Research: Advanced Materials
Cement decarbonization, a techno-economic challenge
Date: 2026-09-25
Decarbonization of the construction industry entered the climate change watchlist in the late 1990s, with coordinated action beginning around the early 2000s. Initial efforts focused on process efficiency, fuel switching and clinker substitution, followed by increasing interest in carbon capture and alternative binders around the 2010s, and more recently, whole-system and lifecycle optimization from raw materials to reuse and recycling. Yet despite repeated efforts, CO₂ emissions from cement production have roughly doubled since the early 2000s, with little sign of decline until recently.
Cement decarbonization can be divided into three broad areas. First, process emissions can be reduced by lowering the clinker ratio through supplementary cementitious materials, developing alternative binders and precursor chemistries, applying electrochemical production routes, and capturing CO₂ released during calcination. Some emitted CO₂ can also be reabsorbed later through carbonation, in which concrete takes up atmospheric CO₂ and stores it as carbonate. Second, process energy can be decarbonized. Cement production still relies heavily on fossil fuels for high-temperature calcination and clinkering. Meanwhile, alternative fuels, renewable electricity, electrified heating and energy storage could progressively replace them. Finally, the entire lifecycle can be optimized through more material-efficient construction, reduced construction waste, reuse and recycling of concrete, repurposing of cement kiln dust, and improved demolition and second-use strategies.
Since 2021, emissions have fallen slightly, returning to roughly mid-2010s levels. At first glance, this appears encouraging. However, when normalized by cement production, CO₂ emissions per kg cement have remained essentially unchanged ~0.37 kg CO₂/kg cement from process emissions alone and ~0.58 kg CO₂/kg cement including process heat. The recent decline therefore appears to reflect lower production rather than meaningful improvements in carbon intensity. Rather than asking whether cement should be produced, the more useful question is how it can be produced with a lower emission factor, or more precisely, why that factor has changed so little despite all the proposed solutions.
Cement remains difficult to decarbonize because of unavoidable carbonate process emissions, very high process temperatures, enormous production volumes and most importantly, the low margins of a commodity industry, which make costly alternatives difficult to adopt. However, advances in adjacent technologies including renewable electricity, energy storage, electrochemistry and carbon capture, may increasingly remove some of these constraints and enable techno-economic viable reductions in cement emissions.
Transition metal dichalcogenide — the flat transistor
Date: 2026-09-21
The nanosheet era of transistor geometry has once again extended the life of transistor scaling. The projected progression from separated n-/p-type nanosheets, to forksheets where n- and p-type devices are brought closer together and separated by a dielectric wall, and ultimately to complementary field-effect transistors, where n- and p-type devices are stacked on top of one another, has opened up significant scaling opportunities. By surrounding the channel on all four sides with the gate, these architectures provide better electrostatic control while increasingly exploiting the vertical dimension. As scaling proceeds into the sub-nanometer regime, however, conventional silicon is approaching intrinsic material limits, including mobility degradation caused by silicon/oxide interface scattering and increased leakage associated with quantum-mechanical tunneling. This has prompted the industry to explore alternatives beyond silicon.
Two-dimensional materials (2DMs) have attracted rapidly growing interest since the first isolation of graphene in the early 2000s. Monolayer transition metal dichalcogenides (TMDs), the semiconducting poster child of 2DMs, emerged prominently in the early 2010s and have since been proposed as promising candidates to replace silicon as transistor scaling enters the nanosheet and sub-nanometer era. TMDs are atomically thin semiconductors with surfaces free of dangling bonds, offering excellent electrostatic control even at monolayer thicknesses. Their lack of dangling bonds also allows lattice-dissimilar materials to be stacked through van der Waals interactions, enabling heterogeneous vertical integration without the strict lattice-matching requirements of conventional epitaxy. Their inherent thinness also makes ultrathin devices possible (provided that other transistor components, such as gate dielectrics and contacts, can be scaled accordingly) potentially facilitating ultra-dense vertical stacking.
Yet despite these advantages, numerous challenges must still be addressed before the practical implementation of 2DM-based electronics. After decades of development around silicon, the semiconductor industry is not immediately ready to accommodate an entirely new family of materials. Almost every aspect of the transistor requires new research and process considerations when 2DMs are introduced. This begins with something as fundamental as obtaining the TMD itself: should it be grown directly on the final substrate, potentially sacrificing optimal growth conditions to protect structures already present underneath, or grown separately on a sacrificial substrate under better conditions and then transferred onto the final substrate, potentially introducing contamination or defects? Challenges continue into post-synthesis processing, particularly contact engineering and dielectric integration. The chemical inertness and dangling-bond-free surfaces of 2DMs complicate conventional oxide nucleation and metal-contacting approaches, creating new difficulties in achieving both low-resistance contacts and uniform, low-defect high-k gate dielectrics.
Researchers are becoming increasingly aware of the importance of fab-compatible processing conditions and often incorporate individual constraints, such as limiting processing temperatures to below 400 °C. However, most studies cannot simultaneously satisfy the full set of requirements expected of a semiconductor fabrication process. As a result, many promising demonstrations remain far from constituting an industry-ready process technology.