Digital technologies and healthcare architects' wellbeing in the National Health Service Estate of England during the pandemic.

Introduction: UK Built Environment is currently undergoing a digital transformation, as is happening in the National Health Service (NHS) of England. In this paper, the focus was on the intersection of the two sectors and specifically the potential digital transformation of the NHS Estate. The NHS has developed a strategy for its workforce, to improve staff health and wellbeing, and support equality, diversity, inclusion and the development of existing staff. Digital technologies (DTs) can relate to all Estates and Facilities Management priorities, as it cross-cuts all proposed actions. As opposed to most studies on the wellbeing of blue-collar workers, this article focuses on white-collar workers, specifically architects working in the NHS, especially since NHS at this stage is developing two important policies: the New Hospital Programme and the Workforce Action Plan. Therefore, it is important for the NHS to look at the digital transformation strategy in the prism of the other two. As architecture traditionally has low job satisfaction, it negatively impacts wellbeing. This study argues that this might have been accentuated during the pandemic for the architects working in the NHS and dealing with the added pressure from three new major tasks: adjusting the infrastructure capacity to fight Covid-19; and creating the infrastructure for the testing and vaccination programs. DTs in architecture potentially affect job satisfaction in terms of creativity, autonomy, time pressure, organisational commitment, and so on. Methodology: The methodology comprises a literature review and a pilot of interviews with healthcare architects/designers working in the NHS or on NHS-related projects. The research context is informed by the COVID-19 crisis that brought healthcare architecture to the frontline of the pandemic, with NHS architects creating new wards and vaccination centers, while private healthcare architects designed new hospitals. Results: In the niche area of healthcare architecture, architects were in their busiest year. Yet, the DTs available to them then could only support limited tasks and did not link well to operational data. Discussion: To explore how DTs transform the wellbeing of healthcare architects, understanding wellbeing in healthcare architecture in light of digital transformation is crucial for creating the necessary leadership for the sector to grow.

Domain-informed graph neural networks: A quantum chemistry case study.

We explore different strategies to integrate prior domain knowledge into the design of graph neural networks (GNN). Our study is supported by a use-case of estimating the potential energy of chemical systems (molecules and crystals) represented as graphs. We integrate two elements of domain knowledge into the design of the GNN to constrain and regularise its learning, towards higher accuracy and generalisation. First, knowledge on the existence of different types of relations/graph edges (e.g. chemical bonds in our case study) between nodes of the graph is used to modulate their interactions. We formulate and compare two strategies, namely specialised message production and specialised update of internal states. Second, knowledge of the relevance of some physical quantities is used to constrain the learnt features towards a higher physical relevance using a simple multi-task learning (MTL) paradigm. We explore the potential of MTL to better capture the underlying mechanisms behind the studied phenomenon. We demonstrate the general applicability of our two knowledge integrations by applying them to three architectures that rely on different mechanisms to propagate information between nodes and to update node states. Our implementations are made publicly available. To support these experiments, we release three new datasets of out-of-equilibrium molecules and crystals of various complexities.

Diffusion-Mediated Nucleation and Growth of fcc and bcc Nanocrystal Superlattices with Designable Assembly of Freestanding 3D Supercrystals.

