NC Formation Research Articles

Photovoltaic limitations of FAPbI3 nanocrystal solar cells associated with ligand washing processes

The processing of perovskite nanocrystals (PNCs) solar cells (SCs) usually incorporates ligand washing (LW) procedures. We show that a LW step of FAI in EtAc assists in the removal of the oleic acid/oleylamine ligands and improves the JSC and FF values of FAPbI3 based SCs. Although by increasing the exposure time of EtAc the removal of oleic acid/oleylamine ligands is more effective, sintering/necking of the FAPbI3 results to NC agglomerations and formation of defects/traps are observed within the active layer by the reported photoluminescence studies. Despite identifying the balanced in LW procedure exposure time, limitations on the performance of FAPbI3 PNCs SCs are reported. To identify the photovoltaic limitations impedance spectroscopy studies are presented and show that in the case of FAPbI3 PNC SCs an intermediate frequency response manifests. The observed impedance spectroscopy intermediate frequency response correlates with a parasitic resistance effect, indicating charge transport limitations and charge recombination losses even after the applied LW processing procedure.

Biogenic ZnO/CuO/Fe2O3 Nanocomposite: A Groundbreaking Approach for Enhanced Degradation Capabilities and Reusability in Dye Removal Applications

We present the successful synthesis of a biogenic ZnO/CuO/Fe2O3 nanocomposite using an aqueous leaf extract of Ocimum Basilicum L. The confirmation of biosynthesis was achieved through UV–Visible spectrophotometry (UV–Vis), which provided evidence of ZnO/CuO/Fe2O3 NC formation. Scanning Electron Microscopy further confirmed the nanoscale size of the NC, measuring at 65 nm. X-Ray Diffraction analysis revealed a hexagonal structure for ZnO and a monoclinic structure for CuO. The successful synthesis of the environmentally friendly ZnO/CuO/Fe2O3 NC was further verified using Fourier transformed infrared (FT-IR) spectroscopy, which identified the functional groups present in the composite. Notably, the ZnO/CuO/Fe2O3 NC demonstrated exceptional degradation capabilities for toluidine blue (TB), p-toluidine (PT), and m-Toluidine (MT), with degradation rates of 99%, 99.1%, and 99.7%, respectively, within a reaction time of 120 min. The reaction kinetics followed a pseudo-first order model, with rate constant (k) values of 0.0314 min−1 and 0.0189 min−1 for TB and PT, respectively. This high rate of dye degradation can be attributed to the low band gap of the NC, which was determined to be 1.44 eV for the indirect bandgap. Furthermore, the nanocomposite exhibited excellent degradation reusability, maintaining a high degradation rate in each cycle.

Photocatalytic Degradation of Methylene Blue from Aqueous Solutions by Using Nano-ZnO/Kaolin-Clay-Based Nanocomposite

Dyes are toxic organic compounds released as effluent from various industries that need proper treatment as they pose serious hazards to the environment and living beings, including humans. Nanocomposites can be employed as photocatalysts for the elimination of such organic compounds from wastewater. One such attempt is made in this present research study, where a zinc-based nanocomposite has been fabricated for the elimination of the methylene blue dye (MB). For the development of nanocomposite, zinc oxide nanoparticles (ZnONPs) were prepared to utilize Allium sativa peel (garlic skin) extract, which was further processed to develop ZnO/kaolin clay NC. ZnONPs and ZnO/kaolin clay NC formation have been confirmed by UV–Vis spectral bands at 379 nm and 423 nm. The NC was rod-shaped, with width of 60–100 nm and length of 200–800 nm and an average size of 50.0 ± 0.58 nm. Both materials were compared for their efficacy in photocatalytic degradation of the MB under solar light irradiation. ZnONPs removed 65% of MB, whereas the degradation efficiency of ZnO/clay NC was calculated to be 96% for 10 ppm MB. A kinetics study for photocatalytic degradation of MB using both nanomaterials showed that the photocatalytic degradation followed the pseudo-first-order (PFO) type of reaction. This investigation represents an expeditious, lucrative, ecological, and appropriate technique for the fabrication of functional nanomaterials for the remediation of diverse organic pollutants.

