Vibrational relaxation as the driving force for wavelength conversion in the peridinin-chlorophyll a-protein

Abstract We present a computationally derived energy transfer model for the peridinin-chlorophyll a-protein (PCP), which invokes vibrational relaxation in the two lowest singlet excited states rather than internal conversion between them. The model allows an understanding of the photoinduced processes without assuming further electronic states or a dependence of the 2Ag state character on the vibrational sub-state. We report molecular dynamics simulations (CHARMM22 force field) and quantum mechanics/molecular mechanics (QM/MM) calculations on PCP. In the latter, the QM region containing a single peridinin (Per) chromophore or a Per-Chl a (chlorophyll a) pair is treated by density functional theory (DFT, CAM-B3LYP) for geometries and by DFT-based multireference configuration interaction (DFT/MRCI) for excitation energies. The calculations show that Per has a bright, green light absorbing 2Ag state, in addition to the blue light absorbing 1Bu state found in other carotenoids. Both states undergo a strong energy lowering upon relaxation, leading to emission in the red, while absorbing in the blue or green. The orientation of their transition dipole moments indicates that both states are capable of excited-state energy transfer to Chl a, without preference for either 1Bu or 2Ag as donor state. We propose that the commonly postulated partial intramolecular charge transfer (ICT) character of a donating Per state can be assigned to the relaxed 1Bu state, which takes on ICT character. By assuming that both 1Bu and 2Ag are able to donate to the Chl a Q band, one can explain why different chlorophyll species in PCP exhibit different acceptor capabilities.PostprintPeer reviewe

High‐throughput area‐selective spatial atomic layer deposition of SiO 2 with interleaved small molecule inhibitors and integrated back‐etch correction for low defectivity

A first‐of‐its‐kind area‐selective deposition process for SiO2 is developed consisting of film deposition with interleaved exposures to small molecule inhibitors (SMIs) and back‐etch correction steps, within the same spatial atomic layer deposition (ALD) tool. The synergy of these aspects results in selective SiO2 deposition up to ~23 nm with high selectivity and throughput, with SiO2 growth area and ZnO nongrowth area. The selectivity is corroborated by both X‐ray photoelectron spectroscopy (XPS) and low‐energy ion scattering spectroscopy (LEIS). The selectivity conferred by two different SMIs, ethylbutyric acid, and pivalic acid has been compared experimentally and theoretically. Density Functional Theory (DFT) calculations reveal that selective surface functionalization using both SMIs is predominantly controlled thermodynamically, while the better selectivity achieved when using trimethylacetic acid can be explained by its higher packing density compared to ethylbutyric acid. By employing the trimethylacetic acid as SMI on other starting surfaces (Ta2O5, ZrO2, etc.) and probing the selectivity, a broader use of carboxylic acid inhibitors for different substrates is demonstrated. It is believed that the current results highlight the subtleties in SMI properties such as size, geometry, and packing, as well as interleaved back‐etch steps, which are key in developing ever more effective strategies for highly selective deposition processes

Al/Ga-Doped Li7La3Zr2O12 Garnets as Li-Ion Solid-State Battery Electrolytes: Atomistic Insights into Local Coordination Environments and Their Influence on 17O, 27Al, and 71Ga NMR Spectra.

Li7La3Zr2O12 (LLZO) garnets are among the most promising solid electrolytes for next-generation all-solid-state Li-ion battery applications due to their high stabilities and ionic conductivities. To help determine the influence of different supervalent dopants on the crystal structure and site preferences, we combine solid-state 17O, 27Al, and 71Ga magic angle spinning (MAS) NMR spectroscopy and density-functional theory (DFT) calculations. DFT-based defect configuration analysis for the undoped and Al and/or Ga-doped LLZO variants uncovers an interplay between the local network of atoms and the observed NMR signals. Specifically, the two characteristic features observed in both 27Al and 71Ga NMR spectra result from both the deviations in the polyhedral coordination/site-symmetry within the 4-fold coordinated Li1/24d sites (rather than the doping of the other Li2/96h or La sites) and with the number of occupied adjacent Li2 sites that share oxygen atoms with these dopant sites. The sharp 27Al and 71Ga resonances arise from dopants located at a highly symmetric tetrahedral 24d site with four corner-sharing LiO4 neighbors, whereas the broader features originate from highly distorted dopant sites with fewer or no immediate LiO4 neighbors. A correlation between the size of the 27Al/71Ga quadrupolar coupling and the distortion of the doping sites (viz. XO4/XO5/XO6 with X = {Al/Ga}) is established. 17O MAS NMR spectra for these systems provide insights into the oxygen connectivity network: 17O signals originating from the dopant-coordinating oxygens are resolved and used for further characterization of the microenvironments at the dopant and other sites.-EPSRC,Grant No: EP/P003532/1 -DFG, Research Fellowship GR 5342/1-1 -EPSRC iCASE (Award No:1834544) -Royal Society Professorship(RP\R1\180147) -Resources by the "Cambridge Service for Data Driven Discovery" (CSD3, http://csd3.cam.ac.uk) system operated by the University of Cambridge Research Computing Service funded by EPSRC Tier-2 capital grant EP/P020259/1. -Resources from the ARCHER UK National Computing Service, funded by the EPSRC (EP/P003532/1)

Al/Ga-Doped Li7La3Zr2O12 Garnets as Li-Ion Solid-State Battery Electrolytes: Atomistic Insights into Local Coordination Environments and Their Influence on 17O, 27Al, and 71Ga NMR Spectra.

