Formation Of Overhangs Research Articles

Effect of Bias Frequency on Bottom-Up SiO2 Gap-Filling Using Plasma-Enhanced Atomic Layer Deposition.

High-aspect-ratio patterns are required for next-generation three-dimensional (3D) semiconductor devices. However, it is challenging to eliminate voids and seams during gap-filling of these high-aspect-ratio patterns, such as deep trenches, especially for nanoscale high-aspect-ratio patterns. In this study, a SiO2 plasma-enhanced atomic layer deposition process incorporated with ion collision using bias power to the substrate was used for bottom-up trench gap-filling. The effect of bias power frequency on SiO2 trench gap-filling was then investigated. Results showed that changes in bias power frequency did not significantly change the process rate, such as SiO2 growth per cycle. At relatively low bias power frequencies, high-energy ions formed an overhang at the entrance of the high-aspect-ratio trench pattern through sputter etching and redeposition, blocking the pattern entrance. However, at relatively high-frequency bias power, overhang formation due to sputtering did not occur. In the trench interior, due to a scattering effect of ions, deposition was thicker at the bottom of the trench than that at the top, achieving bottom-up gap-filling and void-free gap-filling.

THE VALUE OF A RATIONAL ROOF OVERHANG OVER A STAINED-GLASS FACADE USING BIM TECHNOLOGIES

Problem statement. These days, the issue of reducing energy consumption is relevant, including due to the roof overhang formation in winter, when the sun is below the horizon and can use solar heat for heating, and in summer, when the sun rises high above the horizon and solar radiation is maximum. The issue of roof overhangs value therefore becomes relevant in reducing energy consumption. The purpose of the article is to determine the rational roof overhang value to reduce energy consumption and the dependence between stained-glass system height and roof overhang value using Revit software. Conclusions. The roof overhang value can make a significant difference to a building's energy consumption during the heating period, allowing solar radiation to enter the house due to the large open areas of the stained-glass windows. In the summer, for example, the roof overhang can provide shade inside the house during the hottest times of the day, thereby reducing the energy consumption for air-conditioning cooling. The dependence between the height of the stained-glass window and the rational roof overhang value, which provides shade inside the room in summer and does not prevent the sun's energy from entering the room in winter, was determined.

Linking fracturing and rock mechanic properties to the erosion of a beachrock shore platform

The intertidal zone and raised shore (supratidal) platform at Mission Rocks, northern KwaZulu-Natal coast, South Africa, consists of fracture-bounded Holocene beachrock units, and megagravel (boulder) deposits. This area is microtidal and wave-dominated, with swells approaching from the southeast. The area is also influenced by storm wave events. The seaward edge of the intertidal platform is undercut, leading to the formation of overhangs, which are modelled here as cantilevered beams. This analysis shows that beam volume/weight does not control failure because relatively short, thick beams (l:h < 2) are less susceptible to failure, and the beam length-to-thickness ratio is important. This accords with tensile strength testing which demonstrates that the bedding planes are weak and that saturated beachrock (i.e., at the platform edge) is ~25% weaker than unsaturated rock. Fracture, block and boulder analyses of seven coastal sections, and their geomorphological features (elevation, slope, terrain ruggedness), reveal three key relationships: (1) The number of fracture intersections and fracture density are higher in the raised shore platforms than in the intertidal, which is relatively unfractured, lower in elevation and less rugged than the raised shore platform. These parameters correlate positively with the number of fracture-bounded blocks. (2) Fracture-bounded blocks on the raised shore platform (n = 145) have a mean shape ratio of 2.25 and are 10–20 m2 in size, while the disarticulated boulders (n = 172) have a mean shape ratio of 1.3–1.5 and are 2–3 m2 in size. It is considered that the reduction in shape and size of the boulders is the result of fracture-bounded blocks being quarried and transported from the raised shore platform, and not from the intertidal platform, during high-energy storm events. (3) Coast-perpendicular fractures in the intertidal platform deepen and widen towards the sea, forming gullies in which wave run-up and retreat was observed. A relatively good negative correlation (r2 = 0.7) was found between the number of these gullies and values of maximum terrain ruggedness which suggests that platform lowering occurs when an appropriate fracture network (relatively dense and suitably orientated) receives unimpeded swells and waves. Overall, we find that the evolution of the beachrock platform in terms of ruggedness and downwearing is influenced, at least in part, by the fracture networks present, most notably in terms of their orientation, density, persistence and intersection geometry.

