Strong demand for power reduction in state-of-the-art semiconductor devices calls for novel devices and architectures. Since ternary logic architecture can perform the same function as binary logic architecture with a much lower device density and higher information density, a switch device suitable for the ternary logic has been pursued for several decades. However, a single device that satisfies all the requirements for ternary logic architecture has not been demonstrated. We demonstrated a ternary graphene field-effect transistor (TGFET), showing three discrete current states in one device. The ternary function was achieved by introducing a metal strip to the middle of graphene channel, which created an N-P-N or P-N-P doping pattern depending on the work function of the metal. In addition, a standard ternary inverter working at room temperature has been achieved by modulating the work function of the metal in a graphene channel. The feasibility of a ternary inverter indicates that a general ternary logic architecture can be realized using complementary TGFETs. This breakthrough will provide a key stepping-stone for an extreme-low-power computing technology. According to Moore’s law, the number of transistors in an integrated circuit doubles approximately every two years. The channel length and gate oxide thickness of field-effect transistors (FETs) should decrease accordingly, but the scaling of these parameters creates many challenges such as increases in the gate leakage current, process cost, and system power, and a degradation of reliability12At the device level, a number of novel devices have been explored, including carbon nanotube (CNT) FETs, graphene FETs, nanowire FETs, ferroelectric FETs, tunnel FETs, nanoelectromechanical systems (NEMS), single-electron transistors (SETs), and transition metal dichalcogenide (TMD)-material-based FETs4567891112131415Although multivalued logic architecture may be the least popular option among the abovementioned technologies, a multivalued logic architecture—more specifically, a ternary logic architecture—has been investigated for more than six decades. The first ternary computer, SETUN, was commercialized in 195817191620212223242522920An ideal ternary switch should have distinctly separated multiple states within a given operational bias range. For low-power operation, the operational bias should be low enough, for example lower than 1 V. In addition, it is preferred to use an intrinsic mechanism to generate multiple device states rather than combining multiple devices to maximize power efficiency and achieve system scalability. For example, it is possible to generate different states by applying different biases to a silicon MOSFET. However, the variability between the ON and OFF state of a silicon MOSFET will be too high because the thermal emission rate of electrons overcoming the energy barrier at the source side changes exponentially as a function of gate bias.In this sense, graphene is an ideal material for the ternary device function because the conductivity of graphene is linearly proportional to the gate bias. Intrinsic material properties of graphene, such as a zero bandgap and the density of the state being linearly proportional to the external bias, provide this unique opportunity. Thus, the conductivity of a graphene channel can be engineered to have a stepwise function by making a small region of opposite charge carriers in a graphene channel. For example, if a positive gate bias applied to a graphene FET with a channel having an N-P-N doping profile is progressively increased, the channel doping will be eventually changed to N-N-N doping profile. When the P-type region is changed to N-type by the gate bias, the Fermi level moves through the charge neutrality point where the density of state is zero, and then the resistance of that portion of the graphene channel increases rapidly. Because of this increase in the resistance, the transfer curve of graphene EFT shows flat or decreasing shape. Because of this phenomenon, stepwise current-voltage characteristics can be achieved.To realize this device, a stable method to shift the Fermi level of graphene into an electron or hole branch is necessary. Various kinds of doping process for graphene have been reported, including chemical doping, metal contact, self-assembled monolayer, and electrical doping2728292O3/metal strip/graphene. Al2O3 was deposited over the graphene channel to improve the stability of the TGFET by blocking the water-related molecules from ambient condition. We found that this problem could be alleviated by using a low-temperature high-pressure hydrogen annealing process. Using this result, the doping profile of graphene under the metal strip could be controlled from 4.315 eV to 4.688 eV, and a complementary ternary device could be demonstrated. Dirac,0 and VDirac,1) shown in Dirac,0 and VDirac,1, respectively) are the charge neutrality point of the graphene channel without and with the metal strip. The inset of 0’, I1’, and I2’) as a function of gate bias, as shown in Dirac,1 is expected to be in the electron branch. However, both the Pt and Al strips show VDirac,1 in the hole branch  was found to be effective in recovering the effective work function of Pt. The sign of V2 substrate, we checked the influence of high pressure hydrogen annealing on the devices that don’t have metal strip  of graphene with/without metal strip were estimated simultaneously, and the corresponding effective work functions of metal were obtained. As shown in where RM,eff is the effective work function of the metal strip, WG is the work function of graphene (4.5 eV), and C/e is 2.4 × 1011 cm−2V−1. where WM,eff = WM−ΔV(d), where ΔV(d) is the potential change generated by the metal-graphene interaction, WM,eff is the effective work function of metal on graphene, and WM is the work function of the metal.We suppose that this improvement might be a result of the elimination of interface bonding through hydrogenation at the graphene/metal interfaced−Vg curves were measured with VG = 0 V while the substrate temperature was changed from 25 °C to 125 °C with a step size of 25 °C. Since the drain currents at −10 V and +25 V are not significantly affected, the substantial temperature dependence appears to be related to the conductance change in the graphene under the Pt strip. In other words, the effective work function of Pt changes as a function of temperature. When this test was extended for 7200 s, similar stability characteristics were observed at even higher temperatures, as shown in Dirac,1 was not significantly changed during operation up to 1,000 s. This indicates that the stability of an effective work function shift is more directly affected by the device operation temperature than the stress time.To further investigate the physical mechanism, the stability of effective work function modulation using hydrogen annealing was examined. Dirac,0 and VDirac,1) and the activation energy extracted from the temperature dependence of the Dirac voltage change  of Pt was caused by hydrogen diffusion into the interface of the graphene/Pt strip. The hydrogen molecules are adsorbed to the surface of Pt, forming Pt-H or Pt-OH complexes  method was prepared using a wet transfer process. After completing a back-gate graphene FET structure having a Pt source and drain, metal strips  were inserted in the middle of the graphene channel. Then, the doping profile of the graphene channel was tuned to produce N-P-N and P-N-P profiles using high-pressure hydrogen annealing. The electrical characteristics of all devices were measured using a Keithley 4200 parameter analyzer.2 thermally grown on a highly P-doped Si substrate using a poly (methyl methacrylate) (PMMA)-mediated transfer method34A 1 cm × 1 cm monolayer of graphene sheet grown on Cu foil using a CVD process was transferred to 90-nm SiO2O3 using an atomic layer deposition (ALD) process at 130 °C to improve the stability of devices, and annealed in ambient H2 at 300 °C for 2 h at 0 atm and 20 atm to control the doping profile of the graphene channelFor device fabrication, 20-nm Au was deposited on a graphene sheet and patterned using i-line contact photolithography and an etching process. Then, the graphene layer open to air was etched using an oxygen plasma process . After channel patterning using a Au hard mask, a 100-nm Au layer was deposited again using e-beam evaporation and patterned using i-line photolithography and an etching process. The Au hard-mask process was adopted to pattern both the channel and the source/drain region of graphene while minimizing the impact of photoresist residues in the graphene channel. The metal strip  was formed in the middle of the graphene channel using i-line contact photolithography and a lift-off process. The surface of the graphene channel was passivated with 20-nm AlHow to cite this article: Kim, Y. J. et al. Demonstration of Complementary Ternary Graphene Field-Effect Transistors. Sci. Rep.6, 39353; doi: 10.1038/srep39353 (2016).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Voltammetry analysis demonstrated the superior electrochemical performance of graphene produced in LiClO4, resulting in higher sensitivity and linearity for the explosives detection and lower limit of detection (LOD) compared to the graphene obtained in Na2SO4. We attribute this to the presence of oxygen functionalities onto the graphene material obtained in LiClO4 which enable charge electrostatic interactions with the –NO2 groups of the analyte, in addition to π-π stacking interactions with the aromatic moiety. Research findings obtained from this study would assist in the development of portable devices for the on-site detection of nitroaromatic explosives.Detection of nitroaromatic explosives is of paramount importance from security point of view. Graphene sheets obtained from the electrochemical anodic exfoliation of graphite foil in different electrolytes (LiClO Modern military explosives are generally nitrogen-containing aromatic compounds (NAC)13268101214in situ detection and measurement of NAC explosives. In a research paper by Dong et al. comparing the electrochemical and fluorescent detection methods for TNT analysis based on carbon quantum dots, a broader linear detection range was possible for the electrochemical sensor2 group to an –NHOH group2 group26Conventional analytical methods for the qualitative and quantitative analysis of DNT and TNT include gas chromatography22162722211723231010Since the successful isolation of graphene in 2004293032353739511414 and Na2SO4.Recently, a novel and highly efficient method has emerged as a possible avenue for the mass production of graphene: the electrochemical exfoliation of graphite under anodic or cathodic conditions, which enables the intercalation of electrolyte ions between the graphene layers, resulting in their exfoliation4 (G-LiClO4) showed an intense, broad reduction peak at −819 mV and −724 mV in BBS and seawater respectively, whereas graphene synthesised in Na2SO4 (G-Na2SO4) showed a low-intensity peak at −655 mV in BBS which does not seem to appear when measuring in seawater. Overall, relatively similar voltammograms were obtained in both BBS and seawater within the 0 mV to −1000 mV potential range, which