Table of contents

Carbon nanotubes are fascinating nano-objects not only from a fundamental point of view but also with respect to their remarkable properties, holding great potential in new materials design. When combined with organic molecules, these properties can be enhanced or modulated in order to fulfil the demand in domains as diverse as molecular electronics, biomaterials or even construction engineering, to name a few. To adequately conceive these hybrid materials it is essential to fully appreciate the nature of molecule–carbon nanotube interactions. In this review, we will discuss some relevant fundamental and applied research done on encapsulated molecules in carbon nanotubes. We will particularly focus on the weak and van der Waals interactions which rule the molecule–tube coupling. Therefore a small state of the art on the theoretical methods used to describe these interactions is presented here. Then, we will discuss various applications of molecular encapsulation, where we will consider structural, magnetic, charge transfer and transport, and optical properties.

We present a theory for the photoluminescence (PL) and spontaneous emission of semiconductor nanoparticles (quantum dots—QDS) doped in a metamaterial heterostructure. The heterostructure is formed by fabricating a split-ring resonator and metallic rod metamaterial on a dielectric substrate. QDs are doped near the interface in the heterostructure. Our results indicate that the PL and spontaneous emission of the QDs are enhanced in the presence of the metamaterial when the exciton and surface plasmon frequencies are resonant. These findings are consistent with recent experimental studies. The present study can be used to make new types of nanoscale optical devices for sensing, switching and imaging applications based on metamaterials.

An electron beam is deflected when it passes over a silicon-nitride surface, if the surface is illuminated by a low-power continuous-wave diode laser. A deflection angle of up to 1.2 mrad is achieved for an electron beam of 29 µrad divergence. A mechanical beam-stop is used to demonstrate that the effect can act as an optical electron switch with a rise and fall time of 6 µs. Such a switch provides an alternative means to control electron beams, which may be useful in electron lithography and microscopy.

We report a novel GeInSnO_x (GeITO) thin-film transistor (TFT) synthesized by a solution process, utilizing Ge as a charge carrier suppressor and amorphization-promoter, and the dependence of its microstructure, electronic structure and electrical properties on sintering temperature. The amorphous structure was maintained regardless of the sintering temperature. As the sintering temperature increased, the amount of oxygen vacancies increased and GeO₂ bonds transformed into GeO bonds near the film surface above 400 °C. In addition, the In 5sp/Sn 5sp states appeared to act as the dominant electron source in the GeITO channel layers with increasing sintering temperature. These behaviours influenced TFT performances: the saturation mobility was increased from 0.004 to 6.4 cm² V⁻¹ s⁻¹, while the threshold voltage was shifted in the negative direction by increasing the sintering temperature, which demonstrates the high sensitivity of the solution-deposited GeITO to the processing temperature.

A physics-based theoretical model for the low frequency drain noise-current characteristics of AlGaN/GaN heterojunction field effect transistors (HFETs) is developed based on the number fluctuation noise theory. Founded on the calculation of the ground and first excited subband energy levels of the two-dimensional electron gas (2DEG) at an AlGaN/GaN heterointerface using the variational method, the model incorporates both tunnelling and thermally activated processes of trapping/de-trapping of the 2DEG carriers into and out of the trap sites of the barrier and buffer layers. It is found that the thermally activated process is dominant in the frequency range where a 1/f² bulge signature is observed, whereas the tunnelling mechanism is dominant in the frequency range where a 1/f spectrum supersedes. A dominant trap level in the buffer layer, which is responsible for the 1/f² bulge signature, is estimated by fitting the model with temperature-dependent experimental observations. The theoretical results are in good agreement with experimental data.

Nanoscale surface texturing in thin-film solar cells has been shown to enhance device efficiency by increasing light absorption through reduced reflectance and increased light scattering across a broad range of wavelengths and angles. However, light trapping in the industrial thin-film cells is still sub-optimal and creating optimized nanoscale texture over a large area remains challenging. In this article, we present a well-controlled low-cost process to fabricate a periodic nanocone texture optimized for maximum light absorption in thin-film microcrystalline silicon solar cells. The texture is fabricated using nanosphere lithography with the period controlled by the nanosphere diameter and the texture shape and aspect ratio controlled by the reactive ion etching conditions. Finite-difference time-domain optical simulations are used to optimize the texture in the state-of-the-art microcrystalline cells, and optical absorption measurements show that the same cells fabricated on the optimized nanocone-textured substrates exhibit a relative short-circuit current increase of close to 30% compared to a reference state-of-the-art cell with a randomly textured zinc oxide layer. This nanocone texturing technique is compatible with standard thin-film cell fabrication processes and can also be used for other thin-film cells (CIGS, CdTe, CZTS, etc) to maximize light absorption and minimize layer thickness enabling more efficient carrier collection and lower overall cost.