Spatially resolved horizontal spread in smouldering peat combining infrared and visual diagnostics

Smouldering wildfires in peatlands can last for weeks, resulting in the release of large amount of soil carbon and harmful emissions with detrimental effects on human health and the environment. Despite their importance, smouldering fires are poorly understood. An experimental study was carried out here to measure the spread rate of peat fire in detail, using infrared (IR) imaging. Peat samples with different moisture contents were prepared and burned in an open reactor of 20 × 20 cm2 cross section and 10 cm depth, under laboratory-controlled conditions. In total, twelve experiments were studied, each lasting for 8 h on average. Infrared and visual cameras were synchronised, and images were acquired at a frequency of 1/min, for the duration of the experiment. Profiles of smouldering spread on the free surface of peat were tracked using an image intensity threshold and then used to calculate the horizontal spread rate. Temporally and spatially resolved spread rates are presented and analysed. Increasing the moisture content of the peat resulted in a decrease in spread rate and the smouldering front became increasingly irregular. At high moisture contents, spread at the lower layers of peat is faster compared to top surfaces which leads to formation of overhang, and IR is able to measure the formation of the overhang and its collapse as a step increase in horizontal spread. The overhang becomes more prominent when moisture content is increased. The new tool allows the study of unprecedented details in the spread of peat fires and can be adopted in future experimental studies.

Experimental study of the formation and collapse of an overhang in the lateral spread of smouldering peat fires

Smouldering combustion is the driving phenomenon of wildfires in peatlands, and is responsible for large amounts of carbon emissions and haze episodes world wide. Compared to flaming fires, smouldering is slow, low-temperature, flameless, and most persistent, yet it is poorly understood. Peat, as a typical organic soil, is a porous and charring natural fuel, thus prone to smouldering. The spread of smouldering peat fire is a multidimensional phenomenon, including two main components: in-depth vertical and surface lateral spread. In this study, we investigate the lateral spread of peat fire under various moisture and wind conditions. Visual and infrared cameras as well as a thermocouple array are used to measure the temperature profile and the spread rate. For the first time the overhang, where smouldering spreads fastest beneath the free surface, is observed in the laboratory, which helps understand the interaction between oxygen supply and heat losses. The periodic formation and collapse of overhangs is observed. The overhang thickness is found to increase with moisture and wind speed, while the spread rate decreases with moisture and increases with wind speed. A simple theoretical analysis is proposed and shows that the formation of overhang is caused by the spread rate difference between the top and lower peat layers as well as the competition between oxygen supply and heat losses.

Transition from compact to porous films in deposition with temperature-activated diffusion.

We study a thin-film growth model with temperature activated diffusion of adsorbed particles, allowing for the formation of overhangs and pores, but without detachment of adatoms or clusters from the deposit. Simulations in one-dimensional substrates are performed for several values of the diffusion-to-deposition ratio R of adatoms with a single bond and of the detachment probability ε per additional nearest neighbor, respectively, with activation energies are E(s) and E(b). If R and ε independently vary, regimes of low and high porosity are separated at 0.075≤ε(c)≤0.09, with vanishingly small porosity below that point and finite porosity for larger ε. Alternatively, for fixed values of E(s) and E(b) and varying temperature, the porosity has a minimum at T(c), and a nontrivial regime in which it increases with temperature is observed above that point. This is related to the large mobility of adatoms, resembling features of equilibrium surface roughening. In this high-temperature region, the deposit has the structure of a critical percolation cluster due to the nondesorption. The pores are regions enclosed by blobs of the corresponding percolating backbone, thus the distribution of pore size s is expected to scale as s(-τ̃) with τ̃≈1.45, in reasonable agreement with numerical estimates. Roughening of the outer interface of the deposits suggests Villain-Lai-Das Sarma scaling below the transition. Above the transition, the roughness exponent α≈0.35 is consistent with the percolation backbone structure via the relation α=2-d(B), where d(B) is the backbone fractal dimension.

