Curran Kalha

University College London

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Anna Regoutz

University College London

P. Thakur

Diamond Light Source

Nathalie Fernando

University College London

Tien‐Lin Lee

Diamond Light Source

Aysha A. Riaz

University College London

Christoph Schlueter

Deutsches Elektronen-Synchrotron DESY

Laura E. Ratcliff

Argonne National Laboratory

María Ibáñez

Institute of Science and Technology Austria

Mahsa Parvizian

University of Basel

M. B. Trzhaskovskaya

D.I. Mendeleyev All-Russian Institute for Metrology

Cooperative Institutions

University College London

Diamond Light Source

Imperial College London

University of Oxford

Universitat Politècnica de Catalunya

Barcelona Supercomputing Center

Technical University of Darmstadt

Research Complex at Harwell

Transnational Press London

Lawrence Berkeley National Laboratory

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Ultra stable, inkjet-printed pseudo reference electrodes for lab-on-chip integrated electrochemical biosensors

Scientific Reports (2020)

Sotirios Papamatthaiou Uroš Zupančič Curran Kalha Anna Regoutz Pedro Estrela

Abstract Lab-on-Chip technology comprises one of the most promising technologies enabling the widespread adoption of Point-of-Care testing in routine clinical practice. However, until now advances in Lab-on-Chip have not been translated to the anticipated degree to commercialized tools, with integrated device mass manufacturing cost still not at a competitive level for several key clinical applications. Lab-on-PCB is currently considered as a candidate technology addressing this issue, owing to its intuitive compatibility with electronics, seamless integration of electrochemical biosensors and the extensive experience regarding industrial manufacturing processes. Inkjet-printing in particular is a compatible fabrication method, widening the range of electronic materials available and thus enabling seamlessly integrated ultrasensitive electronic detection. To this end, in this work stable pseudo-reference electrodes are fabricated for the first time by means of commercial inkjet-printing on a PCB-integrated electrochemical biosensing platform. SEM and XPS analysis are employed to characterize the electrodes’ structure and composition and identify any special characteristics, compared to published work on alternative substrates. Additionally, this paper analyzes integrated reference electrodes from a new perspective, focusing mainly on their characteristics in real-life operation: chemical sintering as opposed to high budget thermal one, stability under continuous flow, pH dependency and bias stress effects on electrode instability, a parameter often overlooked in electrochemical biosensors.

Lab-on-a-Chip

10.1038/s41598-020-74340-1

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Citations (19)

Capturing the dynamics of Ti diffusion across Ti$_x$W$_{1-x}$/Cu heterostructures using X-ray photoelectron spectroscopy

arXiv (Cornell University) (2023)

Curran Kalha P. Thakur Tien‐Lin Lee Michael Reisinger Johannes Zechner

Interdiffusion phenomena between adjacent materials are highly prevalent in semiconductor device architectures and can present a major reliability challenge for the industry. To fully capture and better understand these phenomena, experimental approaches must go beyond static and post-mortem studies to include in-situ and in-operando setups. Here, soft and hard X-ray photoelectron spectroscopy (SXPS and HAXPES) is used to monitor diffusion in real-time across a proxy device. The device consists of a Si/SiO\textsubscript{2}/Ti$_x$W$_{1-x}$(300 nm)/Cu(25 nm) thin film material stack, with the Ti$_x$W$_{1-x}$ film acting as a diffusion barrier between Si and Cu. The monitoring of diffusion is achieved through the continuous collection of spectra whilst in-situ annealing to 673 K. Ti within the TiW is found to be highly mobile during annealing, diffusing out of the barrier and accumulating at the Cu surface. Increasing the Ti concentration within the Ti$_x$W$_{1-x}$ film increases the quantity of accumulated Ti, and Ti is first detected at the Cu surface at temperatures as low as 550 K. Surprisingly, at low Ti concentrations ($x$ = 0.054), W is also mobile and diffuses alongside Ti. These results provide crucial evidence for the importance of diffusion barrier composition on their efficacy during device application, delivering insights into the mechanisms underlying their effectiveness and limitations.

Diffusion barrier

10.48550/arxiv.2301.02577

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The chemistry of Cu3N and Cu3PdN nanocrystals