A method for controlling the field distribution of a polygonal surface plasmon polariton (SPP) resonator based on anisotropic zero-index metamaterial (AZIM) is proposed and verified by numerical simulations. Results show that radiation loss at the corner of the polygon SPP resonator can be suppressed; the AZIM is also capable of adjusting the mode number and controlling the field distribution in an SPP resonator. Finally, the AZIM eliminates the transmission delay of surface waves and breaks the limitation of a mode number in direct proportion to the perimeter of the resonator. This may open up a new avenue for manipulating the mode number of SPP resonators at will.

GaAs-based In_0.83Ga_0.17As photodetectors (PDs) with cut-off wavelengths up to 2.6 µm are demonstrated. The effects of continuously-graded or fixed-composition InAlAs buffers on the device performances are investigated. The dark current characteristics of the PDs at various temperatures are analysed in detail. The photocurrents are also measured at 300 K; the detectivity of the PDs is extracted. The two GaAs-based PDs with different buffer schemes show different temperature-dependent dark current behaviours. The around room temperature performances of the GaAs-based device on the fixed-composition buffer are not as good, but comparable to those of InP-based devices, revealing a promising candidate for the GaAs-based PDs and focal plane arrays for many low-end applications.

Nanoscale electrochemical metallization (ECM) memories based on amorphous La_1−xSr_xMnO₃ (a-LSMO) were fabricated using ultrathin porous alumina masks. The ultrathin alumina masks, with thicknesses of about 200 nm and pore diameters of about 80 nm, were fabricated through a typical two-step anodization electrochemical procedure and transferred onto conductive Pt/Ti/SiO₂/Si substrates. Resistive switching (RS) properties of the individual Ag/a-LSMO/Pt ECM cell were directly measured using a conductive atomic force microscope. The cells exhibited typical RS characteristics and the OFF/ON resistance ratio is as high as 10². Reproducible RS behaviours on the same ECM cell and the I–V cycles obtained from different ECM cells ensured that the RS properties in nanoscale Ag/a-LSMO/Pt cells are reproducible and reliable. This work provides an effective approach for the preparation of nanostructured large-scale ordered ECM memories or memristors.

A hybrid plasmonic–photonic crystal consisting of a low-cost metal (Al or Cu) covered by self-assembly polystyrene sub-micro sphere arrays is fabricated. The angle-resolved reflection spectra show the existence of propagating optical surface modes in the structure. Especially, under normal incidence, five surface modes can be observed clearly. With the help of theoretical calculation, the origin of surface resonance modes is confirmed. From both the experiment and simulation, the surface plasmon modes supported by this structure possess high Q factors, which are comparable with those of the modes based on noble metals. Moreover, with a dielectric layer deposited on the top of the structure, its potential application for surface plasma polariton sensors is proposed.

Highly oriented polycrystalline graphite (HOPG), boron-doped diamond (BDD), nanocrystalline diamond, ultra-nanocrystalline diamond and diamond-like carbon surfaces are exposed to low-pressure hydrogen plasma in a 13.56 MHz plasma reactor. Relative yields of surface-produced H⁻ ions due to bombardment of positive ions from the plasma are measured by an energy analyser cum quadrupole mass spectrometer. Irrespective of plasma conditions (0.2 and 2 Pa), HOPG surfaces show the highest yield at room temperature (RT), while at high temperature (HT), the highest yield (∼3–5 times compared to HOPG surface at RT) is observed on BDD surfaces. The shapes of ion distribution functions are compared at RT and HT to demonstrate the mechanism of ion generation at the surface. Raman spectroscopy analyses of the plasma-exposed samples reveal surface modifications influencing H⁻ production yields, while further analyses strongly suggest that the hydrogen content of the material and the sp³/sp² ratio are the key parameters in driving the surface ionization efficiency of carbon materials under the chosen plasma conditions.

