Two different types of graphene materials were used as functional nanofillers for the mechanical and tribological improvement of silicon carbide/graphene nanocomposites. On the one hand is thermally reduced graphite oxide (TRGO) reduced at three different temperatures, and on the other hand is graphene made of three different organic precursors, which were directly coated on silicon carbide (SiC) platelets (GSiC). Additionally, benchmark materials were also used as carbon fillers. The SiC/graphene nanocomposites with 2 wt% filler content were manufactured by pressureless sintering (PLS). Some composites were produced with higher graphene contents of 4% and 8% and sintered by spark plasma sintering (SPS). Microstructural analyses were conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Underwater lubrication, the SP sintered TRGO and GSiC materials with high graphene content have shown the most promising tribological performance. Furthermore, the reduced size of the homogeneously distributed nanoparticles promotes the formation of surface states, which improve the friction and wear properties. Reliability and efficiency of these components need to be improved by using high-performance ceramics with superior tribological and good mechanical properties. The main aim of this work is to develop novel, highly efficient materials on the basis of graphene-containing silicon carbide (SiC) nanocomposites and to demonstrate their suitability for technical applications such as slide bearings and face seals in aqueous media. SiC is an advanced ceramic material which is characterized by good mechanical and chemical properties as well as a superior resistance against wear ,2. For t3N4 ,9 and bo3N4  ceramics3N4 ,12, frac3N4  and vari3N4 , a few p3N4  or under3N4 . Though 3N4 ,17,18.As reported by Zhang et al. , mechanoThe research work presented in this paper follows on from the studies of Zhang et al.  investig3 (30 g) were suspended overnight in H2SO4 . At 0 °C, the KMnO4 (180 g) was added in portions within 2 h. The suspension was then stirred for 2 more hours at room temperature. The dispersion was poured slowly on ice water (1.4 L), and H2O2  was added. The resulting mixture was filtered in a buechner funnel. The solid filter cake was rinsed several times with deionized H2O (4 × 5 L) and concentrated HNO3 . The resulting sulphate and manganese impurities in the GO were largely removed by cross-flow filtration [−1) with nitrogen cooling. After milling, the drying procedure was repeated. The dry powder was reduced in a tube furnace at 600 °C, 800 °C and 1000 °C under nitrogen atmosphere  to yield a low-density powder. Accordingly, the produced thermally reduced graphite oxides are referred to as TRGO-600, TRGO-800 and TRGO-1000. To integrate the particles homogeneously into the ceramic matrix, TRGO dispersions  were produced in water. For this purpose, the dispersion was dispersed once in the high-pressure homogenizer  at 1000 bar after an ultrasonic bath pretreatment (2 × 15 min) [Graphite oxide (GO) was prepared by oxidizing graphite via the Hummers method . Graphitltration . After dH2O2 5%, 0 mL was For the preparation of GSiC, three different precursors were used: dopamine (GSiC-D) , furfury2/g, d90 = 2 µm, QSIL Ingenieurkeramik, Frankenblick, Germany) in tris(hydroxymethyl)–aminomethane solution  using an ultrasonic bath (15 min). Then the solution of dopamine hydrochloride (2.00 g) was added to the tris(hydroxymethyl)–aminomethane solution . After stirring the reaction mixture for 72 h the water was removed by freeze-drying. The powder was mortared and carbonated in the tube furnace  in a nitrogen atmosphere. The material was heated to a temperature of 150 °C at a rate of 5 K/min, maintained for 21 h, and then increased to 1000 °C at 5 K/min and thermolyzed for 6 h.Graphene-coated silicon carbide from dopamine (GSiC-D) was first prepared by dispersing SiC  in water (200 mL). This was followed by the addition of furfuryl alcohol (15 mL). Then, after 10 min stirring, p-TsOH (0.33 g in water 10 mL) was added. After 20 min of stirring, the reaction mixture was heated up to 80 °C and held at this temperature for 1 h. After 6 h, the mixture was stirred at 100 °C until the powder was dry. After crushing the powder with a mortar, it was carbonized in the tube furnace  in a nitrogen atmosphere. The material was heated up to a temperature of 150 °C at a rate of 5 K/min, maintained for 21 h, and then increased to 800 °C at 5 K/min and thermolyzed for 6 h.Graphene-coated silicon carbide from furfuryl alcohol (GSiC-F) was produced by dispersing SiC  in water (90 mL) by ultrasonic bath (2 × 15 min). Then the solution of D(+)-glucose (2.00 g in 10 mL water) was added. After predispersion by using an ultrasonic bath (2 × 15 min), the reaction mixture was completely dispersed under ice cooling via an ultrasonic lance. After freeze-drying, the powder was mortared and carbonated in the tube furnace  in a nitrogen atmosphere. The material was heated up to a temperature of 150 °C at a rate of 5 K/min, maintained for 21 h, then increased to 800 °C at 5 K/min and thermolyzed for 6 h.Graphene-coated silicon carbide from glucose (GSiC-G) was produced by dispersing SiC  and BG-grade M (GnP® Grade M–15) both delivered by XG sciences.Four different carbon fillers were chosen as commercially available benchmark materials: Graphite (KFL99.5 graphite AMG Mining), carbon black  and two types of benchmark graphene nanoplatelets (BG): BG-grade C  was performed by using a vario MICRO cube . The specific surface area was measured by the adsorption of nitrogen according to Brunauer–Emmett–Teller (BET) theory by using a Sorptomatic 1990 . The graphene content on top of the coated SiC-particles was measured by thermogravimetric analysis . The mass loss was determined as the filler content in comparison to pure SiC . Scannin2/g, d90 = 2 µm, QSIL Ingenieurkeramik, Frankenblick, Germany) and sintering aids  with the desired amount of graphene material in a planetary ball mill  for the duration of 4 h and a sharker mixer  for another 4 h. TRGO was incorporated in the form of a stable aqueous dispersion . After screening (grain size 63 μm), the sample was redried and granulated by freeze-drying. The granules (grain size < 180 μm) were then compacted to test plates  and sintered by a conventional solid phase sintering process using sintering parameters that generally lead to highly densified microstructures for silicon carbide ceramics . Test specimens were milled from the sintered plates.SiC/graphene nanocomposite slurries were prepared by blending SiC . SPS is a new technique and enables fast and energy-efficient sintering of ceramic parts. However, SPS is only possible with sufficient contents of electrically conductive fillers. This was the case for samples with 4% and 8% of graphene