Table of contents

In this work glucose (G), α-cyclodextrin (α-CD) and sodium salt of carboxymethyl cellulose (CMCNa) are used as dispersing agents for graphene oxide (GO), exploring the influence of both saccharide units and geometric/steric hindrance on the rheological, thermal, wettability and electrochemical properties of a GO/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) nanocomposite. By acting on the saccharide-based additives, we can modulate the rheological, thermal, and wettability properties of the GO/PEDOT:PSS nanocomposite. Firstly, the influence of all the additives on the rheological behaviour of GO and PEDOT:PSS was investigated separately in order to understand the effect of the dispersing agent on both the components of the ternary nanocomposite, individually. Subsequently, steady shear and dynamic frequency tests were conducted on all the nanocomposite solutions, characterized by thermal, wettability and morphological analysis. Finally, the electrochemical properties of the GO/PEDOT composites with different dispersing agents for supercapacitors were investigated using cyclic voltammetry (CV). The CV results revealed that GO/PEDOT with glucose exhibited the highest specific capacitance among the systems investigated.

In certain polymers the graphenization of carbon atoms can be obtained by laser writing owing to the easy absorption of long-wavelength radiation, which generates photo-thermal effects. On a polyimide surface this process allows the formation of a nanostructured and porous carbon network known as laser-induced graphene (LIG). Herein we report on the effect of the process parameters on the morphology and physical properties of LIG nanostructures. We show that the scan speed and the frequency of the incident radiation affect the gas evolution, inducing different structure rearrangements, an interesting nitrogen self-doping phenomenon and consequently different conduction properties. The materials were characterized by infrared and Raman spectroscopy, XPS elemental analysis, electron microscopy and electrical/electrochemical measurements. In particular the samples were tested as interdigitated electrodes into electrochemical supercapacitors and the optimized LIG arrangement was tested in parallel and series supercapacitor configurations to allow power exploitation.

Advancements in single-molecule force spectroscopy techniques such as atomic force microscopy and magnetic tweezers allow investigation of how domain folding under force can play a physiological role. Combining these techniques with protein engineering and HaloTag covalent attachment, we investigate similarities and differences between four model proteins: I10 and I91—two immunoglobulin-like domains from the muscle protein titin, and two α + β fold proteins—ubiquitin and protein L. These proteins show a different mechanical response and have unique extensions under force. Remarkably, when normalized to their contour length, the size of the unfolding and refolding steps as a function of force reduces to a single master curve. This curve can be described using standard models of polymer elasticity, explaining the entropic nature of the measured steps. We further validate our measurements with a simple energy landscape model, which combines protein folding with polymer physics and accounts for the complex nature of tandem domains under force. This model can become a useful tool to help in deciphering the complexity of multidomain proteins operating under force.

Tumorigenesis is related to an imbalance in controlling mechanisms of apoptosis. Expression of the genes BCL-2 and BCL-xL results in the promotion of cell survival by inhibiting apoptosis. Thus, a novel approach to suppress antiapoptotic genes is the use of small interfering RNA (siRNA) in cancer cells. However, there are some limitations for the application of siRNA such as the need for vectors to pass the cell membrane and deliver the nucleic acid. In this study CaP-siRNA-PEG-polyanion hybrid nanoparticles were developed to promote siRNA delivery to cultured human breast cancer cells (MCF-7) in order to evaluate whether the silencing of antiapoptotic genes BCL-2 and BCL-xL by siRNA would increase cancer cell death. After 48 h of incubation the expression of BCL-2 and BCL-xL genes decreased to 49% and 23%, respectively. The siRNA sequence used induced cancer cell death at a concentration of 200 nM siRNA after 72 h of incubation. As the targeted proteins are related to the resistance to chemotherapeutic drugs, the nanocarriers systems were also tested in the presence of doxorubicin (DOX). The results showed a significant reduction in the CC₅₀ of the DOX, after silencing the antiapoptotic genes. In addition, an increase in apoptotic cell counts for both incubations conditions was observed as well. In conclusion, silencing antiapoptotic genes such as BCL-2 and BCL-xL through the use of siRNA carried by hybrid nanoparticles showed to be effective in vitro, and presents a promising strategy for pre-clinical analysis, especially when combined with DOX against breast cancer.

