Observation of a Hydrogen Doublet Site in High Defect Density As-Grown a-Si:H by 1H NMR

Abstract1H NMR studies of hydrogenated amorphous silicon (a-Si:H) with ˜1017 cm-3 defects grown by PECVD with a rate of 5 Å/s show the existence of a hydrogen doublet for both asgrown and light-soaked samples. We observe the doublet over the temperature range from 5 to 20 K in a sample where no light soaking has occurred. The doublet line shapes display no narrowing over this temperature range. Vibrational modes characteristic of SiH2 wagging and scissor modes are seen from infrared spectroscopy. These results suggest that the doublet is due to SiH2 that occurs at a density of approximately 1 at. % in this sample. From line shape analysis, we estimate a lower limit of 1.8 ˜ for the hydrogen-to-hydrogen separation.

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H NMR Evidence for a Change in The Local Hydrogen Environment of Sites Associated with the Staebler-Wronski Effect in a-Si:H

MRS Proceedings ◽

10.1557/proc-715-a11.2 ◽

2002 ◽

Vol 715 ◽

Author(s):

T. Su ◽

Robin Plachy ◽

P. C. Taylor ◽

S. Stone ◽

G. Ganguly ◽

...

Keyword(s):

Line Shape ◽

Defect Density ◽

Hydrogen Atoms ◽

Hydrogen Environment ◽

H Nmr ◽

Line Shapes ◽

Different Temperatures ◽

Staebler Wronski Effect

AbstractWe study the H NMR line shapes of a sample of a-Si:H under several conditions: 1) as grown, 2) light-soaked for 600 hours, and 3) light-soaked followed by annealing at different temperatures. At T = 7 K, the NMR line shape of the sample after light soaking exhibits an additional doublet compared to that of the sample as-grown. This doublet is an indication of a closely separated hydrogen pair. The distance between the two hydrogen atoms is estimated to be about (2.3 ± 0.2) Å. The concentration of these hydrogen sites is estimated to be between 1017 and 1018 cm-3 consistent with ESR measurements of the defect density after light soaking. This doublet disappears after the sample is annealed at 200°C for 4 hours.

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Symmetry, disorder, and dynamics in solid crown ether complexes: 2H NMR studies of 15-crown-5·NaI, 15-crown-5·NaClO4, and 21-crown-7·KI

Canadian Journal of Chemistry ◽

10.1139/v99-207 ◽

1999 ◽

Vol 77 (11) ◽

pp. 1911-1921 ◽

Cited By ~ 3

Author(s):

G W Buchanan ◽

M Gerzain ◽

C I Ratcliffe

Keyword(s):

Phase Transitions ◽

High Temperature ◽

Crown Ether ◽

Detailed Analysis ◽

Room Temperature ◽

2H Nmr ◽

Nmr Studies ◽

H Nmr ◽

Line Shapes ◽

Crown Ether Complexes

2H NMR line shapes have been obtained as a function of temperature for partially deuteriated 15-crown-5·NaI, 15-crown-5·NaClO4 and 21-crown-7·KI. Sudden changes in the line shapes above 330 K correspond to phase transitions: DSC shows transitions at 338, 347 K for 15-crown-5·NaI, and 356, 374, 383 K for 15-crown-5·NaClO4. The 2H NMR line shapes for the room temperature (RT) phases show the onset of a motion of the macrocycles above 200K, which is rapid a little above room temperature. Through detailed analysis of the complicated line shapes it has been shown that the most consistent interpretation of the dynamics in these RT phases is a "merry-go-round" type of motion similar to that found for 18-crown-6 and 12-crown-4 complexes in which O-CH2-CH2 units exchange sites around the ring, simultaneously adjusting their conformation to fit the site. In the high-temperature phases of all three complexes all the ring atoms are dynamically equivalent. This can only happen through a combination of increased symmetry and disorder for which possible models have been devised.Key words: 2H NMR, crown ether complexes, dynamics, disorder.

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Solvent-Ligand Interactions in Colloidal Nanocrystals

10.26434/chemrxiv.6447884 ◽

2018 ◽

Author(s):

Jonathan De Roo ◽

Nuri Yazdani ◽

Emile Drijvers ◽

Alessandro Lauria ◽

Jorick Maes ◽

...

