Real-Time Observation of Collector Droplet Oscillations during Growth of Straight Nanowires

A liquid droplet sitting on top of a pillar is crucially important for semiconductor nanowire growth via a vapor–liquid–solid (VLS) mechanism. For the growth of long and straight nanowires, it has been assumed so far that the droplet is pinned to the nanowire top and any instability in the droplet position leads to nanowire kinking. Here, using real-time in situ scanning electron microscopy during germanium nanowire growth, we show that the increase or decrease in the droplet wetting angle and subsequent droplet unpinning from the growth interface may also result in the growth of straight nanowires. Because our argumentation is based on terms and parameters common for VLS-grown nanowires, such as the geometry of the droplet and the growth interface, these conclusions are likely to be relevant to other nanowire systems

Real-Time Observation of Collector Droplet Oscillations during Growth of Straight Nanowires

A liquid droplet sitting on top of a pillar is crucially important for semiconductor nanowire growth via a vapor–liquid–solid (VLS) mechanism. For the growth of long and straight nanowires, it has been assumed so far that the droplet is pinned to the nanowire top and any instability in the droplet position leads to nanowire kinking. Here, using real-time in situ scanning electron microscopy during germanium nanowire growth, we show that the increase or decrease in the droplet wetting angle and subsequent droplet unpinning from the growth interface may also result in the growth of straight nanowires. Because our argumentation is based on terms and parameters common for VLS-grown nanowires, such as the geometry of the droplet and the growth interface, these conclusions are likely to be relevant to other nanowire systems

Guided Assembly of Gold Colloidal Nanoparticles on Silicon Substrates Prepatterned by Charged Particle Beams

Colloidal gold nanoparticles represent technological building blocks which are easy to fabricate while keeping full control of their shape and dimensions. Here, we report on a simple two-step maskless process to assemble gold nanoparticles from a water colloidal solution at specific sites of a silicon surface. First, the silicon substrate covered by native oxide is exposed to a charged particle beam (ions or electrons) and then immersed in a HF-modified solution of colloidal nanoparticles. The irradiation of the native oxide layer by a low-fluence charged particle beam causes changes in the type of surface-terminating groups, while the large fluences induce even more profound modification of surface composition. Hence, by a proper selection of the initial substrate termination, solution pH, and beam fluence, either positive or negative deposition of the colloidal nanoparticles can be achieved

Rotational Stability of Scaphoid Osteosyntheses: An In Vitro Comparison of Small Fragment Cannulated Screws to Novel Bone Screw Sets

<div><p>Background</p><p>The current standard of care for operative repair of scaphoid fractures involves reduction and internal fixation with a single headless compression screw. However, a compression screw in isolation does not necessarily control rotational stability at a fracture or nonunion site. The single screw provides rotational control through friction and bone interdigitation from compression at the fracture site. We hypothesize that osteosyntheses with novel bone screw sets (BSS) equipped with anti-rotational elements provide improved rotational stability.</p><p>Methods</p><p>Stability of osteosynthesis under increasing cyclic torsional loading was investigated on osteotomized cadaveric scaphoids. Two novel prototype BSS, oblique type (BSS-obl.) and longitudinal type (BSS-long.) were compared to three conventional screws: Acutrak2^®mini, HCS^®3.0 and Twinfix^®. Biomechanical tests were performed on scaphoids from single donors in paired comparison and analyzed by balanced incomplete random block design. Loading was increased by 50 mNm increments with 1,000 cycles per torque level and repeated until a rotational clearance of 10°. Primary outcome measure was the number of cycles to 10° clearance, secondary outcome measure was the maximum rotational clearance for each torque level.</p><p>Findings</p><p>BSS-obl. performed significantly better than Acutrak2^®mini and HCS^® (p = 0.015, p<0.0001). BSS-long. performed significantly better than HCS^® (p = 0.010). No significant difference in performance between BSS-obl. and BSS-long. (p = 0.361), between BSS obl. and Twinfix^® (p = 0.50) and BSS long. and Twinfix^® (p = 0.667) was detected. Within the torque range up to 200 mNm, four of 21 (19%) BSS-long. and four of 21 (19%) BSS-obl. preparations showed early failure. The same loading led to early failure in four (29%) Twinfix^®, seven (50%) Acutrak2^®mini and 10 (71%) HCS^® of 14 screw samples, respectively.</p><p>Conclusions</p><p>For both BSS and to a lesser extent for Twinfix^® (as dual-component screw), higher rotational stabilities were identified in comparison to single component headless compression screws.</p></div

Statistics for secondary outcome by implant.

<p>Adjustment for Multiplicity: Holm- Simulated.</p

a-e. Screw types.

<p>The shown screws were used for the test series: Acutrak^®2mini (Acumed) (Fig 1a), Twinfix^® (Stryker) (Fig 1b), HCS^® 3.0 (Synthes) (Fig 1c), and prototypes of the two new BSS sets with an additional crosswise drill hole with an inner thread in oblique type (BSS-obl.) (Fig 1d) and with a longitudinal groove with an inner thread and longitudinal screw as a longitudinal type (BSS-long.) (Fig 1e).</p

Test array.

<p>Draft of the test array for cyclic load to the scaphoid bone osteosyntheses, which were clamped into the holder.</p

primary outcome (Statistics for primary outcome by implant): dataset on total cycles until failure for all tested screws.

<p>primary outcome (Statistics for primary outcome by implant): dataset on total cycles until failure for all tested screws.</p

Primary outcome.

<p>Observed Cycles until failure by Implant. Median of maximum attained cycles of the respective screw models with average parameter and standard deviation. Box plot of maximum cycles per screw type. Median, 25% and 75% percentiles, the points correspond to the individual results per screw.</p

Histograms of the lacunar volumes for the three different sites are shown.

<p>Histograms are normalized to the area under the total number of lacunae for each site. Bin size is set to 50 µm³. The transparent areas indicate the standard error for each site based on the individual samples.</p