Imaging of carbon nanomembranes with helium ion microscopy

Beyer A, Vieker H, Klett R, Meyer Zu Theenhausen H, Angelova P, Gölzhäuser A. Imaging of carbon nanomembranes with helium ion microscopy. Beilstein Journal of Nanotechnology. 2015;6:1712-1720.Carbon nanomembranes (CNMs) prepared from aromatic self-assembled monolayers constitute a recently developed class of 2D materials. They are made by a combination of self-assembly, radiation-induced cross-linking and the detachment of the cross-linked SAM from its substrate. CNMs can be deposited on arbitrary substrates, including holey and perforated ones, as well as on metallic (transmission electron microscopy) grids. Therewith, freestanding membranes with a thickness of 1 nm and macroscopic lateral dimensions can be prepared. Although free-standing CNMs cannot be imaged by light microscopy, charged particle techniques can visualize them. However, CNMs are electrically insulating, which makes them sensitive to charging. We demonstrate that the helium ion microscope (HIM) is a good candidate for imaging freestanding CNMs due to its efficient charge compensation tool. Scanning with a beam of helium ions while recording the emitted secondary electrons generates the HIM images. The advantages of HIM are high resolution, high surface sensitivity and large depth of field. The effects of sample charging, imaging of multilayer CNMs as well as imaging artefacts are discussed

A 1.2-V analog interface for a 300-MSps HD video digitizer in Core 65-nm CMOS

Aamir SA, Angelova P, Wikner JJ. A 1.2-V analog interface for a 300-MSps HD video digitizer in Core 65-nm CMOS. IEEE Transactions on VLSI Systems. 2014;22(4):888-898.This paper describes the front-end of a fully integrated analog interface for 300 MSps, high-definition video digitizers in a system on-chip environment. The analog interface is implemented in a 1.2 V, 65-nm digital CMOS process and the design minimizes the number of power domains using core transistors only. Each analog video receiver channel contains an integrated multiplexer with a current-mode dc-clamp, a programmable gain amplifier (PGA) and a pseudo second-order RC low-pass filter. The digital charge-pump clamp is integrated with low-voltage bootstrapped tee-switches inside the multiplexer, while restoring the dc component of ac-coupled inputs. The PGA contains a four-stage fully symmetric pseudo-differential amplifier with common-mode feedforward and inherent common-mode feedback, utilized in a closed loop capacitive feedback configuration. The amplifier features offset cancellation during the horizontal blanking. The video interface is evaluated using a unique test signal over a range of video formats for INL+/DNL+, INL-/DNL-. The 0.07-0.39 mV INL, 2-70 μV DNL, and 66-74 dB of SFDR, enable us to target various formats for 9-12 bit Low-voltage digitizers

Sacral nerve root metastasis in a patient with lung carcinoma resembling neurinoma – a case report and literature review

Intradural extramedullary metastases from systemic neoplasms are very rare, with an incidence ranging from 2% to 5% of all secondary spinal diseases. We present the case of a 53-year-old man diagnosed with lung adenocarcinoma with symptoms of severe back pain and tibial paresis. The magnetic resonance imaging (MRI) revealed an intradural lesion originating from the right S1 nerve root mimicking neurinoma. Total tumor removal was achieved via posterior midline approach. The histological examination was consistent with lung carcinoma metastasis. Due to the rarity of single nodular nerve root metastases, MRI images may be misinterpreted as nerve sheath tumors, such as schwannomas or neurofibromas. We performed a brief literature review outlining the mainstay of diagnosis, therapeutic approach, and the prognosis of these rare lesions

Contemporary insight into diffuse axonal injury

Diffuse axonal injury (DAI) is present in approximately 50% of the cases with severe traumatic brain injury. It is one of the leading causes of morbidity and mortality among children and young individuals worldwide. Generally, DAI occurs as a result of high-velocity accidents. Typically, it presents with loss of consciousness for at least 6 hours and neurological deficit dependent on the brain area that is affected by the injury. The final diagnosis is confirmed by neuroimaging studies such as computed tomography and magnetic resonance imaging. According to the injured brain site, DAI is classified into three grades: Grade I–DAI with axonal lesions in the cerebral hemispheres; Grade II–DAI with focal axonal lesions in the corpus callosum; Grade III–DAI with focal or multiple axonal lesions in the brainstem. Each of the three grades is associated with different outcome.Due to the high disability and mortality rate, DAI represents an important medical, personal and social problem. The aim of the current review is to address the unsolved issues connected with the pathogenesis, diagnostics, treatment and outcome of the diffuse axonal injury

