The chemical and structural analysis of graphene oxide with different degrees of oxidation

2.4. Molecular Beam Epitaxy 366 2.5. Laser Ablation 367 2.6. Silicon Monoxide Evaporation 367 3. Catalyst Materials 368 3.1. Gold as Catalyst 368 3.2. Alternative Catalyst Materials 369 3.2.1. Type-A, Au-like Catalysts 370 3.2.2. Type-B, Low Si Solubility Catalysts 371 3.2.3. Type-C, Silicide Forming Catalysts 371 4. Crystallography 372 5. Heterostructures 373 6. Surface Induced Lowering of the Eutectic Temperature 375

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Growth, thermodynamics, and electrical properties of silicon nanowires.

The nonlinear mechanical response of monolayer graphene on polyethylene terephthalate (PET) is characterised using in-situ Raman spectroscopy and atomic force microscopy. While interfacial stress transfer leads to tension in graphene as the PET substrate is stretched, retraction of the substrate during unloading imposes compression in the graphene. Two interfacial failure mechanisms, shear sliding under tension and buckling under compression, are identified. Using a nonlinear shear-lag model, the interfacial shear strength is found to range between 0.46 and 0.69 MPa. The critical strain for onset of interfacial sliding is ∼0.3%, while the maximum strain that can be transferred to graphene ranges from 1.2% to 1.6% depending on the interfacial shear strength and graphene size. Beyond a critical compressive strain of around −0.7%, buckling ridges are observed after unloading. The results from this work provide valuable insight and design guidelines for a broad spectrum of applications of graphene and other 2D nanomaterials, such as flexible and stretchable electronics, strain sensing, and nanocomposites.

/pdf/interfacial-sliding-and-buckling-of-monolayer-graphene-on-a-358cgoou1q.pdf

Interfacial Sliding and Buckling of Monolayer Graphene on a Stretchable Substrate

The last decade has produced record-breaking heat waves in many parts of the world. At the same time, it was globally the warmest since sufficient measurements started in the 19th century. Here we show that, worldwide, the number of local record-breaking monthly temperature extremes is now on average five times larger than expected in a climate with no long-term warming. This implies that on average there is an 80 % chance that a new monthly heat record is due to climatic change. Large regional differences exist in the number of observed records. Summertime records, which are associated with prolonged heat waves, increased by more than a factor of ten in some continental regions including parts of Europe, Africa, southern Asia and Amazonia. Overall, these high record numbers are quantitatively consistent with those expected for the observed climatic warming trend with added stationary white noise. In addition, we find that the observed records cluster both in space and in time. Strong El Nino years see additional records superimposed on the expected long-term rise. Under a medium global warming scenario, by the 2040s we predict the number of monthly heat records globally to be more than 12 times as high as in a climate with no long-term warming.

/pdf/global-increase-in-record-breaking-monthly-mean-temperatures-3dv29oe2yg.pdf

Global increase in record-breaking monthly-mean temperatures

The wrinkling and delamination of stiff thin films adhered to a polymer substrate have important applications in “flexible electronics.” The resulting periodic structures, when used for circuitry, have remarkable mechanical properties because stretching or twisting of the substrate is mostly accommodated through bending of the film, which minimizes fatigue or fracture. To date, applications in this context have used substrate patterning to create an anisotropic substrate-film adhesion energy, thereby producing a controlled array of delamination “blisters.” However, even in the absence of such patterning, blisters appear spontaneously, with a characteristic size. Here, we perform well-controlled experiments at macroscopic scales to study what sets the dimensions of these blisters in terms of the material properties and explain our results by using a combination of scaling and analytical methods. Besides pointing to a method for determining the interfacial toughness, our analysis suggests a number of design guidelines for the thin films used in flexible electronic applications. Crucially, we show that, to avoid the possibility that delamination may cause fatigue damage, the thin film thickness must be greater than a critical value, which we determine.

https://www.pnas.org/content/pnas/106/27/10901.full.pdf

The macroscopic delamination of thin films from elastic substrates

Effect of substrate compliance on the global unilateral post-buckling of coatings: AFM observations and finite element calculations

On the origin of the metastable β-Ta phase stabilization in tantalum sputtered thin films

Thin films deposited on substrates are usually submitted to large residual compression stresses, causing delamination and buckling of the film into various patterns. The present study is focused on the different equilibria arising on strip-shaped delaminated areas. The three most common types of buckling patterns observed on such strips are known as the straight-sided wrinkles, bubble pattern, and telephone cord blisters. The stability of those equilibria as a function of the two stress components of the loading is investigated. The Foppl-Von Karman model for elastic plates is used for theoretical aspects. The post-critical equilibrium paths of the buckling patterns are investigated numerically by means of the finite-element method. The substrate is assumed to be rigid and the contact to be frictionless. The equilibrium solutions can be classified into families of homologous equilibria allowing the identification of dimensionless parameters for the study of stability. A mapping of the different stable post-critical equilibria is given. It is shown that the straight-sided wrinkles and the bubbles are associated with anisotropy of stresses and/or of elastic properties, whereas the telephone cords are stable at high isotropic stresses. The morphological transitions are experimentally evidenced by in situ atomic force microscopy observations of a nickel 50-nm-thick film under stress.

Stability diagram of unilateral buckling patterns of strip-delaminated films.

We have developed a kinetic model for residual stress generation in thin films grown from energetic vapor fluxes, encountered, e.g., during sputter deposition. The new analytical model considers sub-surface point defects created by atomic peening, along with processes treated in already existing stress models for non-energetic deposition, i.e., thermally activated diffusion processes at the surface and the grain boundary. According to the new model, ballistically induced sub-surface defects can get incorporated as excess atoms at the grain boundary, remain trapped in the bulk, or annihilate at the free surface, resulting in a complex dependence of the steady-state stress on the grain size, the growth rate, as well as the energetics of the incoming particle flux. We compare calculations from the model with in situ stress measurements performed on a series of Mo films sputter-deposited at different conditions and having different grain sizes. The model is able to reproduce the observed increase of compressive stress with increasing growth rate, behavior that is the opposite of what is typically seen under non-energetic growth conditions. On a grander scale, this study is a step towards obtaining a comprehensive understanding of stress generation and evolution in vapor deposited polycrystalline thin films.

J. Colin

Papers

Effect of substrate compliance on the global unilateral post-buckling of coatings: AFM observations and finite element calculations

On the origin of the metastable β-Ta phase stabilization in tantalum sputtered thin films

Stability diagram of unilateral buckling patterns of strip-delaminated films.

A kinetic model for stress generation in thin films grown from energetic vapor fluxes

Real-time stress evolution during early growth stages of sputter-deposited metal films: Influence of adatom mobility