B22-Multimode InfraRed imaging And Microspectroscopy
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Diamond Proposal Number(s):
[36374]
Open Access
Abstract: Polydimethylsiloxane (PDMS) is one of the most widely used materials in triboelectric nanogenerators (TENGs) due to its remarkable flexibility and robustness, yet its triboelectric output often limits practical applications. In this study, we presented a method for tuning the triboelectric properties of PDMS through surface functionalization using self-assembled monolayers of siloxane-based molecules. Our results demonstrate that the functionalized PDMS films exhibit distinct charge donating or withdrawing behaviours, confirmed by molecular simulations and experimental characterizations. Notably, trimethylsiloxyphenylmethacrylate (TMSPMA) functionalized PDMS achieved the highest voltage of 189 ± 6 V and current output of 6.75 ± 0.26 µA, leading to a 2-fold increase in peak power density compared with the standard PDMS. Moreover, to elucidate the charge transfer mechanisms between the functionalized PDMS and indium tin oxide (ITO) electrode, nanoanalytical techniques such as nano-Fourier transform infrared spectroscopy (nano-FTIR) and Kelvin probe force microscopy (KPFM) were employed to evaluate the surface chemical and electrical properties at the local scale. This research not only enhances the understanding of polymer/metal contact electrification but also opens avenues for optimizing TENG efficiency through targeted surface functionalization strategies.
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Feb 2025
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[31552, 33389]
Abstract: A set of polar rod-shaped liquid crystalline molecules with large dipole moments (µ > 10.4-14.8 D), their molecular structures based on the ferroelectric nematic prototype DIO, are designed, synthesized, and investigated. When the penultimate fluoro-phenyl ring is replaced by phenylpyrimidine moiety, the molecular dipole moment increases from 9.4 D for DIO to 10.4 D for the new molecule and when the terminal fluoro- group is additionally replaced by the nitrile group, the dipole moment rises to 14.8 D. Such a replacement enhances not only the net dipole moment of the molecule, but it also reduces the steric hindrance to rotations of the moieties within the molecule. The superparaelectric nematic (N) and smectic A (SmA) phases of these compounds are found to exhibit colossal dielectric permittivity, obtained both from dielectric spectroscopy, and capacitance measurements using a simple capacitor divider circuit. The electric polarization is measured vs. the field (E). However, no hysteresis in P vs. E is found in the nematic and smectic A phases. The colossal dielectric permittivity persists over the entire fluidic range. The experimental results lead us to conclude that these materials belong to the class of superparaelectrics (SP) rather than to ferroelectrics. The frequency dependence of the threshold voltage for Freedericksz transition qualitatively matches with the square root of the measured dielectric permittivity. Such an agreement validates the frequency dependence of the dielectric permittivity. The synthesized organic materials are the first fluids for which superparaelectricity is discovered and furthermore these materials show great potential for applications in supercapacitors used in storing energy.
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Nov 2024
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I11-High Resolution Powder Diffraction
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Struan
Simpson
,
Cameron A. M.
Scott
,
Fernando
Pomiro
,
Jeremiah P.
Tidey
,
Urmimala
Dey
,
Fabio
Orlandi
,
Pascal
Manuel
,
Martin R.
Lees
,
Zih-Mei
Hong
,
Wei-Tin
Chen
,
Nicholas C.
Bristowe
,
Mark S.