Diffusion-mediated assembly of octahedral PbS nanocrystals (NCs) in a confined antisolvent environment displays a primary burst nucleation and Ostwald ripening growth of rhombic bcc supercrystals, followed by a secondary seed-based nucleation and oriented attachment growth of triangle fcc supercrystals. As the diffusion proceeds from ethanol across a sharp interface into NC-suspended toluene, a burst nucleation of supercrystal seeds occurs, and such supercrystals are quickly developed into rhombic grains that have a bcc structure. At a critical size of 10 µm, an Ostwald ripening event appears to guide the supercrystal growth. Upon grain growth above 30 µm, the fcc supercrystals start a nucleation at two symmetrical tips of individual rhombic crystals. Such fcc supercrystals are developed with a triangle shape, and two triangles are combined with one bcc rhombus in-between to form a butterfly-like bowtie stacking structure. The fcc triangle wings grow larger at a reduction of bcc rhombus cores. As the bcc cores gradually fade, such butterfly-like bowtie crystals aggregate and undergo an oriented attachment process, leading to the formation of freestanding 3D triangle crystals that have a single fcc lattice. Analysis of experimental observations and defined diffusion parameters reveals that fast solvent diffusion and high-NC concentration promote the growth of rhombic bcc supercrystals, while slow solvent diffusion and low-NC concentration accelerate the development of triangle fcc supercrystals. Upon succeeding in designable growth of 3D fcc supercrystals, this study provides designing principles for controlled fabrication of supercrystals with desired superlattices for additional engineering and applications.

Synthesis, optoelectronic properties, and charge carrier dynamics of colloidal quasi-two-dimensional Cs3Bi2I9 perovskite nanosheets.

Non-toxicity and stability make two-dimensional (2D) bismuth halide perovskites better alternatives to lead-based ones for optoelectronic applications and catalysis. In this work, we synthesize sub-micron size colloidal quasi-2D Cs3Bi2I9 perovskite nanosheets and study their generation and relaxation of charge carriers. Steady-state absorption spectroscopy reveals an indirect bandgap of 2.07 eV, which is supported by the band structure calculated using density functional theory. The nanosheets show no detectable photoluminescence at room temperature at near bandgap excitation which is attributed to the indirect bandgap. However, cathodoluminescence spanning a broad range from 500 nm to 750 nm with an asymmetric and Stokes-shifted emission is observed, indicating the phonon- and trap-assisted recombination of charge carriers. We study the ultrafast charge carrier dynamics in Cs3Bi2I9 nanosheets using femtosecond transient absorption spectroscopy. The samples are excited with photon energies higher than their bandgap, and the results are interpreted in terms of hot carrier generation (<1 ps), thermalization with local phonons (∼1 ps), and cooling (>30 ps). Further, a relatively slow relaxation of excitons (≳3 ns) at the band edge suggests the formation of stable polarons which decay nonradiatively by releasing phonons.

Role of Magnetic Coupling in Photoluminescence Kinetics of Mn2+-Doped ZnS Nanoplatelets.

Mn2+-doped semiconductor nanocrystals with tuned location and concentration of Mn2+ ions can yield diverse coupling regimes, which can highly influence their optical properties such as emission wavelength and photoluminescence (PL) lifetime. However, investigation on the relationship between the Mn2+ concentration and the optical properties is still challenging because of the complex interactions of Mn2+ ions and the host and between the Mn2+ ions. Here, atomically flat ZnS nanoplatelets (NPLs) with uniform thickness were chosen as matrixes for Mn2+ doping. Using time-resolved (TR) PL spectroscopy and density functional theory (DFT) calculations, a connection between coupling and PL kinetics of Mn2+ ions was established. Moreover, it is found that the Mn2+ ions residing on the surface of a nanostructure produce emissive states and interfere with the change of properties by Mn2+-Mn2+ coupling. In a configuration with suppressed surface contribution to the optical response, we show the underlying physical reasons for double and triple exponential decay by DFT methods. We believe that the presented doping strategy and simulation methodology of the Mn2+-doped ZnS (ZnS:Mn) system is a universal platform to study dopant location- and concentration-dependent properties also in other semiconductors.

Colloidal Two-Dimensional Metal Chalcogenides: Realization and Application of the Structural Anisotropy.

