Reducing the delay of backend interconnects is critical in delivering improved performance in next generation computer chips. One option is to implement interlayer dielectric (ILD) materials with increasingly lower dielectric constant (k) values. Despite industry need, there has been a recent decrease in study and production of these materials in academia and business communities. We have generated a backbone and porogen system that allows us to control porosity from 0 to 60% volume, achieve k-values from 3.4 to 1.6, maintain high chemical stability to various wet cleans, and deliver uniquely high mechanical strength at a given porosity. Finite element modeling and experimental results demonstrate that further improvements can be achieved through control of the pore volume into an ordered network. With hopes to spur more materials development, this paper discusses some molecular design and nanoscale hierarchical principles relevant to making next generation low-k ILD materials.

Carbon nanodots (CDs) have generated enormous excitement because of their superiority in water solubility, chemical inertness, low toxicity, ease of functionalization and resistance to photobleaching. Here we report a facile thermal pyrolysis route to prepare CDs with high quantum yield (QY) using citric acid as the carbon source and ethylene diamine derivatives (EDAs) including triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and polyene polyamine (PEPA) as the passivation agents. We find that the CDs prepared from EDAs, such as TETA, TEPA and PEPA, show relatively high photoluminescence (PL) QY (11.4, 10.6, and 9.8%, respectively) at λex of 465 nm. The cytotoxicity of the CDs has been investigated through in vitro and in vivo bio-imaging studies. The results indicate that these CDs possess low toxicity and good biocompatibility. The unique properties such as the high PL QY at large excitation wave length and the low toxicity of the resulting CDs make them promising fluorescent nanoprobes for applications in optical bio-imaging and biosensing.

Silicone Rubber (SR) filled with graphene nanoplatelets (GNPs) and carbon black (CB) is prepared for high performance flexible pressure sensor. Due to the synergetic effect of mixed GNPs and CB, the percolation threshold of GNPs/CB/SR is lower than that of CB/SR, which indicates the addition of GNPs is contributed to enhance the electrical conductivity of GNPs/CB/SR. Moreover, the GNPs/CB/SR has a higher electrical stability and weaker resistance creep than that of GNPs/SR. That is to say, the addition of CB can promote the electrical and mechanical performance of GNPs/CB/SR, simultaneously. The pressure sensor array based on GNPs/CB/SR with weight on different sensing element is tested, and the results show that the size of applied loading on the pressure-sensitivity array can be recognized accurately.

Single-walled carbon nanotube (SWNT) and conductive polymer composite were studied as a potential electrode candidate for plastic electronic devices such as organic light-emitting diodes (OLEDs) and solar cells. A novel conductive polymer, poly(2,7–9,9(di(oxy-2,5,8-trioxadecane))fluorene) (PFO), was synthesized and characterized as a surfactant to disperse SWNTs in solutions. The ethylene oxide (EO) side chain of rigid PFO backbone acts as a template to wrap around SWNTs in solution. Up to 0.02% (by weight) of SWNTs are stabilized and well separated in the solution phase. The carbon nanotube can be dispersed in solutions for over 4 mo. Transmission electron microscopy (TEM) images of solvent cast film suggest highly uniformed SWNT distribution incorporated in the conductive polymer matrix. Transmittance characterization shows the film is as transparent as indium tin oxide conducting glass. Conductivity measurement shows SWNTs can effectively inject charges into the PFO polymer matrix at low voltage. The current versus voltage profile of the SWNT/PFO composite film (2% SWNT in PFO by weight) shows that the majority current conducting is carried by SWNTs.

Nanoporous carbon monoliths with different pore structures were obtained by carbonizing cured phenol–formaldehyde (PF) resin/poly(methyl methacrylate) (PMMA) blends. The effect of the molecular weight of PMMA, reaction activity of PF, and content ratio of compositions on the pore structure of carbon monoliths was systematically investigated, with emphasis on controlling the morphology of the nanostructure and pore size distribution. Nanostructures were an important factor in determining the compressive strength of porous carbon monoliths. The relationship between the nanoporous structure of carbon monoliths and compressive strength was revealed. Co-continuous pores provided escape channels for those volatile gases produced in the carbonization process to escape, reducing inner stress of the carbon materials. During compressive loading, co-continuous pores could also help to scatter and absorb the stress and energy. Porous carbon monoliths with a compressive strength of 34 MPa were obtained, and the compressive strength increased by 580% compared with that of carbon monoliths obtained from pure PF.

