Table of contents

Laser processing of carbon compounds towards the formation of graphene-based structures gains ground in view of the practicality that lasers offer against other conventional graphene preparation methods. The current work explores the viability of low-cost lasers, operating at ambient conditions, for the transformation of various graphitic materials to structures with graphene-like atomic arrangements. Starting materials are at two opposing sides. On one side stands the typical graphite crystal with Bernal stacking and strong sp² character, while nanocrystalline graphitic powders are also investigated. It is demonstrated that graphene-like structures can be prepared either by starting from a well-organized Bernal-stacked network or by irradiating nanocrystalline carbon. The current findings document that laser processing at minimal chamber conditions shows high potential for preparing high-quality graphene-based structures starting from low-cost materials. Apart from being scalable, the proposed method is adaptable to current technological platforms emerging as a viable and eco-friendly graphene production technology.

Many nanomaterials have been reported to have enzyme-like activities and are considered as nanozymes. As a multifunctional nanozyme, nanoceria has received much attention due to the dual oxidation states of Ce³⁺/Ce⁴⁺ which facilitate redox reactions at the particle surface. Despite the advantages of nanozymes, their limited activity and lack of enzyme specificity are still problems to be resolved. DNA is used to modulate the oxidase activity of nanoceria because it has recently become an important molecule in bionanotechnology. However, the current research on the effect of DNA on the oxidase mimetic activity of nanoceria is contradictory. It has been discovered that nanoceria used in recent works are different, including in particle size, doping and concentration, and these differences may affect the interaction between DNA and nanoceria, and then affect the oxidase mimetic activity of nanoceria. Hence, it is important to clarify the factors that affect the interaction between DNA with nanoceria. In this work, the interactions between DNA and nanoceria with three different morphologies (nanoparticles, nanocubes, and nanorods) have been investigated. Experimental results show that DNA has different influences on the oxidase mimetic activity of nanoceria with different morphologies. The oxidase mimetic activity of CeO₂ nanoparticles and nanocubes increased, but that of CeO₂ nanorods decreased, after DNA modification. The mechanism of these experimental results has been explored, and it has been found that it is the interaction between cerium and the phosphate backbone of DNA that changes with the different morphologies, resulting in the varying effect of DNA on the oxidase mimetic activity of nanoceria. These results may provide a better understanding of the effect of DNA on the oxidase mimetic activity of nanoceria and promote the applications of nanoceria.

In this paper, we study intersubband characteristics of GaN/AlN and GaN/Al_0.4Ga_0.6N heterostructures in GaN nanowires structurally designed to absorb in the mid-infrared wavelength region. Increasing the GaN well width from 1.5 to 5.7 nm leads to a red shift of the intersubband absorption from 1.4 to 3.4 μm. The red shift in larger quantum wells is amplified by the fact that one of the GaN/AlN heterointerfaces (corresponding to the growth of GaN on AlN) is not sharp but rather a graded alloy extending around 1.5–2 nm. Using AlGaN instead of AlN for the same barrier dimensions, we observe the effects of reduced polarization, which blue shifts the band-to-band transitions and red shifts the intersubband transitions. In heavily doped GaN/AlGaN nanowires, a broad absorption band is observed in the 4.5–6.4 μm spectral region.

Magnetic multilayer devices, showing large magnetoresistance (MR) effects, have revolutionized magnetic sensing and data storage sectors over the last few decades. Two-dimensional van der Waals layered materials are relatively new entrants in this area, and these materials can give rise to large MR effects with diverse physical origins. Here we report observation of giant MR switching (∼10 orders of magnitude) in multilayered graphene grown on cobalt (Co) substrates, which persists even at room temperature. The origin of this effect is linked with weak interlayer coupling of the graphene stacks, which gives rise to an 'interlayer MR' effect. This effect is found to be robust against some degree of inhomogeneity in the graphene stack, making it an attractive platform for the emerging area of flexible magnetic sensorics.