fillers. For this sintering process, the conductive powder (>20 Ωcm) was compacted between two highly conductive graphite punches . A current was applied to the punches (max. 10 V) until the sinter temperature 2050 °C was reached. The sample was then sintered at this pressure and temperature for 5 min in an argon atmosphere.The density of SiC/graphene nanocomposites was measured by using Archimedes’ method in water. The four-point bending strength (σ) values of ceramic nanocomposites were determined in accordance with DIN EN 843-1 on bars with dimensions 3 mm × 4 mm × 45 mm at ambient temperature and atmosphere. The fracture toughness was measured by the Single Edge V-notch Beam  method. The specimens with dimensions 3 mm × 4 mm × 45 mm were ground and polished by a 15 µm diamond grinding wheel before testing. A sharp V-notch using the razor blade and diamond paste  with total depth of between 0.8 mm and 1.2 mm was prepared. Electrical resistance measurements were performed on specimens with a dimension of 3 mm × 4 mm × 45 mm. The contact area of the specimens was coated with silver paste to assure good contact with the crocodile clip. The specific conductivity was calculated from these values.a: 0.65 µm, Hexaloy SA, Eagle Burgmann, Wolfratshausen, Germany) were performed using a standard pin-on-ring setup . The graphene-containing pins had a spherical tip with a radius of 5 mm and had dimensions of 10 mm × 4 mm × 4 mm in length, width and thickness. The contact geometry of a spherical tip ensures that an initial point of contact is established; thus, there is no risk of contact misalignment. The initial contact stresses were calculated according to Hertzian equations. The normal force and sliding speed were 50 N and 0.1 m/s; consequently, the initial contact pressure amounts measured up to 2.7 GPa. A drawback of the use of a spherical tip radius is that, due to wear of the pins, the contact area continuously increases during the sliding test, which leads to a continuous decrease in the contact pressure. In order to avoid hydrodynamic influence, which would affect the comparability of the results, the test duration was restricted to 4 h. It was therefore ensured that the contact pressures were at least 10 MPa throughout the whole test. The tests were conducted under water-lubricated conditions at room temperature and repeated twice. As reference material combination, SSiC pins without graphene (SSiC#137) were tested against SSiC face seal counter rings under the same conditions.Sliding tests of graphene-infiltrated SiC ceramics against commercially available SSiC face seal counter rings  to determine the wear volumes and wear mechanisms. In the SEM analyses, a low electric voltage of 3 kV and a SE detector were used to resolve surface changes due to wear with high contrast. For selected samples, atomic force microscopy (AFM) was carried out to detect tribologically induced layer formation on top of the surfaces .As it is apparent from As shown in the TEM images in The morphology and particle sizes of the four different benchmark materials are shown in The wear results of the pins are shown in In order to summarize the best results of the pin-on-ring tests, the COFs measured after 4 h are plotted in relation to the respective wear volumes for selected tribosystems in The worn surface of the reference material SSiC#137 is shown in In contrast, there is no microcracking on the surfaces of the TRGO-containing pins after sliding . Sinter Finally, A more surface-sensitive analysis was carried out with scanning electron microscopy using an in-lens detector and, additionally, AFM of the worn surfaces. A representative SEM image of a worn surface of a silicon carbide ring is shown in The starting point of this research work was the analysis of the tribological behavior of SiC ceramics containing graphene in aqueous media, in light of a technical application of these innovative materials for bearings in pumps. Therefore, two different types of graphene materials were chosen: thermally reduced graphite oxide (TRGO), reduced at three different temperatures , and graphene made from three different organic precursors, which was directly coated on SiC platelets . Additionally, four commercially available carbon benchmark materials were chosen as fillers.The material synthesis of SiC-based nanocomposites is very complex, since it depends on a lot of subsequent manufacturing steps, starting with powder synthesis, mixing and processing, shaping and sintering. Our goal was to reach considerable graphene contents to improve tribological properties without losing too much mechanical strength. Concerning the mechanical properties, it is very difficult to reach sufficient mechanical strength (>300 MPa) at higher graphene contents. The problem may be at this point that the carbon fillers act as a diffusion barrier during the sintering process, thus preventing densification and formation compact and pore-free microstructures. If agglomeration cannot be completely prevented, the formation of large microstructural defects is inevitable. In light of the mechanical properties see , it is nFocusing on the microstructural aspects, in the case of GSiC materials, the precursor has to be taken into account. As shown in the results, different numbers of graphene layers can be obtained on the SiC depending on the precursor. In accordance with the observed friction and wear behavior of GSiC-D and GSiC-G, the following applies: The tribological properties are improved if SiC is coated with only few graphene layers so that the filler can be distributed finer within the matrix.From the results obtained, meaningful correlations can be made between the size of the specific surface and the mechanical and tribological properties. The specific surface area of BG-grade C is significantly increased compared to the other benchmark materials, and a significantly improved tribological behavior can be observed. A high specific surface area of the graphene correlates with good mechanical and tribological properties, as they are distributed homogeneously in the SiC matrix, resulting in a defect-free microstructure. For normally sintered SiC ceramics containing 2% TRGO, however, no influence of the specific surface on the tribological behavior can be observed. It is assumed that here the difference in the specific surface is not large enough to significantly affect friction and wear.In addition, the positive influence of SPS sintering leads to improved microstructural properties, which have a positive effect on mechanical and tribological performance. A necessary condition for this sintering process is the sufficiently high electrical conductivity of the ceramic green body. This can be improved by increasing the filler content and by a homogeneous distribution of the graphene in the SiC matrix.In