Charge Collection Characterization of Polycrystalline n-GaAs Layers for Solar Cells

1981 ◽  
Vol 5 ◽  
Author(s):  
O. Paz ◽  
K. N. Bhat ◽  
J. M. Borrego
Keyword(s):  
Solar Cells ◽  
Single Crystal ◽  
Grain Boundaries ◽  
Random Distribution ◽  
Charge Collection ◽  
Typical Cell ◽  
Metal Organic ◽  
Organic Process ◽  
Excitation Volume

ABSTRACTN–type Ga-As polycrystalline layers, grown on Mo substrates by the metal-organic process were investigated using the SEM. Micrographs of charge collection contrast indicate a fairly random distribution of high collection (bright) grains. In a typical cell about 1/3 of its area is bright, with nonuniformities in collection current within and between grains. These results correlate well with Isc measurements, and some of the variations betweencells is explained in terms of insufficient doping of the grain boundaries.Reducing the penetrating depth of the carriers' excitation volume results in lowering of the collection current. The measurements were normalized for changes in beam and EBIC current by a comparison with a single crystal cell of the same geometry. This degradation is explained in terms of contamination or damage of the layer close to the surface during growth.

scholarly journals Gas Permeation Through Single-Crystal ZIF-8 Membranes

2019 ◽  
Author(s):  
Chen Chen ◽  
Aydin Ozcan ◽  
A. Ozgur Yazaydin ◽  
Bradley Ladewig
Keyword(s):  
Single Crystal ◽  
Grain Boundaries ◽  
Gas Permeability ◽  
Metal Organic Framework ◽  
Gas Permeation ◽  
Microstructural Feature ◽  
Polycrystalline Metal ◽  
Transmission Electron ◽  
Metal Organic ◽  
Separation Performances

<b>Abstract</b><div>Grain boundaries are an unavoidable microstructural feature in intergrown polycrystalline metal-organic framework (MOF) membranes. They have been suspected to be less size-selective than a MOF’s micropores, resulting in suboptimal separation performances – a speculation recently confirmed by transmission electron microscopy of MOF ZIF-8. Single-crystal membranes, without grain boundaries, should confine mass transport to micropores and reflect the intrinsic selectivity of the porous material. Here, we demonstrate the feasibility of fabricating single-crystal MOF membranes and directly measuring gas permeability through such a membrane using ZIF-8 as an exemplary MOF. Our single-crystal ZIF-8 membranes achieved ideal selectivities up to 28.9, 10.0, 40.1 and 3.6 for gas pairs CO<sub>2</sub>/N<sub>2</sub>, CO<sub>2</sub>/CH<sub>4</sub>, He/CH<sub>4</sub> and CH<sub>4</sub>/N<sub>2</sub> respectively, much higher than or reversely selective to over 20 polycrystalline ZIF-8 membranes, unequivocally proving the non-selectivity of grain boundaries. The permeability trend obtained in single-crystal membranes aligned with a force field that had been validated against multiple empirical adsorption isotherms.<br></div>

scholarly journals Synthesis of MOFs from Zn,Cd,Ni-4-carboxyphenylboronic acid with DMF solvent

2014 ◽  
Vol 70 (a1) ◽  
pp. C1129-C1129
Author(s):  
Louiza Dimowa ◽  
Rositsa Nikolova ◽  
Ventsi Dyulgerov ◽  
Vladislav Kostov-Kytin ◽  
Boris Shivachev
Keyword(s):  
Single Crystal ◽  
Solvothermal Synthesis ◽  
Chemical Properties ◽  
Porous Metal ◽  
X Ray Diffraction ◽  
X Ray ◽  
Synthesis Strategy ◽  
Metal Organic ◽  
New Type

Synthesis and characterization of porous metal organic frameworks (MOFs) has prompted considerable interest because of the possibility to design the pore size and physical/chemical properties by suitable selection of the organic linkers (ligands). In this work, we have chosen a classical solvothermal synthesis strategy involving 4-carboxyphenylboronic acid, a molecule that is analogic to the terephthalic acid, Zn- Cd- Ni-OAc metal salts and DMF as solvent. It is known that during solvothermal synthesis DMF decomposes to dimethylamine which is easily incorporated in MOF's [1], [2]. The obtained MOFs are characterized by single-crystal X-ray diffraction, X-ray powder diffraction, TG analyses, IR spectroscopy and BET analyses. Preliminary X-ray single crystal diffraction results showed that a new type of structure may be produced in function of the temperature. The Cd- structure crystalizes in the hexagonal Space group P6222, with respective parameters of a = 14.4113(12), c = 13.0416(7) Å (Fig. 1). The cadmium ion is tetra coordinated by the oxygens of the B(OH)2 and COO- moieties. The 4-carboxyphenylboronic acid is disorder and attempts to lower the symmetry to model the disorder resulted in unstable refinement. In the studied systems in addition to the reported new compound isotypical structures to MOF-5 containing 4-carboxyphenylboronic acid instead of 1,4-benzenedicarboxylate were also obtained.

scholarly journals Crystallographic Characterization of the Metal–Organic Framework Fe2(bdp)3 upon Reductive Cation Insertion*

