Nanoscience News (<front>)

vdW Janus topological insulator is presented with stochastic inversion asymmetry via penetrative single-step plasma sulfurization, which enables the large-scale synthesis, one-step process, and low-temperature condition with back-end-of-line process compatibility. Sulfur dominance and its corresponding spatial OOP domain distribution are spatially observed using piezoelectric force microscopy hysteresis mapping, cross-sectional transmission electron microscopy, top-view scanning electroc microscopy, Kelvin probe force microscopy, and force-distance curve mapping. This provides an extendable synthetic solution for stochastic and size-controllable challenge-response pairs generation for PUFs application, which can overcome the conventional limitations of encryption technology.

Abstract

Owing to the exotic state of quantum matter, topological insulators have emerged as a significant platform for new-generation functional devices. Among these topological insulators, tetradymites have received significant attention because of their van der Waals (vdW) structures and inversion symmetries. Although this inversion symmetry completely blocks exotic quantum phenomena, it should be broken down to facilitate versatile topological functionalities. Recently, a Janus structure is suggested for asymmetric out-of-plane lattice structures, terminating the heterogeneous atoms at two sides of the vdW structure. However, the synthesis of Janus structures has not been achieved commercially because of the imprecise control of the layer-by-layer growth, high-temperature synthesis, and low yield. To overcome these limitations, plasma sulfurization of vdW topological insulators has been presented, enabling stochastic inversion asymmetry. To take practical advantage of the random lattice distortion, physically unclonable functions (PUFs) have been suggested as applications of vdW Janus topological insulators. The sulfur dominance is experimentally demonstrated via X-ray photoelectron spectroscopy, hysteresis variation, cross-sectional transmission electron microscopy, and adhesion energy variation. In conclusion, it is envisioned that the vdW Janus topological insulators can provide an extendable encryption platform for randomized lattice distortion, offering on-demand stochastic inversion asymmetry via a single-step plasma sulfurization.

[Ru(bpy)2]2+ photosensitive components are integrated into the Cu-HHTP MOF, coordinating with the Cu-O4 sites to assemble a bi-functional unit, thereby facilitating efficient local electron migration. Compared to the dissociative photosensitizer system, this newly constructed configuration exhibits a significant increase in the efficiency of photoinduced charge carrier transfer, resulting in a 37.2-fold enhancement in the photosynthesis of H2O2.

Abstract

Photosensitizer-assisted photocatalytic systems offer a solution to overcome the limitations of inherent light harvesting capabilities in catalysts. However, achieving efficient charge transfer between the dissociative photosensitizer and catalyst poses a significant challenge. Incorporating photosensitive components into reactive centers to establish well-defined charge transfer channels is expected to effectively address this issue. Herein, the electrostatic-driven self-assembly method is utilized to integrate photosensitizers into metal–organic frameworks, constructing atomically Ru-Cu bi-functional units to promote efficient local electron migration. Within this newly constructed system, the [Ru(bpy)2]2+ component and Cu site serve as photosensitive and catalytic active centers for photocarrier generation and H2O2 production, respectively, and their integration significantly reduces the barriers to charge transfer. Ultrafast spectroscopy and in situ characterization unveil accelerated directional charge transfer over Ru-Cu units, presenting orders of magnitude improvement over dissociative photosensitizer systems. As a result, a 37.2-fold enhancement of the H2O2 generation rate (570.9 µmol g−1 h−1) over that of dissociative photosensitizer system (15.3 µmol g−1 h−1) is achieved. This work presents a promising strategy for integrating atomic-scale photosensitive and catalytic active centers to achieve ultrafast photocarrier transfer and enhanced photocatalytic performance.

Analogic to the design of an anionic framework for inorganic sulfide/oxide solid electrolytes, a copolymeric polycationic electrolyte, P(AT-MBA-6F), that leverages the polycationic backbones with fluorinated microdomain trapping effect is constructed, which enables stable, fast and high-energy all-solid-state LMBs at ambient temperature.

