62 research outputs found
Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films
In the search for phase change materials (PCM) that may rival traditional
random access memory, a complete understanding of the amorphous to crystalline
phase transition is required. For the well-known Ge2Sb2Te5 (GST) and GeTe (GT)
chalcogenides, which display nucleation and growth dominated crystallization
kinetics, respectively, this work explores the nanomechanical morphology of
amorphous and crystalline phases in 50 nm thin films. Subjecting these PCM
specimens to a lateral thermal gradient spanning the crystallization
temperature allows for a detailed morphological investigation. Surface and
depth-dependent analyses of the resulting amorphous, transition and crystalline
regions are achieved with shallow angle cross-sections, uniquely implemented
with beam exit Ar ion polishing. To resolve the distinct phases, ultrasonic
force microscopy (UFM) with simultaneous topography is implemented revealing a
relative stiffness contrast between the amorphous and crystalline phases of 14%
for the free film surface and 20% for the cross-sectioned surface. Nucleation
is observed to occur preferentially at the PCM-substrate and free film
interface for both GST and GT, while fine subsurface structures are found to be
sputtering direction dependent. Combining surface and cross-section
nanomechanical mapping in this manner allows 3D analysis of microstructure and
defects with nanoscale lateral and depth resolution, applicable to a wide range
of materials characterization studies where the detection of subtle variations
in elastic modulus or stiffness are required
Micro-Acoustic-Trap (µAT) for microparticle assembly in 3D
Acoustic tweezers facilitate the manipulation of objects using sound waves. With the current state of the technology one can only control mobility for a single or few microparticles. This article presents a state of the art system where an Acoustic Lens was used for developing a Micro-Acoustic Trap for microparticle assembly in 3D. The model particles, 2 µm diameter polystyrene beads in suspension, were driven via acoustic pressure to form a monolayer at wavelength-defined distances above the substrate defined by the focal point of an Acoustic Lens The transducer was driven at 89 MHz, mixed with 100 ms pulses at a repetition rate of 2 Hz. Beyond a threshold drive amplitude sufficient to overcome Brownian motion, this led to 2D assembly of the microparticles into close-packed rafts >80 µm across (∼5 wavelengths of the carrier wave and >40 particles across). This methodology was further extended to manipulation of live Dictyostelium discoideum amoebae. This approach therefore offers maneuverability in controlling or assembling micrometer-scale objects using continuous or pulsed focused acoustic radiation pressure
Electric field and tip geometry effects on dielectrophoretic growth of carbon nanotube nanofibrils on scanning probes
Single-wall carbon nanotube (SWNT) nanofibrils were assembled onto a variety
of conductive scanning probes including atomic force microscope (AFM) tips and
scanning tunnelling microscope (STM) needles using positive dielectrophoresis
(DEP). The magnitude of the applied electric field was varied in the range of
1-20 V to investigate its effect on the dimensions of the assembled SWNT
nanofibrils. Both length and diameter grew asymptotically as voltage increased
from 5 to 18 V. Below 4 V, stable attachment of SWNT nanofibrils could not be
achieved due to the relatively weak DEP force versus Brownian motion. At
voltages of 20 V and higher, low quality nanofibrils resulted from
incorporating large amounts of impurities. For intermediate voltages, optimal
nanofibrils were achieved, though pivotal to this assembly is the wetting
behaviour upon tip immersion in the SWNT suspension drop. This process was
monitored in situ to correlate wetting angle and probe geometry (cone angles
and tip height), revealing that probes with narrow cone angles and long shanks
are optimal. It is proposed that this results from less wetting of the probe
apex, and therefore reduces capillary forces and especially force transients
during the nanofibril drawing process. Relatively rigid probes (force constant
>= 2 N/m) exhibited no perceivable cantilever bending upon wetting and
de-wetting, resulting in the most stable process control
A Contraction Stress Model of Hypertrophic Cardiomyopathy due to Sarcomere Mutations.
