Optimizing thermoelectric (TE) materials and modules are important factors, which can lead to widespread adoption of waste heat recovery systems. The analytic co-optimization of the TE leg, heat sink, and the load resistance shows that all parameters entering the figure-of-merit (Z) do not have the same impact on cost/performance trade-off. Thermal conductivity of the TE material plays a more important role than the power factor. This study also explores the impact of heat losses and the required contact resistances. Finally, we present the theoretical cost performance ($/W) of TE waste heat recovery systems for vehicle waste heat recovery application, assuming hot side gas temperature of 600 °C and a cooling water temperature of 60 °C.

The divalent alkaline-earth metal hexaboride MB6 (M = Ca, Sr, Ba) one-dimensional (1D) nanostructures are promising n-type thermoelectric materials for high temperature power generation. Understanding fundamental physical and mechanical properties of these new nanostructures is critical for their future applications. Current work focuses on reliable study of mechanical properties of MB6 1D nanostructures by nanoindentation. Factors affecting the measured nanostructure-on-substrate system modulus, such as the stiffness of a supporting substrate, the width and cross section of a nanostructure, the interaction between a nanostructure and a substrate, were systematically studied by both experimental investigation and numerical simulation. The intrinsic modulus of a nanostructure, extracted from the measured system modulus, was determined between two bounds set by the receding contact and the perfect bond interaction between a nanostructure and a substrate, respectively. The extracted modulus increases as the width-to-thickness ratio of a nanostructure increases from 1 to 2.

We report here investigations on the superstructure modulation induced by the ordering of carbon vacancies in the nonstoichiometric zirconium carbide of ZrC0.61, which was prepared by spark plasma sintering (SPS) of the mechanochemically synthesized ZrCx nanopowders. The sintered ZrC0.61 is found to exhibit an interesting microstructure of interlaced laminated sheets. In contrast to the previous long duration post annealing for realization of the ordered carbon vacancies in the rocksalt-structured transition metal carbide, the ordered carbon vacancies are directly obtained during the SPS process, and no post-annealing period is necessary. With the help of transmission electron microscopy, the superstructural nanodomains with the average size of ∼30 nm are identified.

First-principle calculations are performed to investigate the mechanical shear strength and sliding characteristic of Ni(111)/α-Al2O3(0001) interfaces. Two types of interface models are considered, i.e., Al-terminated O-site and O-terminated Al-site models. Mechanical properties such as theoretical shear strength, unstable stacking energy, and critical displacement are examined. It is found that the shear deformation of the Ni/Al2O3 interfaces takes place by a process of successive breaking and rebonding of the Al–O bonds near the Al2 or Al3 atom inside the α-Al2O3 block accompanying the sliding of Ni atomic layer, and finally the Ni/Al2O3 interfaces fail between the Ni atomic layer. Relatively, the Al–O interface possesses a superior shear resistance than the O–Al interface. In addition, the mechanical shear strength and tensile strength are discussed, together with the potential usage of these theoretical results that could offer in fabricating actual thermal barrier coating systems and in analyzing their mechanical response.

The plane strain bulge test technique is a powerful and acknowledged technique for characterizing the mechanical behavior of thin films. In a bulge test analysis, the stress and strain are derived from the measured quantities using analytical approximations of the deformed geometry (bulge equations). To improve the bulge test, the systematic error introduced by these approximations is evaluated and quantified by scrutinizing the method on a finite element model of the bulge test, used as an idealized experiment.

We describe the fabrication of core–shell colloidal spheres composed of a shell of tin sulfide and a core of polystyrene. The tin sulfide shell is deposited on micrometer-sized latex spheres using a sonochemical technique. By angle-dependent light scattering and electron microscopy, we find that the refractive index of the shell is 3.0 at a wave length of 1064 nm, and the shell’s thickness is controllable in the range of 30–60 nm. The resulting spheres have a narrow distribution of sizes, are stable in aqueous suspension, and are very strong scatterers in the near infrared with potential application in photonic band gap materials or other photonic devices.

Electro-optical films composed of liquid crystal (LC) microdroplets encapsulated in an organically modified xerogel matrix were prepared by combined sol-gel and phase separation methods. The incorporation of a titanium alkoxide in the synthesis process as a co-precursor to silicon alkoxides was achieved without any destructive influence on the macroscopic LC phase separation. The consequent increase in the refractive index of the matrix satisfied the important criteria for high-performance films. The prepared films exhibit an outstanding 75.9% change in transmittance as an electric field is applied. An original setup was developed that enables the measurement of the film transmittance versus applied voltage at different temperatures over the full visible and near-infrared (near-IR) spectral range. For the first time, the relationship between these important characteristics (i.e., change in transmittance versus wave length versus temperature) was measured for a xerogel-dispersed LC composite film. The maximum of the curve increased and moved from the IR to the midvisible range with increasing temperature, achieving its maximum at 25.2 °C and 551 nm.