this respect, ceramics with already good tribological properties such as 4% GSiC-containing SiC nanocomposites provided evidence that they are predestined for this process.2O to form strongly hydrated silica layers on the sliding surfaces [Tribochemical reactions: It is well-known that, under water lubrication, SiC reacts chemically with Hsurfaces ,29. ThesSurface passivation by graphenization: There is a strongly growing interest in liquid superlubricity, which means lubricated frictional contacts with extremely low friction coefficients (lower than 0.01) ,31,32. AIn general, the results of the rotating pin on disc tribotests in water show that tribological improvements, i.e., reduction of friction and lower wear rates, can be achieved with increasing the filler content. Furthermore, the tribological experiments show that a homogeneous distribution of small graphene particles in the SiC matrix is desirable in order to guarantee favorable friction and wear properties. On the one hand, the homogeneous distribution ensures that graphene is provided reliably and uniformly on the tribologically stressed surface, which is a fundamental prerequisite for the formation of a carbon-containing tribological film. This layer, in turn, has a friction-reducing effect, as it was verified in previous experimental works  and atomOur present results have shown that pure SiC ceramics actually may show low and stable friction under water lubrication. However, at high contact pressures, these low-friction conditions that completely depend on silica formation may become unstable . In contIn this paper, various SiC/graphene ceramic composites were examined to explore their potential as materials for face seals. Therefore, three groups of composites containing TRGO, GSiC and benchmark materials as carbon fillers were produced and tribologically tested under water-lubricated conditions. In addition to sufficiently good mechanical strength and fracture toughness, all composites—except graphite—show better friction and wear performances in an aqueous environment than the SSiC#137 reference material without graphene. Significant improvement (better than 20%) was observed for higher filled and SPS-treated samples such as all SiC + GSiC-F  materials, SiC + 4% GSiC-D , SiC + 3% TRGO-600, SiC + 4% TRGO-1000 (SPS) and SiC + 4% TRGO-600 (SPS). The results show that, besides the increase in the filler content, a homogeneous distribution of small graphene particles that are well-bonded to the ceramic matrix is necessary to achieve excellent results.With respect to previous and recent publications on wear mechanisms, we propose as a combined tribological mechanism: (1) The tribochemical formation of strongly hydrated silica acting as lubricious oxides, and (2) the release graphene during the wear process leading to partial surface graphenization and therefore chemical passivation.This material approach will therefore be very interesting in the future to develop tribological systems that may even enable stable liquid superlubricity, i.e., friction coefficients lower than 0.1.


The present paper analyses the properties of printed polylactic acid (PLA) samples with admixtures of graphene nanopowder (GNP) at wt. 1%, 2% and 4%. The pure polylactide and admixed polylactide printed samples were examined to determine their chemical-physical properties, stiffness, and strength parameters. The tests of tensile, dynamic mechanical analysis (DMA), difference thermogravimetric (TG), and differential scanning calorimetry (DSC) were executed before and after UV (ultraviolet) treatment. The first part of the paper shows the process of manufacturing granulates and filaments mixed with graphene. The second part of the paper concerns the results of the tests made on printed samples. The analysed samples were printed using a Prusa i3 MK3 printer. It transpired that the content of graphene at 1% improved the mechanical parameters of the printed composite by organising its structure. Increasing the amount of graphene caused the values of the measured parameters to drop. This research indicates how important it is to determine the optimal values of nanoadditives in biopolymers. The industry of manufacturing printed materials, commonly called 3D printing or additive manufacturing (AM), is being strongly developed in many branches. 3D printing technology, by reason of low costs and flexibility, can be applied in prototyping phases. The simplest materials taken into consideration are various polymers. The most-used method of 3D printing is fused deposition modelling (FDM), which relies upon forming a printed shape by using melted wire (filament) under certain physical conditions. Currently, PLA filament is often used in 3D printing because this material is characterised not only by good thermo-plasticity and moderately high mechanical properties, but also by good biodegradability and compatibility. PLA, regarded as biodegradable biopolymers, can be produced from plants, bacteria, mushrooms, or crustacean shells. To enhance the general strength and stiffness of polymers, some reinforcements are applied and added into the structure of polymers. These reinforcements are mostly additives such as glass, graphite, carbon, or organic fibres. Therefore, many recent works have explored the influence of different reinforcements in polymers, especially on their mechanical properties. Sanes et al. , analyseBased on the above-mentioned literature, there is a lot of research on graphene-modified polymers, but there are few analyses that concern the influence of the addition of significant amounts of graphene used in PLA samples, especially those printed from own prepared filament; therefore, this work provides a new look at these and their results. Previously, we performed similar research for samples of small additives of graphene , in whicThe first step of preparation of the samples was based on manufacturing the filament from PLA pellets  and graphene nanoplatelets . The melting temperature in the case of pure PLA and PLA admixed with graphene nanopowder (GNP) was set in the range of 180–185 °C and 150–170 °C, respectively. Setting the parameters of manufacturing pure PLA filament allowed us to achieve PLA wire with the correct diameter of 1.7–1.8 mm. Achieving the correct diameter was essential to create adequate samples during printing. An effective technique for manufacturing the PLA filament was associated with a cooling system which enabled a very fast decrease in the temperature of the hot PLA wire coming from the extruder nozzle. In the case of PLA filament with additives of GNP, the batch to extruder was adequately prepared. The schematic illustration of admixing the batch composed of PLA and graphene pellets is displayed in The addition of graphene decreased (slightly but noticeably) the flow of the