Thick-filament sarcomere mutations are a common cause of hypertrophic cardiomyopathy (HCM), a disorder of heart muscle thickening associated with sudden cardiac death and heart failure, with unclear mechanisms. We engineered four isogenic induced pluripotent stem cell (iPSC) models of β-myosin heavy chain and myosin-binding protein C3 mutations, and studied iPSC-derived cardiomyocytes in cardiac microtissue assays that resemble cardiac architecture and biomechanics. All HCM mutations resulted in hypercontractility with prolonged relaxation kinetics in proportion to mutation pathogenicity, but not changes in calcium handling. RNA sequencing and expression studies of HCM models identified p53 activation, oxidative stress, and cytotoxicity induced by metabolic stress that can be reversed by p53 genetic ablation. Our findings implicate hypercontractility as a direct consequence of thick-filament mutations, irrespective of mutation localization, and the p53 pathway as a molecular marker of contraction stress and candidate therapeutic target for HCM patients
Multiplexed Monitoring of Neurochemicals via Electrografting- Enabled Site-Selective Functionalization of Aptamers on Field-Effect Transistors
Neurochemical corelease has received much attention in understanding brain activity and cognition. Despite many attempts, the multiplexed monitoring of coreleased neurochemicals with spatiotemporal precision and minimal crosstalk using existing methods remains challenging. Here, we report a soft neural probe for multiplexed neurochemical monitoring via the electrografting-assisted site-selective functionalization of aptamers on graphene field-effect transistors (G-FETs). The neural probes possess excellent flexibility, ultralight mass (28 mg), and a nearly cellular-scale dimension of 50 μm × 50 μm for each G-FET. As a demonstration, we show that G-FETs with electrochemically grafted molecular linkers (−COOH or −NH2) and specific aptamers can be used to monitor serotonin and dopamine with high sensitivity (limit of detection: 10 pM) and selectivity (dopamine sensor \u3e22-fold over norepinephrine; serotonin sensor \u3e17-fold over dopamine). In addition, we demonstrate the feasibility of the simultaneous monitoring of dopamine and serotonin in a single neural probe with minimal crosstalk and interferences in phosphate-buffered saline, artificial cerebrospinal fluid, and harvested mouse brain tissues. The stability studies show that multiplexed neural probes maintain the capability for simultaneously monitoring dopamine and serotonin with minimal crosstalk after incubating in rat cerebrospinal fluid for 96 h, although a reduced sensor response at high concentrations is observed. Ex vivo studies in harvested mice brains suggest potential applications in monitoring the evoked release of dopamine and serotonin. The developed multiplexed detection methodology can also be adapted for monitoring other neurochemicals, such as metabolites and neuropeptides, by simply replacing the aptamers functionalized on the G-FETs
Site-specific Forest-assembly of Single-Wall Carbon Nanotubes on Electron-beam Patterned SiOx/Si Substrates
Based on electron-beam direct writing on the SiOx/Si substrates, favorable
absorption sites for ferric cations (Fe3+ ions) were created on the surface
oxide layer. This allowed Fe3+-assisted self-assembled arrays of single-wall
carbon nanotube (SWNT) probes to be produced. Auger investigation indicated
that the incident energetic electrons depleted oxygen, creating more dangling
bonds around Si atoms at the surface of the SiOx layer. This resulted in a
distinct difference in the friction forces from unexposed regions as measured
by lateral force microscopy (LFM). Atomic force microscopy (AFM) affirmed that
the irradiated domains absorbed considerably more Fe3+ ions upon immersion into
pH 2.2 aqueous FeCl3 solution. This rendered a greater yield of FeO(OH)/FeOCl
precipitates, primarily FeO(OH), upon subsequent washing with lightly basic
dimethylformamide (DMF) solution. Such selective metalfunctionalization
established the basis for the subsequent patterned forest-assembly of SWNTs as
demonstrated by resonance Raman spectroscopy
Analysis of IFT74 as a candidate gene for chromosome 9p-linked ALS-FTD
BACKGROUND: A new locus for amyotrophic lateral sclerosis – frontotemporal dementia (ALS-FTD) has recently been ascribed to chromosome 9p. METHODS: We identified chromosome 9p segregating haplotypes within two families with ALS-FTD (F476 and F2) and undertook mutational screening of candidate genes within this locus. RESULTS: Candidate gene sequencing at this locus revealed the presence of a disease segregating stop mutation (Q342X) in the intraflagellar transport 74 (IFT74) gene in family 476 (F476), but no mutation was detected within IFT74 in family 2 (F2). While neither family was sufficiently informative to definitively implicate or exclude IFT74 mutations as a cause of chromosome 9-linked ALS-FTD, the nature of the mutation observed within F476 (predicted to truncate the protein by 258 amino acids) led us to sequence the open reading frame of this gene in a large number of ALS and FTD cases (n = 420). An additional sequence variant (G58D) was found in a case of sporadic semantic dementia. I55L sequence variants were found in three other unrelated affected individuals, but this was also found in a single individual among 800 Human Diversity Gene Panel samples. CONCLUSION: Confirmation of the pathogenicity of IFT74 sequence variants will require screening of other chromosome 9p-linked families
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