is indicative of the absence of electroactive compounds in seawater that may complicate the analysis of NAC explosives. The intense inherent reduction peak recorded for G-LiClO4 in both BBS and seawater can be attributed to the irreversible reduction of the oxygen functionalities present onto this material that can undergo electrochemical reduction. This phenomenon has been investigated more in detail and explained in previous reports484 and 8.8 for the G-Na2SO4  to ascertain the presence of inherent reduction peaks for the graphene materials that may interfere with the electrochemical reduction of DNT and TNT . Cyclic 2SO4 see .Cyclic voltammetry scans were first obtained in BBS to investigate the electrochemical behaviour of DNT and TNT on the electrochemically exfoliated graphenes and then repeated in seawater to determine the feasibility and reliability of real-time environmental analysis .a and b by order of appearance in the CV cathodic wave , for the detection of nitro-substituted aromatic explosives (DNT and TNT) in both borate buffer and seawater. Voltammetry studies reveal that G-LiClO4 which carries the highest amount of oxygen functional groups, is the most suitable electrode system for the detection of NAC explosives, due to a favourable electrostatic interaction with the analytes which resulted in a higher sensitivity and linearity. On the other hand, G-Na2SO4 consistently demonstrates similar electrochemical performance with the unmodified GC electrode for NAC detection. Significant improvements in electrode system sensitivity and linearity for DNT and TNT detection in seawater as compared to BBS were also observed for G-LiClO4, accompanied by the ability of our sensing platform to distinguish between DNT and TNT, which supports the applicability and effectiveness of using G-LiClO4 in real-time environmental analysis of seawater.This study has investigated and compared the sensing abilities of electrochemically exfoliated graphene obtained from the anodic exfoliation of graphite foil in different electrolytes  and acetonitrile were purchased from Merck (Singapore). 2,4,6-trinitrotoulene (TNT) was purchased from AccuStandard  as an analytical standard in the diluted form (1000 ppm in acetonitrile). Graphene electrochemically exfoliated in LiClO4 (G-LiClO4) and Na2SO4 (G-Na2SO4) were prepared and characterised in detail as previously reported4 had a D/G ratio of 1.00 and a C/O ratio of 4.0, whereas G-Na2SO4 had a D/G ratio of 0.95 and a C/O ratio of 8.8. Scanning transmission electron micrographs, XPS and Raman spectra are presented in the Sodium tetraborate decahydrate and 2,4-dinitrotoluene (DNT) were purchased from Sigma-Aldrich. Voltammetry analyses were conducted at room temperature using a μAutolab Type III electrochemical analyser instrument  and controlled by General Purpose Electrochemical Systems Version 4.9 software. The experiments were performed in an electrochemical cell using a three-electrode system. Glassy carbon  working electrode, platinum auxiliary electrode and Ag/AgCl (saturated) reference electrode were obtained from CH Instruments .−1) of the electrochemically exfoliated graphene materials were prepared from the dispersion of graphene flakes in DMF and sonication for 2.5 h. An aliquot (1 μL) of the suspension was then drop-casted onto a GC electrode surface that had been polished with alumina particles (0.05 μm) on a polishing pad, and allowed to evaporate under a heat lamp. The deposition step was performed to obtain one to three layers of graphene material on the GC electrode for the optimisation experiments. DNT was prepared as a stock solution (1000 ppm in acetonitrile). TNT (1000 ppm in acetonitrile) was used as received. Borate buffer  was prepared from dissolving Na2B4O7.10H2O in milli-Q water. Seawater (pH 8.0) was mixed with BBS  in a ratio of 9:1 prior to use. All cyclic voltammetry (CV) measurements were performed with a scan rate of 100 mV s−1. All differential pulse voltammetry (DPV) measurements were performed with a modulation amplitude of 25 mV and a step potential of 5 mV. All voltammetry measurements were repeated three times to ensure measurement reproducibility, with the most representative voltammogram being selected for data presentation. Voltammetry measurements were also conducted on the unmodified GC electrode for reference purposes. Degassing was not carried out prior to electrochemical measurements to simulate real-time environmental analysis.Suspensions .


This enables fully inkjet-printed electronic circuits, such as reprogrammable volatile memory cells, complementary inverters and OR logic gates.Fully printed wearable electronics based on two-dimensional (2D) material heterojunction structures also known as heterostructures, such as field-effect transistors, require robust and reproducible printed multi-layer stacks consisting of active channel, dielectric and conductive contact layers. Solution processing of graphite and other layered materials provides low-cost inks enabling printed electronic devices, for example by inkjet printing. However, the limited quality of the 2D-material inks, the complexity of the layered arrangement, and the lack of a dielectric 2D-material ink able to operate at room temperature, under strain and after several washing cycles has impeded the fabrication of electronic devices on textile with fully printed 2D heterostructures. Here we demonstrate fully inkjet-printed 2D-material active heterostructures with graphene and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet-printed flexible and washable field-effect transistors on textile, reaching a field-effect mobility of ~91 cm Heterojunction structures based on 2D materials show promise for wearable and textile electronics. Here, the authors demonstrate fully inkjet-printed hetero junctions of graphene and h-BN as a platform for FET-based smart electronics on wearable and washable textile substrates. Textile electronics can primarily be grouped into two categories,electronic fibres (e-fibres) and ‘smart’ textiles. E-fibres involve multi-stacking functional layers on the fibres themselves3 or combining functional fibres together to create a device4. Smart textiles involve the assembly of components on to the weave of the textile and can be done in several ways either through the assembly of components on substrates which can subsequently be placed on textile5 or by fabricating devices on the weave of the textile itself6.Flexible and textile electronics are rapidly growing research fields. Several applications in these fields have been developed over the past two decades, such as organic light-emitting diodes (OLED), photovoltaic devices and transistors7, self-heating seats8 or wearable electronics (i.e. the integration of electronics with clothes), for monitoring or security purposes, such as motion sensors9, health monitoring10 and radio-frequency communication11. Inkjet printing is a forefront technique for printed electronics12. Inks based on organic polymers and metal oxides can be inkjet-printed enabling large-scale manufacturing of transistors on a wide range of plastic substrates. However, both printed metal oxides and organic polymer inks have limited charge mobility (μ) (~ 0.01 – 10 cm2 V−1 s−1), which has restricted their prospects to specific applications such as radio-frequency identification tags and control electronics for active matrix displays14. Despite their huge potential, there have been only few attempts to deposit field-effect transistors (FETs) onto textiles, such as by coating organic FETs on polymer fibres to create logic inverters15, or spin-coating organic FETs on a textile modified with polyurethane/photo acryl layer, achieving μ of 0.05 cm2 V−1 s−1 and on/off ~ 105, respectively16.Many electronic components, such as thermoelectric power generators, sensors, energy storage, antennas and light-emitting devices, have been printed onto textiles for application in curtain lighting17, such as graphite, has driven a surge in the exploration of graphene and more recently other two-dimensional (2D) materials with unique electrical, mechanical, optical and thermal properties18. Atomically thin 2D materials, such as graphene and hexagonal-boron nitride (h-BN) can be arranged into heterostructures, thus creating assemblies with novel properties which are different from those of the individual components18. The different combination of conducting, insulating and semiconducting 2D materials allows for a large number of different heterostructures with precisely tailored properties with multiple functionalities and improved performance for novel applications18. Layered materials can be exfoliated in solution by liquid phase exfoliation (LPE)20 or microfluidization21 and developed into single or multi-layer 2D-material inks. Graphene and 2D-material printable inks have already shown great potential in the field of printed electronics enabling devices such as thin film transistors22, photodetectors23, sensors9, supercapacitors24, saturable absorbers25 and solar cells26. Layered structures of 2D-material inks can then be printed in part or as a whole by means of different printing technologies such as inkjet, spray, screen, gravure and flexographic printing12. In particular, inkjet printing is an ideal tool to print graphene inks enabling FETs24 with mobility of up to 95 cm2 V−1 s−1 on surface-modified Si/SiO2 substrate22 and MoS2 photodetectors on Si/SiO2 substrate with photoresponsivity of ~36 μAW−1 and photocurrent of ~57 pA27. Inkjet-printed flexible graphene/MoS2 photodetectors on polyethylene terephthalate (PET) showed photoresponsivity of ~500 nAW−1 and photocurrent of ~ 30 nA23, and more recently inkjet-printed vertically stacked graphene/WS2 photodetector were reported with a photoresponsivity up to ~ 1 mAW−128. More recently, ref. 29 demonstrated current modulation in MoS2, WS2, MoSe2 and WSe2-printed thin films using electrochemical gating by liquid electrolyte29 rather than by heterostructure-based dielectric gating, thus requiring ultra-high vacuum and low temperature for correct device operation, which limits its application to flexible electronics. Moreover, the use of a spray-coated h-BN layer as a porous separator, and not as a dielectric layer may fail to be considered an all-printed 2D-material active heterostructure.The exfoliation of layered materialsN-methyl-2-pyrrolidone—NMP, dimethylformamide—DMF) used for 2D-material-based inks are toxic and when printed the different 2D materials in the stack tend to redisperse at the interface if solvent is present, producing uncontrolled interfaces, thus strongly affecting the uniformity of the multi-layer deposition30. In addition, the concentration of 2D materials in these solvents is low (<1 mg ml−1)31, thus requiring many print passes to obtain functional films30. Another limitation reported, especially with the use of high boiling point solvents is the required annealing during printing or in post-processing for solvent removal32, which poses severe limitations when printing on plastic or textiles. Similar issues are also present in the case of water-based 2D-material-based inks, where the surfactants/polymers removal requires thermal and/or chemical treatments33, which are often not compatible