Desorption Of Sb Research Articles

Kinetics of coupled sorption and abiotic oxidation of antimony(III) in soils

A quantitative evaluation of the dynamics of antimony (Sb) species transformation when Sb(III) enters the soil matrix would facilitate the understanding of the speciation and environmental fate of Sb in natural environments. Towards this end, the coupled sorption and abiotic oxidation kinetics of Sb(III) were examined across 12 soils with a 24 h timeframe. The soil-solution distribution coefficients (Kd) of Sb ranged between 214 and 5965 L kg−1. Both apparent and mechanistic kinetic models were used to described the process. The apparent kinetic model indicated a two-rate oxidation and associated stabilization behavior of Sb in soils. The fast oxidation rate constants ranged from 0.147 to 0.763 h−1, which were one to two orders of magnitudes higher than the slow rate constants (0.002–0.039 h−1). Iron and Mn oxides were identified as the key soil components associated with adsorptive-oxidative sites (SOH) and oxidative sites (Mn-OH) of soils for Sb species, and these were subsequently integrated into the mechanistic kinetic model. This model included the adsorption–desorption of Sb(III) as well as the oxidation product, Sb(V) on the SOH, the oxidation of Sb(III) by SOH and Mn-OH, and the stabilization of both Sb(III) and Sb(V). The model produced a global fit for dissolved and adsorbed Sb species across the 12 soils. This study provides new information for predicting the dynamics of Sb in soils when multiple adsorption–desorption, oxidation and stabilization reactions are coupled in natural environments.

Structure and morphology control of amorphous Mn-doped Fe oxide composite using soft-templates for efficient Sb(V) removal in textile wastewater: Mechanism of solid-liquid interface regulation and Sb(V) adsorption

To achieve high removal rate and efficacy of Sb(V) from textile wastewater and simultaneously realize cyclic Sb(V) recovery, the structure and surface property of amorphous Mn-doped Fe oxide composite (MFOC) were regulated via the combination of facile soft-template synthesis and sintering treatment. Characterization and adsorption results indicated MFOC structure was greatly changed from aggregated large sphere to dispersive small sphere after adjusted by the optimal Brij-58 (SMFO-B). Because of the generated fasciculate micelle, long carbon chain feature and the lowest residual amount of Brij-58, abundant mesopores were generated and the aggregation of unit particles was apparently decreased for SMFO-B. Surface area and total pore volume of SMFO-B became 10 and 6 times of MFOC and more functional hydroxyl groups were generated and exposed on the interface between SMFO-B and water solution. Additionally, the surface positive potential of SMFO-B under neutral condition was also greatly increased. Thus, the maximum adsorption capacity and rate of SMFO-B towards Sb(V) reached to 147 mg/g and 0.1067 mg/(g·min), 2 and 5 times of MFOC. SMFO-B also possessed better selective adsorption ability, exhibited stronger static and dynamic adsorption performance in real textile wastewater and realized the cyclic desorption and enrichment of Sb(V) due to its better phase stability. X-ray absorption spectroscopy showed two main specific forms, such as bidentate edge-(E2) and corner-sharing (C2) complexes, for the inner-sphere complexation during Sb(V) adsorption and E2 complex was proved to play the most important role through the analysis of CD-MUSIC model. This study supplied an excellent adsorbent for Sb(V) removal from textile wastewater and a deeper insight about Sb(V) adsorption onto amorphous Fe oxide.

