Graphene and Graphene Analogs toward Optical, Electronic, Spintronic, Green-Chemical, Energy-Material, Sensing, and Medical Applications

Recent advances in the functionalization, substitutional doping and applications of graphene/graphene composite nanomaterials

Recently, graphene and graphene-based nanomaterials have emerged as advanced carbon functional materials with specialized unique electronic, optical, mechanical, and chemical properties. These properties have made graphene an exceptional material for a wide range of promising applications in biological and non-biological fields. The present review illustrates the structural modifications of pristine graphene resulting in a wide variety of derivatives. The significance of substitutional doping with alkali-metals, alkaline earth metals, and III-VII group elements apart from the transition metals of the periodic table is discussed. The paper reviews various chemical and physical preparation routes of graphene, its derivatives and graphene-based nanocomposites at room and elevated temperatures in various solvents. The difficulty in dispersing it in water and organic solvents make it essential to functionalize graphene and its derivatives. Recent trends and advances are discussed at length. Controlled reduction reactions in the presence of various dopants leading to nanocomposites along with suitable surfactants essential to enhance its potential applications in the semiconductor industry and biological fields are discussed in detail.

Enhanced Stability of Dopamine Delivery via Hydrogel with Integrated Graphene

The synthesis of graphene-based materials for drug delivery represents an area of active research, and the use of graphene in drug delivery systems is promising due to its unique properties. Thus, in the present work, we discuss the potential of few-layer graphene in a hydrogel system for dopamine release. The hydrogels are frequently used for these systems for their special physico-chemical properties, which can ensure that the drug is effectively released in time. However, the release from such structures is mostly determined by diffusion alone, and to overcome this restriction, the hydrogel can be "improved" with nanoscale fillers like graphene. The release kinetics of the composite obtained were analyzed to better understand how the use of graphene, instead of the more common graphene oxide (GO) and reduced graphene oxide (rGO), affects the characteristics of the system. Thus, the systems developed in this study consist of three main components: biopolymer, graphene, and dopamine. The hydrogels with graphene were prepared by combining two different solutions, one with polyacrylic acid and agarose and one with graphene prepared by the exfoliation method with microwave irradiation. The drug delivery systems were developed by adding dopamine to the obtained hydrogels. After 24 h of release, the presence of dopamine was observed, demonstrating that the system developed can slow down the drug's degradation because of the interactions with the graphene nanoplates and the polymer matrix.

Multi-Sensing Platform Based on 2D Monoelement Germanane

Covalently functionalized germanane is a novel type of fluorescent probe that can be employed in material science and analytical sensing. Here, a fluorometric sensing platform based on methyl-functionalized germanane (CH3 Ge) is developed for gas (humidity and ammonia) sensing, pH (1-9) sensing, and anti-counterfeiting. Luminescence (red-orange) is seen when a gas molecule intercalates into the interlayer space of CH3 Ge and the luminescence disappears upon deintercalation. This allows for direct detection of gas absorption via fluorometric measurements of the CH3 Ge. Structural and optical properties of CH3 Ge with intercalated gas molecules are investigated by density functional theory (DFT). To demonstrate real-time and on-the-spot testing, absorbed gas molecules are first precisely quantified by CH3 Ge using a smartphone camera with an installed color intensity processing application (APP). Further, CH3 Ge-paper-based sensor is integrated into real food packets (e.g., fish and milk) to monitor the shelf life of perishable foods. Finally, CH3 Ge-based rewritable paper is applied in water jet printing to illustrate the potential for secret communication with quick coloration and good reversibility by water evaporation.

