Table of contents

The aim of the present study was to evaluate the diverse properties of transferrin (Tf)-conjugated nanostructured lipid carriers (NLCs) prepared using three different fatty amines, including stearylamine (SA), dodecylamine (DA) and spermine (SP), and two different methods for Tf coupling. Etoposide-loaded NLCs were prepared by an emulsion–solvent evaporation method followed by probe sonication. Chemical coupling of NLCs with Tf was mediated by an amide linkage between the surface-exposed amino group of the fatty amine and the carboxyl group of the protein. The physical coating was performed in a Ringer-Hepes buffer medium. NLCs were characterized by their particle size, zeta potential, polydispersity index, drug entrapment percentage, drug release profiles and Tf-coupling efficiency. The cytotoxicity of NLCs on K562 acute myelogenous leukaemia cells was studied by MTT assay, and their cellular uptake was studied by a flow cytometry method. SA-containing NLCs showed the lowest particle size, the highest zeta potential and the largest coupling efficiency values. The drug entrapment percentage and the zeta potential decreased after Tf coupling, but the average particle size increased. SP-containing formulations released their drug contents comparatively slower than SA- or DA-containing NLCs. Unconjugated NLCs released moderately more drug than Tf-NLCs. Flow cytometry studies revealed enhanced cellular uptake of Tf-NLCs compared to unconjugated ones. Blocking Tf receptors resulted in a significantly higher cell survival rate for Tf-NLCs. The highest cytotoxic activity was observed in the chemically coupled SA-containing nanoparticles, with an IC₅₀ value of 15-fold lower than free etoposide.

We propose and demonstrate strongly enhancing electric field and Raman scattering with a large tolerance to the light incident angle and polarization by using x-shaped quasi-3D plasmonic nanostructure arrays (X-Q3D-PNAs). The finite-difference time-domain simulations were used to study the reflectance spectra and electric field profiles of X-Q3D-PNAs. Results show that both surface plasmon polaritons and localized surface plasmon polaritons (LSPPs) can be generated at the metal/dielectric interfaces of the top gold thin film with square grating x-shaped nanoholes. The resonance of the LSPPs generated at the gold islands formed between x-shaped nanoholes at the top gold thin film greatly enhance the electric fields at the tips of the cross-sectors of the x-shaped nanoholes. Both plasmon resonances and electric field enhancements are affected by the structural dimensions. The strong electric field enhancement and the large tolerance to the laser polarization were demonstrated by surface-enhanced Raman scattering experiments. This unique plasmonic property of X-Q3D-PNAs could be attractive for photovoltaics and biosensing applications.

In this investigation, a recent model for assessing the electrical conductivity of nanocomposites comprising a single type of conductive nanofiller was expanded to cases with mixtures of nanofillers. The extended model considers electron tunneling as the effective mechanism for insulator–conductor transition. The model was validated with relevant experimental data based on a mono-nanofiller. Using the extended model, the effective electrical conductivity of a nanocomposite comprising both graphite nanoplatelets and carbon nanotubes was investigated. It was observed that the hybridized nanocomposites filled with a mixture of these conductive nanofillers attain, synergistically, enhanced electrical conductivities at lower volume fractions. The lower filler contents assist in preserving the intrinsic properties of the host polymer in support of several applications. It was also observed that the relative aspect ratios of the conductive fillers play significant roles on the electrical conductivity of the hybrid nanocomposite. Simulations revealed that, generally, the addition of minimal amounts of a higher aspect ratio auxiliary phase to a lower aspect ratio main phase enhances the electrical conductivity of the composite by orders of magnitude

In this paper, we have explored manufacturable approaches to sub-wavelength controlled three-dimensional (3D) nano-patterns with the goal of significantly enhancing the photocurrent in amorphous silicon solar cells. Here we demonstrate efficiency enhancement of about 50% over typical flat a-Si thin-film solar cells, and report an enhancement of 20% in optical absorption over Asahi textured glass by fabricating sub-wavelength nano-patterned a-Si on glass substrates. External quantum efficiency showed superior results for the 3D nano-patterned thin-film solar cells due to enhancement of broadband optical absorption. The results further indicate that this enhanced light trapping is achieved with minimal parasitic absorption losses in the deposited transparent conductive oxide for the nano-patterned substrate thin-film amorphous silicon solar cell configuration. Optical simulations are in good agreement with experimental results, and also show a significant enhancement in optical absorption, quantum efficiency and photocurrent.