Abstract

Solid polymer electrolytes (SPEs) are promising for high-energy and high-safety solid-state lithium metal batteries (LMBs). Here, a polycationic solid electrolyte (PCSE) is described that leverages the inherent high thermal/chemical stability of the polycationic domain and the anion trapping (FMAT) effect of another fluorinated microdomain for stable and fast-charging high-voltage LMBs. Specifically, while the polycationic imidazolium backbone ensures high segmental flexibility facilitating the Li+ mobility, the fluorinated microdomain effectively traps the bis(trifluoromethanesulfonyl)imide anions by strong dipole interactions, imparting localized solvation and restricted mobility of the anions, as well as improved oxidation stability. As a result, the PCSE exhibits a high ionic conductivity of 1.4 mS cm−1, a high Li+ transference number of 0.50, and a wide electrochemical window of ∼5.5 V at 25 °C. By way of in situ thermal polymerization of the electrolyte within assembled cells, the PCSE enables ultra-stable cycling of Li|LiNi0.8Co0.1Mn0.1O2 cells with a capacity retention of 98.1% after 500 cycles at 0.2 C at ambient temperatures. The work on the molecular design of PCSEs represents a fundamentally unique perspective for the rational design of SPEs with balanced properties that are historically challenging for high-energy, long-life, ambient-temperature solid-state LMBs.

Nature Materials, Published online: 19 February 2025; doi:10.1038/s41563-025-02122-z

Antiferromagnetic order blocks interlayer hopping of electron–hole pairs in a two-dimensional magnetic semiconductor, leading to the formation of a type of optical excitation — magnetic surface excitons — with quasi-one-dimensional quantum confinement.

Nature Materials, Published online: 19 February 2025; doi:10.1038/s41563-025-02129-6

The emergence of magnetically confined surface excitons enabled by antiferromagnetic spin correlations is reported, which leads to the confinement of excitons to the surface of layered antiferromagnet CrSBr.

Nature Materials, Published online: 19 February 2025; doi:10.1038/s41563-025-02120-1

The antiferromagnetic-to-paramagnetic phase transition in a two-dimensional semiconducting magnet, CrSBr, induces an exciton confinement transition from a strongly bound quasi-one-dimensional state to a weakly bound interlayer-delocalized state.

Robust estimates of theoretical uncertainties at fixed-order in perturbation theory

Precision computations for standard candle processes are a staple of the physics programme at colliders such as the Large Hadron Collider (LHC). The highest precision can be achieved in perturbative computations. In perturbation theory, however, calculations truncated at a fixed order inevitably have inherent theoretical uncertainty. This uncertainty quantifies the contributions from the missing higher-order terms (MHOU) that have not been accounted for. Traditionally, scale variation has been employed to estimate this uncertainty. In this talk, I introduce a straightforward yet effective prescription to directly incorporate these missing higher-order terms through theory nuisance parameters (TNPs). By varying these parameters, the associated uncertainty can effectively be estimated.

I will elaborate on how this methodology can be applied across various processes pertinent to LHC physics, specifically at next-to-leading (NLO) and next-to-next-to-leading order (NNLO) in perturbation theory. The findings reveal that in scenarios where scale variations yield consistent and reliable results, we can successfully mimic their outcomes using TNPs. Moreover, we will observe a considerable improvement in scenarios where traditional scale variation methods tend to underestimate the uncertainty involved.

• Speaker: Rene Poncelet (Cracow, INP)
• Friday 21 February 2025, 16:00-17:00
• Venue: MR19 (Potter Room, Pavilion B), CMS.
• Series: HEP phenomenology joint Cavendish-DAMTP seminar; organiser: Terry Generet.

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AI for better brain and mental health

Zoe Kourtzi is a Professor of Computational Cognitive Neuroscience at the University of Cambridge. Zoe’s research aims to develop predictive models of neurodegenerative disease and mental health with translational impact in early diagnosis and personalised interventions. Zoe received her PhD from Rutgers University and was a postdoctoral fellow at MIT and Harvard. She was a Senior Research Scientist at the Max Planck Institute for Biological Cybernetics and then a Chair in Brain Imaging at the University of Birmingham, before moving to the University of Cambridge in 2013. She is a Royal Society Industry Fellow, Cambridge University Lead at the Alan Turing Institute and Co-director of Cambridge’s Centre for Data Driven Discovery.’

