96 research outputs found
The effect of rippling on the mechanical properties of graphene
Graphene is the stiffest material known so far but, due to its one-atom
thickness, it is also very bendable. Consequently, free-standing graphene
exhibit ripples that has major effects on its elastic properties. Here we will
summarize three experiments where the influence of rippling is essential to
address the results. Firstly, we observed that atomic vacancies lessen the
negative thermal expansion coefficient of free-standing graphene. We also
observed an increase of the Young's modulus with global applied strain and with
the introduction of small density defects that we attributed to the decrease of
rippling. Here, we will focus on a surprising feature observed in the data: the
experiments consistently indicate that only the rippling with wavelengths
between 5-10nm influences the mechanics of graphene. The rippling responsible
of the negative TEC and anomalous elasticity is thought to be dynamic, i.e.
flexural phonons. However, flexural phonons with these wavelengths should have
minor effects on the mechanics of graphene, therefore other mechanisms must be
considered to address our observations. We propose static ripples as one of the
key elements to correctly understand the thermomechanics of graphene and
suggest that rippling arises naturally due to a competition of symmetry
breaking and anharmonic fluctuations
Formation of conductive DNA-based nanowires via conjugation of dsDNA with cationic peptide
A novel conductive DNA-based nanomaterial, DNA-peptide wire, composed of a DNA core and a peripheral peptide layer, is presented. The electrical conductivity of the wire is found to be at least three orders in magnitude higher than that of native double-stranded DNA (dsDNA). High conductivity of the wires along with a better resistance to mechanical deformations caused by interactions between the substrate and electrode surface make them appealing for a wide variety of nanoelectronic and biosensor applications
Tunable Graphene Electronics with Local Ultrahigh Pressure
We achieve fine tuning of graphene effective doping by applying ultrahigh
pressures (> 10 GPa) using Atomic Force Microscopy (AFM) diamond tips. Specific
areas in graphene flakes are irreversibly flattened against a SiO2 substrate.
Our work represents the first demonstration of local creation of very stable
effective p-doped graphene regions with nanometer precision, as unambiguously
verified by a battery of techniques. Importantly, the doping strength depends
monotonically on the applied pressure, allowing a controlled tuning of graphene
electronics. Through this doping effect, ultrahigh pressure modifications
include the possibility of selectively modifying graphene areas to improve
their electrical contact with metal electrodes, as shown by Conductive AFM.
Density Functional Theory calculations and experimental data suggest that this
pressure level induces the onset of covalent bonding between graphene and the
underlying SiO2 substrate. Our work opens a convenient avenue to tuning the
electronics of 2D materials and van der Waals heterostructures through pressure
with nanometer resolution
AFM manipulation of gold nanowires to build electrical circuits
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters , copyright © American Chemical Society after peer review and technical editing by the publisher. To acces final work see âAFM Manipulation of Gold Nanowires To Build Electrical Circuitsâ, Nano Letters 19.8 (2019): 5459-5468, https://doi.org/10.1021/acs.nanolett.9b01972We introduce scanning-probe-assisted nanowire circuitry (SPANC) as a new method to fabricate electrodes for the characterization of electrical transport properties at the nanoscale. SPANC uses an atomic force microscope (AFM) to manipulate nanowires to create complex and highly conductive nanostructures (paths) that work as nanoelectrodes, allowing connectivity and electrical characterization of other nano-objects. The paths are formed by the spontaneous cold welding of gold nanowires upon mechanical contact, leading to an excellent contact resistance of âŒ9 Ï/junction. SPANC is an easy to use and cost-effective technique that fabricates clean nanodevices. Hence, this new method can complement and/or be an alternative to other well-established methods to fabricate nanocircuits such as electron beam lithography (EBL). The circuits made by SPANC are easily reconfigurable, and their fabrication does not require the use of polymers and chemicals. In this work, we present a few examples that illustrate the capabilities of this method, allowing robust device fabrication and electrical characterization of several nano-objects with sizes down to âŒ10 nm, well below the current smallest size able to be contacted in a device using the standard available technology (âŒ30 nm). Importantly, we also provide the first experimental determination of the sheet resistance of thin antimonene flake
Recommended from our members
Nematicidal effect of Beauveria species and the mycotoxin beauvericin against pinewood nematode Bursaphelenchus xylophilus
The International Union of Forest Research Organisations (IUFRO) Conference: Foliar, Shoot, Stem and Rust Diseases of Trees Jointly organized by IUFRO working parties âFoliage, shoot, and stem diseases" (7.02.02) and "Rusts of Forest Trees" (7.02.05) is taking place in June of 2022 in Durham, New Hampshire, USA.
