scholarly journals Thermally Stable Nitrothiacalixarene Chromophores: Conformational Study and Aggregation Behavior

2020 ◽  
Vol 21 (18) ◽  
pp. 6916
Author(s):  
Anton Muravev ◽  
Tatiana Gerasimova ◽  
Robert Fayzullin ◽  
Olga Babaeva ◽  
Ildar Rizvanov ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Absorption Spectroscopy ◽  
Density Functional ◽  
Langmuir Monolayers ◽  
Supramolecular Organization ◽  
Pressure Potential ◽  
Excellent Thermal Stability ◽  
Lb Films ◽  
Functional Dyes ◽  
And Control

Achieving high thermal stability and control of supramolecular organization of functional dyes in sensors and nonlinear optics remains a demanding task. This study was aimed at the evaluation of thermal behavior and Langmuir monolayer characteristics of topologically varied nitrothiacalixarene multichromophores and phenol monomers. A nitration/azo coupling alkylation synthetic route towards partially O-substituted nitrothiacalixarenes and 4-nitrophenylazo-thiacalixarenes was proposed and realized. Nuclear magnetic resonance (NMR) spectroscopy and X-ray diffractometry of disubstituted nitrothiacalix[4]arene revealed a rare 1,2-alternate conformation. A synchronous thermal analysis indicated higher decomposition temperatures of nitrothiacalixarene macrocycles as compared with monomers. Through surface pressure/potential-molecular area measurements, nitrothiacalixarenes were shown to form Langmuir monolayers at the air–water interface and, through atomic force microscopy (AFM) technique, Langmuir–Blodgett (LB) films on solid substrates. Reflection-absorption spectroscopy of monolayers and electronic absorption spectroscopy of LB films of nitrothiacalixarenes recorded a red-shifted band (290 nm) with a transition from chloroform, indicative of solvatochromism. Additionally, shoulder band at 360 nm was attributed to aggregation and supported by gas-phase density functional theory (DFT) calculations and dynamic light scattering (DLS) analysis in chloroform–methanol solvent in the case of monoalkylated calixarene 3. Excellent thermal stability and monolayer formation of nitrothiacalixarenes suggest their potential as functional dyes.

Supramolecular Organization and Evaporation of Polymeric Tin Trifluoroacetates

2019 ◽  
Author(s):  
Goran Bacic ◽  
Conor D. Rankine ◽  
Jason D. Masuda ◽  
Derek A. Wann ◽  
Sean Barry
Keyword(s):  
Thermal Stability ◽  
Solid State ◽  
Density Functional ◽  
Chemical Vapor ◽  
Atomic Layer ◽  
Building Blocks ◽  
Supramolecular Organization ◽  
Layer Deposition ◽  
Earth Abundant ◽  
Green Potential

<div> <div> <div> <p>Simple tin carboxylates make up a family of important industrial catalysts and precursors for deposition of SnO2 thin films. However, their structures remain disparately characterized, and tin trifluoroacetates have been particularly elusive. Here we report on a combined X-ray diffraction (XRD), gas phase electron diffraction (GED) and density functional theory (DFT) study into the structure and bonding of tin(II) and tin(IV) trifluoroacetates to understand their influence on thermal stability and volatility. Tin(II) bis(trifluoroacetate) (1′) eliminates trifluoroacetic anhydride upon sublimation to form the linear polymeric hexatin(II)-di-μ -oxy-octakis-μ-trifluoroacetate (1F ), which itself sublimes (1 Torr at 191 C) as a 1:1 mixture of 1 and ditin(II)-μ-oxy-bis-μ-trifluoroacetate (1′′). Tin(IV) tetrakis(trifluoroacetate) (2F) is also polymeric in the solid state, but evaporates as a monomer at low temperatures (1 Torr at 84 ◦C). Together they make a family of multifunctional Lewis acidic and basic building blocks for supramolecular organization of clusters and polymers in the solid state. Anomalous trends in the volatility of these trifluoroacetates and their hydrogenated derivatives can be rationalized by consideration of their modes of polymerization with respect to the thermodynamics of evaporation. Both 1F and 2F combine high thermal stability and volatility, and are demonstrated to be complementary, safe, and green potential precursors for chemical vapor deposition (CVD) or atomic layer deposition (ALD) of earth-abundant transparent conducting F-doped SnO2. </p> <div><div><div> <p> </p> </div> </div> </div> </div> </div> </div>

Buckling of Two-Dimensional Covalent Organic Frameworks Under Thermal Stress

2019 ◽  
Author(s):  
Austin Evans ◽  
Matthew Ryder ◽  
Nathan C. Flanders ◽  
Edon Vitaku ◽  
Lin Chen ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Thermal Stress ◽  
Density Functional ◽  
Structural Changes ◽  
Gravimetric Analysis ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
X Ray Diffraction ◽  
Excellent Thermal Stability ◽  
X Ray

