Exhibit Quantum Size Effects Research Articles

Convergence of surface energy calculations for various methods: (0 0 1), (0 1 2), (1 0 0) hematite and the applicability of the standard approach

Three different methods for the calculation of the surface energy, namely the standard approach, the Boettger relation and the linear-fit method, are applied to the (0 0 1), (0 1 2) and (1 0 0) hematite surfaces. The standard approach was previously shown to suffer from a divergence problem, and the Boettger relation was shown to exhibit quantum size effects. While the linear-fit method, in general, leads to a good convergence behavior of the surface energy, the questions arise whether the relative order of the calculated surface energies depends on the chosen calculation method, and whether there is any merit at all in employing the standard approach. The present work investigates these questions with hematite as a benchmark material system. The simulations show that, for the surface facets and slab thicknesses studied here, the relative order of the surface energies is unaffected by the chosen calculation method. A regime is found where the three methods are in reasonably good agreement with respect to the obtained surface energies. Finally, a procedure is put forward to extract meaningful surface energy values from the standard approach.

Hydrogenated Nano-Crystalline Silicon Thin Films in SiO2 Matrix for Next Generation Solar Cells Using Glow Discharged Decomposition

Hydrogenated Nanocrystalline Silicon (nc-Si:H) thin films using SiH4/H2 mixture by glow discharged decomposition were investigated on c-Si and glass substrates. The effects of substrate temperature on the Structural, Optical and Electrical properties of the films were investigated by X-ray diffraction, Raman scattering, FT/IR, Optical transmission and Atomic Force Microscopy (AFM). Substrate temperatures ([TSB]) of the films were changed from 100oC to 250oC. It has been revealed the strong dependence on the film’s properties with the substrate temperatures. XRD and Raman measurements were shown that the higher substrate temperature (250oC) exhibits the highest crystalline volume fraction ([ρ] = 95%) and the lowest crystalline size ([Ω] = 3.5 nm) as well, having the highest H-content and the lowest O-content. At 250oC, the lowest mobility and the highest resistivity were also found to be ~37.5 cm2/v.s and 7.35 Ω-cm. Refractive index and the optical energy gap (Eg) were estimated by 3.8 and 1.9 eV having the growth rate of 4.2 nm/min. At 250oC, it was resulted in a blue shift of the absorption edge having uniform grain distributions. Results indicate that in situ hydrogen cleaning effects is prominent and localized orderly high density Si-Si bonds are exhibiting quantum size effects at highest substrate temperature.

Hydrothermal synthesis of zinc stannate nanoparticles spectroscopic investigation

This paper presents the study conducted on the synthesis and the investigations of Zinc stannate nanoparticles. Hydrothermal method was used for the synthesis. Characterizations for the products obtained were done with the help of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis absorption spectroscopy. The X-ray powder diffraction result was used to characterize the morphology and also it confirmed the well crystalline wurtzite structure. Typical electron microscopic investigations of SEM and TEM were used to study the morphology and the particle size. The formation of Zn2SnO4 nanoparticles and their particle size were confirmed by the TEM analysis. The optical properties were analyzed using UV–Vis absorption and PL spectrum. The FT-IR spectrum confirmed the presence of Zn2SnO4 nanoparticles. The dielectric properties, e.g. dielectric constant, dielectric loss, and AC conductivity of the Zn2SnO4 nanoparticles, were measured and studied as a function of frequency and temperature. Those nanoparticles exhibit quantum size effects of the optical absorption spectrum. The influence of reaction conditions on the growth of Zn2SnO4 nanoparticles demonstrates that high precursor concentration and high reaction temperature (≥200 °C) is a favorable growth in the formation of zinc stannate.

Strong Exciton–Photon Coupling with Colloidal Nanoplatelets in an Open Microcavity

Colloidal semiconductor nanoplatelets exhibit quantum size effects due to their thickness of only a few monolayers, together with strong optical band-edge transitions facilitated by large lateral extensions. In this article, we demonstrate room temperature strong coupling of the light and heavy hole exciton transitions of CdSe nanoplatelets with the photonic modes of an open planar microcavity. Vacuum Rabi splittings of 66 ± 1 meV and 58 ± 1 meV are observed for the heavy and light hole excitons, respectively, together with a polariton-mediated hybridization of both transitions. By measuring the concentration of platelets in the film, we compute the transition dipole moment of a nanoplatelet exciton to be μ = (575 ± 110) D. The large oscillator strength and fluorescence quantum yield of semiconductor nanoplatelets provide a perspective toward novel photonic devices by combining polaritonic and spinoptronic effects.