Senn
Diamond Proposal Number(s):
[32893]
Open Access
Abstract: Magnetoelectric multiferroics hold great promise for the development of new sustainable memory devices. However, practical applications of many existing multiferroic materials are infeasible due to the weak nature of the coupling between the magnetic and electrical orderings, meaning new magnetoelectric multiferroics featuring intrinsic coupling between their component orderings are sought instead. Here, we apply a symmetry-informed design approach to identify and realize the new manganite perovskite CeBaMn2O6 in which magnetoelectric coupling can be achieved via an intermediary non-polar structural distortion. Through first-principles calculations, we demonstrate that our chosen prototype system contains the required ingredients to achieve the desired magnetoelectric coupling. Using high-pressure/high-temperature synthesis conditions, we have been able to synthesize the CeBaMn2O6 perovskite system for the first time. Our subsequent neutron and electron diffraction measurements reveal that the desired symmetry-breaking ingredients exist in this system on a nanoscopic length scale, enabling magnetoelectric nanoregions to emerge within the material. Through this work, we showcase the potential of the new CeBaMn2O6 perovskite material as a promising system in which to realize strong magnetoelectric coupling, highlighting the potential of our symmetry-informed design approach in the pursuit of new magnetoelectric multiferroics for next-generation memory devices.
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Aug 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[24219]
Abstract: Developing transparent p-type oxide semiconductor has been the long-standing subject of interest for optoelectronic devices, but hindered by the strongly localized valence band (VB) structure intrinsic to metal oxides. Sn2+ oxides represented by SnO are proposed as promising p-type semiconductors since the Sn 5s2 state could help to alleviate the carrier localization at the VB. In this work, using a combination of X-ray spectroscopies and density functional theory calculations, we explore the electronic structures of Sn2+ based Sn2Nb2O7 and Sn2Ta2O7 pyrochlores as wide bandgap p-type oxide semiconductors. Our results show that Sn2Nb2O7 and Sn2Ta2O7 have large optical bandgaps of 2.8 eV and 3.4 eV respectively, and better chemical stability over SnO. Both the experiment and theoretical calculations verified the presence of Sn 5s2 states at the top of VB of Sn2Nb2O7 and Sn2Ta2O7, and the Sn 5s2 states increase the VB dispersion and result in lower hole effective masses of 2.09 me and 2.23 me for Sn2Nb2O7 and Sn2Ta2O7 respectively but work less effectively than that for SnO. The different VB features originate from the varied Sn-O interactions influenced by crystal structures. The lattice distortions in SnO allow the hybridization between Sn 5p orbitals with occupied (Sn 5s-O 2p)* states, forming asymmetrically distributed electronic states with enhanced dispersions. However, in Sn2Nb2O7 and Sn2Ta2O7, these interactions are forbidden by their cubic symmetry and lead to the less dispersive electronic states. Increasing lattices distortions in Sn2Nb2O7 and Sn2Ta2O7 would be necessary to achieve higher hole mobilities. Our findings elucidate the microscopic origins of the opto-electronic properties in Tin (II) pyrochlore oxides, highlighting the significant role of synergistic valence band modulation and crystal structural design in advancing high performance p-type oxide semiconductors.
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Jun 2024
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I09-Surface and Interface Structural Analysis
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Niels
Kubitza
,
Isabel
Huck
,
Hanna
Pazniak
,
Curran
Kalha
,
David
Koch
,
Bo
Zhao
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Aysha A.
Riaz
,
Wolfgang
Donner
,
Hongbin
Zhang
,
Benjamin
Moss
,
Ulf
Wiedwald
,
Anna
Regoutz
,
Christina S.
Birkel
Diamond Proposal Number(s):
[29451]
Abstract: MAX phases are almost exclusively known as carbides, while nitrides and carbonitrides form a significantly underrepresented subgroup even though they have been shown to possess enhanced properties in comparison to their carbide counterparts. One example is the nitride phase Cr2GaN which exhibits a spin density wave magnetic state below T = 170 K, while the metallic carbide phase Cr2GaC follows the MAX phase-typical Pauli-paramagnetic behavior. To investigate the influence on the materials/functional properties of mixing carbon and nitrogen on the X-site, this study aims to synthesize and comprehensively characterize the hitherto unknown carbonitride phase Cr2GaC1-xNx and compare it to the parent phases. Due to the challenging synthesis of (carbo)nitrides in general, a sol-gel-assisted approach is applied which was recently developed by our group. This process was further improved by using time-efficient microwave heating, leading to a highly phase pure product. STEM-EDX analyses reveal a C/N ratio of roughly 2:1. Temperature-dependent XRD measurements confirm the literature-known magnetic phase transition of the parent nitride phase Cr2GaN, while the incorporation of carbon suppresses the latter. Nonetheless, magnetic characterization of the phases reveals that the magnetic behavior can be specifically influenced by changing the composition of the X site, resulting in an increase of the susceptibility by increasing the nitrogen amount. Overall, these findings further substantiate the big potential in nitrogen-containing MAX phases, which will also serve as starting materials for future doping studies, i.e. on the M- and A-site, and as precursors for novel 2D MXenes.
