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This study investigated the stress relaxation and fatigue life and strength of laser peened single crystal nickel superalloy specimens compared to un-peened and shot peened specimens following hot corrosion exposure and then fatigue testing. The specimens were treated by conventional laser peening and a new cyclic laser peening plus thermal microstructure engineering process. The latter treatment supports the benefit of a unique process involving application of layers of laser peening using high energy with large footprint spots combined with interspersed cyclic annealing. Stress measurements by slitting showed the plastic penetration depth of laser peening exceeded shot peening by a factor of 24. Un-peened and peened specimens were exposed to sulphate corrosives at 700°C for 300 hours and then fatigue tested. Tests of five non-laser peened specimens all failed in low cycle fatigue regime whereas three identically tested laser peened specimens all achieved multi-million-cycle runout without failure, indicating fully consistent large benefit for life by laser peening. Additional tests also showed fatigue strength improvement of 2:1 by laser peening. Residual stress measurements post hot-corrosion exposure and fatigue testing showed notable 5 mm depth retention of residual eigenstress in a laser peened specimen.

Purpose This paper aims to develop a comprehensive model of a magnetic sensor array that will be operational for a multitude of electric components in continuous and nonintrusive condition monitoring (CM) or in readiness assessment (RA) applications. Design/methodology/approach A universal nonintrusive model of a flexible antenna array is introduced to monitor and identify failures in electric machine drives. An adjustable sensor is designed to serve as a RA for a vast range of electrical elements in a typical power system by capturing the low-frequency radiated magnetic fields. Findings The optimal placement of the most sensitive radiated fields from several components has been discovered in this case study, enabling the detection of healthy current flow throughout. Thereafter, the short-circuit investigation, representing faulty situations, is implemented and compared with healthy cases. Practical implications This sensing technique can be used for nonintrusive CM of components that are out of reach and cannot have the sensor to be held around it such as components in offshore winds, wind energy generation and power and chemical plants. Originality/value The results are provided for three commonly used machines with a single sensor array with numerous settings. The three dimensional (3 D) finite element analysis is applied in the structuring of the sensor, detection of the optimum location and recognition of faults in the machines. Finally, based on the setup design, 3 D printing is used for the construction of the sensor array. Thus, the sensor array with fault detection avoids major component failures and increases system reliability/resiliency.

Pure nanocrystalline akermanite was successfully synthesized by mechanical activation and heat treatment of talc, calcium carbonate, and silicate. Powders were characterized by thermogravimetric analysis (TGA), x-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The formation mechanism was studied in depth. These results showed that akermanite was produced by the formation and consumption of transitionary compounds such as enstatite, wollastonite, larnite, and merwinite. Pure akermanite was synthesized with a crystalline size of 34 nm after ball milling for 20 h and subsequent heat treatment at 900 °C for 1 h.

Various mechanical systems are subjected to inherent oscillatory motions often paired with extreme, high-temperature environments resulting in fretting wear. In this work, the fretting wear resistance of additively manufactured Inconel 625 was studied at room and elevated temperatures. In-situ temperature-controlled nanoindentation was employed to further elucidate mechanical property evolution as a function of temperature. The results showed a 30% decrease in near-surface mean hardness at 510 °C compared to room temperature. However, the material exhibited significantly lower wear and coefficient of friction values at high temperatures, attributed to the formation of a compacted, intermediate oxide layer preventing excessive friction and wear.

In this research, a room temperature multicycle nanoindentation technique was implemented to evaluate the effects of the laser peening (LP) process on the surface mechanical behavior of additively manufactured (AM) Inconel 625. Repetitive deformation was introduced by loading-unloading during an instrumented nanoindentation test on the as-built (No LP), 1-layer, and 4-layer laser peened (1LP and 4LP) conditions. It was observed that laser-peened specimens had a significantly higher resistance to penetration of the indenter and lower permanent deformation. This is attributed to the pre-existing dislocation density induced by LP in the material which affects the dislocation interactions during the cyclic indentation. Moreover, high levels of compressive stresses, which are greater in the 4LP specimen than the 1LP specimen, lead to more effective improvement of surface fatigue properties. The transition of the material response from elastic-plastic to almost purely elastic in 4LP specimens was initiated much earlier than it did in the No LP, and 1LP specimens. In addition to the surface fatigue properties, hardness and elastic modulus were also evaluated and compared.