Advances in metal graphitic nanocapsules for biomedicine

Metal graphitic nanocapsules have the advantages of both graphitic and metal nanomaterials, showing great promise in biomedicine. On one hand, the chemically inert graphitic shells are able to protect the metal core from external environments, quench the fluorescence signal from the biological system, offer robust platform for targeted molecules or drugs loading, and act as stable Raman labels or internal standard molecule. On the other hand, the metal cores with different compositions, sizes, and morphologies show unique physicochemical properties, and further broaden their biomedical functions. In this review, we firstly introduce the preparation, classification, and properties of metal graphitic nanocapsules, then summarize the recent progress of their applications in biodetection, bioimaging, and therapy. Challenges and their development prospects in biomedicine are eventually discussed in detail. We expect the versatile metal graphitic nanocapsules will advance the development of future clinical biomedicine.

Structural, Electronic, and Magnetic Characteristics of Graphitic Carbon Nitride Nanoribbons and Their Applications in Spintronics

The development of quantum information and quantum computing technology requires special materials to design and manufacture nanosized spintronic devices. Possessing remarkable structural, electronic, and magnetic characteristics, graphitic carbon nitride (g-C₃N₄) can be a promising candidate as a building block of futuristic nanoelectronics and spintronic systems. Here, using first-principles calculations, we perform a comprehensive study on the structural stability as well as electronic and magnetic properties of triazine-based g-C₃N₄ nanoribbons (gt-CNRs). Our calculations show that gt-CNRs with different edge conformation exhibit distinct electronic and magnetic characteristics, which can be tuned by the edge H-passivation rate. By investigating gt-CNRs with various possible edge configurations and H-termination rates, we show that while the ferromagnetic (FM) ordering of gt-CNRs stays preserved for all of the studied configurations, half metallicity can only be achieved in nanoribbons with specific edge structure under full H-passivation rate. For spintronic application purposes, we also study spin-transport properties of half-metal gt-CNRs. By determining the suitable gt-CNR configuration, we show the possibility of developing a perfect gt-CNR-based spin filter with a spin filter efficiency (SFE) of 100%. Considering the above-mentioned notable electronic and magnetic characteristics as well as its high thermal stability, we show that gt-CNR would be a remarkable material to fabricate multifunctional spintronic devices.

Revealing intrinsic spin coupling in transition metal-doped graphene

Graphene materials offer attractive possibilities in spintronics due to their unique atomic and electronic structures, which is in contrast to their limited applications in the design of sophisticated spintronic devices. This should be attributed to the lack of knowledge about the intrinsic characteristics of graphene materials, especially the diverse correlations between sites within the materials and their roles in spin-signal generation and propagation. This work comprehensively studies the spin couplings between transition metal atoms doped on graphene and reveals their potential application in spintronic device design through the realization of various logic gates. In addition, the effects of the distance between doped metal atoms and the number of carbon layers on the logic gate implementation further verify that the spin-coupling effect can exhibit a certain distance dependence and space propagation. The achievements in this work uncover the potential value of graphene materials and are expected to open up new avenues for exploring their application in the design of sophisticated spintronic devices.

Carbon Graphitization: Towards Greener Alternatives to Develop Nanomaterials for Targeted Drug Delivery

Carbon nanomaterials have attracted great interest for their unique physico-chemical properties for various applications, including medicine and, in particular, drug delivery, to solve the most challenging unmet clinical needs. Graphitization is a process that has become very popular for their production or modification. However, traditional conditions are energy-demanding; thus, recent efforts have been devoted to the development of greener routes that require lower temperatures or that use waste or byproducts as a carbon source in order to be more sustainable. In this concise review, we analyze the progress made in the last five years in this area, as well as in their development as drug delivery agents, focusing on active targeting, and conclude with a perspective on the future of the field.

