Nanoscale mechanical property variations concerning mineral composition and contact of marine shale

Mechanical properties of shales are key parameters influencing hydrocarbon production – impacting borehole stability, hydraulic fracture extension and microscale variations in in situ stress. We use Ordovician shale(Sichuan Basin, China) as a type-example to characterize variations in mineral particle properties at microscale including particle morphology, form of contact and spatial distribution via mineral liberation analysis(MLA) and scanning electron microscopy(SEM). Deformation-based constitutive models are then built using finite element methods to define the impact of various architectures of fracture and mineral distributions at nanometer scale on the deformation characteristics at macroscale.Relative compositions of siliceous, calcareous and clay mineral particles are shown to be the key factors influencing brittleness. Shales with similar mineral composition show a spectrum of equivalent medium mechanical properties due to differing particle morphology and mineral heterogeneity. The predominance of small particles and/or point-point contacts are conducive to brittle failure, in general, and especially so when quartz-rich. Fracture morphology, length and extent of filling all influence shale deformability. High aspect-ratio fractures concentrate stress at fracture tips and are conducive to extension, as when part-filled by carbonate minerals. As fracture spacing increases, stress transfer between adjacent fractures weakens, stress concentrations are amplified and fracture extension is favored. The higher the fractal dimension of the fracture and heterogeneity of the host the more pervasive the fractures. Moreover, when fractures extend, their potential for intersection and interconnection contributes to a reduction in strength and the promotion of brittle failure. Thus, these results provide important theoretical insights into the role of heterogeneity on the deformability and strength of shale reservoirs with practical implications for their stimulation and in the recovery of hydrocarbons from them.

In situ investigation of the mechanical properties of nanomaterials by transmission electron microscopy

With the progress of modern transmission elec- tron microscopy （TEM） and development of dedicated func- tional TEM specimen holders, people can now manipulate a nano-object with nanometer-range precision and simulta- neously acquire mechanical data together with atomic-scale structural information. This advanced methodology is play- ing an increasingly important role in nanomechanics. The present review summarizes relevant studies on the in situ in- vestigation of mechanical properties of various nanomateri- als over the past decades. These works enrich our knowledge not only on nanomaterials （such as carbon nanotubes, car- bon onions, boron nitride nanotubes, silicon nanowires and graphene, etc.） but also on mechanics at the nanoscate.

Preparation of High-Density Nanocrystalline Bulk Selenium by Rapid Compressing of Melt

The melt＇s solidification behavior of elemental selenium is investigated by a series of experiments including rapid compressing to 2.8 and 3.5 GPa within 20ms respectively, slow compressing to 2.8 GPa for 20 min and natural cooling at ambient pressure. Based on the x-ray diffraction, scanning electron microscope and transmission electron microscope results of the recovered samples, it is clearly shown that homogenous nanostructures are formed only by the rapid compression processes, and that the average crystal sizes are about 18.7 and 19.0 nm in the samples recovered from 2.8 and 3.5 GPa, respectively. The relative density of the nanocrystalline bulk reaches 98.17% of the theoretical value. It is suggested that rapid compression could induce pervasive nucleation and restrain grain growth during the solidification, which is related to fast supercooling, higher viscosity of the melt and lower diffusivity of atoms under high pressure.

Synthesis and Properties of Magnetic Composites of Carbon Nanotubes/Fe Nanoparticle

Magnetic composites of carbon nanotubes （CNTs） are synthesized by the in situ catalytic decomposition of benzene at temperatures as low as 400℃ over Fe nanoparticles （mean grain size = 26 nm） produced by sol-gel fabrication and hydrogen reduction. The yield of CNT composite is up to about 3025% in a run of 6 h. FE- SEM and HRTEM investigations reveal that one-dimensional carbon species are produced in a large quantity. A relatively high value of magnetization is observed for the composite due to the encapsulation of ferromagnetic Fe3 C and/or α-Fe. The method is suitable for the mass-production of CNT composites that contain magnetic nanoparticles.