mixture due to the increase in compounding density (PLA filament/graphene), which resulted in an uneven outflow of polymer from the printing nozzle. By increasing the temperature in composite PLA/graphene, the blends decreased in viscosity. In this case, the printing temperature was also set as low as possible to improve and even the outflow of the composite from the nozzle and avoid excessive degradation. Every sample was printed out using the Prusa i3 MK3 printer with a parameter setting of 100% infill. The printing trajectory was set to be 0–90° along the longitudinal axis of samples. The main printing parameters were assumed: velocity 10–70 mm/s and a single printing layer of 0.05 mm. To investigate the structure of samples, microscopic examinations were performed by employing a Leica s9i microscope with a maximum magnification of 16×. The tensile tests on samples were performed using a Shimadzu AS-X testing machine based on standard UNE EN ISO 527-1:2020-01. These tests were carried out with a constant velocity of moveable traverse of 2 mm/min. As a result of stretching the samples, the plots of force vs elongation were obtained. The dimensions of the samples were based on a standard: L = 80 mm, a1 = 15 mm, w1 = 5 mm, w = 10 mm, and mean thickness t = 4 mm . Mean we2. It is worth mentioning that the average power of UV radiation obtained on the earth coming from the sun is 62 W/m2. This means that one hour of material ageing in an applied container corresponds to about 5645 h of an exposure to a solar radiation. The prepared container was connected to a vacuum pump, forcing airflow. As a result, the ozone formed in the chamber was pumped out. The method was based on loose arrangements of samples on special bases. The entire irradiation process lasted 4 h. A four-hour exposure is equivalent to approximately one year of exposure to solar radiation [One method of determining a material’s life is treating the sample with UV radiation, determining the material’s ageing. The tested samples were placed on an appropriate stand in a glass specially lined with reflective foil. The closed container with the investigated samples was subjected to ultraviolet lamp action with a power of 35 W/cmadiation .With the aim of thermal stability determination, thermogravimetric analysis (TGA) and DTG analyses were used. Thermogravimetric analyser-TGA 550 Discovery of TA Instruments were applied for measures. The tests were conducted in an atmosphere of nitrogen in the scope of temperature from 40 °C to 600 °C with a heating velocity of 10 °C/min.DMA (DMA 850 Discovery of TA Instruments) was used by mounting the sample on the device, but the middle part of the sample was subjected to oscillating motion with a frequency of 10 Hz and amplitude of 10 µm. Firstly, the sample was cooled down to −60 °C and subsequently was heated up with a velocity of 5 °C/min to a temperature of 80 °C.DSC tests were performed by means of scanning the differential calorimeter from the Mettler Toledo company. For controlling and data elaborations, STARe Thermal software was applied. The tests were executed in the nitrogen atmosphere at a flow of 30 mL/min.This subsection presents the results of the tension of considered samples before and after UV treatment. The application of UV rays caused the supply of high-energy radiation to the PLA crystal lattice, which resulted in the shortening of the main PLA polymer lattice (degradation by electromagnetic radiation). Shorter chains are easier to change position in relation to other chains that build the polymer structure (lower coefficient of viscous friction). Shorter chains and the current energy available in the system (from UV radiation) caused the possibility of PLA crystallization. This situation meant that after UV, an increase in PLA strength was noted; however, this is a negative situation in the long term, as DMA tests proved that the storage module for non-aged samples was higher in the entire range of temperature. Static tests showed only the resistance of the crystal lattice at one temperature (room temperature), with the possibility of easy lattice relaxation (low test speed). There were no chain movements, and the main factor determining high strength was the quality and quantity of the crystal phase in the 3D print. The changes in the network were also indicated by a large dispersion in the static test of prints after ageing.Based on the data obtained from mechanical tests, it can be noticed that the statistical dispersion of the obtained results increases with the amount of graphene in PLA. This may indicate that the dispersion of the nanoclave in the PLA matrix deteriorated despite the use of solvent dispersion in DCM prior to granulation.This subsection presents the results of TGA. Taking into account that the greatest differences in the rate of weight loss were recorded in pure PLA samples compared to pure PLA after UV radiation. The reason for this is primarily the translucency of the PLA transparent radiation and the penetration of high-energy UV radiation of the PLA chains’ presence in the depths of the sample. The degradation and shortening of the polymer chains are the fastest in this case, because degradation takes place throughout the volume of PLA. Graphene retains and disperses high energy from radiation, and in addition blocks UV rays from penetrating into the PLA/graphene biocomposite. With the increase in graphene content, the thermal stability slightly increases .Based on the results of DMA, graphene applied in printed samples decreases the value of behaviour modulus a,b. ThisThe samples containing 4% graphene lost the value of a loss modulus after the ageing process. This can be explained by the fact that if the content of graphene in the PLA sample is too great, and then the graphene might have become a simple insertion. The loss moduli were also subjected to change under the influence of graphene presence and the ageing process. The single graphene decreased a loss modulus, meaning that in composite, more crystal phase exists than in the structure of a pure PLA sample. The UV process hydrolysed the PLA chains; therefore, the loss modulus was lower after the ageing process. In the case of modulus loss, composites with 1% and 2% graphene were characterised slightly by greater values of loss moduli after the UV process. It transpired that shorter chains in the presence of 1% or 2% graphene could easily move to each other at small distances. The characteristic values of DMA are shown in DMA studies on modified (plasticized) PLA are known in the literature ,28. In tThe DSC study of the produced composites allowed us to determine the changes in the structure of the PLA polymer under the influence of UV radiation, under the influence of the addition of graphene and its amount in PLA (ii), under the influence