DNA/RNA sequencing using germanene nanoribbons via two dimensional molecular electronic spectroscopy: an ab initio study

Developing fast, reliable, and cost effective, yet practical DNA/RNA sequencing methods and devices is a must. In this regard, motivated by the recently introduced two-dimensional electronic molecular spectroscopy (2DMES) technique for molecular recognition, and the compatibility of 2D layers of group IV elements with the current technology of manufacturing electronic devices, we investigate the capability of germanene nanoribbons (GeNRs) as a feasible, accurate, and ultra-fast sequencing device under the application of 2DMES. We show that by employing 2DMES, not only can GeNRs unambiguously distinguish different nucleobases to sequence DNA/RNA, they are also capable of recognizing methylated nucleobases that could be related to cancerous cell growth. Our calculations indicate that, compared to frequently used graphene layers, germanene provides more distinct adsorption energies for different nucleobases which implies its better ability to recognize various molecules unambiguously. By calculating the conductance sensitivity of the system for experimental purposes, we also show that the introduced sequencing device possesses a high sensitivity and selectivity characteristic. Thus, our proposed system would be a promising device for next-generation DNA sequencing technologies and would be realizable using the current protocols of fabricating electronic devices.

Magnetic Resonance Studies of Hybrid Nanocomposites Containing Nanocrystalline TiO2 and Graphene-Related Materials

Nanocomposites based on nanocrystalline titania modified with graphene-related materials (reduced and oxidized form of graphene) showed the existence of magnetic agglomerates. All parameters of magnetic resonance spectra strongly depended on the materials’ modification processes. The reduction of graphene oxide significantly increased the number of magnetic moments, which caused crucial changes in the reorientation and relaxation processes. At room temperature, a wide resonance line dominated for all nanocomposites studied and in some cases, a narrow resonance line derived from the conduction electrons. Some nanocomposites (samples of titania modified with graphene oxide, prepared with the addition of water or butan-1-ol) showed a single domain magnetic (ferromagnetic) arrangement, and others (samples of titania modified with reduced graphene oxide) exhibited magnetic anisotropy. In addition, the spectra of EPR from free radicals were observed for all samples at the temperature of 4 K. The magnetic resonance imaging methods enable the capturing of even a small number of localized magnetic moments, which significantly affects the physicochemical properties of the materials.

Structural, thermal, and electronic properties of two-dimensional gallium oxide(ß-Ga2O3) from first-principles design

Two-dimensional (2D) materials with exotic electronic, optical and mechanical properties have attracted tremendous attention in the last two decades, due to their potential applications in electronics, energy storage and conversion technologies. However, only a few dozen 2D materials have been successfully synthesized or exfoliated. Motivated by the recent discovery of 2D gallenene, we have explored new 2D allotropes of ß-Ga 2 O 3 , an emerging wide-band gap transparent conductive oxide (TCO) with a wide range of semiconducting applications. All the possible 2D allotropes of ß-Ga 2 O 3 with high energetic stability have been predicted using particle swarm optimization, combined with density functional theory calculations. The structural and dynamical stability of the predicted 2D allotropes has been analyzed. Although ß-Ga 2 O 3 is not a van der Waals material, results predict that one or two allotropes of ß-Ga 2 O 3 are stable. In addition, the accurate band structures of these 2D semiconducting oxides have been calculated using both the GGA and LDA-1/2 approach. Remarkably, monolayer Ga 2 O 3 (100) has a larger indirect band gap of 4 eV, demonstrating a new avenue for the discovery of 2D ß-Ga 2 O 3 based nano-devices with enhanced electronic properties.

Supra-Binary Polarization in a Ferroelectric Nanowire

The prediction and observation of supra-binary polarization in a ferroelectric nanowire (FNW) covered with a semicylindrical gate that provides an anisotropic electric field in the FNW are reported. There are gate-voltage-driven transitions between four polarization states in the FNW's cross-section, dubbed vertical-up, vertical-down, radial-in, and radial-out. They are determined by the interplay between the spatial depolarization energy and the free energy induced by an anisotropic external electric field, in clear distinction from the conventional film-based binary ferroelectricity. When the FNW is mounted on a biased graphene nanoribbon (GNR), these transitions induce exotic current-voltage hysteresis in the FNW-GNR transistor. This discovery suggests new operating mechanisms of ferroelectric devices. In particular, it enables intrinsic quaternary-digit information manipulation in parallel to the bit manipulation employed in conventional data storage.

