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ErAsSb nanoparticle (NP) growth is investigated on GaAs surface by molecular beam epitaxy. ErAsSb NP grown under Sb flux is compared to pure ErAs NP grown under As flux. It is found the incorporation of Sb is rather low in ErAsSb. However, ErAsSb NP exhibits very different structural and optical properties. ErAsSb NPs on GaAs preferentially elongates along the [1–10] direction with increasing deposition and growth temperature. The absorption peak for light polarized parallel to the long axis of the particles is found to occur at longer wavelengths than those for light polarized perpendicular to the long axis of the particles. The results can be attributed to Sb surfactant effect.

ErAs metal nanoparticles (NPs) embedded in GaAs have multiple applications in plasmonic, terahertz, and tunneling devices. Growing a high quality thin GaAs layer over the ErAs NP layer is vital to these applications. In this work, the authors study the surface stability of a thin GaAs cap (1–5 nm) annealed in a temperature range of 450–620 °C. The thin GaAs cap covered a single layer of ErAs NPs [0.5–1.33 monolayer (ML)] grown using molecular beam epitaxy on GaAs(001) substrates at 450–500 °C. For 1.33 ML ErAs coverage, although a 1 nm GaAs cap exhibited a root-mean-square surface roughness close to 0.3 nm, the authors expected that 1 nm GaAs was not thick enough to overgrow the NPs in a height of 3–4 nm; thus, a large number of pinholes should be left on the surface. By increasing the GaAs cap thickness to 3 nm, the authors were able to achieve atomically smooth surfaces with few remaining pinholes. At a lower coverage of ErAs, 0.5 ML, the authors were able to achieve atomically flat pinhole-free GaAs ca...

In their rocksalt structure, rare-earth monosulfides offer a more stable alternative to alkali metals to attain low or negative electron affinity when deposited on various III-V and II-VI semiconductor surfaces. In this article, we first describe the successful deposition of Lanthanum Monosulfide via pulsed laser deposition on Si and MgO substrates and alumina templates. These thin films have been characterized by X-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy, ellipsometry, Raman spectroscopy, ultraviolet photoelectron spectroscopy and Kelvin probe measurements. For both LaS/Si and LaS/MgO thin films, the effective work function of the submicron thick thin films was determined to be about 1 eV from field emission measurements using the Scanning Anode Field Emission Microscopy technique. The physical reasons for these highly desirable low work function properties were explained using a patchwork field emission model of the emitting surface. In this model, nanocrystals of low work function materials having a orientation perpendicular to the surface and outcropping it are surrounded by a matrix of amorphous materials with higher work function. To date, LaS thin films have been used successfully as cold cathode emitters with measured emitted current densities as high as 50 A/cm2. Finally, we describe the successful growth of LaS thin films on InP substrates and, more recently, the production of LaS nanoballs and nanoclusters using Pulsed Laser Ablation.

In this chapter we describe silica precipitation using unmodified synthetic R5 polypeptide—a nineteen amino acid sequence corresponding to the homologous repeating sequence in silaffin-1A protein extracted from diatom C. fusiformis. The particle formation was investigated using modern materials characterization methods, namely AFM, SEM and EDS. It was found that silica particles of sizes ∼150–200 nm were produced and that they formed aggregates. Furthermore, we propose that the R5 polypeptide self-organizes in solution and catalyzes and scaffolds the silica formation in vitro. We believe that silaffin proteins and other proteins facilitating silica formation in vivo behave in a similar fashion and this may provide insights into the role of proteins in biosilicification.

Lanthanum monosulfide (LaS) films were grown by pulsed laser deposition on the (100) magnesium oxide (MgO) substrates at an elevated substrate temperature and in a background gas of H2S. The thin films have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), and high resolution transmission electron microscopy. The film surface is composed of grainlike features with an average size of approximately 34nm. The root-mean-square variation of the film surface roughness measured over a 2×2μm2 area by AFM was found to be approximately 1.5nm. XRD data indicate that the average size of the nanocrystalline grains in the film is about 26nm, which is about twice the size of the grains found in LaS thin films deposited at room temperature on Si. The field emission (FE) properties of the films have been characterized by scanning anode field emission microscopy and are interpreted in terms of a recently developed patchwork FE model. The FE data indicate that there is roughly a seven times incre...

Three distinct types of nanostructures—nanodomes, nanodots, and nanowires—have been simultaneously self-assembled by pulsed laser deposition of lanthanum monosulfide on anodic alumina films containing hexagonal arrays of pores about 50nm wide and 500nm deep. The nanostructures have been characterized by x-ray diffraction, atomic force microscopy (AFM), and field emission scanning electron microscopy (FE-SEM). Nanodomes preferentially grow on the boundary separating regions (grains) of the alumina template that have near perfect pore ordering, and their density is ∼109∕cm2. The diameter of a nanodome at the base is about 100nm and their aspect ratio (height/diameter at the base) is between 1 and 3. Additionally, nanodots nucleate on top of the alumina walls that separate adjacent pores. They have a diameter of ∼50nm, a density equal to the pore density (1010∕cm2), and an aspect ratio less than 1. Finally, cross sectional FE-SEM images of the templates indicate that LaS nanowires grow inside the pores with ...

