Deposition Stoichiometry Research Articles

Nitrogen wet deposition stoichiometry: the role of organic nitrogen, seasonality, and snow

Nitrogen wet deposition stoichiometry: the role of organic nitrogen, seasonality, and snow

Rapid stoichiometric analysis of calcium‑phosphorus ratio on hydroxyapatite targets by one-point calibration laser-induced breakdown spectroscopy

The calcium‑phosphorus ratio (Ca/P) has an important role in calcium phosphate applications, as a slight change in this ratio results in substantial modifications of their characteristics. Hydroxyapatite is a bioactive ceramic of the calcium phosphate family, and its composition and crystalline structure are similar to the human bone. For this reason, it is widely used to promote bone integration in prosthetics and scaffolds. Prosthetics are usually made of metal and coated with bioceramics and the some techniques used to make these coatings depositions conserve the stoichiometry from the target during deposition. Therefore, studying the target Ca/P is a way to guaranteeing the final deposition stoichiometry. In this study, we investigated the One Point Calibration – Laser Induced Breakdown Spectroscopy (OPC-LIBS) method for the measurement of the Ca/P of hydroxyapatite targets. This method is quantitative, based on the determination of correction parameters via analysis of a standard sample with known stoichiometry. Results were compared to well-established techniques of X-ray Fluorescence (XRF) and Atomic Absorption Spectroscopy (AAS) and showed that the deviation in the difference is less than 5%, proposing a substitute for elemental analysis. Moreover, this method has technical advantages such as rapid measurements, no need for sample preparation or destruction and easy automation.

Cuprous or cupric? How substrate polarity can select for different phases of copper sulfide films in chemical bath deposition.

Copper sulfides have many applications from thermoelectrics to biotechnology. While the properties of different copper sulfide phases are well understood, controlling the deposited copper sulfide stoichiometry remains a significant challenge, especially in solution-phase synthesis techniques. In this work, we investigate the chemical bath deposition of CuxS on functionalized self-assembled monolayers (SAMs). Time-of-flight mass spectrometry, Raman spectroscopy, and x-ray photoelectron spectroscopy are employed to analyze the deposited films. We show that the use of thiourea as a sulfur source leads to the deposition of different copper sulfide phases and is controlled by the interaction of sulfur-containing ions in solution with the functionalized SAMs. For -COOH terminated SAMs, copper sulfide deposition is controlled by the surface polarity of the substrate. At the bath pH used in these experiments, the -COOH terminal groups are deprotonated. The resulting -COO- terminated SAM surface repels negatively charged sulfur-containing ions, leading to the deposition of Cu2S. For -CH3 terminated SAMs, which are non-polar, there is no specific interaction between the SAM terminal group and sulfur-containing ions and CuS is deposited. For -OH terminated SAMs, which have a polar terminal group, there are two competing effects: the repulsion of S-containing ions by the small negative charge of the terminal -OH group and the increase in the concentration of sulfur-containing ions in solution as the bath pH increases. This competition leads to the deposit stoichiometry changing from Cu2S at pH 9 to CuS at pH 12.

Electrodeposition of Fe-Sn from the chloride-based electrolyte

ABSTRACTThe conditions for electrodeposition of Fe-Sn alloys from a novel, environmentally friendly, ferrous chloride-based electrolyte were studied. The influence of the pH on the electrolyte stability and deposit stoichiometry was studied and discussed. Anodic stripping voltammetry (ASV), XRD and SEM/EDX were used to characterise the electrodeposited phases. The results from ASVs indicated the possibility to deposit at least two different phases at high overpotentials. Hull cell depositions in an electrolyte with a Sn to Fe ratio 1:1 and a pH value of 2.8 showed regular deposition of Fe-Sn. Fe-rich deposits (54.84 at.-%) were obtained from an electrolyte with Sn to Fe ratio 1:10. The XRD results were compatible with the electrochemical investigations. In all studied samples β-Sn, FeSn2 and Fe5Sn3 were detected. The presence of ferromagnetic Fe5Sn3 was not influenced by the Sn to Fe ions ratio in the electrolyte.

Effect of electrolyte on the growth of thermoelectric Bi2Se3 thin films

Bismuth Selenide (Bi2Se3) is a thermoelectrical material showing high Seebeck coefficient and figure of merit. It can be obtained by electrodeposition which makes it highly suitable for application in sensor and thermoelectric generators. Here, electrodeposition of Bi2Se3 on silicon(100) substrate was studied using different deposition baths by changing the salts and acid concentrations. The thin films were characterized to obtain the morphology, structural and thermoelectric properties. An optimal bath was found that leads to crystalline thin films with compact and uniform morphology, showing high values of Seebeck coefficient. The total salt concentration directly changes the structural properties of the samples, while the relative salt concentration essentially modifies the stoichiometry of deposits. The acid concentration, otherwise, promotes changes in the grain size and morphology.