Green Approaches to Carbon Nanostructure-Based Biomaterials

The family of carbon nanostructures comprises several members, such as fullerenes, nano-onions, nanodots, nanodiamonds, nanohorns, nanotubes, and graphene-based materials. Their unique electronic properties have attracted great interest for their highly innovative potential in nanomedicine. However, their hydrophobic nature often requires organic solvents for their dispersibility and processing. In this review, we describe the green approaches that have been developed to produce and functionalize carbon nanomaterials for biomedical applications, with a special focus on the very latest reports.

Scalable Production of Boron Quantum Dots for Broadband Ultrafast Nonlinear Optical Performance

A simple and effective approach based on the liquid phase exfoliation (LPE) method has been put forward for synthesizing boron quantum dots (BQDs). By adjusting the interactions between bulk boron and various solvents, the average diameter of produced BQDs is about 7 nm. The nonlinear absorption (NLA) responses of as-prepared BQDs have been systematically studied at 515 nm and 1030 nm. Experimental results prove that BQDs possess broadband saturable absorption (SA) and good third-order nonlinear optical susceptibility, which are comparable to graphene. The fast relaxation time and slow relaxation time of BQDs at 515 nm and 1030 nm are about 0.394–5.34 ps and 4.45–115 ps, respectively. The significant ultrafast nonlinear optical properties can be used in optical devices. Here, we successfully demonstrate all-optical diode application based on BQDs/ReS₂ tandem structure. The findings are essential for understanding the nonlinear optical properties in BQDs and open a new pathway for their applications in optical devices.

Two-dimensional aluminium, gallium, and indium metallic crystals by first-principles design

Rapidly emerging two-dimensional (2D) atomic layer crystals exhibit diverse, tunable electronic properties. They appear to be more flexible than 3D crystals with greater versatility and improved functionality in a wide range of potential applications. Among these 2D materials, metallic crystals are relatively unexplored although two allotropes of gallenene (2D gallium) have been synthesized on a range of substrates. Based on these experimental findings, we investigate systematically the group 13 metals using first-principles density functional theory calculations and an unbiased structural search. In this study, the electronic structure, bonding characteristics, and phonon properties of predicted 2D allotropes of group 13 metals are calculated, including the expected effects of strain induced by substrates on the dynamical stability. Theoretical results predict that most group 13 elements have one or more stable 2D allotropes with the preferred allotrope depending on the cell shape relaxation and strain, indicating that the substrate will determine the overall allotrope preferred. This demonstrates a new avenue for the discovery of thermodynamically stable 2D metallic layers, with properties potentially suitable for electronic and optoelectronic applications.

A high performance N-doped graphene nanoribbon based spintronic device applicable with a wide range of adatoms

Designing and fabricating nanosize spintronic devices is a crucial task to develop information technology of the future. However, most of the introduced spin filters suffer from several limitations including difficulty in manipulating the spin current, incapability in utilizing a wide range of dopants to provide magnetism, or obstacles in their experimental realization. Here, by employing first principles calculations, we introduce a structurally simple and functionally efficient spin filter device composed of a zigzag graphene nanoribbon (ZGNR) with an embedded nitrogenated divacancy. We show that the proposed system, possessing a robust ferromagnetic (FM) ordering, exhibits perfect half metallic behavior in the absence of frequently used transition metals (TMs). Our calculations also show that the suggested system is compatible with a wide range of adatoms including basic metals, metalloids, and TMs. It means that besides d electron magnetism originating from TMs, p electrons of incorporated elements of the main group can also cause half metallicity in the electronic structure of the introduced system. Our system exploiting the robustness of doping-induced FM ordering would be beneficial for promising multifunctional spin filter devices.