Powders of BaSnO3 were synthesized to obtain gas sensor thick films (using the screen printing technique) for the detection of O2 and CO. Impedance spectroscopy was used at different atmospheres and temperatures. In the presence of O2, the films showed a maximum value of sensitivity at 300 °C, with the powders formed by Pechini presenting greater reproducibility and sensitivity (with an order of magnitude greater than that for the powders formed by precipitation). Results showed that the films formed with powders obtained using the Pechini method presented a better response to CO, with a maximum sensitivity at 450 °C. In addition, in the presence of CO and for T > 250 °C, these films showed an anomalous behavior regarding their sensitivity as a function of time when platinum electrodes were used: a great increase in the electrical resistance value for exposure times greater than 10 min.

In this study, resistive switching (RS), polarization switching, and charge distribution under DC bias in undoped ZnO thin films are studied by applying scanning probe microscopy (SPM) techniques on the same location. The techniques include Piezoresponce Force Microscopy, Kelvin Probe Force Microscopy, and Conductive Atomic Force Microscopy. The effects of oxygen partial pressure during the film deposition are also investigated. The results show that high resistance state (HRS) is accompanied by the polarization switching and charges storage. By comparing the SPMs results from the same location, it is found that the oxygen partial pressure during film deposition is an important factor over the holes injection during the poling processes in the HRS. On the other hand, the low resistance state (LRS) may be dominated by the electrons injection. Based on these findings, the energy band diagrams in the Pt-tip/ZnO-film/Pt-bottom-electrode structure with the applications of the external biases are illustrated schematically. This study also proposes a more persuasive mechanism of RS in ZnO films.

Thermoluminescence (TL) and radioluminescence (RL) are reported over the temperature range 25–673 K from MgSiO4:Tb and MgSiO4:Eu. The dominant signals arise from the transitions within the Rare Earth (RE) dopants, with limited intensity from intrinsic or host defect sites. The Tb and Eu ions distort the lattice and alter the stability of the TL sites and the peak TL temperature scales with the Tb and Eu ion size. The larger Eu ions stabilize the trapped charges more than for the Tb, and so the Eu TL peak temperatures are ∼20% higher. There are further size effects linked to the TL driven by the volume of the upper state orbitals of the rare earth transitions. For Eu the temperatures of the TL peaks are wavelength dependent since higher excited states couple to distant traps via more extensive orbits. The same pattern of peak temperature data is encoded in RL during heating. The data imply that there are sites in which the rare earth and charge stabilizing defects are closely associated within the host lattice, and the stability of the entire complex is linked to the lattice distortions from inclusions of impurities.

Hot compression tests were carried out on the duplex α + β leaded brass CuZn39Pb3 in temperature range of 600–800 °C and at strain rates of 0.001–1 s−1. A self-consistent model was used to analyze the flow behavior of the constituents and the material. A linear viscoplastic model was used to relate the flow stress of β and α + β composite to strain rate and the corresponding viscosity parameters were calculated at various deformation conditions. Using the viscosity parameters of β and α + β and the volume fractions of the constituents, the viscosity parameter of α was calculated. The values of the viscosity-like parameters and strain rate sensitivity for β and α + β composite were calculated using the nonlinear powerlaw viscoplastic equation. The results showed that the flow stress of α calculated using the self-consistent model was considerably higher than that of β. The difference could be attributed to the lower Zn content in α. The flow stress of α + β composite was calculated using the law of mixture rule. The law of mixture modeling of α + β composite for the iso-strain condition resulted to the overestimation of flow stress. The difference between the experimental and predicted results was attribute to the strain partitioning between α and β.