Two-dimensional Covalent organic frameworks (2D COFs) are periodic, permanently porous, and lightweight solids that are polymerized from topologically designed monomers. The predictable design and structural modularity of these materials make them promising candidates for applications including catalysis, environmental remediation, chemical separations, and organic electronics, many of which will require stability to mechanical and thermal stress. Based on their reinforced structures and high degradation temperatures as determined by thermal gravimetric analysis (TGA), many reports have claimed that COFs have excellent thermal stability. However, their stability to heat and pressure has not been probed using methods that report on structural changes rather than the loss of volatile compounds. Here we explore two structurally analogous 2D COFs with different polymerization chemistries using in operando X-ray diffraction, which demonstrates the loss of crystallinity at lower temperatures than the degradation temperatures measured by TGA. Density functional theory calculations suggest that an asymmetric buckling of the COF lattice is responsible for the observed loss of crystallinity. In addition to their thermal stability, x-ray diffraction of the 2D COFs under gas pressures up to 100 bar showed no loss in crystallinity or structural changes, indicating that these materials are robust to mechanical stress by applied pressure. We expect that these results will encourage further exploration of COF stability as a function of framework design and isolated form, which will guide the design of frameworks that withstand demanding application-relevant conditions.

Supramolecular Organization and Evaporation of Polymeric Tin Trifluoroacetates

2019 ◽  
Author(s):  
Goran Bacic ◽  
Conor D. Rankine ◽  
Jason D. Masuda ◽  
Derek A. Wann ◽  
Sean Barry
Keyword(s):  
Thermal Stability ◽  
Solid State ◽  
Density Functional ◽  
Chemical Vapor ◽  
Atomic Layer ◽  
Building Blocks ◽  
Supramolecular Organization ◽  
Layer Deposition ◽  
Earth Abundant ◽  
Green Potential

<div> <div> <div> <p>Simple tin carboxylates make up a family of important industrial catalysts and precursors for deposition of SnO2 thin films. However, their structures remain disparately characterized, and tin trifluoroacetates have been particularly elusive. Here we report on a combined X-ray diffraction (XRD), gas phase electron diffraction (GED) and density functional theory (DFT) study into the structure and bonding of tin(II) and tin(IV) trifluoroacetates to understand their influence on thermal stability and volatility. Tin(II) bis(trifluoroacetate) (1′) eliminates trifluoroacetic anhydride upon sublimation to form the linear polymeric hexatin(II)-di-μ -oxy-octakis-μ-trifluoroacetate (1F ), which itself sublimes (1 Torr at 191 C) as a 1:1 mixture of 1 and ditin(II)-μ-oxy-bis-μ-trifluoroacetate (1′′). Tin(IV) tetrakis(trifluoroacetate) (2F) is also polymeric in the solid state, but evaporates as a monomer at low temperatures (1 Torr at 84 ◦C). Together they make a family of multifunctional Lewis acidic and basic building blocks for supramolecular organization of clusters and polymers in the solid state. Anomalous trends in the volatility of these trifluoroacetates and their hydrogenated derivatives can be rationalized by consideration of their modes of polymerization with respect to the thermodynamics of evaporation. Both 1F and 2F combine high thermal stability and volatility, and are demonstrated to be complementary, safe, and green potential precursors for chemical vapor deposition (CVD) or atomic layer deposition (ALD) of earth-abundant transparent conducting F-doped SnO2. </p> <div><div><div> <p> </p> </div> </div> </div> </div> </div> </div>

Buckling of Two-Dimensional Covalent Organic Frameworks Under Thermal Stress

2019 ◽  
Author(s):  
Austin Evans ◽  
Matthew Ryder ◽  
Nathan C. Flanders ◽  
Edon Vitaku ◽  
Lin Chen ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Thermal Stress ◽  
Density Functional ◽  
Structural Changes ◽  
Gravimetric Analysis ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
X Ray Diffraction ◽  
Excellent Thermal Stability ◽  
X Ray

Two-dimensional Covalent organic frameworks (2D COFs) are periodic, permanently porous, and lightweight solids that are polymerized from topologically designed monomers. The predictable design and structural modularity of these materials make them promising candidates for applications including catalysis, environmental remediation, chemical separations, and organic electronics, many of which will require stability to mechanical and thermal stress. Based on their reinforced structures and high degradation temperatures as determined by thermal gravimetric analysis (TGA), many reports have claimed that COFs have excellent thermal stability. However, their stability to heat and pressure has not been probed using methods that report on structural changes rather than the loss of volatile compounds. Here we explore two structurally analogous 2D COFs with different polymerization chemistries using in operando X-ray diffraction, which demonstrates the loss of crystallinity at lower temperatures than the degradation temperatures measured by TGA. Density functional theory calculations suggest that an asymmetric buckling of the COF lattice is responsible for the observed loss of crystallinity. In addition to their thermal stability, x-ray diffraction of the 2D COFs under gas pressures up to 100 bar showed no loss in crystallinity or structural changes, indicating that these materials are robust to mechanical stress by applied pressure. We expect that these results will encourage further exploration of COF stability as a function of framework design and isolated form, which will guide the design of frameworks that withstand demanding application-relevant conditions.