with the substrate.Several issues also still exist in the optimisation of 2D-material inkjet-printed multi-layer heterostructures, which have impeded the inkjet printing of 2D-material-based dielectrically gated field-effect devices, such as FETs. The main manufacturing issue is that the common solvents , surface tension γ (mN m−1), density ρ (g cm−3) and the nozzle diameter a (μm) influence the jetting of individual drops from a nozzle34. On the one hand, suitable inkjet printable ink formulations, which are produced by LPE20 typically contain surfactants or polymer stabilisation agents, which can act as a source of contamination and may hinder device performance, however they can also positively impact the ink by acting as an adhesion or rheology modifier21. On the other hand, high boiling point solvents (>100 °C), such as NMP can suspend 2D materials without stabilisation agents due to a matching of the Hansen solubility parameters20. However, they are still far from ideal as they are based on toxic and expensive solvents, which require high annealing temperatures (>100 °C) to remove residual solvent28. Low boiling point inks (≤100 °C) are a suitable alternative, due to their fast evaporation at room temperature and have been reported to create stable inks though two solvent formulation where the solvent mixture is tuned to improve the affinity of the solvent to the 2D materials35. However, the different evaporation rate of the two solvents can result in rheological instabilities and particle aggregation over time. We select an alternative ink formulation route based on solvent exchange, whereby layered materials can be exfoliated effectively in a high boiling point solvent and subsequently transferred to a low boiling-point solvent, with any desired concentration36.In this study we used a drop-on-demand (DoD) inkjet printer. The ink viscosity η, γ and ρ), ηh-BN ~ 1.7 mPa s, γh-BN ~ 72 mN m−1, ρh-BN ~ 1.01 g cm−3, ηGR ~ 1 mPa s, γGR~ 30 mN m−1, ρGR ~ 0.82 g cm−3, which are consistent with previous reports22. The inverse Ohnesorge number (Oh) is used as a figure of merit, Z = Oh−1 = (γρa)1/2/η and is commonly used to characterize the drop formation, stability and assess the jettability of an ink from the nozzle37. An overall range of 2 < Z < 24 has been identified as an optimal range for printing37. We found Z ~ 19.4 and Z ~ 22 for the h-BN and graphene inks, respectively, which fall within the optimal Z range37.We formulated the graphene and h-BN inks (see ‘Methods’) with the following rheological parameters  and graphene (black curve), respectively. The spectra for the graphene ink is mostly featureless due to the linear dispersion of the Dirac electrons38, whereas the peak in the UV region is a signature of the Van Hove singularity in the graphene density of states38. The spectra for the h-BN ink shows a peak located at 218 nm, which corresponds to the interband transitions in the density of states39 revealing an optical bandgap, Eg of 5.69 eV (see ‘Methods’), which is consistent with previous reports determining the optical band gap for thin h-BN films41.Optical absorption spectroscopy Fig.  was usedt) of the graphene and h-BN flakes was estimated by atomic force microscopy (AFM). Figure 42 is peaked at t ~ 6 nm and t ~ 9 nm and assuming an approximate 1 nm water layer29 and an interlayer distance of 0.34 nm, we calculate that the solutions consist of an average number of layers, N ~ 15 and N ~ 24 for graphene and h-BN, respectively44. The 42 as x and y are the length and width of the flake were also investigated to verify that the flake dimensions match with the inkjet requirements for DoD inkjet (a to avoid nozzle clogging). The lateral size distributions follow a log-normal distribution42, which is peaked at ~121 and ~495 nm for graphene and h-BN flakes, respectively. Scanning electron microscopy (SEM) was also used to corroborate the lateral size of the flakes in the inks  of 500 μm2 and t of 1.2 μm, we estimate a capacitance per unit area is 8.7 nF cm−2, which is consistent with the 0.24 to 1.1 nF cm−2 range previously reported45. Before moving to the textile substrate, we investigated top-gate (coplanar) and bottom-gate (inverted-staggered) FET structures and optimised the inkjet-printed graphene/h-BN heterostructures on a PET substrate , which was coated with SiO2 nanoparticles . The coplanar FET heterostructure is shown in the schematics in Fig. t ~ 100 nm, measured with AFM on Si/SiO2) with the graphene ink. Ref. 22 determined the percolation threshold of the graphene flakes forming a graphene film at t ~ 25 nm22 on a Si/SiO2 substrate , so for our graphene/h-BN FETs on a rougher PET substrate (Rq = 68 nm) we print a thicker graphene channel to ensure that graphene flakes fall above the percolation threshold. The source and drain are then printed (t ~ 500 nm) using a silver ink  (Z ≈ 3). The gate dielectric layer was then inkjet-printed with the h-BN ink forming a film of t ~ 1.2 μm and was placed under vacuum overnight at room temperature to remove any bubbles that may be trapped inside the dielectric46. Finally, a silver top-gate (t ~ 200 nm) electrode was inkjet-printed on the structure and the sample was annealed on a hot plate at 100 °C for 1 h to remove residual solvent. Using the same printing conditions (see 'Methods'), the inverted-staggered FET heterostructures were fabricated by printing a silver gate (t ~ 500 nm), then the h-BN dielectric (t ~ 1.2 μm) followed by the graphene channel (t ~ 100 nm) and finally defining the source and drain electrodes with silver ink (t ~ 200 nm), arrays of these devices can be observed in Supplementary Fig. We first investigated the dielectric properties of the h-BN ink in a Ag/h-BN/Ag parallel plate capacitor configuration  and their orientation ensure significant overlap amongst the flakes, preventing the formation of pin-holes (i.e connections from the top contact to the channel) in the dielectric region45. We performed EDX analysis of the lamellae to identify the local chemical composition along the cross section of the heterostructure. The identification of the graphene layer (t ~ 100 nm) from the STEM images is very challenging due to its thickness and the coexistence of carbon throughout the layers. In the EDX spectra, the carbon signal is generated both from carboxymethylcellulose sodium salt (CMC), used as stabilisation polymer, and the graphene layer. Therefore, the identification of the carbon presence in the EDX maps is not a good marker for univocally identifying the graphene flakes within the device. Hence, we employed multivariate analysis (see ‘Methods’) to localise EDX signals from compounds, rather than individual elements  analysis. Two lamellae, each ~200 nm wide, were prepared from the coplanar device using focused ion beam (FIB) milling. The cross-sections of the graphene/h-BN FET were extracted from the channel region  originates from the SiO2 nanoparticles coating on the PET substrate  in the gate and source electrodes and from the TEM grid. In particular, Fig. Kα peak, and the relative contour map  ≈ 0.01 cm−1 nm−1, which is lower than what expected for disordered carbon48 (see more details in ‘Methods’). In the case of the h-BN film (red curve), we observe a single peak at 1368 cm−1 corresponding to the E2g phonon vibration mode50. Typically for bulk h-BN, this peak is found at 1366 cm−1, whereas the upshifting of the peak indicates the successful exfoliation from the bulk material to few layer h-BN50. The Raman spectrum of the graphene/h-BN heterostructure (blue curve) shows the fingerprints of graphene flakes and h-BN flakes. The spectrum is in fact the superimposition of that of the graphene film and the h-BN film.Raman spectroscopy (Renishaw 1000 InVia micro-Raman) is used to monitor the quality of materials used in the heterostructure. Figure Vds=1 V, 500 mV and 50 mV, and the output characteristics  increases linearly with Vds, which is typical of zero-bandgap semiconductors and consistent with the behaviour of graphene FETs51. From Fig. 51 (Vds = 1 V) on all the coplanar and staggered graphene/h-BN-printed devices as is expected for graphene-based FETs52. The gate current in all the devices is more than a magnitude lower (<100 nA) than the drain current, indicating that the device is modulating current in the graphene channel. When a forward Vgs sweep (from negative to positive Vgs) is applied (red curve) in both coplanar and inverted-staggered heterostructures , occurs at positive voltage, which means graphene channel was lightly p-doped. We also noticed a hysteretic behaviour for both devices when a forward Vgs sweep (from more negative to more positive Vgs) is applied (red curve), which causes a shift of the Dirac point of ΔV ~ 3 V between forward Vgs sweep and backward Vgs sweep /(dId/dVgs), where L (μm) and W (μm) are the channel length and width, respectively, and C is the dielectric capacitance51. We use L ≈ 50 μm, W ≈ 580 μm and L ≈ 65 μm and W ≈ 500 μm for coplanar and inverted-staggered FETs, respectively, and the previously calculated dielectric capacitance per unit area of ~8.7 nF cm−2 at Vds = 1 V. The average field-effect mobility for holes (μh) and electrons (μe) for the coplanar devices are calculated to be μh ~ 150 ± 18 cm2 V−1 s−1 and μe ~ 78 ± 10 cm2 V−1 s−1, respectively, whereas having an on/off current ratio (defined as the maximum Id divided by the minimum Id) of ∼2.5 ± 0.1. The best device demonstrated a mobility of μh ~ 204 cm2 V−1 s−1 and μe ~ 118 cm2 V−1 s−1. For the inverted-staggered devices, we find an on/off ratio of ∼1.5 ± 0.2, μh ~32 ± 5 cm2 V−1 s−1 and μe ~10 ± 4 cm2 V−1 s−1, which are one magnitude lower than the coplanar structure field-effect mobility on PET. We attribute this decrease in mobility to the rougher surface of the h-BN layer  in contrast to the PET film (Rq ~15.2 nm), which could affect the stacking quality of the graphene flakes. Such difference between μh and μe corresponds to a preferential hole conduction over electron conduction, which may be due in part to the unintentional doping of the graphene channel54. Moreover, a preferential hole conduction has been reported for various graphene FETs on SiO2 substrate, including FETs made with graphene from CVD55 and mechanical exfoliation52. The field-effect mobility of our graphene/h-BN heterostructure FET is higher than that of printed CNT FETs 56 and is about 15 times higher than μ in the organic 57 and metal-oxide transistors 58, while comparable to that of inkjet-printed graphene FETs 22 and reduced graphene oxide FETs 59. However, the on/off ratio is lower than that of printed organic, metal-oxide and CNT FETs58, but consistent with the on/off measured on previously reported FETs from printed graphene59. An array of coplanar FETs is shown in Supplementary Fig. μh at a bending radius of 8 mm , while μh drops to ∼19 cm2 V−1 s−1 at a smaller bending radius . For the inverted-staggered FETs, μh drops to ~6 cm2 V−1 s−1 at a bending radius of 8 mm and remains constant until 4 mm bending radius, as shown in Supplementary Fig. 60 and the longevity of the h-BN encapsulating properties61.The field-effect mobility of the coplanar and inverted-staggered devices were derived from the slope of the transfer characteristic according to Rq) of