# Category: publications

## Deep Eutectic Solvents as Non-flammable Electrolytes for Durable Sodium-ion Batteries

 Authors: Dries De Sloovere, Danny E. P. Vanpoucke, Andreas Paulus, Bjorn Joos, Lavinia Calvi, Thomas Vranken, Gunter Reekmans, Peter Adriaensens, Nicolas Eshraghi, Abdelfattah Mahmoud, Frédéric Boschini, Mohammadhosein Safari, Marlies K. Van Bael, An Hardy Journal: Advanced Energy and Sustainability Research 3(?), 2100159 (2022) doi: 10.1002/aesr.202100159 IF(2022): ?? export: bibtex pdf: (OA)

 Graphical Abstract: Understanding the electronic structure of Na-TFSI interacting with NMA.

## Abstract

Sodium-ion batteries are alternatives for lithium-ion batteries in applications where cost-effectiveness is of primary concern, such as stationary energy storage. The stability of sodium-ion batteries is limited by the current generation of electrolytes, particularly at higher temperatures. Therefore, the search for an electrolyte which is stable at these temperatures is of utmost importance. Here, we introduce such an electrolyte using non-flammable deep eutectic solvents, consisting of sodium bis(trifluoromethane)sulfonimide (NaTFSI) dissolved in N-methyl acetamide (NMA). Increasing the NaTFSI concentration replaces NMA-NMA hydrogen bonds with strong ionic interactions between NMA, Na+, and TFSI. These interactions lower NMA’s HOMO energy level compared to that of TFSI, leading to an increased anodic stability (up to ~4.65 V vs Na+/Na). (Na3V2(PO4)2F3/CNT)/(Na2+xTi4O9/C) full cells show 74.8% capacity retention after 1000 cycles at 1 C and 55 °C, and 97.0% capacity retention after 250 cycles at 0.2 C and 55 °C. This is considerably higher than for (Na3V2(PO4)2F3/CNT)/(Na2+xTi4O9/C) full cells containing a conventional electrolyte. According to the electrochemical impedance analysis, the improved electrochemical stability is linked to the formation of more robust surface films at the electrode/electrolyte interface. The improved durability and safety highlight that deep eutectic solvents can be viable electrolyte alternatives for sodium-ion batteries.

## Assigning probabilities to non-Lipschitz mechanical systems

 Authors: Danny E. P. Vanpoucke and Sylvia Wenmackers Journal: Chaos 31, 123131 (2021) doi: 10.1063/5.0063388 IF(2021): 3.642 export: bibtex pdf:    (Open Access) github:

 Graphical Abstract: Examples of Malament’s Mounds, of which the Norton Dome is the special case where α=½.

## Abstract

We present a method for assigning probabilities to the solutions of initial value problems that have a Lipschitz singularity. To illustrate the method, we focus on the following toy-example: $\ddot{r} = r^{a}$, $r(t = 0) = 0$, and $\dot{r}|_{r(t=0)}= 0$, with a∈]0; 1[. This example has a physical interpretation as a mass in a uniform gravitational field on a dome of particular shape; the case with a = ½ is known as Norton’s dome. Our approach is based on (1) finite difference equations, which are deterministic; (2) elementary techniques from alpha-theory, a simplified framework for non-standard analysis that allows us to study infinitesimal perturbations; and (3) a uniform prior on the canonical phase space.  Our deterministic, hyperfinite grid model allows us to assign probabilities to the solutions of the This allows us to assign probabilities to the solutions of the initial value problem in the original, indeterministic model.

Phase space vector field for all Malament’s mounds

# Happy New Year

2020 will forever be the year of viruses for me and a lot of us. At Maastricht University, the year started with a university wide cyber-attack with ransomware. After the computer-viruses came the human viruses, with COVID-19 shutting down one country after the other, and shutting down education systems as well.

Hopefully 2021 will be better behaved, though we know already some of the hurdles which will make life interesting the coming year. COVID-19 is far from over, and it will take at least a year to vaccinate everyone. Furthermore, as of the first of today, the United Kingdom is no longer a part of the EU, making travel inside Europe a little harder again.

But before we launch into these new and interesting times, lets look back at 2020 one last time, keeping up with  tradition. What have I done during the last year of academic merit.

