Self-assembling Of Clusters Research Articles

Fabrication of Polymer Magnetic Nanocomposites Containing Carbon Nanoparticles Doped with Cobalt Nanoclusters and Study Their Conductivity, Self-Healing and Adhesion Properties

The technology of fabrication of polymer nanocomposites on basis of carbon nanoparticles doped with cobalt clusters, synthesized by original Chemical Vapore Deposition (CVD) technology developed by authors, was elaborated. Carbon shells provide both the protection of ferromagnetic impurities from aggressive environment and new unique properties to the hybride nanostructures. The self-assembling of magnetic clusters coated by carbon shells presents just such example which could be used in the contemporary materials, for example, in strong magnets, analytic instruments (nuclear magnetic resonance tomographs) and nanosensors. Their good conductivity, self-healing and adhesion properties were demonstrated by applying the combined action of temperature, pressure, steady and alternating magnetic fields to stimulate diffusion of magnetic nanoparticles in direction to defect sites. Due to these properties fabricated magnetic polymer nanocomposites could have perspective for potential.

Self-assembling of impurity clusters in AlN:(Ga, BV, CV), (BV, CV = P, As; P, Sb; As, Sb)

The self-assembling conditions of arrays of tetrahedral impurity clusters of two types in zinc blende AlN:(Ga, BV, CV), (BV, CV=P, As; P, Sb; As, Sb) are represented. Doping with one cation and two anion isoelectronic impurities transforms AlN into AlN-rich GaxAl1−xBVyCVzN1−y−z alloy of GaBV, GaCV, GaN, AlBV, AlCV and AlN. The cause of self-assembling is the preference of GaBV, GaCV and AlN bonding over that of GaN, AlBV, AlCV. The conditions are considered from 0°C to 1000°C in the dilute and ultra dilute limits for the cation and anion impurities, correspondingly. The temperature ranges between the cluster occurrence and self-assembling completion when the same anion impurities are in clusters are very small. 1P4Ga and 1As4Ga cluster occurrence temperatures are equal, correspondingly, to 797°C and 736°C at Ga content 2% and P and As contents 0.01%. 1P4Ga and 1Sb4Ga cluster occurrence temperatures are equal, correspondingly, to 976°C and 736°C at the same impurity contents. The cluster densities in AlN:(Ga, As, Sb) are close to those in AlN:(Ga, P, Sb). The results demonstrate that studied semiconductors are promising materials to produce arrays of identical ∼1nm low band gap objects of two types embedded in the wide band gap matrix.

Self-assembling of In and nitrogen in GaP:(In, N)

Highly mismatched GaP:N attracts now considerable interest in fabricating ensembles of single photon sources. Significant reduction of undesirable internal strains around nitrogen atoms can be achieved by additional doping with In due to self-assembling of 4N10In and 1N4In clusters in GaP:(In, N). Double doping transforms GaP into GaP-rich InxGa1−xNyP1−y substitutional alloy of InN, InP, GaN and GaP. Self-assembling of clusters results in the decrease of the sum of the free energies of the constituent compounds and strain energy. The self-assembling conditions are considered from 0°C to 1000°C in the dilute and ultra dilute limits for In and nitrogen impurities, respectively. Almost all nitrogen atoms are in 4N10In clusters over the entire temperature range if x=1×10−3, y=1×10−4; x=1×10−4, y=1×10−5 and x=1×10−5, y=1×10−6. Both types of clusters with considerable densities are in GaP-rich InxGa1−xNyP1−y if the ratio between the In and nitrogen contents is 100. If this ratio is ≈1000 then all nitrogen impurities are in 1N4In clusters over the entire temperature range. The fulfilled estimates demonstrate that GaP:(In, N) is a promising candidate to fabricate ensembles of single photon sources due to small strains around nitrogen atoms in 4N10In and 1N4In clusters.

Toward hyperuniform disordered plasmonic nanostructures for reproducible surface-enhanced Raman spectroscopy.

We report on the self-assembling of clusters of gold-nanoparticles (Au-NPs) directed by the phase separation of poly(styrene)-b-poly(methylmethacrylate) (PS-b-PMMA) block-copolymer (BCP) on indium tin oxide coated glass, which induces the onset of vertical lamellar domains. After thermal evaporation of gold on BCP, Au-NPs of 4 nm are selectively included into PS-nanodomains by thermal annealing, and then clustered with large density of hot spots (> 10(4) μm(2)) in a random two-dimensional pattern. The resulting nanostructure exhibits near-hyperuniform long-range correlations. The consequent large degree of homogeneity of this isotropic plasmonic pattern gives rise to a highly reproducible Surface-Enhanced Raman Scattering (SERS) enhancement factor over the centimeter scale (std. dev. ∼ 10% over 0.25 cm(2)). We also discuss the application of a static electric field for modulating the BCP host morphology. The electric field induces an alignment of Au-NP clusters into ordered linear chains, exhibiting a stronger SERS activity, but reduced SERS spatial reproducibility.