Telomeric 3′ Overhangs Derive from Resection by Exo1 and Apollo and Fill-In by POT1b-Associated CST

A 3' overhang is critical for the protection and maintenance of mammalian telomeres, but its synthesis must be regulated to avoid excessive resection of the 5' end, which could cause telomere shortening. How this balance is achieved in mammals has not been resolved. Here, we determine the mechanism for 3' overhang synthesis in mouse cells by evaluating changes in telomeric overhangs throughout the cell cycle and at leading- and lagging-end telomeres. Apollo, a nuclease bound to the shelterin subunit TRF2, initiates formation of the 3' overhang at leading-, but not lagging-end telomeres. Hyperresection by Apollo is blocked at both ends by the shelterin protein POT1b. Exo1 extensively resects both telomere ends, generating transient long 3' overhangs in S/G2. CST/AAF, a DNA polα.primase accessory factor, binds POT1b and shortens the extended overhangs produced by Exo1, likely through fill-in synthesis. 3' overhang formation is thus a multistep, shelterin-controlled process, ensuring functional telomeric overhangs at chromosome ends.

Cell Cycle-Dependent Role of MRN at Dysfunctional Telomeres: ATM Signaling-Dependent Induction of Nonhomologous End Joining (NHEJ) in G1 and Resection-Mediated Inhibition of NHEJ in G2

Here, we address the role of the MRN (Mre11/Rad50/Nbs1) complex in the response to telomeres rendered dysfunctional by deletion of the shelterin component TRF2. Using conditional NBS1/TRF2 double-knockout MEFs, we show that MRN is required for ATM signaling in response to telomere dysfunction. This establishes that MRN is the only sensor for the ATM kinase and suggests that TRF2 might block ATM signaling by interfering with MRN binding to the telomere terminus, possibly by sequestering the telomere end in the t-loop structure. We also examined the role of the MRN/ATM pathway in nonhomologous end joining (NHEJ) of damaged telomeres. NBS1 deficiency abrogated the telomere fusions that occur in G(1), consistent with the requirement for ATM and its target 53BP1 in this setting. Interestingly, NBS1 and ATM, but not H2AX, repressed NHEJ at dysfunctional telomeres in G(2), specifically at telomeres generated by leading-strand DNA synthesis. Leading-strand telomere ends were not prone to fuse in the absence of either TRF2 or MRN/ATM, indicating redundancy in their protection. We propose that MRN represses NHEJ by promoting the generation of a 3' overhang after completion of leading-strand DNA synthesis. TRF2 may ensure overhang formation by recruiting MRN (and other nucleases) to newly generated telomere ends. The activation of the MRN/ATM pathway by the dysfunctional telomeres is proposed to induce resection that protects the leading-strand ends from NHEJ when TRF2 is absent. Thus, the role of MRN at dysfunctional telomeres is multifaceted, involving both repression of NHEJ in G(2) through end resection and induction of NHEJ in G(1) through ATM-dependent signaling.

Restoration techniques and marginal overhang in Class II composite resin restorations

Objectives The objective of the study was to compare in vitro interproximal overhang formation of Class II composite resin restoration when using different matrix systems. Methods 240 lower left molar phantom head teeth with an MO-preparation were divided into 12 groups ( n = 20). In six groups a circumferential matrix (Tofflemire X-thin matrix, HaweNeos 1001-c, SuperCap) was used, combined with either a hand-instrument (PFI49 or OptraContact) or separation ring (Composi-Tight Gold). In the other six groups two sectional matrix systems were used (flexible and dead-soft), with three separation rings (Composi-Tight Gold, Contact Matrix, Palodent BiTine). Matrices were secured with wooden wedges and preparations were restored with composite resin Clearfil AP-X (Kuraray) placed and polymerized in increments. After matrix removal overhang was measured on a standardized digital macroscopic image in mm 2. For analysis a multiple linear regression model was used. Results Use of circumferential matrices resulted in less overhang than sectional matrices (−0.85 mm 2, p < 0.001). A flexible matrix led to less overhang than dead-soft matrices ( −0.54 mm 2, p < 0.001), and no difference was found between straight and pre-contoured matrices ( p = 0.945). The insertion of the OptraContact resulted in a much increased overhang of 2.54 mm 2 ( p < 0.001). The Composi-Tight Gold and the Contact Matrix System rings resulted in less overhang, −0.69 and −0.68 mm 2, respectively (both p < 0.001), whereas the Palodent BiTine ring did not. Conclusions Use of circumferential matrices or sectional flexible matrices resulted in the least marginal overhang when combined with a Contact Matrix separation ring or a Composi-Tight Gold ring.