Despite the potential and promising future of additive manufacturing (AM), the quality and performance of the products from metal additive manufacturing has been susceptible to skepticism. Herein, a nanoindentation method was implemented to compare the hardness, Young’s modulus, and fracture toughness in AM and hot-rolled Inconel 718. Results indicated that Young’s modulus and hardness of AM IN718 were nearly 25% and 50% smaller, respectively, compared to hot-rolled specimens. Indentation fracture toughness measurements showed that the traditionally fabricated specimens had a fracture toughness close to the reported range, but that of the AM samples was almost 25% smaller.

Self-healing materials with the ability to partially or completely restore their mechanical properties by healing the damage inflicted on them have great potential for applications where there is no or only limited access available to conduct a repair. Here, we demonstrate a bio-inspired new design for self-healing materials, where unit cells embedded in the structure are filled with a UV-curable resin and act as reservoirs for the self-healing agent. This design makes the repeated healing of mechanical damage possible. When a crack propagates and reaches one of these embedded reservoirs, the healing agent is released into the crack plane through the capillary action, and after polymerization through UV light exposure, bonds the crack faces. The structures here were fabricated using a stereolithography technique by a layer-by-layer deposition of the material. “Resin trapping” as a unique integration technique is developed for the first time to expand the capability of additive manufacturing technique for creating components with broader functionalities. The self-healing materials were manufactured in one step without any needs for any sequential stages, i.e. filling the reservoir with the healing agent, in contrast with the previously reported self-healing materials. Multiscale mechanical tests such as nanoindentation and three-point bending confirm the efficiency of our method.

The use of additive manufacturing for prototyping and manufacturing purposes is becoming a crucial topic in both industry and research. Multi Jet Fusion printing technology possesses advantages in fabricating engineering-quality parts, but the dependency of their mechanical characteristics on process parameters is not well understood. In this work, multiscale mechanical analyses were conducted with the goal of investigating the effect of build orientation on Multi Jet Fusion manufactured polyamide 12 samples. Tensile tests of samples printed in two orientations showed that build orientation resulted in different strain and stress behaviors, with vertical samples having 25% smaller fracture strains, but slightly higher (5.8%) fracture stresses than horizontal samples. Nanoindentation showed vertical samples with reduced elastic modulus (Er) values double that of horizontal, and with hardness values nearly 30% larger. Nanoscratch tests showed that vertical samples had an almost 50% increase in lateral forces. Experimental and numerical creep analyses demonstrated higher creep resistance of vertical samples as compared to the horizontal specimens. Additionally, macroscale friction measurements showed that the friction coefficient of horizontal samples was independent of the direction of sliding while coefficient of friction for vertical samples showed a 60% drop when sliding directions were varied. These results point to a dependence on print orientation in the resulting mechanical and tribological properties.

Pure nanocrystalline akermanite (Ca2MgSi2O7) powder was synthesized by mechanical activation with subsequent annealing of talc, calcium carbonate, and silicate powders as the initial materials. Powder samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. The results showed that pure nanocrystalline akermanite with a crystalline size of 35 nm was synthesized after ball milling the initial powders for 20 h with subsequent annealing at 900 &deg, C for 1 h. Mechanical properties of bulk akermanite samples were studied as well. The results showed that the produced akermanite tablets sintered at 1200 &deg, C for 5 h had a Young&rsquo, s modulus of 3800 MPa, an ultimate compressive strength of 24.7 MPa, and a density of 2.489 g/cm3. The in-vitro behavior of the produced akermanite was evaluated by soaking the samples in an SBF solution. The results showed that the produced akermanite had the apatite formation ability on its surface and can be a good candidate for bone tissue engineering applications.