A diffuse discharge is produced in atmospheric pressure air between porous alumina dielectric barriers using low-frequency (60 Hz) alternating current. To study its formation mechanism, both the discharge current and voltage are measured while varying the dielectric barrier porosity (0%, 48% or 85%) and composition (99% Al₂O₃,99% SiO₂ or 75% Al₂O₃ + 16% SiO₂ + 9% other oxides). Time-resolved imaging of the emission is carried out to understand the discharge structure. The results indicate that the ionization is driven by an electron avalanche process. This Townsend discharge is found to persist for quite some time (∼3 ms) when the barriers are alumina with a high porosity (>48%). Micro-streamers are observed for the low porosity alumina barriers as well as for other oxide barriers. This discharge formation with highly porous alumina in air is attributed to a relatively low volume dielectric barrier resistivity (∼10⁵ Ω m). Simulations are carried out, accounting for the surface charge loss due to this porosity, as well as for charge accumulation at the barriers.

CH₃F/O₂ inductively coupled plasmas at 10 mTorr were investigated using optical emission spectroscopy. A 'self-actinometry' method was developed to measure the absolute number density of CO that formed in reactions following dissociation of CH₃F and O₂ in the plasma. In this method, small amounts of CO were added to the plasma, leading to small increases in the CO emission intensity. By carefully accounting for small perturbations to the plasma electron density and/or electron energy distribution, and by showing that very little of the CO added to the plasma was decomposed by electron impact or other reactions, it was possible to derive absolute number densities for the CO content of the plasma. With equal fractions (0.50) of CH₃F and O₂ in the feed gas, the CO mole fraction as a function of plasma power saturated at a value of 0.20–0.25. As O₂ in the feed gas was varied at a constant power of 100 W, the CO mole fraction went through a maximum of about 0.25 near an O₂ feed gas fraction of 0.5. The relative CO number densities determined by 'standard' actinometry followed the same functional dependence as the absolute mole fractions determined by self-actinometry, aided by the fact that electron temperature did not change appreciably with power or feed gas composition.

The effects of amplitude modulation (AM) on an atmospheric pressure microwave argon jet is investigated using time-resolved optical emission spectroscopy, passive acoustic diagnostic and digital camera imaging. These techniques show significant changes of the effluent plasma properties with varying AM frequency. Operation in AM mode can enhance the plasma jet length or width over continuous-wave mode with the same mean power, which could be advantageous in many practical applications of plasma jets.

The paper investigates the influences of fluid flow on static and dynamic behaviours of electrostatically actuated carbon nanotubes (CNTs) using strain gradient theory. This nonclassical elasticity theory is applied in order to obtain more accurate results possessing higher agreement with the experimental data. The effects of various fluid parameters such as the fluid viscosity, velocity, mass and temperature on the pull-in properties of the CNTs with two cantilever and doubly clamped boundary conditions are studied. The results reveal the applicability of the proposed nano-system as nano-valves or nano-fluidic sensors.

In this work, we report on crystalline quality and optical characteristics of molybdenum trioxide (MoO₃) bulk and nano-microribbons grown by rapid thermal oxidation (RTO). The developed RTO procedure allows one to synthesize highly crystalline (α-phase) bulk and nano-microribbons of MoO₃. For R–Γ indirect transitions in bulk single crystals of MoO₃, it has been found that the width of the bandgap along the E||c polarization, associated with transitions R_v1–Γ_c1, is lower than the width of the band gap in polarization E ⊥ c, associated with transitions R_v2–Γ_c2. This result is indicative of splitting of the absorption edge due to α-MoO₃ structural anisotropy. Studies of the polarization dependence of the absorption in nano-microribbons (d ≈ 15–500 nm) demonstrated that the energy gap corresponding to R_v1–X_c1 (E||c) transition is smaller than that of R_v2–X_c2 (E ⊥ c) transition. Similar dependence has been found for the R–Y indirect transitions. The results of the investigation of the reflectance spectra in the energy range from 3 to 6 eV are shown. By using the Kramers–Kronig method, the optical functions were derived from the reflection spectra of nano-microribbons, and the polarization dependence of direct energy transitions at the point R in the Brillouin zone are determined. The alternation in splitting caused by polarization of the absorption edge related to indirect transitions due to polarization opens new prospects for the design and fabricating interesting optoelectronic devices based on α-MoO₃ bulk and nano-microribbons with characteristics dependent on the polarization of light waves.