Synthetic Tunability and Biophysical Basis for Fabricating Highly Fluorescent and Stable DNA Copper Nanoclusters.

The real motivation in the present work is to tune the synthesis variables that can result in a highly fluorescent and stable DNA copper nanocluster (CuNC) and also to understand the intricate mechanism behind this process. Here, carefully optimized concentrations of various reactants enabled the creation of a DNA-encapsulated CuNC for AT-DNA, displaying a size of <1.0 nm as confirmed by transmission electron microscopy and dynamic light scattering. The extremely small size of the AT-DNACuNC supports the discrete electronic transitions, also characterized by an exceptionally strong negative circular dichroism (CD) band around 350 nm, whose intensity is well correlated with the observed strong fluorescence emission intensity. This remarkably strong CD can open new applications in the detection and quantification of a specific DNACuNC. Further, time-dependent fluorescence analysis suggested stronger photostabilization of these DNACuNCs. The simulation study, based on Cu ion distribution, explained how AT-DNA is a better candidate for NC formation than GC-DNA. In conclusion, the better-tuned synthesis procedure has resulted in a highly compact, well-defined three-dimensional conformation that promotes a more favorable microenvironment to sequester a DNA-based CuNC with high brightness and outstanding photostability.

From Uncommon Ethylzinc Complexes Supported by Ureate Ligands to Water-Soluble ZnO Nanocrystals: A Mechanochemical Approach

Urea and its derivatives, due to their unusual versatility of coordination modes to metal centers and the presence of multiple hydrogen-bond donor sites, are widely utilized as neutral or monoanionic ligands in coordination and bioinorganic chemistry and as building units of bioinspired materials. However, metal complexes with ureate ligands have essentially not been applied as precursors of hybrid organic–inorganic nanomaterials. We report on the synthesis and structure characterization of two novel organozinc ureate complexes incorporating N-phenylureate or N,N′-dicyclohexylureate ligands, the latter being the first reported complex with the μ3-μ2(O):κ1(N) ureate coordination mode. These findings not only expand the horizon of urea–zinc chemistry but also pave the way for efficient bottom-up mechanochemical synthesis of sub-10 nm diameter zinc oxide nanocrystals (ZnO NCs) coated by the ureate ligands. We explored the NC formation triggered by mechanical force from both a well-defined monocrystalline precursor and an insoluble hard-to-process amorphous organozinc precursor. Moreover, the organic shell of the N-phenylureate-coated ZnO NCs was modified via a facile, fast, and solventless host–guest complexation with β-cyclodextrin using a mechanochemical approach, which afforded water-soluble ZnO NCs. The reported procedure is the first example of rapid and sustainable mechanochemical synthesis of hybrid nanomaterials from organometallic precursors.

