High-quality epitaxial silicon thin films have been deposited by plasma-enhanced chemical vapor deposition (PECVD) at 200 °C in a standard radiofrequency (RF) PECVD reactor. We optimized a silicon tetrafluoride (SiF4) plasma to clean the surface of <100> crystalline silicon wafers and without breaking vacuum, an epitaxial silicon film was grown from SiF4, hydrogen (H2), and argon (Ar) gas mixtures. We demonstrate that the H2/SiF4 flow rate ratio is a key parameter to grow high-quality epitaxial silicon films. Moreover, by changing this ratio, we can fine-tune the composition of the interface between the crystalline silicon (c-Si) wafer and the epitaxial film. In this way, at low values of the H2/SiF4 flow rate ratio, an abrupt interface is achieved. On the contrary, by increasing this ratio we can obtain a porous and fragile interface layer, composed of hydrogen-rich microcavities, which allows the transfer of the epitaxial film to foreign substrates.

“Nanostructured” germanium (Ge; also known as “voided,” “porous,” “nanoporous,” “cratered,” and “honeycomb” Ge) created via ion beam modification has been studied for many years. This work reviews the progress made in studying and characterizing the nanostructured morphology, particularly via the use of experimental techniques such as scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Specifically, the empirical observations of the structural evolution of Ge as a function of ion beam modification conditions are discussed with added emphasis placed on quantification of the microstructure. The experimental observations and microstructure quantification are further discussed in terms of the implications for proposed formation mechanisms of the nanostructured morphology. Potential uses of the nanostructured morphology in chemical sensor and energy storage applications and suggested future lines of research to further the fundamental understanding of nanostructuring in Ge using ion beam modification are also presented.

Semicoherent interfaces containing discrete dislocations are more energetically favorable than those containing continuous distributions because of lower chemical energy. The classical Frank-Bilby theory provided a way to determine the interface Burgers vectors content but could not effectively predict the characteristics of discrete dislocations. Atomistic simulations provide insights into analyzing the characteristics of discrete dislocations but the analysis is often disturbed by the reaction of interface dislocations. By combining the classical Frank-Bilby theory and atomistic simulations, an atomically informed Frank-Bilby theory proposed in this work can overcome shortcomings in both the classic Frank-Bilby theory and atomistic simulations, and enable quantitative analysis of interface dislocations. The proposed method has been demonstrated via studying two typical dissimilar metallic interfaces. The results showed that Burgers vectors of interface dislocations can be well defined in a Commensurate/Coherent Dichromatic Pattern (CDP) and the Rotation CDP (RCDP) lattices. Most importantly, the CDP and RCDP lattices are not simply a geometric average of the two natural lattices, that is the lattice misfit and the relative twist take the nonequal partition of the misfit strain and the twist angle.

Bismuth silicate with two morphologies (nanoflowers/nanoplates) was successfully fabricated with silica aerogels via a hydrothermal method in polyvinylpyrrolidone (PVP)-mediated processes for the first time. The obtained nanomaterials were characterized using x-ray powder diffraction, scanning electron microscopy, the Brunauer–Emmett–Teller (BET) surface area analysis, and UV-vis diffuse reflectance spectroscopy. It was found that the concentration of PVP plays an important role in the formation of the hierarchical nanoflowers. The formation mechanism for this novel morphology was proposed on the basis of experimental results. Moreover, the photocatalytic performances of Bi2SiO5 nanoflowers/nanoplates were also investigated. The results revealed that Bi2SiO5 nanoflowers exhibited higher activity than Bi2SiO5 nanoplates due to its suitable morphology, higher BET surface area.

We have investigated the formation of the rutile and the anatase polymorphs of TiO2, with emphasis on epitaxial growth characteristics, and defect content as a function of laser and substrate variables. X-ray diffraction (XRD) studies revealed that the rutile phase is more stable at higher substrate temperatures and lower oxygen pressures; in contrast, decreasing the temperature and increasing the oxygen pressure gave rise to formation of anatase. Epitaxial rutile films with a <100] orientation were obtained at 450 °C using the pressure of 5 × 10−4 Torr, and laser energy of 3.5–4.0 J/cm2. The epitaxial relationship, determined by 2θ−θ and φ scan of XRD and confirmed by transmission electron microscopy (TEM) diffraction patterns, was shown to be rutile(100)||sapphire(0001), rutile[001]||sapphire[10$\bar 1$0] and rutile[010]||sapphire[1$\bar 2$10]. An atomically sharp interface between the rutile epitaxial film and the sapphire substrate was observed in the scanning transmission electron microscopy (STEM) images. The films exhibited a transmittance of 75–90% over the visible region. The absorption edge was observed to shift toward longer wave lengths at higher deposition temperatures or lower pressures. X-ray photoelectron spectroscopy and photoluminescence results showed that concentration of lattice point defects, namely oxygen vacancies and titanium interstitials, increased at lower oxygen pressures. Formation of nanostructured films with a surface roughness of -1.5–13.1 nm was confirmed by atomic force microscopy investigations.