Owing to the capability of integrating the information storage and computing in the same physical location, in-memory computing with memristors has become a research hotspot as a promising route for non von Neumann architecture. However, it is still a challenge to develop high performance devices as well as optimized logic methodologies to realize energy-efficient computing. Herein, filamentary Cu/GeTe/TiN memristor is reported to show satisfactory properties with nanosecond switching speed (<60 ns), low voltage operation (<2 V), high endurance (>10⁴ cycles) and good retention (>10⁴ s @85 °C). It is revealed that the charge carrier conduction mechanisms in high resistance and low resistance states are Schottky emission and hopping transport between the adjacent Cu clusters, respectively, based on the analysis of current–voltage behaviors and resistance–temperature characteristics. An intuitive picture is given to describe the dynamic processes of resistive switching. Moreover, based on the basic material implication (IMP) logic circuit, we proposed a reconfigurable logic method and experimentally implemented IMP, NOT, OR, and COPY logic functions. Design of a one-bit full adder with reduction in computational sequences and its validation in simulation further demonstrate the potential practical application. The results provide important progress towards understanding of resistive switching mechanism and realization of energy-efficient in-memory computing architecture.

Phosphorene nanoribbons with magnetic edges are potentially attractive for nanoelectronic and spintronic applications. Here, the attention is focused on electronic and magnetic properties of these materials. Using a self-consistent computational method it is shown that, in general, two types of configuration with spontaneous edge magnetization can be responsible for lifting the spin degeneracy, and consequently for the appearance of the half-metallic behavior. Namely, in addition to the well-known configuration with edge states ferromagnetically coupled along each edge and aligned in parallel between the two edges, there is another one (much less explored) with edge states ferromagnetically aligned on only one edge. The ground state magnetic configurations strongly depend on the chemical potential position (electron filling factor), and can be controlled by means of the external perpendicular gate voltage, and by changing the nanoribbon width. It is also shown that the magnetic edge configurations responsible for the half-metallicity can be stabilized with ferromagnetic substrates, due to the proximity effect.

Plasmon nanoresonators in graphene have many applications in biosensing, photodetectors and modulators. As a result, an efficient and precise patterning technique for graphene is required. Helium ion lithography (HIL) emerges as a promising tool for direct writing fabrication because it owns improved fabrication precision compared to electron beam lithography and conventional gallium focused ion beam technique. In this paper, utilizing HIL, a set of graphene triangles are patterned and excellent plasmon response is detected. Particularly, the evolution of breathing mode in these structures is unveiled by scattering-type scanning near-field optical microscopy. Besides, the plasmon response of graphene structures can be efficiently tuned by adjusting the irradiated ion dose during the etching process, which can be explained by the phenomenal simulation model. Our work demonstrates that HIL is a feasible way for precise plasmonic nanostructure fabrication, and can be applied to graphene plasmon control at the nanoscale as well.

Achieving enhanced coupling of solar radiation over the full range of the silicon absorption spectrum up to the bandgap is essential for increased efficiency of solar cells, especially thin film versions. While many designs for enhancing trapping of radiation have been explored, detailed measurements of light scattering inside silicon cells is still lacking. Here, we demonstrate experimentally and computationally that plasmonic-assisted localized and traveling modes can efficiently couple red and infrared radiation into ultrathin amorphous silicon (a-Si) layers. Utilizing patterned periodic arrays of aluminum nanostructures on thin a-Si, we perform specular and diffuse reflectivity and transmission measurements over a broad spectrum. Based on these results, we are able to separate parasitic absorption in aluminum plasmonic arrays from enhanced light absorption in the 200 nm thick amorphous silicon layer, as compared to a blank silicon layer. We discover a very efficient near-infrared a-Si absorption mechanism that occurs at the transition from the radiative to evanescent diffractive coupling, analogous to earlier surface-enhanced infrared studies. These results represent a direct demonstration of enhanced radiation coupling into silicon due to large angle scattering and show a path forward to improved ultrathin solar cell efficiency.