The impact of phosphate on the interaction of Sb(III) with ferrous sulfide

Phosphate may affect the behavior of metal(loid)s in environments, so the interaction of Sb(III) with FeS affected by phosphate was investigated in this study. Sb(III) was reacted with synthesized FeS in solution at pH 5.5, 7.0, and 9.0 with and without the addition of phosphate. The concentrations of Fe(II), Sb(III), and phosphate in the solution were monitored, and the solid phases were examined by XRD, TEM, and XPS. For the interaction of Sb(III) with FeS in the absence of phosphate, the formation of Sb2S3 was very important at pH 5.5 and 7.0, whereas Sb(III) adsorption was the dominant process at pH 9.0. The interaction of Sb(III) with FeS could be significantly affected by phosphate, and this impact was dependent of pH and phosphate concentration. At pH 5.5 and 7.0, the effect of phosphate varied markedly with increasing phosphate concentration. Low phosphate loadings (9.5 and 19 mg/L) had a negligible effect on the mobility of Sb(III), while high phosphate loadings (95 and 475 mg/L) notably enhanced the uptake of Sb(III) by FeS. In the case of high phosphate loadings, Fe3(PO4)2‧8H2O was formed and resulted in the dissolution of FeS, which was favorable for the formation of Sb2S3 and consequently the uptake of Sb(III). In the experiments at pH 9.0, the addition of phosphate only resulted in minor desorption of Sb(III) because FeS was very stable and consequently both Fe3(PO4)2‧8H2O and Sb2S3 were unlikely to be formed. The results of this work may help to better understand the effect of phosphate on the behavior of Sb in some anoxic environments where FeS is present.

Sorption–desorption of Sb(III) in different soils: Kinetics and effects of the selective removal of hydroxides, organic matter, and humic substances

To examine the Sb(III) retention by three soils with different properties (Ferrosol, Primosol and Isohumosol), kinetic batch experiments were carried out for Sb(III) adsorption–desorption, followed by Sb release using a sequential extraction procedure. In addition, hydroxides, organic matter, and humic substances were selectively removed by washing the soil with oxalate, sodium dithionate–citrate–bicarbonate, H2O2, and NaOH. The effects of removing these substances on Sb(III) retention were investigated by comparing the Sb distribution coefficients and desorption rates. The results indicated that exogenous Sb(III) was adsorbed onto all three soils rapidly at first and then more slowly. After 168 h of adsorption, most of the adsorbed Sb(III) was irreversibly retained in stable fractions by the Ferrosol. Oxidation reactions negatively affected Sb(III) retention by the Primosol and Isohumosol, and a large proportion of the Sb adsorbed remained mobilizable. The oxalate washing markedly enhanced Sb retention but the sodium dithionate–citrate–bicarbonate washing decreased Sb retention in all three soils. The H2O2 and NaOH washings affected Sb retention by the Ferrosol more than Sb retention by the Primosol and Isohumosol. Changes in the pH and hydroxides caused by the washing strongly affected Sb sorption–desorption. The results improve our understanding of the mobility and bioavailability of exogenous Sb(III) in soils and might benefit future remediation option of Sb-contaminated soils.

Adsorption and desorption of Sb(III) on goethite

The present study examined the effect of pH and ionic strength on Sb(III) adsorption on goethite and desorption of Sb(III) binding to goethite. Adsorption of Sb(III) is favored by low pH and high ionic strength. Desorption of Sb(III) from Sb(III) treated goethite is dependent on the adsorption suspension pH and increased with increasing the original suspension pH.

Removal of antimonate and antimonite from water by schwertmannite granules

In order to overcome the drawbacks of small particle-sized adsorbents, schwertmannite powder was fabricated into granules in the present study. These granules were evaluated for Sb(III) and Sb(V) removal from water and intraparticle mass transfer resistance of Sb(III) and Sb(V) onto the porous adsorbent was modeled. Schwertmannite granules (SG) exhibited capacities of 32.9 mg/g for Sb(III) and 23.2 mg/g for Sb(V), respectively, which are superior to many reported granular adsorbents and even powder adsorbents. Mass transfer was separately modeled using the pore volume diffusion model and surface diffusion model. The film diffusion coefficients, kL, range from 1.09 × 10−5 to 3.08 × 10−5 cm/s. The pore diffusion coefficients, Dep, range from 6.20 × 10−5 to 10.85 × 10−5 cm2/s, and the surface diffusion coefficients, Ds, range from 1.12 × 10−9 to 3.57 × 10−9 cm2/s. The concentration decay data-sets were successfully fitted with these best obtained parameters. Sb(III) was effectively removed over a wide pH range, while the removal of Sb(V) was pH dependent and could be enhanced by lowering solution pH. Sb(III)-loaded SG was regenerated with 91.2% re-adsorption capacity retained after five cycles when using 0.6% NaOH as the stripping solution. The desorption of Sb(V) was not as successful as Sb(III). Before breakthrough (5 μg/L) occurred, 1,690 and 712 bed volumes (BVs) of Sb(III), and 769 and 347 BVs of Sb(V) were treated when operating at space velocity values of 2 and 6 h−1, respectively. Considering the low cost and the granular form of schwertmannite, the adsorbent is a promising modestly priced adsorbent and can be easily used in packed bed or filter units for practical application.