Graphene-laden hydrogels: A strategy for thermally triggered drug delivery

The synthesis of graphene-based materials has attracted considerable attention in drug delivery strategies. Indeed, the conductivity and mechanical stability of graphene have been investigated for controlled and tunable drug release via electric or mechanical stimuli. However, the design of a thermo-sensitive scaffold using pristine graphene (without distortions related to the oxidation processes) has not been deeply investigated yet, although it may represent a promising approach for several therapeutic treatments. Here, few-layer graphene was used as a nanofiller in a hydrogel system with a thermally tunable drug release profile. In particular, varying the temperature (25 °C, 37 °C and 44 °C), responsive drug releases were noticed and hypothesized depending on the formation and perturbation of π-π interactions involving graphene, the polymeric matrix and the model drug (diclofenac). As a result, these hybrid hydrogels show a potential application as thermally triggered drug release systems in several healthcare scenarios.

Synthesis of Active Graphene with Para-Ester on Cotton Fabrics for Antistatic Properties

The excellent electrical properties of graphene provide a new functional finishing idea for fabricating conductive cotton fabrics with antistatic properties. This work develops a novel method for synthesizing active graphene to make cotton fabrics conductive and to have antistatic properties. The graphite was oxidized to graphene oxide (GO) by the Hummers method, and was further acid chlorinated and reacted with the para-ester to form the active graphene (JZGO). JZGO was then applied to cotton fabrics and was bonded to the fiber surface under alkaline conditions. Characterizations were done using FT-IR, XRD and Raman spectroscopy, which indicated that the para-ester group was successfully introduced onto JZGO, which also effectively improved the water dispersibility and reactivity of the JZGO. Furthermore, this study found that the antistatic properties of the fabric were increased by more than 50% when JZGO was 3% by weight under low-humidity conditions. The washing durability of the fabrics was also evaluated.

Stability, electronic, and optical properties of two-dimensional phosphoborane

The structure and properties of two-dimensional phosphoborane sheets were computationally investigated using Density Functional Theory calculations. The calculated phonon spectrum and band structure point to dynamic stability and allowed characterization of the predicted two-dimensional material as a direct-gap semiconductor with a band gap of ~1.5 eV. The calculation of the optical properties showed that the two-dimensional material has a relatively small absorptivity coefficient. The parameters of the mechanical properties characterize the two-dimensional phosphoborane as a relatively soft material, similar to the monolayer of MoS₂ . Assessment of thermal stability by the method of molecular dynamics indicates sufficient stability of the predicted material, which makes it possible to observe it experimentally.

Multilayer graphite nano-sheet composite hydrogel for solar desalination systems with floatability and recyclability

The application of carbon-based nanomaterials with high photothermal conversion efficiencies in solar desalination has the advantages of economy, environmental protection, availability and sustainability.

Multi-functional stretchable sensors based on a 3D-rGO wrinkled microarchitecture

The structural design of sensing active layers plays a critical role in the development of electromechanical sensors. In this study, we established an innovative concept for constructing sensors, pre-straining & laser reduction (PS&LR), based on a laser-induced wrinkle effect. This method combines and highlights the advantages of a wrinkled structure in the flexibility of sensors and the advantages of laser in the efficient reduction of GO; thus, it can efficiently introduce tunable, stretchable 3D-rGO expansion bulges in wrinkled GO films. Particularly, the sensors based on this special structure (1.5 cm × 3 cm) demonstrated a multi-functional and distinguished sensing ability in the cases of bending, stretching and touching modes. Moreover, the 3D-rGO architecture endowed the sensors with great sensitivity and design flexibility, i.e., a high sensing factor of 122, relative current value change of 60 times at the bending angle of 60°, decreased relative resistance-strain curve and diverse bending strategies for various detection purposes. Thus, the established design and preparation strategy provides large design flexibility for various promising applications.