A Unified Guide to Two Opposite Size Effects in Nano Elastic Materials

The microstructural variation near surface of nano elastic materials is analyzed based on different potentials. The atomic/molecular mechanism underlying the variation and its effect on elastic modulus are such that the nature of long-range interactions （attractive or repulsive） in the atomic/molecular potentials essentially governs the variation near surface （looser or tighter） and results in two opposite size effects （decreasing or increasing modulus） with decreasing size.

Production of ZnO Nanobelts and Meso-Scale Study of Mechanical Properties

We investigate a peculiar phenomenon by processing ZnO nanobelts with an atomic force microscope （AFM）. In the contact mode of AFM, peculiar bending occurs in meso-scale when the nanobelt is applied with force in lateral direction. We study the mechanical properties of ZnO nanobelts under the influence of small size effect, with finite element analysis and mathematical analysis by means of Matlab. Based on this abnormal effect, a novel measuring method is proposed, which allows the surface morphology and surface properties to be characterized at the same time.

Growth of Pure Zinc Blende GaAs Nanowires： Effect of Size and Density of Au Nanoparticles

Pure zinc blende GaAs nanowires were grown by metal organic chemical vapor deposition on GaAs（111）B substrates via Au catalyzed vapor-liquid-solid mechanism. The diameter, size distribution, and density of Au particles can be changed by varying the Au film thickness. We find that the grown nanowires are of rod-like shapes and pure zinc blende structure; moreover, the growth rate depends on the density of Au particles and it is independent of its diameters. It can be concluded that the nanowire was grown with main contributions from the direct impingement of vapor species onto the Au-Ga droplets and contributions from adatom diffusion can be negligible. The results indicate that the droplet acts as a catalyst rather than an adatom collector.

Raman Spectrum of Epitaxial Graphene on SiC （0001） by Pulsed Electron Irradiation

We report new Raman features of epitaxial graphene （EG） on Si-face 4H-SiC prepared by pulsed electron irradiation （PEI）. With increasing graphene layers, frequencies of G and 2D peaks show blue-shifts and approach those of bulk highly-oriented pyrolytic graphite. It is indicated that the EG is slightly tension strained and tends to be strain-free. Meanwhile, single Lorentzian line shapes are well fitted to the 2D peaks of EG on SiC（O001） and their full widths at half maximum decrease with the increasing graphene layers, which indicates that the multilayer EG on Si-face can also contain turbostratic stacking by our PEI route instead of only AB Bernal stacking by a traditional thermal annealing method. It is worth noting that the stacking style plays an important role on the charge carrier mobility. Therefore our findings will be a candidate for growing quality graphene with high carrier mobility both on the Si- and C-terminated SiC substrate. Mechanisms behind the features are studied and discussed.

Effect of In Composition on Two-Dimensional Electron Gas in Wurtzite AlGaN/InGaN Heterostructures

The effect of In composition on two-dimensional electron gas in wurtzite AlGaN/InGaN heterostructures is theoretically investigated. The sheet carrier density is shown to increase nearly linearly with In mole fraction x, due to the increase in the polarization charge at the AlGaN/InGaN interface. The electron sheet density is enhanced with the doping in the AlGaN layer. The sheet carrier density is as high as 3.7×1013 cm^-2 at the donor density of 10×1018 cm^-3 for the HEMT structure with x=0.3. The contribution of additional donor density on the electron sheet density is nearly independent of the In mole fraction.