of graphene content on changes in the structure of the PLA/graphene composite, and the influence of UV radiation (iii). Graphene has a significant influence on the structure in which PLA crystallises. The research shows that the best amount of graphene tested in PLA is 1%. This significantly increased the energy of cold crystallisation (10% ↑). This means that graphene acts as a nucleation centre to accelerate PLA to form a crystalline phase. With the increase in the amount of graphene in PLA, the value of cold crystallisation energy decreased, which proves that above 1% graphene, the nanoadditive forms aggregate or there is too much of it between PLA chains, making it difficult to crystallise the polymer chains . The presence of graphene in the PLA matrix delayed the effects of degradation under the influence of UV light. Exposing pure PLA to UV action caused a slight decrease in the energy of cold crystallisation and a slight increase at the beginning of cold crystallisation. Adding 1% graphene to PLA increased the energy of cold crystallisation by 10%. This amount of additive made the ability to form PLA crystals under the influence of graphene the most effective even after degradation. The addition of 4% graphene in PLA is characterised by similar values of cold crystallisation energy to the raw PLA samples not subjected to UV treatment. With the increase in graphene content, the glass transition temperature and the energy of this transformation of the tested printed PLA polymer decreased. With 1% graphene, the decrease in the energy and temperature of this transformation was the most noticeable—by as much as 4 °C in the case of temperature and the decrease in energy value by as much as 0.1 J/gK (decrease of 20%). The glass transition temperature drop for PLA samples with 2% and 4% graphene was at the level of 5 °C and 6 °C, compared to the glass transition temperature of pure PLA. The energy value of this transformation was maintained at the level of the energy value of the composite containing 1% graphene; interestingly, the decrease in the phase transition energy of the glass transition was at the level of composites containing 1% PLA. The decrease in temperature (and thus the reduced amount of energy) of the glass transition, as well as the value of the energy of this phase transition, was caused by the increase in the distance between PLA chains due to the presence of 2D graphene. Graphene allows the polymer chains to slide between each other because it allows the chains to slide on their surface, and the increase in the interchain distance meant that the phase changes associated with the glass transition required lower energy values. Exposing pure PLA to UV action caused a decrease in the glass transition start temperature. The data obtained from the DSC test are summarized in The addition of graphene stopped this temperature drop; the strongest effect was in the case of 1% graphene in the PLA matrix, and the sample containing 4% graphene had almost identical glass transition parameters to the pure PLA sample after UV treatment. In the case of the scattering of UV radiation on the carbon nanoadditive, one would obtain an increase in UV resistance along with an increase in the amount of graphene in the composite with an increase in its amount. There was a decrease in parameters , which means that the enhancement of the UV resistance by graphene is on a structural basis, and its too-high presence in the PLA matrix may lead to a decrease in this resistance compared to pure PLA. The phase transition energy, which is melting from the solid phase to the liquid phase of PLA, was at a similar level for PLA, PLA 2% and PLA 4% graphene. The melting energy for the PLA 1% composite was 20% higher, which proves that in these samples, graphene acted as a nucleation centre, facilitating the formation of PLA crystal structures. The temperature of the beginning of the PLA melting transformation was similar for all samples. The addition of graphene in the PLA matrix did not change the nature of the PLA melting transformation in the composite. The fusion energy values and the temperature range over which this transformation occurred were similar. This means that the degree of degradation of PLA and the hydrolysis of the biopolymer chains under the influence of light was not great because graphene causes the non-transparency of the PLA/graphene composite, and thus the degradation progress is lower, as it takes place only on the surface and propagates deep into composite much slower than in the case of raw light-transparent PLA samples).The presence of GNP in PLA samples caused a slight decrease in Young’s moduli before UV radiation. However, after UV ageing, this parameter was greater compared to pure PLA (before radiation). Of course, after UV treatment, pure PLA was characterised by a weaker Young’s modulus and maximum stress. The content of GNP 1%, 2%, and 4% in samples indicated comparable strength;DMA results on GNP samples showed a decrease in storage modulus. The lowest drop of storage modulus was observed for 4% GNP samples. The greatest decrease in storage modulus was noticed for the sample with 2% graphene. It is seen that the loss modulus of aged samples containing 4% GNP decreased;TG results proved that the presence of GNP in samples enhanced thermal stability. The content of graphene of at least 1% positively affects the growth of weight loss.Graphene has a significant influence on the structure in which PLA crystallises. This is due to its direct influence on the formed crystal structure of the polymer. With the increase in the amount of graphene in PLA, the value of the cold crystallisation energy decreases, which proves that graphene can form aggregates;With the increase in the content of graphene, the glass transition temperature and the energy of this transformation of the tested printed PLA polymer decreases, and the exposure of pure PLA to UV action causes a decrease the temperature of the glass transition at the beginning;The presence of graphene in the PLA matrix delays the effects of degradation under the influence of UV light. The addition of graphene does not change the nature of the PLA melting transformation in the composite. This means that the degree of PLA degradation and the hydrolysis of the biopolymer chains under the influence of light is not great and is related to the transparency of the printed composite;Graphene changes the rheology of the bioplastic filament and requires a higher pre-production temperature. It also dissipates UV energy in the composite and protects PLA chains against radiation penetration into the composite.This paper presents the results of mechanical and physical-chemical parameters of printed pure PLA and PLA admixed with GNP. We determined the influence of graphene on the mechanical properties and the modulus of elasticity. In our research, we investigated the loss or improvement of the properties of biocomposites as a function of temperature and time after exposure to UV radiation in the ageing chamber. Based on the DSC and TG studies, the changes taking place in the structure of the biopolymer were determined. This allowed us to determine the real impact of graphene on the PLA matrix, which we have looked at comprehensively: graphene does not have significant influence on mechanical properties; therefore, graphene should not be added as modificator. We also described the degradation process of PLA in the presence of graphene. The essential aspects of graphene addition can be stated as:


An elicited imitation task was administered to L2 learners at beginner, intermediate and advanced Chinese proficiency levels. L1 influence is not observed at beginner levels, but it appears at intermediate and advanced levels, L1 influence disappears at different time in English and Korean learners’ oral production of verb-ellipsis and ΣP-ellipsis. It is proposed that the absence of L1 influence at beginner levels is due to a breakdown of syntax-stylistics interface and beginners’ difficulty in implementing checking and deleting operations in their L2 oral production. The different timings of the disappearance of L1 influence in the two language groups at advanced levels is attributed to interactions between the persistence of L1 influence and the computational complexity involved in the target elliptical structures.The article reports on an empirical study investigating the role of L1 at the initial and developmental stages of L2 speech production. It examines two types of Chinese verb- phrase-ellipsis, ΣP-ellipsis licensed by the auxiliary  Specifically, unlike English wh-questions, where a wh-word is required to be raised from its base-generated position to the initial position of a sentence, a wh-word in Chinese wh-questions remains in situ. However, his study finds no evidence in the results that wh-movement in English is transferred into L1 English learners’ L2 Chinese wh-questions and causes problem in this aspect of their L2 Chinese grammars. Also, Chinese and English share the same restriction on attitude-bearing wh-questions, which regulates that a question cannot have more than one attitude. Yuan’s study shows that English speakers are unable to rule out ungrammatical Chinese wh-questions with two attitude features embedded in them, indicating that the similarities between English and Chinese in attitude-bearing wh-questions have very limited facilitation to L1 English learners’ handling of L2 Chinese wh-questions with more than one attitude feature. On the basis of It is widely observed that in contrast to the uniform success of children acquiring their first language (L1), few adult learners can achieve native-like competence in their acquisition of a second language (L2). Obviously, L2 learners already have a language, i.e., their L1, in their mind, which can exert influence on their L2 acquisition. FTFA, , 1996 prThe present study is an attempt to track the role of L1 in L2 speech production at different stages of L2 development. It aims to examine whether L1 grammar is transferred to L2 oral production at initial stages of L2 development, as predicted by the FT Hypothesis FTFA, , 1996, hThe article is structured as follows. Section “Cross-linguistic differences of verb-phrase ellipsis in Chinese, Korean and English” discusses syntactic analyses of verb-phrase ellipsis in Chinese, English and Korean, and Section “Prior studies of L1 influence on L2 oral production” briefly reviews prior studies on the L2 production of Chinese elliptical structures and outlines the research questions. Section “Present study” introduces the methodology of the present study, and Section “Results” reports the scoring methods and results. The results are discussed in Sections “Discussion” and “Conclusion” contains our conclusions.shi是 “BE”, as exemplified in (1), and a verb-phrase ellipsis licensed by auxiliaries other than shi “BE”, as illustrated in (2). As noted in shi ‘BE’ is larger than that licensed by the other auxiliaries like hui 会 ‘will’. As shown in the contrast between (1) and (2), the elided constituent in the latter includes the verb phrase likai yingguo “leave the UK”, whereas that in the former includes the auxiliary hui ‘will’ as well as the verb phrase likai yingguo ‘leave the UK’. Also, as can be seen in the contrast between (3) and (4), when containing the negator bu 不 ‘not’ in the antecedent clause, the scope of ellipsis licensed by shi ‘BE’, as shown in (3), includes the negator bu ‘not’, but that licensed by the auxiliary hui ‘will’ does not, as shown in (4).Chinese allows two types of verb-phrase ellipsis: a verb-phrase ellipsis licensed by the auxiliary 会 离开 英国。1. 张三 会 离开 英国， 李四 也 是 hui likai yingguo.Zhangsan hui likai yingguo, Lisi ye shi Zhangsan will leave the UK Lisi also BE will leave the UK.‘Zhangsan will leave the UK, and Lisi will (leave the UK) too.’离开 英国。2. 张三 会 离开 英国， 李四 也 会 likai yingguo.Zhangsan hui likai yingguo, Lisi ye hui Zhangsan will leave the UK Lisi also will leave the UK.‘Zhangsan will leave the UK, and Lisi will (leave the UK) too.’不 会 离开 英国。3. 张三 不 会 离开 英国， 李四 也 是 bu hui likai yingguo.Zhangsan bu. hui likai yingguo, Lisi ye shi Zhangsan not will leave the UK Lisi also BE not will leave the UK.‘Zhangsan will leave the UK, and Lisi will (leave the UK) too.’离开 英国。4. 张三 不 会 离开 英国， 李四 也 不 会 likai yingguo.Zhangsan bu. hui likai yingguo, Lisi ye bu hui Zhangsan not will leave the UK Lisi also not will leave the UK.‘Zhangsan will not leave the UK, and Lisi will not (leave the UK) either.’shi ‘BE’, a dummy auxiliary in Chinese, occupies the head of TP, a position higher than the other auxiliaries such as hui ‘will’ in the hierarchy. Following hui ‘will’ are generated under a Mod node, which is lower than T, where shi ‘BE’ is located. The positions of the auxiliary shi ‘BE’ and the other auxiliaries in the hierarchy in hui ‘will’ occupy the head of ModP, lower than the category Σ, which can be realized by the negator bu ‘not’ to express negative meaning; in contrast, shi ‘BE’ occupies the head of TP, which is higher than ΣP.Based on the above observations, the present study follows shi ‘BE’ and the other auxiliaries occupy different structural positions implies that they also differ in terms of the constituent they license. Thus, in line with shi ‘BE’ is a ΣP, whilst that licensed by the other auxiliaries like hui ‘will’ is a vP.The fact that cf.According to It should be noted that complete sentences without verb-phrase ellipsis, as shown in (5), are perfectly grammatical in Chinese. However, they are stylistically heavy and unconcise, and thus are less preferred than the elliptical counterparts. Then, combining the above facts, we assume that in the derivation of a sentence with verb-phrase ellipsis, the deletion of the vP or ΣP is triggered at the syntax-stylistics interface, on the premise that the verbal identity condition is met.5. 