Effect of Charge Transfer upon Li- and Na-Ion Insertion in Fine-Grained Graphitic Material as Probed by NMR

We investigated the insertion-extraction behaviors of Li and Na ions in graphitic materials using solid-state NMR. A unique advantage of high-degree ¹³C-isotope enrichment of graphitic material allowed sensitive and metastable graphite intercalation compounds to be measured in a short time. Ex situ ¹³C magic-angle spinning NMR spectra of ¹³C fine-grained graphite are presented as a function of state-of-charge. The observations are discussed with respect to graphite intercalation phenomena, which include the effects of charge transfer and the demagnetizing field. Dramatic narrowing of the ¹³C NMR signal in metal-intercalated graphite evidences quasi-complete charge transfer occurring between lithium and graphite host material and resulting in reducing the macroscopic field effects. Upon Na insertion, incomplete charge transfer is observed and explained by inaccessibility of graphitic interlayer space for Na ions in our study. In addition, critical issues of reversibility of Li- and Na-ion electrochemical cells and solid electrolyte interphase formation are considered on the atomic scale. The knowledge gained in the present work can be applied to advanced high-power-density electrode materials for safe and fast-charging metal-ion batteries or for novel spintronic concepts with controlled spin-polarized charge carrier injection and transport combined with the possibility to manipulate magnetic anisotropy.

Enhanced Interfacial Kinetics of Carbon Monolith Boosting Ultrafast Na-Storage

Slow ion kinetics of negative electrode materials is the main factor of limiting fast charge and discharge of batteries. Sluggish Na⁺ kinetics property leads to large electrode polarization, resulting in poor rate and cyclic performances. Herein, an electrode of ultrasmall tin nanoparticles decorated in N, S codoped carbon monolith (TCM) with exceptional high-rate capability and ultrastable cycling behavior for Na-storage is reported. The resulted TCM electrode exhibits an extremely high retention of 96% initial charge capacity after 500 cycles at a current density of 500 mA g^-1 . Significantly, when the current density is elevated to an ultrahigh rate of 5000 mA g^-1 , a high reversible capacity of 228 mAh g^-1 after the 2000th cycle is still maintained. More importantly, the stable and fast Na-storage of TCM is investigated and understood by experimental characterizations and kinetics calculations, including interfacial ion/electron transport behavior, ion diffusion, and quantitative pseudocapacitive analysis. These investigations elucidate that the TCM shows improved ion/electron conductivity and enhanced interfacial kinetics. An entirely new perspective to deep insights into the fast ion/electron transport mechanisms revealed by interfacial kinetics of sodiation/desodiation, which contributes to the profound understanding for developing fast charging/discharging and long-term stable electrodes in sodium-ion batteries, is provided.

Effective modulation of intramolecular ferromagnetic interaction of diradicals by functionalization of cross-conjugated coupler

Cross-conjugated molecules are an interesting class of conjugated systems possessing a spatially separated HOMO and LUMO. Most previous studies have taken advantage of this property by using it in organic semiconductor applications. Herein, we undertake a new investigation on the use of this type of molecule, in particular benzo[1,2-d;4,5-d']bisoxazole (BBO), as a coupler for organic diradicals. BBO has two sites available for adding a substituent and a spin center (SC) which are along its 4,8- and 2,6-axes. Functionalizations using electron donating (ED) and electron withdrawing (EW) groups were imposed to tune its FMOs and it was found that the longer 2,6-axis is an ideal site with a broader LUMO range via substituent effects. Diradicalization of these BBOs using nitronyl nitroxide (NN) and nitroxide (NO) as SCs was done using the remaining available axis. The calculated J values are linearly dependent on the LUMO energy of the coupler, but with 4,8-NH2-2,6-SC as an outlier. This exceptional case is related to 4,8-NH2-2,6-SC having the lowest BBO-NN dihedral angle. Moreover, the diradicals 4,8-X-2,6-SC (with X = H, NH2, CH3) have higher J values than 2,6-X-4,8-SC (with X = H, NH2, CH3), which is counterintuitive because the latter have a shorter coupling path. These diradicals are positioned to the right of the intersection of their trend lines, which implies that diradicals with LUMO values to the right of this intersection have the tendency to attain J values that are higher than those diradicals with a shorter coupling path. 4,8-NH2-2,6-SC even surpasses the projected JMax values which we associate with the highest attainable J values due to LUMO tuning via substituent effects. These results provide useful insights, especially into the interplay between the LUMO and the dihedral angle and how these affect magnetism in diradicals. In conclusion, we found that BBO can be a good candidate as an effective coupler for diradicals with tunable J values via incorporation of ED and EW groups. This first approach to studying the application of cross-conjugated molecules as couplers also paves the way for new candidates for the development of more effective diradical systems.