Inconel 617 is among the best candidates for utilization in high temperature gas cooled reactor tribo-components. However, the combined effects of sliding contact, along with intermittent idle times and very high temperature material degradation, deteriorates the alloy tribological performance, especially under a helium atmosphere. Laser peening is a surface treatment technique which can enhance the properties at the surface and subsurface by generating deep residual stresses and enhanced microstructure. Herein, we report the tribological behavior of regular laser peened as well as thermally-engineered laser peened Inconel 617 under helium and air atmospheres at 800°C. In addition to friction and wear studies, the specimens are characterized by different analytical techniques to further understand the mechanisms involved in the peening process and sliding contact. Regardless of the peening process and post-process treatment types, it is observed that laser peening improves the tribological characteristics of Inconel 617. Interestingly, laser peening followed by helium thermal aging shows highly enhanced tribological behavior. This is attributed to the strengthening effect of the laser peening on the surface oxides providing an excellent and lasting protective and lubricating film under helium exposure.

Marine biological fouling or ‘biofouling’, the unwanted aggregation of aquatic organisms such as algae, barnacles, and marine microorganisms has been a detriment to maritime industries. Previous antifouling strategies included the use of toxic, biocide-containing paints; however, as humanity strives to lessen its environmental impact, a shift towards ecological deterrents which draw inspiration from nature are starting to be developed. In this work, the manipulation of the surface topography of nontoxic polydimethylsiloxane elastomer (PDMSe) was performed in order to mimic natural-occurring antifouling surfaces like those found on shark skin by means of a micro-molding technique using etched silicon molds. Previous polymer-based antifouling patterns which draw influence from shark skin have been successful in mitigating microorganism settlement; however, they lack a degree of biological accuracy as the features are of constant height. Our novel designs utilize various microfabrication techniques and micro-molding to generate placoid scale patterns with an engineered height gradient to deter organism settlement. Surface durability studies showed that the patterns can effectively keep their integrity under external sliding motion. Significant decreases in Escherichia coli (E. coli) settlement up to 75% were observed when measuring the effectiveness of pristine patterns, and up to 56% when patterns underwent extreme mechanical wear.

Recent developments in architectural design and additive manufacturing (AM) techniques have led to advances in the design and fabrication of metamaterials. We demonstrate that by precisely designing the architecture of a lattice structure and implementing the accurate and cost-effective capabilities of polymer-based AM, it is possible to create lightweight and strong structures that are highly energy absorbing, able to recover their shape after extreme deformation, and have a high strength-over-weight ratio. Largescale AM lattices with various densities of unit cells were fabricated from two different polymers. The densities of the structures ranged from 66 kg/m3 to 192 kg/m3. Compression experiments established the scaling of their strength and stiffness with their relative density and revealed that the structures were able to recover their original shape after a compression up to 70% strain. The energy absorption efficiency of the structures was 11% higher than Duocel® aluminum foam and comparable to that of aluminum honeycomb, expanded polystyrene (EPS) foams, and Skydex twin hemispheres. These unconventional mechanical properties substantiate the potential of architectural design along with additive manufacturing in various applications, not only at laboratory scale, but also at industrial level. Keywords: Metamaterials, Additive manufacturing, 3D printing, Shape-recovering, Energy absorption

In the present study, nanotribological measurements were performed via atomic force microscopy on Si/SiO2-supported graphene monolayers with varying oxide layer thicknesses. The observations uncovered significant discrepancies in resulting friction forces between each graphene sample. Nanoscale interfacial friction forces were observed to increase from ∼0.49 nN to ∼1.00 nN when the oxide layer thickness was increased from 90 nm to 300 nm. The findings were determined to be the result of increased phonon scattering which is responsible for the removal of the vibrational reduction of nanoscale friction. Such discrepancies in friction forces points toward the potential tunability of nanoscale friction in supported graphene.