Control of native acceptor density in epitaxial Cu2O thin films grown by electrochemical deposition

Controlling the native carrier is essential for using Cu2O in devices such as solar cells. The origin of the native p-type carrier in Cu2O is thought to be copper vacancies (VCu). In this work, epitaxially grown Cu2O thin films were prepared by electrochemical deposition at a low temperature of 45°C on a Pt (111) cathodic electrode. The sources of Cu and O for Cu2O were Cu2+ and OH− in the electrolyte and the ion concentrations were changed to control the stoichiometry of deposition and the density of VCu. The density of ionized acceptors (NA+) in the Cu2O films was evaluated by the C-V properties measured with Schottky electrodes. NA+ did not depend on [Cu2+], whereas NA+ increased with increasing [OH−] when [OH−] was larger than 10−3mol/L (electrolyte pH >11) with [Cu2+] fixed at 10−1mol/L. The ion concentration dependence of NA+ and the dependence of the total cathodic current density revealed that the generation of VCu was affected by a complex combination of the ion concentrations and film growth rate.

Electrodeposition of In2Se3 Using Potential Pulse Atomic Layer Deposition

Indium(III) selenide, In2Se3, thin films were electrodeposited at room temperature from an aqueous solution containing ionic precursors for both In and Se, using potential pulse atomic layer deposition (PP-ALD). Cyclic voltammetry was used to determine approximate cycle potentials, and anodic and cathodic potentials were systematically examined to optimize the potential pulse program for In2Se3. Electron probe microanalysis was used to follow the In:Se atomic ratio as a function of the cycle conditions, and annealing studies were performed on stoichiometric deposits. Film thickness was a function of both the anodic and cathodic potentials. The optimum growth rate was consistent with previous PP-ALD studies in which similar concentrations and pulse times were employed, 0.02 nm/cycle. The use of the potential pulse cycle for film growth resulted in surface-limited control over the deposit stoichiometry each cycle and thus a layer-by-layer growth process.

Photon Synthesis of Nanometric Films Based on Transitional Metal oxides for Multi-Parameter Sensors

The reactive pulsed laser deposition (RPLD) based on a KrF laser was used for photon synthesis of nanometric iron and chromium oxides films. RPLD allows controlling the thickness and stoichiometry of deposits with definite band gap. So RPLD was used for synthesizing nanometric iron and chromium oxides films for thermo-photo-chemical sensors. We compared sensing properties of iron and chromium oxides nanometric films deposited on <100>Si substrate by RPLD. These iron and chromium oxides films have semiconductor properties with the band gaps less than 1.0 eV. The largest photosensitivity of iron and chromium oxides films was about 44 Vc/W and 2.5 Vc/W, accordingly, for white light at power density ~ 6x10-3 W/cm2. Vc is “chemical” photo e.m.f.. Maximum value of thermo electromotive force (e.m.f.) coefficient of iron and chromium oxides films was about 1.65 mV/K and 3.5-4.5mV/K, accordingly. Iron oxides films were tested as chemical sensors: the largest sensitivity of NO molecules was at the level of 7x1012 cm-3. Our results showed that nanometric iron and chromium oxides films synthesized by UV photons can be used as up-to-date materials for multi-parameter sensors operating at moderate temperature.

Impact of DOC trends resulting from changing climatic extremes and atmospheric deposition chemistry on periphyton community of a freshwater tropical lake of India

Recent measurements have demonstrated unprecedented increase in atmospheric deposition of nutrients in many parts of India. To determine whether atmospheric nutrient inputs would increase phytoplankton growth and catchment dissolved organic carbon (DOC) flushing to constrain benthic algae, we analyzed NO3 − and PO 4 −3 in atmospheric deposits; nutrients and DOC in runoff and lake water and standing crop biomass of phytoplankton and periphyton at Jaisamand Lake of Rajasthan, India. Atmospheric deposition of NO3 − (7.18–29.95 kg ha−1 year−1) and PO 4 −3 (0.56–2.15 kg ha−1 year−1) showed a consistently rising trend across the year. Microbial biomass and activity in catchment increased in response to atmospheric deposition. Lake DOC and nutrients showed strong coherence with their terrestrial and atmospheric fluxes. Phytoplankton development showed significant linearity with atmospheric input of nutrients. Air-driven input appeared to have compensated the nutrient constraints to phytoplankton during drought. The N:P stoichiometry of deposition and that of lake water indicated that, although there was a seasonal switchover to N- or P-limitation, phytoplankton were mainly co-limited by N and P due probably to the synergistic effects of combined N + P enrichment in the pelagic zone of the lake. Periphyton standing crop showed inverse relationship with phytoplankton and lake DOC. The study indicated that enhanced phytoplankton development and terrestrial DOC flushing in response to atmospheric nutrient input attenuated light penetration to constrain algal periphyton. We suggests that data on these issues may be considered in developing aquatic ecosystem models to establish future links between changing air–water–land interactions and associated shifts in lake ecosystem functioning for more accurately predicting climate change drivers and designing integrated lake basin management strategies.