ConspectusDue to the spatial confinement, two-dimensional metal chalcogenides display an extraordinary optical response and carrier transport ability. Solution-based synthesis techniques such as colloidal hot injection and ion exchange provide a cost-effective way to fabricate such low-dimensional semiconducting nanocrystals. Over the years, developments in colloidal chemistry made it possible to synthesize various kinds of ultrathin colloidal nanoplatelets, including wurtzite- and zinc blende-type CdSe, rock salt PbS, black phosphorus-like SnX (X = S or Se), hexagonal copper sulfides, selenides, and even transition metal dichalcogenides like MoS2. By altering experimental conditions and applying capping ligands with specific functional groups, it is possible to accurately tune the dimensionality, geometry, and consequently the optical properties of these colloidal metal chalcogenide crystals. Here, we review recent progress in the syntheses of two-dimensional colloidal metal chalcogenides (CMCs) and property characterizations based on optical spectroscopy or device-related measurements. The discoveries shine a light on their huge prospect for applications in areas such as photovoltaics, optoelectronics, and spintronics. In specific, the formation mechanisms of two-dimensional CMCs are discussed. The growth of colloidal nanocrystals into a two-dimensional shape is found to require either an intrinsic structural asymmetry or the assist of coexisted ligand molecules, which act as lamellar double-layer templates or "facet" the crystals via selective adsorption. By performing optical characterizations and especially ultrafast spectroscopic measurements on these two-dimensional CMCs, their unique electronic and excitonic features are revealed. A strong dependence of optical transition energies linked to both interband and inter-subband processes on the crystal geometry can be verified, highlighting a tremendous confinement effect in such nanocrystals. With the self-assembly of two-dimensional nanocrystals or coupling of different phases by growing heterostructures, unconventional optical performances such as charge transfer state generation or efficient Förster resonance energy transfer are discovered. The growth of large-scale individualized PbS and SnS nanosheets can be realized by facile hot injection techniques, which gives the opportunity to investigate the charge carrier behavior within a single nanocrystal. According to the results of the device-based measurements on these individualized crystals, structure asymmetry-induced anisotropic electrical responses and Rashba effects caused by a splitting of spin-resolved bands in the momentum space due to strong spin-orbit-coupling are demonstrated. It is foreseen that such geometry-controlled, large-scale two-dimensional CMCs can be the ideal materials used for designing high-efficiency photonics and electronics.

Two-dimensional halide perovskites: synthesis, optoelectronic properties, stability, and applications.

Halide perovskites are promising materials for light-emitting and light-harvesting applications. In this context, two-dimensional perovskites such as nanoplatelets or Ruddlesden-Popper and Dion-Jacobson layered structures are important because of their structural flexibility, electronic confinement, and better stability. This review article brings forth an extensive overview of the recent developments of two-dimensional halide perovskites both in the colloidal and non-colloidal forms. We outline the strategy to synthesize and control the shape and discuss different crystalline phases and optoelectronic properties. We review the applications of two-dimensional perovskites in solar cells, light-emitting diodes, lasers, photodetectors, and photocatalysis. Besides, we also emphasize the moisture, thermal, and photostability of these materials in comparison to their three-dimensional analogs.

In Situ Constructing the Kinetic Roadmap of Octahedral Nanocrystal Assembly Toward Controlled Superlattice Fabrication.

Crystallization and growth of anisotropic nanocrystals (NCs) into distinct superlattices were studied in real time, yielding kinetic details and designer parameters for scale-up fabrication of functional materials. Using octahedral PbS NC blocks, we discovered that NC assembly involves a primary lamellar ordering of NC-detached Pb(OA)2 molecules on the front-spreading solvent surfaces. Upon a spontaneous increase of NC concentration during solvent processing, PbS NCs preferentially self-assembled into an orientation-disordered face-centered cubic (fcc) superlattice, which subsequently transformed into a body-centered cubic (bcc) superlattice with single NC-orientational ordering across individual domains. Unlike the deformation-based transformation route claimed previously, this solid-solid phase transformation involved a hidden intermediate formation of a lamellar-confined liquid interface at cost of the disassembly (melting) of small fcc grains. Such highly condensed and liquidized NCs recrystallized into the stable bcc phase with an energy reduction of 1.16 kBT. This energy-favorable and high NC-fraction-driven bcc phase grew as a 2D film at a propagation rate of 0.74 µm/min, smaller than the 1.23 µm/min observed in the early nucleated fcc phase under a dilute NC environment. Taking such insights and defined parameters, we designed experiments to manipulate the NC assembly pathway and achieved scalable fabrication of a large/single bcc supercrystal with coherent ordering of NC translation and atomic plane orientation. This study not only provides a design avenue for controllable fabrication of a large supercrystal with desired superlattices for application but also sheds new light on the nature of crystal nucleation/growth and phase transformation by extending the lengths from the nanoscale into the atomic scale, molecular scale, and microscale levels.