2020 ◽  
Author(s):  
Naomi Biggins ◽  
Michael Ziebel ◽  
Miguel Gonzalez ◽  
Jeffrey R. Long
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Metal Organic Framework ◽  
X Ray Diffraction ◽  
X Ray ◽  
Π Interactions ◽  
Cation Framework ◽  
Metal Organic ◽  
Organic Framework

<div><p>Precisely locating extra-framework cations in anionic metal–organic framework compounds remains a long-standing, yet crucial, challenge for elucidating structure-performance relationships in functional materials. Single-crystal X-ray diffraction is one of the most powerful approaches for this task, but single crystals of frameworks often degrade when subjected to post-synthetic metalation or reduction. Here, we demonstrate the growth of sizable single crystals of the robust metal–organic framework Fe<sub>2</sub>(bdp)<sub>3</sub> (bdp<sup>2−</sup> = benzene-1,4-dipyrazolate) and employ single-crystal-to-single-crystal chemical reductions to access the solvated framework materials A<sub>2</sub>Fe<sub>2</sub>(bdp)<sub>3</sub>∙<i>y</i>THF<sub> </sub>(A = Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>). X-ray diffraction analysis of the sodium and potassium congeners reveals that the cations are located near the center of the triangular framework channels and are stabilized by weak cation–π interactions with the framework ligands. Freeze-drying with benzene enables isolation of activated single crystals of Na<sub>0.5</sub>Fe<sub>2</sub>(bdp)<sub>3 </sub>and Li<sub>2</sub>Fe<sub>2</sub>(bdp)<sub>3</sub> and the first structural characterization of activated metal–organic frameworks wherein extra-framework alkali metal cations are also structurally located. Comparison of the solvated and activated sodium-containing structures reveals that the cation positions differ in the two materials, likely due to cation migration that occurs upon solvent removal to maximize stabilizing cation­–π interactions. Hydrogen adsorption data indicate that these cation-framework interactions are sufficient to diminish the effective cationic charge, leading to little or no enhancement in gas uptake relative to Fe<sub>2</sub>(bdp)<sub>3</sub>. In contrast, Mg<sub>0.85</sub>Fe<sub>2</sub>(bdp)<sub>3</sub> exhibits enhanced H<sub>2</sub> affinity and capacity over the non-reduced parent material. This observation shows that increasing the charge density of the pore-residing cation serves to compensate for charge dampening effects resulting from cation–framework interactions and thereby promotes stronger cation–H<sub>2</sub> interactions.</p></div>

scholarly journals Crystallographic Characterization of the Metal–Organic Framework Fe2(bdp)3 upon Reductive Cation Insertion*

2020 ◽  
Author(s):  
Naomi Biggins ◽  
Michael Ziebel ◽  
Miguel Gonzalez ◽  
Jeffrey R. Long
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Metal Organic Framework ◽  
X Ray Diffraction ◽  
X Ray ◽  
Π Interactions ◽  
Cation Framework ◽  
Metal Organic ◽  
Organic Framework

<div><p>Precisely locating extra-framework cations in anionic metal–organic framework compounds remains a long-standing, yet crucial, challenge for elucidating structure-performance relationships in functional materials. Single-crystal X-ray diffraction is one of the most powerful approaches for this task, but single crystals of frameworks often degrade when subjected to post-synthetic metalation or reduction. Here, we demonstrate the growth of sizable single crystals of the robust metal–organic framework Fe<sub>2</sub>(bdp)<sub>3</sub> (bdp<sup>2−</sup> = benzene-1,4-dipyrazolate) and employ single-crystal-to-single-crystal chemical reductions to access the solvated framework materials A<sub>2</sub>Fe<sub>2</sub>(bdp)<sub>3</sub>∙<i>y</i>THF<sub> </sub>(A = Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>). X-ray diffraction analysis of the sodium and potassium congeners reveals that the cations are located near the center of the triangular framework channels and are stabilized by weak cation–π interactions with the framework ligands. Freeze-drying with benzene enables isolation of activated single crystals of Na<sub>0.5</sub>Fe<sub>2</sub>(bdp)<sub>3 </sub>and Li<sub>2</sub>Fe<sub>2</sub>(bdp)<sub>3</sub> and the first structural characterization of activated metal–organic frameworks wherein extra-framework alkali metal cations are also structurally located. Comparison of the solvated and activated sodium-containing structures reveals that the cation positions differ in the two materials, likely due to cation migration that occurs upon solvent removal to maximize stabilizing cation­–π interactions. Hydrogen adsorption data indicate that these cation-framework interactions are sufficient to diminish the effective cationic charge, leading to little or no enhancement in gas uptake relative to Fe<sub>2</sub>(bdp)<sub>3</sub>. In contrast, Mg<sub>0.85</sub>Fe<sub>2</sub>(bdp)<sub>3</sub> exhibits enhanced H<sub>2</sub> affinity and capacity over the non-reduced parent material. This observation shows that increasing the charge density of the pore-residing cation serves to compensate for charge dampening effects resulting from cation–framework interactions and thereby promotes stronger cation–H<sub>2</sub> interactions.</p></div>

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