• Speaker: Professor Zoe Kourtzi - University of Cambridge
• Tuesday 18 February 2025, 13:30-14:30
• Venue: Lecture Theatre 1, Department of Chemical Engineering and Biotechnology, West Cambridge Site.
• Series: Chemical Engineering and Biotechnology Departmental Seminars; organiser: ejm94.

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Exploring dietary behaviours, narratives and attitudes in Cambridge colleges

Global appetite for meat exerts a devastating toll on human and planetary health but also offers a unique opportunity to achieve both climate and health benefits through a reduction in consumption. The potential is reflected in multiple national and international policy recommendations, but the UK lags behind targets​. Urgent improvement is needed at scale and speed.

My research aims to contribute to knowledge around reduction in meat consumption by addressing the research question: what are the main barriers and levers to achieving reduction in meat consumption in Cambridge colleges? I recently surveyed Cambridge college users to explore attitudes and narratives around meat consumption, prevailing dietary habits, and key levers and barriers for meat reduction. The survey ran from the 16th of December 2024 to the 2nd of February 2025 and resulted in more than 56,000 data points from 849 responses – a response rate of approximately 3% of the entire University population. The survey data contains a highly representative sample drawn from significant contributions from all the 31 colleges, and students, staff, postdoctoral researchers, and fellows alike. My talk will reveal some of the interim findings from the survey and discuss what these could tell us about the challenges and opportunities involved in reducing meat consumption here in Cambridge.

• Speaker: Sigurdur Martinsson, MSt in Sustainability Leadership, Darwin College
• Tuesday 25 February 2025, 13:10-14:00
• Venue: Richard King room, Darwin College.
• Series: Darwin College Humanities and Social Sciences Seminars; organiser: Dr Amelia Hassoun.

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Assessing language-specific capabilities of LLMs: Lessons from Swedish NLP

Abstract: In this talk, I discuss benchmarking and interpreting large language models in the context of Swedish. I present a selection of work from my PhD thesis, which analyze LLMs Swedish-specific capabilities in different areas: English-Swedish language transfer, multi-task benchmarking on Swedish NLU and targeted analysis of a specific case of Swedish linguistic variation. I outline some of the challenges that arise when trying to assess the language-specific capabilities of LLMs, some lessons I’ve learned throughout from my work and give a future outlook.

Bio: Felix Morger is a software engineer and computational linguist based in Gothenburg, Sweden. He recently defended his PhD thesis, titled “In the minds of stochastic parrots: Benchmarking, evaluating and interpreting large language models”. His main research interests are in benchmarking and model interpretability of large language models with a large focus on Swedish.

• Speaker: Felix Morger (University of Gothenburg)
• Friday 21 February 2025, 12:00-13:00
• Venue: ONLINE ONLY. Here is the Zoom link: https://cam-ac-uk.zoom.us/j/4751389294?pwd=Z2ZOSDk0eG1wZldVWG1GVVhrTzFIZz09..
• Series: NLIP Seminar Series; organiser: Suchir Salhan.

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The Case for Decentralized Scheduling in Modern Datacenters

Modern data centres serve as a backbone for executing diverse user workloads. The growing demand for their resources has led to high volumes of traffic, requiring clusters to operate at high utilization. In this talk, I shall detail how data centre schedulers, which are responsible for mapping workload tasks to resources, perform under such challenging conditions. I will present how centralized schedulers, while globally informed, do not scale well under high load since they generate a lot of network traffic when continuously transferring updated node data. Conversely, distributed schedulers scale well but lack a precise global view of cluster resources, leading to suboptimal task allocations. Consequently, these existing schedulers impose up to three times longer wait times on tail tasks, leading to large variance in inter-task start times, and hence, longer task and job completion times.

I will then describe recent advances in decentralized scheduling, focusing on performance, scalability, and load balancing. I will present our approach of job-aware decentralized scheduling which effectively reduces task wait times even under high cluster load. I will also talk about how distributed optimization algorithms can be implemented within the framework of decentralized scheduling, in order to provide theoretical guarantees for convergence to an optimal schedule. By the end of this talk, I hope to convince you that decentralized schedulers achieve a good balance in both scale and performance, and are indeed the most practical solution for data centres.