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Apr 2024
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I15-Extreme Conditions
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Silva M.
Kronawitter
,
Richard
Röß-Ohlenroth
,
Sebastian A.
Hallweger
,
Marcel
Hirrle
,
Hans Albrecht
Krug
,
Tobias
Luxenhofer
,
Emily
Myatt
,
Jem
Pitcairn
,
Matthew J.
Cliffe
,
Dominik
Daisenberger
,
Jakub
Wojciechowski
,
Dirk
Volkmer
,
Gregor
Kieslich
Diamond Proposal Number(s):
[30815]
Open Access
Abstract: Fe(II)-containing Metal-Organic Frameworks (MOFs) that exhibit temperature-induced spin-crossover (SCO) are candidate materials in the field of sensing, barocalorics, and data storage. Their responsiveness towards pressure is therefore of practical importance and is related to their longevity and processibility. The impact of Fe(II) spin-state on the pressure responsiveness of MOFs is yet unexplored. Here we report the synthesis of two new Fe(II)-based MOFs, i.e. Fe(cta)2 ((cta)– = 1,4,5,6-tetrahydrocyclopenta[d][1,2,3]triazolate) and Fe(mta)2 ((mta)– = methyl[1,2,3]triazolate), which are both in high-spin at room temperature. Together with the isostructural MOF Fe(ta)2 ((ta)– = [1,2,3]triazolate), which is in its low-spin state at room temperature, we apply these as model systems to show how spin-state controls their mechanical properties. As a proxy, we use their bulk modulus, which was obtained via high-pressure powder X-ray diffraction experiments. We find that an interplay of spin-state, steric effects, void fraction, and absence of available distortion modes dictates their pressure-induced structural distortions. Our results show for the first time the role of spin-state on the pressure-induced structural deformations in MOFs and bring us a step closer to estimating the effect of pressure as a stimulus on MOFs a priori.
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Feb 2024
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Open Access
Abstract: The sensitivity of luminescence properties in materials doped with transition metal (TM) ions to changes of temperature makes them particularly promising for thermometric applications. Designing and optimizing such materials requires a deep understanding of their structure, local environment of emission centres, and luminescence processes. In this work, we investigate the potential of Li2SnO3 doped with Cr3+ and Mn4+ as a dual-emitting luminescence temperature sensor. Li2SnO3 was chosen as the host material due to it being able to host both Cr3+ and Mn4+ at Sn octahedral positions. As a result, Mn4+ ions exhibit a distinctive 2E → 4A2 line emission due to a strong crystal field, and Cr3+ ions experience an intermediate crystal field strength resulting in both, 2E → 4A2 and 4T2 → 4A2 emissions. Through thorough examination, using powder X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and photoluminescence techniques we identified two distinct types of [SnO6] octahedral centers that correspond to two types of slightly different Cr3+ and Mn4+ emission centers in the Li2SnO3 structure. The high sensitivity of the decay time constant for the 2E → 4A2 emission of Li2SnO3–Cr3+, Mn4+ to temperature changes (2.0%/K at 190 K and 5.8%/K at 220 K for Cr3+ and Mn4+, respectively) positions the material as an attractive non-contact temperature sensor. Furthermore, application of such a dual-emitter luminescence material as a temperature sensor expands its sensitivity across a broader temperature range and offers the additional advantage of cross-checking measurements compared to materials solely doped with Cr3+ or Mn4+.