张三 会 离开 英国， 李四 也 会 离开 英国。Zhangsan hui likai yingguo, Lisi ye hui likai yingguo.Zhangsan will leave the UK Lisi also will leave the UK.‘Zhangsan will leave the UK, and Lisi will leave the UK too.’will and can  and (4) respectively. Here we adopt will in (6), is also a vP.It is widely observed that English allows its verb-phrase ellipsis to be licensed by auxiliaries like  can cf., 2004. Aleave the UK too.6. a. John will leave the UK and Bill will leave the UK either.b. John will not leave the UK, and Bill will not do, which is believed to behave similarly to the Chinese shi ‘BE’ in licensing some ΣP-ellipsis in English . According to do is positioned at the head of ModP, which is the same as the other auxiliaries in English but different from shi ‘BE’ in Chinese, which is at the head of TP. Consequently, what is elided after the dummy do is a vP rather than a ΣP, leading to the fact that English allows vP-ellipsis but not ΣP-ellipsis.It is worth mentioning that a verb-phrase ellipsis in English can also be licensed by the dummy  English . As can 喜欢 小红7. 张三 喜欢 小红， 李四 也 是 xihuan Xiaohong.Zhangsan xihuan Xiaohong, Lisi ye shi Zhangsan like Xiaohong Lisi also BE like Xiaohong.‘Zhangsan likes Xiaohong, and Lisi does (like Xiaohong) too.’will leave the UK too.8. a. *Zhangsan will leave the UK, and Lisi does will not leave the UK either.b. *Zhangsan will not leave the UK, and Lisi does -eul ‘will’ in the Korean sentence in (9), are verbal suffixes, and thus deleting a verb phrase in a sentence and leaving the auxiliary alone would produce a ‘stray affix’It has been observed in the literature that languages like Japanese and Korean do not allow auxiliaries to license a verb-phrase ellipsis. This is because auxiliaries in these languages, like 9. 존이 영국을 떠날 거야. 빌도 영국을 떠날 거야.Jon-i yeonggug-eul tteona-l geoya. Bil-do yeonggug-eul tteona-l geoya.John-NOM England-ACC leave will Bill-too England-ACC leave will.‘John will leave the UK, and Bill will (leave the UK) too.’ya야 ‘BE’ya ‘BE’ in Korean can include an auxiliary ) and a negator ). According to ya is inserted to the head of TP after a focus-movement process and the deletion of a ModP. Based on the derivation analysis and the examples above, it can be summarised that the lexical item ya occupies the head of TP, a position higher than auxiliaries in Korean. On the basis of this analysis, we can assume that in Korean, the scope of the ellipsis licensed by ya is a ΣP, which can include an auxiliary and a negator, and that Korean allows ΣP-ellipsis, but not vP-ellipsis.However, it is found that a verb-phrase ellipsis in Korean can be licensed by a lexical item 영국을 떠날 거야.10. a. 존이 영국을 떠날 거야. 빌도 yeonggug-eul tteona-l geoya.10. a. Jon-i yeonggug-eul tteona-l geoya. Bil-do John-NOM England-ACC leave-will Bill-too England-ACC leave-will.‘John will leave the UK, and Bill will (leave the UK) too.’영국을.b. 존이 영국을 떠나지 않을 거야. 빌도 yeonggug-eul.Jon-i yeonggug-eul tteona-ji an-heul geoya. Bil-do John-NOM England-ACC leave not will Bill-too England-ACC.떠나지 않을 거야.tteona-ji an-heul geoya.leave not will.‘John will not leave the UK, and Bill will not (leave the UK) either.’Cross-linguistic differences with regard to the availability of vP-ellipsis and ΣP-ellipsis are summarised in Much evidence of L1 influence on adult L2 speech production has been reported in the literature, and many features in L2 oral production find their origin in the.L1  there is no decrease in the suppliance of /is/ or /s/ when there is a complex subject; (iii) suppliance of /s/ with a complex subject is disrupted when there is an intervening prepositional phrase (PP); however, suppliance of the copula /is/ is only disrupted where the PP contains a plural N, not when both Ns are singular. The similar behaviours of the two groups in two groups. Results of an oral completion task show that both groups perform strikingly similarly; (i) the copula While evidence for the absence of L1 influence in L2 speech production is emerging, it is still not as robust as evidence for such influence. In addition, the variety of language phenomena tested for the former is still rather limited. More importantly, answers are yet to be found as to why there is absence of L1 influence on some L2 structures given that L1 transfer is a rather pervasive phenomenon in L2 speech production.There has been considerable linguistic research on the syntactic mechanism underlying ellipsis e.g., , as wellOn the basis of the cross-linguistic differences with regard to the (un)availability of vP-ellipsis and ΣP-ellipsis in English, Korean as well as Chinese, the following research questions are asked in this study.Research Question 1. Is English- and Korean-speaking L2 Chinese beginners’ oral production of vP- and ΣP-ellipses influenced by their L1s?Predictions: On the basis of the Full Transfer (FT) Hypothesis  were selected. Payments were given to every participant as a token of thanks for their participation in the study.Participants’ working memory capacity is also controlled. The task chosen in the current study to test participants’ working memory capacity is the backward digit span task, which is one of the subtests of Wechsler Adult Intelligence Scale–Fourth UK Edition , and hasF = 465.763, p < 0.001). Post hoc Scheffé tests indicate that all learner groups are significantly different from the NS group. The results also show that there is no significant difference between any of the two corresponding language groups in their scores in the cloze test; that is, no significant difference is found between the EB Group and the KB Group (p > 0.05), between the EI Group and the KI Group (p > 0.05), or between the EA Group and the KA Group (p > 0.05). These indicate that all of the English groups are compatible with their corresponding Korean groups with regard to their Chinese language proficiency.The remaining participants are divided into seven groups based on their native languages and their performance in a cloze test. The cloze test is adopted from Participants are required to complete a language background questionnaire and the working memory test prior to the main experiment, which includes an elicited imitation taskqing huida ‘please answer’. Participants are then required to make a decision about whether the sentence they have just heard matches the contextual information on the screen, by selecting an option of “Match,” “Mismatch” or “I do not know” on an answer sheet provided. This serves as a comprehension task to draw participants’ attention to the meaning rather than the form of the eliciting utterance. This also provides a way to measure participants’ comprehension of the utterance. Obviously, without correct comprehension, it would be difficult for the participant to recall the utterance. These procedures are also to ensure that there will be a time interval of at least 3 s between the presentation of the eliciting utterance and the start of the recalling. All this helps to make sure that the utterance produced by the participant is reconstructive, “requiring participants to process, rather than repeat verbatim, language stimuli”  and (12)), with each condition having six test sentences. Each test sentence consists of three clauses, and each sentence contains 22 or 23 Chinese characters. The pictures and contextual information for (11) and (12) are provided in 11. Example of the vP-ellipsis condition:hui, tamen hui yiqi qu.Mingtian Xiaoming hui qu Beijing, Xiaoli ye Tomorrow Xiaoming will go Beijing Xiaoli also will they will together go.kan Tian’an Men.see Tian’an Men.