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A new type of graphene-based quantum Hall standards is tested for electrical quantum metrology applications at alternating current (ac) and direct current (dc). The devices are functionalized with Cr(CO)3 to control the charge carrier density and have branched Hall contacts based on NbTiN superconducting material. The work is an in-depth study about the characteristic capacitances and related losses in the ac regime of the devices and about their performance during precision resistance measurements at dc and ac. [ABSTRACT FROM AUTHOR]

The magnetotransport properties of a hybrid InSe/monolayer graphene in a SiC system are systematically studied. Compared to those of its bare graphene counterpart, in InSe/graphene, we can effectively modify the carrier density, mobility, effective mass, and electron–electron (e–e) interactions enhanced by weak disorder. We show that in bare graphene and hybrid InSe/graphene systems, the logarithmic temperature (lnT) dependence of the Hall slope RH = δRxy/δB = δρxy/δB can be used to probe e–e interaction effects at various temperatures even when the measured resistivity does not show a lnT dependence due to strong electron–phonon scattering. Nevertheless, one needs to be certain that the change of RH is not caused by an increase of the carrier density by checking the magnetic field position of the longitudinal resistivity minimum at different temperatures. Given the current challenges in gating graphene on SiC with a suitable dielectric layer, our results suggest that capping a van der Waals material on graphene is an effective way to modify the electronic properties of monolayer graphene on SiC. [ABSTRACT FROM AUTHOR]

In this paper, we show that quantum Hall resistance measurements using two terminals may be as precise as four-terminal measurements when applying superconducting split contacts. The described sample designs eliminate resistance contributions of terminals and contacts such that the size and complexity of next-generation quantized Hall resistance devices can be significantly improved. [ABSTRACT FROM AUTHOR]

Stimuli-responsive materials, also known as smart materials, can change their structure and, consequently, original behavior in response to external or internal stimuli. This is due to the change in the interactions between the various functional groups. Graphene, which is a single layer of carbon atoms with a hexagonal morphology and has excellent physiochemical properties with a high surface area, is frequently used in materials science for various applications. Numerous surface functionalizations are possible for the graphene structure with different functional groups, which can be used to alter the properties of native materials. Graphene-based hybrids exhibit significant improvements in their native properties. Since functionalized graphene contains several reactive groups, the behavior of such hybrid materials can be easily tuned by changing the external conditions, which is very useful in biomedical applications. Enhanced cell proliferation and differentiation of stem cells was reported on the surfaces of graphene-based hybrids with negligible cytotoxicity. In addition, pH or light-induced drug delivery with a controlled release rate was observed for such nanohybrids. Besides, notable improvements in antimicrobial activity were observed for nanohybrids, which demonstrated their potential for biomedical applications. This review describes the physiochemical properties of graphene and graphene-based hybrid materials for stimuli-responsive drug delivery, tissue engineering, and antimicrobial applications. [ABSTRACT FROM AUTHOR]

Abstracts Surface modification of graphene oxide has been performed using diamine moieties with varying chain length and subsequently chemically grafted with long chain polyurethane for wrapping up of graphene sheet with large polymer chains. Functionalization of graphene and its subsequent grafting have been verified through spectroscopic measurements like NMR, FTIR and UV–visible spectroscopy and the uniform dispersion of graphene sheet in polyurethane matrix is achieved. Nanohybrids exhibit better thermal and mechanical responses along with greater self-assembly as compared to pure polymer. Nanometer dimension molecular sheet to gradual increased size of the order of tens of nanometer, hundreds of nanometer to micron scale assembly has been captured through XRD, small angle neutron scattering, AFM and optical microscopy, respectively. Nature of self-assembly associated with stronger interactions sustain the release of embedded drug (anticancerous dexamethasone) from nanohybrid and larger size of inhomogeinities for longer spacer length further sustain the drug release and thereby able to control the release rate of drug by articulating the chemistry of graphene modifications with suitable spacer length of diamine. Biocompatibility of the nanohybrids is verified with cell line studies using human breast cancer cells MDA-MB-231in terms of cell viability, cell adhesion, fluorescence image, reactive oxygen species and mitochondrial tracker measurements indicating better responses of nanohybrid vis-à-vis pure polyurethane. Thus, the control release of the dexamethasone drug from the nanohybrids along with better biological responses clearly suggests a novel biomaterial for the drug carrier. [ABSTRACT FROM AUTHOR]