Bio: Smita Vijayakumar recently completed her PhD in Computer Science from the University of Cambridge, under the supervision of Evangelia Kalyvianaki. As a part of her thesis, she developed a decentralized scheduling framework to reduce tail task latencies in highly utilized datacenters. She has over twelve years of industry experience at companies like Cisco and Juniper, working on cloud computing, networking, and distributed systems. She also has an MS in Computer Science from The Ohio State University, where her work investigated cloud resource allocation to bottleneck stages for processing streaming applications. Her research has been published in top-tier ACM and IEEE conferences. She has also been actively involved in mentoring, teaching, and community leadership, including founding Women Who Go in India. Smita’s expertise spans cloud scheduling, resource management, and scalable distributed systems.

• Speaker: Smita Vijayakumar, Systems Research Group, Cambridge University Computer Laboratory
• Thursday 01 May 2025, 15:00-16:00
• Venue: FW11.
• Series: Computer Laboratory Systems Research Group Seminar; organiser: Richard Mortier.

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Formalising Brauer Group and Group Cohomology in Lean4

The concept of Brauer Groups, originally developed to classify division algebras, has now found many uses in scheme theory and class field theory. Brauer Groups over a field k is defined as the collection of central simple algebras over k modulo certain equivalence relations and this project is set out to formalise the correspondence between the Brauer groups and the second Galois cohomology groups Br(k) ≅ H²(Gal(k_sep/k) , k ⃰_sep). In this talk, we give a complete formalisation between the relative Brauer group of a finite dimensional field extension Br(K/k) and the second group cohomology H²(Gal (K/k) , K ⃰) as the first step.

=== Hybrid talk ===

Join Zoom Meeting https://cam-ac-uk.zoom.us/j/87143365195?pwd=SELTNkOcfVrIE1IppYCsbooOVqenzI.1

Meeting ID: 871 4336 5195

Passcode: 541180

• Speaker: Jujian Zhang (Imperial College London)
• Thursday 20 February 2025, 17:00-18:00
• Venue: MR14 Centre for Mathematical Sciences.
• Series: Formalisation of mathematics with interactive theorem provers ; organiser: Anand Rao Tadipatri.

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Simplicial volume and aspherical manifolds

Simplicial volume is a homotopy invariant for compact manifolds introduced by Gromov that measures the complexity of a manifold in terms of singular simplices. A celebrated question by Gromov (~’90) asks whether all oriented closed connected aspherical manifolds with zero simplicial volume also have vanishing Euler characteristic. In this talk, we will describe the problem and we will show counterexamples to some variations of the previous question. Moreover, we will describe some new strategies to approach the problem as well as the relation between Gromov’s question and other classical problems in topology. This will include joint works with Clara Löh and George Raptis, and with Alberto Casali.

• Speaker: Marco Moraschini (Università di Bologna)
• Wednesday 19 February 2025, 16:00-17:00
• Venue: CMS, MR15.
• Series: Differential Geometry and Topology Seminar; organiser: Oscar Randal-Williams.

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Physical-Layer Security of Satellite Communications Links

In recent years, building and launching satellites has become considerably cheaper, making satellite systems more accessible to an expanding user base. This accessibility has led to a diverse array of applications—such as navigation, communications, and earth observation—that depend on satellites. However, hardware limitations and operational considerations often render cryptographic solutions impractical for these systems. Furthermore, the availability of low-cost software-defined radios has made signal capture, injection, and interference attacks more attainable for a wider range of potential attackers.

Therefore, mitigations must be developed for satellites that have already been launched without adequate protections in place. This talk introduces some of our research into how satellite systems are vulnerable, as well as ways to protect these systems.

Bio: Simon Birnbach is a Senior Research Associate and a Royal Academy of Engineering UK IC Postdoctoral Research Fellow in the Systems Security Lab of Professor Ivan Martinovic in the Department of Computer Science at the University of Oxford. He specialises in the security of cyber-physical systems, with a focus on smart home, aviation, and aerospace security.