Electrochemical Deposition of CdSe Nanorods for Photovoltaic Cell Applications

Electrochemical deposition characteristics of CdSe nanorods were investigated for hybrid solar cell applications. CdSe nanorods were fabricated by electrochemical method in <TEX>$CdSO_4$</TEX> and <TEX>$H_2SeO_3$</TEX> dissolved aqueous solution using an anodic aluminum oxide (AAO) template. Uniformity of CdSe nanorods was dependent on the diameter and the height of holes in AAO. The current density, current mode, bath composition and temperature were controlled to obtain a 1:1 atomic composition of CdSe. CdSe nanorods deposited by direct-current method showed better uniformity compared to those deposited by purse-current and/or purse-reverse current methods due to the bottom-up filling characteristics. <TEX>$H_2SeO_3$</TEX> concentration showed more significant effects on pH of solution and stoichiometry of deposits compared to that of <TEX>$CdSO_4$</TEX>. A 1:1 stoichiometry of uniform CdSe nanorods was obtained from 0.25M <TEX>$CdSO_4-5$</TEX> mM <TEX>$H_2SeO_3$</TEX> electrolytes with a direct current of 10 <TEX>$mA/cm^2$</TEX> at room temperature. X-ray diffraction and electron diffraction pattern investigations demonstrate that CdSe nanorods are a uniform cubic CdSe crystal.

Preparation of&lt;tex&gt;$rm Y_1rm Ba_2rm Cu_3rm O_7-delta$&lt;/tex&gt;Superconducting Tapes via a Continuous Electrochemical Process

Our recent advancements about a continuous process for the production of electrochemical deposited Y1Ba2Cu 3O7-delta (Y-123) films are presented. The process consists of alternate elemental deposition steps and thermal treatments. By unreeling through sequential modular sections, several tens meter long tapes are processed in a continuous way yielding the final coated superconductor (Y-123/Ag), suitable for industrial applications. The Y-123 phase constituting elements (Cu, Y, and Ba) are sequentially electrodeposited on both sides of an untextured 50 mum-thick silver tape. Following copper and Yttrium hydroxide deposition steps, an intermediate annealing transforms the precursors into a mixture of CuO and Y2Cu2O5. After Barium hydroxide electroplating, a final thermal treatment in pure flowing oxygen allows the formation of the Y-123 superconducting phase. A strict control on deposit stoichiometry and thermal parameters seems to be crucial in order to achieve a good microstructure and high performances. To date the process allows to deposit on both sides of the substrate 0.5 mum-thick Y-123 films that exhibit critical current densities in excess of 20 kA/cm2 (77 K, self-field), the highest reported value for this material obtained via an electrochemical process on untextured metal tape

Properties of 6H–SiC crystals grown by hydrogen-assisted physical vapor transport

Effects of hydrogen addition to the growth ambient during physical vapor transport (PVT) growth of 6H–SiC were investigated using secondary ion mass spectrometry, deep level transient spectroscopy, and Hall effect measurement. The background nitrogen concentration and the free electron density decrease with increasing hydrogen content. The formation of electron traps (activation energies of 0.4eV, 0.6eV, 0.7eV, 0.9eV, and 1eV) was also strongly suppressed. The above results are interpreted as a consequence of hydrocarbon formation produced by the reaction of hydrogen with the SiC source and the graphite parts of the furnace. This leads to more congruent evaporation of SiC and the shift of the gas phase and the SiC deposit stoichiometry due to less Si-rich conditions than in standard PVT growth.

