Publications de Brennan James Walder

Iron incorporation in synthetic precipitated calcium silicate hydrates

Paul Bowen, Jirawan Siramanont, David Lyndon Emsley, Brennan James Walder

Effect of Fe3+ on the precipitation of synthetic calcium silicate hydrates (C-S-H) under controlled conditions has been evaluated. Using extremely basic either initial calcium nitrate or sodium silicate solutions (pH > 11), incipient formation of ferrihydr ...

Pergamon-Elsevier Science Ltd2021

Colloidal-ALD-Grown Core/Shell CdSe/CdS Nanoplatelets as Seen by DNP Enhanced PASS-PIETA NMR Spectroscopy

David Lyndon Emsley, Brennan James Walder, Laura Piveteau

Ligand exchange and CdS shell growth onto colloidal CdSe nanoplatelets (NPLs) using colloidal atomic layer deposition (c-ALD) were investigated by solid-state nuclear magnetic resonance (NMR) experiments, in particular, dynamic nuclear polarization (DNP) e ...

2020

Cd-113 Solid-State NMR at 21.1 T Reveals the Local Structure and Passivation Mechanism of Cadmium in Hybrid and All-Inorganic Halide Perovskites

Dominik Józef Kubicki, David Lyndon Emsley, Albert Hofstetter, Brennan James Walder, Daniel Prochowicz

Cadmium doping has recently emerged as an efficacious strategy for defect suppression and band gap tuning in hybrid as well as all-inorganic halide perovskites. However, the cadmium speciation in these materials is unknown. Here, we use high-field cadmium- ...

2020

Hyperpolarization transfer pathways in inorganic materials

Nicolas Luc Matthey, David Lyndon Emsley, Brennan James Walder, Snaedis Björgvinsdóttir, Pinelopi Moutzouri

Dynamic nuclear polarization can be used to hyperpolarize the bulk of proton-free inorganic materials in magic angle spinning NMR experiments. The hyperpolarization is generated on the surface of the material with incipient wetness impregnation and from th ...

Academic Press Inc - Elsevier Science2020

The Atomic-Level Structure of Cementitious Calcium Aluminate Silicate Hydrate

Paul Bowen, Karen Scrivener, Aslam Kunhi Mohamed, Jirawan Siramanont, David Lyndon Emsley, Brennan James Walder, Maya Nicole Harris, Pierrick Berruyer, Pinelopi Moutzouri, Mattia Negroni

Despite use of blended cements containing significant amounts of aluminum for over 30 years, the structural nature of aluminum in the main hydration product, calcium aluminate silicate hydrate (C-A-S-H), remains elusive. Using first-principles calculations ...

2020

Measurement of Proton Spin Diffusivity in Hydrated Cementitious Solids

David Lyndon Emsley, Brennan James Walder, Jayasubba Reddy Yarava, Federico Maria Paruzzo, Bradley Floyd Chmelka

The study of hydration and crystallization processes involving inorganic oxides is often complicated by poor long-range order and the formation of heterogeneous domains or surface layers. In solid-state NMR, H-1-H-1 spin diffusion analyses can provide info ...

2019

Atomic-level passivation mechanism of ammonium salts enabling highly efficient perovskite solar cells

Michael Graetzel, Jacques-Edouard Moser, Shaik Mohammed Zakeeruddin, Fabrizio Giordano, Dominik Józef Kubicki, Jingshan Luo, Andrés Burgos Caminal, David Lyndon Emsley, Brennan James Walder, Essa Awadh R Alharbi, Anwar Qasem M Alanazi, Alexander Roland Uhl

The high conversion efficiency has made metal halide perovskite solar cells a real break-through in thin film photovoltaic technology in recent years. Here, we introduce a straight-forward strategy to reduce the level of electronic defects present at the i ...

Nature Research2019

Characterization of semiconductor nanocrystals using advanced NMR spectroscopy

David Lyndon Emsley, Brennan James Walder, Laura Piveteau

AMER CHEMICAL SOC2019

Chemical exchange at the ferroelectric phase transition of lead germanate revealed by solid state Pb-207 nuclear magnetic resonance

Arnaud Magrez, David Lyndon Emsley, Brennan James Walder, Jasmine Viger-Gravel, Claudia Esther Avalos

The nature of the dynamics and structural changes that take place at the ferroelectric phase transition in lead oxides is a rich field of study. Solid-state nuclear magnetic resonance (NMR) of Pb-207 is well suited to study the local structure and disorder ...

