Due to events of the past two decades, there has been new and increased usage of radiation-detection technologies for applications in homeland security, nonproliferation, and national defense. As a result, there has been renewed realization of the materials limitations of these technologies and greater demand for the development of next-generation radiation-detection materials. This review describes the current state of radiation-detection material science, with particular emphasis on national security needs and the goal of identifying the challenges and opportunities that this area represents for the materials-science community. Radiation-detector materials physics is reviewed, which sets the stage for performance metrics that determine the relative merit of existing and new materials. Semiconductors and scintillators represent the two primary classes of radiation detector materials that are of interest. The state-of-the-art and limitations for each of these materials classes are presented, along with possible avenues of research. Novel materials that could overcome the need for single crystals will also be discussed. Finally, new methods of material discovery and development are put forward, the goal being to provide more predictive guidance and faster screening of candidate materials and thus, ultimately, the faster development of superior radiation-detection materials.

A new technique called energy-loss magnetic chiral dichroism (EMCD) has recently been developed [P. Schattschneider, et al. Nature441, 486 (2006)] to measure magnetic circular dichroism in the transmission electron microscope (TEM) with a spatial resolution of 10 nm. This novel technique is the TEM counterpart of x-ray magnetic circular dichroism, which is widely used for the characterization of magnetic materials with synchrotron radiation. In this paper we describe several experimental methods that can be used to measure the EMCD signal [P. Schattschneider, et al. Nature441, 486 (2006); C. Hébert, et al. Ultramicroscopy108(3), 277 (2008); B. Warot-Fonrose, et al. Ultramicroscopy108(5), 393 (2008); L. Calmels, et al. Phys. Rev. B76, 060409 (2007); P. van Aken, et al. Microsc. Microanal.13(3), 426 (2007)] and give a review of the recent improvements of this new investigation tool. The dependence of the EMCD on several experimental conditions (such as thickness, relative orientation of beam and sample, collection and convergence angle) is investigated in the transition metals iron, cobalt, and nickel. Different scattering geometries are illustrated; their advantages and disadvantages are detailed, together with current limitations. The next realistic perspectives of this technique consist of measuring atomic specific magnetic moments, using suitable spin and orbital sum rules, [L. Calmels, et al. Phys. Rev. B76, 060409 (2007); J. Rusz, et al. Phys. Rev. B76, 060408 (2007)] with a resolution down to 2 to 3 nm.

In this study, the effects of electromigration (EM) on the growth of Cu–Sn intermetallic compounds (IMCs) in Cu/SnBi/Cu solder joints under 5 × 103 A/cm2 direct current stressing at 308, 328, and 348 K were investigated. For each Cu/SnBi/Cu solder joint under current stressing, the IMCs at the cathode side grew faster than that at the anode side. The growth of these IMCs at the anode side and the cathode side were enhanced by electric current. The growth of these IMCs at the cathode followed a parabolic growth law. The kinetics parameters of the growth of the IMCs were calculated from the thickness data of the IMCs at the cathode side at different ambient temperatures. The calculated intrinsic diffusivity (D0) of the Cu–Sn IMCs was 9.91 × 10−5 m2/s, and the activation energy of the growth of the total Cu–Sn IMC layer was 89.2 kJ/mol (0.92 eV).

Fe-doped In2O3 nanocubes were synthesized by a solvothermal method. The lattice constant a decreases linearly as Fe doping concentration increases, and Raman scattering measurement proves the incorporation of Fe ions into the In2O3 crystal lattice. Mössbauer spectra show the presence of mixed valence of Fe ions instead of Fe3O4, while the sample is superparamagnetic. The products with an average diameter of 80 nm have a single-crystalline phase and appear as a square shape. Magnetic measurements confirm the superparamagnetic properties of the nanocubes, and electron paramagnetic resonance studies indicate Fe ions occupy different sites in the In2O3 matrix.

Large area uniform nanoplates of molybdenum oxide (MoO3), a typical semiconductor material, have been synthesized under soft conditions by using carboxymethyl cellulose (CMC) as template. Under ambient condition, hydrolysis of ammonium molybdate into layered molybdenum oxide, and its subsequent inclusion of CMC polymers results in formation of lamellar CMC/molybdenum oxide hybrid. Calcinations of this lamellar hybrid at 500 °C lead to formation of large area uniform nanoplates of orthorhombic phase of MoO3. Scanning electron microscopy and transmission electron microscopy images show that these MoO3 nanoplates are regularly packed, about 100 nm in thickness and 10–100 μm in length. The mechanism of the hybrid reaction and the templating ability of CMC polymers have been extensively discussed. The oriented growth of short molybdenum oxide flakes into long-range ordered plates has been induced by CMC polymers because of the shrinking of CMC during the hybrid reaction. This is the first report that large area highly ordered molybdenum oxide nanometer materials have been obtained under soft reaction conditions.