Observation of nonconservation characteristics of radio frequency noise mechanism of 40-nm n-MOSFET

Bias non-conservation characteristics of radio-frequency noise mechanism of 40-nm n-MOSFET are observed by modeling and measuring its drain current noise. A compact model for the drain current noise of 40-nm MOSFET is proposed through the noise analysis. This model fully describes three kinds of main physical sources that determine the noise mechanism of 40-nm MOSFET, i.e., intrinsic drain current noise, thermal noise induced by the gate parasitic resistance, and coupling thermal noise induced by substrate parasitic effect. The accuracy of the proposed model is verified by noise measurements, and the intrinsic drain current noise is proved to be the suppressed shot noise, and with the decrease of the gate voltage, the suppressed degree gradually decreases until it vanishes. The most important findings of the bias non-conservative nature of noise mechanism of 40-nm n-MOSFET are as follows.（i） In the strong inversion region, the suppressed shot noise is weakly affected by the thermal noise of gate parasitic resistance. Therefore, one can empirically model the channel excess noise as being like the suppressed shot noise.（ii） In the middle inversion region, it is almost full of shot noise.（iii） In the weak inversion region, the thermal noise is strongly frequency-dependent, which is almost controlled by the capacitive coupling of substrate parasitic resistance. Measurement results over a wide temperature range demonstrate that the thermal noise of 40-nm n-MOSFET exists in a region from the weak to strong inversion, contrary to the predictions of suppressed shot noise model only suitable for the strong inversion and middle inversion region. These new findings of the noise mechanism of 40-nm n-MOSFET are very beneficial for its applications in ultra low-voltage and low-power RF, such as novel device electronic structure optimization, integrated circuit design and process technology evaluation.

Entanglement Purification for Mixed Entangled Quantum Dot States via Superconducing Transmission Line Resonators

An entanglement purification protocol for mixed entangled states is presented via double quantum dot molecules inside a superconducing transmission line resonator （TLR）. In the current scenario, coupling for arbitrary double quantum dot molecules can be tuned via the TLR in the large detuning region by controlling the qubit level splitting. The TLR is always empty and only virtually excited, so the interaction is insensitive to both the TLR decay and thermal field. Discussion about the feasibility of our scheme shows that the entanglement purification can be implemented with high fidelity and successful probability.

Heat transport in low-dimensional materials: A review and perspective

Heat transport is a key energetic process in materials and devices. The reduced sample size, low dimension of the problem and the rich spectrum of material imperfections introduce fruitful phenomena at nanoscale. In this review, we summarize recent progresses in the understanding of heat transport process in low-dimensional materials, with focus on the roles of defects, disorder, interfaces, and the quantum- mechanical effect. New physics uncovered from computational simulations, experimental studies, and predictable models will be reviewed, followed by a perspective on open challenges.

Raman Investigation of Sodium Titanate Nanotubes under Hydrostatic Pressures up to 26.9GPa

High pressure behavior of sodium titanate nanotubes （Na2Ti2O5） is investigated by Raman spectroscopy in a diamond anvil cell （DAC） at room temperature. The two pressure-induced irreversible phase transitions are observed under the given pressure. One occurs at about 4.2 GPa accompanied with a new Raman peak emerging at 834 cm-1 which results from the lattice distortion of the Ti-O network in titanate nanotubes. It can be can be assigned to Ti-O lattice vibrations within lepidocrocite-type （H0.7Ti1.825V0.175O4＆#12539;H2O）TiO6 octahedral host layers with V being vacancy. The structure of the nanotubes transforms to orthorhombic lepidocrocite structure. Another amorphous phase transition occurs at 16.7 GPa. This phase transition is induced by the collapse of titanate nanotubes. All the Raman bands shift toward higher wavenumbers with a pressure dependence ranging from 1.58-5.6 cm-1/GPa.

Thermal Properties of Poly（vinyl chloride-co-vinyl acetate-co-2-hydroxypropyl acrylate） （PVVH） Polymer and Its Application in ZnO Based Nanogenerators ：

A novel piezoelectricity based nano energy conversion device using vertically aligned ZnO nanowires/PVVH matrix as the working unit is proposed. Thermal energy is converted to electricity via the interaction of the PVVH polymer and ZnO nanowires. The thermal properties of PVVH ave studied using Raman spectroscopy under different temperatures. The results show that the structure of PVVH is sensitive to fluctuations of the environmental temperatures. With the increasing temperature, PVVH tends to be crystallized and stress can be developed inside the polymer. The stress is responsible for the deformation and voltage generation of the ZnO nanowires.