Zoom link: https://cam-ac-uk.zoom.us/j/87594645761?pwd=qlkBblRXyjku3I3C3mnWcCZuidMP7B.1

Meeting ID: 875 9464 5761 Passcode: 648387

• Speaker: Simon Birnbach, University of Oxford
• Tuesday 18 February 2025, 14:00-15:00
• Venue: Webinar & SS03, Computer Laboratory, William Gates Building..
• Series: Computer Laboratory Security Seminar; organiser: Tina Marjanov.

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Towards a Faster Finality Protocol for Ethereum

Ethereum’s Gasper consensus protocol typically requires 64 to 95 slots—the units of time during which a new chain extending the previous one by one block is proposed and voted—to finalize, even under ideal conditions with synchrony and honest validators. This exposes a significant portion of the blockchain to potential reorganizations during changes in network conditions, such as periods of asynchrony.

In this talk, I will introduce 3SF, a novel consensus protocol that addresses these limitations. With 3SF, finality is achieved within just three slots after a proposal, drastically reducing the exposure to reorganizations. This presentation will explore the motivation, design, and implications of 3SF, offering a new perspective on the future of Ethereum’s consensus protocol.

Paper: https://arxiv.org/abs/2411.00558

• Speaker: Luca Zanolini, Ethereum Foundation
• Tuesday 04 March 2025, 14:00-15:00
• Venue: Webinar & GN06, Computer Laboratory, William Gates Building..
• Series: Computer Laboratory Security Seminar; organiser: Tina Marjanov.

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Some problems in coarse graph theory

Coarse graph theory is a developing area, which focuses on the large-scale geometric structure of graphs, particularly through the lens of quasi-isometry. A central goal here is to find coarse analogues of classical graph-theoretic results. We discuss some initial steps in this direction. Joint work with Tung Nguyen and Paul Seymour.

• Speaker: Alexander Scott (Oxford)
• Thursday 20 February 2025, 14:30-15:30
• Venue: MR12.
• Series: Combinatorics Seminar; organiser: ibl10.

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Owing to their atomic-scale thickness and dangling-bond-free surfaces, 2D materials have become promising alternatives for electronic devices operating at high temperatures. This review comprehensively summaries the recent progresses on the interface engineering of 2D materials toward high-temperature electronic devices, including FETs, optoelectronic devices, sensors, and neuromorphic devices.

Abstract

High-temperature electronic materials and devices are highly sought after for advanced applications in aerospace, high-speed automobiles, and deep-well drilling, where active or passive cooling mechanisms are either insufficient or impractical. 2D materials (2DMs) represent promising alternatives to traditional silicon and wide-bandgap semiconductors (WBG) for nanoscale electronic devices operating under high-temperature conditions. The development of robust interfaces is essential for ensuring that 2DMs and their devices achieve high performance and maintain stability when subjected to elevated temperatures. This review summarizes recent advancements in the interface engineering of 2DMs for high-temperature electronic devices. Initially, the limitations of conventional silicon-based materials and WBG semiconductors, alongside the advantages offered by 2DMs, are examined. Subsequently, strategies for interface engineering to enhance the stability of 2DMs and the performance of their devices are detailed. Furthermore, various interface-engineered 2D high-temperature devices, including transistors, optoelectronic devices, sensors, memristors, and neuromorphic devices, are reviewed. Finally, a forward-looking perspective on future 2D high-temperature electronics is presented. This review offers valuable insights into emerging 2DMs and their applications in high-temperature environments from both fundamental and practical perspectives.

To investigate the effects of topological characteristics of polymers on their lymph node (LN) targeting activity and how their molecular weight (MW) influences pharmacokinetics to support LN homing, a series of polymer-TLR agonist conjugates (PTACs) are designed. Among the conjugates, the dendritic 6-arm PTAC with an MW of 60 kDa demonstrated the highest LN drainage, deepest penetration, and prolonged retention. As a result, it induced broad antibody and T cell responses, enhancing vaccine immunogenicity and suppressing tumor growth.