The main objective of this research is the experimental investigation of the surface properties of polymethyl methacrylate (PMMA) such as wettability and the roughness effect on Escherichia coli (gram negative) cell adhesion. Radio frequency (RF; 13.56 MHz) oxygen plasma was used to enhance the antibacterial and wettability properties of this polymer for biomedical applications, especially ophthalmology. The surface was activated by O₂ plasma to produce hydrophilic functional groups. Samples were treated with various RF powers from 10 to 80 W and different gas flow rates from 20 to 120 sccm. Optical emission spectroscopy was used to monitor the plasma process. The modified surface hydrophilicity, morphology and transparency characteristics were studied by water contact angle measurements, atomic force microscopy and UV–vis spectroscopy, respectively. Based on the contact angle measurements of three liquids, surface free energy variations were investigated. Moreover, the antibacterial properties were evaluated utilizing the method of plate counting of Escherichia coli. Also, in order to investigate stability of the plasma treatment, an ageing study was carried out by water contact angle measurements repeated in the days after the treatment. For biomedical applications, especially eye lenses, highly efficient antibacterial surfaces with appropriate hydrophilicity and transparency are of great importance. In this study, it is shown that the plasma process is a reliable and convenient method to achieve these purposes. A significant alteration in the hydrophilicity of a pristine PMMA surface was observed after treatment. Also, our results indicated that the plasma-modified PMMAs exhibit appropriate antibacterial performance. Moreover, surface hydrophilicity and surface charge have more influence on bacterial adhesion rate than surface roughness. UV–vis analysis results do not show a considerable difference for transparency of samples after plasma treatment.

Plasma sterilization is a promising alternative to commonly used sterilization techniques, because the conventional methods suffer from certain limitations, e.g. incompatibility with heat-sensitive materials, or use of toxic agents. However, plasma-based sterilization mechanisms are not fully understood yet. A low-pressure very high frequency capacitively coupled plasma is used to investigate the impact of a hydrogen discharge on the protein glyceraldehyde 3-phosphate dehydrogenase (GapDH). GapDH is an enzyme of glycolysis. As a part of the central metabolism, it occurs in nearly all organisms from bacteria to humans. The plasma is investigated with absolutely calibrated optical emission spectroscopy in order to identify and to quantify plasma components that can contribute to enzyme inactivation. The contribution of UV photons and heat to GapDH inactivation is investigated separately, and neither seems to be a major factor. In order to investigate the mechanisms of GapDH inactivation by the hydrogen discharge, samples are investigated for etching, induction of amino acid backbone breaks, and chemical modifications. While neither etching nor strand breaks are observed, chemical modifications occur at different amino acid residues of GapDH. Deamidations of asparagines as well as methionine and cysteine oxidations are detected after VHF-CCP treatment. In particular, oxidation of the cysteine in the active centre is known to lead to GapDH inactivation.

Several efforts have been made to explain thermal conductivity enhancements in fluids due to the addition of nanoparticles. However, until now, there has been no general consensus on this issue. In this work a simple experiment is described that demonstrates a possible cause of misinterpretation of the experimental data of thermal conductivity obtained when using the hot-wire technique (HWT) in these systems. It has been demonstrated that the thermal conductivity of a two-layer sample of two non-miscible phase systems determined by means of the HWT must be modelled using a series thermal resistance model with consideration of the interfacial layers between different phases. This result sheds light on the thermal conductivity enhancement in nanofluids with respect to the values corresponding to the base fluid, suggesting that this increase can be explained using the above-mentioned model and not by application of empirical formulae for effective media, as done before.

Total ankle replacement is recognized as one of the best procedures to treat painful arthritic ankles. Even though this method can relieve patients from pain and reproduce the physiological functions of the ankle, an improper design can cause an excessive amount of metal debris due to wear, causing toxicity in implant recipient. This paper develops a contact model to treat the interaction of tibia and talus implants in an ankle joint. The contact model describes the interaction of implant rough surfaces including both elastic and plastic deformations. In the model, the tibia and the talus surfaces are viewed as macroscopically conforming cylinders or conforming multi-cylinders containing micrometre-scale roughness. The derived equations relate contact force on the implant and the minimum mean surface separation of the rough surfaces. The force is expressed as a statistical integral function of asperity heights over the possible region of interaction of the roughness of the tibia and the talus implant surfaces. A closed-form approximate equation relating contact force and minimum separation is used to obtain energy loss per cycle in a load–unload sequence applied to the implant. In this way implant surface statistics are related to energy loss in the implant that is responsible for internal void formation and subsequent wear and its harmful toxicity to the implant recipient.