The microstructures, high-temperature mechanical properties, and fracture behavior of Mg–Gd–Y–Zr alloy components produced by low-pressure sand casting with different Gd and Zr contents, have been investigated. The ultimate tensile strength (UTS), tensile yield strength, and total elongation (EL) were measured within the 25–300 °C range. At the same temperatures, the UTS and yield strength (YS) of the T6 treated Mg–xGd–3Y–0.5Zr alloys increased with Gd content increasing from 9 to 11%, which was attributed to the improvement of precipitation strengthening. Increasing the Zr content from 0.3 to 0.5% leads to dramatic decrease in grain size and improved tensile properties of T6 treated Mg–10Gd–3Y–yZr alloys which is considered to be due to grain-boundary strengthening. With the increase of tensile temperature, both UTS and YS of the T6 treated Mg–xGd–3Y–yZr alloys initially increase and then decrease. The β′ precipitates provide important strengthening sources in experimental alloys, especially at elevated temperatures. The Mg–10Gd–3Y–0.5Zr alloy shows good combination of strength and EL within the 25–300 °C range.

By combining the techniques of directional solidification and coating Y2O3, a Cr–20Nb–40Ti alloy was manufactured successfully with various growth rates. The revolution of microstructures and corresponding mechanical properties was discussed to develop the Cr2Nb based alloys with good combination of mechanical properties. The results show that the favorable growth dynamics of plane (220) of Laves phase Cr2Nb was observed with the increase of growth rate. Phase selection took place in microstructures evolved from the primary Cr2Nb, via the dendrite-like eutectic Cr2Nb/β-Ti, and finally to the primary β-Ti, with increasing the growth rate from 5 to 200 μm/s. Based on the coupled zone of eutectic, the competitive growth of solidified phases in the directionally solidified Cr–20Nb–40Ti alloy was elucidated. In addition, the mechanical properties of alloy depended on the growth rate, and the fracture toughness of the alloy reached 16.50 MPa m1/2 at 200 μm/s, much larger than 1.40 MPa m1/2 for single-phase Cr2Nb.

This study modified the surfaces of three kinds of TiNi-based shape memory alloys (SMAs) by dry electrical discharge machining (EDM) in nitrogen (N2) and acetylene (C2H2) gas mixture. The effects of composition of the dielectric medium and work-piece on the machining performance and surface characteristics were investigated. Increasing the ratio of acetylene gas in gas mixture was beneficial for improving the material removal rate (MRR). However, adding a large amount of acetylene gas resulted in unstable discharge. A recast layer, comprising nitrides and carbides, which well adhered on the EDMed surface exhibited high hardness. Among Ti50Ni50, Ti50Ni49.5Cr0.5, and Ti40.5Ni49.5Zr10 SMA as a work-piece, Ti40.5Ni49.5Zr10 SMA has the lowest MRR owing to it possessed the highest melting temperature and thermal conductivity. The recast layer on Ti40.5Ni49.5Zr10 SMA, comprising zirconium nitride, exhibited the highest hardness and adhesion among all the SMAs. However, the high-hardness recast layer deteriorated the shape recovery of the SMA.

Electrochemical micromachining (ECMM) with microtool electrodes is a promising method for microshaping bulk metallic glasses (BMGs) at room temperature. A key challenge is the control of the electrode reactions to impede the disturbing passive layer formation on machined surface regions. In the example case of a Fe-based glassy Fe65.5Cr4Mo4Ga4P12C5B5.5 alloy, it will be demonstrated that by using an aqueous electrolyte based on 0.1 M H2SO4 solution with up to 0.1 M Fe2(SO4)3 addition and by applying ultrashort voltage pulses, complex microstructures can be machined with high precision. Potentiodynamic polarization measurements reveal that the salt addition reduces the charge transfer resistance of the microtool and therefore, the negative bias potential effect. The free corrosion and passive state of the BMG workpiece are affected, but not the transpassive regime. Systematic ECMM studies were conducted to obtain optimum parameters for shaping complex lateral structures with very smooth and well-defined machining areas.

Microstructural and property evolution of 1050 commercial pure aluminum subjected to high-strain-rate deformation (1.2–2.3 × 103 s−1) by split Hopkinson pressure bar (SHPB) and subsequent annealing treatment were investigated. The as-deformed and their annealed samples at 373–523 K were characterized by transmission electron microscopy (TEM) and microhardness tests. TEM observations reveal that the as-deformed sample is mainly composed of a lamellar structure, whose transverse/longitudinal average subgrain/cell sizes are 293 and 694 nm, respectively. The initial coarse grains are refined significantly. The initial lamellar grain structures are subdivided into pancake-shaped subgrains due to a gradual transition by triple junction motion at 473 K, and then a dramatic microstructural coarsening is observed at 523 K. It is suggested that annealing behavior of this dynamic loading structure is better considered as a continuous process of grain coarsening or continuous recovery.