Among the major groups of materials, some polymers and resins are limited in usage due to their brittleness. To date, we lack a comprehensive solution to overcome brittleness. Mimicking from biological structures made up of ceramics with excellent strength and flexibility can help us to find a solution to this problem. In this study, for the first time, we mimicked the structure of spicules in Euplectella aspergillum (EA) sponges and developed a novel structure to improve the mechanical properties of brittle rods. In the newly developed structure, cylinders with various diameters were printed by a 3D printer and then inserted into each other. The nested cylindrical structures (NCSs) with optimized mechanical properties had a cylinder wall thickness of 1.30 mm with a density of 1.27 ± 0.01 g/cm3 (approximately 8.6% less than that of solid rods (SRs)). The flexural strength, strain, modulus and toughness of SR were improved in the NCSs from 108.04 ± 11.30 MPa, 1.95 ± 0.20%, 3.98 ± 0.05 GPa and 1.42 ± 0.20 kJ/m3 to 168.45 ± 14.45 MPa, 4.10 ± 0.41%, 5.52 ± 0.05 GPa and 6.71 ± 0.80 kJ/m3, respectively. The NCSs showed a lower density as well as improved mechanical properties compared to SRs. According to the SEM observations, the dominant mechanisms on the toughening of NCSs with a cylinder wall thickness of 0.80 mm were crack branching, crack bridging, and crack deflection. However, for NCSs with a cylinder wall thickness of 1.00 and 1.30 mm the dominant mechanism was crack deflection. The results of this paper open a new horizon for designing new structures from brittle materials with higher strength and flexibility.

Structural elements made of nickel-based superalloys usually operate at high temperatures. Many surface failure mechanisms such as creep, fatigue, fretting fatigue, corrosion, and stress corrosion cracking start from the surface. Thus, studying the surface mechanical properties and deformation behavior of materials is vital in order to draw a correlation between the surface properties and failures. Herein, a nanoindentation technique was implemented to characterize surface properties of a widely used additively manufactured (AM) superalloy, i.e., Inconel 625. The specimens were tested in a range of temperatures in a vacuum chamber. Serrated plastic flow characterized by pop-in events during nanoindentation, known as Portevin-Le Chatelier (PLC) effect, was observed in all three tested elevated temperatures. This phenomenon depicts itself as bursts of plasticity in the loading section of the load-displacement curves. These bursts were studied comprehensively to explore incipient plasticity. Hertzian contact mechanics were implemented to extract the maximum shear stress beneath the indenter from the pop-in loads. The results show that the initial pop-in load increases as the temperature increases. The average initial pop-in load increases by almost four times from 300 °C to 650 °C. This was attributed to the formation of strengthening precipitates. The average size of the serrations and the magnitude of dislocation nucleation increase from 300 °C to 500 °C and decrease from 500 °C to 650 °C. The serrations are attributed to the dislocation generation and movement as well as their interaction with the solute atoms and precipitates.

We report the optical properties and solar reflectance of catalyst-free vertical graphene (VG) sheets grown on two types of substrate, copper and silicon, over a wide range of wavelengths and for the first time, a method for the separation of the sheets from the substrate. The index of refraction of the VG sheets was close to unity in the visible and infrared range, while the coefficient of absorption was higher than those of forests of carbon nanotubes (CNTs). A total reflectance (diffuse and specular) of less than 10% was observed for the VG sheets in the visible range. For VG sheets grown on a copper substrate, the specific absorption (absorption divided by the areal density) at a wavelength of 633 nm was measured to be two times higher than previously reported results for VG sheets grown on a silicon substrate and much higher than that of a CNT forest.