The conductive-bridge random access memory (CBRAM) has become one of the most suitable candidates for non-volatile memory in next-generation information and communication technology. The resistive switching (RS) mechanism of CBRAM depends on the formation/annihilation of the conductive filament (CF) between the active metal electrode and the inert electrode. However, excessive ion injection from the active electrode into the solid electrolyte reduces the uniformity and reliability of the RS devices. To solve this problem, we investigated the RS characteristics of a CuSn alloy active electrode with different compositions of Cu_x–Sn_1–x (0.13 < X < 0.55). The RS characteristics were further improved by inserting a dysprosium (Dy) or lutetium (Lu) buffer layer at the interface of Cu_x–Sn_1–x/Al₂O₃. Electrical analysis of the optimal Cu_0.4–Sn_0.73/Lu-based CBRAM exhibited stable RS behavior with low operation voltage (SET: 0.7 V and RESET: −0.3 V), a high on state/off state resistive ratio (10⁶), AC cyclic endurance (>10⁴), and stable retention (85 °C/10 years). To achieve these performance parameters, CFs were locally formed inside the electrolyte using a modified CuSn active electrode, and the amount of Cu-ion injection was reduced by inserting the Dy or Lu buffer layer between the CuSn active electrode and the electrolyte. In particular, conductive-atomic force microscopy results at the Dy or Lu/Al₂O₃ interface directly showed and defined the diameter of the CF.

We show that blister-based-laser-induced forward-transfer can be used to cleanly desorb and transfer nano- and micro-scale particles between substrates without exposing the particles to the laser radiation or to any chemical treatment that could damage the intrinsic electronic and optical properties of the materials. The technique uses laser pulses to induce the rapid formation of a blister on a thin metal layer deposited on glass via ablation at the metal/glass interface. Femtosecond laser pulses are advantageous for forming beams of molecules or small nanoparticles with well-defined velocity and narrow angular distributions. Both fs and ns laser pulses can be used to cleanly transfer larger nanoparticles including relatively fragile monolayer 2D transition metal dichalcogenide crystals and for direct transfer of nanoparticles from chemical vapour deposition growth substrates, although the mechanisms for inducing blister formation are different.

As one of the significant electron transporting materials (ETMs) in efficient planar heterojunction perovskite solar cells (PSCs), SnO₂ can collect/transfer photo-generated carriers produced in perovskite active absorbers and suppress the carrier recombination at interfaces. In this study, we demonstrate that a mild solution-processed SnO₂ compact layer can be an eminent ETM for planar heterojunction PSCs. Here, the device based on chemical-bath-deposited SnO₂ electron transporting layer (ETL) exhibits a power conversion efficiency (PCE) of 16.10% and with obvious hysteresis effect (hysteresis index = 19.5%), owing to the accumulation and recombination of charge carriers at the SnO₂/perovskite interface. In order to improve the carrier dissociation and transport process, an ultrathin TiO₂ film was deposited on the top of the SnO₂ ETL passivating nonradiative recombination center. The corresponding device based on the TiO₂@SnO₂ electron transporting bi-layer (ETBL) exhibited a high PCE (17.45%) and a negligible hysteresis effect (hysteresis index = 1.5%). These findings indicate that this facile solution-processed TiO₂@SnO₂ ETBL paves a scalable and inexpensive way for fabricating hysteresis-less and high-performance PSCs.

The one-dimensional-core/double-shell arrays on Ni foam were prepared by the hydrothermal, carbonized and electrodeposition processes, consisting of NiMoO₄ nanowire as a core, an ultrathin carbon layer as an internal shell and Ni₃S₂ nanosheets an external shell (abbr. NiMoO₄@C@Ni₃S₂), respectively. The ternary heterostructure demonstrates the synergistic effect on the dimensional, interface, surface structures and compositions, resulting from the ordered and functionalized architectures. Therefore, the NiMoO₄@C@Ni₃S₂ electrode integrated the advantages of the electron transfer, electrolyte penetration and ion diffusion. The asymmetric supercapacitor exhibited a high energy density of 1.29 mW h cm⁻³ at a power density of 13.99 W cm⁻³. Furthermore, we compared the changes in composition, structure and morphology before and after 3000 cycles using the three electrode system. These observations demonstrated that the dissolution of NiMoO₄@C@Ni₃S₂ induced the decay of capacitance and cycling stability, suggesting that we can further develop a strategy to consolidate the electrode structure.