This international conference, which meets every two to four years, provides a great opportunity for discussion among colleagues working with rust, foliage and stem diseases of forest trees in different regions of the world. Plant pathogens do not recognize boundaries, therefore maintaining a global perspective when it comes to forest health protection is essential.
Topics of interest that will be covered at the conference include:
- invasive forest pathogens;
- disease management and control;
- plant defence;
- climate change;
- rust, foliage, shoot, and stem diseases.
The goal of this Research Topic is to feature recent advances in research concerning forest diseases, climate change and their management, welcoming abstracts presented at the IUFRO Foliar, Shoot, Stem and Rust Diseases of Trees 2022
Recommended from our members
Nematicidal effect of Beauveria species and the mycotoxin beauvericin against pinewood nematode Bursaphelenchus xylophilus
Introduction and main objective: Bursaphelenchus xylophilus, commonly known as pine wood nematode (PWN), is considered one of the greatest threats to European and Asian pines. Regarding its management, most efforts have been directed toward control measures for the major vector (Monochamus spp.) and screening for genetic resistance in its hosts. However, an integrated pest management strategy which also implements pinewood nematode control is currently lacking. The aim of this study was to evaluate the nematicidal effect of two Beauveria species, a genus well known for its entomopathogenic activity.
Summary methodology: For this purpose, in vitro antagonism tests of fungi (Beauveria bassiana and B. pseudobassiana) and the mycotoxin beauvericin (C45H57N3O9) on B. xylophilus populations were conducted. Finally, the production of beauvericin in B. bassiana and B. pseudobassiana strains was
quantified by high-performance liquid chromatography - mass spectrometry (HPLC-MS).
Results and discussion: Both the B. bassiana and B. pseudobassiana fungal species and the mycotoxin beauvericin showed a clear nematicidal effect on B. xylophilus populations, substantially reducing their survival rate and even attaining 100% mortality in one case. HPLC-MS analysis confirmed and quantified the production of beauvericin by B. bassiana and demonstrated for the first-time beauvericin production in B. pseudobassiana.
Final conclusion: These findings highlight the potential of Beauveria species and the mycotoxin beauvericin to be implemented in an integrated pest management strategy to control both nematode and vector
Resolving Structure and Mechanical Properties at the Nanoscale of Viruses with Frequency Modulation Atomic Force Microscopy
Structural Biology (SB) techniques are particularly successful in solving virus structures. Taking advantage of the symmetries, a heavy averaging on the data of a large number of specimens, results in an accurate determination of the structure of the sample. However, these techniques do not provide true single molecule information of viruses in physiological conditions. To answer many fundamental questions about the quickly expanding physical virology it is important to develop techniques with the capability to reach nanometer scale resolution on both structure and physical properties of individual molecules in physiological conditions. Atomic force microscopy (AFM) fulfills these requirements providing images of individual virus particles under physiological conditions, along with the characterization of a variety of properties including local adhesion and elasticity. Using conventional AFM modes is easy to obtain molecular resolved images on flat samples, such as the purple membrane, or large viruses as the Giant Mimivirus. On the contrary, small virus particles (25â50 nm) cannot be easily imaged. In this work we present Frequency Modulation atomic force microscopy (FM-AFM) working in physiological conditions as an accurate and powerful technique to study virus particles. Our interpretation of the so called âdissipation channelâ in terms of mechanical properties allows us to provide maps where the local stiffness of the virus particles are resolved with nanometer resolution. FM-AFM can be considered as a non invasive technique since, as we demonstrate in our experiments, we are able to sense forces down to 20 pN. The methodology reported here is of general interest since it can be applied to a large number of biological samples. In particular, the importance of mechanical interactions is a hot topic in different aspects of biotechnology ranging from protein folding to stem cells differentiation where conventional AFM modes are already being used
Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study
Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28â2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65â3·22], p\textless0·0001), American Society of Anesthesiologists grades 3â5 versus grades 1â2 (2·35 [1·57â3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01â2·39], p=0·046), emergency versus elective surgery (1·67 [1·06â2·63], p=0·026), and major versus minor surgery (1·52 [1·01â2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research
Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic
This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic
- âŠ