Atomic Force Microscope (AFM) was used to perform surface force measurements in contact mode to investigate surface properties of model systems at the nanoscale. Model systems were considered and compared. The first one was related to systems of controlled chemical surface properties with identical mechanical properties (chemically modified silicon substrates with hydroxyl, amine, methyl and ester functional groups). The second one deals with model polymer networks (Cross-linked polydimethylsiloxane or PDMS) of controlled mechanical properties and identical surface chemistry. The third system consists in a model polymer network, whose surface is chemically controlled with the same groups as before with silicon substrates. The results show that the viscoelastic contribution is dominating in the adhesion force measurement. Finally, we propose a relationship (derived from the Gent and Schultz's one), which expresses the AFM adhesion force as a function of mechanical energy dissipated in the contact and the surface properties of the material.

A multiscale Green's function method is described for modeling the mechanical response of quantum nanostructures in semiconductors. The method accounts for the discreteness of the lattice in and around the nanostructure, and uses the continuum Green's function to model extended defects such as free surfaces in the host solid. The method is applied to calculate the displacement field due to a Ge quantum dot in a semi-infinite Si lattice. Corresponding continuum values of the displacement field are also reported.

Aerosol deposition method (ADM) for shock-consolidation of fine ceramics powder to form dense and hard layers is reported. Submicron ceramic particles were accelerated by gas flow in the nozzle up to velocity of several hundred m/s. During interaction with substrate, these particles formed thick (10 ∼ 100 μm), dense, uniform and hard ceramics layers. Experiments were fulfilled at room temperature. The results of fabrications, microstructure and mechanical properties of oxides (Al2O3; (Ni,Zn)Fe2O3; Pb(Zr0.52,Ti0.48)O3 and non-oxide (AlN; MgB2) materials are presented. Every layer has polycrystalline structure with nano-meter order scale.

This study focuses on the atomistics of interface-mediated plasticity in thin metallic films. Molecular statics simulations are carried out to model the tensile stress-strain response of the free-standing and substrate-bonded films. In the free-standing film dislocation glide readily occurs, inducing slip steps at both surfaces of the film. The existence of an interface with the substrate constrains the dislocation motion in the film and restricts the slip steps to only the free surface. The propensity of film plasticity is dictated by the capability of atoms to slide along the interface. The flow stress of the film can be correlated with the dislocation activities obtained from the simulation. The propensity of spreading of relatively energetic atoms associated with the dislocation near the interface is also discussed.

We present a detailed nanoindentation study of micron-scale thin films of polystyrene (PS), poly(phenylene oxide) (PPO), poly(methyl methacrylate) (PMMA), a metal-centered PMMA-Ruthenium block copolymer, and a PS-poly(ethylene-propylene) (PS-PEP) block copolymer with lamellar morphology. The results show that size-dependence is most readily noticeable for the lamellar PS-PEP film, indicating that the nanoidentation approach has sufficient sensitivity to capture scale dependence on scales in the range of tens of nanometers. The less pronounced scale-dependence (or lack thereof) in the other films is discussed in the context of identifying the physical length-scale of elementary processes of plastic deformation. The results indicate that the upper limit on the size of plastic shear zones in amorphous polymers is approximately 1200-9600 nm3 (i.e. a sphere with a diameter in the range of 20-40 nm).

In this paper, we have studied the capability of the AFM to perform nanoindentation experiments. We mainly focused on the importance of a rigorous experimental procedure to get quantitative and reproducible data with the Atomic Force Microscopy (AFM). Systematic calibration procedure of AFM measurements, as well as a complete description of the mechanical behavior of the soft material is necessary before producing reliable quantitative data. In particular, the influences of the creep and of the strain rate have been studied. Then, this technique was used to probe model cross-linked polydimethylsiloxane (PDMS) and to extract their surface mechanical properties at the nanoscale. Young modulus of each sample was calculated by comparing different contact mechanics theories (Hertz and JKR theories and a power law expression). In conclusion, the contact mechanics relationships have to be redefined and adapted to soft materials. In particular, it appears necessary to consider the specific mechanical contribution of the polymers.