Modeling growth from the vapor and thermal annealing on micro- and nanopatterned substrates

We propose a -dimensional mesoscopic model to describe the most relevant physical processes that take place while depositing and/or annealing micro- and nanopatterned solid substrates. The model assumes that a collimated incident beam impinges over the growing substrate; scattering effects in the vapor and reemission processes are introduced in a phenomenological way as an isotropic flow. Surface diffusion is included as the main relaxation process at the micro- or nanoscale. The stochastic model is built following population dynamics considerations; both stochastic simulations and the deterministic limit are analyzed. Numerical aspects regarding its implementation are also discussed. We study the shape-preserving growth mode, the coupling between shadowing effects and random fluctuations, and the spatial structure of noises using numerical simulations. We report important deviations from linear theories of surface diffusion when the interfaces are not compatible with the small slope approximation, including spontaneous formation of overhangs and nonexponential decay of pattern amplitudes. We discuss the dependence of stationary states with respect to the boundary conditions imposed on the system.

Taz1, Rap1 and Rif1 act both interdependently and independently to maintain telomeres

Telomere protection and maintenance are accomplished through the coordinated actions of telomere-specific DNA binding proteins and their interacting partners. The fission yeast ortholog of human TRF1/2, Taz1, binds telomeric DNA and regulates numerous aspects of telomere function. Here, we ask which aspects of Taz1 function are mediated through its interacting proteins, Rap1 and Rif1. We demonstrate that rap1+ deletion phenocopies some, but not all, aspects of taz1Delta telomere dysfunction, while Rif1 exhibits a very different functional spectrum. Rap1 acts in a Taz1-dependent pathway to prevent chromosome end fusions and regulate telomeric 3' overhang formation, while Rif1 is dispensable for these functions. Telomerase inhibition by Taz1 is mediated by two separate pathways, one involving Rap1 and the other involving Rif1. In contrast, Taz1 is uniquely required to prevent chromosomal entanglements and missegregation at cold temperatures. Strikingly, while rap1+ deletion exacerbates the cold sensitivity of taz1Delta cells, rif1+ deletion restores full viability. Thus, Rap1 and Rif1 are each required for a subset of the functions of Taz1, but each acquires Taz1-independent functions in its absence. Furthermore, Taz1 can function independently of its known binding partners.

Influence of ice and snow covers on the UV exposure of terrestrial microbial communities: dosimetric studies

Bacillus subtilis spore biological dosimeters and electronic dosimeters were used to investigate the exposure of terrestrial microbial communities in micro-habitats covered by snow and ice in Antarctica. The melting of snow covers of between 5- and 15-cm thickness, depending on age and heterogeneity, could increase B. subtilis spore inactivation by up to an order of magnitude, a relative increase twice that caused by a 50% ozone depletion. Within the snow-pack at depths of less than ∼3 cm snow algae could receive two to three times the DNA-weighted irradiance they would receive on bare ground. At the edge of the snow-pack, warming of low albedo soils resulted in the formation of overhangs that provided transient UV protection to thawed and growing microbial communities on the soils underneath. In shallow aquatic habitats, thin layers of heterogeneous ice of a few millimetres thickness were found to reduce DNA-weighted irradiances by up to 55% compared to full-sky values with equivalent DNA-weighted diffuse attenuation coefficients ( K DNA) of >200 m −1. A 2-mm snow-encrusted ice cover on a pond was equivalent to 10 cm of ice on a perennially ice covered lake. Ice covers also had the effect of stabilizing the UV exposure, which was often subject to rapid variations of up to 33% of the mean value caused by wind-rippling of the water surface. These data show that changing ice and snow covers cause relative changes in microbial UV exposure at least as great as those caused by changing ozone column abundance.

