Role In Cracking Research Articles

Mask material effects in cryogenic deep reactive ion etching

Cryogenic silicon etching in inductively coupled SF6∕O2 plasma has been studied, especially the behavior of mask materials. Suitability of eight different mask materials for cryogenic silicon deep reactive ion etching has been investigated. Three of the five photoresists suffered from cracking during cryogenic etching. We clarified the stages of the etching process and identified two mechanisms behind the cracking: thermal expansion mismatch and mechanical deformation from wafer clamping and backside helium pressure. Also thickness of the photoresist plays a role in cracking, but, contrary to common conception that all thick resists suffer from cracking in cryogenic etching, we found that SU-8 negative resist did not crack, even for very thick layers. This is explained to be due to its high cross-linking density. All three hard mask materials had high selectivities and were free of cracking problems. However, aluminum mask resulted in poor surface quality, while thermally grown SiO2 and amorphous Al2O3 deposited by atomic layer deposition showed smooth surfaces and sidewalls. Silicon dioxide had selectivity of 150:1, while Al2O3 selectivity was 66 000:1. This extreme selectivity of Al2O3 mask, combined with good surface quality, is shown to be highly beneficial in both shallow and through-wafer etching.

Nano‐ and macropores in the model for current oscillations at the Si/electrolyte contact

AbstractThe transition from sustained to damped current oscillations or to stationary behavior is described using a model based on morphological aspects. A roughening of the oxide and of the underlying Si surface is predicted, in accordance with measurements. The role of cracks and nanopores in silicon oxide is discussed with regard to roughness increase and macropore formation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Management of Irrigation with Saline Water in Cracking Clay Soils

Management scenarios aimed at optimizing irrigation in a Sicilian vineyard characterized by a cracking clay soil irrigated with saline water were explored for seven soil profiles (Baglio 1–Baglio 7), by using the simulation model soil‐water‐atmosphere‐plant environment (SWAP), which accounts for shrinkage and cracking. Accurate prediction of water content, θ, was obtained for the seven profiles by expressing the soil hydraulic properties according to the Brutsaert retention equation coupled with the hydraulic conductivity model proposed by Gardner (B‐G model). A satisfactory prediction of the electrical conductivity of saturated extract (ECsat) was obtained using for the dispersivity (Ldis), a calibration value of 20 cm. Different irrigation schedulings and alternating waters of different quality were then explored as viable management options. The results showed that bypass flow determined a favorable water distribution, and that the best irrigation strategy was to make a minimum number of irrigations, by maximizing at the same time the amount of water supplied at each irrigation. Water storage in cracks was found to promote salt‐leaching; neglecting cracks and bypass flow was shown to overestimate salinization. Alternating two different irrigation waters proved to be the best strategy, which could be adopted to reduce soil salinization and enhance crop transpiration. Findings concerning the role of cracks in the process of salt‐leaching suggested that, under field conditions, application of a leaching solution was more efficient if the soil presented a considerable degree of cracking.

Crack Dynamics of Thermally Dried Sludge Cake

We examined in this work the dynamics of crack in drying sludge cake using an X-ray micro-computerized tomography scanner (micro-CT). The three-dimensional crack structure model was reconstructed, and the geometric parameters of cracks were evaluated over time. Internal cracks were found to grow fast in the initial phase of drying, and to then develop into shapes that exhibited zigzagging with non-circular cross-sections and fractal-like boundaries. The role of cracks on sludge drying is discussed.

Mechanical analysis for crack-free release of chemical-vapor-deposited diamond wafers

Chemical-vapor-deposited (CVD) diamond thick films for electronic applications must be released without cracks from the substrate as freestanding wafers. In this study, the mechanism of cracking in the CVD films was investigated experimentally and theoretically. Experimental observations showed that cracks initiated at the edge of the diamond wafer and then propagated towards the center. Finite-element analysis (FEA) reveals that, during cooling, compressive thermal stresses concentrate at the thick film's edge and additional tensile stress acts circumferentially. This was verified by the experimental analysis of diamond films deposited on Si, Mo and W substrates. Observations on low interfacial adhesion and crack-free film on the W substrate indicated that, in addition to the high thermal stress, low interfacial adhesion plays an important role in cracking. Thus, film cracking depends on the fracture strength of the film and its relative magnitude with respect to interfacial adhesion. Methods of crack suppression were suggested on the basis of this cracking mechanism: increase of film thickness and minimization of the substrate's CTE and interfacial adhesion. The analysis was confirmed by successful suppression of cracking by application of a low-adhesion interlayer prior to deposition of diamond film.