An Interpretation for Defect-Induced Structural Transformation in SiC

Silicon carbide (SiC) has been considered as one of the alternative power semiconductor materials due to its excellent properties such as wide band gap, high break down field, and high thermal conductivity. Although SiC with 3C (zinc blende) is suitable for high-frequency power devices from its high electron mobility and high electron-saturation-velocity, SiC is well known as having dozens of polytypes including 4H and 6H in addition to 2H (wurtzite) and 3C that consist of different ordered stacking sequences of SiC atomic double layers. The 3C-SiC is believed to be more stable than the hexagonal structure at low temperatures. In contrast, 2H-SiC, which has the simplest stacking sequence, is rarely observed at high temperatures. Moreover, point defects also affect the stable polytype in SiC. Heavily Nitrogen (N)-doped single crystals of 6H-SiC were completely transformed into 3C-SiC by annealing in vacuum at presence of Si vapor at 2080 K and 2180 K (hereafter Case I). The 3C-SiC-like bands was also observed in 4H-SiC epilayers with heavily N-doping after thermal annealing (hereafter Case II). Presuming that vacancy formation is related to temperature, point defects such as vacancy and N in SiC are crucial factor for the structural transformation between hexagonal and cubic structures. In this study, the structural transformation in SiC is simply interpreted by considering point defect formation with the aid of ab initio calculations. Ab initio total energy calculations in a √3×√3×12 unit cell imply that stable stacking for SiC is 6H with Si-vacancy (VSi), 4H with C-vacancy (VC) and N substituting for Si (NSi), and 3C with N substituting for C (NC), whereas 2H-stacking does not appear as a stable stacking in these systems. Furthermore, the formation energy calculations reveal that vacancy formation depends on C chemical potential m C, where VSi and VC formations are favorable at large m C (corresponding to C-rich) and small m C (Si-rich), respectively. On the other hand, NC formation is more favorable than NSi formation over the entire range of m C and independent of conditions because of very small difference in covalent radius between N and C. Comparing these calculated results with the experimental finding in the Case I for transformation from 6H to 3C, thermal treatment with presence of Si vapor at high temperatures suppresses VSi formation favoring 6H-stacking while it enhances VC formation to be occupied by N (NC) in addition to N substitution for C (NC) that transform 6H to 3C. The Case II can be also interpreted by considering NC. Thermal annealing for N-doped 4H-SiC favored by VC easily produces NC with N occupying VC and substituting for C to realize 3C-SiC bands at high N-doped region in 4H-SiC epilayers. These results suggest that NC is crucial for the transformation from hexagonal stacking such as 6H and 4H to cubic stacking 3C. In order to give physical interpretation for the transformation to 3C-SiC with NC, the interaction energies Jn between nth neighbor SiC double layers are estimated in the range of n ≤ 3 using the axial next nearest neighbor Ising (ANNNI) model and calculated total energies for SiC polytypes obtained in this study. The calculated results elucidate that the absolute value of positive J 1 (51.70 meV) with J 3 (9.92 meV) favoring 3C-stacking is much larger than that of negative J 2 (-16.66 meV) inducing hexagonal stacking. It should be noted that the Jn values are one order of magnitude greater than those of perfect SiC such as J 1 (2.33 meV), J 2 (-1.41 meV), and J 3 (0.51 meV). This implies that the layer interaction in SiC becomes strong and long-range due to N-doping. Considering coordinate of (|J 2|/J 1, J 3/J 1) in the ANNNI phase diagram, it is also found that (0.31, 0.19) for SiC with NC is located in the stable region of 3C and is more distant from the multi-phase degeneracy point (0.5, 0) inducing polytype and phase boundary between 3C and 4H than (0.61, 0.21) for perfect SiC. This clarifies that the large J 1 in SiC with NC stabilizes 3C-stacking to dominate the structural transformation to 3C due to N-doping. Furthermore, atomistic interaction between the nearest neighbor layers corresponding to J 1 is also qualitatively discussed in terms of electrostatic interaction between bond charges located at the center of interatomic bonds and that between ionic charges located at the lattice sites on the basis of a simple energy description and charge distribution obtained by ab initio calculations.

Stress evolution of Ge nanocrystals in dielectric matrices

Germanium nanocrystals (Ge NCs) embedded in single and multilayer silicon oxide and silicon nitride matrices have been synthesized using plasma enhanced chemical vapor deposition followed by conventional furnace annealing or rapid thermal processing in N2 ambient. Compositions of the films were determined by Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy. The formation of NCs under suitable process conditions was observed with high resolution transmission electron microscope micrographs and Raman spectroscopy. Stress measurements were done using Raman shifts of the Ge optical phonon line at 300.7 cm−1. The effect of the embedding matrix and annealing methods on Ge NC formation were investigated. In addition to Ge NCs in single layer samples, the stress on Ge NCs in multilayer samples was also analyzed. Multilayers of Ge NCs in a silicon nitride matrix separated by dielectric buffer layers to control the size and density of NCs were fabricated. Multilayers consisted of SiNy:Ge ultrathin films sandwiched between either SiO2 or Si3N4 by the proper choice of buffer material. We demonstrated that it is possible to tune the stress state of Ge NCs from compressive to tensile, a desirable property for optoelectronic applications. We also observed that there is a correlation between the stress and the crystallization threshold in which the compressive stress enhances the crystallization, while the tensile stress suppresses the process.