Mahsa Parvizian Alejandra Durán Balsa Rohan Pokratath Curran Kalha Seungho Lee

Cu3N and Cu3PdN nanocrystals are attractive materials with numerous applications ranging from optoelectronics to catalysis. However, their chemical formation mechanism and surface chemistry are unknown or contested. In this work, we first optimize the synthesis and purification to yield phase pure, colloidal stable Cu3N and Cu3PdN nanocubes. Second, we elucidate the precursor conversion mechanism that leads to the formation of Cu3N from copper(II) nitrate and oleylamine. We find that oleylamine is both the reductant and nitrogen source. Oleylamine is oxidized to a primary aldimine and the latter reacts further with oleylamine to a secondary aldimine, eliminating ammonia. Ammonia reacts with Cu(I) to form Cu3N. Third, we investigated the surface chemistry of the nanocrystals using solution NMR spectroscopy and X-ray photoelectron spectroscopy (XPS). We find a mixed ligand shell of aliphatic amines and carboxylates. The carboxylate is produced in situ during the synthesis. While the carboxylates appear tightly bound, the amines are easily desorbed from the surface. Finally, we analyze the optoelectronic properties by UV-Vis and XPS. Doping with palladium decreases the bandgap but the material remains a semiconductor. These results bring insight into the chemistry of metal nitrides and will help the development of other metal nitride nanocrystals.

Oleylamine

10.26434/chemrxiv-2022-2tjc0

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From MAX Phase Carbides to Nitrides: Synthesis of V₂GaC, V₂GaN, and the Carbonitride V₂GaC_1–xN_x

Inorganic Chemistry (2022)

Niels Kubitza Andreas Reitz Anne‐Marie Zieschang Hanna Pazniak Barbara Albert

The research in MAX phases is mainly concentrated on the investigation of carbides rather than nitrides (currently >150 carbides and only <15 nitrides) that are predominantly synthesized by conventional solid-state techniques. This is not surprising since the preparation of nitrides and carbonitrides is more demanding due to the high stability and low diffusion rate of nitrogen-containing compounds. This leads to several drawbacks concerning potential variations in the chemical composition of the MAX phases as well as control of morphology, the two aspects that directly affect the resulting materials properties. Here, we report how alternative solid-state hybrid techniques solve these limitations by combining conventional techniques with nonconventional precursor synthesis methods, such as the "urea-glass" sol-gel or liquid ammonia method. We demonstrate the synthesis and morphology control within the V-Ga-C-N system by preparing the MAX phase carbide and nitride─the latter in the form of bulkier and more defined smaller particle structures─as well as a hitherto unknown carbonitride V2GaC1-xNx MAX phase. This shows the versatility of hybrid methods starting, for example, from wet chemically obtained precursors that already contain all of the ingredients needed for carbonitride formation. All products are characterized in detail by X-ray powder diffraction, electron microscopy, and electron and X-ray photoelectron spectroscopies to confirm their structure and morphology and to detect subtle differences between the different chemical compositions.

Chemical state

Morphology

Chemical Stability

10.1021/acs.inorgchem.2c00200

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Citations (22)

Digitisation of Trzhaskovskaya Dirac-Fock Photoionisation Parameters for HAXPES Applications, Part II

Figshare (2020)

Joe Willis Curran Kalha M. B. Trzhaskovskaya V. G. Yarzhemsky David O. Scanlon

This document provides a digitised version of the tabulated Dirac-Fock photoionisation parameters for HAXPES applications, Part II: Inner atomic shells (2019), calculated by M.B. Trzhaskovskaya and V.G. Yarzhemsky. The data from the original paper was mined, checked and deposited into a Microsoft Excel spreadsheet for easy access.

10.6084/m9.figshare.13292174

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Satellites in the Ti~1$s$ core level spectra of SrTiO$_3$ and TiO$_2$

arXiv (Cornell University) (2022)

Atsushi Hariki Keisuke Higashi Jiebin Li Curran Kalha Manfred Mascheck

Satellites in core level spectra of photoelectron spectroscopy (PES) can provide crucial information on the electronic structure and chemical bonding in materials, in particular in transition metal oxides. This work explores satellites of the Ti 1$s$ and 2$p$ core level spectra of SrTiO$_3$ and TiO$_2$. Conventionally, soft X-ray photoelectron spectroscopy (SXPS) probes the Ti 2$p$ core level, however, it is not ideal to fully capture satellite features due to its inherent spin-orbit-splitting (SOS). Here, hard X-ray photoelectron spectroscopy (HAXPES) provides access to the Ti 1$s$ spectrum instead, which allows to study intrinsic charge responses upon core-hole creation without the complication from SOS and with favourable intrinsic line widths. The experimental spectra are theoretically analysed by two impurity models, including an Anderson impurity model (AIM) built on local density approximation (LDA) and dynamical mean-field theory (DMFT), and a conventional TiO$_6$ cluster model. The theoretical results emphasise the importance of explicit inclusion of higher-order Ti-O charge-transfer processes beyond the nearest-neighbouring Ti-O bond to simulate the core level spectra of SrTiO$_3$ and TiO$_2$. The AIM approach with continuous bath orbitals provided by LDA+DMFT represents the experimental spectra well. Crucially, with the aid of the LDA+DMFT method this work provides a robust prescription of how to use the computationally-cheap cluster model in fitting analyses of core level spectra.

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