The paradigm of molecular discovery in the chemical and pharmaceutical industry has followed a repetitive succession of screening and synthesis, involving the analysis of individual molecules that were both natural and produced. This ability to generate and screen libraries of compounds has found an echo in solid-state physics with the demand to explore and produce new materials for testing. In response to this demand, a golden age of materials discovery is being developed, with progress on important areas of both basic science and device applications. The confluence of theoretical and simulation methods, together with the availability of computation resources, has established the “materials genome” approach that is used by a growing number of research groups around the world with the goal of innovating on materials through systematic discovery. In this Prospective, an overview of this group of methodologies in tackling the ever-increasing complexity of computational materials science simulations is provided. Computational simulation is highlighted as a major component of rational design and synthesis of new materials with targeted properties, describing progress on databases and large data treatment. Tools for new materials discovery, including progress on the deployment of new data repositories, the implementation of high-throughput simulation approaches, and the development of artificial intelligence algorithms, are discussed.

The authors report effects of placing a very thin metallic interlayer, such as W and Ni, in between the Cu film and the Si substrate on cyclic thermal stress-induced interfacial sliding and hillock growth in Cu. Cu–Si samples with no interlayer were the most prone to both interfacial sliding and hillock growth, whereas samples with the Ni interlayer were the most resistant against these deleterious phenomena. While the rate of interfacial sliding decreased with each consecutive thermal cycle, hillocks continued to grow undeterred. The obtained experimental results are discussed, considering the compressive stress field generated in the Cu film.

The unique properties of graphene have led to the use of this allotrope of carbon in a wide range of applications, including semiconductors, energy devices, diffusion barriers, heat spreaders, and protective overcoats. The synthesis of graphene by process methods that either directly or indirectly rely on physical vapor deposition, thermal annealing, laser irradiation, and ion/electron beam irradiation has drawn significant attention in recent years, mainly because they can provide high purity, low temperature, high throughput, and controllable growth of graphene on various substrates. This article provides a comprehensive assessment of these methods by grouping them into two main categories, i.e., indirect methods in which a carbon layer is first deposited on a substrate and then converted to graphene by some type of energetic post-treatment process and direct methods in which graphene is directly synthesized on a substrate surface by a process that uses a solid carbon source. The underlying growth mechanisms of these processes and the challenging issues that need to be overcome before further advances in graphene synthesis can occur are interpreted in the context of published results.

In many materials development projects, scientists and research heads make decisions to guide the project direction. For example, scientists may decide which processing steps to use, what elements to include in their material selection, or from what suppliers to source their materials. Research heads may decide whether to invest development effort in reducing the environmental impact or production cost of a material. When making these decisions, it would be helpful to know how those decisions affect the achievable performance of the materials under consideration. Often, these decisions are complicated by trade-offs in performance between competing properties. This paper presents an approach for visualizing and evaluating design spaces, where a design space is defined as the set of possible materials under consideration given specified constraints. This design space visualization approach is applied to two case studies with environmental impact motivations: one in biodegradability for solvents, and the other in sustainable materials sourcing for Li-ion batteries. The results demonstrate how this visualization approach can enable data-driven, quantitative decisions for project direction.

We show interlayer stacking shifts occur in transition metal dichalcogenides (TMD) bilayers due to the strain introduced during sample heating, and attributed to rippling of one layer relative to the other. The atomic structure of the interlayer stacking is studied using annular dark field scanning transmission electron microscopy with an in situ heating holder. Before heating, bilayers show uniform interlayer stacking of AA′ and AB. When heated, contrast change is seen and associated with interlayer stacking changes at the atomic scale due to ripples. When cooled down to room temperature, these contrast features disappear, confirming it is a reversible process that is not related to defects or vacancies. Because the bottom layer is attached to the in situ heating chip made from Si3N4 and the top layer is in contact with the underlying TMD layer with weak van der Waals interaction, the two layers experience different forces during thermal expansion.

Structural evolution induced and driven by a dual system and simultaneous passivation of phosphorene are reported. Different nano-objects of phosphorene or black phosphorus (BP) are obtained using a new method of exfoliation, in which solvent and an ionic polymer are combined to weaken the van der Waals forces and to scissor the nanosheets. Nanoribbons, nanorods, and nanoneedles are obtained under mechanical force and ambient conditions. Ionic polymer chains assist in curling the monolayer or few-layer nanosheet. Nafion is chosen to exfoliate the bulk BP and induce a morphological transition in BP nanosheets. The exfoliation of BP nanosheets results into thin and specific structures such as nanosheets/rods/needles. The nanosheets of phosphorene are covered and passivated simultaneously by the polymeric sheath that protects the nanosheets from degradation or oxidation and can be integrated with a device directly without any further coating.

A detailed electron backscatter diffraction (EBSD) characterization was utilized to investigate abnormal grain growth behavior of nanocrystalline (NC) Au films constrained by a flexible substrate under cyclic loading. Abnormally grown grains (AGGs) in front of about 15 fatigue cracks were picked out to investigate the grain reorientation behavior during abnormal grain growth in the fatigue crack tip in the cyclically deformed thin films. It shows that the AGGs exhibited 〈001〉 orientation along the loading direction, whereas grains grown far away from fatigue cracks had no significant texture change. The cyclic cumulative shear strain was found to play a key role in grain reorientation. A lattice rotation model was proposed to elucidate the grain reorientation mechanism during abnormal grain growth. Such grain reorientation behavior of NC metals was found to provide an intrinsic resistance of the NC metals to fatigue damage.