The microstructures and mechanical properties of Mg–6Zn–5Al–4Gd–1RE (RE = Ce or Y) alloys were investigated. The addition of Ce or Y obviously refines the grain size for the Mg–6Zn–5Al–4Gd-based alloy, while the Y element has a better refining effect. The Ce and Y show different grain-refining mechanisms: Ce addition mostly promotes the growth of secondary dendrite, while Y addition mainly increases the heterogeneous nucleation sites. The hardness-versus-aging time curves indicate that all the alloys have excellent aging-hardening behavior, but the response to maximum hardness was delayed by the Ce or Y addition. The microstructure observation of the peak-aged alloys indicated a large number of nanocrystalline τ-Mg32(Al, Zn)49 precipitates in the matrix. The Y addition is beneficial to improve the mechanical properties, and the alloy has optimal values. However, the Ce addition decreases the ultimate tensile strength and elongation of the alloy due to formation of a lot of shrinkage porosities.

The electrochemical and corrosion behaviors of solder alloys—SnAgCu (SAC), SnZnBi, SnPb, and Sn—and printed circuit board finish materials Cu and AuNi were investigated in carboxylic acids (flux) and NaCl solutions using the potentiodynamic scanning technique. The results show that SAC and Sn are passivated in the diluted flux solution, but SnPb, SnZnBi, Cu, and AuNi are under active dissolution when anodically polarized. However, passivation of SAC alloy is not observed in concentrated flux solution. Although a passive film forms on SAC in a 2% NaCl solution, the film is less stable than in the flux solution. In addition, oxidation of the most commonly used lead-free and lead solders, SAC and SnPb, at high temperature was evaluated via sequential electrochemical reduction analysis (SERA). The SERA results revealed that the SAC alloy oxidized more significantly than SnPb under hot, dry conditions.

Cyclic stress–strain response of an equal channel angularly pressed Sn-3.8Ag-0.7Cu alloy was investigated to seek a mechanistic understanding of cyclic softening in Sn-rich alloys. The equal channel angular pressing (ECAP) was applied to modify the microstructure of the solder alloy by breaking up the needlelike Ag3Sn intermetallic phase into fine granules and by reducing the large β-Sn dendrites into smaller and equiaxed grains. The extruded alloys were subjected to strain-controlled fatigue test at various strain amplitudes. It was found that the extruded alloy exhibited a sharp decrease of the stress amplitude within the initial few cycles compared with the as-cast alloy. After only a few cycles, the alloy suffered from noticeable surface damage. In situ scanning electron microscopy observations of the cyclic bending specimens revealed an approximately logarithmic relationship between crack density and the number of cycles. A theoretical model of microcrack accumulation was constructed to explain the rapid cyclic softening behavior. The predicted results, based on the model, agreed well with the experimental data and indicated that the rapid softening had resulted from an increased tendency for grain boundary cracking in the ECAPed microstructure due to the increase in the grain boundary area per unit volume and the reduced resistance of Ag3Sn to grain boundary sliding.

Single-crystal SnO2 nanofibers have been formed from SnO2 polycrystals via reaction at low oxygen partial pressures. Polycrystalline SnO2 disks coated with Au nanoparticles were exposed to humid H2/N2 at 700 to 800 °C. Single-crystal SnO2 nanofibers formed beneath Au nanoparticles, with the nanofiber length oriented parallel to the [100] crystallographic direction of SnO2. Because this simple process does not require either a separate source of a Sn–O-bearing vapor species located upstream of the substrate or a temperature gradient, single-crystal nanofibers may be formed on large area SnO2-bearing substrates.