Metal homoepitaxial growth at very low temperatures: Lattice-gas models with restricted downward funneling

We develop and analyze $1+1$- and $2+1$-dimensional (d) models for multilayer homoepitaxial growth of metal films at low temperatures $(T),$ where intralayer terrace diffusion is inoperative. This work is motivated by recent variable-temperature scanning tunneling microscopy studies of Ag/Ag(100) homoepitaxy down to 50 K. Adsorption sites are bridge sites in our $1+1d$ models, and fourfold hollow sites in our $2+1d$ models for fcc(100) or bcc(100) surfaces. For growth at 0 K, we introduce a ``restricted downward funneling'' model, wherein deposited atoms can be trapped on the sides of steep nanoprotrusions rather than always funneling down to lower adsorption sites. This leads to the formation of overhangs and internal defects (or voids), and associated ``rough'' growth. Upon increasing T, we propose that a series of interlayer diffusion processes become operative, with activation barriers below that for terrace diffusion. This leads to ``smooth'' growth of the film for higher T (but still within the regime where terrace diffusion is absent), similar to that observed in models incorporating ``complete downward funneling.''

Modeling of Metal(100) Homoepitaxial Film Growth at Very Low Temperatures

ABSTRACTWe model the growth of Ag films deposited on Ag(100) below 140K. Our recent Variable-Temperature Scanning Tunneling Microscopy (VTSTM) studies reveal “smooth growth” from 120-140K, consistent with earlier diffraction studies. However, we also find rougher growth for lower temperatures. This unexpected behavior is modeled by describing the deposition dynamics using a “restricted downward funneling” model, wherein deposited atoms get caught on the sides of steep nanoprotrusions (which are prevalent below 120K), rather than always funneling down to lower four-fold hollow adsorption sites. At OK, where no thermal diffusion processes are operative, this leads to the formation of overhangs and internal defects (or voids). Above 40K, low barrier interlayer diffusion processes become operative, producing the observed smooth growth by 120K. We also discuss how the apparent film morphology mapped out by the STM tip “smears” features of the actual film morphology (which are small at low temperature), and also can lead to underestimation of the roughness.

Directional and preferential sputtering-based physical vapor deposition

Physical sputtering techniques are characterized by a mostly isotropic deposition profile, which is useful for depositing films over steps, edges and lines. However, it fails for deposition into modest (>1 : 1) aspect ratio features due to overhang formation and subsequent void formation. A number of techniques have addressed this issue. Sputtering at high sample temperatures has been used to allow some degree of surface tension to help fill structures. Bias sputtering has been found to be useful for reducing void formation in low aspect ratio features. Collimated sputtering has been developed to filter the depositing atoms, resulting in mostly-normal incidence deposition. Finally, post-ionization of the sputtered atoms has been developed to deposit films primarily from metal ions, which are accelerated to the sample surface by means of a d.c. sample bias. Each of these techniques can lead to deposition within high aspect ratio features and will allow the application of sputter deposition for future semiconductor manufacturing processes.

Incommensurate phase on a disordered surface: Instability against the formation of overhangs and finite loops.

The stability of the quenched incommensurate phase in two dimensions against the creation of overhangs (OHs) and finite loops (FLs) in the fermion replica space is investigated for a model of domain walls with N colors. Introducing a chemical potential \ensuremath{\epsilon} for OHs and FLs, the probability for the formation of these objects is studied for \ensuremath{\epsilon}\ensuremath{\rightarrow}0. In the pure limit this probability vanishes with \ensuremath{\epsilon}, whereas the fluctuations are long-range correlated in the quenched system. This indicates an instability related to the symmetry in replica space. It is accompanied by the creation of a massless boson. The latter leads to a power law decay with exponent \ensuremath{\propto}1/N for the product of the correlation functions along the domain walls.

The mechanism of overhang formation in diazide/novolak photoresist film by chlorobenzene soak process

The mechanism of overhang formation in a diazide/novolak photoresist film by the chlorobenzene soak process for lift‐off stencil fabrication is investigated by gel permeation chromatography. The experimental results show that overhang profile formation is controlled mainly by the removal of photoactive compounds (PAC’s) from a resist film. The amount of PAC loss within the modified region in a resist film must be precisely controlled to form a desired overhang profile. The amount of PAC loss depends mainly upon the molecular weight of the PAC’s and the kind of soaking solvent used.