A novel sort of cellular titanium foam with the porosity of 86–90% and the main-pore size of 0.5–3.0 mm was successfully prepared. Such foam exhibited a compressive curve showing three regimes: the initial elasticity, the middle zigzag plateau, and the final “densification.” This “densification” presented a course that the broken pieces continually accumulated in those pores which were unbroken or not entirely broken. The fracture morphology suggested that the compressive failure was typically brittle for this titanium foam. The electromagnetic shielding performance was investigated in the radio wave frequency range (0.3–3000 MHz) for this foam, which showed an evident effectiveness with a good performance at low frequencies. On the whole, the effectiveness would be superior while the porosity of the sample was relatively small. It could be inferred that the present foam samples would perform their electromagnetic shielding mainly by the reflection loss mechanism in the low-frequency range, and give priority to the absorption loss mechanism at the upper-frequencies.

Copper–silver core–shell nanowires were synthesized using a combination of two methods: electrodeposition in a polycarbonate membrane as a template for the synthesis of a copper core and a galvanic replacement reaction for the elaboration of a silver shell. A comparative study between aqueous and ionic liquid media was performed for the silver shell elaboration. The kinetics of the reaction in both media was monitored by using energy dispersive x-ray spectroscopy. The shape and size of the nanowires were observed by both scanning electron microscopy and transmission electron microscopy. The core–shell structure was determined by electron energy loss spectroscopy analyses for the Cu90Ag10 composition. A homogenous silver shell was formed in aqueous media. Whereas in ionic solvent, well defined silver crystals were obtained at the surface of the nanowires but without a total formation of a silver shell structure.

The work hardening behavior of electrodeposited nanocrystalline nickel (29 and 19 nm) was investigated under multiaxial loading and compared with coarse-grained nickel. Plastic strain gradients were introduced into the materials using large Rockwell D hardness indentations, and measured through cross-sectional hardness profiles. The results showed that the coarse-grained material exhibited substantial hardening up to twice the hardness of the deformation-free area due to dislocation mediated deformation, while the nanocrystalline materials displayed small hardness variations along the strain gradient, indicative of considerably reduced dislocation interactions. Moreover, the grain structure analysis (cumulative volume fraction and size distribution) for the nanocrystalline materials suggested the operation of both dislocation mediated and grain boundary controlled deformation mechanisms, the latter becoming more significant with increasing cumulative sample volume of very small grains. The plastic deformation zone sizes under Rockwell indentation of the 29 nm Ni are similar to those conventional materials with reduced strain hardening. Microhardness-indentation size effects were negligible in both the nanocrystalline and coarse-grained materials.

Indentation as a means to extract creep properties has the advantage that it can be applied directly to micro/nano-structures. Many studies on indentation creep reported at least partially poor agreement with creep parameters derived from uniaxial test. One important reason for the incompatibility is the neglect of transient creep. Another one is the choice of equivalent stress and strain measures to relate the different material responses. Applying a material model that accounts for transient creep effects we propose an efficient method for deriving creep properties from short-time spherical indentation tests. We first determine a subsurface point where the material response is very close to that observed in uniaxial tests. We then map the load–displacement data to the material response, expressed in terms of two dimensionless variables, at this point. Converting the dimensionless variables data to stress, strain, and strain rate data, we finally determine the material's creep coefficient and exponent.

Crack propagation behaviors in a precracked single crystal Ag under mode I loading at different temperatures are studied by molecular dynamics simulation. The simulation results show that the crack propagation behaviors are sensitive to external temperature. At 0 K, the crack propagates in a brittle manner. Crack tip blunting and void generation are first observed followed by void growth and linkage with the main crack, which lead to the propagation of the main crack and brittle failure immediately without any microstructure evolution. As the temperature gets higher, more void nucleations and dislocation emissions occur in the crack propagation process. The deformation of the single crystal Ag can be considered as plastic deformation due to dislocation emissions. The crack propagation dynamics characterizing the microstructure evolution of atoms around the crack tip is also shown. Finally, it is shown that the stress of the single crystal Ag changes with the crack length synchronously.