The current work explores the excitation of surface plasmon polaritons (SPPs) on a one dimensional (1D) silver nano-grating device, simulated on glass substrate, which can sense a very small change in the refractive index of an analyte adjacent to it. The most recent modeling technique finite element analysis is applied in this work by using a COMSOL RF module. The models of 1D grating devices of different slit widths with fixed periodicity and film thickness are simulated. The data is collected and then used to study higher refractive index unit per nanometer (RIU/nm) as well as the effect of the widths of the slits on the RIU. A number of investigations are done by the simulated data, like a dip in the transmission spectra of p-polarized light. This dip is due to SPP resonance with the variation of slit width. Furthermore, the most fascinating part of the research is the COMSOL modeling that provides an opportunity to look into factors affecting higher RIU/nm, while visualizing the cross-sectional view of the grating device and strong electric field enhancement at the surface of the metallic device. When the slit width is almost equal to half of the periodicity of the grating device, SPP resonance increases and it is at maximum for the slit width equal to two-thirds of the periodicity, because the coupling efficiency is at maximum.

Graphene can acquire salient properties by the intercalated nano structures, and to functionalize the graphene as designed, understanding the growth kinetics of the nano structures is a prerequisite. In that regards, Kr atoms are selectively intercalated just below the surface graphene of C(0001) by the incidence of low energy Kr ions. The growth kinetics of the encapsulated Kr nano structures is investigated by both scanning tunneling microscopy and molecular dynamics simulations. The intercalation proceeds via defect sites, such as surface vacancies. At room temperature, the thermal diffusion of intercalated Kr is almost frustrated by the strain field of the encapsulating graphene layers, and the growth of Kr nano structures proceeds via the transient mobility of both the intercalating Kr atoms and previously intercalated Kr atoms that are mobilized by collision with the incident Kr ions. At the elevated temperatures where thermal diffusion becomes effective, some Kr nano structures disappear, releasing pressurized Kr atoms, while others coalesce to form blisters via the delamination of the adjacent graphene. Some of the larger blisters explode to leave craters of varying depths at the surface. In contrast to growth on the substrate, the growth of each encapsulated nano structure depends significantly on extrinsic variables, such as surface vacancies and local topography around the nano structure, that affect the Kr diffusion and limit the maximal Kr pressure.

A facile method to prepare nitrogen anion-decorated cobalt tungsten disulfides solid solutions, retaining ultra-thin WS₂-like nanosheet structures (The N–Co_xW_1−xS₂) anchored on carbon nanofibers (CNFs), is developed. The synergistic effect of the WS₂ nanosheets provides a secure framework for stabilizing the amorphous Co–S clusters, CNFs substrate and nitrogen anion-decoration significantly enhances the inherent conductivity of the catalyst, resulting in a significantly promoted hydrogen evolution reaction activity and stable performance compared to pure Co₉S₈ nanoparticles or ultra-thin WS₂ nanosheets. The N–Co_xW_1−xS₂ electrode demonstrates the excellent electrocatalytic performance, with current density of 10 mA cm⁻² at a low overpotential of 93 mV and Tafel slope of 85 mV dec⁻¹, as well as the long-term stability in acid electrolyte. The present investigation may provide a feasible strategy for incorporating other heteroatoms into transitional metal disulfides materials to design catalysts with highly active and stable performance for water splitting.

Ultra-small and monodispersed zinc sulfide nanocrystals (NCs) (d ≤ 3 nm) have been prepared without the use of any surfactants by a synthetic route using benzyl mercaptan as a source of sulfur. The prepared NCs are dispersible in highly polar solvents and display the capability to closely pack-up in a bulky film. The NCs were characterized by TEM, XRD and UV–vis optical absorption as well as by steady-state and time-resolved photoluminescence (PL) spectroscopies. Uniform films of ZnS were spin-coated on glass and ITO-glass substrates using a NCs dispersion in N,N-dimethylformamide. The NCs and the resulting films were characterized by morphological and optoelectronic probing techniques such as AFM, SEM, diffuse reflectance, PL and photoelectron spectroscopy in air. These physical investigations confirmed that the chalcogenide NCs grown by this method have the potential to be utilized directly as photocatalysts and are potentially useful building-blocks/starting materials for the fabrication of semiconductor thin films for optoelectronic applications such as LED, luminescent screens, field effect transistor and solar cells. Insights on the chemistry involved in the NCs growth have been provided revealing that their formation proceeds through a mechanism involving a thioether elimination reaction.