Anisotropic circular photogalvanic effect in colloidal tin sulfide nanosheets.

Tin sulfide promises very interesting properties such as a high optical absorption coefficient and a small band gap, while being less toxic compared to other metal chalcogenides. However, the limitations in growing atomically thin structures of tin sulfide hinder the experimental exploration of these properties. Due to the flexibility of the colloidal synthesis, it is possible to synthesize very thin and at the same time large nanosheets. Electrical transport measurements show that these nanosheets can function as field-effect transistors with an on/off ratio of more than 105 at low temperatures and p-type behavior. The temperature dependency of the charge transport reveals that defects in the crystal are responsible for the formation of holes as majority carriers. During illumination with circularly polarized light, these crystals generate a helicity dependent photocurrent at zero-volt bias, since their symmetry is broken by asymmetric interfaces (substrate and vacuum). Further, the observed circular photogalvanic effect shows a pronounced in-plane anisotropy, with a higher photocurrent along the armchair direction, originating from the higher absorption coefficient in this direction. Our new insights show the potential of tin sulfide for new functionalities in electronics and optoelectronics, for instance as polarization sensors.

Photoexcitation of PbS nanosheets leads to highly mobile charge carriers and stable excitons.

Solution-processable two-dimensional (2D) semiconductors with chemically tunable thickness and associated tunable band gaps are highly promising materials for ultrathin optoelectronics. Here, the properties of free charge carriers and excitons in 2D PbS nanosheets of different thickness are investigated by means of optical pump-terahertz probe spectroscopy. By analyzing the frequency-dependent THz response, a large quantum yield of excitons is found. The scattering time of free charge carriers increases with nanosheet thickness, which is ascribed to reduced effects of surface defects and ligands in thicker nanosheets. The data discussed provide values for the DC mobility in the range 550-1000 cm2 V-1 s-1 for PbS nanosheets with thicknesses ranging from 4 to 16 nm. Results underpin the suitability of colloidal 2D PbS nanosheets for optoelectronic applications.

From Wurtzite Nanoplatelets to Zinc Blende Nanorods: Simultaneous Control of Shape and Phase in Ultrathin ZnS Nanocrystals.

Ultrathin semiconductor nanocrystals (NCs) with at least one dimension below their exciton Bohr radius receive a rapidly increasing attention due to their unique physicochemical properties. These superior properties highly depend on the shape and crystal phase of semiconductor NCs. Here, we demonstrate not only the synthesis of well-defined ultrathin ZnS nanoplatelets (NPLs) with excitonic absorption and emission, but also the shape/phase transformation between wurtzite (WZ) NPLs and zinc blende (ZB) nanorods (NRs). UV-vis absorption spectra of WZ-ZnS NPLs clearly exhibit a sharp excitonic peak that is not observed in ZB-ZnS NRs. Besides, the photoluminescence characterization shows that WZ-ZnS NPLs have a narrow excitonic emission peak, while ZB-ZnS NRs exhibit a broad collective emission band consisting of four emission peaks. The appearance of excitonic features in the absorption spectra of ZnS NPLs is explained by interband electronic transitions, which is simulated in the framework of atomic effective pseudopotentials (AEP).

Micron-Size Two-Dimensional Methylammonium Lead Halide Perovskites.