Speciation of inorganic antimony (III & V) employing polyurethane foam loaded with bromopyrogallol red

In this work, the speciation analysis of inorganic antimony (Sb(III) and Sb(V)) is proposed using polyurethane foam loaded with bromopyrogallol red (PUF-BPR) as a selective sorbent for Sb(III). The quantification of Sb in the solutions was performed by graphite furnace atomic absorption spectrometry (GF AAS), and several variables that could affect the performance of the method were carefully evaluated. The best conditions for the sorption of Sb(III) were achieved by shaking 50mg of PUF-BPR with the solutions containing Sb(III) at pH 4.0 for 90min. In this condition, the retention of Sb(V) was not significant, whereas the removal of Sb(III) from the solution was higher than 95%. The desorption of Sb(III) from loaded PUF-BPR was possible by shaking the loaded foam with 7.5mL of a 2.5molL−1 HNO3 solution for 30min. No interference of metal cations was observed on the solid-phase extraction of Sb(III) by PUF-BPR. The developed method was applied in the speciation analysis of antimony in river water samples fortified with different concentrations of Sb(III) and Sb(V). Also, we performed the determination of Sb(III) in a sample of a Sb-based drug utilized in the treatment of leishmaniasis. The results show that Sb(III) can be separated from high concentrations of Sb(V), since recoveries in the range of 81–110% were obtained in the analysis of the samples. The method presented limits of detection and quantification of 0.6 and 2µgL−1, respectively, for Sb(III) and 1 and 3µgL−1 for Sb(V), respectively.

Kinetic modeling of pH-dependent antimony (V) sorption and transport in iron oxide-coated sand

Understanding the mechanisms and kinetics controlling the retention and transport of antimony (Sb) is prerequisite for evaluating the risk of groundwater contamination by the toxic element. In this study, kinetic batch and saturated miscible displacement experiments were performed to investigate effects of protonation–deprotonation reactions on sorption–desorption and transport of Sb(V) in iron oxide-coated sand (IOCS). Results clearly demonstrated that Sb(V) sorption was highly nonlinear and time dependent, where both sorption capacity and kinetic rates decreased with increasing solution pH. Breakthrough curves (BTCs) obtained at different solution pH exhibited that mobility of Sb(V) were higher under neutral to alkaline condition than under acidic condition. Because of the nonlinear and non-equilibrium nature of Sb(V) retention and transport, multi-reaction models (MRM) with equilibrium and kinetic sorption expressions were utilized successfully to simulate the experiment data. Equilibrium distribution coefficient (Ke) and reversible kinetic retention parameters (k1 and k2) of both kinetic sorption and transport experiment showed marked decrease as pH increased from 4.0 to 7.5. Surface complexation is suggested as the dominant mechanism for the observed pH-dependent phenomena, which need to be incorporated into the kinetic models to accurately simulate the reactive transport of Sb(V) in vadose zone and aquifers.