This review paper discusses the recent progress in laser shock peening (LSP) of additively manufactured (AM) parts. LSP is an advanced post-processing technique that optimizes the service lives of critical components for various applications by inducing severe plastic deformation accompanied by the enhancement of surface properties in treated materials. Material improvement is enabled through the generation of high-density dislocations, grain refinement, and beneficial phase transformations. These mechanisms produce high magnitude compressive residual stresses which harden treated regions to depths exceeding 1 mm. However, a major roadblock for AM parts stems from the various fabrication processes themselves where detrimental tensile residual stresses are introduced during part manufacturing, along with near-surface voids and cracks, all of which severely limit their applications. In addition to post-fabrication heat treatment that is typically required to homogenize the microstructure and relieve the residual stresses of AM parts, post-processing surface treatments have also been developed to manipulate the residual stresses of AM materials. Tensile residual stresses generated during manufacturing affect the fatigue life of AM material negatively and could potentially surpass the material’s yield strength, resulting in acute geometric distortion. Recent studies have shown the potential of LSP to mitigate these stresses, modify the mechanical properties of the AM parts, and to close near-surface voids and cracks. Furthermore, the thermal stability of favorable microstructural modifications in laser peened AM parts, which allows for its use in high temperature environments, is not well understood and is currently limiting its effective utilization in these scenarios. The main goal of this review is to provide the detailed insight needed for widespread acceptance of this technique as a post-processing method for AM materials.

The superior intrinsic mechanical properties of graphene have been widely studied and utilized to enhance the mechanical properties of various composite materials. However, it is still unclear how heterostructures incorporating graphene behave, and to what extent graphene influences their mechanical response. In this work, a series of graphene/Al

The fabrication and characterization of a field effect transistor using a radial core/shell structure based on ZnTe nanowires is reported here. The electronic and photoconductive performance of the devices is successfully controlled by tuning the shell to core ratios in the integrated devices. The ZnO shell around the ZnTe nanowire has a significant effect on the optical properties of the transistor, and the photo-to-dark current ratio, responsivity and photoconductive gain are greatly enhanced to 199, 196 and 8.12 × 104% respectively for the 17.5% shell/core ratio. The ability to control the core/shell ratio presented here is promising in device design for optoelectronic applications for covering a wide range of wavelengths.

We report systematically tuning the mechanical properties of vertical graphene (VG) sheets through fluorination. VG sheets were synthesized using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and were functionalized through exposure to xenon difluoride (XeF2) gas. An atomic force microscopy technique, PeakForce Quantitative Nanomechanical Mapping (QNM®), was used to measure the mechanical properties of the VG sheets. We show that fluorination can significantly enhance the reduced modulus of surfaces comprised of VG sheets. Samples with only ∼3.5% fluorine had a reduced modulus approximately eight times higher than unfunctionalized VG sheets, which is attributed to sp2 to sp3 conversion and a change of the C–C bond length after functionalization. Fluorination also decreased the energy dissipation of the VG sheets and reduced their adhesion to the AFM tip. This method represents a unique approach towards modification of the mechanical properties of nanostructures without a significant increase in weight or change of the VG sheet morphology.

While planar graphene has revolutionized science and engineering in many different areas, one of its close relatives, vertical graphene (VG), also known as carbon nanowalls, has not been investigated as extensively. Compared to planar graphene that is grown parallel to the substrate, VG can grow almost vertically on a wide variety of substrates. In this study, we report the fabrication and characterization of VG-based nanocomposite thin films, where the graphene sheets are uniformly distributed in the host polymer. A novel fabrication method was developed and the properties of the fabricated nanocomposites were characterized. The results showed that in our method graphene sheets are much more uniformly dispersed and common issues in graphene nanocomposites, such as agglomeration and breaking of the sheets during dispersion, are avoided. The increase in the Young’s modulus and tensile strength of the fabricated nanocomposites is much higher than that of the samples fabricated using the traditional methods of randomly dispersing graphene using a sonicator or high-speed stirrer.

We report here the effect of thermal annealing on the thermal conductivity of ZnTe nanowires measured on a microfabricated suspended device. Molecular dynamics simulation was used to calculate the effect of contacts on the measurements at different temperatures and to estimate the intrinsic nanowire thermal conductivity values. A decrease in thermal conductivity was observed after each thermal annealing step at all the measured temperatures. Thermal annealing can be a potential method to improve the thermoelectric efficiency of nanowires, not only by enhancing the electrical conduction as demonstrated before, but also by suppressing the thermal transport at the same time.