#### 2. Completed refereeing tasks: +17

• Applied Physics Letters
• Journal of Physical Chemistry (2x)
• Computational Materials Science (2x)
• Materials Chemistry and Physics
• Journal of Physics: Condensed Matter (5x)
• Diamond and Related Materials (6x)

#### 3. Conferences & workshops in times of Corona: +3/+1 (Attended & Organised), >+4 internal

ACOS poster prize 2020

With regard to conferences, 2020 was the year everyone came into contact with the concept of the online conference. Many conferences and events got canceled: such as TEDx@UHasselt (which will return in 2021)

• ACOS 2020, Online, Oktober 28th, 2020 [poster presentation and video-pitch, 2nd poster prize]
• RSC Chemical Science Symposium 2020, Online, September 29th-30th, 2020 [iposter presentation]
• D-NL-HIT project meetings [oral presentations]
• Virtual Partner Meeting, April 8th, 2020
• Adhesives Pilot Branch meeting, October 7th, 2020
• Virtual Partner Meeting, October 15th, 2020
• UV-Curing Branch meeting, October 22nd, 2020
• SBDD XXV, Hasselt University, Belgium, March 11th-13th, 2020 [(invited) oral presentation, poster presentation] …On Friday13th Belgium went into it’s first lock-down.
• Pilot Branch meeting adhesives D-NL-HIT project, Maastricht University, Brighlands campus, February 26th, 2020 [Organised]

#### 4. Science Communication & Social media:

• In February 2020, I finally caved and joined Twitter as @DelocalizedD .
• Added several new repositories to my github account, with the most important ones being:
• Started a YouTube channel (for the ACOS video pitch)

#### 5. Current size of HIVE:

• Continued work on a public version of HIVE at github: HIVE 4.x   (26K lines, 9 commands available)
• 61K lines of program (code: 69 %)
• ~100 files
• 49 (command line) options

## Impact of methane concentration on surface morphology and boron incorporation of heavily boron-doped single crystal diamond layers

 Authors: Rozita Rouzbahani, Shannon S.Nicley, Danny E.P.Vanpoucke, Fernando Lloret, Paulius Pobedinskas, Daniel Araujo, Ken Haenen Journal: Carbon 172, 463-473 (2021) doi: 10.1016/j.carbon.2020.10.061 IF(2019): 8.821 export: bibtex pdf:

 Graphical Abstract: Artist impression of B incorporation during CVD growth of diamond.

## Abstract

The methane concentration dependence of the plasma gas phase on surface morphology and boron incorporation in single crystal, boron-doped diamond deposition is experimentally and computationally investigated. Starting at 1%, an increase of the methane concentration results in an observable increase of the B-doping level up to 1.7×1021 cm−3, while the hole Hall carrier mobility decreases to 0.7±0.2 cm2 V−1 s−1. For B-doped SCD films grown at 1%, 2%, and 3% [CH4]/[H2], the electrical conductivity and mobility show no temperature-dependent behavior due to the metallic-like conduction mechanism occurring beyond the Mott transition. First principles calculations are used to investigate the origin of the increased boron incorporation. While the increased formation of growth centers directly related to the methane concentration does not significantly change the adsorption energy of boron at nearby sites, they dramatically increase the formation of missing H defects acting as preferential boron incorporation sites, indirectly increasing the boron incorporation. This not only indicates that the optimized methane concentration possesses a large potential for controlling the boron concentration levels in the diamond, but also enables optimization of the growth morphology. The calculations provide a route to understand impurity incorporation in diamond on a general level, of great importance for color center formation.

## Small Data Materials Design with Machine Learning: When the Average Model Knows Best

 Authors: Danny E. P. Vanpoucke, Onno S. J. van Knippenberg, Ko Hermans, Katrien V. Bernaerts, and Siamak Mehrkanoon Journal: Journal of Applied Physics 128, 054901 (2020) doi: 10.1063/5.0012285 IF(2019): 2.286 export: bibtex pdf:    (Open Access) github:

 Graphical Abstract: Correlation plot of the RMSE of the validation set and the intercept value for linear model instances trained on 1000 subsets of a 25 point data set. The distribution of the correlation data is indicated by the black curve.