Self-assembling of 1Sb4Mn magnetic clusters in GaAs:(Mn, Sb)

The developed technology allowing to grow GaAs:Mn as substitutional alloys opens new perspectives for these materials and materials based on them. Self-assembling of 1Sb4Mn identical magnetic clusters in GaAs:(Mn, Sb) considered as MnxGa1−xSbyAs1−y substitutional alloys is represented. The self-assembling conditions with Mn and Sb contents in the dilute and ultra dilute limits, respectively, are obtained by the free energy minimization. The cluster occurrence temperatures do not depend on Sb content. The cluster occurrence and final stage of self-assembling when all Sb atoms are in clusters are results of continuous phase transitions. The portions of Mn atoms in clusters are 0.40, 0.53 and 0.80 at 255°C, 191°C and 88°C, at Mn contents 2%, 3% and 4%, respectively, and at Sb content 0.4%.

Nanoscale Order in ZnTe:(Cd, O)

Self-assembling of 1O4Cd identical tetrahedral clusters resulting to nanoscale order in ZnTe:(Cd, O) is presented. Such co-doping transforms ZnTe into CdxZn1-xOyTe1-yalloy. The decrease of the strain energy is a cause of this phenomenon. The self-assembling conditions are obtained by the minimum condition of the free energy of ZnTe:(Cd, O) at the Cd and oxygen in the dilute and ultra dilute limits, respectively. An occurrence of 1O4Cd clusters and completion of self-assembling (all oxygen atoms are in clusters) are results of the continuous phase transitions. The temperature of the occurrence of self-assembling does not depend on the oxygen content and it is a function of Cd concentration only. CdxZn1-xOyTe1-ywith all oxygen atoms in clusters may be obtained in temperature ranges fromT= 270 °C (x= 0.002,y= 1×10-4) toT= 620 °C (x= 0.02,y= 1×10-4) and fromT= 240 °C (x= 0.005,y= 0.001) toT= 580 °C (x= 0.02,y= 0.001).

Self-assembling of 4B10Sb and 1B4Sb clusters in GaP:(B, Sb)

The self-assembling conditions of identical 4B10Sb and 1B4Sb clusters were studied in GaP:(B, Sb). The conditions are considered in the ultra dilute impurity concentration ranges and from 0°C to 800°C. Co-doping with boron and Sb transforms GaP into GaP-rich BxGa1−xSbyP1−y quaternary alloy of four binary compounds BSb, BP, GaSb and GaP. The formation of clusters decreases a sum of the enthalpies of the constituent compounds and strain energy. 4B10Sb clusters self-assemble mainly and almost maximal quantities of such clusters should form up to 600°C. The insignificant density of 1B4Sb clusters should also occur in GaP:(B, Sb). The results demonstrate that GaP:(B, Sb) is a semiconductor with array of ∼1nm identical low band gap objects embedded in the wide band gap matrix.

Nanoscale order in GaAs:(B, Sb)

Nanoscale order caused by self-assembling of 1B4Sb and 4B10Sb clusters in GaAs:(B, Sb) is described. Self-assembling occurs in wide ranges of temperature and impurity concentration. Co-doping with boron and Sb isoelectronic impurities transforms GaAs into GaAs-rich B x Ga 1− x Sb y As 1− y quaternary alloy. The self-assembling conditions are obtained from 0 to 800 °C with boron and Sb concentrations from x=1×10 –5 to x=2×10 –4 and from y=5×10 –4 to y=0.01, respectively. If Sb content is much larger than that of boron almost all boron atoms are in 1B4Sb clusters up to 800 °C and other boron impurities are isolated. If boron content is nearly equal or larger than that of Sb the formation of 4B10Sb clusters is preferential.

Self-assembling of 1C4Sn and 4C10Sn clusters in Ge:(C, Sn)

Carbon and Sn co-doping transforms Ge into Ge-rich CxSnyGe1−x−y alloy. Self-assembling of 1C4Sn and 4C10Sn clusters decreases the strain energy. These cluster formation processes are competing. The self-assembling conditions of 1C4Sn and 4C10Sn clusters are represented from 0 °C to 800 °C and at 5 × 10−5 ≤ x ≤ 0.015 and 1 × 10−4 ≤ y ≤ 0.015. The conditions demonstrate that only 1C4Sn clusters form if carbon is a minority impurity. Both types of clusters with the preferential formation of 4C10Sn clusters over 1C4Sn occur if the impurity concentrations are nearly equal or if Sn is a minority impurity.