Critical thickness theory was developed to account for the ability of thin epitaxial metal and semiconductor layers to support high misfit or coherency strain. The thermodynamic equilibrium theory is correct, and is well approximated by a theory based on geometrical arguments. The latter theory is readily extended to arbitrary misfit strain profiles including linearly graded layers, for which a surface layer free of misfit dislocations. This result applies as well to linear strain gradients introduced by deformation, in which case the misfit dislocations are known as geometrically necessary dislocations. We show that a consequence of this surface layer is that the apparent yield strength of the material increases in small structures such as thin wires in torsion. Under large plastic deformation, even if the material is perfectly plastic, critical thickness theory also predicts an apparent work-hardening. The predictions of critical thickness theory are in excellent agreement with experimental data in the literature.

TiN and AlN are promising thin film materials. There is continuing interest in their mechanical, electronic and optoelectronic properties. Our studies have shown that mechanical properties can be changed by forming thin film heterostructures of the two materials. We report on our pulsed laser deposition assisted synthesis, microstructural characterizations and mechanical properties of TiN/AlN multi-layer structures. The TiN/AlN superlattice structures are fabricated on (100) silicon substrates at different temperatures (400-800oC) and different nitrogen ambient pressures. The nano-mechanical hardness properties of the multi-layered structures were examined as a function of thickness of individual layers keeping the overall thickness of heterostructures constant. Thickness variations of the films are measured with a optical phase-shift interferometer. The mechanical properties of the TiN-AlN heterostructures have been found to be associated with interfacial interaction between layers. The interfacial interaction, in turn, depends on processing parameters the most important among which is substrate temperature.

The effects of the addition of mixed cations, i.e. Na+/Cs+, Ba2+/Cs+, and Ba2+/Zn2+, to the acid form sulfonated styrene copolymers on their dynamic mechanical properties and morphology were investigated. It was found that the matrix glass transition temperatures did not change with the ratio of the one cation to the other. As expected, however, the ratio of one cation to the other in the mixed cations affected cluster glass transition temperatures significantly. It was also found that the activation energies for the glass transitions for the matrix phase remained constant, while those for the cluster phase changed with the ratio of the two cations. In addition, the position of the SAXS peak was found to be affected by the type of cations. From the results obtained above, the decrease in the cluster Tg with increasing the amount of cesium and zinc cations in Na/Cs, Ba/ Cs, and Ba/Zn mixtures, were explained on the basis of the considerations of the size, charge, and type of cations, which alter the degree of clustering as well as ion-hopping mechanism.

The effects of ternary element addition of manganese on microstructure and mechanical properties of nanocrystalline L12 (Al+X at.%Mn)3Ti (X=0 - 12) fabricated by mechanical alloying and spark plasma sintering (SPS) were investigated. The SPS method was used to consolidate nanocrystalline L12 (Al+X at.%Mn)3Ti with the pressure of 50 MPa. The heating rate was 100°C /min. The final sintering temperature was determined from the observation of the shrinkage of the specimen. In binary Al3Ti, the final sintering temperature was 864°C. The sintering temperature was reduced down to 658°C with increasing Mn concentration. After SPS, the L12 structure was maintained in the specimens which contained Mn concentration of 8- 12 at.%. The microhardness test, grain size measurements, and fracture toughness test were conducted as a function of Mn concentration. In order to investigate the effect of the grain size on the microhardness and fracture toughness of the (Al+8 at.%Mn)3Ti, heat treatments were performed in a vacuum furnace ( 10-3 torr ). With increasing heat treatment temperature, the microhardness decreased due to the formation and growth of Al4C3, Al2O3, and TiC, while fracture toughness increased. The fracture toughness of 4.12 MPa m1/2 was attained for the (Al+8 at.%Mn)3Ti specimen and it was the highest value among the specimens after 1h heat treatment at 1100°C. The grain sizes were about 60 nm and 100 nm after 1 h heat treatment at 900°C and 1100°C, respectively.