Amorphous oxide semiconductor thin-film transistors (TFT) have been considered as outstanding switch devices owing to their high mobility. However, because of their amorphous channel material with a certain level of density of states, a fast transient charging effect in an oxide TFT occurs, leading to an underestimation of the mobility value. In this paper, the effects of the fast charging of high-performance bilayer oxide semiconductor TFTs on mobility are examined in order to determine an accurate mobility extraction method. In addition, an approach based on a pulse I_D–V_G measurement method is proposed to determine the intrinsic mobility value. Even with the short pulse I_D–V_G measurement, a certain level of fast transient charge trapping cannot be avoided as long as the charge-trap start time is shorter than the pulse rising time. Using a pulse-amplitude-dependent threshold voltage characterization method, we estimated a correction factor for the apparent mobility, thus allowing us to determine the intrinsic mobility.

Using remote N₂ plasma treatment to promote dielectric deposition on the dangling-bond free MoS₂ is explored for the first time. The N₂ plasma induced damages are systematically studied by the defect-sensitive acoustic-phonon Raman of single-layer MoS₂, with samples undergoing O₂ plasma treatment as a comparison. O₂ plasma treatment causes defects in MoS₂ mainly by oxidizing MoS₂ along the already defective sites (most likely the flake edges), which results in the layer oxidation of MoS₂. In contrast, N₂ plasma causes defects in MoS₂ mainly by straining and mechanically distorting the MoS₂ layers first. Owing to the relatively strong MoS₂–substrate interaction and chemical inertness of MoS₂ in N₂ plasma, single-layer MoS₂ shows great stability in N₂ plasma and only stable point defects are introduced after long-duration N₂ plasma exposure. Considering the enormous vulnerability of single-layer MoS₂ in O₂ plasma and the excellent stability of single-layer MoS₂ in N₂ plasma, the remote N₂ plasma treatment shows great advantage as surface functionalization to promote dielectric deposition on single-layer MoS₂.

Thermal scanning probe lithography (t-SPL) is applied to the fabrication of chemical guiding patterns for directed self-assembly (DSA) of block copolymers (BCP). The two key steps of the overall process are the accurate patterning of a poly(phthalaldehyde) resist layer of only 3.5 nm thickness, and the subsequent oxygen-plasma functionalization of an underlying neutral poly(styrene-random-methyl methacrylate) brush layer. We demonstrate that this method allows one to obtain aligned line/space patterns of poly(styrene-block-methyl methacrylate) BCP of 18.5 and 11.7 nm half-pitch. Defect-free alignment has been demonstrated over areas of tens of square micrometres. The main advantages of t-SPL are the absence of proximity effects, which enables the realization of patterns with 10 nm resolution, and its compatibility with standard DSA methods. In the brush activation step by oxygen-plasma exposure, we observe swelling of the brush. This effect is discussed in terms of the chemical reactions occurring in the exposed areas. Our results show that t-SPL can be a suitable method for research activities in the field of DSA, in particular for low-pitch, high-χ BCP to achieve sub-10 nm line/space patterns.

A comparative study of the monovalent (Li, Na, and K) and multivalent (Be, Mg, Ca, and Al) metal ion adsorption and diffusion on an electronically semi-metallic two-dimensional nanosheet of 1T structured TiS₂ is presented here to contribute to the search for abundant, cheap, and nontoxic ingredients for efficient rechargeable metal ion batteries. The total formation energy of the metal ion adsorption and the Bader charge analysis show that the divalent Mg and Ca ions can have a charge storage density double that of the monovalent Li, Na, and K ions, while the Be and Al ions form metallic clusters even at a low adsorption density because of their high bulk energies. The adsorption of Mg ions shows the lowest averaged open circuit voltage (0.13 V). The activation energy barriers for the diffusion of metal ions on the surface of the monolayer successively decrease from Li to K and Be to Ca. Mg and Ca, being divalent, are capable of storing a higher power density than Li while K and Na have a higher rate capability than the Li ions. Therefore, rechargeable Li ion batteries can be totally or partially replaceable by Mg ion batteries, where high power density and high cell voltage are required, while the abundant, cheap, and fast Na ions can be used for green grid applications.

Recently, many researchers have been paying attention to nanogenerators (NGs) as energy sources for self-powered mirco-nano systems, and studying how to achieve their higher power generation. Hence, we propose a hybrid-type NG for harvesting both the piezoelectric and triboelectric effect simultaneously. In the proposed hybrid NG, the piezoelectric NG (PNG) and triboelectric NG (TENG) are fabricated using polydimethylsiloxane (PDMS) and perovskite zinc stannite (ZnSnO₃) nanocubes with a high charge polarization of 59 uC cm⁻² composite (PDMS + ZnSnO₃) and UV surface-treated PDMS, respectively. To effectively combine a high output current of PNG and a high voltage of TENG, these two NGs are stacked upon each other, and separated by sponge spacers providing a uniform air gap for the triboelectric effect. In particular, this fabricated structure has a low Young's modulus for piezoelectricity. The proposed hybrid NG device effectively achieves a combined peak voltage of 300 V on an open circuit, a power density of 10.41 mW cm⁻² at 1 MΩ load, and a maximum short circuit current density of 16 mA cm⁻² at 50 Ω load. It is feasible that the proposed NG can be utilized as a source for various self-powered systems.