NaGd(WO4)2:Eu3+ nanotubes have been successfully synthesized by the hydrothermal method using carbon nanotubes (CNTs) as removable templates. X-ray diffraction, thermogravimetric and differential thermal analysis, transmission electron microscopy, and photoluminescence were used to characterize the product. It is demonstrated that CNTs are fully coated with an amorphous NaGd(WO4)2:Eu3+ layer, which is about 7 nm thick and almost continuous and uniform. After the NaGd(WO4)2:Eu3+/CNTs composites have been calcined at 500 or 600 °C, NaGd(WO4)2:Eu3+ nanotubes are obtained by removing the CNTs templates, and the outer diameter of that is about 40 nm. The luminescence properties of the NaGd(WO4)2:Eu3+ nanotubes calcined at various temperatures have been investigated. The results indicate that the products exhibit a characteristic red emission peak of Eu3+ ions at 615 nm. The emission intensity decreases with the increasing of annealing temperature, which is probably because a few residual carbons doped in NaGd(WO4)2:Eu3+ nanotubes and many oxygen vacancies could promote the intensity of red emission of Eu3+.

Characterizing the residual stress of thick nanocrystalline electrodeposits poses several unique challenges due to their fine grain structure, thickness distribution, and matte surface. We use a three-dimensional profilometry-based approach that addresses each of these complicating factors and enables quantitative analysis of residual stress with reasonable accuracy. The specific emphasis of this work is on thick (10–100 μm), nanocrystalline Ni-W electrodeposits of the finest grain sizes (4–63 nm), in which residual stresses arise during the deposition process as well as during postdeposition annealing. The present measurements offer quantitative insight into the mechanisms of stress development and evolution in these alloys, suggesting that the grain boundary structure is out of equilibrium (unrelaxed) and contains the excess free volume that controls the resulting residual stress levels in these films. There are apparently two factors contributing to this stress: the percentage of excess free volume contained in the grain boundaries, which is affected by the processing conditions, and the total volume fraction of grain boundaries, which is controlled by the grain size.

The hardening effect caused by the relaxation of nonequilibrium grain boundary structure has been explored in nanocrystalline Ni–W alloys. First, the kinetics of relaxation hardening are studied, showing that higher annealing temperatures result in faster, more pronounced strengthening. Based on the temperature dependence of relaxation strengthening kinetics, triple junction diffusion is suggested as a plausible kinetic rate limiter for the removal of excess grain boundary defects in these materials. Second, the magnitude of relaxation strengthening is explored over a wide range of grain sizes spanning the Hall–Petch breakdown, with an apparent maximum hardening effect found at a grain size below 10 nm. The apparent activation volume for plastic deformation is unaffected by annealing for grain sizes down to ∼10 nm, but increases with annealing for the finest grain sizes, suggesting a change in the dominant deformation mechanism for these structures.

The effects of temperature and alloying elements on deformation in the high-strain-rate regime were investigated by testing fine-grained magnesium alloys with an average grain size of 2 ∼ 3 μm by a nanoindentation technique. The dynamic hardness measurements aligned well with existing quasistatic data, together spanning a wide range of strain rates, 10−3 ∼ 150/s. The high-rate hardness was influenced by various alloying elements (Al, Li, Y and Zn) to different degrees, consistent with expectations based on solid solution strengthening. Transmission electron microscopy observations of the indented region revealed no evidence for deformation twins for any alloying elements, despite the high strain-rate. The activation energy for deformation in the present alloys was found to be 85 ∼ 300 kJ/mol within the temperature range of 298 ∼ 373 K, corresponding to a dominant deformation mechanism of dislocation glide.

The effect of direct current (dc) substrate bias on the promotion of nanocrystallization in Si network has been studied, specifically within He-diluted SiH4 plasma in radio frequency (RF)-plasma-enhanced chemical vapor deposition. In view of organizing nanocrystallinity, controlled transmission of energy to the growing surface is needed and that is obtainable from metastable helium (He*) bombardment and, in particular, ionic helium (He+) bombardment under negative substrate bias. The structural morphology has been adequately regulated to a homogeneous network restraining from an exclusive columnar structure that is coherent to low-temperature growth. Notable improvements in the film quality in terms of enhanced crystallinity with low hydrogen content as well as reduced incubation volume, bulk void, and surface roughness have been demonstrated, even at low substrate temperature and low RF power. Use of appropriate dc substrate-bias has been identified as a supplementary parameter efficiently organizing the growth, making it more device-friendly.

Boron-doped, single (∼54 nm) or double (∼21 + 54 nm) Si1−xGex layers were epitaxially grown on 300-mm-diameter p−-Si(100) device wafers with 20 nm technology node design features, by ultrahigh vacuum chemical vapor deposition. The Si1−xGex/Si wafers were annealed in the temperature range of 950–1050 °C for 60 s to investigate the effect of annealing on possible changes of Ge content and Si stress near the Si1−xGex/Si interface. High spectral resolution, micro-Raman spectroscopy was used as a nondestructive characterization technique with five excitation wavelengths of 363.8, 441.6, 457.9, 488.0, and 514.5 nm. Ge diffusion and generation of compressive stress at the Si1−xGex/Si interface were measured on all annealed wafers. Ge diffusion and the accumulation of compressive Si stress after annealing showed significantly different behaviors between single- and double-layer Si1−xGex/Si wafers. Raman characterization results were compared with secondary ion mass spectroscopy and high-resolution x-ray diffraction results.