Keyword(s):

Direct Method ◽

Line Broadening ◽

H Nmr ◽

Size Dependent ◽

Line Shape Analysis ◽

Wide Range ◽

Nanocrystal Synthesis ◽

Ligand Interactions ◽

Indispensable Tool ◽

Theoretical Evidence

<p>Although solvent-ligand interactions play a major role in nanocrystal synthesis, dispersion formulation and assembly, there is currently no direct method to study this. Here we examine the broadening of <sup>1</sup>H NMR resonances associated with bound ligands, and turn this poorly understood descriptor into a tool to assess solvent-ligand interactions. We show that the line broadening has both a homogeneous and a heterogeneous component. The former is nanocrystal-size dependent and the latter results from solvent-ligand interactions. Our model is supported by experimental and theoretical evidence that correlates broad NMR lines with poor ligand solvation. This correlation is found across a wide range of solvents, extending from water to hexane, for both hydrophobic and hydrophilic ligand types, and for a multitude of oxide, sulfide and selenide nanocrystals. Our findings thus put forward NMR line shape analysis as an indispensable tool to form, investigate and manipulate nanocolloids.</p>

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1H NMR Conformational Studies in Water of Angiotensin II Analogues Modified at the N- and C-Termini: Interactions of the Aromatic Side Chains and Folding of the N-Terminal Domain

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19942523 ◽

1994 ◽

Vol 59 (11) ◽

pp. 2523-2532 ◽

Cited By ~ 4

Author(s):

John Hondrelis ◽

John Matsoukas ◽

George Agelis ◽

Paul Cordopatis ◽

Ning Zhou ◽

...

Keyword(s):

Shielding Effect ◽

Resonance Spectroscopy ◽

Nmr Studies ◽

Previous Suggestion ◽

Aminoisobutyric Acid ◽

H Nmr ◽

Neutral Ph ◽

Angiotensin Ii Analogues ◽

Proton Resonances ◽

Cosy Nmr

The conformation of [Sar1]angiotensin II in water at neutral pH has been examined by proton magnetic resonance spectroscopy at 400 MHz and in particular by comparing its 1H NMR spectral data with those of analogues modified at positions 1,4 and 6, namely [Sar1,Cha8]ANGII, [Des Asp1,Cha8]ANGII, [Aib1,Tyr(Me)4]ANGII, [Aib1,Tyr(Me)4,Ile8]ANGII, [N-MeAib1,Tyr(Me)4]ANGII, [N-MeAib1,Tyr(Me)4,Ile8]ANGII, ANGIII and [Sar1,Ile8]ANGII. Assignment of all proton resonances in these analogues was made possible by 2D COSY NMR experiments. The H-2 and H-4 protons for the histidine ring in [Sar1]ANGII, ANGII and ANGIII were shielded compared with the same protons in [Sar1,Ile8]ANGII, [Sar1,Cha8]ANGII and [Des Asp1,Cha8]ANGII; this shielding effect was not disturbed upon methylation of the tyrosine hydroxyl and/or replacement of residue 1 (sarcosine or aspartic acid) with aminoisobutyric acid (Aib) or N-methyl aminoisobutyric acid (N-MeAib). These data are consistent with our previous suggestion based on NMR studies in neutral DMSO that a characteristic folded conformation for ANGII previously observed in non-polar solvents can also be detected in water at neutral pH, but to a lesser degree.

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Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp2)-C(aryl) Bond; Adamantan-1-yl 3-Bromo-2,4,6-trimethylphenyl Ketone

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19980955 ◽

1998 ◽

Vol 63 (7) ◽

pp. 955-966

Author(s):

Eva Přibylová ◽

Miroslav Holík

Keyword(s):

Thermodynamic Parameters ◽

Shape Analysis ◽

Rate Constants ◽

Line Shape ◽

Microsoft Excel ◽

Hindered Rotation ◽

H Nmr ◽

Line Shape Analysis ◽

Coalescence Temperature

Four programs for the 1H NMR line shape analysis: two commercial - Winkubo (Bruker) and DNMR5 (QCPE 165) and two written in our laboratory - Newton (in Microsoft Excel) and Simtex (in Matlab) have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond. For this purpose four testing criteria were used, two of them were also developed by us. As supplementary determinations the rate constants obtained for the coalescence temperature and for the thermal racemization of chromatographically separated enantiomers were used which fitted well the temperature dependence of the rate constants determined by the line shape analysis. As a test compound adamantan-1-yl 3-bromo-2,4,6-trimethylphenyl ketone was prepared and studied. It was shown that supermodified simplex method used in our algorithm (Simtex), though time consuming, gives the most accurate values of the rate constants and consequently the calculated thermodynamic parameters Ea, ∆H≠, and ∆S≠ lay in relatively narrow confidence intervals.

