Sreebrata Goswami
Email Address
phygos@nus.edu.sg
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Publication Size-selective Pt siderophores based on redox active azo-aromatic ligands(Royal Society of Chemistry, 2020-08-20) Debabrata Sengupta; Sreetosh Goswami; Rajdeep Banerjee; Matthew J. Guberman-Pfeffer; Abhijeet Patra; Anirban Dutta; Rajib Pramanick; Shobhana Narasimhan; Narayan Pradhan; Victor Batista; T. Venkatesan; Sreebrata Goswami; ELECTRICAL AND COMPUTER ENGINEERING; PHYSICS; NUS NANOSCIENCE & NANOTECH INITIATIVEWe demonstrate a strategy inspired by natural siderophores for the dissolution of platinum nanoparticles that could enable their size-selective synthesis, toxicological assessment, and the recycling of this precious metal. From the fabrication of electronics to biomedical diagnosis and therapy, PtNPs find increasing use. Mitigating concerns over potential human toxicity and the need to recover precious metal from industrial debris motivates the study of bio-friendly reagents to replace traditional harsh etchants. Herein, we report a family of redox-active siderophore-viz. ã-acceptor azo aromatic ligands (L) that spontaneously ionize and chelate Pt atoms selectively from nanoparticles of size ó6 nm. The reaction produces a monometallic diradical complex, PtII(L??)2, isolated as a pure crystalline compound. Density functional theory provides fundamental insights on the size dependent PtNP chemical reactivity. The reported findings reveal a generalized platform for designing ã-acceptor ligands to adjust the size threshold for dissolution of Pt or other noble metals NPs. Our approach may, for example, be used for the generation of Pt-based therapeutics or for reclamation of Pt nano debris formed in catalytic converters or electronic fabrication industries.Publication Nanometer-Scale Uniform Conductance Switching in Molecular Memristors(WILEY, 2020-09-06) Sreetosh Goswami; Debalina Deb; Agnès Tempez; Marc Chaigneau; SANTI PRASAD RATH; Manohar Lal; Ariando; R. Stanley Williams; SREEBRATA GOSWAMI; Thirumalai Venkatesan; DEPT OF PHYSICS; ELECTRICAL AND COMPUTER ENGINEERING; NUS NANOSCIENCE & NANOTECH INITIATIVEOne common challenge highlighted in almost every review article on organic resistive memory is the lack of areal switching uniformity. This, in fact, is a puzzle because a molecular switching mechanism should ideally be isotropic and produce homogeneous current switching free from electroforming. Such a demonstration, however, remains elusive to date. The reports attempting to characterize a nanoscopic picture of switching in molecular films show random current spikes, just opposite to the expectation. Here, this longstanding conundrum is resolved by demonstrating 100% spatially homogeneous current switching (driven by molecular redox) in memristors based on Ru-complexes of azo-aromatic ligands. Through a concurrent nanoscopic spatial mapping using conductive atomic force microscopy and in operando tip-enhanced Raman spectroscopy (both with resolutionPublication Robust resistive memory devices using solution-processable metal-coordinated azo aromatics(Nature Research, 2017-10-23) Sreetosh Goswami; Adam J. Matula; Santi P. Rath; Svante Hedström; Surajit Saha; Meenakshi Annamalai; Debabrata Sengupta; Abhijeet Patra; Siddhartha Ghosh; Hariom Jani; Soumya Sarkar; Mallikarjuna Rao Motapothula; Christian A. Nijhuis; Jens Martin; Sreebrata Goswami; Victor S. Batista; T. Venkatesan; ELECTRICAL AND COMPUTER ENGINEERING; PHYSICS; CHEMISTRY; NUS NANOSCIENCE & NANOTECH INITIATIVENon-volatile memories will play a decisive role in the next generation of digital technology. Flash memories are currently the key player in the field, yet they fail to meet the commercial demands of scalability and endurance. Resistive memory devices, and in particular memories based on low-cost, solution-processable and chemically tunable organic materials, are promising alternatives explored by the industry. However, to date, they have been lacking the performance and mechanistic understanding required for commercial translation. Here we report a resistive memory device based on a spin-coated active layer of a transition-metal complex, which shows high reproducibility (∼350 devices), fast switching (≤30 ns), excellent endurance (∼1012 cycles), stability (>106 s) and scalability (down to ∼60 nm2). In situ Raman and ultraviolet–visible spectroscopy alongside spectroelectrochemistry and quantum chemical calculations demonstrate that the redox state of the ligands determines the switching states of the device whereas the counterions control the hysteresis. This insight may accelerate the technological deployment of organic resistive memories.Publication An organic approach to low energy memory and brain inspired electronics(AIP Publishing, 2020-04-21) Sreetosh Goswami; Sreebrata Goswami; T. Venkatesan; DEPT OF PHYSICS; ELECTRICAL AND COMPUTER ENGINEERING; NUS NANOSCIENCE & NANOTECH INITIATIVEBrain inspired electronics with organic memristors could offer a functionally promising and cost-effective platform for flexible, wearable, and personalized computing technologies. While there are different material approaches (viz. oxides, nitrides, 2D, organic) to realize memristors, organic materials are characteristically unique, as they could, in principle, offer spatially uniform switching, tunable molecular functionalities, and ultra-low switching energies approaching atto joules that are highly desirable but elusive with other material systems. However, despite a long-standing effort spanning almost 2 decades, the performance and mechanistic understanding in organic memristors are quite far from a translational stage and even a single suitable candidate is yet to emerge. Almost all the reported organic memristors lack reproducibility, endurance, stability, uniformity, scalability, and speed that are needed for an industrial application. In this review, we analyze the root cause of the prolonged failures of organic memory devices and discuss a new family of organic memristors, made of transition metal complexes of redox active organic ligands (RAL), that satisfy and go beyond the requirements specified in the 2015 ITRS roadmap for RRAM devices. These devices exhibit cyclability > 1012, retention of several months, on/off ratio > 103 , switching voltage approaching 100 mV, rise time less than 30 ns, and switching energy