Abstract

Strategically targeting lymph nodes (LNs) to orchestrate the initiation and regulation of adaptive immune responses is one of the most pressing challenges in the context of vaccination. Herein, a series of polymer-TLR agonist conjugates (PTACs) is developed to investigate the impact of dendritic-topological characteristics on their LN targeting activity in vivo, and their molecular weight (MW) on their pharmacokinetics in support of their LN homing. Notably, the dendritic 6-arm PTAC with a MW of 60 kDa (6A-PTAC-60k) rapidly delivered cargo to draining LNs after administration to peripheral tissues. Specifically, this topologic structure ameliorated the targeting behavior within lymphatic vessels and LNs, including an elevated amount of TLR7/8 agonist delivered to the LNs, an improved distribution pattern among barrier cells and immune cells, increased permeability, and prolonged retention. Furthermore, the 6A-PTAC-60k formulation induced broad antibody and T cell responses, enhancing vaccine immunogenicity and suppressing tumor growth. The results revealed that both the topology and MW of polymers are crucial factors for immunoadjuvant distribution and their functional activity in the draining LNs, which, in turn, enhanced the immunogenicity of the vaccine formulation. This study may provide a chemical and structural basis for optimizing the design of immunoadjuvant delivery systems.

Diluted heterojunctions are employed to increase the structure order in the layer-by-layer fabricated solar cells and polymeric diluent is found superior that the small molecular diluent, creating OSC having dual fibrils with significantly increased absorption and reduced charge recombination to realize an efficiency of 21.0% (certified value of 20.25%).

Abstract

As an exitonic photovoltaic device, organic solar cells (OSCs) consist of electron donating and accepting components in their photoactive layer, in which the molecular interactions between donor and acceptor can significantly affect the nanoscale morphology as well as the photovoltaic performance of OSCs. In this work, by diluting electron donor with electron acceptor having opposite electrostatic potentials to promote the structural order via strengthened intermolecular interactions, this study shows that polymeric diluent is more effective due to its long-ranged conjugated backbone compared with small molecular diluent. The ternary heterojunction made of C5-16:L8-BO binary acceptors diluted with D18 shows the strongest structural order, benefiting from the strong interactions between L8-BO and C5-16. The enhanced structural order within the photoactive layer prepared by layer-by-layer deposition of the diluted p-type and n-type heterojunctions contributes to enhanced light absorption, improved charge transport, and inhibited charge recombination. As the result, OSC based on D18 (PY-IT diluted)/L8-BO:C5-16 (D18 diluted) having donor and acceptor dual fibrils obtains an unprecedented power conversion efficiency of 21.0% (certified value of 20.25%), which is one of the highest certified PCE up to date.

This study explores ultrathin epitaxial La2Ti2O7 films, a layered perovskite from the Carpy-Galy family, grown on various substrates. Remarkably, high epitaxial strain promotes layer-by-layer growth and stabilizes the correct phase. The films exhibit a polarization significantly higher than previously reported, exceeding 18 µCcm−2, and retain ferroelectricity down to a single-unit-cell thickness, highlighting their potential for advanced nanoscale devices.

Abstract

Layered perovskite-based compounds offer a range of unconventional properties enabled by their naturally anisotropic structure. Among these, the Carpy-Galy phases (A n B n O3n+2), characterized by (110)-oriented perovskite planes interleaved with additional oxygen layers, stand out for robust in-plane polarization. However, the challenges associated with the synthesis of ultrathin Carpy-Galy films and understanding the impact of strain on their properties limit their integration into devices. Here, La2Ti2O7 (n = 4) films grown on substrates imposing tensile, compressive, or negligible epitaxial strains are investigated. Surprisingly, a 3% tensile strain from DyScO3 (100) substrates facilitates layer-by-layer growth mode, whereas compressive (LaAlO3-Sr2TaAlO6 (110)) or negligible (SrTiO3 (110)) epitaxial strains require post-deposition annealing to reach comparable crystallinity. Using density-functional theory calculations, scanning probe microscopy, X-ray diffraction, scanning transmission electron microscopy, and polarization switching experiments, it is confirmed that these films possess exceptional ferroelectric properties, including a polarization of 18 µCcm−2 – more than three times higher than previously reported – as well as persistence of ferroelectricity down to a single-unit-cell thickness. This study not only advances the understanding of Carpy-Galy phases as epitaxial thin films but also lays a foundation for their integration into advanced ferroelectric device architectures.