A crystalline silicon surface, loaded by a Berkovich indenter to a constant maximum load, was unloaded using three unload functions, each consisting of five linear segments of equal time period. The first function had an exponentially decaying unload rate and was found to promote a pop-out event more readily than the second function, having a linear unload rate, or the third case with its unload rate increasing with time. Statistical analyses of experimental data suggest that the unload rate within 20%–30% of the maximum load, when the mean contact pressure in the indent volume is roughly 5 to 6 GPa, is the most dominant factor influencing the probabilistic occurrence of a pop-out event. Unload rates at higher load levels were shown to have a much less significant effect on the probability of pop-out occurrence.

Depth penetration per cycle and its retardation exhibited in specimens of 6061 Al were studied. By holding the maximum load reached during loading prior to cyclic oscillating, the creep could be effectively attenuated from the cyclic indentation. Constant depth penetration of sub-nanometers per cycle was found. The interrupt segments with different amplitudes (over- and underloading) or frequencies (frequency increasing and decreasing), but with same mean load, induced immediate retardations of cyclic indentation. As the interrupt segments have more than 10 cycles, the retardation is enhanced with the increase of cycle number. Accumulation of strain hardening due to stress concentration under the indenter tip is proposed to be the mechanism by which interrupt oscillation retards subsequent cyclic indentation.

Tungsten oxide comblike nanostructures were synthesized using a two-step thermal evaporation method. The first step involving high reactor pressure and temperature was to synthesize the cores of the comb structures, upon which the teeth of the comb were grown in the second step using low operation pressures and temperatures. The teeth of the comb structure are well aligned and vertical to the side surfaces of the cores. The effects of growth parameters were examined, and the growth mechanism was investigated.

The mechanical properties of Zr52.5Ni14.6Al10Cu17.9Ti5 and Ti40Zr25Ni3Cu12Be20 metallic glasses were investigated under uniaxial compressive loading and small punch loading, respectively. The Zr-based metallic glass displays higher density of shear bands, larger critical shear offsets and higher energy absorbing capability than the Ti-based metallic glass under the small punch tests. A concept of critical shear offset is proposed to explain the difference in shear deformation abilities or plasticity of different metallic glasses. The current experiments demonstrate that, in contrast with the small difference between the responses of the Zr- and Ti-based metallic glasses under uniaxial compressive loading, the biaxial tension produced by the small punch test is an effective way to evaluate the difference in shear deformation abilities and can be used to distinguish the brittleness or plasticity of various metallic glasses.

In this work, we report a method to synthesize a peculiar composite structure of tubular carbon nanofibers (CNFs) growing on a microsized tin (Sn) whisker. The material used is a commercially available copper clad laminate (CCL). The CCL is composed of a surface copper (Cu) layer and a bottom polymer (phenol-formaldehyde resin) board, in which the polymer board is used as the carbon source. Using lithography and lift-off techniques, the Cu layer was patterned to a stripelike Cu trace. A Sn thin film was then evaporated on the polymer board near the Cu trace. To release the residue stress that resulted from the evaporation; Sn whiskers with diameters of about 2 to 5 μm were formed on the Sn thin film after evaporation. By passing an electric current through the Cu trace, the Cu trace was heated due to Joule heating and served as a heating source for the thermal decomposition of phenol-formaldehyde. After heat treatment, the CNFs grew on the surface of the Sn whiskers with tubular hollow-cored structure. The diameter of the tubular CNFs is about hundreds of nanometers and their length can reach several micrometers. The growth mechanism of the brushlike composite structure is also discussed.

The phase equilibria and phase transformation of the body-centered cubic (bcc) phase in the Cu–Ti–Al system were investigated by the diffusion couple method, metallographic examination, differential scanning calorimetry, and x-ray diffraction. The isothermal sections at 700 and 900 °C and vertical sections at 18 at.% Al, 22 at.% Al, and 25 at.% Al in the Cu-rich portion were determined. These results indicate that (i) the Cu2TiAl compound with the L21 Heusler structure has a larger solubility range; (ii) the stable B2 + L21 miscibility gap of the ordered bcc phase exists until the liquid phase, and the tie lines of this miscibility gap are almost parallel with the Cu–Ti side; (iii) the composition and temperature for the eutectic reaction (L ↔ B2 + L21) are about 7 at.% Ti and about 970 °C, respectively, and (iv) the velocity of the eutectoid decomposition [bcc ↔ face-centered cubic (fcc) + D83] of the bcc phase with martensitic morphology in the Cu–Ti–Al alloys is slower than that of the Cu–Al alloys.