Microstructure studies of tungsten silicide schottky contacts on Gaas

1987 ◽  
Vol 45 ◽  
pp. 328-329
Author(s):  
Yih-Cheng Shih ◽  
E. L. Wilkie
Keyword(s):  
Thermal Stability ◽  
Field Effect Transistors ◽  
Schottky Contact ◽  
Schottky Contacts ◽  
Excellent Thermal Stability ◽  
Barrier Heights ◽  
Gaas Substrates ◽  
Film Adhesion ◽  
Threshold Voltages ◽  
Thermal Stability Of

Tungsten silicides (WSix) have been successfully used as the gate materials in self-aligned GaAs metal-semiconductor-field- effect transistors (MESFET). Thermal stability of the WSix/GaAs Schottky contact is of major concern since the n+ implanted source/drain regions must be annealed at high temperatures (∼ 800°C). WSi0.6 was considered the best composition to achieve good device performance due to its low stress and excellent thermal stability of the WSix/GaAs interface. The film adhesion and the uniformity in barrier heights and ideality factors of the WSi0.6 films have been improved by depositing a thin layer of pure W as the first layer on GaAs prior to WSi0.6 deposition. Recently WSi0.1 has been used successfully as the gate material in 1x10 μm GaAs FET's on the GaAs substrates which were sputter-cleaned prior to deposition. These GaAs FET's exhibited uniform threshold voltages across a 51 mm wafer with good film adhesion after annealing at 800°C for 10 min.

A Rare Low Spin Co(IV) Bis-Silyldiamide with High Thermal Stability: Exploring the Origin of an Unusual S = 1/2 Configuration

2020 ◽  
Author(s):  
David Zanders ◽  
Goran Bačić ◽  
Dominique Leckie ◽  
Oluwadamilola Odegbesan ◽  
Jeremy M. Rawson ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Density Functional ◽  
Atomic Layer ◽  
Epr Spectrum ◽  
Functional Theory ◽  
Cluster Calculations ◽  
Layer Deposition ◽  
Starting Point ◽  
Higher Spin ◽  
Surface Saturation

Attempted preparation of a chelated Co(II) β-silylamide re-sulted in the unprecedented disproportionation to Co(0) and a spirocyclic cobalt(IV) bis(β-silyldiamide): [Co[(NtBu)2SiMe2]2] (1). Compound 1 exhibits a room temperature magnetic moment of 1.8 B.M and a solid state axial EPR spectrum diagnostic of a rare S = 1/2 configuration. Semicanonical coupled-cluster calculations (DLPNO-CCSD(T)) revealed the doublet state was clearly preferred (–27 kcal/mol) over higher spin configurations for which density functional theory (DFT) showed no energetic preference. Unlike other Co(IV) complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self-limiting monolayer in initial atomic layer deposition (ALD) surface saturation tests. The ease of synthesis and high-stability make 1 an attractive starting point to begin investigating otherwise inaccessible Co(IV) intermediates and synthesizing new materials.

scholarly journals Boosted piezoelectricity with excellent thermal stability in tetragonal NaNbO3-based ceramics

2020 ◽  
Author(s):  
Lu Wang ◽  
Shengdong Sun ◽  
Huajie Luo ◽  
Yang Ren ◽  
Hui Liu ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Temperature Stability ◽  
Lead Free ◽  
Excellent Thermal Stability ◽  
Lead Free Ceramics ◽  
Piezoelectric Performance

The realization of high piezoelectric performance and excellent temperature stability simultaneously in lead-free ceramics is the key for replacing Pb-containing perovskites in industry. In this study, large piezoelectric performance (d33...

scholarly journals Theory of the Thermal Stability of Silicon Vacancies and Interstitials in 4H–SiC

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 167
Author(s):  
José Coutinho
Keyword(s):  
Thermal Stability ◽  
Fermi Level ◽  
Density Functional ◽  
Dynamic Properties ◽  
Type Material ◽  
Temperature Threshold ◽  
Effect Analysis ◽  
Mobile Species ◽  
Two Stages ◽  
Thermal Stability Of

This paper presents a theoretical study of the electronic and dynamic properties of silicon vacancies and self-interstitials in 4H–SiC using hybrid density functional methods. Several pending issues, mostly related to the thermal stability of this defect, are addressed. The silicon site vacancy and the carbon-related antisite-vacancy (CAV) pair are interpreted as a unique and bistable defect. It possesses a metastable negative-U neutral state, which “disproportionates” into VSi+ or VSi−, depending on the location of the Fermi level. The vacancy introduces a (−/+) transition, calculated at Ec−1.25 eV, which determines a temperature threshold for the annealing of VSi into CAV in n-type material due to a Fermi level crossing effect. Analysis of a configuration coordinate diagram allows us to conclude that VSi anneals out in two stages—at low temperatures (T≲600 °C) via capture of a mobile species (e.g., self-interstitials) and at higher temperatures (T≳1200 °C) via dissociation into VC and CSi defects. The Si interstitial (Sii) is also a negative-U defect, with metastable q=+1 and q=+3 states. These are the only paramagnetic states of the defect, and maybe that explains why it escaped detection, even in p-type material where the migration barriers are at least 2.7 eV high.

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