Formation of the first monolayers of CdTe on Au(111) by electrochemical atomic layer epitaxy (EC-ALE): studied by LEED, Auger, XPS, and in-situ STM

The two-step alternated electrodeposition of Cd and Te atomic layers to form CdTe monolayers, electrochemical atomic layer epitaxy (EC-ALE), was studied on Au(111) using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), in-situ scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS). Well ordered (√7×√7) R19.1°-CdTe and (3×3)-CdTe structures were formed using either Te or Cd as the first layer, and model structures are proposed for both. STM images suggest that previously proposed hexagonal structures based on a plane of zinc blende CdTe may be incorrect. A chain structure is suggested to account for the (√7×√7) R19.1°, based on 3/7 (0.43) ML each of Cd and Te. The (3×3)-CdTe structure results from the deposition of a CdTe sandwich: first an atomic layer of Cd on Au, followed by a layer of Te, and then a second Cd layer. Based on this three layer model for the (3×3), a three step deposit was formed, starting with Cd, then Te, and finally Cd. This resulted in an excellent quality LEED pattern, suggesting a well-ordered (3×3)-CdTe deposit and strongly supporting the proposed model. The importance of deposit stoichiometry was also investigated using STM, which indicated that too low a coverage in the first atomic layer resulted in cluster formation and the degradation of surface morphology.

Experimental study of atmospheric pressure chemical vapor deposition of silicon carbide from methyltrichlorosilane

A comprehensive study of the chemical vapor deposition of SiC from methyltrichlorosilane at atmospheric pressure was conducted in this study; its main objectives were to identify the range of operating parameters in which stoichiometric SiC could be deposited and the generation of reliable kinetic data that could be used for the design of atmospheric pressure processes of chemical vapor deposition or chemical vapor infiltration of SiC. Deposition experiments were conducted in a hot-wall, cylindrical reactor at temperature ranging from 1273 to 573 K on flat graphite substrates or thin molybdenum wires aligned with the axis of the reactor. The obtained results showed that the deposition rate and the deposit stoichiometry varied markedly with the distance from the entrance of the reactor. The deposition rate exhibited, depending on the reaction temperature, one or two pronounced maxima before the beginning of the isothermal zone of the reaction, whereas the deposit stoichiometry showed an abrupt transition from almost silicon to stoichiometric silicon carbide after the first maximum. Experiments with HCl added in the feed showed that the presence of HCl could cause complete suppression of the deposition of silicon and lead to smoother variation of the SiC deposition rate with the residence time in the reactor. It is believed that this effect could be exploited to improve the uniformity of SiC deposition in chemical vapor deposition reactors or in the interior of porous preforms.

Layer-by-Layer Deposition: A Tool for Polymer Surface Modification

Layer-by-layer deposition of polyelectrolytes onto poly(ethylene terephthalate) (PET) film is reported as a method for polymer surface modification. Poly(allylamine hydrochloride) (PAH) and poly(sodium styrenesulfonate) (PSS) were sequentially adsorbed to unmodified (neutral) PET as well as PET samples that had been surface modified to contain carboxylate (PET-CO2-) and ammonium (PET-NH3+) functionality. XPS and contact angle data indicate that the layers are extremely thin (2−6 Å) and stratified to a significant extent. The wettability of the multilayer films is controlled by the outermost polyelectrolyte layer and the thickness of the individual layers (sublayers have an influence in multilayers with thinner layers). The substrate surface chemistry controls the thickness of all of the layers in the multilayer assembly as well as the stoichiometry (ammonium ion:sulfonate ion ratio) of the deposition process. The effect of the ionic strength of the polyelectrolyte solutions was studied for the case of the neutral substrate (PET); both the individual layer thickness and deposition stoichiometry are affected by ionic strength. Peel tests indicate that the multilayer assemblies have significant mechanical strength.

Surface Nucleation and Template Growth of Ti Silicides

AbstractThe direct nucleation and growth of Ti silicide on the surfaces of Si(100) and amorphous Si were studied. Silicide phase formation depended on the temperature and the stoichiometry of deposition and the crystallinity of the substrate. A very low temperature, − 500°C, for the nucleation of the low-resistivity C54-TiSi2 phase was observed on amorphous Si. Stoichiometric and uniform TiSi2 layers were grown with the depositions of pure Ti. On crystalline Si, uniform TiSi2 layers were also grown at ∼ 500°C with a co-deposited template layer. The much reduced C54 formation temperature is discussed in terms of a possible circumvention of precursor amorphous silicide phases during surface nucleation.

A visual analogy for metallic deposition

Metallic deposition stoichiometry problems are difficult for students to visualize. A clever visual tool is explained in this article.

Activated Reactive Evaporation Process for High Rate Deposition of Compounds

Activated reactive evaporation is a new process developed for the high rate deposition of compounds. It circumvents problems associated with direct evaporation of compounds. Metal vapors from high rate evaporation sources are reacted with a gas in the vapor phase to form and deposit compounds. The vapor phase reaction has to be activated by ionization of the reacting species, i.e., metal vapor and gas in the reaction zone. The steps of compound synthesis and compound deposition are thus separated. Control of deposit stoichiometry, e.g., [C/M] ratio for TiC synthesis is readily achieved by controlling the relative amounts of reactants. Results on the synthesis of carbides, oxides, and nitrides are presented.