A radio frequency plasma enhanced chemical vapor deposition system was used for the successful growth of thin vertical carbon nanowalls, also known as vertical graphene, on various substrates. Transmission electron microscopy studies confirmed the presence of vertical graphene walls, which are tapered, typically consisting of 10 layers at the base tapering off to 2 or 3 layers at the top. The sides of the walls are facetted at quantized angles of 30° and the facetted sides are usually seamless. Growth occurs at the top open edge which is not facetted. Hydrogen induced etching allows for nucleation of branch walls apparently involving a carbon onion-like structure at the root base. Characterization by a superconducting quantum interference device showed magnetic hysteresis loops and weak ferromagnetic responses from the samples at room temperature and below. Temperature dependence of the magnetization revealed a magnetic phase transition around T = 50 K highlighting the coexistence of antiferromagnetic interactions as well as ferromagnetic order.

The use of printed electronics in conjunction with nanomaterials such as carbon nanotubes (CNTs) proves to be an effective means for simple, efficient and cost-effective chemical and bio sensing applications due to their high surface area to volume ratio and other attractive properties. However, successful commercial implementation of nanosensors has been elusive due to inconsistent performance across the sensors, which translates to decreased credibility and reproducibility. Furthermore, the process uniformity in printed electronics is inferior to solid-state microfabrication technology as printed sensors suffer from material and process-induced variability at the current level of maturity. In order to take advantage of the promise of nanotechnology driven sensors, we herein propose an array of chemiresistors formed on one substrate as a single input multiple output (SIMO) sensor. Then, individual responses from sub-sensors in a SIMO sensor are aggregated and result in a statistical mean response to overcome variability issues. Random sampling was performed in this work from a sufficiently large population of CNT-based sub-sensors to define a representative set whose behavior closely mimics a larger array. The convergence of the population mean is proven from randomly chosen samples beyond a certain number of sub-sensors. An optimal strategy including sensor layout and power consumption is provided based on the resulting data analysis.

We report the fabrication and characterization of graphene nanostructures with mechanical properties that are tuned by conformal deposition of alumina. Vertical graphene (VG) sheets, also called carbon nanowalls (CNWs), were grown on copper foil substrates using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and conformally coated with different thicknesses of alumina (Al2O3) using atomic layer deposition (ALD). Nanoindentation was used to characterize the mechanical properties of pristine and alumina-coated VG sheets. Results show a significant increase in the effective Young's modulus of the VG sheets with increasing thickness of deposited alumina. Deposition of only a 5 nm thick alumina layer on the VG sheets nearly triples the effective Young's modulus of the VG structures. Both energy absorption and strain recovery were lower in VG sheets coated with alumina than in pure VG sheets (for the same peak force). This may be attributed to the increase in bending stiffness of the VG sheets and the creation of connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed.

ZnTe nanowires, grown by a vapor–liquid–solid technique are p-type and show a very high intrinsic resistivity. Enhancement of the nanowire conductivity was investigated by vacuum annealing, doping and Joule heating. The current–voltage ( I – V ) characteristics were measured in all cases and electrical parameters such as resistivity, carrier concentration and mobility were computed from the I – V curves. An improvement of five orders of magnitude in the electrical conductivity was seen after thermal annealing and Joule heating, comparable to the enhancement in conductivity obtained by doping.

As the applications for inorganic nanowires continuously grow, studies on the stability of these structures under high electrical/thermal stress conditions are needed. ZnTe nanowires are grown by the vapor-liquid-solid technique and their breakdown under Joule heating is studied through in situ monitoring in a transmission electron microscope (TEM). The experimental setup, consisting of a scanning tunneling microscope (STM) and a movable piezotube inside the TEM, allows the manipulation of a single nanowire. A voltage applied to the STM tip in contact with a ZnTe nanowire leads to the breakdown of the nanowire into Zn and Te particles or balls which is observed in real time. These balls grow by Ostwald ripening, rendering the surface morphology of the ZnTe nanowire progressively rough. Diffraction patterns along the stem of the wire after the partial breakdown showed substantially smaller lattice spacing compared to 0.35 nm for pristine ZnTe nanowires.