We present a methodology for preparing silicon nitride nanopores that provides in situ control of size with sub-nanometer precision while simultaneously reducing electrical noise by up to three orders of magnitude through the cyclic application of high electric fields in an aqueous environment. Over 90% of nanopores treated with this technique display desirable noise characteristics and readily exhibit translocation of double-stranded DNA molecules. Furthermore, previously used nanopores with degraded electrical properties can be rejuvenated and used for further single-molecule experiments.

We have successfully prepared a face-centered cubic Au–Pd nanoporous structure (NPS) in a one-pot reaction under thermal decomposition of single-source precursor [Pd(NH₃)₄][AuCl₄]₂. The precursor employed contains both desired metals 'mixed' on the molecular level, thus providing its significant advantages for obtaining alloys. The observation using a high-resolution transmission electron microscope has shown that the nanostructure was composed of interconnected polycrystalline ligaments with an average diameter of 14 ± 3 nm. The measurements made by energy-dispersive x-ray analysis and powder x-ray diffraction (XRD) confirm that the nanostructure consists of Au_0.67Pd_0.33 alloy. In situ real-time synchrotron XRD was used to study the formation mechanism for Au–Pd alloy NPS. We provide the correlation of control parameters (such as temperature, rate of increase of temperature and gas atmosphere) with the microstructure and phase behavior of bimetallic products. Under reducing conditions (H₂ atmosphere) the first step is the formation of alloy nanowires. Finally, bimetallic alloy 3D nanostructure is formed after the complete decomposition of the precursor (100 °C).

We report on photovoltaic cells based on ternary PbS_0.9Se_0.1 quantum dots utilizing a heterojunction type device configuration. The best device shows an AM 1.5 power conversion efficiency of 4.25%. Furthermore, this ternary PbS_xSe_1−x quantum dot heterojunction device has a peak external quantum efficiency above 100% at 2.76 eV, approximately 2.7 ×  the bandgap energy. The ternary quantum dots combine the higher short circuit currents of the binary PbSe system with the higher open circuit voltages of the binary PbS system.

The hydride vapor phase epitaxy (HVPE) process exhibits unexpected properties when growing GaN semiconductor nanowires (NWs). With respect to the classical well-known methods such as metal organic vapor phase epitaxy and molecular beam epitaxy, this near-equilibrium process based on hot wall reactor technology enables the synthesis of nanowires with a constant cylinder shape over unusual length. Catalyst-assisted HVPE shows a record short time process (less than 20 min) coupled to very low precursor consumption. NWs are grown at a fast solidification rate (50 μm h⁻¹), facilitated by the high decomposition frequency of the chloride molecules involved in the HVPE process as element III precursors. In this work growth temperature and V/III ratio were investigated to determine the growth mechanism which led to such long NWs. Analysis based on the Ni–Ga phase diagram and the growth kinetics of near-equilibrium HVPE is proposed.

Semiconductor nanopyramids (NPs) provide advantages in the development of novel functional optoelectronic devices due to their unique size-dependent properties. Here we demonstrate a new method for the fabrication of selectively self-assembled single-crystalline GaN NPs on the m-plane of periodically strained GaN/InGaN multiquantum disks embedded in the middle of GaN nanorods. The GaN NPs, which have ∼100 nm diameters and heights, are observed by scanning electron microscopy and their crystalline structure is confirmed by high-resolution transmission electron microscopy. Experimental analysis directly reveals the strain distribution along the growth direction of the NPs. Cathodoluminescence measurements on a single NP show that its emission energy redshifts compared with that of bulk GaN, corroborating the results showing the formation of tensile strain in the NP. Observations of the uniform distribution and localization of these NPs show the possibility of further tuning their size and density by controlling periodically strained nanorod surfaces.

Platinum nanoparticles were deposited on oxygen plasma treated carbon nanotubes (CNTs) by atomic layer deposition (ALD). The treatment time with oxygen plasma generated by microwaves under a power of 600 W varied from 5 to 20 s. The number of ALD cycles was controlled at 5–125. X-ray photoelectron spectroscopic analysis indicated that oxygen plasma can graft oxygen-containing functional groups to the CNT surface to act as nucleation sites for growth of Pt nanoparticles. Formation of very uniform and well distributed Pt nanoparticles of a size of 1.60–4.80 nm was achieved. The growth rate of Pt nanoparticles could be controlled by the number of ALD cycles and oxygen plasma treatment time. This offers a dry process to deposit well-dispersed metallic nanoparticles on selected support materials.