textiles affects the electrical properties of printed devices. Therefore, we minimised this effect by adopting a planarization layer. Typical planarization layers such as polydimethylsiloxane (PDMS), polyimide, polyurethane or poly (PVA) decrease the rms roughness and thus improve the device performance62. For example, ref. 63 used laminated polyurethane (t ~ 20–50 μm) on polyester reducing Rq from 10 μm to < 5 μm63, whereas ref. 64 used spin-coated polyimide (t ~ 500 nm) on polyimide, reducing Rq from 2.5 to 0.3 nm64. Here we employed polyester satin fabric (Wuxi Yihong Textile Co.) as a substrate for our textile graphene/h-BN FETs because it is highly durable and represents about ~80% of the synthetic fibre market. Polyurethane-coated fabric is identified as having the lowest Rq (~14.8 μm) after one coating layer (t ~ 600 nm), as compared to the other coating layers where Rq ~ 25–34 μm was measured  for the least number of coatings  due to the Rq of the substrate being orders of magnitude higher the channel thickness, which hinders the development of a coplanar FET structure. Moreover, increasing the thickness of the graphene layer further will inevitably decrease the transistor mobility22. On the other hand, the inverted-staggered heterostructure offers a higher resilience to roughness variation of the substrate than the coplanar structure, given that the channel sits on the top of a thick h-BN dielectric layer, which in this case shows Rc of ~10 kΩ for a 200 nm thick graphene channel. We thus adopt this layout for our graphene/h-BN FET on textile.The roughness (2O)65. It is worth noting that the PEDOT:PSS ink (Z ≈ 30) was successfully jetted from the inkjet nozzles despite being slightly outside the previously found Z range (2 < Z < 24)37. Figure t ~ 6.5 μm, determined by profilometry), followed by a h-BN dielectric layer  that also reduces residual roughness of the polyurethane planarization layer (Rq ~ 1.9 μm). Then we printed a ∼200 nm thick graphene channel and finally deposited the PEDOT:PSS source and drain contacts (t ∼ 800 nm). We found that the Rq of the channel decreased further from ~1.9 μm to ~588 nm (as determined by AFM), thanks to the PEDOT:PSS and h-BN bottom layers in the inverted-staggered configuration. Similarly to the FET heterostructures on PET, the samples were annealed at 100 °C for 1 h to remove residual solvent in the devices. Figure L ≈ 80 μm, W ≈ 500 μm and t ≈ 200 nm. Figure Vds = 1 V and the output characteristic for different gate voltages Vgs = −2, 0 and 2 V. The average field-effect mobility of the devices is μh ~91 ± 29 cm2 V−1 s−1 and μe ~22 ± 10 cm2 V−1 s−1, respectively, whereas the on/off ratio is ∼1.23 ± 0.3. This behaviour is expected, as μ of printed graphene channels increases with thickness until percolation is reached22. Our μ is two to three magnitudes larger than what has currently been achieved for organic FETs on e-textile fibres 66 while reaching one magnitude greater mobility than inverted-staggered FETs spin-coated on polyester textile with a ion gel dielectric/P3HT smoothing layer 67. We also printed the same inverted FET with ~100 nm graphene channel thickness, reaching field-effect current modulation , which is a key requirement for the low-power consumption of textile electronics devices68.Electronic devices on textile require not only flexibility but the ability to conform with the textile with little or no effect on the electrical and optical performances. Hence, we replace the printed silver electrodes with a highly conformable conductive polymer such as poly polystyrene sulphonate (PEDOT:PSS)  and to ~27 cm2 V−1 s−1 at 4 mm bending radius  voltage was required to reach the Dirac point of the top FET with respect to that of the bottom FET71. This is illustrated in Fig. 69. Although the strongest signal inversion is obtained in the complementary mode, the inverter is capable of signal inversion in a slightly larger input voltage range69, i.e. in the range between the maximum and minimum of the static voltage transfer characteristic shown in Fig. VDD = 1 V), the inverter correctly inverted the input digital signal, as shown in Fig. VDD = 1 V and logical low 0 V. The output signal of the inverter (red line) with the input signal is shown in Fig. VDD/2)73. The output voltage swing is 10% of the input voltage swing, indicating low voltage gain (A = dVOUT/dVIN ≈ 0.1) of the inverter. The reason for the low gain is a very thick (~1 µm) gate insulator, which corresponds to a very large equivalent oxide thickness (EOT) of 557 nm. Nevertheless, the obtained gain is still larger than that of the first exfoliated complementary graphene inverters with EOT = 300 nm69.The versatility of the inkjet-printed FETs allows to arbitrarily design electronic circuits. The goal of an ‘all inkjet-printed’ circuit with 2D-material heterostructures has been a dream pursued for long timeter Fig. , a reproter Fig. , a singlter Fig.  and p-tyter Fig.  using thVDD = 0.2 V as shown in Fig. VA and VB (corresponding to Boolean variables A and B) were connected to the gate of the bottom graphene field-effect transistor (GFET) via two identical resistors. This gives for the gate voltage of the bottom GFET VGS = (VA + VB)/275. As the input logic signals had a low VL (Boolean 0) or high VH (Boolean 1) voltage level, the gate voltage had three discrete levels: low VL (both inputs 0), high VH (both inputs 1), and half way between (VL + VH)/2 (inputs different). Depending on the position of the gate voltage levels with respect to the Dirac voltage, different logic gates can be obtained74. Figure 74. The low output voltage swing originates from the bottom FET operating very close to the Dirac point due to the small difference between the high (VH = 0.4 V) and low (VL = VH − VDD = 0.2 V) level and from the thick gate insulator in the GFETs.We also realized an OR logic gate to demonstrate the versatility of the printed graphene/h-BN FET heterostructures. Two printed FETs were connected to a low-voltage power supply 69.These results demonstrate the robustness of our technology based on all inkjet-printed 2D-material heterostructures to fabricate flexible and integrated electronic circuits, such as memories and logic gates exhibiting the same functionality as the some of the first circuits fabricated by standard lithographic methods with heterostructures of 2D materials µh and µe up to 91 cm2 V−1 s−1 and 22 cm2 V−1 s−1 in ambient conditions, withstand up to ∼4% strain and are washable for up to at least 20 cycles. The viability of the printed graphene/h-BN heterostructures FETs for electronic circuits was also demonstrated with fully printed complementary inverters, logic gates and rewriteable volatile memory.We demonstrated fully inkjet-printed dielectrically gated field-effect transistors based on graphene/h-BN heterostructures for flexible and textile electronic circuits. The graphene/h-BN heterostructure FETs on polyester textile show −1, Sigma-Aldrich No. 332461, <100 μm size) and ultrasonicating  for 9 h in NMP19, providing surfactant/polymer-free exfoliation of graphite. The graphene ink in NMP was then solvent exchanged to ethanol so that we facilitate solvent removal at ambient temperature during printing, thus improving the uniformity of the multi-layer deposition25. The h-BN ink was prepared by mixing h-BN powder  with deionized water and carboxymethylcellulose sodium salt  (3 mg ml−1), a biocompatible and biodegradable stabilisation agent and rheology modifier21. The h-BN/CMC mixture was then processed with a shear fluid processor,  with a Z-type geometry interaction chamber with microchannels ∼87 µm wide for 50 cycles, at 207 MPa system pressure and at room temperature (20 °C)21. We used the microfluidic process to disperse and exfoliate h-BN while the high shear rate generated (7 s−1) helped to achieve high concentration dispersions21. The h-BN and graphene dispersions were then ultracentrifuged  at 3 k rpm (20 min) and 10 k rpm (1 h), respectively, to remove thick flakes, which would clog the printer nozzles. Subsequently, the supernatant (i.e. top 70%) was decanted for further characterisation.The graphene ink was prepared by dispersing graphite flakes (10 mg mlFirst (~20 ml) of graphene/NMP ink is passed through a PTFE membrane . The process is hastened with the use of Büchner flask which is attached to a vacuum pump. The membrane is then placed into 5 ml of ethanol and bath sonicated  for 10 min to redisperse the flakes into the ethanol.ρ = m/V, m is the mass and V the volume.The surface tension is measured using the pendent drop method (First Ten Angstroms FTA1000B). The shape of the drop suspended from a needle results from the relationship between the surface tension and gravity. The surface tension is then calculated from the shadow image of a pendant drop using drop shape analysis. A parallel plate rotational rheometer (DHR rheometer TA instruments) is used to evaluate the viscosity as a function of shear rate, the infinite-rate viscosity for each ink is found. Ink density is evaluated from a (Sartorius ME5) microbalance where the density is A = αcl, with the beam path length l (m) the concentration c (g l−1) and the absorption coefficient α (l g−1 m−1). The h-BN and graphene inks were diluted 1:20 with water/CMC and ethanol, respectively. Absorption coefficients of αh-BN ~ 2350 l g−1 m−1 for the h-BN ink76 and αGR ~ 2460 l g−1 m−1 for the graphene ink19 at 660 nm were utilised. The optical bandgap of the h-BN ink is obtained using Eg defined by hc/λg, where h is the Planck constant, c is the speed of light in vacuum and λg is the resonance wavelength of the peak.The flake concentration in the graphene and h-BN inks are obtained via the Beer-Lambert law, which correlates the absorbance 2 substrate and the Raman spectra are acquired with a Renishaw 1000 InVia micro-Raman spectrometer at 457, 514.5, and 633 nm and a 20× objective, with an incident power of below ∼1 mW to avoid possible thermal damage. The system is within 1.5 cm−1 spectral resolution at 514 nm. The G peak dispersion is defined as Disp(G) = ΔPos(G)/ΔλL, where λL is the laser excitation wavelength. In disordered carbon, the G peak position, Pos(G), increases as the excitation wavelength λL decreases from the IR to UV77. Therefore, the dispersion of the G peak, increases with disorder and allows one to discriminate between disorder localised at the edges or in the bulk of the samples77.Films of each ink and a graphene/h-BN heterostructure are inkjet-printed on Si/SiOScanning electron microscopy images were acquired with a high resolution Magellan 400L SEM. The field emission gun was operated at an accelerating voltage of 5 kV and gun current of 6.3 pA. Images were obtained in secondary electron detection mode using an immersion lens and TLD detector. A 3–5 nm platnium coating was sputtered (Emitech sputter coater) on to the surface of the h-BN flakes to reduce the build-up of electrons.2 in area and arranged symmetrically around the optical axis to achieve a collection solid angle of 0.9 sr. The windowless design of the detector allows qualitative mapping of light elements. Spectrum images were acquired with an acceleration voltage of 80 kV, a spatial sampling of 10 nm pixel−1 and 100 ms pixel−1 dwell time. We employed