Carbon-based composite materials with tunable, ordered mesoporous structures were prepared via the hydrothermal carbonization/soft-template method, with nickel nitrate as the doping source, straw as the carbon source, and F127 as the soft template. By adjusting the additive amounts of Ni and F127, the mesoporous structure was controllable, and results were obtained that varied from an irregular stripe-like hexagonal, a regular stripe-like hexagonal, mixed hexagonal and cubic, to cubic. With a specific surface area in the range of 339–963 m² g⁻¹, the percentage of mesoporous structures increased from 39.6% to 58.3%. Ni doped into the carbon skeletons existed in the form of metallic Ni and nickel oxide. Increased amounts of nickel nitrate for doping as well as F127 is beneficial for the generation of metallic Ni during the preparation process. The average particle diameter of Ni decreased when the Ni-doped content was increased, and all the average particle sizes were less than 10 nm after F127 was added. The Ni_m/CSF_n catalyst demonstrated high catalytic activity when used for the hydrogenation reaction of p-nitrophenol (PNP) to p-aminophenol (PAP). The conversion of PNP reached 98.79%, and the selectivity for PAP reached 89.6% for Ni_2.0/CSF_1.5, with a corresponding apparent rate constant of 1.56 × 10⁻³ S⁻¹, apparent activation energy of 41.86 kJ mol⁻¹, and with the added benefit that the catalyst could be separated and recycled by applying an external magnetic field.

Perovskite-type oxides have become the hotspots of functional materials due to their various excellent performances. As a typical material with a perovskite structure, CaTiO₃ (CTO) possesses a similar band gap to TiO₂ with less defects and recombination centers, which makes it a promising alternative material to TiO₂. In particular, the CTO nanotube structure has a large specific surface area and unique photochemical and electron-transport properties, and these advantages further expand its application range. In this paper, a highly ordered and vertically aligned CTO nanotube array was successfully synthesized by a simple hydrothermal method with TiO₂ nanotube (TNT) arrays as the precursor. It was found that the CTO nanotube had a higher optical absorption ability (3.4 eV), photovoltage (500 mV) and photocurrent density (0.004 A cm⁻¹) under ultraviolet irradiation, compared to the TNT (350 mV and 0.0036 A cm⁻¹). At the same time, the electrochemical impedance spectroscopy, Mott–Schottky and stability tests indicate that the CTO nanotube might be a promising alternative choice as the photoelectric material for a TNT.

Mechanical properties of polymer nanocomposites depend primarily on nanointerphases as transitional zones between nanoparticles and surrounding matrices. Due to the difficulty in the quantitative characterisation of nanointerphases, previous literature generally deemed such interphases as one-dimensional uniform zones around nanoparticles by assumption for analytical or theoretical modelling. We hereby have demonstrated for the first time direct three-dimensional topography and physical measurement of nanophase mechanical properties between nanodiameter bamboo charcoals (NBCs) and poly (vinyl alcohol) (PVA) in polymer nanocomposites. Topographical features, nanomechanical properties and dimensions of nanointerphases were systematically determined via peak force quantitative nanomechanical tapping mode. Significantly different mechanical properties of nanointerphases were revealed as opposed to those of individual NBCs and PVA matrices. Non-uniform irregular three-dimensional structures and shapes of nanointerphases are manifested around individual NBCs, which can be greatly influenced by nanoparticle size and roughness, and nanoparticle dispersion and distribution. Elastic moduli of nanointerphases were experimentally determined in range from 25.32 ± 3.4 to 66.3 ± 3.2 GPa. Additionally, it is clearly shown that the interphase modulus strongly depends on interphase surface area and interphase volume. Different NBC distribution patterns from fully to partially embedded nanoparticles are proven to yield a remarkable reduction in elastic moduli of nanointerphases.