Textured epitaxial HfO2 thin films of monoclinic structure were grown on r-cut Al2O3 by atomic layer deposition from HfCl4 and H2O at temperatures 450–750 °C. The film-to-substrate out-of-plane orientation was determined to have a single (001)HfO2//(1$\bar 1$02)α-Al2O3 relationship. The in-plane orientation showed the existence of two possible relationships: [100]HfO2//[110]α-Al2O3 and [$\bar 1$00]HfO2//[110]α-Al2O3. In films deposited at 400 °C traces of (010) growth plane were observed in addition to the preferential (001) growth. The lattice of HfO2 was compressed in the surface plane and expanded in the surface normal direction. The strain was highest in the films grown at 450–550 °C. With the increase of deposition temperature to 750 °C, the strain decreased. The strain relaxation in films deposited at 750 °C was in correlation with marked surface roughening in the initial stage of deposition at this temperature. The roughness of the epitaxial films was lower than that of polycrystalline films with comparable thickness deposited on Si(100) and SiO2 substrates.

Buffer leakage in aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure transistors is recognized as an issue that has deleterious consequences on device performance for high-power, high-frequency transistors and has been related to the presence of uncharged threading screw dislocations. In this study, we demonstrate that measurements of buffer leakage in AlGaN/GaN heterostructures grown on bulk gallium nitride (GaN) substrates are consistent with a mechanism based on the concept of dislocations acting as quantum wires in series with unintentional silicon (Si) impurity incorporation at the bulk GaN substrate/GaN buffer interface. The number of electronic channels N deduced from the leakage data using Landauer’s formula for the quantum resistance of N electronic channels is consistent with the number of dislocations along the ohmic contact pads determined from panchromatic cathodoluminescence and x-ray diffraction measurements of the dislocation density. This mechanism is consistent with Shockley’s suggestion that dislocations can act as one-dimensional conductors due to the presence of edge states along the dislocation core.

To explore the relationships between microstructure and growth direction, metallic A-type antiferromagnetic and anisotropic magnetoresistant Nd0.45Sr0.55MnO3 (NSMO) thin films were grown on SrTiO3(110) by pulsed laser deposition method and characterized by (scanning) transmission electron microscopy. The interface between NSMO and SrTiO3 (110) is flat and sharp. The NSMO thin films exhibit a two-layered structure: a continuous perovskite layer epitaxially grown on the substrate followed by an epitaxially grown columnar nanostructure [Fig. 1(a)]. High-density stacking faults were found in the nanostructured layer with an in-plane translational displacement of 1/2a<111>, accompanied by 1/2a[001] partial dislocations or (110) antiphase boundaries (APBs). These stacking faults terminate either at pores or in the grain matrix to eliminate (1$\bar 1$0) APBs. The formation mechanisms of the nanostructured NSMO films and the relevant stacking faults are discussed from the viewpoint of both film growth and specific substrate direction.

In this study, we are reporting the time- and temperature-dependence of the electrical resistivity and temperature-dependence of the Hall voltage in neodymium nickelate thin films. The films were deposited on a lanthanum aluminate substrate [LaAlO3 (001)] by a pulsed laser deposition technique, with thicknesses ranging from 0.6 to 120 nm. Time-dependent electrical transport measurements indicated the formation of a kinetically stable metallic glassy phase rather than a stable insulating phase on cooling below the transition temperature, TM-I. Comparisons of the low-temperature behavior with that of common insulators further supported this claim. Hall effect measurements on the 1.2-nm sample showed a local maximum in the carrier concentration just below the TM-I on both the heating and cooling cycles. This again confirmed the proposed low-temperature structure, in that, for the 1.2-nm sample, there was a minimal degree of supercooling before transitioning to a kinetically stable glassy phase.

