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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Conductivity of Composite Films Based on Conductive Polymer PEDOT:PSS, Graphene Oxide and Nanoparticles TiO{sub 2} for Contact Layers of Perovskite Photovoltaic Structures

The electrical properties of composite films based on conductive polymer PEDOT: PSS, graphene oxide (GO), and titanium dioxide nanoparticles (TiO{sub 2}) (PEDOT: PSS– TiO{sub 2} and GO–TiO{sub 2}) used as contact layers of organic and perovskite photovoltaic structures have been studied. As a result of the study of morphology by atomic force microscopy, it was found that the PEDOT: PSS–TiO{sub 2} and GO–TiO{sub 2} films have a globular structure with a grain size of ~200–300 nm. The current–voltage characteristics of the PEDOT: PSS–TiO{sub 2} and GO–TiO{sub 2} films are measured in the temperature range of 80–300 K, the dependences of the resistivity versus temperature, ρ(T), which have an activation character, are obtained. It is established that as the temperature decreases, the ρ(T) dependences show a transition from large values of the activation energy (570 meV and 329 meV) to lower values (25 meV and 2.2 meV) for the PEDOT: PSS–TiO{sub 2} and GO–TiO{sub 2} films, respectively. The mechanisms of transport of charge carriers in the materials studied are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Nanomechanical investigation of thin-film electroceramic/metal-organic framework multilayers

Thin-film multilayer stacks of mechanically hard magnetron sputtered indium tin oxide (ITO) and mechanically soft highly porous surface anchored metal-organic framework (SURMOF) HKUST-1 were studied using nanoindentation. Crystalline, continuous, and monolithic surface anchored MOF thin films were fabricated using a liquid-phase epitaxial growth method. Control over respective fabrication processes allowed for tuning of the thickness of the thin film systems with a high degree of precision. It was found that the mechanical indentation of such thin films is significantly affected by the substrate properties; however, elastic parameters were able to be decoupled for constituent thin-film materials (E{sub ITO} ≈ 96.7 GPa, E{sub HKUST−1} ≈ 22.0 GPa). For indentation of multilayer stacks, it was found that as the layer thicknesses were increased, while holding the relative thickness of ITO and HKUST-1 constant, the resistance to deformation was significantly altered. Such an observation is likely due to small, albeit significant, changes in film texture, interfacial roughness, size effects, and controlling deformation mechanism as a result of increasing material deposition during processing. Such effects may have consequences regarding the rational mechanical design and utilization of MOF-based hybrid thin-film devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Stability of the anodic growth porous tungsten oxide in different solutions

This article presents the study of the stability of the anodic growth porous tungsten oxide (WO{sub 3}) film in different solutions. As-anodized films are relatively stable in acidic electrolytes like sulphuric acid (H{sub 2}SO{sub 4}), hydrochloric acid (HCl) but not in oxalic acid. In higher pH solution, rate of dissolution of the WO{sub 3} film is higher. Annealing at 400 °C for 2 h transform the as-grown sample from amorphous phase to the crystalline phase and this significantly improve the stability of the film in high pH solution. Photocurrent measurements reveal that there is no significant difference of the electrolyte used (0.5 M H{sub 2}SO{sub 4}, 0.33 M H{sub 3}PO{sub 4}, 0.1 M sodium sulfate (Na{sub 2}SO{sub 4})) on the photocurrent. As-annealed films exhibit good stablility for the long photoelectrochemical (PEC) measurements (1700 s) in 0.5 M H{sub 2}SO{sub 4} and 0.1 M Na{sub 2}SO{sub 4}. There is no effect on the photocurrent for the variation of the concentration of the acidic solution (H{sub 2}SO{sub 4}). However, lower photocurrent was obtained as the concentration of Na{sub 2}SO{sub 4} was increased.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Two-dimensional electron systems in perovskite oxide heterostructures: Role of the polarity-induced substitutional defects