The effect of electropulsing treatment (EPT) on the solution behavior of aged Mg alloy AZ61 strip was investigated using scanning electron microscope (SEM) and x-ray diffraction (XRD). It was found that EPT accelerated tremendously the dissolution of β phase into α matrix in an aged Mg alloy AZ61 strip. The dissolution of β phase took place in less than 4 s at relatively low temperature under EPT, compared with that in conventional heat treatment. A mechanism for rapid solid solution process during EPT was proposed based on the coupling of the thermal and athermal effects. The results in this investigation indicated that EPT played an important role in the nonequilibrium microstructural evolution in the alloy. It is supposed that EPT can provide a highly efficient approach for solid solution treatment of the alloy.

Laser Engineered Net Shaping (LENS™) is a laser-assisted manufacturing process that offers the possibility of producing metallic coatings and components with highly nonequilibrium microstructures. In this work, the microstructure developed by LENS deposition of Cu47Ti33Zr11Ni8Si1 powder on a bulk metallic glass substrate, with nominal composition Zr58.5Nb2.8Cu15.6Ni12.8Al10.3, is investigated. Single-layer deposition results in the formation of an inhomogeneous but partially amorphous layer above a crystalline heat-affected zone. Elemental analysis of the deposited layer indicates incomplete mixing of the powder with the melt pool. The as-deposited alloy exhibits a single glass transition event and its primary crystallization event is consistent with the first crystallization temperature of the Cu-based powder. Subsequent remelting of this layer results in a still partially amorphous deposit with a uniform composition of (Zr + Nb)51.8Cu24.7Ti3.4Ni16.4Al3.7. The remelted layer exhibits a structural rearrangement immediately prior to the primary crystallization event, possibly associated with the formation of a quasicrystalline phase.

Micro texturing of titanium implant surfaces is commonly used to enhance fixation by osseointegration, and devising robust and specific correlations between surface topographic features and implant performance is an area of active current research. In this context, we present a detailed analysis of the topographies of titanium surfaces prepared by grit blasting (GB) and grit blasting followed by acid etching (GB+AE) at two different imaging scales over a full range of statistical parameters. The surfaces were characterized using white light interferometry and atomic force microscopy, and the topographic images were processed to extract the amplitude, spatial, hybrid, and functional parameters of the surface. Although GB+AE surfaces are known to elicit significantly higher bone response than GB surfaces, the topographies differed by less than 20% (over all parameters) when averaged over 242 × 181 μm interferometric images. In contrast, measurements over smaller 25 × 25 μm areas obtained using high-resolution atomic force microscopy indicated that the GB+AE surfaces exhibit a 26% increase in root-mean-square (rms) roughness, a 63% increase in rms slope, a 75% increase in the curvature of the summits, and a 21% increase in surface area over GB surfaces. These results constitute the first identification of rms slope and summit curvatures as important topographic variables that must be considered in ongoing efforts to correlate surface topography with the performance of endosseous titanium implants.

Influence of casting temperature on the thermal stability of Cu- and Zr-based metallic glasses (MGs) was analyzed based on the monomer-cluster structural model using the Johnson–Mehl–Avrami (JMA) equation. The result indicates that increasing the casting temperature can enhance the thermal stability of MGs. It is suggested that it be attributed to the decrease in the amount of the local ordering clusters induced by the elevating casting temperature. The prediction is confirmed by continuous heating transformation diagrams constructed for the Cu- and Zr-amorphous samples obtained under different casting temperatures.

A combustion synthesis method for the synthesis of α-Si3N4 from a reactant compact composed of Si, NaN3, and NH4X and wrapped up with an igniting agent was investigated. Wrapping the reactant compact with the igniting agent (i.e., a mixture of Ti and C powders) was found necessary for the synthesis of Si3N4. In addition to NH4Cl, which was considered previously to function as a catalytic agent, other ammonium halides (i.e., NH4F, NH4Br, and NH4I) were found to be capable of catalyzing the synthesis reaction with NH4Cl being the most effective. Si3N4 could not be produced when NaN3 was replaced by C3H6N6. NaN3 was thus considered to exert an essential effect on the combustion synthesis reaction other than functioning as a solid-state nitrogen source as considered previously. It was proposed that Na vapor produced by decomposition of NaN3 reduces SiXx (formed by reaction of Si and NH4X), promoting the nitridation reaction to form Si3N4. NaN3 thus plays a role as a reducing agent in the synthesis reaction.