Behavior of Antimony(V) during the Transformation of Ferrihydrite and Its Environmental Implications

In this study, we investigated the behavior of Sb(V) during the transformation of poorly crystalline Fe(III) oxyhydroxides (two-line ferrihydrite) with various Sb/Fe molar ratios at pH 6.0. Both XRD and Fe EXAFS analyses confirmed that goethite and hematite are the primary transformation products of the ferrihydrite in the presence of Sb(V). The crystallization kinetics showed that the transformation rate with Sb(V) was approximately the same as that of the control (without Sb(V)), which indicates that the presence of Sb(V) does not influence the transformation rate to a noticeable extent. Throughout the transformation, Sb(V) dominantly partitioned in the solid phase and no desorption of Sb(V) was observed. Furthermore, Sb EXAFS analyses suggested that Sb(V) in the solid phase is structurally incorporated into crystalline goethite and/or hematite generated by the ferrihydrite transformation. Hence, Sb(V) transfers into the thermodynamically stable solids from the metastable ferrihydrite with aging, indicating a rigid immobilization of Sb(V). These findings are valuable for making predictions on the long-term fate of Sb associated with ferrihydrite in natural environments.

Desorption of Hg(II) and Sb(V) on extracellular polymeric substances: Effects of pH, EDTA, Ca(II) and temperature shocks

Extracellular polymeric substances (EPS) existed ubiquitously in biological systems affect the mobility and availability of heavy metals in the environments. The adsorption–desorption behaviors of Hg(II) and Sb(V) on EPS were investigated. The sorption rates follow Sb(V)>Hg(II), and the desorption rates follow reverse order. Applications of ethylene diamine tetraacetic acid (EDTA), Ca(II) and pH shocks affect desorption rates and desorbed quantities of Hg(II) from EPS–Hg complex. Temperature shock minimally affects the desorption rate of Hg(II). Conversely, the EPS–Sb complex is stable subjected to EDTA, Ca(II), temperature or pH shocks. The excitation–emission matrix (EEM) fluorescence spectroscopy and fast-Fourier (FT-IR) analysis showed that Hg(II) and Sb(V) principally interacted with polysaccharides and protein-like compounds in the EPS, respectively. The EPS–Hg complex presents a time bomb that may release high levels of Hg(II) in short time period under environmental shocks.

Retention of Heavy Metals by Carboxyl Functional Groups of Biochars in Small Arms Range Soil

Long-term effectiveness of biochar for heavy metal stabilization depends upon biochar's sorptive property and recalcitrance in soil. To understand the role of carboxyl functional groups on heavy metal stabilization, cottonseed hull biochar and flax shive steam-activated biochar having a low O/C ratio (0.04-0.06) and high fixed carbon content (~80% dry weight basis) were oxidized using concentrated H(2)SO(4)/HNO(3) and 30% HNO(3). Oxidized and unoxidized biochars were characterized for O/C ratio, total acidity, pH, moisture, ash, volatile matter, and fixed carbon contents, Brunauer-Emmett-Teller surface area, and attenuated total reflectance Fourier transform infrared spectral features. Characterized biochars were amended (2%, 5%, 10%, and 20% in grams of biochar per gram of soil) on a sandy, slightly acidic (pH 6.27) heavy metal contaminated small arms range soil fraction (<250 μm) having low total organic carbon (0.518%) and low cation exchange capacity (0.95 cmol(c) kg(-1)). Oxidized biochars rich in carboxyl functional groups exhibited significantly greater Pb, Cu, and Zn stabilization ability compared to unoxidized biochars, especially in pH 4.9 acetate buffer (standard solution for the toxicity characteristic leaching procedure). Oppositely, only oxidized biochars caused desorption of Sb, indicating a counteracting impact of carboxyl functional groups on the solubility of anions and cations. The results suggested that appropriate selection of biochar oxidant will produce recalcitrant biochars rich in carboxyl functional groups for a long-term heavy metal stabilization strategy in contaminated soils.