ROYAL SOC CHEMISTRY2019

Line narrowing in H-1 NMR of powdered organic solids with TOP-CT-MAS experiments at ultra-fast MAS

David Lyndon Emsley, Brennan James Walder, Federico Maria Paruzzo

The residual broadening observed in H-1 spectra of rigid organic solids at natural abundance under 111 kHz magic angle spinning (MAS) is typically a few hundred Hertz. Here we show that refocusable and non-refocusable interactions contribute roughly equall ...

Academic Press Inc - Elsevier Science2019

Lead-Oxygen Bond Length Distributions of the Relaxor Ferroelectric 0.67PbMg(1/3)Nb(2/3)O(3)-0.33PbTiO(3) from Pb-207 Nuclear Magnetic Resonance

David Lyndon Emsley, Brennan James Walder, Claudia Esther Avalos

We investigate changes in the local environment of Pb-207 sites in the relaxor ferroelectric 0.67PbMg(1/3)Nb(2/3)O(3)-0.33PbTiO(3) using variable temperature magic angle spinning nuclear magnetic resonance. We observe a Gaussian distribution of Pb-207 chem ...

AMER CHEMICAL SOC2019

One- and Two-Dimensional High-Resolution NMR from Flat Surfaces

David Lyndon Emsley, Aaron James Rossini, Brennan James Walder

Determining atomic-level characteristics of molecules on two-dimensional surfaces is one of the fundamental challenges in chemistry. High-resolution nuclear magnetic resonance (NMR) could deliver rich structural information, but its application to two-dime ...

AMER CHEMICAL SOC2019

Maximizing nuclear hyperpolarization in pulse cooling under MAS

Nicolas Luc Matthey, David Lyndon Emsley, Brennan James Walder

It has recently been shown how dynamic nuclear polarization can be used to hyperpolarize the bulk of proton-free solids. This is achieved by generating the polarization in a wetting phase, transferring it to nuclei near the surface and relaying it towards ...

Academic Press Inc - Elsevier Science2019

Bulk Nuclear Hyperpolarization of Inorganic Solids by Relay from the Surface

Arthur César Pinon, David Lyndon Emsley, Brennan James Walder, Snaedis Björgvinsdóttir

2018

DNP enhanced NMR with flip-back recovery

Arthur César Pinon, David Lyndon Emsley, Brennan James Walder, Jayasubba Reddy Yarava, Snaedis Björgvinsdóttir

Academic Press Inc - Elsevier Science2018

207Pb NMR of ferroelectric perovskite lead germanate at and below the paraelectric phase transition

David Lyndon Emsley, Brennan James Walder, Jasmine Viger-Gravel, Claudia Esther Avalos

AMER CHEMICAL SOC2018

Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASS-PIETA NMR Spectroscopy

David Lyndon Emsley, Brennan James Walder, Laura Piveteau

Understanding the surface of semiconductor nanocrystals (NCs) prepared using colloidal methods is a long-standing goal of paramount importance for all their potential optoelectronic applications, which remains unsolved largely because of the lack of site-s ...

2018

Using 207Pb NMR to investigate temperature dependent nuclear spin relaxation and Pb-O bond covalency in relaxor ferroelectrics

David Lyndon Emsley, Brennan James Walder, Claudia Esther Avalos

AMER CHEMICAL SOC2018

Determining the Surface Structure of Silicated Alumina Catalysts via Isotopic Enrichment and Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy

David Lyndon Emsley, Brennan James Walder, Jasmine Viger-Gravel

Isotopic enrichment of Si-29 and DNP-enhanced NMR spectroscopy are combined to determine the detailed surface structure of a silicated alumina catalyst. The significant sensitivity enhancement provided by DNP is vital to the acquisition of multinuclear and ...

American Chemical Society2017

The Atomic-Level Structure of Cementitious Calcium Silicate Hydrate

Paul Bowen, Karen Scrivener, Aslam Kunhi Mohamed, Abhishek Kumar, David Lyndon Emsley, Aaron James Rossini, Albert Hofstetter, Bhuvanesh Srinivasan, Brennan James Walder

Efforts to tune the bulk physical properties of concrete are hindered by a lack of knowledge related to the atomic-level structure and growth of calcium silicate hydrate phases, which form about 50-60% by volume of cement paste. Here we describe the first ...

2017