multivariate analysis to localise EDX signals from compounds by applying a statistical analysis algorithm (non-negative matrix factorisation—NMF—in this case)78 to the EDX dataset, comprising several thousand spectra, and identifying correlations between spectral features. Data were acquired with Tecnai Imaging and Analysis (TIA) and analysed within Hyperspy79, an open source analysis tool-kit where statistical analysis algorithms such as NMF, are implemented.Drops of boron nitride and graphene inks were dispensed on holey carbon TEM grids and then analysed in a FEI Osiris operating in bright field mode at 80 kV. A FEI Helios dual beam Focus Ion Beam/Field Emission Gun—Scanning Electron Microscope (FIB/FEG-SEM) was employed to prepare lamellae for STEM imaging and analysis. The same microscope was used for slice and view imaging. EDX data were acquired using a FEI Osiris TEM equipped with a high-brightness Schottky X-FEG gun and a Bruker Super-X EDX system composed of four silicon drift detectors, each ~30 mm2 substrates wafer substrates. For the graphene and h-BN inks, 150 flakes were counted to determine the statistics for the lateral size and thickness. For the rms, roughness measurement areas of 50 μm2 were scanned.A Bruker Dimension Icon working in peakforce mode was used. From the centrifuged graphene and h-BN dispersions, samples were collected and after 10 times dilution they were drop casted onto pre-cleaned (with acetone and isopropanol) Si/SiO−1 in all devices.All devices were measured with a probe station  that is connected to a semiconductor device analyser  to obtain I-V curves. We use a sweeping time of 0.59 V s80. In addition, nozzle clogging can be an issue unless the particles are ~1/50 or less the nozzle diameter22. When inkjet printing, the ejected drop contacts the substrate and spreads according to Young’s equation, γSV − γSL − γLV cos θc = 0 . The γLV of the graphene ink (30 mN m−1) and PEDOT:PSS ink (44 mN m−1) is minimised so that the droplets will coalesce even on low γSV surfaces (such as polyurethane) allowing uniform printed lines. Furthermore, similarly to CNTs81 low boiling point solvents (≤100 °C) are used to disperse the graphene, h-BN and PEDOT:PSS inks, which evaporate quickly minimising both the transport of particulates (which causes ‘coffee ring’) and the re-dispersion of material at the heterostructure interfaces, thus improving the morphological uniformity of the layered arrangement. The drop then dries through solvent evaporation and the resulting thickness will depend on the number of droplets delivered per unit area , the drop volume and the concentration of material in the ink.We used a DoD ink-jet printer (Fujifilm Dimatix DMP-2800) equipped with a 21 µm diameter nozzle (Fujifilm DMC-11610) where the volume of individual droplets from this nozzle is ~10 pl. The platen temperature was kept as 20 °C throughout printing of heterostructures. Each ink was printed at a maximum jetting frequency of 2 kHz. During droplet ejection a primary drop may be followed by secondary (satellite) droplets which need to be avoided during printing−1 sodium carbonate and 5 mg ml−1 soap at 50 °C, and tumble washed for 30 min according to industry standards9.For each washing test, the sample was washed by immersion in a sealed beaker of 100 ml deionized water containing 2 mg mlThe data that support the findings of this study are available from the corresponding author upon request.Supplementary Information


Graphene has been studied intensively in opto-electronics, and its transport properties are well established. However, efforts to induce intrinsic optical properties are still in progress. Herein, we report the production of micron-sized sheets by interconnecting graphene quantum dots (GQDs), which are termed ‘GQD solid sheets’, with intrinsic absorption and emission properties. Since a GQD solid sheet is an interconnected QD system, it possesses the optical properties of GQDs. Metal atoms that interconnect the GQDs in the bottom-up hydrothermal growth process, induce the semiconducting behaviour in the GQD solid sheets. X-ray absorption measurements and quantum chemical calculations provide clear evidence for the metal-mediated growth process. The as-grown graphene quantum dot solids undergo a Forster Resonance Energy Transfer (FRET) interaction with GQDs to exhibit an unconventional 36% photoluminescence (PL) quantum yield in the blue region at 440 nm. A high-magnitude photocurrent was also induced in graphene quantum dot solid sheets by the energy transfer process. It can be prepared in different forms, such as sheets7, nanoribbons8, and graphene quantum dots (GQDs)9, by various methods. The size and shape, in turn, determine the properties and applications of graphene. For example, GQDs and graphene nanoribbons have photoluminescence properties10, whereas graphene sheets do not, due to their metallic character4. While GQDs are finding applications in biology as biomarkers12, graphene sheets are being used in optoelectronic device fabrication13. As far as preparation is concerned, graphene sheets are obtained by exfoliating graphite using various methods, which include Bordie’s and Hummer’s methods19. The chemical vapour deposition method is also used to prepare pristine graphene sheets13. In contrast, GQDs are obtained by top-down and bottom-up methods20. A pristine graphene sheet is a zero-band-gap material due to the convergence of the valence band maximum and conduction band minimum at the Dirac point21. Photo-excited electron-hole pairs will undergo a non-radiative relaxation process through the continuum band states towards the band edge states, and therefore, photoluminescence is not possible. If a graphene sheet has to be used as an active layer in device fabrication, similar to other semiconducting materials, its band gap must be opened. By producing isolated domains of sp2 islands on the surface of graphene sheets, one can discretize the energy levels (molecular-like energy levels)20 so that the photo-excited electron–hole pairs will undergo radiative recombination through those discrete energy levels, resulting in an intrinsic emission. This intrinsic emission is an indication that the band gap has been opened in the graphene sheet sample. To produce such isolated sp2 domains on the surface of a graphene sheet, surface modifications/treatments involving either oxidation or partial reduction methods have been used23. For example, H. Yoon et al. formed oxidation-controlled graphene quantum dots from graphite oxide that was prepared by the modified Hummer’s method and studied their intrinsic PL behaviour24. N. Amirhasan et al. used a plasma treatment on micromechanically exfoliated single-layer graphene to produce semiconducting graphene sheets and found broad green emission at approximately 550 nm25. In the reported case of plasma treated graphene sheets, a single-layer configuration is necessary to avoid the highly possible interlayer PL quenching effect; this is because the increase in the number of layers results in abrupt quenching of PL, as reported elsewhere26.Graphene is an interesting two-dimensional honeycomb carbon structure with very good electrical and thermal conductivities, strong chemical stability and high mechanical strength28. The best way to obtain a high emission yield from a graphene system is by preparing the samples in size-reduced form as QDs. In such smaller-sized GQDs, the sp2 domains are of nanoscale dimensions, and therefore, one can expect quantum size-effect-induced intrinsic emission to occur naturally. Mostly blue emission is reported from GQDs ranging from 1.8 to 7 nm9. The problem with GQDs is that not only the size affects the emission; (i) the edge effects (free zigzag sites/carbene states)20 and (ii) n-π* transitions from C=O and C=N bonds also contribute to the emission at 450 nm29. For example, carbene-like states and the n-π* transition due to the absorption at 350 nm always show Stokes-shifted emissions at 450 nm, which matches the size-effect-induced emissions at 450 nm. Hence, it is always difficult to obtain a true size-effect-induced strong intrinsic emission from a GQD sample. There are few reports that claim to have obtained size-effect-induced emissions from GQDs30. Others have mostly attributed the reason for the emissions to n-π* transitions of C=O/C=N. Hence, there is an open challenge in graphene research to obtain high-yield photoluminescence that is purely of an intrinsic nature arising from the structure and not involving any functional groups. In the present work, we have successfully prepared GQD interconnected solid sheets that can be induced to give 36% intrinsic emission yield and a high photocurrent. This was possible because the surface effect of the GQDs was drastically reduced in the GQD interconnected solid sheets.Overall observations indicate that it is always difficult to obtain strong intrinsic emission yield from a graphene sheet sample. In fact, there are no reports on the strong intrinsic emission behavior from graphene sheet samples, to the best of our knowledge. However, there are several reports that show the weak emission from graphene sheet samples is due to surface-attached molecules and is always excitation-energy dependent in nature34. As far as such QD solid preparation is concerned, different shaped/faceted nanocrystals made up of heavier elements were interconnected with lighter organic/inorganic groups by slow evaporation and ligand exchange processes35. Such inorganic QD solid systems are weakly coupled and sensitive to external parameters such as temperature, thus limiting the effective utilization of the QD solid systems. The strong coupling between QDs is required for the effective usage of QD solid systems in a wide range of applications such as terahertz lasing and quantum computing36. In the present work, we have successfully prepared GQD solid sheet structures of a single-crystalline nature by interconnecting GQDs with metal atoms. Since the basic building block (GQD) is made up of a light element and is of planar dimensions, it was possible to interconnect them through heavier metal atoms, and thus a stronger coupling is established between the GQDs. Oxygen has also played an important role in the interconnection process. The isolated sp2 domains were created in the interconnection process, which in turn helped to retain the quantum behaviour of the individual dots in the solid sheet. As a consequence, a new material system of graphene with a band gap was made possible. In this present paper, we discuss these results in detail.Recently, research on QD solids has attracted interest because one cannot use the as-prepared colloidal QDs for applications requiring electrical transport properties due to the poor inter-dot charge transport mechanism. By interconnecting the QDs together, one can prepare a solid system with the desired absorption and emission properties. It is even possible to prepare an alternative material to silicon by this method. However, the preparation of such QD solid structures is a challenging process and, to the best of our knowledge, only a few reports are available on the successful preparation of QD solid systems, mostly involving inorganic systems such as PbS, CdSe and