year period were identified through the local microbiology database, and a retrospective audit of their medical records was carried out. Clinical information was gathered from medical records, and smear, culture, and antibiotic resistance results were from the microbiology database. An index of disease severity was calculated for each patient from scores for the magnitude of the epithelial defect and anterior-chamber reaction and the location of the lesion. Associations between risk factors for keratitis and variables such as patient demographics, causative organism and antibiotic resistance, disease severity, and outcome were analyzed by using analysis of variance and χ tests with appropriate correction for multiple comparisons.
RESULTS:Two hundred fifty-three cases of microbial keratitis in 231 patients were included. Sixty percent of patients were men, and there was a bimodal distribution in the age of presentation. Common risk factors for keratitis were contact lens wear (53; 22%), ocular surface disease (45; 18%), ocular trauma (41; 16%), and prior ocular surgery (28; 11%). Gram stains were positive in 33%, with a sensitivity of 53% and specificity of 89%. Cultures of corneal scrapings were positive in 65% of cases, and Pseudomonas aeruginosa (44; 17%), coagulase-negative staphylococci (22; 9%), Staphylococcus aureus (19; 8%), and fungi (7; 3%) were commonly recovered. P. aeruginosa was more common than other culture results in contact lens-related cases (55% vs. 0%-23%; P < 0.001), and S. aureus was more common than other culture results in ocular surgery-related cases (29% vs. 0%-21%; P < 0.001). Patients with keratitis related to prior ocular surface disease had more severe keratitis at the time of scraping (P = 0.037). Cultures positive for Fusarium, P. aeruginosa, and other Gram-negative organisms had statistically significantly more severe keratitis at the time of scraping, whereas patients with negative cultures had milder keratitis (P = 0.030). Only 2% of all bacterial isolates were resistant to ciprofloxacin, 20% of Gram-positive isolates were resistant to cephalothin, and no Gram-negative isolates were resistant to gentamicin.
CONCLUSIONS:In this series, the most common risk factor for keratitis was contact lens wear and the most commonly isolated organism was P. aeruginosa.
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