Influence of Oxygen Pressure on Structural and Sensing Properties of β-Ga2O3 Nanomaterial by Thermal Evaporation

We prepare the gallium oxide （β-Ga2O3） nanomaterials from gallium and oxygen by thermal evaporation in the argon atmosphere and research their oxygen sensing under UV illumination with different oxygen pressures. X-ray diffraction reveals that the synthesized product is monoclinic gallium oxide, it is further confirmed by electron diffraction of transmission electron microscope, and its morphology through the observation using scanning electron microscope reveals thatβ-Ga2O3 nanobelts with a breadth less than lOOnm and length of severai micrometers are synthesized under low oxygen pressure, while the nano/microbelts are synthesized under high oxygen pressure. Room-temperature oxygen sensing is tested under at 254 nm illumination and it is found that the current decreases quickly first and then slowly with oxygen pressure from low to high.

Electromechanical Behavior of Interdigitated SiO2 Cantilever Arrays

Bending and first flexural mode vibration behavior of electrostatic actuated nanometer-sized interdigitated cantilever arrays are characterized under vacuum conditions. The pull-in＇＇ effect in dc driving and the hard spring effect＇＇ in ac driving are observed. A mass sensitivity of 20 fg is expected for our devices due to the ultra-small mass of the arm and relative high Q factor. The mass-spring lump model combined with Green＇s function method is used to fit the dc driving behaviors including the pull-in voltage. For the ac driving case, the polynomial expansion of the capacitive force is used in the model. The successfully fittings of the pull-in voltage and the hard spring effect prove that our simulation method could be used for guiding the geometrical design of cantilever-based sensors.

Population Swap of a Pair of Quantum Dots Coupling to a Plasmonic Nanocavity

We theoretically design a single-mode plasmonic ring nanocavity. Based on the plasmonic cavity, the exciton dynamics between two identical quantum dots （QD-p, QD-q） coupled to the nanocavity are investigated. It is shown that the coupling factors gi （i = p, q） between QD-i and surface plasmons are both equal to 12.53meV in our model and exeiton population swap between the two QDs can be realized. The periods and amplitudes of population oscillations can be modified by the coupling factors. Our results may have potential applications in quantum information and quantum computation on a chip.

Effect of oxide film on nanoscale mechanical removal of pure iron

In this paper, the properties of an oxide film formed on a pure iron surface after being polished with an H2O-based acidic slurry were investigated using an atomic force microscope （AFM）, Auger electron spectroscopy （AES）, and angle-resolved X-ray photoelectron spectroscopy （AR-XPS） to partly reveal the material removal mechanism of pure iron during chemical mechanical polishing （CMP）. The AFM results show that, when rubbed against a cone-shaped diamond tip in vacuum, the material removal depth of the polished pure iron first slowly increases to 0.45 nm with a relatively small slope of 0.11 nm/μN as the applied load increases from 0 to 4 μN, and then rapidly increases with a large slope of 1.98 nm/μN when the applied load further increases to 10 μN. In combination with the AES and AR-XPS results, a layered oxide film with approximately 2 nm thickness （roughly estimated from the sputtering rate） is formed on the pure iron surface. Moreover, the film can be simply divided into two layers, namely. an outer layer and an inner layer. The outer layer primarily consists of FeOOH （most likely α-FeOOH） and possibly Fe2O3 with a film thickness ranging from 0.36 to 0.48 nm （close to the 0.45 nm material removal depth at the 4 μN turning point）, while the inner layer primarily consists of Fe304. The mechanical strength of the outer layer is much higher than that of the inner layer. Moreover, the mechanical strength of the inner layer is quite close to that of the pure iron substrate. However, when a real CMP process is applied to pure iron, pure mechanical wear by silica particles generates almost no material removal due to the extremely high mechanical strength of the oxide film. This indicates that other mechanisms, such as in-situ chemical corrosion-enhanced mechanical wear, dominate the CMP process.