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Dec 2023
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[16177]
Open Access
Abstract: Many luminescent platinum(II) complexes undergo face-to-face interactions between neighbouring molecules, leading to bimolecular excited states that may emit at lower energy (dimers and/or excimers). Detailed photophysical studies are reported on dinuclear complexes, in which two NCN-coordinated Pt(II) units are covalently linked by a xanthene such that intramolecular formation of such dimeric or excimeric states is possible. These complexes display strong excimer-like photoluminescence at low concentrations where their monometallic analogues do not. However, a striking difference emerges between complexes where the Pt(NCN) units are directly connected to the xanthene through the tridentate ligand (denoted Class a) and a new class of compounds reported here (Class b) in which the attachment is through a monodentate acetylide ligand. The former require a substantial geometrical rearrangement to move the metal centres of the Pt(NCN) units to a distance short enough to form excimer-like states. The latter require only a small deformation. Consequently, Class a compounds display negligible excimer-like emission in solid films, as the rigid environment hinders the requisite geometric rearrangement. Class b complexes, in contrast, display strong excimer-like emission in film, even at very low loadings. The new dinuclear molecular architecture may thus offer new opportunities in the quest for efficient NIR-emitting devices.
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Oct 2023
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[26879]
Open Access
Abstract: [Fe(bpp)2][BF4]2 (bpp = 2,6-bis{pyrazol-1-yl}pyridine) undergoes abrupt thermal spin-crossover (SCO) at 261 K with a small 2–3 K thermal hysteresis. Different compositions of doped materials [FezZn1−z(bpp)2][BF4]2 and [FezRu1−z(bpp)2][BF4]2 (0 < z < 1) show similar broadening of the SCO transition with increased doping, but differ in their effect on the transition temperature. Doping with zinc strongly lowers T½, which is consistent with previous work. In contrast, doping with ruthenium increases T½ to a smaller degree, which cannot be explained by the chemical pressure arguments that are conventionally applied to doped SCO materials. Mechanoelastic simulations imply that different dopants exert opposite effects on the lattice elastic interactions in the material during the SCO transition. Consistent with that, the materials show a complicated dependence of the crystallographic lattice parameters and thermal expansion properties on the iron spin state, for different dopant ions. These changes correlate with small perturbations to the molecular structure of high-spin [Fe(bpp)2]2+, in the presence of dopants with different geometric preferences and conformational rigidities. We conclude the effect of isomorphous dopants on T½ reflects how the dopant influences the coordination geometry of the iron centres, as well as the chemical pressure exerted by the dopant ion size.
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Aug 2023
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Open Access
Abstract: Hole transport materials (HTMs) based on truxene cores have emerged as promising candidates in recent years. They are noted by properties such as higher hole mobility and higher glass transition temperature than the 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenamine)-9,9′-spirobiflourene (spiro-MeOTAD), as well as good hydrophobicity and energy alignment. Truxene derivatives have been studied for application in transistors, OLEDs, lasers, supercapacitors, etc., however, there are only a few studies on their use as HTMs in perovskite solar cells (PSCs). In this study, we synthesised a novel small organic molecule HTM with a monothiatruxene (TrxS) core, namely TrxS-2MeOTAD, and characterised its basic properties and ability as an HTM in n–i–p planar PSCs. The TrxS-2MeOTAD showed suitable electrochemical, optical, structural and thermal properties for an HTM, such as a relatively high glass transition temperature (145 °C) and stable amorphous nature when deposited as films. The PSCs using TrxS-2MeOTAD achieved 18.9% power conversion efficiency (PCE) compared to the reference spiro-MeOTAD at 19.3% PCE. The unencapsulated TrxS-2MeOTAD devices showed better operational stability than spiro-MeOTAD, with a 1.5 times longer lifetime under constant AM1.5G illumination. Our results suggest that small molecules based on the TrxS core can be a promising direction for the development of alternative HTMs.
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Mar 2023
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