Hybrid lead halide perovskites with 2D stacking structures have recently emerged as promising materials for optoelectronic applications. We report a method for growing 2D nanosheets of hybrid lead halide perovskites (I, Br and Cl), with tunable lateral sizes ranging from 0.05 to 8 µm and a structure consisting of n stacked monolayers separated by long alkylamines, tunable from bulk down to n = 1. The key to obtaining such a wide range of perovskite properties hinged on utilizing the respective lead halide nanosheets as precursors in a hot-injection synthesis that afforded careful control over all process parameters. The layered, quantum-confined ( n ≤ 4) nanosheets were comprised of major and minor fractions with differing n. Energy funneling from low to high n (high to low energy) regions within a single sheet, mediated by the length of the ligands between stacks, produced photoluminescent quantum yields as high as 49%. These large, tunable 2D nanosheets could serve as convenient platforms for future high-efficiency optoelectronic devices.

Field Effect and Photoconduction in Au25 Nanoclusters Films.

Quantum-confined Au nanoclusters exhibit molecule-like properties, including atomic precision and discrete energy levels. The electrical conductivity of Au nanocluster films can vary by several orders of magnitude and is determined by the strength of the electronic coupling between the individual nanoclusters in the film. Similar to quantum-confined, semiconducting quantum dots, the electrical coupling in films is dependent on the size and structure of the Au core and the length and conjugation of the organic ligands surrounding it. Unlike quantum dots, however, semiconducting transport has not been reported in Au nanocluster films. Here, it is demonstrated that through a simple yet careful choice of cluster size and organic ligands, stable Au nanocluster films can electronically couple and become semiconducting, exhibiting electric field effect and photoconductivity. The molecule-like nature of the Au nanoclusters is evidenced by a hopping transport mechanism reminiscent of doped, disordered organic semiconductor films. These results demonstrate the potential of metal nanoclusters as a solution-processed material for semiconducting devices.

In-Plane Anisotropic Faceting of Ultralarge and Thin Single-Crystalline Colloidal SnS Nanosheets.

The colloidal synthesis of large, thin two-dimensional (2D) nanosheets is fascinating but challenging, since the growth along the lateral and vertical dimensions needs to be controlled independently. In-plane anisotropy in 2D nanosheets is attracting more attention as well. We present a new synthesis for large colloidal single-crystalline SnS nanosheets with the thicknesses down to 7 nm and lateral sizes up to 8 µm. The synthesis uses trioctylphosphine-S (TOP-S) as sulfur source and oleic acid (with or without trioctylphosphine, TOP) as ligands. Upon adjusting the capping ligand amount, the growth direction can be switched between anisotropic directions (armchair and zigzag) and isotropic directions ("ladder" directions), leading to an edge-morphology anisotropy. This is the first report on solution-phase synthesis of large thin tin(II) sulfide (SnS) nanosheets (NSs) with tunable edge faceting. Furthermore, electronic transport measurements show strong dependency on the crystallographic directions confirming structural anisotropy.

Preparation of high-yield and ultra-pure Au25 nanoclusters: towards their implementation in real-world applications.

Colloidal approaches allow for the synthesis of Au nanoclusters (NCs) with atomic precision and sizes ranging from a few to hundreds of atoms. In most of the cases, these processes involve a common strategy of thiol etching of initially polydisperse Au nanoparticles into atomically precise NCs, resulting in the release of Au-thiolate complexes as byproducts. To the best of our knowledge, neither the removal of these byproducts nor the mass spectra in the relevant mass region were shown in previous studies. A thorough analysis of inorganic byproducts in the synthesis of [Au25(PPh3)10(PET)5X2]2+ NC, abbreviated as Au25 NC, reveals that published protocols lead to Au25 NCs in vanishingly small quantities compared to their byproducts. Three purification methods are presented to separate byproducts from the desired Au25 NCs which are proposed to be applicable to other promising Au NC systems. Additionally, critical factors for a successful synthesis of Au25 NCs are identified and discussed including the role of residual water. An important finding is that the etching duration is very critical and must be monitored by UV-Vis spectroscopy resulting in synthetic yields as high as 40%.