We investigate colloidal Fe₃O₄ nanocrystals as a catalyst system for carbon nanotube (CNT) growth that allows for decoupling the CNT growth step from the catalyst shaping and activation step. The system consists of 6.4 nm Fe₃O₄ nanocrystals synthesized using a solution-based thermal decomposition reaction and, subsequently, transferred as hexagonally ordered Langmuir–Blodgett (LB) monolayers on TiN substrates. We demonstrate for the first time aligned CNT growth from LB deposited nanocrystals on a metallic underlayer. The hexagonally ordered monolayers of catalyst particles show promising stability up to the CNT growth temperature. In situ TEM heating experiments were performed to find this onset of particle deformation and showed stability of the nanoparticles up to 600 °C. The particle coalescence at high temperatures was also evidenced by the increasing CNT diameter, from 9.5 nm at 580 °C to 16 nm at 630 °C. By choosing to work at temperatures below the onset particle coalescence temperature, equivalent CNT diameters were obtained under different catalyst activation and growth conditions. The high stability of the catalyst on the metallic underlayer enables us to study CNT growth kinetics independently of the catalyst shaping step. This work opens a route towards combining growth studies with an electrical evaluation of the CNT growth as the TiN can be used as the bottom contact.

In this work, the influence of air pressure during the annealing of Ge quantum dot (QD) lattices embedded in an amorphous Al₂O₃ matrix on the structural, morphological and compositional properties of the film is studied. The formation of a regularly ordered void lattice after performing a thermal annealing process is explored. Our results show that both the Ge desorption from the film and the regular ordering of the QDs are very sensitive to the annealing parameters. The conditions for the formation of a void lattice, a crystalline Ge QD lattice and a disordered QD lattice are presented. The observed effects are explained in terms of oxygen interaction with the Ge present in the film.

Cobalt–silver (Co–Ag) core–shell nanoparticles with different silver thicknesses were prepared by the microemulsion method in a two-step reduction process. Transmission electron microscopy (TEM) characterization revealed the almost monodispersity and nanometric size (in the range 3–5 nm depending on the shell thickness) of the synthesized nanoparticles. However, it was the use of high-resolution TEM that revealed the correct core–shell formation of the nanometric material. The selected area electron diffraction pattern indicated the fcc (face-centered cubic) and hcp (hexagonal close packed) nature for silver and cobalt, respectively. Cyclic voltammetry also allowed the correct core–shell formation to be assured. The magnetic properties revealed the presence of both superparamagnetic and ferromagnetic contributions. Because of the lack of methodology, it was necessary to develop a method to measure the magnetotransport properties of the prepared nanoparticles. The strategy which followed was successful as it was possible to measure these properties: giant magnetoresistance values of 0.1% at room temperature were obtained. The numerical analysis of magnetic and magnetoresistance data indicated the presence of superparamagnetic particles showing interaction among the magnetic moments.

We have investigated the self-breaking mechanism of atomic scale Au nanocontacts at room temperature in air. In the conductance traces, we frequently observed traces showing both a 1G₀ (2e²/h) and 3G₀ plateaux, or only a 2G₀ plateau in the conductance regime below 3G₀. The statistical analysis showed a negative correlation between the appearance of 1G₀ and 2G₀ peaks, and a positive correlation between 1G₀ and 3G₀ peaks. This conductance behavior suggested that the symmetric triple atomic rows changed into a symmetric single row, while the asymmetric double rows broke without changing into a symmetric single row. The regular self-breaking process can be explained by the breaking of the thermodynamically stable Au nanocontacts which were formed during the self-breaking of the contacts.

A non-contact atomic force microscopy-based method has been used to map the static lateral forces exerted on an atomically sharp Pt/Ir probe tip by a graphite surface. With measurements carried out at low temperatures and in the attractive regime, where the atomic sharpness of the tip can be maintained over extended time periods, the method allows the quantification and directional analysis of lateral forces with piconewton and picometer resolution as a function of both the in-plane tip position and the vertical tip–sample distance, without limitations due to a finite contact area or to stick-slip-related sudden jumps of tip apex atoms. After reviewing the measurement principle, the data obtained in this case study are utilized to illustrate the unique insight that the method offers. In particular, the local lateral forces that are expected to determine frictional resistance in the attractive regime are found to depend linearly on the normal force for small tip–sample distances.