The discovery of a two-dimensional electron system (2DES) at the interfaces of perovskite oxides such as LaAlO 3 and SrTiO 3 has motivated enormous efforts in engineering interfacial functionalities with this type of oxide heterostructures. However, the fundamental origins of the 2DES are still not understood, e.g., the microscopic mechanisms of coexisting interface conductivity and magnetism. In this paper, we report a comprehensive spectroscopic investigation on the depth profile of 2DES-relevant Ti 3d interface carriers using depth- and element-specific techniques like standing-wave excited photoemission and resonant inelastic scattering. We found that one type of Ti 3d interface carriers, which give rise to the 2DES are located within three unit cells from the n-type interface in the SrTiO 3 layer. Unexpectedly, another type of interface carriers, which are polarity-induced Ti-on-Al antisite defects, reside in the first three unit cells of the opposing LaAlO3 layer (~10 Å). Our findings provide a microscopic picture of how the localized and mobile Ti 3d interface carriers distribute across the interface and suggest that the 2DES and 2D magnetism at the LaAlO 3 /SrTiO 3 interface have disparate explanations as originating from different types of interface carriers.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Strained-Induced Morphological Reconstruction of RuO 2 (110) Thin-Film Electrocatalysts

Strain is a widely used strategy for electrocatalyst engineering. Overstraining, however, can lead to unintentional materials transformation. We investigate the impact of strain on the surface morphology of a rutile RuO 2 (110) film grown on a symmetry-matching rutile TiO 2 (110) substrate. When the film thickness exceeds 9 nm, the RuO 2 surface relaxes by forming step edges that expose the {011} plane. Density functional theory (DFT) calculation shows that the (011) facet is among the lower energy surfaces of rutile RuO 2 , suggesting that this formation incurs minimal energetic penalties. In situ atomic force microscopy (AFM) shows that the film maintains the (110) structure of the terrace during electrochemistry. Inductively coupled plasma–mass spectrometry (ICP-MS) further reveals the insensitivity of the Ru dissolution to strain. Here, our findings show a strain-relieving pathway via surface reconstruction in RuO 2 (110) and provide an example of a strain-relieving mechanism that does not affect dissolution.

Evolution reactions↗
DOE OSTI2018

Extended investigation of sol aging effect on TiO2 electron transporting layer and performances of perovskite solar cells

Highlights: • Conditions of deposition of compact sol-gel TiO{sub 2} significantly influence the parameters of perovskite cells. • Sol aging originally considered as beneficial was proved to be adverse due to no repeatability, defects and residual water. • Free from such disadvantages TiO{sub 2} made from fresh sol can support as good cell parameters. • Roughness of transparent conductive oxide influences the optimal thickness of electron transporting layer. - Abstract: Organic−inorganic hybrid perovskites have created significant opportunities for low-cost and high-performance solar cells. The electron transporting layer (ETL) is one of the main components of the solar cell, which selectively transports electrons and at the same time acts as a barrier for holes. This paper focuses on the ETL composed of titanium dioxide deposited by sol-gel method. In particular, perovskite solar cells with ETL from aged titanium sol revealed significant differences of short circuit current which is 8% higher than their counterpart with ETL from fresh sol. Analysis of ETL morphology by atomic force microscopy combined with electrochemical impedance spectroscopy and optical properties measurements enabled to determine the source of this diversity. Additionally, the role of roughness of transparent electrode was indicated. The in-depth material analysis revealed some disadvantages of the ETL material, originally considered as supporting higher photovoltaic performance. The results indicated several problems associated with hardly controlled aging conditions, defects and presence of residual water, strongly advocate for TiO{sub 2} ETL form the fresh sol, which after optimization can guarantee the same good solar cell performance.