Fabrication of Electrochemical Biosensor for Cholesterol Using CNT-Gold Nanohybrid Buckypaper

An electrochemical biosensor for cholesterol has been developed based on carbon nanaotube and gold nanoparticle hybrid materials. A free standing buckypaper electrode composed of functionalized multiwallled carbon nanotubes (MWCNT) and gold nanoparticles (AuNP) has been used as electrode in an electrochemical biosensor for cholesterol. Carbon nanotubes (CNTs) have been recognized as one of the most promising electrode materials[1,2] due to their high chemical stability, good electrical conductivity, and tubular structure . On the other hand gold nanoparticles exhibit quantum size effects leading to unique optical, electronic and catalytic properties. AuNPs enhance the electrode conductivity and facilitate the electron transfer, thus improving the analytical sensitivity and selectivity[3]. Due to their compatibility with biolmoecules gold nanoparticles are widely used in medical diagnosis area. The combination of AuNPs and CNTs creates a new nanohybrid material with the integrated properties of the two components. This nanohybrid material can offer new opportunities for the development of biosensors with high analytical performance. In this work we have created a thin sheet of nanohybrid material, commonly known as buckypaper( thickness~50-60micron). Buckyppaer shows better electrochemical signal [4] compared to the dispersion formed by MWCNT and gold nanoparticles. We have reported that work earlier [4]with respect to several biomolecules such as tyrosine, tryptophan, myoglobin and glucose[5]. Due to the enhanced surface area, engineered CNT buckyppaer shows much enhanced signal and higher sensitivity. For this cholesterol biosensor, Cholesterol oxidase has been immobized on AuNP modified buckypaper. In addition to that buckypaper with carboxyl functionality was also modified by 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide, (EDC) and N-hydroxy succinimide(NHS) and after this activation cholesterol oxidase was immobilized. These two series of Buckypaers were used as electrodes. biosensor. Cholesterol was dissolved in 10mM tritobn X and different solution of cholesterol were made using 0.1 M phosphate buffer solution. Cyclic voltametry, amperometry and differential pulse voltammetry techniques wesr used to study the electrochemical behavior of this biosensor and to determine the sensitivity. Above figures show DPV results and the calibration plot obtained for cholesterol solution concentration ranging from from 0.2-1mM/L using AuNP –MWCNT hybrid buckypaper/. A detection limit obtained was 3 mmole/L which is higher than many reported biosensors based on other CNT dispersion based biosensors.

Characterization of early growth stages of Pb/Ge(001)

Early stages of thin Pb film growth on Ge(001) substrate, exhibiting quantum size effects (QSE), are characterized by means of Photoelectron Diffraction and Helium Atom Scattering. Pb is found to form a commensurate first monolayer, while an ordered layer-by-layer growth only sets in after deposition of 4 monolayers. In the intermediate coverage range no long range order of the overlayer is established and we find that uncorrelated islands of preferred four-layer thickness are formed. Continuous Pb film with long range order emerges through islands coalescence close to a coverage of 4 monolayers, upon which a more regular layer-by-layer growth mode sets in.

Electron exchange between an H − ion and a spherical cluster of aluminum atoms

The resonant charge transfer (RCT) between a hydrogen anion and a cluster of aluminum atoms is investigated by means of the wave-packet propagation method that does not exploit the perturbation theory. The RCT on a spherical cluster is found to exhibit quantum size effects due to the finite size of the cluster. The survival amplitude of an ion state has been calculated as a function of the distance to the ion-surface in a normal collision. It is shown that depending on the velocity of the impinging particle, the cluster can behave either as a bulk metal or as a quantum structure with discrete energy states existing over two coordinates.

A facile single-source route to CdS nanorods

CdS nanorods were synthesized on a large scale by thermolyzing a single-source precursor,(Me4N)4[S4Cd10(SPh)16], in a single surfactant system. Transmission electron microscopy (TEM), high resolutiontransmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD) have beenused to characterize the morphology and crystal structure of the sample. TheTEM images show that the CdS nanorods are uniform with an aspect ratio ofabout 9:1. The XRD result demonstrates that the nanorods are in a wurtzitestructure. The nanorods exhibit quantum size effects from the optical absorptionspectrum. The influence of reaction conditions on the growth of CdS nanorodsdemonstrates that high precursor concentration and high reaction temperature(>190 °C) are favorable for the formation of CdS nanorods.