In this work and with a view to optimizing their FE properties, LaS films of increased crystallinity were obtained by PLD on lattice matched MgO substrates, at elevated substrate temperatures and in a background gas of H2S. The thin films have been characterized by high resolution transmission electron microscopy, atomic force microscopy (AFM), X-ray diffraction, ellipsometry and Raman spectroscopy. The FE properties of the films have been characterized by scanning anode field emission microscopy., 20th International Vacuum Nanoelectronics Conference

Successful growth of lanthanum monosulfide (LaS) nanodot and nanowire arrays has been performed by pulsed laser deposition (PLD) using self-assembled nanoporous alumina templates containing pores about 50 nm wide and 200-300 nm deep. The arrays were characterized by X-ray diffraction, atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and scanning anode field emission microscopy (SAFEM). The array of LaS nanodots grows selectively at boundaries between different regions of the alumina film with local hexagonal symmetry of pores. The density of these dots is about 109 /cm2. Cross sectional FE-SEM showed that LaS nanowires also grow inside the pores with a density of 1010/cm2 , which is equal to the pore density of the templates. The field emission properties of the LaS nanodots grown on top of the alumina templates were measured using SAFEM. A typical current-voltage characteristic is shown. Using the conventional Fowler-Nordheim relation, the work function of the LaS nanodots has been extracted from the slope of the plot ln(J/F2) vs 1/F, where J is the field emission current density and F is the local applied field. This leads to an outstanding, reproducible effective work function value of ~1 eV for the LaS nanodots. The threshold for an emission current density of 1 mA/cm2 occurs around a 150 V/mum which is considerably lower than the 230 V/mum threshold value reported recently for LaS thin films., 19th International Vacuum Nanoelectronics Conference and 50th International Field Emission Symposium, 2006

The effect of interface anisotropy on the electronic structure of InAs/GaSb type-II superlattices is exploited in the design of thin-layer superlattices for mid-IR detection threshold. The design is based on a theoretical envelope function model that incorporates the change of anion and cation species across InAs/GaSb interfaces, in particular, across the preferred InSb interface. The model predicts that a given threshold can be reached for a range of superlattice periods with InAs and GaSb layers as thin as a few monolayers. Although the oscillator strengths are predicted to be larger for thinner period superlattices, the absorption coefficients are comparable because of the compensating effect of larger band widths. However, larger intervalence band separations for thinner-period samples should lead to longer minority electron Auger lifetimes and higher operating temperatures in p-type SLs. In addition, the hole masses for thinner-period samples are on the order the free-electron mass rather than being effectively infinite for the wider period samples. Therefore, holes should also contribute to photoresponse. A number of superlattices with periods ranging from 50.6 to 21.2 Å for the 4 μm detection threshold were grown by molecular beam epitaxy based on the model design. Low temperature photoluminescence and photoresponse spectra confirmed that the superlattice band gaps remained constant at 330 meV although the period changed by the factor of 2.5. Overall, the present study points to the importance of interfaces as a tool in the design and growth of thin superlattices for mid-IR detectors for room temperature operation.

The authors report growth studies to develop an InAs/GaInSb superlattice (SL) material for very long wavelength infrared detection. They select a SL structure of 47.0 A InAs/21.5 A Ga0.75In0.25Sb that is designed for the greatest possible detectivity, and tune growth conditions to achieve the best quality ternary material. Since the material quality of grown layers is particularly sensitive to extrinsic defects such as nonradiative recombination centers generated during the growth process, the authors investigate the effect of the growth temperature (Tg) on the spectral photoresponse (PR) and carrier recombination lifetime using photoconductivity and time-resolved differential reflectivity measurements. Results indicate that a molecular beam epitaxy growth process the authors developed produces a consistent energy gap around 50 meV, determined from the PR spectra, but the intensity of the spectra is sensitive to Tg. For SLs grown at Tg between 390 and 470 °C, the PR signal intensity gradually increases as...

Metal nanoparticles coupled to semiconductor quantum dots have been studied recently due to the enhancement in absorption, emission, and nonlinearities expected from these hybrid structures. These properties stem from the ability of the metal to focus light as well as shift the phase, which occurs at the metal–dielectric interface. To date, most quantum dots metal nanoparticle couples are formed by the attachment of a ligand to both particles. The extension of this idea to bulk semiconductor films is being attempted by the formation of a composite structure of ErAs, which forms semimetallic nanoparticles (SMNP) in GaAs, and InAs self-assembled quantum dots (SAQD). In this work, the authors analyze structures composed of periods of InAs SAQDs and ErAs SMNPs and analyze these with spectroscopic ellipsometry in the spectral region 0.7–4.0 eV with 0.02 eV steps. Initially, individual structures composed of InAs SAQD stacks or ErAs SMNP stacks, both capped with layers of GaAs, are analyzed. The authors have al...

Two types of nanoscale field emitter arrays have been self-assembled using either flexible alumina templates containing hexagonal close packed pores that are 50nm wide and 500nm long or nanoporous Si templates. The first type is an array of gold “nanopinetrees” obtained by e-beam evaporation of a few nanometers of gold on bare alumina templates. The second type is a nickel “nanoblade” array formed by e-beam evaporation of a few nanometers of nickel on nanoporous Si templates. The field emission characteristics of both mesoscopic structures were measured using a scanning field emission microscope, and results were analyzed in terms of the cathode material emission. This synthetic approach for producing nanoscale field emitters could lead to a versatile and inexpensive technology for synthesizing flexible arrays of nanoscale cold cathode emitters.