PbSe37  type, in which energy from the excited donor is non-radiatively transferred to the acceptor. The fundamental conditions for the FRET-based interaction are (i) spectral overlap between the donor emission and acceptor absorption/excitation and (ii) minimum distance between the donor and acceptor, which directly controls the dipole-dipole interactions40. The other factors that affect the FRET efficiency are the screening of the electric field of the donor dipole in the acceptor medium and the dimensionalities of the donor and acceptor41. To ensure that FRET occurs in the as-prepared samples, we obtained the excitation spectra from the filtered-out GQD and filtered-in sheet samples separately. Interestingly, we noticed a new excitation peak at 410 nm from the sheet sample  according to their electron lifetime values. In the present case, an increased energy transfer interaction that resulted in maximum emission yield was observed up to sample Z7, which has a thickness value of 8 nm, as measured from the AFM analysis . The as-prepared samples were then characterized in terms of morphology, chemical purity and absorption/emission properties. It has been observed that there is an increase in size of the graphene with increase in the zinc metal dopant concentration. Figure tra Fig. , the brotra Fig.  correspotra Fig.  was perfple Fig. , which i2 domains in the solid sheets. This band is not visible in GQDs, which could be because the dominant contribution to the excitation spectrum is from the surface-attached functional groups that usually show a band at 350 nm. Since the surface-to-volume ratio is very high in the GQDs, the contribution of surface-attached functional groups to the absorption/excitation spectra will be high. In the case of GQD solid sheets, the surface-to-volume ratio is minimum, which means that the surface effect is minimum, and therefore, the quantum-size-effect-induced excitation band starts to appear. It is because of this effect in the solid sheets the emission is Stokes-shifted by only 30 nm.Now, the following question arises: why did the sheet samples not produce high emission yields when excited directly at 350 nm? The answer is that the sheet samples have poor absorption at 350 nm. Interestingly, these sheet samples do not produce strong emission, even when excited at 410 nm. We believe that the reason could be related to the nature of the GQD solid sheet structure: the GQDs are connected here, and therefore, the photoexcited electron-hole (e-h) pair will preferably relax through these coupled structures, finally undergoing a non-radiative recombination through the mid-band-gap energy levels that arise due to the presence of surface-attached functional groups in the solid sheet structure. The lifetime measurements, which will be discussed later, also support this claim. However, in the presence of GQDs, most of the domains in the graphene sheets are excited simultaneously through an energy-transfer-assisted interaction with GQDs, and therefore, the excited electrons are in each of the excited states of the respective domains, as schematically depicted in Fig. 45. In our work, we have obtained an average lifetime value of 7.85 ns from the mixture sample, which is higher than the acceptor systems’ average lifetime value of 6.03 ns  in the absence and presence of the acceptor system. Therefore, we have monitored the PL decay curve of the acceptor system at 440 nm and compared it with the PL decay curve of the donor-acceptor mixture system to confirm the energy transfer mechanism. It has been reported that the average lifetime value of the mixture system is usually higher than the average lifetime value of the acceptor system because the charge carriers that are photoexcited in the donor system are non-radiatively transferred to the acceptor system and excite the acceptor system to produce emission; therefore, naturally, a longer lifetime value results20. In our GQDs, the emission is also quenched, leaving behind a small amount of emission at low pH value. This minimum unaffected emission from the GQDs originates from the quantum size effect. However, in the case of GQD solid sheets, the emission is insensitive to pH, which indicates that the emission of the solid-sheet sample is only due to the size effect , which was obtained as a function of energy by scanning the monochromator over a specific energy range.The EXAFS measurements at the Zn K-edge were carried out at room temperature at the Energy Scanning EXAFS beamline (BL-9) at the Indus-2 Synchrotron source  at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, IndiaThe computational details of quantum chemical calculations for adsorption energy calculation and charge analysis are given in the Supplementary information.2SO4 was used as the electrolyte.The samples were electrophoretically coated onto a pre-cleaned FTO substrate under a constant potential of 5 V from a DC regulated power supply. Photocurrent measurements were carried out using an LOT-Quantum Design 150 Watt solar simulator with 1 sun illumination attached to a metrohm Autolab PGSTAT 302 N instrument. The EPD-coated samples were used as working electrodes, while the platinum wire and Ag/AgCl were used as counter and reference electrodes, respectively. A total of 0.5 M NaThe data that support the findings of this study are available from the corresponding author and the same will be provided upon reasonable request.Supplementary Information


Nanostructured and chemically modified graphene-based nanomaterials possess intriguing properties for their incorporation as an active component in a wide spectrum of optoelectronic architectures. From a technological point of view, this aspect brings many new opportunities to the now well-known atomically thin carbon sheet, multiplying its application areas beyond transparent electrodes. This article gives an overview of fundamental concepts, theoretical backgrounds, design principles, technological implications, and recent advances in semiconductor devices that integrate nanostructured graphene materials into their active region. Starting from the unique electronic nature of graphene, a physical understanding of finite-size effects, non-idealities, and functionalizing mechanisms is established. This is followed by the conceptualization of hybridized films, addressing how the insertion of graphene can modulate or improve material properties. Importantly, it provides general guidelines for designing new materials and devices with specific characteristics. Next, a number of notable devices found in the literature are highlighted. It provides practical information on material preparation, device fabrication, and optimization for high-performance optoelectronics with a graphene hybrid channel. Finally, concluding remarks are made with the summary of the current status, scientific issues, and meaningful approaches to realizing next-generation technologies. As the technological needs of the modern society have become more diversified than ever, it might be desirable to create new electronic materials that can provide on-demand functions every time a new need arises. However, given the limited possibility of synthesizing or isolating totally new materials, hybridized use of known materials can be a smart yet realistic alternative, and this has indeed become an important trend in current materials science and electronics research. Notable examples are organic-inorganic hybrid thin-film devices ,2,3 and In this context, graphene-based nanohybrid materials can be considered as a versatile platform for next-generation optoelectronics. Since its first detailed characterization reported in 2004, graphene has revealed its extraordinary electronic, optical, thermal, and mechanical properties, which are particularly promising for use as a transparent and flexible electrode in conventional semiconductor devices ,9,10,11.However, the observed device behaviors tend to vary widely between architectures and often seem not to be sufficiently rationalized, which can be above all due to the complex nanoscale phases and interfaces that dominate effective macroscopic functionalities. Acknowledging this issue, the purpose of this review is to provide essential understanding on the governing structural and physicochemical properties of active hybrid materials incorporating nanostructured graphene and to link this understanding to reviewing and digesting state-of-the-art devices. Such a procedure is intended to fill the conceptual gap between proposed devices and observed performances, and it is expected to also provide practical guidelines for designing new hybrid materials and devices with tailored characteristics.2-hybridized carbon atoms, each of which donates one π electron that is delocalized to carry electrical conductivity over the entire lattice structure  or equivalent Λ-shape resistivity-GV plots of a graphene channel field-effect transistor (FET) . This explains symmetric V-shape ambipolar transfer curves (gate voltage or (FET)  . Tw. Tw62]. 2TPP-graphene showed n-doping characteristics, while both Al(III)TPP- and ZnTPP-graphenes exhibited p-type doping (2 and a source-drain bias (DV) of 50 mV, H2TPP-, ZnTPP-, and Al(III)TPP-graphene exhibited a responsivity of 0.22 A/W, 0.54 A/W, and 5.36 A/W, respectively, proving substantial enhancement compared to pristine graphene and beneficial effects of metallization. This performance metric showed apparent voltage and power dependence, reaching a high value over 100 A/W in the case of Al(III)TPP-graphene at 2 V ]  and . Th. Th66]. bis(4-decyltetradecyl)-6-methyl-6′---2,2′-dione) (IIDDT-C3) and n-type poly-alt-5,5′-] (P(DNI2OD-T2)) were used as a semiconducting material (2 (up to 50%), by changing the volume of a drop-cast solution up to 20 μL. The polymer semiconductor was then spin-cast to passivate LPE-G islands  shift was observed by applying programming and erasing gate pulses. Also, this electrical cycle was highly reproducible, as evidenced by the durability test results in Interestingly, the ionization energy of LPE-G was dramatically tunable by changing the thermal annealing duration and atmosphere. The graphene’s energy level could be placed either within or at the outside of the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of the semiconducting polymers, and tunable transport regimes were observed in a hybridized channel. By adjusting the energy level of graphene, the FETs were addressed as a memory device. As shown in The nanostructured graphene/organic systems introduced in this section can be compared to planar-junction devices where a sheet-type graphene forms a continuous interface with an organic film or crystal. Our previous review described many of these structures . A recenDue to their strongly ionic character, metal-oxide semiconductors have a large band gap and are generally transparent to visible light ,70. Zhan2-graphene active layer . This allowed for the fabrication of photodetectors on plastic (2 (ca. 2.7 eV) makes it sensitive to the ultraviolet (UV) region. As shown in As another example of hybrid diodes, Manga et al. demonstrated vertical photodetectors based on a ternary PbSe-TiOve layer  72]. In. In2-gramposites a,b. Also plastic c. Anothe2 V−1 s−1 in an IGZO-only device to 