The effects of boundaries such as grain boundaries and phase boundaries on low-field magnetoresistance (LFMR) have been investigated in single-phase lanthanum strontium manganates, in this case La0.7Sr0.3MnO3 (LSMO) and LSMO: zinc oxide (ZnO) nanocomposite thin films. In the pure LSMO films with similar grain size, it is found that the LFMR increases as the grain misorientation factor (β) increases. The LFMR in the nanocomposite films is greatly enhanced, as compared with single-phase films, due to the reduced grain size, and increased phase boundary (PB) and β effects. The composition study shows that the LFMR can be dramatically enhanced when the secondary phase content approaches the percolation threshold. The increased β and secondary phase concentration reduce the cross-section of electron conduction paths and favor the formation of the quasi-one-dimensional transport channels. Our results demonstrate that the reduction of cross-section of the electron conduction paths by tuning the grain orientation and secondary phase composition is necessary for enhancing LFMR effect.

Ultrathin metal film dewetting continues to grow in interest as a simple means to make nanostructures with well-defined properties. Here, we explored the quantitative thickness-dependent dewetting behavior of Au films under nanosecond (ns) pulsed laser melting on glass substrates. The trend in particle spacing and diameter in the thickness range of 3–16 nm was consistent with predictions of the classical spinodal dewetting theory. The early stage dewetting morphology of Au changed from bicontinuous-type to hole-like at a thickness between 8.5 and 10 nm, and computational modeling of nonlinear dewetting dynamics also captured the bicontinuous morphology and its evolution quite well. The thermal gradient forces were found to be significantly weaker than dispersive forces in Au due to its large effective Hamaker coefficient. This also resulted in Au dewetting length scales being significantly smaller than those of other metals such as Ag and Co.

A special type of epitaxial growth appears during solid-phase thin film reactions, where the reaction product grows epitaxially on the substrate. Some metal silicide layers and nanostructures are known to develop such epitaxial structures. In this study, iron silicide was used to study the effect of the growth mode on the epitaxial growth. Strain-induced, self-assembled iron silicide nanostructures were grown on Si(001) substrates by electron gun evaporation of 1.0 nm iron and subsequent annealing at 500–850 °C for 60 min. The growth processes were checked by reflection high-energy electron diffraction, and the formed structures were characterized by scanning electron microscopy and optical microscopy. The iron silicide nanostructures were oriented in square directions epitaxially fitting to the surface of Si(001). The shape and size of the nanostructures depended on the annealing temperature. In some cases, the nanoparticles were arranged in circles. This might be the direct consequence of a nucleation-controlled type transition of iron monosilicide to iron disilicide phase at nanoscale.

Sputter-deposited epitaxial (111) and (110) Ag films have high-density nanotwins with respective twin boundary orientations perpendicular and angled to the growth direction. Twin density in as-deposited (111) Ag films is much greater than in (110) films, leading to higher hardness in the (111) films. Annealing up to 800 °C (homologous temperature of 0.85 Tm) leads to increased twin thickness, although the average twin thickness remains <100 nm in both systems. Twinned volume fraction falls dramatically in annealed (110) films but remains constant at ∼50% in (111) films. The mechanisms leading to the elimination of nanotwins in (110) films and their remarkable stability in (111) films at elevated temperatures are discussed. Coarsening and elimination of twins result in hardness reduction after annealing. The variety of microstructures achieved via annealing allows for the introduction of a strengthening model considering both twin and grain boundaries.

Copper (I) oxide (Cu2O) is a direct band gap semiconductor with p-type conductivity and is a potential candidate for multi-junction solar cells. In this work, incoherent light source based photo-assisted metal-organic chemical vapor deposition (MOCVD) was used to deposit high quality Cu2O thin films on n-type <100> silicon and quartz substrates. X-ray diffraction studies reveal that crystalline Cu2O is deposited. UV-Vis-NIR spectroscopy results indicated a band gap of 2.44 eV for Cu2O thin films. Transmission electron spectroscopy results show that the Cu2O film grows in the form of three-dimensional islands composed of smaller nanocrystalline grains in the range of 10–20 nm. I–V measurements indicate that the Cu2O/n-Si device fabricated using the MOCVD process has a lower dark current density than other devices reported in the literature.