Heating or Cooling: Temperature Effects on the Synthesis of Atomically Precise Gold Nanoclusters

Developing an efficient, well-controlled synthesis strategy for gold nanoclusters (Au NCs) is crucial for delivering their expected applications in many fields; and such development requires fundamental understandings on the synthetic chemistry. The synthesis of Au NCs typically consists of a pair of reversible reactions: a fast reduction-growth reaction and a slow size-focusing reaction. Here we demonstrate that the above two reactions can be well-balanced while accelerated in a heated synthesis protocol, thus providing an efficient and scalable synthesis method to obtain thermodynamically favorable Au25(SR)18 NCs (SR denotes thiolate ligand) with high yield (>95% on gold atom basis) and fast kinetics. By investigating the Au NC formation behavior at different temperature, we identified the endothermic nature of the reductive formation of Au25(SR)18 NCs from Au(I)-thiolate complex precursors. More interestingly, if overheated, after the formation of Au25(SR)18, there exists an irreversible first-order re...

Self-assembled silicon nanocrystal arrays for photovoltaics

Silicon nanocrystals (Si NCs) are a promising candidate for the top cell of Si tandem solar cells since their bandgap exceeds that of bulk silicon and can be tuned by adjusting nanocrystal size. Due to this effect, size control is required to maintain a uniform bandgap throughout a Si NC film. This can be achieved by annealing superlattices of Si-rich and stoichiometric dielectrics. This paper reviews the progress that has been made using host matrices SiO2, Si3N4, and SiC. Si NCs in SiO2 show excellent NC size and shape control and strong quantum-confinement-related photoluminescence, however electrical conductivity is poor. Ordering and size control is also obtained in Si3N4, but conclusive evidence of quantum confinement is lacking. Preparing ordered but separated Si NCs in SiC is difficult, but the narrow parameter space in which this is possible has been elucidated, good electrical conductivity was obtained, and functioning single-junction and tandem cells have been produced. Si NC formation can now be well-controlled in all three materials, and the key weaknesses for photovoltaics have been identified to be the electrical conductivity of SiO2, and defect density for Si3N4 and SiC. Addressing these is expected to lead to competitive Si tandem solar cells.

Silver nanoclusters for RNA nanotechnology: steps towards visualization and tracking of RNA nanoparticle assemblies.

The growing interest in designing functionalized, RNA-based nanoparticles (NPs) for applications such as cancer therapeutics requires simple, efficient assembly assays. Common methods for tracking RNA assemblies such as native polyacrylamide gels and atomic force microscopy are often time-intensive and, therefore, undesirable. Here we describe a technique for rapid analysis of RNA NP assembly stages using the formation of fluorescent silver nanoclusters (Ag NCs). This method exploits the single-stranded specificity and sequence dependence of Ag NC formation to produce unique optical readouts for each stage of RNA NP assembly, obtained readily after synthesis.

Abstract 3600: NanoChannel-mediated communication between tumor cells and endothelium mediates metastatic parasitism