Investigation of the effect of temperature on growth mechanism of nanocrystalline ZnS thin films

In this paper the temperature effect on the growth mechanism of ZnS thin films prepared in a chemical bath containing zinc acetate, ethylenediamine, and thioacetamide aqueous solutions has been studied in the temperature range between 25 and 75 °C. These ZnS thin films possess a nanocrystalline structure, exhibit quantum size effects due to the small crystal size and produce a blue shift in the optical spectra. This blue shift was attributed to a decrease in crystal size by using X-ray diffraction and scanning electron microscopy. The growth mechanism of the thin films is suggested to proceed by two fundamental steps: in the first step, the ZnS nanocrystallites coalesce into small grains through homogeneous nucleation in the solution phase. In the second step, eventually, these small grains or large-sized clusters diffuse and stick to the surface of the substrate to form the ZnS thin film, in a way called a cluster-by-cluster manner, resulting in particulate thin film.

Quantum size effect in the electron exchange between aH−ion and a thin metal disk

The resonant charge transfer (RCT) between a hydrogen anion and a thin aluminum disk is investigated by means of the wave-packet propagation method that does not exploit the perturbation theory. The RCT on a thin metal disk is found to exhibit quantum size effects due to the finite size of the disk. Survival amplitude of ion state has been calculated as a function of the distance to the ion-surface in a normal collision. It is shown that depending on the projectile velocity, the ion can interact with disk as if with bulk metal, thin film or nano-structure with the energy quantized by polar and normal coordinates.

Evidence for intergranular tunnelling in polyaniline passivatedα-Fe nanoparticles

Nanoparticles are of immense importance both from the fundamental and applicationpoints of view. They exhibit quantum size effects which are manifested in their improvedmagnetic and electric properties. Mechanical attrition by high energy ball milling(HEBM) is a top down process for producing fine particles. However, finenessis associated with high surface area and hence is prone to oxidation which hasa detrimental effect on the useful properties of these materials. Passivation ofnanoparticles is known to inhibit surface oxidation. At the same time, coating polymerfilm on inorganic materials modifies the surface properties drastically. In thiswork a modified set-up consisting of an RF plasma polymerization technique isemployed to coat a thin layer of a polymer film on Fe nanoparticles producedby HEBM. Ball-milled particles having different particle size ranges are coatedwith polyaniline. Their electrical properties are investigated by measuring the dcconductivity in the temperature range 10–300 K. The low temperature dc conductivity(I–V) exhibited nonlinearity. This nonlinearity observed is explained on the basis of the criticalpath model. There is clear-cut evidence for the occurrence of intergranular tunnelling. Theresults are presented here in this paper.

Synthesis and Photophysical Properties of CuS Nanoparticles Stabilized by Sodium Polyphosphate

We have synthesized nanosized colloidal CuS particles which exhibit quantum size effects. Using an indirect synthesis of CuS from CdS nanoparticles of known average size, we have determined the dependence of the width of the forbidden band (the gap) of the CuS nanoparticles on their size. We have studied the effect of the CuS colloid synthesis conditions on their spectral characteristics.

Effect of the oxidation process on the luminescence of HF-treated porous silicon

Abstract Porous silicon (PS) films were prepared by lateral anodization of crystalline silicon in HF based solutions at different current densities. The oxidation mechanism of the HF-treated PS films has been monitored by means of photoluminescence (PL) and Fourier transform infra-red vibrational studies. HF treatment of PS films for a short duration of ∼10 s resulted in the increment of polysilane/hydride species on the surface of PS rather than any change in the dimensions of the silicon-crystallites. It has been found that HF-treated PS surfaces are relatively stable against oxidation as compared to untreated PS films. Upon oxidation of the HF-treated PS films, the PL intensity initially increases as a result of reduction in crystallite size to exhibit quantum size effects and then decreases owing to loss of luminescing structures due to over-oxidation of the Si-columns. We infer that the surface passivation either by hydrogen or oxygen is one of the requisite conditions for obtaining strong PL efficiency in PS. It seems that more than one emission mechanisms are responsible to explain the luminescence properties of PS.

X-Ray Diffuse Scattering on Self-Organized Mesoscopic Structures

We highlight the great potential of x-ray diffuse scattering for the characterization of mesoscopic structures. The mesoscopic length scale plays a fundamental role at semiconductors, since structures with spatial dimensions in the nanometer regime exhibit quantum size effects. Also the driving forces during epitaxial growth of these structures are most relevant at mesoscopic length scales and they may lead to self-organization processes in that structures can form spontaneously during epitaxial growth. One of the most interesting features are quantum dots (QDs) since they exhibit zero-dimensional electronic properties and thus show an impressive potential for applications in optoelectronic devices. X-ray diffuse scattering is an excellent tool to investigate shape, size, and positional correlation and to characterize the strain field inside and in the vicinity of such self-organized mesoscopic structures. It provides non-destructive structural information over the entire mesoscopic length scale. X-ray scattering is complementary to direct imaging techniques in that it gives a statistical average over large ensembles with high strain sensitivity. The application of different scattering techniques for the structural characterization of mesoscopic structures will be demonstrated. For the example of SiGe islands on Si (001) substrate it will be shown that x-ray diffuse scattering is able to reveal details of germanium distribution in such islands. In a second example the investigation of the asymmetric shape and size of InP QDs that are grown on (001) In0.48Ga0.52 P/GaAs is described. The influence of positional correlation on the diffuse scattering will be discussed.