Nanoparticle chain aggregates (NCA) serve as reinforcing fillers that are combined with molecular polymers to produce nano-composite materials, e.g. carbon black in rubber. The reinforcing mechanism due to the incorporation of nanoparticle aggregates is not well understood. Molecular dynamics (MD) computer simulations are employed to investigate the behavior of nanoparticle chain aggregates under strain. The interaction potential used is that of Cu obtained with the embedded atom method (EAM). Three single-crystal Cu nanoparticles are placed in contact in two different configurations (linear and kinked) and the structures are initially relaxed with MD steps for 300 ps. We observe plastic deformation during the sintering process for very small particles (∼2.5 nm in diameter) at temperatures as low as 300 K. The relaxed configurations are then strained to the breaking point at strain rates in the order of 1 m/s. We identify mechanisms of strain accommodation that lead to nanoparticle plastic deformation and eventually fracture. The linear and the kinked configurations break at strains of 0.263 and 0.344 respectively, while the maximum stress is close to 4 GPa (strain rate: 0.625 m/s). Both structures fail at the low-angle grain boundaries developed during the sintering process, while the higher strain for fracture for the kinked configuration is associated with interface sliding not observed in the linear case.

Bicrystal experiments were performed to investigate atomic structures and high-temperature creep properties of [0001] symmetric tilt grain boundaries in Al2O3. Al2O3 bicrystals with Σ7, Σ31 and Σ39 boundaries were fabricated by a diffusion bonding technique, and their atomic arrangements at the grain boundary cores were analyzed by high-resolution transmission electron microscopy (HRTEM), in combination with static lattice calculations based on two-body ionic potentials. Compressive creep tests were also conducted to examine the behavior of grain boundary sliding for the above bicrystals. It was found that the behavior of grain boundary sliding depends on the grain boundary characters, whereas the trend of grain boundary sliding was not related to their Σ values. In contrast, HRTEM observations showed that the Σ31 boundary exhibiting the highest sliding rate has open spaces at the boundary core. Since grain boundary diffusion is expected to accommodate strains at grain boundary cores during sliding, it is likely that such open spaces give rise to high diffusivity at the grain boundary core, which results in the rapid grain boundary sliding of Σ31.

Four point bend (4PB) tests are currently used to characterize the adhesive strength of thin films. Of particular interest are low k films whose strength properties are normally less than traditional dielectrics. A finite element analysis (FEA) of a 4PB specimen is conducted in order to better understand the results and limitations of such testing. We discuss the classical equation used to convert 4PB test data into fracture energy and have validated this classical formula using finite element analysis. We also present a theory that explains one possible reason for the occurrence of anomalous test results where the film fails in a cohesive rather than an adhesive mode.

The microstructure of W, W2N single layers and W2N/W multilayers are related to their mechanical properties. We study the hardness of multilayers as function of the period thickness. Two partial pressures of nitride (PN2 = 10 % and 50 %) for W2N deposition are investigated. For the single layers, the hardness value increases with the nitrogen partial pressure. The hardness of W2N/W multilayers using PN2 = 50% for W2N deposition increases when the layer spacing decreased. A hardness value of 19.5 GPa is reached for a multilayer with PN2 = 50% and, close to 20 GPa with PN2 = 10% for all the period studied.

The MAX phases are new, thermodynamically stable, nanolayered ternary carbides and nitrides. These materials have a big potential in tribological applications due to their structure, similar to graphite or molybdenum disulfide. For example, the friction coefficients of the basal planes of Ti3SiC2 have been shown to exhibit very low (<; 5 × 10-3) friction coefficients. The aim of this study is to better understand the tribological behavior of polycrystalline Ti3SiC2 against stainless steel. Experiments were conducted on a ball-on-flat tribometer (∼ 25°C and ∼ 30% relative humidity) that simultaneously measures friction coefficients and electrical contact resistance. Different stainless steel ball diameters and normal loads were used and resulted in contact pressures between 0.35 and 1.25 GPa. Two different tribological behaviors were observed, both with relatively low friction coefficients for ceramics. The first behavior, referred to as type I, is characterized by low friction coefficients (≍ 0.15); low wear and a transfer film containing titanium and carbon formed on the ball. The other behavior, type II, is characterized by friction coefficients that starts at ≍ 0.15, and then increases to about 0.4. At the end of the experiment, the ball is worn, and compacted wear debris containing iron can be found on the plane. The two behaviors seem to be independent of contact pressure, but are rather sensitive to normal applied load. The transition between these two regimes will be discussed.