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Monitoring the encapsulation of chlorin e6 derivatives into polymer carriers by NMR spectroscopy

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424619501815 ◽

2019 ◽

Vol 23 (11n12) ◽

pp. 1576-1586 ◽

Cited By ~ 1

Author(s):

Sara Pfister ◽

Luca Sauser ◽

Ilche Gjuroski ◽

Julien Furrer ◽

Martina Vermathen

Keyword(s):

Relaxation Time ◽

Nmr Spectroscopy ◽

Core Region ◽

Chlorin E6 ◽

Polypropylene Glycol ◽

Polymer Carriers ◽

H Nmr ◽

Line Shape Analysis ◽

Dynamic Methods ◽

Derivatives Of

The encapsulation of five derivatives of chlorin e6 with different hydrophobicity and aggregation properties into a series of five poloxamer-type triblock copolymer micelles (BCMs) with varying numbers of polyethylene and polypropylene glycol (PEG, PPG) units was monitored using 1H NMR spectroscopy. NMR chemical shift and line shape analysis, as well as dynamic methods including diffusion ordered spectroscopy (DOSY) and T1 and T2 relaxation time measurements of the chlorin and the polymer resonances, proved useful to assess the chlorin–BCM compatibility. The poloxamers had high capability to break up aggregates formed by chlorins up to intermediate hydrophobicity. Physically entrapped chlorins were always localized in the BCM core region. The loading capacity correlated with chlorin polarity for all poloxamers among which those with the lowest number of PPG units were most efficient. DOSY data revealed that relatively weakly aggregating chlorins partition between the aqueous bulk and micellar environment whereas more hydrophobic chlorins are well retained in the BCM core region, rendering these systems more stable. T1 and T2 relaxation time measurements indicated that motional freedom in the BCM core region contributes to encapsulation efficiency. The BCM corona dynamics were rather insensitive towards chlorin entrapment except for the poloxamers with short PEG chains. The presented data demonstrate that 1H NMR spectroscopy is a powerful complementary tool for probing the compatibility of porphyrinic compounds with polymeric carriers such as poloxamer BCMs, which is a prerequisite in the development of stable and highly efficient drug delivery systems suitable for medical applications like photodynamic therapy of tumors.

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Is Thermal and Light-Induced Annealing of Met Astable Defects in a-Si:H Driven by Electrons?

MRS Proceedings ◽

10.1557/proc-377-343 ◽

1995 ◽

Vol 377 ◽

Cited By ~ 1

Author(s):

Helena Gleskova ◽

S. Wagner

Keyword(s):

Electrical Conductivity ◽

Light Intensity ◽

Defect Density ◽

Hydrogenated Amorphous Silicon ◽

Free Electrons ◽

Free Electron Density ◽

Independent Variables ◽

The Third ◽

Defect Annealing ◽

Hydrogenated Amorphous

ABSTRACTWe report results of a search for a unifying rate law for the annealing of metastable defects in hydrogenated amorphous silicon (a-Si:H). We tested the hypothesis that defect-annealing by both heating or illumination is driven by the density of free electrons. This hypothesis is formulated via the rate equation - dN/dt = A nα N f (T), where N is the defect density, t the time, A a constant, n the free electron density, and f (T) a function of temperature derived from a distribution of annealing energies. The model fits two sets of data, with light-intensity and electrical conductivity as the independent variables, reasonably well, with a ranging from 0.39 to 0.76, but not the third set, where we varied the temperature.

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Hydrogen Separation and Purification from Various Gas Mixtures by Means of Electrochemical Membrane Technology in the Temperature Range 100–160 °C

Membranes ◽

10.3390/membranes11040282 ◽

2021 ◽

Vol 11 (4) ◽

pp. 282

Author(s):

Leandri Vermaak ◽

Hein W. J. P. Neomagus ◽

Dmitri G. Bessarabov

Keyword(s):

Hydrogen Permeability ◽

Gas Mixtures ◽

Open Circuit ◽

Hydrogen Separation ◽

Proton Exchange ◽

Limiting Current ◽

Separation Performance ◽

Separation And Purification ◽

Irreversible Damage ◽

Temperature Range

This paper reports on an experimental evaluation of the hydrogen separation performance in a proton exchange membrane system with Pt-Co/C as the anode electrocatalyst. The recovery of hydrogen from H2/CO2, H2/CH4, and H2/NH3 gas mixtures were determined in the temperature range of 100–160 °C. The effects of both the impurity concentration and cell temperature on the separation performance of the cell and membrane were further examined. The electrochemical properties and performance of the cell were determined by means of polarization curves, limiting current density, open-circuit voltage, hydrogen permeability, hydrogen selectivity, hydrogen purity, and cell efficiencies (current, voltage, and power efficiencies) as performance parameters. High purity hydrogen (>99.9%) was obtained from a low purity feed (20% H2) after hydrogen was separated from H2/CH4 mixtures. Hydrogen purities of 98–99.5% and 96–99.5% were achieved for 10% and 50% CO2 in the feed, respectively. Moreover, the use of proton exchange membranes for electrochemical hydrogen separation was unsuccessful in separating hydrogen-rich streams containing NH3; the membrane underwent irreversible damage.

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