Molybdenum oxide (MoO₃) has gained immense attention because of its high electron mobility, wide band gap, and excellent optical and catalytic properties. However, the synthesis of uniform and large-area MoO₃ is challenging. Here, we report the synthesis of wafer-scale α-MoO₃ by plasma oxidation of Mo deposited on Si/SiO₂. Mo was oxidized by O₂ plasma in a plasma enhanced chemical vapor deposition (PECVD) system at 150 °C. It was found that the synthesized α-MoO₃ had a highly uniform crystalline structure. For the as-synthesized α-MoO₃ sensor, we observed a current change when the relative humidity was increased from 11% to 95%. The sensor was exposed to different humidity levels with fast recovery time of about 8 s. Hence this feasibility study shows that MoO₃ synthesized at low temperature can be utilized for gas sensing applications by adopting flexible device technology.

Cationic polymers as non-viral gene delivery carriers are widely used because of their strong condensing properties and long-term safety, but acute cytotoxicity is a persistent challenge. In this study, two types of polyplexes were prepared by co-formulating plasmid DNA and two cationic diblock copolymers PABOXA₅-b-PMOXA₃₃-PA (primary amine) and PABOXA₅-b-PMOXA₃₃-TA (tertiary amine) to check their transfection efficacies in HeLa cells and HEK293T cells, respectively. The plasmid DNA/PABOXA₅-b-PMOXA₃₃-PA polyplex showed higher transfection efficacy compared to the plasmid DNA/PABOXA₅-b-PMOXA₃₃-TA polyplex under an N/P ratio of 40. Both polymers exhibited low toxicity, attributed to the shielding effect of a hydrophilic, noncharged block. Mechanistic insight into differential transfection efficiencies of the polymers were gained by visualization and comparison of the condensates via transmission electron and atomic force microscopy. The results provide information suited for further structure optimization of polymers that are aimed for targeted gene delivery.

Gallium selenide is one of the most promising candidates to extend the window of band gap values provided by existing two-dimensional semiconductors deep into the visible potentially reaching the ultraviolet. However, the tunability of its band gap by means of quantum confinement effects is still unknown, probably due to poor nanosheet stability. Here, we demonstrate that the optical band gap band of GaSe nanosheets can be tuned by ∼120 meV from bulk to 8 nm thick. The luminescent response of very thin nanosheets (<8 nm) is strongly quenched due to early oxidation. Oxidation favors the emergence of sharp material nanospikes at the surface attributable to strain relaxation. Simultaneously, incorporated oxygen progressively replaces selenium giving rise to Ga₂O_3, with a residual presence of Ga₂Se₃ that tends to desorb. These results are relevant for the development and design of visible/ultraviolet electronics and optoelectronics with tunable functionalities based on atomically thin GaSe.

Fluorescent composite hydrogels have found widespread applications, especially in spatial and temporal monitoring of in vivo hydrogel behaviors via the emitting optical signal. However, most existing fluorescent composite hydrogels suffer from limited capability of deep tissue imaging and complicated fabrication routes. We herein report a facile method for fabricating fluorescent composite hydrogels based on the in situ synthesis of NaYF₄:Yb, Er upconversion nanoparticles (UCNPs). This approach employs polyacrylamide (PAAm) hydrogels as a template, where the interconnected pores within the hydrogel act as nanoreactors to confine the growth of nanocrystals. We then obtained a fluorescent composite hydrogel exhibiting upconversion fluorescence and enhanced mechanical properties. The fluorescence spectra show that the fluorescence intensity decreases with decreasing size of the UCNPs. We investigated the relationship between the optical properties of the fluorescent composite hydrogel and the incorporated UCNPs based on the morphology, size, and distribution of the UCNPs by using scanning electron microscopy and transmission electron microscopy. In addition, we demonstrated the applicability of the synthesized hydrogel for deep tissue imaging through an in vitro tissue penetration experiment. Compressive and dynamic rheological testing reveal enhanced mechanical properties with increasing UCNP concentration. The fabricated upconversion fluorescent composite hydrogel may pave the way for monitoring the in vivo behavior of biomimetic materials via deep tissue imaging.