Nanocomposites of aligned multi-walled carbon nanotubes (CNTs) embedded in a polymer matrix yield a unique combination of thermal and electrical properties and mechanical strength. These properties are intimately related to the composite nanostructure and to the growth and processing conditions. The alignment of the tubes, the filling fraction and the contact junction between the nanotubes are key parameters controlling the composite electrical conductivity. For this purpose, a full description of the composite nanostructure is required. Among the non-destructive scanning probe techniques, scanning spreading resistance microscopy is found to be a powerful technique in identifying the carbon nanotubes with true nanometer resolution, thus competing with SEM and TEM imaging. Additionally, the technique provides valuable information about the electrical conduction mechanism within the composite structure. Indeed, by using a controlled contact force and an appropriate model of conduction at the nanoscale, the tip–CNT contact resistance, the CNT intrinsic resistance and the CNT–epoxy–CNT resistance junction are evaluated. This latter is found to be the factor controlling the overall electrical conductivity of the composite.

Carbon nanotube terminated atomic force microscopy (AFM) probes have been used for the imaging of 5 nm wide surface supported Pt nanoclusters by non-contact (dynamic mode) AFM in an ultra-high vacuum. The results are compared to AFM measurements done with conventional Si-tips, as well as with transmission electron microscopy images, which give accurate measures for cluster widths. Despite their ideal aspect ratio, tip-broadening is concluded to be a severe problem even when imaging with carbon nanotube tips, which overestimates the cluster width by several times the nominal width of the nanotube tip. This broadening is attributed to a bending of the carbon nanotubes, and not to pure geometrical factors, which coincidentally results in a significant improvement for relative height measurements of tightly spaced high aspect ratio structures, as compared to what can be achieved with geometrically limited conventional probes. Superior durability also stands out as a defining feature of carbon nanotube terminated probes, allowing them to give results with a greatly enhanced reproducibility.

Si nanowires (NWs) integrated in a field effect transistor device structure are characterized using scanning electron (SEM), atomic force, and scanning Kelvin probe force (KPFM) microscopy. Reactive ion etching (RIE) and vapor–liquid–solid (VLS) growth were used to fabricate NWs between predefined electrodes. Characterization of Si NWs identified defects and/or impurities that affect the surface electronic structure. RIE NWs have defects that both SEM and KPFM analysis associate with a surface contaminant as well as defects that have a voltage dependent response indicating impurity states in the energy bandgap. In the case of VLS NWs, even after aqua regia, Au impurity levels are found to induce impurity states in the bandgap. KPFM data, when normalized to the oxide-capacitance response, also identify a subset of VLS NWs with poor electrical contact due to nanogaps and short circuits when NWs cross that is not observed in AFM images or in current–voltage measurements when NWs are connected in parallel across electrodes. The experiments and analysis presented outline a systematic method for characterizing a broad array of nanoscale systems under device operation conditions.

Silicon-based thermoelectric nanowires were fabricated by using complementary metal–oxide–semiconductor (CMOS) technology. 50 nm width n- and p-type silicon nanowires (SiNWs) were manufactured using a conventional photolithography method on 8 inch silicon wafer. For the evaluation of the Seebeck coefficients of the silicon nanowires, heater and temperature sensor embedded test patterns were fabricated. Moreover, for the elimination of electrical and thermal contact resistance issues, the SiNWs, heater and temperature sensors were fabricated monolithically using a CMOS process. For validation of the temperature measurement by an electrical method, scanning thermal microscopy analysis was carried out. The highest Seebeck coefficients were  − 169.97 μV  K⁻¹ and 152.82 μV  K⁻¹ and the highest power factors were 2.77 mW m⁻¹ K⁻² and 0.65 mW m⁻¹ K⁻² for n- and p-type SiNWs, respectively, in the temperature range from 200 to 300 K. The larger power factor value for n-type SiNW was due to the higher electrical conductivity. The total Seebeck coefficient and total power factor for the n- and p-leg unit device were 157.66 μV  K⁻¹ and 9.30 mW m⁻¹ K⁻² at 300 K, respectively.

We demonstrate that it is possible to mechanically exfoliate graphene under ultrahigh vacuum conditions on the atomically well defined surface of single crystalline silicon. The flakes are several hundred nanometers in lateral size and their optical contrast is very faint, in agreement with calculated data. Single-layer graphene is investigated by Raman mapping. The graphene and 2D peaks are shifted and narrowed compared to undoped graphene. With spatially resolved Kelvin probe measurements we show that this is due to p-type doping with hole densities of n_h ≃ 6 × 10¹² cm⁻². The in vacuo preparation technique presented here should open up new possibilities to influence the properties of graphene by introducing adsorbates in a controlled way.