The identification of hydrogen trapping states in an Al-Li-Cu-Zr alloy using thermal desorption spectroscopy

Thermal desorption spectroscopy (TDS) was utilized to identify several metallurgical states in an Al -2Li - 2Cu-0.1Zr (wt pct) alloy, which trap absorbed hydrogen. Six distinct metallurgical desorption states for hydrogen were observed for tempers varying from the T3 to peakaged condition. Lower energy thermal desorption states were correlated with interstitial sites, lithium in solid solution, and δ′ (Al3Li) precipitates. These states have trap-binding energies ≤25.2 kJ/mol. Under the charging conditions utilized, approximately 4 pct of the total (e.g., trapped and lattice) hydrogen content was associated with interstitial sites, consistent with the view that the intrinsic lattice solubility of hydrogen in aluminum is very low. In contrast, dislocations, grain boundaries, and T1 (Al2CuLi) particles were found to be higher energy-trap states with trap-binding energies ≥31.7 kJ/mol. Approximately 78 pct of all absorbed hydrogen occupied these states. Moreover, greater than 13 pct of the available trap sites at grain boundaries were occupied. Such a high hydrogen coverage at grain-boundary sites supports the notion that hydrogen contributes to grain-boundary environmental cracking in Al-Li-Cu-Zr alloys. Also, it points out the error in assuming that hydrogen cannot play a major role in cracking of Al-based alloys due to the low lattice solubility.

Microcracks tunneling in brittle matrix composites driven by thermal expansion mismatch

During processing, brittle composites are susceptible to cracks caused by residual stress. Matrix cracks parallel to fibers are considered in this paper. Each crack initiates from a porosity, confined by the neighboring fibers, tunneling in the matrix. The analysis uses the concept of steady-state tunneling, which eliminates several analytical artifacts in a previous calculation. The cracking coefficient is computed for the full range of elastic mismatch and several fiber arrangements, and is presented in a form that can be used in selecting viable constituents. Calculations also demonstrate that fiber-matrix interface plays a major role in cracking. A sliding interface relaxes tunnel edges, and thereby the energy release rate at the tunnel front.

Observations on the crack-enhanced creep-fracture of a polycrystalline alumina with a glassy grain-boundary phase

An experimental study was conducted of the role of cracks in the creep-rupture behaviour of a polycrystalline alumina with glassy grain-boundary phase at stress regimes and temperatures at which failure is anticipated to occur from pre-existing flaws. Samples were tested without and with artificial flaws in the form of slots or indentation cracks. All three sample types exhibited non-linear creep. The relative rate of increase in creep rate with increasing dimension of slot-depth greatly exceeded the corresponding increase in specimen compliance, as expected for non-linear creep. An analysis of the data indicated that the observed creep behaviour was primarily controlled by crack-enhanced creep with a minor contribution from elastic creep by crack growth. Very poor correlations were found for the stress dependence of the creep rate and time-to-failure. In terms of Monkman-Grant behaviour, good correlations existed between creep rate and time-to-failure, independent of stress and size of the slots or indentation cracks. Because failure originated from pre-existing flaws, the experimental findings of this study suggest the existence of a failure mechanism referred to by the present authors as “crack-enhanced creep fracture”.