Li7La3Zr2O12 (LLZO) garnets are among the most promising solid electrolytes for next-generation all-solid-state Li-ion battery applications due to their high stabilities and ionic conductivities. To help determine the influence of different supervalent dopants on the crystal structure and site preferences, we combine solid-state 17O, 27Al, and 71Ga magic angle spinning (MAS) NMR spectroscopy and density-functional theory (DFT) calculations. DFT-based defect configuration analysis for the undoped and Al and/or Ga-doped LLZO variants uncovers an interplay between the local network of atoms and the observed NMR signals. Specifically, the two characteristic features observed in both 27Al and 71Ga NMR spectra result from both the deviations in the polyhedral coordination/site-symmetry within the 4-fold coordinated Li1/24d sites (rather than the doping of the other Li2/96h or La sites) and with the number of occupied adjacent Li2 sites that share oxygen atoms with these dopant sites. The sharp 27Al and 71Ga resonances arise from dopants located at a highly symmetric tetrahedral 24d site with four corner-sharing LiO4 neighbors, whereas the broader features originate from highly distorted dopant sites with fewer or no immediate LiO4 neighbors. A correlation between the size of the 27Al/71Ga quadrupolar coupling and the distortion of the doping sites (viz. XO4/XO5/XO6 with X = {Al/Ga}) is established. 17O MAS NMR spectra for these systems provide insights into the oxygen connectivity network: 17O signals originating from the dopant-coordinating oxygens are resolved and used for further characterization of the microenvironments at the dopant and other sites.-EPSRC,Grant No: EP/P003532/1 -DFG, Research Fellowship GR 5342/1-1 -EPSRC iCASE (Award No:1834544) -Royal Society Professorship(RP\R1\180147) -Resources by the "Cambridge Service for Data Driven Discovery" (CSD3, http://csd3.cam.ac.uk) system operated by the University of Cambridge Research Computing Service funded by EPSRC Tier-2 capital grant EP/P020259/1. -Resources from the ARCHER UK National Computing Service, funded by the EPSRC (EP/P003532/1)

Computational discovery of superior vanadium niobates based cathode materials for next-generation all-solid-State lithium-ion battery applications

All-solid-state lithium-ion batteries (ASSLIBs) are at the forefront of green and sustainable energy development research. One of the key challenges in the development of ASSLIBs for commercial applications is to find cathode materials that have high capacity, voltage and power density. Using a combination of first-principles calculations and various crystal structure prediction algorithms, we explore the LiVO2-Li3NbO4 pseudobinary tieline to identify novel stoichiometries with improved properties as cathode materials for ASSLIB applications. Based on more than 10,000 Density Functional Theory (DFT + U) calculations using crystal structures obtained from ab initio random structure searching (AIRSS), genetic algorithm, and configuration enumeration procedures, we predict five novel stoichiometries, Li23Nb7V2O32, Li10Nb3VO14, Li7Nb2VO10, Li11Nb3V2O16, Li4NbVO6, along with an experimentally known stoichiometry, Li5NbV2O8. All the novel stoichiometries are found to have cation-disordered rock-salt crystal structures and fall within 30 meV/atom from the convex hull of the parent compositions. These new phases are predicted to have superior properties compared to the current vanadium-niobates-based electrode materials, including a higher theoretical capacity, lower band gap, higher average Li intercalation voltage, minor volume change upon full Li delithiation, good mechanical & dynamical stability, improved Li- conduction activation barrier and high-temperature stability. Our results are anticipated to inspire further experiments to synthesise and test these specific vanadium-niobate-based materials for their actual performance as Li-ion cathode materials

Atomic insights into the oxygen incorporation in atomic layer deposited conductive nitrides and its mitigation by energetic ions

Oxygen is often detected as impurity in metal and metal nitride films prepared by atomic layer deposition (ALD) and its presence has profound and adverse effects on the material properties. In this work, we present the case study of HfNx films prepared by plasma-assisted ALD by alternating exposures of CpHf(NMe2)3 and H2 plasma. First, we identify the primary source of O contamination in the film. Specifically, we find that the extent of O incorporation in HfNx films is determined by the flux of background H2O/O2 residual gases reaching the HfNx surface during the ALD process and leads to the formation of Hf–O bonds. Then, we report on the decrease in the concentration of Hf–O bonds in the film upon application of an external radiofrequency (rf) substrate bias during the H2 plasma step. The experimental work is accompanied by first principles calculations to gain insights into the O incorporation and its mitigation upon the impingement of energetic ions on the surface. Specifically, we find that the dissociative binding of H2O on a bare HfN surface is highly favored, resulting in surface Hf–OH groups and concomitant increase in the oxidation state of Hf. We also show that energetic cations (H+, H2+ and H3+) lead to the dissociation of surface Hf–OH bonds, H2O formation, and its subsequent desorption from the surface. The latter is followed by reduction of the Hf oxidation state, presumably by H˙ radicals. The atomic-level understanding obtained in this work on O incorporation and its abstraction are expected to be crucial to prevent O impurities in the HfNx films and contribute to the fabrication of other technologically relevant low resistivity ALD-grown transition metal nitride films

Uniform Atomic Layer Deposition of Al2O3 on Graphene by Reversible Hydrogen Plasma Functionalization.