Short-term outcome of treatment of elderly patients with epidural hematomas

Introduction: There is substantial literature data dedicated to intracranial epidural hematomas affecting young and middle-aged individuals, but studies focusing on their characteristics in elderly patients are scarce, assuming that old age is a poor prognostic factor. Aim: The aim of the current study was to review the typical features of the etiology, clinical presentation, disease course, and outcome in a series of cases with epidural hematomas in elderly patients. Materials and methods: The etiology, clinical presentation, neuroimaging findings, treatment, and outcome in elderly patients operated for traumatic epidural hematomas were investigated in the Clinic of Neurosurgery at St George University Hospital, Plovdiv between January 2015 and December 2020. The study included patients with isolated traumatic epidural hematoma, as well as those with epidural hematoma in combination with other traumatic intracranial lesions (cerebral contusion, subarachnoid hemorrhage, subdural and intracerebral hematoma). Postoperative epidural hematomas were not included in the study. The neurological status of patients at admission was assessed using the Glasgow Coma Scale. The Glasgow Outcome Scale was used to monitor their condition during the first month after discharge. Results: 121 patients with epidural hematomas underwent surgery during the study period in the Clinic of Neurosurgery at St George University Hospital, Plovdiv. Of these patients, 13 (10.7%) were people aged over 65 years (8 women and 5 men, mean age - 69 years). The most common cause of injury was a fall. Twelve patients (92.3%) had associated craniocerebral lesions and only one had an isolated epidural hematoma. Upon admission, 6 patients (46.2%) were neurologically intact. Ten patients were treated surgically, two – conservatively. Good outcome (GOS=4–5) was achieved in 8 patients (61.5%), poor outcome – in one patient, and four patients (30.8%) died. Conclusions: Good outcome in elderly patients with epidural hematoma can be achieved in two-thirds of the cases, despite the negative influence of the age as a prognostic factor

Tailoring the Mechanics of Ultrathin Carbon Nanomembranes by Molecular Design

Zhang X, Neumann C, Angelova P, Beyer A, Gölzhäuser A. Tailoring the Mechanics of Ultrathin Carbon Nanomembranes by Molecular Design. Langmuir. 2014;30(27):8221-8227.Freestanding carbon nanomembranes (CNMs) with a thickness between 0.6 and 1.7 nm were prepared from self-assembled monolayers (SAMs) of diverse polyaromatic precursors via low-energy electron-induced cross-linking. The mechanical properties of CNMs were investigated using AFM bulge test, where a pressure difference was applied to the membrane and the resulting deflection was measured by atomic force microscopy. We found a correlation between the rigidity of the precursor molecules and the macroscopic mechanical stiffness of CNMs. While CNMs from rigid and condensed precursors like naphthalene and pyrene thiols prove to exhibit higher Young's moduli of 15-19 GPa, CNMs from nonfused oligophenyls possess lower Young's moduli of similar to 10 GPa. For CNMs from less densely packed SAMs, the presence of defects and nanopores plays an important role in determining their mechanical properties. The finite element method (FEM) was applied to examine the deformation profiles and simulate the pressure-deflection relationships

Chemisorbed Monolayers of Corannulene Penta-Thioethers on Gold

Angelova P, Solel E, Parvari G, et al. Chemisorbed Monolayers of Corannulene Penta-Thioethers on Gold. Langmuir. 2013;29(7):2217-2223.Penta(tert-butylthio)corannulene and penta(4-dimethylaminophenylthio)corannulene form highly stable monolayers on gold surfaces, as indicated by X-ray photoelectron spectroscopy (XPS). Formation of these homogeneous monolayers involves multivalent coordination of the five sulfur atoms to gold with the peripheral alkyl or aryl substituents pointing away from the surface. No dissociation of C-S bonds upon binding could be observed at room temperature. Yet, the XPS experiments reveal strong chemical bonding between the thioether groups and gold. Temperature-dependent XPS study shows that the thermal stability of the monolayers is higher than the typical stability of self-assembled monolayers (SAMs) of thiolates on gold