23.8 cm2 V−1 s−1 in a GNSs/a-IGZO FET. At higher concentrations, off-state currents started to increase as the percolation takes place. Eventually, at graphene contents over 0.45 vol %, balanced ambipolar behavior was observed, reflecting the dominant transport through well-connected GNSs. After finishing this mechanism analysis on rigid FETs on Si, the authors also presented low-voltage flexible devices using an ultra-thin glass substrate and a high dielectric constant Ta2O5 insulator. Interestingly, the formation of a hybrid channel also enhanced bending stability. The hybrid FET showed only 8% reduction in mobility after 100 times of bending, while the pristine device suffered from serious 70–80% decrease (Solution-processable In-Ga-Zn-O compounds (IGZO) are promising n-type semiconductors for printed large-area electronics ,74,75. Ddecrease c. This sDI was observed for the ZnO NRs/Gr device. The current increases as the incident power increases, and this photocurrent effect was reversible. A large band gap of ZnO allowed for the efficient absorption of UV photons, and the electron transfer from ZnO to graphene enabled electrical read out. The real-time UV response shown in Dang et al. recently published research on photosensitive hybrid FETs based on a graphene sheet channel decorated with ZnO nanorods (NRs)  77]. Th. Th77]. DI, and this was explained by the desorption of molecular p-type dopants on the graphene surface. The ZnO NPs-based channel exhibited a lower photoresponse than the NR counterpart, and this was attributed to the smaller absorption cross-section and the larger bandgap due to the quantum confinement. Because ZnO acted solely as the absorber medium with a defined bandgap, a high selectivity of photodetection (maximum response at wavelengths around 365 nm) was obtained. Interestingly, this is in sharp contrast to the system reviewed in UV irradiation on pristine device resulted in a decrease in The overview given in the previous section is convincing evidence that nanostructured graphene hybrid optoelectronics has witnessed a considerable growth over a relatively short period of time. Many new deposition methods, advanced composites, device designs, and fabrication techniques have been developed, and they have all significantly contributed to the current status of the field. However, important issues exist that need to be tackled in the near future for this new research area to get necessary momentum and turn into a viable technology.Firstly, material processing can be further improved. For instance, strongly acidic or toxic chemical environments are still widely utilized for growth, synthesis, and structural control, and this is not desirable in terms of sustainability and commercialization. Aqueous routes or other green chemistry approaches have been appreciated in organic electronics, where harsh chemicals and hazardous solvents have been traditionally used . This caSecondly, better structural control can be an added value. The hybrid system, by its nature, often develops very complex nanostructures with distinct phase separation mechanisms. Failing to fully manipulate the distribution of multiple components in a composite-based channel, for instance, may lead to limited reproducibility and large-area uniformity. In addition to the control over the blend solution and annealing, area-selective deposition through anchoring groups and/or the addition of functionally inactive scaffolds can help improve the controllability over phase separation or guide the formation of new nanostructures ,82.Finally, new hybrid materials and devices are of great interest. This review has provided a clear indication that many creative and original systems are being tested. Given the improved understanding of graphene handling and the emergence of new semiconductors, there should be other potentially important hybrid architecture that is worth looking at. As another benchmark, the traditional boundary between organic and inorganic material systems has been challenged by many recent developments, such as 4G thin-film solar cells  or polymNanostructured and modified graphene possesses a great utility for enabling new optoelectronic devices with hybridized structures and properties. Combining the functional diversity with the processing versatility, including solution printing, novel device concepts have been demonstrated with a variety of semiconductors and nanomaterials. In many representative systems, graphene has been used as a sheet-type channel that is decorated with additives, or it has been mixed into a host that serves as a bulk semiconducting medium and dispersion agent. Various devices such as planar photodetectors, multi-component PVs, hybrid FETs, transport-tunable memories, quantum-dot sensitized diodes, and nanowire UV detectors have been suggested with organic and inorganic matching components. Here, graphene successfully served a range of roles including chemical hosts/dopant materials, photocarrier acceptors, energetic cascades, percolation bridges, charge floating gates, growth templates/linkers, ambipolar transporters, electrical transducers, and so on. This array of novel devices has shown that graphene-based hybrid architecture can be a major building block for next-generation optoelectronics. Major issues regarding processing, controllability, efficiency, sustainability, scalability, and performance need to be solved in the near future, and the technological developments will be further accelerated, benefiting from extensive research efforts that will be continuously put into this highly promising area.


The data show alveolar macrophage expression of a pro-inflammatory, tissue remodeling and angiogenic complex activation pattern, suggesting that iron accumulation may play a role in macrophage activation.Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease of unknown cause characterized by alveolar epithelial damage, patchy interstitial fibrosis and diffuse microvascular abnormalities. In IPF, alveolar clustering of iron-laden alveolar macrophages—a common sign of microhemorrhage, has been associated with vascular abnormalities and worsening of pulmonary hypertension. As iron-dependent ROS generation has been shown to induce unrestrained macrophage activation in disease models of vascular damage, we explored alveolar macrophage activation phenotype in IPF patients (n = 16) and healthy controls  by RNA sequencing of bronchoalveolar lavage (BAL) cells. The frequencies of macrophages in BAL cells were 86+4% and 83.4+8% in IPF and CTR groups, respectively . In IPF patients, BAL cells showed increased iron-dependent ROS generation . Gene expression analysis showed overrepresentation of Gene Ontology processes/functions and KEGG pathways enriched in upregulated M1-type inflammatory , M2-type anti-inflammatory/tissue remodeling , and MTPP-type chronic inflammatory/angiogenic  chemokine and cytokine genes. The  Idiopathic pulmonary fibrosis (IPF), a progressive interstitial pneumonia of unknown cause disproportionately affecting older adults, is defined by the histopathological pattern of usual interstitial pneumonia (UIP) that is characterized by patchy distribution of fibrosis areas with peripheral honeycombing and scattered fibroblastic foci resulting from microscopic centers of acute alveolar epithelium injury of yet unrecognized cause .The role of alveolar macrophage-driven lung inflammation in the pathogenesis of IPF has been long debated . A numbeRecent studies in murine models of pulmonary fibrosis have shown that alveolar macrophages play a key role in fibrosis pathogenesis . In partHistopathological and BAL IPF studies have shown that increased numbers of iron-laden macrophages cluster in the alveolar and interstitial spaces in a significant proportion of affected individuals. In particular, alveolar macrophage iron accumulation has been described in IPF, in association with increased capillary density , pulmonaIn this context and with the background of the above IPF macrophage studies –13, 17, Sixteen patients  diagnosed according to international guidelines by multidisciplinary discussion (MDD). HRCT scans were evaluated systematically according to the ATS/ERS/JRS/ALAT guidelines , includiSeven healthy controls  underwent fiberoptic bronchoscopy (FOB) and BAL under an investigational protocol  after written informed consent.BAL of controls and IPF patients was carried out using standard procedures, according to ATS guidelines , as prev5) were washed twice in PBS, and incubated in RPMI without phenol red (Sigma Aldrich) in the dark for 1 hr  with/out 100 μM DFP. CM-H2DCFDA (5 mM) was then added and fluorescence measured after 1 h incubation  as described   for 24, 72, 120 hours. Macrophage iron accumulation was assessed using the Prussian Blue Stain and staining intensity quantified by the Golde score as previously described . ROS genescribed  using a Macrophage activation phenotype was assessed by quantitative PCR (qPCR) analysis of the expression of M1, M2, and MTPP genes Ccl4, Cxcl2, Cxcl10, Il1rn, and Cxcl7.in vitro study data are expressed as mean and standard deviation or percentage as appropriate. Comparisons between groups were made by using the Fisher’s exact test (for contingency tables), or non-parametric test, Mann-Whitney test and one way ANOVA with Scheffe multiple comparison. A p-value <0.05 was considered significant. All analyses were performed using the GraphPad Prism 6.0  software package.Study population and Normalization of RNA sequence data was carried out using the upper-quartile method, followed by RUV technique, using housekeeping genes (HKG) to remove unwanted effects and generate accurate estimation of gene fold change using GLM with a negative binomial distribution as described above.Alveolar macrophages recovered by BAL from IPF patients  were characterized by significant iron accumulation, as measured by Golde score , Principal Component Analysis showed separation between healthy control and IPF patient BAL macrophage gene expression . Based oSimilarly, in the KEGG Pathway analysis the “Cytokine-cytokine receptor interaction”, “Chemokine signaling” and “TNF signaling” pathways were identified as most significantly overrepresented. These pathways comprised differentially expressed cytokine and chemokine genes largely overlapping with those identified by GO Biological Process and Molecular Function analysis . They inTPP–type activation patterns. Alveolar macrophage differentially expressed genes were concurrently, and significantly (p<0.05), enriched in M1 , M2  as well as in MTPP-type activation genes .In addition, over-representation of the GO Molecular Function “Haptoglobin binding” suggested ectopic expression of the hemoglobin genes HBA1, HBA2 and HBB by BAL cells. We thus compared the IPF alveolar macrophage differentially expressed genes  and time dependent increase in the expression of the selected M1, M2 and MTPP-type chemokine and cytokine genes , a chronic disorder associated with tobacco smoke exposure whereby patients with advanced disease show alveolar macrophages with increased accumulation of iron . FerritiS1 File(DOCX)Click here for additional data file.S1 Fig(TIF)Click here for additional data file.S2 Fig(TIF)Click here for additional data file.