Abstract Uncovering mechanisms underlying metastasis is the final frontier in cancer biology. Metastasis is a complex process with many discrete stages. While there has been much research on the seed (metastatic tumor cells) and the soil (colonized host tissue) hypothesis, limited knowledge exists on the interaction between metastatic cells and vascular endothelial cells, prerequisite for the development of metastatic disease. Here we describe nanoscale tubular structures, or nanoChannels (nCs), which mediate early intercellular communication between tumor epithelial cells and the endothelium in vitro and in vivo. These structures were examined in a 3D in vitro co-culture model system capturing molecular and physical interactions between metastatic cells and the endothelium. Unlike classical modes of cell-cell communication (i.e. paracrine, endocrine, and autocrine signaling), nCs allow for both rapid and directed transfer of intracellular contents from metastatic breast cancer cells to the endothelium. The ability to form nanoChannels correlates with metastatic potential of the tumor cells and enables direct tracking of both synthetic materials (chemicals and nanoparticles) and bioorganic macromolecules (proteins and miRNAs). As one specific example, we show that miR-132, which is implicated in pathological angiogenesis, can translocate from tumor cells to the endothelial cells through nCs, resulting in decreased p120RasGAP and activation of AKT in the recipient endothelial cells. Furthermore, nC-mediated communication resulted in upregulation of pathological angiogenesis markers, such as CD137 (26x, p&amp;lt;0.001) and CD276 (2x, p&amp;lt;0.001). The increase in these pathological angiogenesis markers could be reduced by pharmacological inhibition of nC formation. Combination of 500pM Docetaxel with 30nM Latrunculin A or 50nM Cytoclasin D resulted in a 3x (p&amp;lt;0.01) disruption of TNT structures, reducing TNT-mediated communication by 42% (p&amp;lt;0.0001) and 56.6% (p&amp;lt;0.0001), respectively. In summary, we describe a novel form of heterotypic intercellular communication between cancer cells and the host endothelium, where tumor cells can physically hijack and transform normal endothelial cells to a pathological angiogenesis phenotype. We define this process as metastatic parasitism. NanoChannel-mediated transfer of microRNAs may emerge as a new signaling mechanism in metastasis, which may function to prime the endothelium to facilitate transmigration of tumor cells and/or recruitment of vasculature to growing metastases. Elucidation of microRNAs transported through the nanoChannels presents a powerful opportunity to explain mechanisms underlying pathological angiogenesis and for the development of metastasis-specific therapeutics. Targeting the formation of these nCs and the resulting metastatic parasitism may potentially emerge as a new therapeutic opportunity in the management of metastatic cancer. Citation Format: Yamicia D. Connor, Sarah Tekleab, Amjad Husain, Cherelle Walls, Bruce Zetter, Harold Dvorak, Shiladitya Sengupta. NanoChannel-mediated communication between tumor cells and endothelium mediates metastatic parasitism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3600. doi:10.1158/1538-7445.AM2014-3600

TCT-362 Relation between renal function and neointimal tissue characteristics after drug-eluting stent implantation: virtual histology-intravascular ultrasound analysis

Introduction: Patients with chronic kidney disease (CKD) had more mortality, myocardial infarction, repeat revascularization, and bleeding complication after percutaneous coronary intervention compared with those with patients with normal renal function. Hypothesis: It has been suggested that renal insufficiency may predict cardiovascular events due to an association with more severe coronary artery disease. However, few data are available about neointimal tissue characteristics according to the renal function after drug-eluting stent (DES) implantation. Therefore, the purpose of the present study was to attempt to assess the neointimal tissue components between patients with CKD and those without CKD using virtual histology-intravascular ultrasound (VH-IVUS). Methods: We compared neointimal tissue components between patients with CKD [n=19, estimated creatinine clearance (CrCl) Results: Mean follow-up durations between DES implantation and follow-up VH-IVUS study were 12.0±4.1 months in CKD group and 11.4±5.6 months in non-CKD group ( p = 0.519). At follow-up, neointima volume was significantly greater (72±47 mm 3 vs. 47±26 mm 3 , p p = 0.012) in CKD group compared with non-CKD group. There was negative correlation between CrCl and neointima volume ( r = -0.250, p r = -0.034, p = 0.591). Only independent predictor of follow-up %neointima NC volume ≥10% was neointima volume (odds ratio 1.025, 95% confidence interval 1.013-1.036, p Conclusions: Renal function was associated with in-stent neointimal growth, but it was not associated with neointima NC formation, instead the amount of neointima was associated with more neoatherosclerosis in patients who underwent DES implantation.

Development of a new catalase activity assay for biological samples using optical CUPRAC sensor

A novel catalase activity assay was developed for biological samples (liver and kidney tissue homogenates) using a rapid and low-cost optical sensor-based ‘cupric reducing antioxidant capacity’ (CUPRAC) method. The reagent, copper(II)–neocuproine (Cu(II)–Nc) complex, was immobilized onto a cation-exchanger film of Nafion, and the absorbance changes associated with the formation of the highly-colored Cu(I)–Nc chelate as a result of reaction with hydrogen peroxide (H2O2) was measured at 450nm. When catalase was absent, H2O2 produced the CUPRAC chromophore, whereas catalase, being an effective H2O2 scavenger, completely annihilated the CUPRAC signal due to H2O2. Thus, the CUPRAC absorbance due to H2O2 oxidation concomitant with Cu(I)–Nc formation decreased proportionally with catalase. The developed sensor gave a linear response over a wide concentration range of H2O2 (0.68–78.6μM). This optical sensor-based method applicable to tissue homogenates proved to be efficient for low hydrogen peroxide concentrations (physiological and nontoxic levels) to which the widely used UV method is not accurately responsive. Thus, conventional problems of the UV method arising from relatively low sensitivity and selectivity, and absorbance disturbance due to gaseous oxygen evolution were overcome. The catalase findings of the proposed method for tissue homogenates were statistically alike with those of HPLC.