In this contribution, we use heavy ion irradiation and photoluminescence (PL) spectroscopy to demonstrate that defects can be used to tailor the optical properties of two-dimensional molybdenum disulfide (MoS2). Sonicated MoS2 flakes were deposited onto Si/SiO2 substrate and subjected to 3 MeV Au2+ ion irradiation at room temperature to fluences ranging from 1 × 1012 to 1 × 1016 cm−2. We demonstrate that irradiation-induced defects can control optical excitations in the inner core shell of MoS2 by binding A1s- and B1s-excitons, and correlate the exciton peaks to the specific defects introduced with irradiation. The systematic increase of ion fluence produced different defect densities in MoS2, which were estimated using B/A exciton ratios and progressively increased with ion fluence. We show that up to the fluences of 1 × 1014 cm−2, the MoS2 lattice remains crystalline and defect densities can be controlled, whereas at higher fluences (≥1 × 1015 cm−2), the large number of introduced defects distorts the excitonic structure of the material. In addition to controlling excitons, defects were used to split bound and free trions, and we demonstrate that at higher fluences (1 × 1015 cm−2), both free and bound trions can be observed in the same PL spectrum. Most importantly, the lifetimes of these states exceed trion and exciton lifetimes in pristine MoS2, and PL spectra of irradiated MoS2 remains unchanged weeks after irradiation experiments. Thus, this work demonstrated the feasibility of engineering novel optical behaviors in low-dimensional materials using heavy ion irradiation. The insights gained from this study will aid in understanding the many-body interactions in low-dimensional materials and may ultimately be used to develop novel materials for optoelectronic applications.

In this paper, the atomic resolution high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) was used as the main research method. Using HAADF-STEM, two types of long-period stacking ordered structure (LPSO)—14H and 18R-LPSO—were observed in Mg96Gd2Y1Ni1 alloy, and the precipitates at various stages of aging were observed. Moreover, a type of rectangular β precipitates were found, and the atomic models of β precipitates along the [0001]Mg and ${\tf="TeXGyrePagella-Bold (TrueType)"\char9001} 11\bar 20\hbox{]}_{{\rm{Mg}}}$ directions were identified. At the aging peak stage, a three-dimensional network structure composed of LPSO/γ′ precipitates and β′ precipitates and β precipitates was observed. The hardness of the unaged homogenized Mg96Gd2Y1Ni1 alloy was only 87 HV and the hardness value of aging peak was 128.4 HV. Compared with the unaged alloy, the hardness of the peak-aged alloy increased by 47.59%. The composite strengthening of the three types of precipitates induced a significant strengthening to the alloy.

Titanium and its alloys are probably the most suitable materials for selective laser melting (SLM) additive manufacturing to process. However, the high cost of raw powder materials limits the industrial application of as-printed Ti products. In this study, we have formulated a cost-affordable Ti–TiB composite powder for SLM, to simultaneously achieve excellent mechanical performance and cost effectiveness. The optimization of the processing parameters will be shown to lead to high relative density (99.3%) for the as-printed Ti–TiB composites containing (0.5, 1, and 2 wt%) TiB2. Furthermore, by incorporating TiB2, the as-printed composites exhibit much improved fracture strength (up to 1813 MPa) and microhardness (up to 412 HV), among which the Ti–0.5 wt% TiB2 has demonstrated a great combination of strength (1007 and 1646 MPa as yield and fracture strengths, respectively) and tensile ductility (~8%). The solidification pathway for the Ti–TiB composite during SLM has been investigated, and the underlying mechanism for achieving high yield strength is discussed based on existing models for shear-lag strengthening, grain refinement, and dispersion strengthening.

The tensile yield strength of high-density polyethylene using instrumented indentation tests with a flat-ended cylindrical indenter was evaluated. The variation in the field expressed by stress and strain beneath the flat-ended cylindrical indenter is investigated using a new expanding cavity model to study the relation between tension and indentation. This model starts from the separation of forces into the compressive force on the material and the frictional one, which is generated during indentation on the sides of indenter. The authors propose a method to correct the frictional force based on the saturation of indentation hardening and obtain load–depth curve with compressive component only. For conversion of indentation force and displacement, our new representation model is applied. By modifying Johnson's model, the new assumption of conservation of indentation plastic volume is suggested. This model proves and supports conventional relations of the strain rates between indentation and tension theoretically. These are verified through the experiments: instrumented indentation and uniaxial tensile test. The authors find a good agreement between the tensile yield strengths at various strain rates.

Nanoindentation and microcrystal deformation are two methods that allow probing size effects in crystal plasticity. In many cases of microcrystal deformation, scale-free and potentially universal intermittency of event sizes during plastic flow has been revealed, whereas nanoindentation has been mainly used to assess the stress statistics of the first pop-in. Here, we show that both methods of deformation exhibit fundamentally different event-size statistics obtained from plastic instabilities. Nanoindentation results in scale-dependent intermittent microplasticity best described by Weibull statistics (stress and magnitude of the first pop-in) and lognormal statistics (magnitude of higher-order pop-ins). In contrast, finite-volume microcrystal deformation of the same material exhibits microplastic event-size intermittency of truncated power-law type even when the same plastic volume as in nanoindentation is probed. Furthermore, we successfully test a previously proposed extreme-value statistics model that relates the average first critical stress to the shape and scale parameter of the underlying Weibull distribution.