Quantum size effect in the resonant electron transfer between an ion and a thin metal film

The resonant charge transfer (RCT) process between an ${\mathrm{H}}^{\ensuremath{-}}$ ion and a thin Al film is studied using a wave-packet propagation method. Both the static situation, with a fixed ion surface distance, and the dynamical situation, with a moving ion, are investigated. The RCT on a thin metal film is found to exhibit quantum size effects due to the finite thickness of the film. The way the case of the semi-infinite metal is recovered for thick films is discussed in detail. The conditions for observing quantum size effects in the RCT process are defined and discussed in terms of the various characteristic times of the system. In particular, it is shown that the quantum size effects disappear in the case of fast collisions, where the RCT on a thin metal film becomes basically identical to that on a semi-infinite metal surface.

Use of Dialkyldithiocarbamato Complexes of Bismuth(III) for the Preparation of Nano- and Microsized Bi2S3 Particles and the X-ray Crystal Structures of [Bi{S2CN(CH3)(C6H13)}3] and [Bi{S2CN(CH3)(C6H13)}3(C12H8N2)

A range of bismuth(III) dithiocarbamato complexes were prepared and characterized. The X-ray crystal structures of the compounds [Bi{S2CN(CH3)(C6H13)}3] (1) and [Bi{S2CN(CH3)(C6H13)}3(C12H8N2)] (2) are reported. The preparation of Bi2S3 particulates using a wet chemical method and involving the thermalysis of Bi(III) dialkyldithiocarbamato complexes is described. The influence of several experimental parameters on the optical and morphological properties of the Bi2S3 powders was investigated. Nanosized Bi2S3 colloids were obtained having long-term stability and showing a blue shift on the optical band edge; the presence of particles exhibiting quantum size effects is discussed. Morphological well-defined Bi2S3 particles were obtained in which the fiber-type morphology is prevalent.

Dependence of Elastic Properties on Morphology in Single-Wall Carbon Nanotubes

Small-diameter nanotubes are predicted to exhibit quantum size effects involving an interdependence between the diameter of the nanotubes and their electronic and magnetic properties. These authors ask whether this dependence on diameter might be extended to the mechanical properties of single-wall carbon nanotubes (SWNTs). Results were obtained by inducing a compressive deformation in SWNTs embedded in a polymer matrix by cooling the specimen to 81 K and monitoring the deformation via the Raman D* band frequency shift of the embedded nanotubes.

Epitaxial Growth of Two-Dimensional Dichalcogenides and Modification of Their Surfaces with Scanning Probe Microscopes

ABSTRACTMethods for epitaxial growth of two dimensional materials are described. The lack of interlayer bonding in these materials allows for epitaxial growth with large lattice mismatches. Growth of MoSe2 on MoS2 (a 5% mismatch) or on SnS2 (10% mismatch) can be demonstrated. Scanning tunneling microscopy (STM) revealed remarkable structures in the epilayer as a result of the large mismatches. A technique using the STM or atomic force microscope (AFM) to selectively remove single molecular layers from the surface of layered materials is also described. The combination of these two technologies may result in the ability to produce nanoscale devices exhibiting quantum size effects.

Thermo-electric properties of quantum point contacts

The conductance, the thermal conductance, the thermopower and the Peltier coefficient of a quantum point contact all exhibit quantum size effects. The authors review and extend the theory of these effects. In addition, they review their experimental work on the quantum oscillations in the thermopower, observed using a current heating technique. New data are presented showing evidence for quantum steps in the thermal conductance, and (less unequivocally) for quantum oscillations in the Peltier coefficient. For these new experiments the authors have used a quantum point contact as a miniature thermometer.

Continuous-wave lasing (300 K) in an active layer of zinc telluride exhibiting quantum size effects

A source of coherent radiation was made from a superlattice structure with a perfect interface. The structure was made from the same material (ZnTe), but use was made of two different crystallographic modifications: sphalerite and wurtzite.