Novel aliphatic polyurethane (PU) nanohybrids have been prepared using varying amount of graphene by dispersing it in the early stage of polymerization ( in situ ) and achieved uniform distribution throughout the matrix, required for the improvement of properties. The alteration of self-assembly in presence of graphene have been explored through X-ray diffraction, small angle neutron scattering, atomic force and optical microscopy in the length scale of nanometer, tens of nanometer, hundreds of nanometer and micron range, respectively, indicating the layer by layer self-assembly of polymer and graphene in nanohybrids. The cause of self-assembly has been studied through spectroscopic techniques like FTIR and UV–vis measurements revealing strong interaction between polymer chain (both hard and soft segments) and graphene which is further confirmed from the depression of melting point and decrease in heat of fusion with increasing graphene content in the nanohybrids. The toughness of nanohybrids in solid state improves considerably as compared to pure PU and the mechanical strength in liquid state also dramatically increases with graphene content showing a dip at a particular frequency depending on the strength of self-assembly (greater for higher graphene content nanohybrid) followed by its reformation at higher frequency. Sustained drug release has been achieved in presence of graphene explaining the phenomena from the greater tortuousity in nanohybrids arising from the 2-D graphene and small but uniform cluster size of self-assembly as compared to pure PU. The suitability of the developed nanohybrids has been testified for its use in biomedical arena by checking the complete biocompatibility of the nanohybrids as compared to pure PU using bone marrow derived mesenchymal stem cells. [ABSTRACT FROM AUTHOR]

Graphene is a two-dimensional sp2 hybridized carbon material that has attracted tremendous attention for its stimuli-responsive applications, owing to its high surface area and excellent electrical, optical, thermal, and mechanical properties. The physicochemical properties of graphene can be tuned by surface functionalization. The biomedical field pays special attention to stimuli-responsive materials due to their responsive abilities under different conditions. Stimuli-responsive materials exhibit great potential in changing their behavior upon exposure to external or internal factors, such as pH, light, electric field, magnetic field, and temperature. Graphene-based materials, particularly graphene oxide (GO), have been widely used in stimuli-responsive applications due to their superior biocompatibility compared to other forms of graphene. GO has been commonly utilized in tissue engineering, bioimaging, biosensing, cancer therapy, and drug delivery. GO-based stimuli-responsive platforms for wound healing applications have not yet been fully explored. This review describes the effects of different stimuli-responsive factors, such as pH, light, temperature, and magnetic and electric fields on GO-based materials and their applications. The wound healing applications of GO-based materials is extensively discussed with cancer therapy and drug delivery. [ABSTRACT FROM AUTHOR]

We report large, non-saturating magnetoresistance (MR) of ∼140% in single layer chemical vapor deposition (CVD) graphene with an h-BN capping layer at room temperature at B  = 9 T. Based on the classical model developed by Parish and Littlewood, our results show that the MR is proportional to the average mobility < μ > and decreases with increasing temperature. In contrast, in a large-area, extremely homogenous single layer epitaxial graphene (EG) device, the MR is saturating and is inversely proportional to < μ >, which is consistent with the finite resistance network picture. By comparing the results obtained from CVD graphene with an h-BN capping layer with those from the EG device, we show that the non-saturating linear characteristics come from multi-channel current paths in a two-dimensional plane due to the intrinsic grain boundaries and domains of CVD graphene by capping an h-BN layer that increase the < μ > of CVD graphene. Our results on CVD graphene with an h-BN capping layer pave the way for industrial schemes of graphene-based and air-stable magnetic field sensors with a linear, large response at room temperature. [ABSTRACT FROM AUTHOR]

A mathematical approach is introduced for predicting quantized resistances in graphene p-n junction devices that utilize more than a single entry and exit point for electron flow. Depending on the configuration of an arbitrary number of terminals, electrical measurements yield nonconventional, fractional multiples of the typical quantized Hall resistance at the ν = 2 plateau ( R H ≈ 12906 Ω) and take the form: a b R H . This theoretical formulation is independent of material, and applications to other material systems that exhibit quantum Hall behaviors are to be expected. Furthermore, this formulation is supported with experimental data from graphene devices with multiple source and drain terminals. Image 1 • Mathematical determination of quantum Hall resistances using multiple terminals. • Simulations performed with LTspice to obtain formulae for generalized cases. • Graphene p-n junctions show fractional multiples of quantum Hall resistances. [ABSTRACT FROM AUTHOR]