Turning is ubiquitous in activities of daily living. For people with hemiplegia, persistent impairments in strength, balance, and coordination will affect their ability to turn safely. Consequently, turning retraining should be addressed in rehabilitation programs. To measure turning for these individuals, a reliable clinical tool is required. To investigate (i) the intrarater, interrater, and test-retest reliability of the timed 180° turn test; (ii) the correlation of the timed 180° turn test with other measures of stroke-specific impairments; and (iii) the cut-off time that best discriminates individuals with hemiplegia from chronic stroke and healthy older adults. 33 individuals with hemiplegia due to chronic stroke and 32 healthy elderly individuals participated in this cross-sectional study. The timed 180° turn test was administered along with other measures of stroke-specific impairment. The timed 180° turn test demonstrated excellent intrarater, interrater, and test-retest reliability in individuals with hemiplegia from chronic stroke. The timed 180° turn test (times) significantly correlated with the Fugl-Meyer Assessment of the Lower Extremities (FMA-LE), affected ankle plantar flexion strength, the 5-Times-Sit-To-Stand test, the Berg Balance Scale (BBS), and the Timed Up and Go (TUG) test. The timed 180° turn test is a reliable clinical tool to assess the turning ability of subjects with hemiplegia from chronic stroke.  Turning is a fundamental motor skill of mobility and is essential in the execution of many activities of daily living . Basic fSedgman et al.  investigThe mini-BESTest , the FigWalking and turning are common activities reported at the time of a fall in older adults  and fallThe objectives of the study were (i) to establish the intrarater, interrater, and test-retest reliability of the timed 180° turn test for times and number of steps for people with hemiplegia from chronic stroke, (ii) to investigate the concurrent validity of the timed 180° turn test by exploring correlations with other impairment and activity limitation measures, including the Fugl-Meyer Assessment of the Lower Extremities (FMA-LE), ankle dorsiflexion and plantar flexion strength, the 5-Times-Sit-To-Stand test, the BBS, the TUG test, and the Activities-specific Balance Confidence (ABC) Scale. This study was also designed to (iii) determine the cut-off times that best discriminate individuals with hemiplegia from chronic stroke from healthy older adults when completing the timed 180° turn test to either direction.This was a cross-sectional study. Good intrarater reliability (intraclass correlation coefficient [ICC] = 0.828) has been reported for the number of steps taken to turn 180° in older adults . AssuminIndividuals with hemiplegia from chronic stroke were recruited from a local self-help group and were included if they (i) were ≥55 years of age; (ii) had hemiplegia due to a single stroke at least one year previously; (iii) were able to walk at least 10 m with or without a walking aide; (iv) had an Abbreviated Mental Test score ≥ 7 ; and (v)The study was approved by the ethics committee of The Hong Kong Polytechnic University and was conducted according to the guidelines of the Declaration of Helsinki. Written informed consent was obtained from all participants before commencement of the study.For the timed 180° turn test, a piece of coloured tape is placed on the floor to mark the starting position. Each subject was required to stand with arms by side and feet comfortably apart and pointing to the tape. All subjects were asked to turn 180° on the spot from a standing start position and within a designated area marked on the floor. Subjects were asked to turn “as fast as you can” and wore their usual footwear. Timing (with a stopwatch) was started from the word “GO” and stopped when the shoulders and feet were facing in the opposite direction. The number of steps taken to turn 180° were also counted. Each subject performed three turns to each direction with 1-minute rest break between trials.The FMA-LE is a comprehensive quantitative measure of the motor impairment of the lower extremities following stroke . SeventeThe maximum isometric contraction of the subjects ankle dorsiflexors and plantar flexors was measured bilaterally using the Nicholas hand-held dynamometer (model 01160) (supplier: Lafayette Instrument Co.) in a standardised testing position . Hand-heFunctional muscle strength of the lower extremities was assessed with the 5-Times-Sit-To-Stand test . It has Clinical balance was measured with the BBS . The BBSFunctional mobility was assessed by the TUG test . The TUGThe ABC Scale measures a subjects' confidence in performing sixteen tasks without falling . The subThe subjects with hemiplegia from chronic stroke were assessed on two separate occasions, 7 to 10 days apart. The interval of 7–10 days was chosen to avoid fatigue, learning, or memory effects for the subjects but also to avoid genuine change occurring during the study period . The timIn addition to the timed 180° turn test, the subjects with hemiplegia from chronic stroke completed the FMA-LE, ankle dorsiflexor and plantar flexor muscle strength testing, the 5-Times-Sit-To-Stand test, the BBS, the TUG test, and the ABC Scale questionnaire. The outcome measures were completed in random order by drawing lots. Subjects were given a 2-minute rest break between outcome measures to avoid fatigue.The healthy older adults completed the timed 180° turn test in one session. Their data was used to determine the timed 180° turn test cut-off times to distinguish healthy older adults from people with hemiplegia from chronic stroke.t-test and the Chi-square test. The within-group differences were assessed using the paired t-test for parametric data and the Wilcoxon signed-ranks test for nonparametric data.Data analysis was completed with SPSS software (version 23) . The normality of the data and homogeneity of variances were tested using the Shapiro-Wilk test and Levene's test, respectively. Between-group differences in demographic data were assessed by the independent 3,1), interrater reliability , and test-retest reliability . Model 3 was chosen to establish that specific investigators were reliable in their data collection (rater is considered a fixed effect) and model 2 was chosen to generalise results to other raters with similar characteristics (rater and subjects are considered random effects).The ICC was computed to measure the intrarater reliability  reflects the reliability and stability of the measurement instrument  and was 95) is calculated to determine how much change must occur in a variable to reflect true change [95 for the times and number of steps to turn 180° for each direction was calculated with the following formula: MDC95 = 1.96 × SEM × √2.The minimal detectable change with 95% confidence interval  after Bonferroni adjustment. The strength of correlation was classified into fair (r = 0.25–0.49), moderate to good (r = 0.50–0.75), and good to excellent (r ≥ 0.75) [Correlations between the timed 180° turn test times and number of steps (to both directions) and other outcome measures were quantified using Spearman rho due to nonparametric data. Six primary outcomes were chosen  and the  ≥ 0.75) .Receiver operating characteristic curves were generated and by using Youden's index the timed 180° turn test cut-off times in seconds to both the affected and unaffected direction were obtained . This cuThirty-three subjects with hemiplegia due to chronic stroke  with a mean age of 60.18 ± 6.42 years and a mean time since stroke of 112.21 ± 51.30 months participated in this study. Thirty-two healthy control subjects  with a mean age of 61.84 ± 4.59 years were recruited. The subjects' demographics are summarized in The mean times and number of steps taken to turn 180° for both subject groups are shown in 95 values for subjects turning towards the affected side were 0.62 seconds and 0.83 steps and towards the unaffected side were 0.64 seconds and 0.81 steps.The timed 180° turn test demonstrated excellent intrarater reliability for Rater 1 and Rater 2 for both turn directions, with ICCs ranging from 0.930 to 0.983 for times and 0.945 to 0.969 for number of steps . ExcelleThe details of the correlations are summarized in A cut-off time of 2.59 seconds was found to best discriminate healthy subjects from those with hemiplegia towards both the affected side  and unaffected side . The receiver operating characteristic curves are presented in 95.This is the first study to investigate the reliability and concurrent validity of the timed 180° turn test for individuals with hemiplegia from chronic stroke. It is also the first to determine the cut-off times of the timed 180° turn test best discriminating individuals with hemiplegia from chronic stroke and healthy older adults and to calculate the SEM and the MDCTurn direction (towards affected or unaffected side) did not have a significant effect on the timed 180° turn test times and number of steps for the subjects with hemiplegia from chronic stroke. This finding supports previous published studies. For subjects with stroke, turn direction does not have a significant effect on the time to complete the TUG test , the disTwo types of turn strategy have been reported: the spin turn and the step turn . The ste95 . Similarly, the average number of steps taken to turn 180° for the hemiplegia group was 0.98 (towards the affected side) and 1.09 (towards the unaffected side) more than the healthy control group which is also greater than the calculated MDC95 . Therefore, the difference in time and number of steps taken between the hemiplegia and healthy group to turn 180° is unlikely to be due to measurement error but is the result of a true difference in performance ability. This finding supports previous published studies reporting that subjects with stroke take significantly more time and more steps to turn 180° than healthy controls, independent of turn direction [Compared to the healthy control group, the hemiplegia group on average took 1.14 seconds longer to turn towards the affected side and 1.28 seconds longer to turn towards the unaffected side. This difference is greater than the calculated MDCirection . IndividThe TUG test has a 180° turn component and has been shown to have excellent test-retest reliability (ICC = 0.95) for individuals with chronic stroke . For thiSignificant negative correlation was found between the FMA-LE and the time taken to turn 180° (to both the affected and unaffected side). The FMA-LE measures motor impairment after stroke by assessing reflexes, coordination, and isolated movement  and turnρ = −0.860, P < 0.01) [Affected ankle plantar flexion strength demonstrated a significant negative correlation with the timed 180° turn test times to both directions. This is similar to the findings of Ng and Hui-Chan who reported that affected ankle plantar flexion strength had a significant negative correlation with the TUG test in subjects with chronic stroke ( < 0.01) . The ank < 0.01) . Followi < 0.01) . The lac < 0.01) .The BBS scores demonstrated significant negative correlation with the timed 180° turn test times and number of steps. This may be the result of similarity between turning and 3 items within the BBS. Item 11 of the BBS (turn 360°), item 12 , and item 14 (standing on one leg) have components of weight shifting, alternate stepping, and single support stance, which are also components of turning. The TUG test has a 180° turn component; therefore it is not surprising that this variable had a significant positive correlation to the timed 180° turn test times and number of steps taken to both directions. Subjects with better turning ability would be expected to perform well in both the TUG and 180° turn tests.It is interesting to note that following Bonferroni correction the ABC Scale did not correlate significantly with the timed 180° turn test. The ABC Scale requires subjects to rate their balance confidence in performing 16 tasks without falling; therefore the subjects' perceived ability may not have a strong association with physical performance of turning measured by the timed 180° turn test . In addiIndependent of turn direction, the time to turn 180° correlated with more outcome measures and consistently demonstrated a stronger correlation to those outcome measures than the number of steps taken to turn. One hypothesis for this finding is based on turn strategy. Without recording the type of strategy used, it is unknown whether significant heterogeneity may exist within the sample if some subjects were using a step turn and others were using a spin turn. This would reduce the sample size and power and hence its ability to detect a relationship between the number of steps taken to turn and measures of motor impairment and strength.The area under the curve for the timed 180° turn test times was 84.6% towards the unaffected side and 85.1% towards the affected side. A perfect test instrument would have an area under the curve (true positive rate) of 100% . Based oThe strategy and quality of the turn were not recorded as this would be too difficult for the raters to assess while also timing and counting the steps. By recording the turn strategy used by the subjects, the relationship between turn strategy, muscle strength, balance, and functional ability could be further investigated.Caution should be exercised when interpreting the cut-off results due to the majority of hemiplegic subjects being male (66.7%) whereas the majority of the healthy subjects were female (68.8%). Previous research has shown that gender differences exist in lower extremity strength, functional mobility, and balance  which coThe results can only be generalised to subjects fulfilling the same selection criteria because of the small sample size. The sample size calculation was based on previous reliability findings , as the In conclusion, the timed 180° turn test has excellent intrarater, interrater, and test-retest reliability in individuals with hemiplegia from chronic stroke. The timed 180° turn test (times) significantly correlated with the Fugl-Meyer Assessment of the Lower Extremities (FMA-LE), affected ankle plantar flexion strength, the 5-Times-Sit-To-Stand test, the Berg Balance Scale (BBS), and the Timed Up and Go (TUG) test.The timed 180° turn test is a simple and reliable clinical tool to assess the turning ability of subjects with hemiplegia from chronic stroke.