Tailoring the Mechanics of Ultrathin Carbon Nanomembranes by Molecular Design

Freestanding carbon nanomembranes (CNMs) with a thickness between 0.6 and 1.7 nm were prepared from self-assembled monolayers (SAMs) of diverse polyaromatic precursors via low-energy electron-induced cross-linking. The mechanical properties of CNMs were investigated using AFM bulge test, where a pressure difference was applied to the membrane and the resulting deflection was measured by atomic force microscopy. We found a correlation between the rigidity of the precursor molecules and the macroscopic mechanical stiffness of CNMs. While CNMs from rigid and condensed precursors like naphthalene and pyrene thiols prove to exhibit higher Young’s moduli of 15–19 GPa, CNMs from nonfused oligophenyls possess lower Young’s moduli of ∼10 GPa. For CNMs from less densely packed SAMs, the presence of defects and nanopores plays an important role in determining their mechanical properties. The finite element method (FEM) was applied to examine the deformation profiles and simulate the pressure–deflection relationships

Charge Transport through Carbon Nanomembranes

Penner P, Zhang X, Marschewski E, et al. Charge Transport through Carbon Nanomembranes. The Journal of Physical Chemistry C. 2014;118(37):21687-21694.Molecular junctions incorporating pristine and cross-linked aromatic self-assembled monolayers (SAMs) are fabricated and investigated. A two-terminal setup composed of a eutectic Ga-In (EGaIn) top electrode and the gold substrate on which SAMs are prepared as a bottom electrode was used to characterize the charge transport. SAMs of phenylthiol (PT), biphenylthiol (BPT), p-terphenylthiol (TPT), and p-quaterphenylthiol (QPT) are then irradiated with low-energy electrons and converted into carbon nanomembranes (CNMs). A comparison of charge transport through SAMs and CNMs reveals a decrease of conductance of CNM-based junctions by 1 order of magnitude, as well as a conversion of asymmetric junctions with SAMs into symmetric junctions with CNMs, which could be attributed to the decoupling of CNMs from the Au substrate and the partial loss of aromaticity of CNMs after irradiation. Transition voltage spectroscopy (TVS) was also employed to investigate both types of junctions. We observe the length-dependent behavior of transition voltages in both systems and a reduction of transition voltages of CNM-based junctions in comparison to SAM-based junctions

Evaluation of thermal and electrical conductivity of carbon-based PLA nanocomposites for 3D printing

PLA nanocomposites for fused-deposition modeling (FDM) technique are considered. Thermal and electrical conductivity of carbon-based PLA nanocomposites are investigated looking at the different morphological characteristic of the carbon nanoparticles. In particular commercial multi-walled carbon nanotubes (CNTs) and graphene nanoplates (GNPs) are considered as filler in order to realize filament for 3D printed devices for electrical and thermal application. In this paper a filler concentration up to 12% in weight is investigated. Transient Plane Source (TPS) measurements of thermal conductivity show that better heat conduction is obtained through the incorporation in the PLA matrix of carbonaceous nanostructures with predominantly two-dimensional shape (GNPs). DC electrical measurements show that the nanocomposite filled with the predominant mono-dimensional carbon nanoparticle (i.e. CNT) exhibits lower electrical percolation threshold, whereas a greater post percolation electrical conductivity is established with the two-dimensional filler (i.e. GNP). Such characteristics are to be considered in order to make robust and cost effective 3D printed device, by preferring 1D filler or 2D filler for electrical or thermal application respectively. Moreover, multiphase nanocomposites obtained with an optimized combination of CNT and GNP nanoparticles could be exploited to realize devices for joint electrical and thermal application