## Abstract

Machine Learning is quickly becoming an important tool in modern materials design. Where many of its successes are rooted in huge data sets, the most common applications in academic and industrial materials design deal with data sets of at best a few tens of data points. Harnessing the power of Machine Learning in this context is therefore of considerable importance. In this work, we investigate the intricacies introduced by these small data sets. We show that individual data points introduce a significant chance factor in both model training and quality measurement. This chance factor can be mitigated by the introduction of an ensemble-averaged model. This model presents the highest accuracy while at the same time it is robust with regard to changing data set size. Furthermore, as only a single model instance needs to be stored and evaluated, it provides a highly efficient model for prediction purposes, ideally suited for the practical materials scientist.

## Partitioning the vibrational spectrum: Fingerprinting defects in solids

 Authors: Danny E. P. Vanpoucke Journal: Computational Materials Science 181, 109736 (2020) doi: 10.1016/j.commatsci.2020.109736 IF(2019): 2.863 export: bibtex pdf:    (Open Access) github:

 Graphical Abstract: Finger printing defects in diamond through the creation of the vibrational spectrum of a defect.

## Abstract

Vibrational spectroscopy techniques are some of the most-used tools for materials
characterization. Their simulation is therefore of significant interest, but commonly
performed using low cost approximate computational methods, such as force-fields.
Highly accurate quantum-mechanical methods, on the other hand are generally only used
in the context of molecules or small unit cell solids. For extended solid systems,
such as defects, the computational cost of plane wave based quantum mechanical simulations
remains prohibitive for routine calculations. In this work, we present a computational scheme
for isolating the vibrational spectrum of a defect in a solid. By quantifying the defect character
of the atom-projected vibrational spectra, the contributing atoms are identified and the strength
of their contribution determined. This method could be used to systematically improve phonon
fragment calculations. More interestingly, using the atom-projected vibrational spectra of the
defect atoms directly, it is possible to obtain a well-converged defect spectrum at lower
computational cost, which also incorporates the host-lattice interactions. Using diamond as
the host material, four point-defect test cases, each presenting a distinctly different
vibrational behaviour, are considered: a heavy substitutional dopant (Eu), two intrinsic
point-defects (neutral vacancy and split interstitial), and the negatively charged N-vacancy
center. The heavy dopant and split interstitial present localized modes at low and high
frequencies, respectively, showing little overlap with the host spectrum. In contrast, the
neutral vacancy and the N-vacancy center show a broad contribution to the upper spectral range
of the host spectrum, making them challenging to extract. Independent of the vibrational behaviour,
the main atoms contributing to the defect spectrum can be clearly identified. Recombination of
their atom-projected spectra results in the isolated spectrum of the point-defect.

## UV-Curable Biobased Polyacrylates Based on a Multifunctional 2 Monomer Derived from Furfural

 Authors: Jules Stouten, Danny E. P. Vanpoucke, Guy Van Assche, and Katrien V. Bernaerts Journal: Macromolecules 53(4), 1388-1404 (2020) doi: 10.1021/acs.macromol.9b02659 IF(2019): 5.918 export: bibtex pdf: (Open Access)

 Graphical Abstract: The formation of biobased polyacrylates.

## Abstract

The controlled polymerization of a new biobased monomer, 4-oxocyclopent-2-en-1-yl acrylate (4CPA), was

## Influence of diamond crystal orientation on the interaction with biological matter

 Authors: Viraj Damle, Kaiqi Wu, Oreste De Luca, Natalia Ortí-Casañ, Neda Norouzi, Aryan Morita, Joop de Vries, Hans Kaper, Inge Zuhorn, Ulrich Eisel, Danny E.P. Vanpoucke, Petra Rudolf, and Romana Schirhagl, Journal: Carbon 162, 1-12 (2020) doi: 10.1016/j.carbon.2020.01.115 IF(2019): 8.821 export: bibtex pdf: (Open Access)

 Graphical Abstract: The preferential adsorption of biological matter on oriented diamond surfaces.