Adsorption of antimony(III) and antimony(V) on bentonite: Kinetics, thermodynamics and anion competition

This research attempted to study the adsorption of Sb(III) and Sb(V) on bentonite using batch experiments. The effects of reaction time, temperature, initial Sb concentration, and competitive anions at different concentrations on the adsorption of Sb(III) and Sb(V) were investigated. Kinetic studies suggested that the adsorption equilibriums for both Sb(III) and Sb(V) were reached within 24 h. The desorption of Sb adsorbate on the bentonite was observed following Sb(III) adsorption, probably due to the oxidation of Sb(III) on the bentonite surface and subsequent desorption of Sb(V). In addition, oxidation of Sb(III) can occur in the solution medium also, which decreases the concentration of Sb(III) in the solution thereby driving the equilibrium in the direction of desorption from the surface. The adsorption data at three temperatures were successfully modeled using Langmuir (r 2 > 0.82) and Freundlich (r 2 > 0.99) isotherms. The thermodynamic parameters (ΔG 0, ΔH 0, and ΔS 0) were calculated from the temperature dependence, suggesting that the adsorption process of Sb(III) is spontaneously exothermic, while the adsorption process of Sb(V) is spontaneously endothermic. Competitive anions such as NO 3 − , SO 4 2 − , and PO 4 3 − hardly affected the Sb(III) adsorption on bentonite, while SO 4 2 − and PO 4 3 − could compete with Sb(OH) 6 − for adsorption sites. The competition between PO 4 3 − and Sb(OH) 6 − on adsorption sites was presumably due to the formation of surface complexes and the surface accumulation or precipitation of PO 4 3 − on bentonite surface.

Adsorption and desorption of antimony acetate on sodium montmorillonite

The adsorption of antimony acetate (Sb(OAc) 3) on sodium montmorillonite (Na-MMT) was studied at five different initial concentrations, and data from the adsorption isotherm were modeled using the Langmuir, Freundlich and D–R isotherm equations. The kinetics of adsorption was also discussed using three kinetic models: the pseudo-first-order, the pseudo-second-order and the intraparticle diffusion model. The rate constants of pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetics, and the amount of Sb(OAc) 3 adsorbed at equilibrium were determined. Moreover, the desorption of Sb(OAc) 3 from several kinds of Sb-MMT (Na-MMT was intercalated by antimony acetate) was investigated at room temperature and 180 °C. The results show that according to the maximum amounts of adsorbate and correlation coefficients calculated from the three isotherm equations mentioned above, the corresponding data from adsorption experiments fit fairly well to the Langmuir isotherm. The adsorption data show a good compliance with the pseudo-second-order kinetic model and also follow the intraparticle diffusion model up to 30 min. The equilibrium adsorption capacity of Sb(OAc) 3 on MMT is close to the cation exchange capacity (CEC) of the montmorillonite. The desorption amount of Sb(OAc) 3 is correlated with both the temperature of desorption and the drying temperature of Sb-MMT.

Adsorption of antimony(V) on kaolinite as a function of pH, ionic strength and humic acid

The present work investigated the adsorption and mobility (desorption) of Sb(V) on kaolinite using batch experiments. The adsorption of Sb(V) on kaolinite was studied as a function of contact time, pH, ionic strength, humic acid (HA), initial Sb(V) concentration and temperature. Kinetic studies suggest that the equilibrium is achieved within 24 h. The adsorption of Sb(V) was strongly affected by changes in I at low ionic strength and unaffected at high ionic strength. The adsorption is weakly dependent on the presence of humic acid, but is strongly dependent on pH. Within the range tested, the optimal pH for Sb(V) adsorption is 3.6, and close to 75% removal can be achieved. Desorption is dependent on the original suspension pH. The addition sequence of Sb(V)/HA do not influence the adsorption of Sb(V) on kaolinite. The adsorption data fit both the Freundlich and Langmuir isotherm. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) were calculated from the temperature dependence, and the results suggest the endothermic and spontaneous nature of the process.