Alloy nanoparticles with variable compositions add a new dimension to nanoscience and have many applications. Here we suggest a novel approach for the fabrication of variable composition alloy nanoparticles that is based on a Haberland type gas aggregation cluster source with a custom-made multicomponent target for magnetron sputtering. The approach, which was demonstrated here for gold-rich AgAu nanoparticles, combines a narrow nanoparticle size distribution with in operando variation of composition via the gas pressure as well as highly efficient usage of target material. The latter is particularly attractive for precious metals. Varying argon pressure during deposition, we achieved in operando changes of AgAu alloy nanoparticle composition of more than 13 at%. The alloy nanoparticles were characterized by x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. The characteristic plasmon resonances of multilayer nanoparticle composites were analyzed by UV–vis spectroscopy. Tuning of the number of particles per unit area (particle densities) within individual layers showed an additional degree of freedom to tailor the optical properties of multilayer nanocomposites. By extension of this technique to more complex systems, the presented results are expected to encourage and simplify further research based on plasmonic multi-element nanoparticles. The present method is by no means restricted to plasmonics or nanoparticle based applications, but is also highly relevant for conventional magnetron sputtering of alloys and can be extended to in operando control of alloy concentration by magnetic field.

In this study, a simple and fast approach of band gap formation in a single layer graphene nanoribbon (sGNR) is demonstrated by using hexaazatriphenylenehexacarbonitrile (HAT-CN₆) as an adsorbate molecule. sGNRs were successfully synthesized through the unzipping of double-walled carbon nanotubes followed by casting HAT-CN₆ in acetone solution to alter the electronic properties of the sGNRs. Then, the electrical property of a sGNR was measured using a field effect transistor structure and also by point-contact current imaging atomic force microscopy. The results demonstrate the formation of electron trapping sites with the nanoparticles and the neck structure of the sGNR near the adsorbed region of the molecule. Therefore, the charge carriers on the sGNR can only pass through the neck region, which works similarly to a narrow sGNR. Such a narrow sGNR has a lateral confinement of charge carriers around the neck region; hence, the device becomes semiconducting. The fabricated semiconducting sGNR could be widely used in electronic devices.

From environmental and health perspectives, the acquisition of a surface anti-biofouling property holds important significance for the usability of VO₂ intelligent windows. Herein, we firstly deposited amorphous Ta₂O₅ nanoparticles on VO₂ film by the magnetron sputtering method. It was found that the amorphous nano-Ta₂O₅ coating possessed a favorable anti-biofouling capability against Pseudomonas aeruginosa as an environmental microorganism model, behind which lay the mechanism that the amorphous nano-Ta₂O₅ could interrupt the microbial membrane electron transport chain and significantly elevate the intracellular reactive oxygen species (ROS) level. A plausible relationship was established between the anti-biofouling activity and physicochemical nature of amorphous Ta₂O₅ nanoparticles from the perspective of defect chemistry. ROS-induced oxidative damage gave rise to microbial viability loss. In addition, the amorphous nano-Ta₂O₅ coating can endow VO₂ with favorable cytocompatibility with human skin fibroblasts. This study may provide new insights into understanding the anti-biofouling and antimicrobial actions of amorphous transition metal oxide nanoparticles, which is conducive to expanding their potential applications in environmental fields.

Three sets of β-NaGdF₄:Yb³⁺, Er³⁺ nanocrystals (NCs) with different shapes (spherical and more complex flower shapes), different sizes (6–17 nm) and Yb³⁺ concentrations (2%–15%) were synthesized by a co-precipitation method using oleic acid as a stabilizing agent. The uncommon, single-crystalline flower-shaped NCs were obtained by simply adjusting the fluorine-to-lanthanides molar ratio. Additionally, some of the NCs with different sizes have been covered by the un-doped shell. The crystal phase, shapes and sizes of all NCs were examined using transmission electron microscopy and x-ray diffraction methods. Simultaneously, upconversion luminescence and lifetimes, under 980 nm excitation, were measured and the changes in green to red (G/R) emission ratios as well as emission decay times were correlated with the evolution of nanocrystal sizes and surface to volume ratios. Three different mechanisms responsible for the changes in G/R ratios were presented and discussed.