Role of cracks in progressive permeability reduction during flow of heated aquerous fluids through granite : Vaughan, P J; Moore, D E; Morrow, C A; Byerlee, J D J Geophys ResV91, NB7, 10 June 1986, P7517–7530

Role of cracks in progressive permeability reduction during flow of heated aquerous fluids through granite : Vaughan, P J; Moore, D E; Morrow, C A; Byerlee, J D J Geophys ResV91, NB7, 10 June 1986, P7517–7530

Role of cracks in progressive permeability reduction during flow of heated aqueous fluids through granite

Permeability was measured continuously during an experiment in which a heated, aqueous fluid was pumped through a cylindrical sample of Westerly Granite. Fluid flowed radially outward from an axial borehole down a temperature gradient to the outer edge of the sample. The fluid temperature in the borehole was maintained at 300°C, while a pore pressure difference of 0.5 MPa provided the driving force for fluid flow. Permeability decreased by a factor of 25 during the 2‐week experiment. Scanning electron microscope examination of this altered sample indicates that about half of the grain boundaries involving quartz are cracked or were cracked at some time during the experiment and now contain a filling material. Grain boundaries between the two feldspars are closed in the starting material and in all areas of the altered sample that were examined. Intragranular cracks in all three major minerals are open in the starting material. These observations suggest that initially, the quartz forms a more effective fluid pathway than do the feldspars. About half of the intragranular cracks near the borehole are open, whereas the other half contain a massive deposit which is either Si‐rich or Ca‐rich. In most cracks at the outer edge of the altered sample a Si‐rich filling is present. In crack intersections in this area the filling has a platy texture. At several times during the experiment the discharged fluids were sampled and chemically analyzed. The silica content of fluids passing through the sample was calculated as a function of radius, using rate equations for the dissolution and precipitation of silica. The calculated silica concentrations for the discharged fluids are approximately in agreement with measured values. A separate calculation of the reduction of crack porosity due to uniform dissolution and reprecipitation of quartz indicates that these processes caused a maximum of 10% crack porosity change for an experiment with a borehole temperature of 300°C. Assuming that reprecipitation of quartz was homogeneous, this porosity change corresponds to a permeability reduction of 27%, whereas the observed value was 96%. Therefore other processes besides the simple homogeneous precipitation of a layer of quartz must be operating to reduce permeability. Four possible processes are (1) nonhomogeneous precipitation, (2) precipitation in critical narrow places in cracks, (3) precipitation of other minerals in addition to quartz, and (4) crack healing.

The role of cracks in mass transfer in the soil

The role of cracks in mass transfer in the soil

Role of cracks in the creep deformation of brittle polycrystalline ceramics

A discussion is presented of the effect of cracks formed during the creep deformation of polycrystalline ceramics on the rate of creep deformation. Four distinct regions of the creep curve are identified. In region I, creep is controlled by the basic creep mechanism without cracks. Creep in region II is the combined effect of elastic creep by crack growth due to time-dependent changes in elastic properties and crack-enhanced creep described by Weertman. I n region III, in which the cracks have reached their final size, the rate of creep is governed by the sole effect of crack-enhanced creep. Region IV, not discussed in detail, is represented by accelerated creep due to crack coalescence prior to failure. The apparent stress exponent of crack-enhanced creep is shown to be governed by the value of the stress exponent of the basic creep mechanism as well as the stress dependence of the number of cracks formed per unit area or volume. The dependence of crack density on grain size also modifies the grain-size dependence of Nabarro-Herring and Coble creep. Depending on the specific mechanism of crack growth, region II creep can exhibit an apparent activation energy which can differ from the corresponding values for region I and III creep. Detailed microstructural information on crack size, crack density and other relevant variables is required for the quantitative analysis of the creep kinetics of polycrystalline ceramics subject to crack formation.

Role of Cracks, Pores, and Absorbing Inclusions on Laser Induced Damage Threshold at Surfaces of Transparent Dielectrics

The concentration of the electric field strength in the neighborhood of micropores and cracks may lower the nominal external intensity for electric avalanche breakdown by a factor 2-100 depending on the geometry of the crack and the dielectric constant. The presence of absorbing inclusions at the edge of microcracks will often be the dominant mechanism giving the lowest surface damage threshold. Inclusions and cracks with characteristic dimensions less than about 10(-6) cm will not lower the breakdown threshold appreciably.

Strong Solids

Much of this book is devoted to the principles and theory of the manner in which solids cleave or flow apart when deformed in uniaxial tension. In particular, the role of cracks, notches and dislocations in these processes is fully described.

The Role of Cracks in Subsoil on Underdrainage in Clayey Reclaimed Paddy Fields

The Role of Cracks in Subsoil on Underdrainage in Clayey Reclaimed Paddy Fields