14 SOLAR ENERGY↗
DOE OSTI2026

Strain and Defect-Tailored Magnetotransport in NiCo 2 O 4 Thin Films and Freestanding Membranes

Magnetic spinel NiCo 2 O 4 is promising for developing spintronic applications due to its high magnetic Curie temperature, high spin polarization, fast spin dynamics, and strain-tunable magnetic anisotropy, while its electronic and magnetic properties depend sensitively on epitaxial strain and disorder. Here, in this study, we use epitaxial NiCo 2 O 4 thin films and freestanding NiCo 2 O 4 membranes as model systems to reveal the complex interplay of strain and defects in determining the metallicity and magnetotransport properties of the ferrimagnetic spinel. NiCo 2 O 4 on perovskite substrates and NiCo 2 O 4 membranes exhibit insulating behaviors and spin canting, in sharp contrast to the metallic NiCo 2 O 4 films on spinel substrates that possess strong perpendicular magnetic anisotropy. Anisotropic magnetoresistance studies provide critical information about disorder-induced spin scattering and strain-induced tetragonal magnetocrystalline anisotropy, which is corroborated by comprehensive electron microscopy characterizations. Our study presents a promising venue for designing flexible magnetic memory, sensor, and spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2026

4D-STEM Coupled with Unsupervised Machine Learning to Reveal at Large-Scale the Microstructural Evolution in Li- and Mn-Rich Cathodes

Li- and Mn-rich (LMR) layered oxides are known to exhibit a thin surface reconstruction layer, which grows during electrochemical cycling in a manner that depends on exposed crystallographic facets, cycling conditions, and electrolyte chemistry. Direct characterization of this layer has traditionally relied on high-resolution electron microscopy, which is inherently limited to small fields of view. Here, we employ four-dimensional scanning transmission electron microscopy (4D-STEM) combined with unsupervised machine-learning clustering to quantitatively map phase distributions over large areas and track their evolution in LMR cathodes during electrochemical aging. Our results show that the surface reconstruction layer consists predominantly of a rocksalt phase, whose thickness varies across different facets following activation cycling and becomes substantially thicker and more uniform during calendar aging. In contrast, a spinel-like phase is observed within the particle bulk. Large-area phase mapping and correlative high-resolution imaging reveal that this spinel-like phase preferentially nucleates at bulk crystallographic defects, including boundaries between 60°-rotated layered domains and associated mixed-phase regions, rather than exclusively at the particle surface. Our findings establish a mechanistic distinction between surface-driven rocksalt formation and bulk-defect-mediated spinel nucleation while demonstrating the unique capability of 4D-STEM to provide statistically robust, mesoscale insight into complex phase-evolution processes in LMR cathodes.

4D-STEM↗
DOE OSTI2014

Effects of ion and nanosecond-pulsed laser co-irradiation on the surface nanostructure of Au thin films on SiO{sub 2} glass substrates

Ion irradiation and short-pulsed laser irradiation can be used to form nanostructures on the surfaces of substrates. This work investigates the synergistic effects of ion and nanosecond-pulsed laser co-irradiation on surface nanostructuring of Au thin films deposited under vacuum on SiO{sub 2} glass substrates. Gold nanoparticles are randomly formed on the surface of the substrate after nanosecond-pulsed laser irradiation under vacuum at a wavelength of 532 nm with a repetition rate of 10 Hz and laser energy density of 0.124 kJ/m{sup 2}. Gold nanoparticles are also randomly formed on the substrate after 100-keV Ar{sup +} ion irradiation at doses of up to 3.8 × 10{sup 15} ions/cm{sup 2}, and nearly all of these nanoparticles are fully embedded in the substrate. With increasing ion irradiation dose (number of incident laser pulses), the mean diameter of the Au nanoparticles decreases (increases). However, Au nanoparticles are only formed in a periodic surface arrangement after co-irradiation with 6000 laser pulses and 3.8 × 10{sup 15} ions/cm{sup 2}. The periodic distance is ∼540 nm, which is close to the wavelength of the nanosecond-pulsed laser, and the mean diameter of the Au nanoparticles remains at ∼20 nm with a relatively narrow distribution. The photoabsorption peaks of the ion- or nanosecond-pulsed laser-irradiated samples clearly correspond to the mean diameter of Au nanoparticles. Conversely, the photoabsorption peaks for the co-irradiated samples do not depend on the mean nanoparticle diameter. This lack of dependence is likely caused by the periodic nanostructure formed on the surface by the synergistic effects of co-irradiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A futuristic approach towards interface layer modifications for improved efficiency in inverted organic solar cells

