Low temperature 2D GaN growth on Si(111) 7 × 7 assisted by hyperthermal nitrogen ions.

As the characteristic dimensions of modern top-down devices are getting smaller, such devices reach their operational limits imposed by quantum mechanics. Thus, two-dimensional (2D) structures appear to be one of the best solutions to meet the ultimate challenges of modern optoelectronic and spintronic applications. The representative of III-V semiconductors, gallium nitride (GaN), is a great candidate for UV and high-power applications at a nanoscale level. We propose a new way of fabrication of 2D GaN on the Si(111) 7 × 7 surface using post-nitridation of Ga droplets by hyperthermal (E = 50 eV) nitrogen ions at low substrate temperatures (T < 220 °C). The deposition of Ga droplets and their post-nitridation are carried out using an effusion cell and a special atom/ion beam source developed by our group, respectively. This low-temperature droplet epitaxy (LTDE) approach provides well-defined ultra-high vacuum growth conditions during the whole fabrication process resulting in unique 2D GaN nanostructures. A sharp interface between the GaN nanostructures and the silicon substrate together with a suitable elemental composition of nanostructures was confirmed by TEM. In addition, SEM, X-ray photoelectron spectroscopy (XPS), AFM and Auger microanalysis were successful in enabling a detailed characterization of the fabricated GaN nanostructures.

Strategy of pulseless pink supracondylar humerus fracture treatment in children: a comparison of two approaches.

PURPOSE: The appropriate treatment of pulseless pink supracondylar humerus fractures (SCHF) remains controversial. In this study, the outcomes of two treatment approaches (with and without vascular surgery) were compared. MATERIAL AND METHODS: This was a retrospective multicenter study of patients with pulseless pink SCHFs treated in ten pediatric surgery, trauma, or orthopedics departments in the Czech and Slovak Republic between 2014 and 2018. RESULTS: Of the total 3608 cases of displaced SCHF, 125 had the pulseless pink SCHF. Of those, 91% (114/125) did not undergo vascular surgery and 9% (11/125) underwent vascular surgery. The patients who did undergo vascular surgery had radial artery pulsation restored more frequently in the operating room (73% vs. 36%; p = 0.02), within 6 h (91% vs. 45%; p = 0.004), and within 24 h of surgery (91% vs. 57%; p = 0.05). However, 72 h after surgery, there was no significant difference in palpable radial artery pulsation between the vascular surgery and the non-vascular surgery groups (91% vs. 74%; p = 0.24). Additionally, no significant differences in long-term neurological (9% vs. 22%; p = 0.46) or circulatory (9% vs. 7%; p = 0.57) deficits were found between the two groups. CONCLUSION: While vascular surgery in patients with pulseless pink SCHFs is associated with a more prompt restoration of radial artery pulsation, no statistical significant differences in terms of the restoration of neurological deficits or the risks of long-term neurological or circulatory deficits were found between patients with and without vascular surgery.

Mechanism and Suppression of Physisorbed-Water-Caused Hysteresis in Graphene FET Sensors.

Hysteresis is a problem in field-effect transistors (FETs) often caused by defects and charge traps inside a gate isolating (e.g., SiO2) layer. This work shows that graphene-based FETs also exhibit hysteresis due to water physisorbed on top of graphene determined by the relative humidity level, which naturally happens in biosensors and ambient operating sensors. The hysteresis effect is explained by trapping of electrons by physisorbed water, and it is shown that this hysteresis can be suppressed using short pulses of alternating gate voltages.

Complementary SEM-AFM of Swelling Bi-Fe-O Film on HOPG Substrate.

The objective of this work is to study the delamination of bismuth ferrite prepared by atomic layer deposition on highly oriented pyrolytic graphite (HOPG) substrate. The samples' structures and compositions are provided by XPS, secondary ion mass spectrometry (SIMS) and Raman spectroscopy. The resulting films demonstrate buckling and delamination from the substrates. The composition inside the resulting bubbles is in a gaseous state. It contains the reaction products captured on the surface during the deposition of the film. The topography of Bi-Fe-O thin films was studied in vacuum and under atmospheric conditions using simultaneous SEM and atomic force microscopy (AFM). Besides complementary advanced imaging, a correlative SEM-AFM analysis provides the possibility of testing the mechanical properties by using a variation of pressure. In this work, the possibility of studying the surface tension of the thin films using a joint SEM-AFM analysis is shown.

Kelvin Probe Force Microscopy and Calculation of Charge Transport in a Graphene/Silicon Dioxide System at Different Relative Humidity.

The article shows how the dynamic mapping of surface potential (SP) measured by Kelvin probe force microscopy (KPFM) in combination with calculation by a diffusion-like equation and the theory based on the Brunauer-Emmett-Teller (BET) model of water condensation and electron hopping can provide the information concerning the resistivity of low conductive surfaces and their water coverage. This is enabled by a study of charge transport between isolated and grounded graphene sheets on a silicon dioxide surface at different relative humidity (RH) with regard to the use of graphene in ambient electronic circuits and especially in sensors. In the experimental part, the chemical vapor-deposited graphene is precisely patterned by the mechanical atomic force microscopy (AFM) lithography and the charge transport is studied through a surface potential evolution measured by KPFM. In the computational part, a quantitative model based on solving the diffusion-like equation for the charge transport is used to fit the experimental data and thus to find the SiO2 surface resistivity ranging from 107 to 1010 Ω and exponentially decreasing with the RH increase. Such a behavior is explained using the formation of water layers predicted by the BET adsorption theory and electron-hopping theory that for the SiO2 surface patterned by AFM predicts a high water coverage even at low RHs.

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.