Self-assembling of 4C10Sn clusters in Ge co-doped with C and Sn

Self-assembling of 4C10Sn clusters in Ge co-doped with C and Sn is considered. The free energies of Ge-rich C x Sn y Ge 1− x−y ( x⩽0.02, x⩾0.4 y) random alloys and alloys with 4C10Sn and 1C4Sn clusters are estimated at temperature of 773 K. The concentration conditions when the free energy of C x Sn y Ge 1− x−y with 4C10Sn clusters is smaller than those of random alloys and alloys with 1C4Sn clusters are obtained. Occurrence of 4C10Sn clusters is a result of a stronger decrease of the strain energy after such self-assembling than after self-assembling of 1C4Sn clusters.

Phase diagram of AlN:(Ga, As)

Self-assembling of 1As4Ga tetrahedral clusters in zinc blende AlN doped with Ga and As in the ultradilute As impurity limit is described by a phase diagram. The occurrence of these clusters is an initial stage of self-assembling. The final stage of self-assembling when all As impurities are in 1As4Ga clusters is reached at a finite temperature. Both stages are results of the second-order transitions. The conditions of these phase transitions are represented. It is shown that the phase diagram of wurtzite AlN:(Ga, As) should be quantitatively similar to the considered zinc blende one.

Self-assembling of 1O4Mg clusters in ZnTe doped with Mg and O

Self-assembling of 1O4Mg tetrahedral clusters in ZnTe-rich Mg x Zn 1 - x O y Te 1 - y alloys in the ultra dilute oxygen impurity limit from y = 1 × 10 - 8 to y = 1 × 10 - 3 is presented for the lower growth and higher annealing temperatures of 300 and 500 ∘ C , respectively. Under estimated conditions the free energies of the random alloys and alloys in which all impurity atoms are placed in the clusters are equal to each other. The advantage of the MgO and ZnTe bonding over the MgTe and ZnO one as well as a decrease of the strain energy after formation of 1O4Mg clusters are the origins of this phenomenon.

Self-assembling of silver and copper small clusters within the zeolite cavities: prediction of geometry

The factors affecting a self-assembling of certain kind of silver and copper clusters during reduction of ion-exchanged forms of zeolites in hydrogen were studied. Conditions leading to the preferable M 8 cluster formation were revealed. A matching of zeolite void and cluster sizes was found to be the key factor facilitating this process. Ag 8 clusters can be easily stabilized in the zeolites with certain pore size (a cross-section in the range of 0.63–0.67 nm). Zeolites possessing voids wider than 0.70 nm stabilize these clusters only for low reduction temperatures. Small pores possessing at least one axis of pore cross-section ≤0.63 nm do not stabilize Ag 8 clusters. Cu clusters assigned to Cu 8 were predicted to be formed in narrow pores of erionite much easier than in mordenite voids. Comparison of experimental UV–Vis spectra with the results of ab initio calculations for selected M 8 isomers was performed. The difference between Ag 8 and Cu 8 cluster models is discussed.

Nondisturbing and Stable SERS-Active Substrates with Increased Contribution of Long-Range Component of Raman Enhancement Created by High-Temperature Annealing of Thick Metal Films

High-temperature annealing of thick silver films (TSFs) deposited onto a smooth dielectric substrate leads to high-order self-organization of metal clusters on the film surface. A comparative atomic force microscopic (AFM) analysis of “as-deposited” and annealed TSFs (aTSFs) shows that uniform ellipsoidal roughness ∼41 × 25 nm in lateral cross section and ∼45 nm in height results after annealing. These metal clusters are mutually oriented so that the main lateral axes of the ellipsoids are nearly parallel. UV−visible data demonstrate a ∼300 nm hypsocromic shift of the bands corresponding to the collective surface plasmon modes. Additionally, a new (∼350 nm) band related to the normal component of the plasmon oscillations appears after annealing. This band was found to be strongly angle-dependent for p-polarized light. The aTSFs appeared extremely time- and organic solvent-stable versus as-deposited films. The aTSFs were found to be nondisturbing surface-enhanced Raman scattering (SERS)-active substrates in the application to studies of complexation of crown ether styryl dyes with metal ions. A pronounced SERS signal of the analyte rhodamine 6G was observed with aTSFs, even when the analyte was separated from the silver surface with five Langmuir−Blodgett monolayers of stearic acid. At the same time, depositing only a monolayer of stearic acid on the as-deposited film completely suppressed the SERS signal of the analyte. Finally, the self-assembling of Ag clusters on the surface of the aTSF, stimulated by the high-temperature annealing, results in the creation of a time- and organic solvent-stable SERS substrate with nanometer-scale quasi-periodical roughness, and this substrate exhibits an increased contribution of the electromagnetic component to the overall Raman enhancement.