Inverted polymer Solar Cells of the classical poly (3-hexylthiophene) (P3HT):(6,6)-phenyl-C{sub 61}butyric acid methyl ester (PC{sub 61}BM) blend on indium tin oxide substrates were fabricated, which shows improved device performance, by using a facile solution–processed ZnO-polyelectrolytes [poly (diallyldimethylammonium chloride) (PDADMAC), Poly (acrylic acid sodium salt) (PAS), poly (4-styrenesulfonic acid) (PSS), and Polyvinylpyrrolidone (PVP)] nanocomposite as a cathode interface layer compared to devices using pristine ZnO as cathode buffer layer in ambient conditions. The devices with different combinations of polyelectrolyte with ZnO show different improvements in the device efficiency. The combinations of ZnO with PVP and PDADMAC show highest amount of improvements in the efficiency by a factor of ∼17–19. The improvement of the efficiency may be due to various phenomena, such as the passivation of ZnO surface as well as bulk traps, work function modification, improved energy level alignment, improved electronic coupling of the inorganic/organic interface, improved light harvesting, and decrease of surface as well as bulk charge recombination in the device. The introduction of polyelectrolyte into ZnO inhibits the aggregation of ZnO nanoparticles yielding the large area ZnO nanoclusters; and hence, forming the uniform film of ZnO resulting in the modifications of morphology as well as electronic structure of ZnO-polyelectrolyte nano-composite favouring better electronic coupling between cathode and active layer and hence enhancing the current and, consequently, the efficiency. This simple low temperature ZnO-polyelectrolyte nanocomposite based protocol proposed for cathode interface layer modification may be very much useful for roll to roll industrial manufacturing of organic solar cells.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Enhancing photovoltaic performance of dye-sensitized solar cells by rare-earth doped oxide of SrAl{sub 2}O{sub 4}:Eu{sup 3+}

Graphical abstract: Current–voltage characteristics of DSSCs based on the photoanodes doping different SrAl{sub 2}O{sub 4}:Eu{sup 3+} and doping 3% SrAl{sub 2}O{sub 4}. - Highlights: • A down-conversion (DC) nanocrystal (SrAl{sub 2}O{sub 4}:Eu{sup 3+}) was synthesized. • The effect of SrAl{sub 2}O{sub 4}:Eu{sup 3+} doped in photoanode in DSSCs was investigated. • SrAl{sub 2}O{sub 4}:Eu{sup 3+} doped in photoanode appeared the better photovoltaic performances. • The dual function of DC and p-type doping effect were explained. - Abstract: SrAl{sub 2}O{sub 4}:Eu{sup 3+} down-conversion (DC) nanocrystals were synthesized by a sol–gel method and then doped in TiO{sub 2} as a photoanode in dye-sensitized solar cells (DSSCs). Differential thermal analysis, fourier transform infrared spectroscopy, X-ray diffraction and Brunauer–Emmet–Teller analysis confirmed the formation of SrAl{sub 2}O{sub 4}:Eu{sup 3+} nanocrystals with diameters of ∼47 nm, pore size of ∼25 nm, sintering temperature of 1300 °C. The photoluminescence and UV–vis absorption spectra of the SrAl{sub 2}O{sub 4}:Eu{sup 3+} revealed a DC from ultraviolet light to visible light which matched the strong absorbing region of the N719 dye. The photoelectric conversion efficiency of the DSSCs with a TiO{sub 2} photoanode doped with 3 wt% SrAl{sub 2}O{sub 4}:Eu{sup 3+} was 20% higher than that with a pure TiO{sub 2} photoanode. This phenomenon could be mainly explained by SrAl{sub 2}O{sub 4}:Eu{sup 3+} nanocrystals’ ability of DC and increased the short-circuit current density. It could be minorly due to the p-type doping effect and slightly improved the open-circuit voltage.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microwave irradiation induced band gap tuning of MoS{sub 2}-TiO{sub 2} nanocomposites