Specific recognition of DNA bulge sites by in situ grown fluorescent Ag nanoclusters with high selectivity

There is much demand for the development of reliable methods of bulge site recognition in DNA in order to find disease-related mutations and identify bulge sequence environments. Herein, we found that the bulge site in the DNA duplex can be used to selectively grow fluorescent silver nanoclusters (Ag NCs). The as-prepared Ag NCs exhibit an emission behavior dependent on the base environment near the bulge site and can be employed in situ as a readout for specific bulge site recognition. Fluorescent signal-on sensing for the bulge site based on this inorganic fluorophore is substantially advantageous over the organic fluorophores previously used as probes, in which a fluorescent signal-off response was usually observed with context guanines flanking the bulge site. The strong dependence of the fluorescent Ag NCs' formation on the bases surrounding the bulge site is successfully used to identify the bulge environment near the codon 177 of cancer suppression gene p53. We expect that bulge site-determined Ag NC formation is very likely to be developed into a simple method for bulge site recognition with high selectivity and sensitivity.

Silicon nanocrystals from high‐temperature annealing: Characterization on device level

AbstractSilicon nanocrystals (Si NCs) embedded in Si‐based dielectrics provide a Si‐based high band gap material (1.7 eV) and enable the construction of all‐crystalline Si tandem solar cells. However, Si nanocrystal formation involves high‐temperature annealing which deteriorates the properties of any previously established selective contacts. The inter‐diffusion of dopants during high‐temperature annealing alters Si NC formation and limits the built‐in voltage. Furthermore, most devices presented so far also involve electrically active bulk Si and therefore do not allow a clear separation of the observed photovoltaic effect of the nanocrystal layer from that of the bulk Si substrate. A membrane route is presented for nanocrystal based p–i–n solar cells to overcome these limitations. In this approach, the formation of both selective contacts is carried out after high‐temperature annealing and therefore not affected by the latter. p–i–n Solar cells are investigated with Si NCs embedded in silicon carbide in the intrinsic region. Device failure due to damaged insulation layers is analyzed by electron‐ and light beam induced current measurements. Open‐circuit voltages of 176 mV are shown for the NC layer. An optical model of the device is presented for improving the cell current. Comparison of the optical limit and the measured short circuit current demonstrates that the device is governed by recombination within the absorber layer. magnified imageVertical p–i–n solar cell with a Si nanocrystal thin film in the intrinsic region and selective electron and hole contacts by doped amorphous silicon carbide (a‐SixC1−x:H).

Alteration of nC60 in the Presence of Environmentally Relevant Carboxylates

C(60) forms colloidally stable nanoscale particles (nC(60)) when mixed with water for extended periods. Past studies have shown that macromolecules such as natural organic matter (NOM) and proteins accelerate nC(60) formation and stabilize the resulting nanoparticles. To better elucidate the mechanisms underlying this behavior, nC(60) was produced via extended mixing in the presence of sodium citrate and other carboxylates. Carboxyl groups are a predominant functional group in many environmentally relevant macromolecules, thus studies examining carboxyl-C(60) interactions are merited. nC(60) produced in the presence of citrate (cit/nC(60)) and other carboxylates differs from nC(60) produced in water alone (aq/nC(60)), exhibiting enhanced negative surface charge, smaller particle size, and different spectroscopic characteristics. Importantly, the simultaneous detection of irregular nC(60) nanoparticles and small, regularly shaped nC(60) suggests that mixing-mediated "top-down" and carboxyl group-mediated "bottom-up" processes occur concurrently when nC(60) is produced in the presence of carboxylates and, by extension, in the presence of carboxylate-containing macromolecules. The "bottom-up" process is expected to involve molecular C(60) or small clusters of C(60) molecules as an important intermediate.