The tip motion of the dynamic atomic force microscope in liquids shows complex transient behaviors when using a low stiffness cantilever. The second flexural mode of the cantilever is momentarily excited. Multiple impacts between the tip and the sample might occur in one oscillation cycle. However, the commonly used Fourier transform method cannot provide time-related information about these transient features. To overcome this limitation, we apply the wavelet transform to perform the time-frequency analysis of the tip motion in liquids. The momentary excitation of the second mode and the phenomenon of multiple impacts are clearly shown in the time-frequency plane of the wavelet scalogram. The instantaneous frequencies and magnitudes of the second mode are extracted by the wavelet ridge analysis, which can provide quantitative estimations of the tip motion in the second mode. Moreover, the relations of the maximum instantaneous magnitude (MIM) to the amplitude setpoint and the Young's modulus of the sample surface are investigated. The results suggest that the MIM can be used to characterize the nanomechanical property of the sample surface at high amplitude setpoints.

Vertically aligned graphene nanosheets (VAGNs) are a class of graphitic carbon in which few layers of graphene nanosheets are aligned perpendicular to the plane of the substrate. The change in water contact angle (from 103° to 135°) with VAGNs, as a function of change in the surface geometry, is analysed. Theoretical calculations and comparison with the experimental data shows that the apparent contact angle values of VAGNs are closer to that of the fully non-wetting mode or ideal Cassie mode of wetting. The ideal Cassie mode of wetting also explains the variation of the water contact angle of VAGNs with the surface morphology of the material and predicts how surface parameters can be modified to get the required wettability for a certain application of this material.

Devices with metallic nanoconstrictions functionalized by organic molecules are promising candidates for the role of functional devices in molecular electronics. However, at the moment little is known about transport and noise properties of nanoconstriction devices of this kind. In this paper, transport properties of bare gold and molecule-containing tunable cross-section nanoconstrictions are studied using low-frequency noise spectroscopy. Normalized noise power spectral density (PSD) S_I/I² dependencies are analyzed for a wide range of sample resistances R from 10 Ohm to 10 MOhm. The peculiarities and physical background of the flicker noise behavior in the low-bias regime are studied. It is shown that modification of the sample surface with benzene-1,4-dithiol molecules results in a decrease of the normalized flicker noise spectral density level in the ballistic regime of sample conductance. The characteristic power dependence of normalized noise PSD as a function of system resistance is revealed. Models describing noise behavior for bare gold and BDT modified samples are developed and compared with the experimental data for three transport regimes: diffusive, ballistic and tunneling. Parameters extracted from models by fitting are used for the characterization of nanoconstriction devices.

Biomedical applications based on the magnetic properties of superparamagnetic iron oxide nanoparticles (SPIONs) may be altered by the mechanical attachment or cellular uptake of these nanoparticles. When nanoparticles interact with living cells, they are captured and internalized into intracellular compartments. Consequently, the magnetic behavior of the nanoparticles is modified. In this paper, we investigated the change in the magnetic response of 14 nm magnetic nanoparticles (Fe₃O₄) in different solutions, both as a stable liquid suspension (one of them mimicking the cellular cytoplasm) and when associated with cells. The field-dependent magnetization curves from inert fluids and cell cultures were determined by using an alternating gradient magnetometer, MicroMagTM 2900. The equipment was adapted to measure liquid samples because it was originally designed only for solids. In order to achieve this goal, custom sample holders were manufactured. Likewise, the nuclear magnetic relaxation dispersion profiles for the inert fluid were also measured by fast field cycling nuclear magnetic relaxation relaxometry. The results show that SPION magnetization in inert fluids was affected by the carrier liquid viscosity and the concentration. In cell cultures, the mechanical attachment or confinement of the SPIONs inside the cells accounted for the change in the dynamic magnetic behavior of the nanoparticles. Nevertheless, the magnetization value in the cell cultures was slightly lower than that of the fluid simulating the viscosity of cytoplasm, suggesting that magnetization loss was not only due to medium viscosity but also to a reduction in the mechanical degrees of freedom of SPIONs rotation and translation inside cells. The findings presented here provide information on the loss of magnetic properties when nanoparticles are suspended in viscous fluids or internalized in cells. This information could be exploited to improve biomedical applications based on magnetic properties such as magnetic hyperthermia, contrast agents and drug delivery.