A CO2-pulsed laser plasma deposition (CO2-PLD) system is installed and used for the quick synthesis of various hexagonal boron nitride (h-BN) and zinc oxide (ZnO) nanostructures. Each part of the CO2-PLD system, such as focusing of laser beam on the target surface, sample holder, shutter, heater, type of the gas, and gas flow rate, can be easily controlled independently to fit different experimental conditions. After installation of the system, a series of experiments were conducted using hBN and ZnO targets. Scanning electron microscopy images showed that the entire surface (2 × 2 cm2) of the substrate is covered with the conical- and disk-shaped BN nanostructures and web-like highly dense ZnO nanowires, indicating a significantly short-time approach to grow mass product nanostructures. Raman spectroscopy identified the hexagonal structure of the synthesized samples.

Zinc oxide (ZnO)–single-walled carbon nanotubes (SWCNTs) nanocomposite thin films have been grown by chemical bath deposition method. The changes in structural and chemical properties were studied by means of x-ray diffraction, field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The average crystallite size of ZnO doped with 0.1 and 0.5 wt% SWCNTs was measured about 14.69 and 17.76 nm, respectively. Texture coefficient of the carbon peak (002) was investigated as more than 3.2995 for ZnO mixed with 0.5 wt% SWCNTs. SEM images revealed the ZnO and SWCNTs entangled between the particles. TEM images estimated the inner and outer diameters of SWCNTs to be about 4.86 and 11.32 nm, respectively. FTIR analysis proved the formation of Zn–O and C bonding in the thin films. The performance of the dye-sensitized solar cells (DSSCs) was found to depend on the loading of SWCNTs. The power conversion efficiency increased from 0.078 to 0.684% after loading with 0.1 wt% SWCNTs. Higher amount of SWCNTs (0.5 wt%) was determined as ineffective in improving the performance of ZnO-based DSSCs.

Self-assembled nanostructures often exhibit unique properties that are distinct from those of bulk materials. During the past decade, significant progress has been made in the assembly of nanorods and understanding some of the self-directing assembly mechanisms, particularly related to gold nanorods. Nonetheless, methods that can be scaled up to large areas for device-scale applications are yet to be established. This review describes various routes that are being actively pursued to achieve assembly of nanorods. Self-assembly methods that utilize external forces such as electric field or gravitational forces are reviewed. Additionally, self-assembly schemes using chemical and biomolecule linkers are presented. Other important routes, such as template assisted assembly, Langmuir-Blodgett, and nanorod assembly methods carried out in solution phase are also discussed. The latter includes recently reported approaches to produce superstructured particles through self-assembly. Solvent evaporation and drying can also strongly contribute to the assembly of nanostructures. The final section presents self-assembly routes that primarily exploit the drying kinetics of solvents.

A nanocomposite-modified electrode has been prepared by functionalizing multiwalled carbon nanotubes (MWCNTs) with N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (p-PDA). The physical characterization of the prepared composite has been done using infrared spectroscopy and ultraviolet-visible spectroscopy. The morphologies of the prepared p-PDA/MWCNTs/ionophore film have been characterized using scanning electron microscopy and transmission electron microscopy. The electrochemical studies of the prepared composite electrode have been investigated by cyclic voltammetry technique. We observed that the p-PDA/MWCNTs/ionomer composite has better electrochemistry, film adhesion with homogeneous dispersion at the electrode surface and an electrocatalytic activity toward the oxidation of dopamine (DA) in 0.1 M phosphate buffer solution (pH 7.0) at a potential of 50 mV. The linear range and detection limit for the detection of DA was found to be 62–625 and 5 µM respectively. The modified electrode also exhibited several attractive features such as simple preparation, fast response, good stability and repeatability.

Data from the literature and our laboratory have been reviewed regarding the maximum homologous temperatures that can be attained by the addition of solute elements that may induce thermodynamic or kinetic (Zener pinning) stabilization of a nanocrystalline grain size (<100 nm) to elevated temperatures. The results of this review suggest that kinetic stabilization by Zener pinning by nanoscale second phases may be the more effective strategy for keeping a nanoscale grain microstructure at the highest homologous temperatures. More research is necessary to confirm this suggestion and to determine the influence of nanoscale grain boundary second phases on the mechanical behavior of the nanocrystalline matrix.