Coverage dependence ofSb∕Si(111)adsorption and desorption modes: Interplay between chemical interactions and site transitions

The kinetic and thermodynamic properties of adsorption and desorption of Sb onto a Si(111) surface are analyzed by mass spectrometry and ab initio calculations. Two domains of temperature are evidenced. At $T&lt;600\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ there is an irreversible adsorption involving a subtle competition between sticking, adsorption, then dissociation of ${\mathrm{Sb}}_{4}$ tetramers associated to a partial reflection of ${\mathrm{Sb}}_{4}$ molecules on the Sb-covered surface. At $T&gt;800\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, ${\mathrm{Sb}}_{4}$ molecules are dissociated close to the surface leading to a simple reversible adsorption/desorption of Sb monomers. In this temperature range, adsorption/desorption isotherms can be recorded for various temperatures, which reveal a surprising behavior since quasi-Langmuir isotherms appear to be the consequence of a two-dimensional (2D) phase transition. More precisely, as shown by ab initio calculations, during the submonolayer adsorption process, the adsorption site evolves (as a function of coverage) from ternary towards on-top position and the character of the Sb-Sb effective interactions changes from repulsive towards attractive. The 2D phase transition close to $\ensuremath{\theta}\ensuremath{\approx}0.7$ ML seems to be associated to characteristic signatures in many other experiments. Then for high enough supersaturations, it is possible to overpass $\ensuremath{\theta}=1$ ML by the formation of dimers, first partially located on top sites which repel one another, up to a second phase transition around $\ensuremath{\theta}=1.3$ ML in which dimers leave the on top sites and stand up to occupy almost vertically the hollow ones for building the second Sb layer. Lastly surfactant effect is quantified.

Sorption of Sb(III) and Sb(V) to Goethite: Influence on Sb(III) Oxidation and Mobilization

Antimony is an element of growing interest for a variety of industrial applications, even though Sb compounds are classified as priority pollutants by the Environmental Protection Agency of the United States. Iron (Fe) hydroxides appear to be important sorbents for Sb in soils and sediments, but mineral surfaces can also catalyze oxidation processes and may thus mobilize Sb. The aim of this study was to investigate whether goethite immobilizes Sb by sorption or whether Sb(III) adsorbed on goethite is oxidized and then released. The sorption of both Sb(III) and Sb(V) on goethite was studied in 0.01 and 0.1 M KClO4 M solutions as a function of pH and Sb concentration. To monitor oxidation processes Sb species were measured in solution and in the solid phase. The results show that both Sb(III) and Sb(V) form inner-sphere surface complexes at the goethite surface. Antimony(III) strongly adsorbs on goethite over a wide pH range (3-12), whereas maximum Sb(V) adsorption is found below pH 7. At higher ionic strength, the desorption of Sb(V) is shifted to lower pH values, most likely due to the formation of ion pairs KSb(OH)6 degrees. The sorption data of Sb(V) can be fitted by the modified triple-layer surface complexation model. Within 7 days, Sb(III) adsorbed on goethite is partly oxidized at pH 3, 5.9 and 9.7. The weak pH-dependence of the rate coefficients suggests that adsorbed Sb(III) is oxidized by 02 and that the coordination of Sb(III) to the surface increases the electron density of the Sb atom, which enhances the oxidation process. At pH values below pH 7, the oxidation of Sb(III) did not mobilize Sb within 35 days, while 30% of adsorbed Sb(III) was released into the solution at pH 9.9 within the same time. The adsorption of Sb(III) on Fe hydroxides over a wide pH range may be a major pathway for the oxidation and release of Sb(V).

Sb-induced reconstructions on Si(113): Adatoms as the key elements

The adatom site is identified and determined as the main structural element of Sb-induced surface reconstructions of Si(113) by means of x-ray standing waves, x-ray photoelectron spectroscopy, and low-energy electron diffraction (LEED) in combination with density functional theory calculations. The analysis yields that the Sb adatom site can be found prevalently at Sb coverages below 1 ML. With increasing coverage, the relative amount of Sb residing in adatom sites is reduced in favor of mainly Sb tetramer formation, leading to a complex mixture of $(2\ifmmode\times\else\texttimes\fi{}2)$ reconstructions at coverages above 1 ML. The observation of $(1\ifmmode\times\else\texttimes\fi{}2)$ LEED patterns can be explained by the formation of small antiphase domains of $(2\ifmmode\times\else\texttimes\fi{}2)$ reconstructions. Upon annealing, partial desorption of Sb leads to the formation of a missing-row structure with a $(1\ifmmode\times\else\texttimes\fi{}n)$ LEED pattern.