Colloidal lead iodide nanorings.

Colloidal chemistry of nanomaterials experienced a tremendous development in the last decades. In the course of the journey 0D nanoparticles, 1D nanowires, and 2D nanosheets have been synthesized. They have in common to possess a simple topology. We present a colloidal synthesis strategy for lead iodide nanorings, with a non-trivial topology. First, two-dimensional structures were synthesized in nonanoic acid as the sole solvent. Subsequently, they underwent an etching process in the presence of trioctylphosphine, which determines the size of the hole in the ring structure. We propose a mechanism for the formation of lead iodide nanosheets which also explains the etching of the two-dimensional structures starting from the inside, leading to nanorings. In addition, we demonstrate a possible application of the as-prepared nanorings in photodetectors. These devices are characterized by a fast response, high gain values, and a linear relation between photocurrent and incident light power intensity over a large range. The synthesis approach allows for inexpensive large-scale production of nanorings with tunable properties.

Copper sulfide nanosheets with shape-tunable plasmonic properties in the NIR region.

2D copper sulfide nanocrystals are promising building blocks of plasmonic materials in the near-infrared (NIR) spectral region. We demonstrate precise shape and size control (hexagonal/triangle) of colloidal plasmonic copper sulfide (covellite) nano-prisms simply by tuning the precursor concentration without the introduction of additional ligands. The ultra-thin 2D nanocrystals possess sizes between 13 and 100 nm and triangular or hexangular shapes. We also demonstrate CuS nanosheets (NSs) with lateral sizes up to 2 microns using a syringe pump. Based on the experimental findings and DFT simulations, we propose a qualitative and quantitative mechanism for the formation of different shapes. The analysis of the spectral features in the NIR region of the synthesized CuS nanocrystals has been performed with respect to the shape and the size of particles by the discrete dipole approximation method and the Drude-Sommerfeld theory.

A New Synthesis Approach for Carbon Nitrides: Poly(triazine imide) and Its Photocatalytic Properties.

Poly(triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C3N4, especially in photocatalysis. As most of the carbon nitrides, PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH-dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous melamine solution, coupling of resulting melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH-dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI, which we investigated in dye degradation experiments.

Insights into the formation mechanism of two-dimensional lead halide nanostructures.

We present a colloidal synthesis strategy for lead halide nanosheets with a thickness of far below 100 nm. Due to the layered structure and the synthesis parameters the crystals of PbI2 are initially composed of many polytypes. We propose a mechanism which gives insight into the chemical process of the PbI2 formation. Further, we found that the crystal structure changes with increasing reaction temperature or by performing the synthesis for longer time periods changing for the final 2H structure. In addition, we demonstrate a route to prepare nanosheets of lead bromide as well as lead chloride in a similar way. Lead halides can be used as a detector material for high-energy photons including gamma and X-rays.

Molecular Doping of Electrochemically Prepared Triazine-Based Carbon Nitride by 2,4,6-Triaminopyrimidine for Improved Photocatalytic Properties.

Copolymerization of melamine with 2,4,6-triaminopyrimidine (TAP) in an electrochemically induced polymerization process leads to the formation of molecular doped poly(triazine imide) (PTI). The polymerization is based on the electrolysis of water and evolving radicals during this process. The incorporation of TAP is shown by techniques such as elemental analysis, Fourier transform infrared and NMR spectroscopies, and powder X-ray diffraction, and it is shown that the carbon content can be tuned by the variation of the molar ratio of the two precursors. This incorporation of TAP directly influences the electronic structure of PTI and as a result, a red shift can be observed in UV-vis spectroscopy. The smaller band gap and the increased absorption in the visible range lead to improved photocatalytic properties. In dye degradation experiments, it was possible to observe an increase of the rate of the degradation of methylene blue by a factor of 4 in comparison to undoped PTI or 7 if compared to melon.