Akash Ramdas

All Publications

• Multi-Objective Optimization for Rapid Identification of Novel Compound Metals for Interconnect Applications. Small (Weinheim an der Bergstrasse, Germany) Ramdas, A., Zhou, G., Li, Y., Lu, P. L., Antoniuk, E. R., Reed, E. J., Hinkle, C. L., da Jornada, F. H. 2024: e2308784

  Abstract

  Interconnect materials play the critical role of routing energy and information in integrated circuits. However, established bulk conductors, such as copper, perform poorly when scaled down beyond 10 nm, limiting the scalability of logic devices. Here, a multi-objective search is developed, combined with first-principles calculations, to rapidly screen over 15,000 materials and discover new interconnect candidates. This approach simultaneously optimizes the bulk electronic conductivity, surface scattering time, and chemical stability using physically motivated surrogate properties accessible from materials databases. Promising local interconnects are identified that have the potential to outperform ruthenium, the current state-of-the-art post-Cu material, and also semi-global interconnects with potentially large skin depths at the GHz operation frequency. The approach is validated on one of the identified candidates, CoPt, using both ab initio and experimental transport studies, showcasing its potential to supplant Ru and Cu for future local interconnects.

  View details for DOI 10.1002/smll.202308784

  View details for PubMedID 38593360

• Surface conduction and reduced electrical resistivity in ultrathin noncrystalline NbP semimetal. Science (New York, N.Y.) Khan, A. I., Ramdas, A., Lindgren, E., Kim, H. M., Won, B., Wu, X., Saraswat, K., Chen, C. T., Suzuki, Y., da Jornada, F. H., Oh, I. K., Pop, E. 2025; 387 (6729): 62-67

  Abstract

  The electrical resistivity of conventional metals such as copper is known to increase in thin films as a result of electron-surface scattering, thus limiting the performance of metals in nanoscale electronics. Here, we find an unusual reduction of resistivity with decreasing film thickness in niobium phosphide (NbP) semimetal deposited at relatively low temperatures of 400°C. In films thinner than 5 nanometers, the room temperature resistivity (~34 microhm centimeters for 1.5-nanometer-thick NbP) is up to six times lower than the resistivity of our bulk NbP films, and lower than conventional metals at similar thickness (typically about 100 microhm centimeters). The NbP films are not crystalline but display local nanocrystalline, short-range order within an amorphous matrix. Our analysis suggests that the lower effective resistivity is caused by conduction through surface channels, together with high surface carrier density and sufficiently good mobility as the film thickness is reduced. These results and the fundamental insights obtained here could enable ultrathin, low-resistivity wires for nanoelectronics beyond the limitations of conventional metals.

  View details for DOI 10.1126/science.adq7096

  View details for PubMedID 39745958

• Predicting Reactivity and Passivation of Solid-State Battery Interfaces. ACS applied materials & interfaces Lomeli, E. G., Ransom, B., Ramdas, A., Jost, D., Moritz, B., Sendek, A. D., Reed, E. J., Devereaux, T. P. 2024

  Abstract

  In this work, we build a computationally inexpensive, data-driven model that utilizes atomistic structure information to predict the reactivity of interfaces between any candidate solid-state electrolyte material and a Li metal anode. This model is trained on data from ab initio molecular dynamics (AIMD) simulations of the time evolution of the solid electrolyte-Li metal interfaces for 67 different materials. Predicting the reactivity of solid-state interfaces with ab initio techniques remains an elusive challenge in materials discovery and informatics, and previous work on predicting interfacial compatibility of solid-state Li-ion electrolytes and Li metal anodes has focused mainly on thermodynamic convex hull calculations. Our framework involves training machine learning models on AIMD data, thereby capturing information on both kinetics and thermodynamics, and then leveraging these models to predict the reactivity of thousands of new candidates in the span of seconds, avoiding the need for additional weeks-long AIMD simulations. We identify over 300 new chemically stable and over 780 passivating solid electrolytes that are predicted to be thermodynamically unfavored. Our results indicate many potential solid-state electrolyte candidates have been incorrectly labeled unstable via purely thermodynamic approaches using density functional theory (DFT) energetics, and that the pool of promising, Li-stable solid-state electrolyte materials may be much larger than previously thought from screening efforts. To showcase the value of our approach, we highlight two borate materials that were identified by our model and confirmed by further AIMD calculations to likely be highly conductive and chemically stable with Li: LiB13C2 and LiB12PC.

  View details for DOI 10.1021/acsami.4c06095

  View details for PubMedID 39277815

• Targeted materials discovery using Bayesian algorithm execution NPJ COMPUTATIONAL MATERIALS Chitturi, S. R., Ramdas, A., Wu, Y., Rohr, B., Ermon, S., Dionne, J., da Jornada, F. H., Dunne, M., Tassone, C., Neiswanger, W., Ratner, D. 2024; 10 (1)

  View details for DOI 10.1038/s41524-024-01326-2

  View details for Web of Science ID 001271730700002

• Electrolyte Coatings for High Adhesion Interfaces in Solid-State Batteries from First Principles. ACS applied materials & interfaces Ransom, B., Ramdas, A., Lomeli, E., Fidawi, J., Sendek, A., Devereaux, T., Reed, E. J., Schindler, P. 2023

  Abstract

  We introduce an adhesion parameter that enables rapid screening for materials interfaces with high adhesion. This parameter is obtained by density functional theory calculations of individual single-material slabs rather than slabs consisting of combinations of two materials, eliminating the need to calculate all configurations of a prohibitively vast space of possible interface configurations. Cleavage energy calculations are used as an upper bound for electrolyte and coating energies and implemented in an adapted contact angle equation to derive the adhesion parameter. In addition to good adhesion, we impose further constraints in electrochemical stability window, abundance, bulk reactivity, and stability to screen for coating materials for next-generation solid-state batteries. Good adhesion is critical in combating delamination and resistance to lithium diffusivity in solid-state batteries. Here, we identify several promising coating candidates for the Li7La3Zr2O12 and sulfide electrolyte systems including the previously investigated electrode coating materials LiAlSiO4 and Li5AlO8, making them especially attractive for experimental optimization and commercialization.

  View details for DOI 10.1021/acsami.3c04452

  View details for PubMedID 37682811