Metal Adsorption and Nucleation on Free-Standing Graphene by Low-Energy Electron Point Source Microscopy

The interaction of metals with carbon materials (and specifically with graphene) is of importance for various technological applications. In particular, the intercalation of alkali metals is believed to provide a means for tuning the electronic properties of graphene for device applications. While the macroscopic effects of such intercalation events can readily be studied, following the related processes at an atomic scale in detail and under well-defined experimental conditions constitutes a challenge. Here, we investigate in situ the adsorption and nucleation of the alkali metals K, Cs, and Li on free-standing graphene by means of low-energy electron point source microscopy. We find that alkali metals readily intercalate between the layers of bilayer graphene. In fact, the equilibrium distribution of K and Cs favors a much-higher particle density between the layers than on the single-layer graphene. We obtain a quantitative value for the difference of the free energy of the binding between these two domains. Our study is completed with a control experiment introducing Pd as a representative of the nonalkali metals. Now, we observe cluster formation in equal measure on both single-layer and bilayer graphene; however, there was no intercalation. Our investigations thus constitute the first in situ study of metal-atom sorption of different specificity on free-standing graphene.

The graphene/n-Ge(110) interface: structure, doping, and electronic properties

The implementation of graphene in semiconducting technology requires precise knowledge about the graphene-semiconductor interface. In our work the structure and electronic properties of the graphene/n-Ge(110) interface are investigated on the local (nm) and macro (from μm to mm) scales via a combination of different microscopic and spectroscopic surface science techniques accompanied by density functional theory calculations. The electronic structure of freestanding graphene remains almost completely intact in this system, with only a moderate n-doping indicating weak interaction between graphene and the Ge substrate. With regard to the optimisation of graphene growth it is found that the substrate temperature is a crucial factor, which determines the graphene layer alignment on the Ge(110) substrate during its growth from the atomic carbon source. Moreover, our results demonstrate that the preparation route for graphene on the doped semiconducting material (n-Ge) leads to the effective segregation of dopants at the interface between graphene and Ge(110). Furthermore, it is shown that these dopant atoms might form regular structures at the graphene/Ge interface and induce the doping of graphene. Our findings help to understand the interface properties of the graphene-semiconductor interfaces and the effect of dopants on the electronic structure of graphene in such systems.

Lyotropic Liquid Crystal Phases from Anisotropic Nanomaterials

Liquid crystals are an integral part of a mature display technology, also establishing themselves in other applications, such as spatial light modulators, telecommunication technology, photonics, or sensors, just to name a few of the non-display applications. In recent years, there has been an increasing trend to add various nanomaterials to liquid crystals, which is motivated by several aspects of materials development. (i) addition of nanomaterials can change and thus tune the properties of the liquid crystal; (ii) novel functionalities can be added to the liquid crystal; and (iii) the self-organization of the liquid crystalline state can be exploited to template ordered structures or to transfer order onto dispersed nanomaterials. Much of the research effort has been concentrated on thermotropic systems, which change order as a function of temperature. Here we review the other side of the medal, the formation and properties of ordered, anisotropic fluid phases, liquid crystals, by addition of shape-anisotropic nanomaterials to isotropic liquids. Several classes of materials will be discussed, inorganic and mineral liquid crystals, viruses, nanotubes and nanorods, as well as graphene oxide.