This article reviews and assesses recent progress in atomic layer deposition (ALD) and highlights how the field of ALD is expanding into new applications and inspiring new vapor-based chemical reaction methods. ALD is a unique chemical process that yields ultra-thin film coatings with exceptional conformality on highly non-uniform and non-planar surfaces, often with subnanometer scale control of the coating thickness. While industry uses ALD for high-κ dielectrics in the manufacturing of electronic devices, there is growing interest in low-temperature ALD and ALD-inspired processes for newer and more wide-ranging applications, including integration with biological and synthetic polymer structures. Moreover, the conformality and nanoscale control of ALD film thickness makes ALD ideal for encapsulation and nano-architectural engineering. Articles in this issue of MRS Bulletin present details of several growing interest areas, including the extension of ALD to new regions of the periodic table, and molecular layer deposition and vapor infiltration for synthesis of organic-based thin films. Articles also discuss ALD for nanostructure engineering and ALD for energy applications. A final article shows how the challenge of scaling ALD for high rate nanomanufacturing will push advances in plasma, roll-to-roll, and atmospheric pressure ALD.

Over the past 10 years, the number of materials that can be processed by atomic layer deposition (ALD) has expanded rapidly. Significant progress has been seen in ALD of high-κ oxides, ternary oxides, and noble metals, which have been studied quite extensively. High-κ oxide processes are used today in various industrial applications. However, many new applications are pushing the need for less common compounds, and therefore new processes are being developed (e.g., for fluorides, Li containing compounds, and phosphates). New ALD processes require new designs for volatile precursors to deliver elements with ligands that ensure self-limiting surface reactions. In addition to inorganics, new polymeric and inorganic-organic hybrid materials are opening new frontiers for ALD, including expansion of the process to include molecular layer deposition. A combination of inorganic and organic parts in the deposited layers offers expanding opportunities for tailoring materials properties.

Atomic layer deposition (ALD) not only presents a direct way to prepare nanomaterials when combined with templates, but also allows surface engineering to fine-tune the properties of the material. Here, we review recent progress in the field of nanostructured materials and devices that have been fabricated by ALD. Various materials, including semiconducting, magnetic, noble metallic, and insulating materials, can be used to form three-dimensional (3D), complex nanostructures with controlled composition and physical properties. We begin this review with ALD nanomaterials that can be prepared from porous templates with a 2D pore arrangement, such as anodic aluminum oxide, and advance toward opal structures with a 3D pore arrangement. We also discuss surface engineering by ALD on existing nanowires/nanotubes, devices, and chemical patterns that has the potential for application in high-performance transistors, sensors, and green energy conversion. Finally, we provide perspectives for future device applications that could arise from ALD nanomaterials.

Atomic layer deposition (ALD) uses self-limiting chemical reactions between gaseous precursors and a solid surface to deposit materials in a layer-by-layer fashion. This process results in a unique combination of attributes, including sub-nm precision, the capability to engineer surfaces and interfaces, and unparalleled conformality over high-aspect ratio and nanoporous structures. Given these capabilities, ALD could play a central role in achieving the technological advances necessary to redirect our economy from fossil-based energy to clean, renewable energy. This article will survey some of the recent work applying ALD to clean energy conversion, utilization, and storage, including research in solid oxide fuel cells, thin-film photovoltaics, lithium-ion batteries, and heterogenous catalysts. Throughout the manuscript, we will emphasize how the unique qualities of ALD can enhance device performance and enable radical new designs.

As applications of atomic layer deposition (ALD) in emerging areas such as nanoelectronics, photovoltaics, and flexible electronics expand beyond single-wafer semiconductor processing, there is a growing need for novel approaches to integrate new process designs, substrate materials, and substrate delivery methods. An overview is given of new means to extend the capabilities of ALD and to improve the speed and simplicity of ALD coatings using new reactor designs. These include energy-enhanced and spatial ALD schemes involving plasma, direct-write, atmospheric pressure, and roll-to-roll processing. The long-term goal of this work is to integrate viable high-throughput capabilities with ALD processes.

Ionic motion and electrochemistry in bulk materials and at their surfaces have long been studied for their relevance in several areas of science and technology, ranging from ionic conductors to batteries to fuel cells. The ability to engineer materials at the nanometer scale, however, has made these concepts even more relevant. This is due to the large surface-to-volume ratios typical of nanostructures. This implies, for instance, that chemical reactivity and defect motion at surfaces or interfaces are enhanced or may be fundamentally different compared to their bulk counterparts. In addition, nominally modest voltages or differences in chemical potential when applied across nanoscale distances can produce large electric fields and diffusive forces. While all of this may complicate the interpretation of experimental results, it also presents us with new opportunities for materials engineering. In this article, we will briefly review the current research status of several systems where ionic motion and electrochemical effects are of particular importance. These include resistive switching systems, oxide heterostructures, ferroelectric materials, and ionic liquids. We will report on experimental results and also emphasize open questions regarding their interpretation. We will conclude by discussing future research directions in the field.