High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO₂ were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO₂/floating gate of single layer of Ge QDs in HfO₂/tunnel HfO₂/p-Si wafers. Both Ge and HfO₂ are nanostructured by RTA at moderate temperatures of 600–700 °C. By nanostructuring at 600 °C, the formation of a single layer of well separated Ge QDs with diameters of 2–3 nm at a density of 4–5 × 10¹⁵ m^–2 is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO₂ nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO₂ NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO₂ NCs boundaries, while another part of the Ge atoms is present inside the HfO₂ lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8 ± 0.5 V and a capacitance–time characteristic with 14% capacitance decay in the first 3000–4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO₂, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.

Monolayer blue phosphorus has recently been synthesized by molecular beam epitaxial growth on Au(111) substrate. It is intriguing to compare this new 2D phase of phosphorus with phosphorene as to both fundamental properties and application prospects. Here, first-principles calculations are carried out to explore the adsorption behaviors of environmental gas molecules on monolayer blue phosphorus, including O₂, NO, SO₂, NH₃, H₂O, NO₂, CO₂, H₂S, CO, and N₂, and address their effects on the electronic properties of the material. Our calculations show that O₂ is prone to dissociate and tends to chemisorb on the blue phosphorus sheet, phenomena which has also been observed in phosphorene. The other gas molecules can stably physisorb on monolayer blue phosphorus, showing different interaction strengths with the monolayer. These molecules induce distinct modifications to the band gap, carrier effective mass, and work function, which also depends on the molecular coverage. The responses of the electronic properties are subject to the charge transfer as well as alignment of the frontier molecular orbital levels of the gaseous molecules and band edges of the parent sheet. These results suggest that monolayer blue phosphorus is a promising candidate for novel gas sensors.

The aging of supported Ag nanostructures upon storage in ambient conditions (air and room temperature) for 20 months has been studied. The samples are produced on glass substrates by pulsed laser deposition (PLD); first a 15 nm thick buffer layer of amorphous aluminum oxide (a-Al₂O₃) is deposited, followed by PLD of Ag. The amount of deposited Ag ranges from that leading to a discontinuous layer up to an almost-percolated layer with a thickness of <6 nm. Some regions of the as-grown silver layers are converted, by laser induced dewetting, into round isolated nanoparticles (NPs) with diameters of up to ∼25 nm. The plasmonic, structural and chemical properties of both as-grown and laser exposed regions upon aging have been followed using extinction spectroscopy, scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. The results show that the discontinuous as-grown regions are optically and chemically unstable and that the metal becomes oxidized faster, the smaller the amount of Ag. The corrosion leads to the formation of nitrile species due to the reaction between NO_x species from the atmosphere adsorbed at the surface of Ag, and hydrocarbons adsorbed in defects at the surface of the a-Al₂O₃ layer during the deposition of the Ag nanostructures by PLD that migrate to the surface of the metal with time. The nitrile formation thus results in the main oxidation mechanism and inhibits almost completely the formation of sulphate/sulphide. Finally, the optical changes upon aging offer an easy-to-use tool for following the aging process. They are dominated by an enhanced absorption in the UV side of the spectrum and a blue-shift of the surface plasmon resonance that are, respectively, related to the formation of a dielectric overlayer on the Ag nanostructure and changes in the dimensions/features of the nanostructures, both due to the oxidation process.

The modulation of charge carrier concentration allows us to tune the Fermi level (E_F) of graphene thanks to the low electronic density of states near the E_F. The introduced metal oxide thin films as well as the modified transfer process can elaborately maneuver the amounts of charge carrier concentration in graphene. The self-encapsulation provides a solution to overcome the stability issues of metal oxide hole dopants. We have manipulated systematic graphene p-n junction structures for electronic or photonic application-compatible doping methods with current semiconducting process technology. We have demonstrated the anticipated transport properties on the designed heterojunction devices with non-destructive doping methods. This mitigates the device architecture limitation imposed in previously known doping methods. Furthermore, we employed E_F-modulated graphene source/drain (S/D) electrodes in a low dimensional transition metal dichalcogenide field effect transistor (TMDFET). We have succeeded in fulfilling n-type, ambipolar, or p-type field effect transistors (FETs) by moving around only the graphene work function. Besides, the graphene/transition metal dichalcogenide (TMD) junction in either both p- and n-type transistor reveals linear voltage dependence with the enhanced contact resistance. We accomplished the complete conversion of p-/n-channel transistors with S/D tunable electrodes. The E_F modulation using metal oxide facilitates graphene to access state-of-the-art complimentary-metal-oxide-semiconductor (CMOS) technology.