With the advent of additive manufacturing, fabrication of complex structures with high efficiency for energy absorption and blast and impact mitigation has entered a new era. In this research the role of the architecture and material properties on the static and dynamic energy absorption properties of additively-manufactured complex cellular structures out of two different materials were studied under puncture and crush tests. A finite element simulation of the unit cell was also conducted to study the effect of loading rate on the final response of the material where the results showed good agreement with the experimental observations. It is shown that the studied additively manufactured structures were able to recover their shape significantly after a major deformation due to the impact. These results show the potential of additive manufacturing as a versatile tool for creating structures with complex geometries for energy absorption.

Unusual mechanical properties of mechanical metamaterials are determined by their carefully designed and tightly controlled geometry at the macro- or nanoscale. We introduce a class of nanoscale mechanical metamaterials created by forming continuous corrugated plates out of ultrathin films. Using a periodic three-dimensional architecture characteristic of mechanical metamaterials, we fabricate free-standing plates up to 2 cm in size out of aluminium oxide films as thin as 25 nm. The plates are formed by atomic layer deposition of ultrathin alumina films on a lithographically patterned silicon wafer, followed by complete removal of the silicon substrate. Unlike unpatterned ultrathin films, which tend to warp or even roll up because of residual stress gradients, our plate metamaterials can be engineered to be extremely flat. They weigh as little as 0.1 g cm−2 and have the ability to ‘pop-back' to their original shape without damage even after undergoing multiple sharp bends of more than 90°., Unusual mechanical properties can be obtained with careful design of metamaterials. Here, Davami et al. use a microscale periodic cellular design to create plate mechanical metamaterials which exhibit ultralow mass per unit area, enhanced bending stiffness and ability to recover after extreme deformations.

Many applications of graphene can benefit from the enhanced mechanical robustness of graphene-based components. We report how the stiffness of vertical graphene (VG) sheets is affected by the introduction of defects and fluorination, both separately and combined. The defects were created using a high-energy ion beam while fluorination was performed in a XeF2 etching system. After ion bombardment alone, the average effective reduced modulus (E r), equal to ∼4.9 MPa for the as-grown VG sheets, approximately doubled to ∼10.0 MPa, while fluorination alone almost quadrupled it to ∼18.4 MPa. The maximum average E r of ∼32.4 MPa was achieved by repeatedly applying fluorination and ion bombardment. This increase can be explained by the formation of covalent bonds between the VG sheets due to ion bombardment, as well as the conversion from sp2 to sp3 and increased corrugation due to fluorination.

The electronic and photoconductive characteristics of CdTe nanowire-based field effect transistors were studied systematically. The electrical characterization of a single CdTe nanowire FET verifies p-type behavior. The CdTe NW FETs respond to visible-near infrared (400-800 nm) incident light with a fast, reversible and stable response characterized by a high responsivity (81 A W(-1)), photoconductive gain (∼2.5 × 10(4)%) and reasonable response and decay times (0.7 s and 1 s, respectively). These results substantiate the potential of CdTe nanowire-based photodetectors in optoelectronic applications.

This paper reports rigid MEMS structures made of ALD films, which had thicknesses as low as 10 nanometers and were patterned in the shape of a 3D honeycomb. Hexagonal honeycomb lattices offer a dramatically higher flexural stiffness compared to that of planar films, allowing us to fabricate large-area suspended devices without significant warping. Both alumina (Al2O3) and silica (SiO2) structures were fabricated, each presenting a different set of fabrication challenges. The spring constants of the cantilever structures were measured and compared with the simulation results.