DNA abasic site-directed formation of fluorescent silver nanoclusters for selectivenucleobase recognition

DNA single-nucleotide polymorphism (SNP) detection has attracted much attentiondue to mutation related diseases. Various methods for SNP detection have beenproposed and many are already in use. Here, we find that the abasic site (AP site) inthe DNA duplex can be developed as a capping scaffold for the generation offluorescent silver nanoclusters (Ag NCs). As a proof of concept, the DNA sequencesfrom fragments near codon 177 of cancer supression gene p53 were used as amodel for SNP detection by in situ formed Ag NCs. The formation of fluorescentAg NCs in the AP site-containing DNA duplex is highly selective for cytosinefacing the AP site and guanines flanking the site and can be employed in situas readout for SNP detection. The fluorescent signal-on sensing for SNP basedon this inorganic fluorophore is substantially advantageous over the previouslyreported signal-off responses using low-molecular-weight organic ligands. Thestrong dependence of fluorescent Ag NC formation on the sequences surroundingthe AP site was successfully used to identify mutations in codon 177 of cancersupression gene p53. We anticipate that this approach will be employed to developa practical SNP detection method by locating an AP site toward the midwaycytosine in a target strand containing more than three consecutive cytosines.

Formation of iridium nanocrystals with highly thermal stability for the applications of nonvolatile memory device with excellent trapping ability

This paper presents the formation of iridium nanocrystals (Ir-NCs) embedded in SiO2 matrix and it can be used for potential applications of nonvolatile memory devices. The NC formation is investigated by varying Ir film thickness; and the thermal agglomeration is also studied by applying various annealing temperatures and process time. The results of systematic characterization including capacitance-voltage, transmission electron microscopy, and x-ray photoelectron spectroscopy show that the high work-function (5.27 eV) metallic-NCs have a highly thermal stability (up to 900 °C) and the resulted Al/SiO2/Ir-NCs/SiO2/Si/Al stack can have a good retention ability and significant hysteresis window of 17.4 V.

Correlation between optical properties and Si nanocrystal formation of Si-rich Si oxide films prepared by plasma-enhanced chemical vapor deposition

We have investigated the phase separation and silicon nanocrystal (Si NC) formation in correlation with the optical properties of Si suboxide (SiO x , 0 < x < 2) films by thermal annealing in high vacuum. The SiO x films were deposited by plasma-enhanced chemical vapor deposition at different nitrous oxide/silane (N 2O/SiH 4) flow ratios. The as-deposited films show increased Si concentration with decreasing N 2O/SiH 4 flow ratio, while the deposition rate and surface roughness have strong correlations with the flow ratio in the N 2O/SiH 4 reaction. After thermal annealing at temperatures above 1000 °C, Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy manifest the progressive phase separation and continuous growth of crystalline-Si (c-Si) NCs in the SiO x films with increasing annealing temperature. We observe a transition from multiple-peak to single peak of the strong red-range photoluminescence (PL) with increasing Si concentration and annealing temperature. The appearance of the single peak in the PL is closely related to the c-Si NC formation. The PL also redshifts from ∼1.9 to 1.4 eV with increasing Si concentration and annealing temperature (i.e., increasing NC size). The good agreements of the PL evolution with NC formation and the PL peak energy with NC size distribution support the quantum confinement model.

Nanocrystalline Formation during Mechanical Attrition of Cobalt

The nanocrystalline (nc) formation was studied in cobalt (a mixture of ε (hexagonal close packed) and γ (face-centered cubic) phases) subjected to surface mechanical attrition treatment. Electron microscopy revealed the operation of { 10 10 }〈 1120 〉 prismatic and {0001}〈 1120 〉 basal slip in the ε phase, leading to the successive subdivision of grains to nanoscale. In particular, the dislocation splitting into the stacking faults was observed to occur in ultrafine and nc grains. By contrast, the planar dislocation arrays, twins and martensites were evidenced in the γ phase. The strain-induced γ→ε martensitic transformation was found to progress continuously in ultrafine and nc grains as the strain increased. The nc formation in the γ phase was interpreted in terms of the martensitic transformation and twinning.