## Abstract

Diamond has been a popular material for a variety of biological applications due to its favorable chemical, optical, mechanical and biocompatible properties. While the lattice orientation of crystalline material is known to alter the interaction between solids and biological materials, the effect of diamond’s crystal orientation on biological applications is completely unknown. Here, we experimentally evaluate the influence of the crystal orientation by investigating the interaction between the <100>, <110> and <111> surfaces of the single crystal diamond with biomolecules, cell culture medium, mammalian cells and bacteria. We show that the crystal orientation significantly alters these biological interactions. Most surprising is the two orders of magnitude difference in the number of bacteria adhering on <111> surface compared to <100> surface when both the surfaces were maintained under the same condition. We also observe differences in how small biomolecules attach to the surfaces. Neurons or HeLa cells on the other hand do not have clear preferences for either of the surfaces. To explain the observed differences, we theoretically estimated the surface charge for these three low index diamond surfaces and followed by the surface composition analysis using x-ray photoelectron spectroscopy (XPS). We conclude that the differences in negative surface charge, atomic composition and functional groups of the different surface orientations lead to significant variations in how the single crystal diamond surface interacts with the studied biological entities.

## Investigation of structural, electronic and magnetic properties of breathing metal–organic framework MIL-47(Mn): a first principles approach

 Authors: Mohammadreza Hosseini, Danny E. P. Vanpoucke, Paolo Giannozzi, Masoud Berahman  and Nasser Hadipour Journal: RSC Adv. 10, 4786-4794 (2020) doi: 10.1039/C9RA09196C IF(2019): 3.119 export: bibtex pdf: (Open Access)

 Graphical Abstract: The breathing MIL-47(Mn) Metal-Organic Framework. Upon breathing, the electronic structure of this MOF undergoes a transition from an anti-ferromagnetic semiconductor, to a ferromagnetic semi-metal.

## Abstract

The structural, electronic and magnetic properties of the MIL-47(Mn) metal–organic framework are investigated using first principles calculations. We find that the large-pore structure is the ground state of this material. We show that upon transition from the large-pore to the narrow-pore structure, the magnetic ground-state configuration changes from antiferromagnetic to ferromagnetic, consistent with the computed values of the intra-chain coupling constant. Furthermore, the antiferromagnetic and ferromagnetic configuration phases have intrinsically different electronic behavior: the former is semiconducting, the latter is a metal or half-metal. The change of electronic properties during breathing posits MIL-47(Mn) as a good candidate for sensing and other applications. Our calculated electronic band structure for MIL-47(Mn) presents a combination of flat dispersionless and strongly dispersive regions in the valence and conduction bands, indicative of quasi-1D electronic behavior. The spin coupling constants are obtained by mapping the total energies onto a spin Hamiltonian. The inter-chain coupling is found to be at least one order of magnitude smaller than the intra-chain coupling for both large and narrow pores. Interestingly, the intra-chain coupling changes sign and becomes five times stronger going from the large pore to the narrow pore structure. As such MIL-47(Mn) could provide unique opportunities for tunable low-dimensional magnetism in transition metal oxide systems.

## Can Europium Atoms form Luminescent Centres in Diamond: A combined Theoretical-Experimental Study

 Authors: Danny E. P. Vanpoucke, Shannon S. Nicley, Jorne Raymakers, Wouter Maes, and Ken Haenen Journal: Diam. Relat. Mater 94, 233-241 (2019) doi: 10.1016/j.diamond.2019.02.024 IF(2019): 2.650 export: bibtex pdf:

 Graphical Abstract: Spin polarization around the various Eu-defect models in diamond. Blue and red represent the up and down spin channels respectively.

## Abstract

The incorporation of Eu into the diamond lattice is investigated in a combined theoretical-experimental study. The large size of the Eu ion induces a strain on the host lattice, which is minimal for the Eu-vacancy complex. The oxidation state of Eu is calculated to be 3+ for all defect models considered. In contrast, the total charge of the defect-complexes is shown to be negative: -1.5 to -2.3 electron. Hybrid-functional electronic-band-structures show the luminescence of the Eu defect to be strongly dependent on the local defect geometry. The 4-coordinated Eu substitutional dopant is the most promising candidate to present the typical Eu3+ luminescence, while the 6-coordinated Eu-vacancy complex is expected not to present any luminescent behaviour. Preliminary experimental results on the treatment of diamond films with Eu-containing precursor indicate the possible incorporation of Eu into diamond films treated by drop-casting. Changes in the PL spectrum, with the main luminescent peak shifting from approximately 614 nm to 611 nm after the growth plasma exposure, and the appearance of a shoulder peak at 625 nm indicate the potential incorporation. Drop-casting treatment with an electronegative polymer material was shown not to be necessary to observe the Eu signature following the plasma exposure, and increased the background
luminescence.