Sb adsorption and desorption pathways on (2 × 1) and c(4 × 4) reconstructed Si(0 0 1) surfaces

The role of initial surface reconstruction on the kinetics of heteroepitaxial growth of Sb on Si(0 0 1) surface is elucidated. The adsorption and desorption of Sb, from the clean-(2 × 1) and c(4 × 4) reconstructions of Si(0 0 1) surface, is investigated by in situ auger electron spectroscopy (AES) and low energy electron diffraction (LEED). Sb is adsorbed at room-temperature (RT) onto clean-(2 × 1) and c(4 × 4) reconstructed Si(0 0 1) surfaces at a base pressure of 3 × 10 −11 Torr. At the very low flux rates adopted (0.06 monolayer/min), Sb grows epitaxially at RT and forms a (1 × 1) surface phase for coverages greater than 1.0 monolayer (ML) on both the (2 × 1) and c(4 × 4) surfaces. Residual thermal desorption studies done on these RT-adsorbed systems are observed to adopt different pathways. The ‘(2 × 1) case’ results in an intermediate novel 0.6-ML (8 × 4) phase, while the ‘c(4 × 4) case’ directly yields the 0.25-ML c(4 × 4) phase. The 0.25-ML Sb covered c(4 × 4) obtained from the Si(0 0 1)-c(4 × 4) phase is observed to be sharper than that obtained from the (2 × 1) reconstructed surface. Upon complete Sb desorption both the cases result in the clean Si(0 0 1)-(2 × 1) surface. The difference in desorption pathways is related to the Sb monolayer formation.

A phase diagram of the Sb/Si(001) interfacial system

Abstract The dynamics of adsorption and desorption of Sb on atomically clean dimer reconstructed Si(0 0 1) surface is carefully monitored. Superstructure formation of the Sb/Si(0 0 1)-(2 × 1) system is studied by submonolayer Sb adsorption and in situ characterization in ultra-high vacuum by surface sensitive techniques such as low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS). Sb is adsorbed onto double-domain (DD) (2 × 1)-reconstructed Si(0 0 1) surface at a flux rate of 0.06 ML/min at various substrate temperatures. A complete phase diagram for this Sb/Si(0 0 1)-(2 × 1) system is drawn for the first time by consolidating the results of the adsorption–desorption studies for Sb adsorbed at various substrate temperatures and coverages. The 0.6 ML (8 × 4) surface superstructure shown in the phase diagram was reported earlier by us and the novel 0.25 ML (12 × 2) is reported here for the first time. The results demonstrate the ability of kinetic control in forming several stable novel superstructures, depending on the pathway adopted in the formation of the interface.

Effect of Sb on Si/Si and Ge/Si growth process

In this paper, we investigate the surfactant effect of Sb on the growth of Ge on Si(1 1 1) and on Si(1 0 0). We show that Sb has mainly two effects: first it delays the 2D–3D growth mode transition and consequently permits to produce thicker flat Ge layers; second Sb promotes the layer by layer 2D nucleation growth mode. The latter effect can be used to considerably reduce the lateral size of Ge islands at 550 °C on both Si(1 1 1) and Si(0 0 1). In order to understand the fundamental role of Sb on the growth processes, we have determined the microstructure and the growth mode of Ge layers deposited on Si and on one monolayer Sb/Si surfaces by atomic force microscopy and reflection high-energy electron diffraction (RHEED). We show that the growth mode changes induced by Sb at 350 and 550 °C (thicker 2D wetting layer and smaller islands, respectively) are explained by the conjugated effects of thermodynamics (decrease of the surface energy) and of kinetics (decrease the surface diffusion length) induced by Sb. We finally suggest that partial desorption of Sb is responsible for the formation of islands at 550 °C.