The MoS{sub 2}-TiO{sub 2} nanocomposites have been synthesized by sol-gel method and characterized by different microscopic and spectroscopic techniques. The crystallinity of these nanocomposites has been confirmed by X-ray diffraction (XRD) analysis. The Raman spectrum of MoS{sub 2}-TiO{sub 2} nanocomposites consists of three distinct peaks (E{sup 1} {sub g}, E{sup 1} {sub 2g} and A{sub 1g}) which are associated with TiO{sub 2} and MoS{sub 2}. The morphological study is carried out by scanning electron microscope. The effect of microwave irradiation on the band gap of MoS{sub 2}-TiO{sub 2} nanocomposites has been investigated; it is observed that the microwave irradiation causes decrease in the band gap of MoS{sub 2}-TiO{sub 2} nanocomposites. The microwave treated MoS{sub 2}-TiO{sub 2} thin films offers a novel process route in treating thin films for commercial applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Tunable charge to spin conversion in strontium iridate thin films

Efficient charge to spin conversion is important for low-power spin logic devices. Spin and charge interconversion is commonly performed using heavy metals and topological insulators, while the field of oxides is not yet fully explored. Strontium iridate thin films were grown, where the different crystal structures form a perfect playground to understand the key factors in obtaining high charge to spin conversion efficiency (i.e.,large spin Hall angle). It was found that the semiconducting Sr 2 IrO 4 has a spin Hall angle of ~0.1 (depending on measurement technique), which is promising for a spin-orbit coupled electronic system and comparable to Pt. In contrast, the perovskite SrIrO 3 , reported to have a Dirac cone near the Fermi level, has a larger spin Hall angle of 0.3–0.4 degrees. The largest difference between the two materials is a large degree of spin-momentum locking in SrIrO 3 , comparable to known topological insulators. A simple semiclassical relationship is found where thespin Hall angle increases for higher degrees of spin-momentum locking and it also increases for lower Fermi wave vectors. Here this relationship is then able to explain the decreased spin Hall angle below 10 nm film thickness in SrIrO 3 , by relating it to the correspondingly higher carrier concentration (related to the higher Fermi wavevector). Breaking the commonly believed anticorrelation between resistivity and carrier concentration paves apathway to lower power losses due to resistance while keeping large spin Hall angles.

36 MATERIALS SCIENCE↗
NASA NTRS1992

An acetate precursor process for BSCCO (2223) thin films and coprecipitated powders

Since the discovery of high temperature superconducting oxides much attention has been paid to finding better and useful ways to take advantage of the special properties exhibited by these materials. One such process is the development of thin films for engineering applications. Another such process is the coprecipitation route to producing superconducting powders. An acetate precursor process for use in thin film fabrication and a chemical coprecipitation route to Bismuth based superconducting materials has been developed. Data obtained from the thin film process were inconclusive to date and require more study. The chemical coprecipitation method of producing bulk material is a viable method, and is preferred over the previously used solid state route. This method of powder production appears to be an excellent route to producing thin section tape cast material and screen printed devices, as it requires less calcines than the oxide route to produce quality powders.

Haertling, Gene H.↗
NASA NTRS1986

Oxidation and emittance of superalloys in heat shield applications

Recently developed superalloys that form alumina coatings have a high potential for heat shield applications for advanced aerospace vehicles at temperatures above 1095C. Both INCOLOY alloy MA 956 (of the Inco Alloys International, Inc.), an iron-base oxide-dispersion-strengthened alloy, and CABOT alloy No. 214 (of the Cabot Corporation), an alumina-forming nickel-chromium alloy, have good oxidation resistance and good elevated temperature strength. The oxidation resistance of both alloys has been attributed to the formation of a thin alumina layer (alpha-Al2O3) at the surface. Emittance and oxidation data were obtained for simulated Space Shuttle reentry conditions using a hypersonic arc-heated wind tunnel. The surface oxides and substrate alloys were characterized using X-ray diffraction and scanning and transmission electron microscopy with an energy-dispersive X-ray analysis unit. The mass loss and emittance characteristics of the two alloys are discussed.