PTFE-based coatings have been widely used, for example, on aluminum molds for molding of polyolefin packaging materials for its non-stick property. However, these coatings do not meet the users' scratch resistance and durability requirements. This paper describes a preliminary study on the synthesis and characterization of a PTFE/sol-gel composite coating material which combines the required non-stick and low friction properties of PTFE filler with the high scratch resistance and durability of a silica-based sol-gel matrix. The non-stick and low friction properties were achieved by using both the PTFE filler and the lubricious compound resulting from the reaction of a solvent with siloxane. The high scratch resistance was attributed to the enhanced adhesion to the electro-chemically pre-treated surface and the optimized silica and alumina filler contents in the sol-gel material. FE-SEM/EDX, FTIR, contact angle goniometry, scratch testing and a pin-on-disc tribometry were used to evaluate the coating properties.

The boron modified poly(vinyl)silazane polymer precursor with the chemical composition (B[C2H4Si(CH3)NH]3)n was milled and sieved. The polymer particles from different size fractions were compacted using a graphite die in a uni-axial warm pressing machine at a pressure of 48 MPa and in the temperature range 250°C to 330°C. The green bodies were pyrolysed in an argon atmosphere at a temperature of 1300°C when the organic polymer converts into an inorganic amorphous Si-B-C-N ceramic. These amorphous ceramics were annealed under various conditions of temperature, nitrogen overpressure and holding time in order to crystallize them and to produce nano-crystalline microstructures. Compression creep experiments were carried out in atmospheric ambience at loads varying from 5 – 100 MPa and in the temperature range 1350°C – 1500°C to investigate the high temperature deformation behaviour of the crystalline material. The interest is to understand the mechanisms of deformation in these nanocrystalline Si-B-C-N ceramics at elevated temperatures and to compare the results with that of amorphous ceramics. The investigation also includes the determination of viscosity of the material at high temperatures.

Controlling material properties over nanometer length scales is crucial for current and emerging high-density microelectronic device packages. Miniaturization of devices is increasingly limited by the ability to “connect” to the device, and the required packaging structures must be fabricated where layer thickness and feature sizes approach micron size scales while achieving the required mechanical, thermal and electrical properties. Second phase additions such as sub-micron sized particles are often added to locally adjust the material properties of constituent layers in the complex package structure. This results in significant variation of mechanical properties over sub-micron length scales. Such manipulation of material structure and its effects on mechanical and interfacial fracture behavior are addressed using experimental and modeling studies. Underfill layers consisting of an epoxy matrix with dispersed silica beads are shown to exhibit variations of elastic and flow properties in excess of three-fold across the layer thickness. Mechanical properties are not only affected by the distribution of second-phase fillers, but also by the adhesion properties of the filler/matrix interface. Interfaces are susceptible to stress corrosion cracking associated with moisture which can lead to progressive debond growth at loads much lower than that required to exceed the critical interface fracture energies. Subcritical debonding is affected by temperature, humidity, and the bond chemistry of the interface. The effects of these variations are considered on the adhesive and subcritical debonding behavior of interfaces between model epoxy underfills and SiNx chip passivation. Implications for other constrained complex layered structures are considered.

Deformations of Au nanowires of helical structures under enforced elongation are addressed by the molecular-dynamics simulation. The embedded-atom method potential is employed for calculating the interaction between Au atoms. Model nanowires of the two kinds of helicities are prepared. Before elongation, a model nanowire is equilibrated at a specified temperature. Then, the Au atoms at one end of the nanowire are translationally moved in the axial direction. The simulation results show that a model nanowire can be elongated to form a single-atom chain of Au atoms under some circumstances.