A novel method to form ultrathin, uniform Al2O3 layers on graphene using reversible hydrogen plasma functionalization followed by atomic layer deposition (ALD) is presented. ALD on pristine graphene is known to be a challenge due to the absence of dangling bonds, leading to nonuniform film coverage. We show that hydrogen plasma functionalization of graphene leads to uniform ALD of closed Al2O3 films down to 8 nm in thickness. Hall measurements and Raman spectroscopy reveal that the hydrogen plasma functionalization is reversible upon Al2O3 ALD and subsequent annealing at 400 °C and in this way does not deteriorate the graphene's charge carrier mobility. This is in contrast with oxygen plasma functionalization, which can lead to a uniform 5 nm thick closed film, but which is not reversible and leads to a reduction of the charge carrier mobility. Density functional theory (DFT) calculations attribute the uniform growth on both H2 and O2 plasma functionalized graphene to the enhanced adsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysis of the possible reaction pathways for TMA precursor adsorption on hydrogenated graphene predicts a binding mechanism that cleans off the hydrogen functionalities from the surface, which explains the observed reversibility of the hydrogen plasma functionalization upon Al2O3 ALD

Area-selective atomic layer deposition of ZnO by area activation using electron beam-induced deposition

Area-selective atomic layer deposition (ALD) of ZnO was achieved on SiO2 seed layer patterns on H-terminated silicon substrates, using diethylzinc (DEZ) as the zinc precursor and H2O as the coreactant. The selectivity of the ALD process was studied using in situ spectroscopic ellipsometry and scanning electron microscopy, revealing improved selectivity for increasing deposition temperatures from 100 to 300 °C. The selectivity was also investigated using transmission electron microscopy and energy-dispersive X-ray spectroscopy. Density functional theory (DFT) calculations were performed to corroborate the experimental results obtained and to provide an atomic-level understanding of the underlying surface chemistry. A kinetically hindered proton transfer reaction from the H-terminated Si was conceived to underpin the selectivity exhibited by the ALD process. By combining the experimental and DFT results, we suggest that the trend in selectivity with temperature may be due to a strong DEZ or H2O physisorption on the H-terminated Si that hampers high selectivity at low deposition temperature. This work highlights the deposition temperature as an extra process parameter to improve the selectivity

Area-selective atomic layer deposition of In2O3 : H using a μ-plasma printer for local area activation

Researchers present a novel method for area-selective atomic layer deposition (AS-ALD) large-area electronics. It is a direct-write ALD process of In 2O 3:H, a highly promising and relevant transparent conductive oxide (TCO) material which makes use of printing technology for surface activation. first the surface of H-terminated silicon materials is locally activated by a μ-plasma printer in air or O 2, and In 2O 3:H is deposited selectively on the activated areas. The selectivity stems from the fact that ALD In 2O 3:H leads to very long nucleation delays on H-terminated silicon materials

Towards the implementation of atomic layer deposited In2O3 : H in silicon heterojunction solar cells

Hydrogen doped indium oxide (In2O3:H) with excellent optoelectronic properties, deposited using atomic layer deposition (ALD), has been made applicable as a window electrode material for silicon heterojunction (SHJ) solar cells. It is particularly challenging to integrate ALD In2O3:H into SHJ solar cells due to a low reactivity of the metalorganic precursor cyclopentadienyl indium (InCp) with the H-terminated surface of a-Si:H. This challenge has been overcome by a simple and effective plasma-based surface pretreatment developed in this work. A remote inductively coupled O2 or Ar plasma has been used to modify the surface of a-Si:H, thereby promoting the adsorption of InCp on the surface. The impact of the short plasma exposure on c-Si/a-Si:H interface passivation has also been studied. It has been found that the observed degradation of the interface is not due to ion bombardment, but rather due to ultraviolet emission from the plasma. Fortunately, these light-induced defects have been found to be metastable, and the interface passivation can thus easily be fully recovered by a short post-annealing. Using such a mild Ar plasma pretreatment, ALD In2O3:H has been successfully implemented in a SHJ solar cell. A short-circuit current density of 40.1 mA/cm2, determined from external quantum efficiency, is demonstrated for a textured SHJ solar cell with an In2O3:H window electrode, compared to 38.5 mA/cm2 for a reference cell that has the conventional Sn-doped indium oxide (In2O3:Sn, ITO) window electrode. The enhanced photocurrent stems from a reduced parasitic absorption of In2O3:H in the entire wavelength range of 400–1200 nm