Wiedemann, K. E.↗
DOE OSTI2017

From graphite-clay composites to graphene electrode materials: In-situ electrochemical oxidation and functionalization

Highlights: • Graphene was synthesized by electrochemical exfoliation of graphite-clay rods with different clay:graphite ratios. • In-situ electrochemical oxidation and functionalization were used in the exfoliated process. • Graphene thin-film electrodes were constructed for supercapacitors and lithium ion batteries. • This work provided a value-added way that can transform the low-purity graphite resources to graphene electrode materials. - Abstract: The development of cost- and time-effective methods to synthesize graphene materials is very urgent in order to promote its large-scale application in electrochemical energy storage devices. Herein, graphene materials were synthesized by the electrochemical exfoliation (electrochemical oxidation) of graphite-clay rods with different clay:graphite ratios in aqueous solution and in short reaction time (1 h). The dual role of electrochemical oxidation reaction was presented: (1) the electrochemical oxidation reaction facilitates the exfoliation of pencil graphite leads and in-situ forms functional groups on graphene; (2) the electrochemical oxidation reaction enhances the Faradaic reaction in supercapacitor. The in-situ electrochemical oxidation and functionalization methods can transform low purity graphite to high-value graphene electrode materials for supercapacitors and lithium ion batteries. The specific capacitances of exfoliated graphene are 20-time larger than that of graphite-clay composites. This work provided a value-added way that can transform the low-purity graphite resources to high performance graphene electrode materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effects of oxidant gas for atomic layer deposition on crystal structure and fatigue of ferroelectric Hf x Zr 1-x O 2 thin films

TiN/Hf x Zr 1-x O 2 (HZO)/TiN capacitors were prepared using two types of HZO films fabricated by atomic layer deposition using H 2 O or O 2 plasma as an oxidant gas, and post-deposition annealing at 400 °C was performed before the TiN top-electrode fabrication. The ferroelectric orthorhombic phase was dominantly formed for the O 2 plasma-based capacitor due to the strongly oxidizing source of O 2 plasma, resulted in higher remanent polarization (2P r = 20 µC/cm 2 ) than that (13 µC/cm 2 ) of the H 2 O-based capacitor. The fatigue properties for the O 2 plasma-based capacitor were improved by 14 % after 106 cycles compared to the H 2 O-based capacitor. This could be attributed to an oxygen-rich interface reaction layer (IRL) including TiO x between the HZO film and TiN bottom-electrode for the O 2 plasma-based capacitor. In conclusion, based on these results, superior 2P r and fatigue properties can be obtained using O 2 plasma-based HZO films.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Water film-driven Mn (oxy)(hydr)oxide nanocoating growth on rhodochrosite

Minerals exposed to moist air stabilize thin water films that drive a score of chemical reactions of great importance to water-unsaturated terrestrial environments. In this study, we identified Mn (oxy)(hydr)oxide nanocoatings formed by the dissolution, oxidation and precipitation of Mn in oxygenated water films grown on rhodochrosite (MnCO 3 ) microparticles. Nanocoatings that could be identified by vibrational spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and (scanning and transmission) electron microscopy formed in water films containing the equivalent of at least 7 monolayers (~84 H 2 O/nm 2 ). These films were formed by exposing microparticles to moist air with at least 50% relative humidity (RH). Films of neutral pH reacted up to 14% of the Mn II located in the topmost ~5 nm region of the microparticles in atmospheres of up to 90% RH for 7 d. These reactions produced MnOOH, birnessite (MnO 2 ) and hausmannite (Mn 3 O 4 ) nanoparticles of low crystallinity, while exposure to atmospheric air for 1 yr. converted only 2% of Mn II in this region to MnOOH. In contrast, reactions in alkaline water films converted up to ~75% of the Mn II but only after 16 d of reaction. These films produced MnOOH and MnO 2 of low crystallinity, as well as crystalline hausmannite. Kinetic modeling of the time-resolved growth of the Mnsingle bondO stretching vibrational bands of these nanocoatings revealed two concurrent reaction processes. A 1 rst -order process was assigned to nucleation events terminating only after a few hours, and a 0-order process was assigned to the sustained growth of nanocoatings from these nuclei over longer reaction time. By identifying nanocoatings formed by water film-driven reactions on rhodochrosite, our study adds new insight into mineralogical transformations relevant to anoxic–oxic boundaries in water-unsaturated environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