‘Xiaoming will go to Beijing tomorrow, and Xiaoli will too. They will go to see Tian’an Men together.’12. Example of the ΣP-ellipsis condition:Mingtian Xiaoming hui qu Lundun, Xiaoli ye shi. Tamen dou shi diyi-ci.tomorrow Xiaoming will go London Xiaoli also BE they both be first-CL.chuguo lvxing.go abroad travel.‘Xiaoming will go to London tomorrow, and Xiaoli will too. This is their first time to travel abroad.’Xiao Wei instead of Xiao Li) and replacement of verbs or nouns with synonyms, were not treated as incorrect responses, as this kind of mistake does not affect the use of ellipsis. We categorized the responses into four categories, as described in (13).Participants’ responses in the elicited imitation task were recorded, transcribed and analysed. In the data trimming process, unclear responses, responses not immediately produced, and responses where the second clause is not produced or largely incomplete were removed and treated as missing values. Note that the choice of incorrect names  were considered to have attended to meanings of the eliciting sentences. The results show that all groups’ accuracy rates are higher than 93%, indicating that they have good comprehensions of the eliciting sentences in the task.As can be seen in As shown in In the ΣP-ellipsis condition, the two beginner groups again behave similarly; they rarely produce target responses with ΣP-ellipsis (the EB Group: 0% and the KB Group: 1%) even though ΣP-ellipsis is allowed in Korean. In contrast, they produce responses with overt ΣP at very high rates (the EB Group: 90% and the KB Group: 96%), in spite of that fact that the eliciting utterances contain ΣP-ellipsis. Again, absence of L1 transfer is observed in beginners’ oral production of ΣP-ellipsis. With the increase of their Chinese proficiency at intermediate and advanced levels, L1 Korean groups produce an increasingly higher proportions of target responses with ΣP-ellipsis  than L1 English groups .The number of L2 learners’ target responses were submitted to a linear mixed-effect models under the lme4 package in R version 4.1.0 . The fixed predictors include Proficiency , L1  and Condition , and the interactions of Proficiency * L1, Proficiency * Condition, Condition * L1, and Condition * L1 * Proficiency. Participant and test items were entered as random factors for intercepts and slopes. A maximal model was first established, based on which the optimal model was found by backword elimination procedure. The formula of the optimal model is Score ~ Condition x L1 x Proficiency + (1 + L1 + Condition | Participant) + (1 + Proficiency + L1 | Item).p = 0.149). Similarly, p = 0.444). In contrast, p< 0.001). Consequently, there is no overall effect of either L1 or condition, but there is a crossover interaction. From p< 0.001). This indicates that the number of target responses varied across different proficiency groups. p = 0.279).The model output is presented in post hoc comparisons were conducted through the emmeans package . This suggests that L1 English beginners do not produce more vP-ellipsis sentences in their L2 Chinese speech production than L1 Korean beginners, and L1 Korean beginners do not produce more ΣP-ellipsis sentences in their L2 Chinese speech production than L1 English beginners.In order to explore difference between target responses of proficiency-matched L1 English and L1 Korean groups, thereby answering the questions about the occurrence and disappearance of L1 influence at different L2 stages, Turkey  package  in a simβ^ = 0.2692, SE = 0.0779, t = 3.458, p < 0.05; ΣP-ellipsis condition, EI vs. KI: β^ = −0.3421, SE = 0.0779, t = −4.394, p < 0.01), indicating that L1 influence is absent at the beginner levels, but occurs at the intermediate level. At the advanced level, L1 English and L1 Korean groups’ frequencies of target responses in the ΣP-ellipsis condition differ significantly from each other , indicating the persistence of L1 influence in the two advanced groups’ L2 Chinese oral production of ΣP-ellipsis. In contrast, the advanced groups’ frequencies of target responses in the vP-ellipsis condition are not significantly different , suggesting disappearance of L1 influence in the two advanced groups’ L2 Chinese oral production of vP-ellipsis.To explore the answer to the second research question about the role of L1 in L2 developmental stages, intermediate and advanced learner groups’ results were examined. In contrast, L1 difference is found to be a significant factor in L1 English and L1 Korean intermediate learners’ L2 Chinese production of vP- and ΣP-ellipsis  Hypothesis FTFA, , 1996, wRecall that in comparison with utterances with vP- or ΣP-ellipsis, “complete” sentences with no ellipsis are grammatical but stylistically heavy and unconcise in Chinese. It seems likely that no syntax-stylistics interface is established in beginner learners’ L2 Chinese, leading to a breakdown at a syntax-stylistics interface in their handling of sentences with vP- or ΣP-ellipsis. As beginner learners have limited L2 knowledge and unsophisticated coordination between information from different cognitive domains, such as syntax and stylistics, the mechanisms for their L2 oral production tend to be geared for syntactic “completeness” and are unlikely to be susceptible to any stylistic requirement, even though the syntax-stylistics interface is available in their L1s. As a result, this insensitivity to stylistic requirements at L2 initial stages leads to the absence of vP- and ΣP-ellipsis observed in L1 English and L1 Korean beginners’ L2 Chinese oral production. That is, L2 learners’ production at the beginner level is governed exclusively by basic essential syntactic computations and it is immune to stylistic requirements, which overrides L1 transfer of the syntax-stylistics interface from their L1s to their L2 speech production, leading to the absence of the influence of their L1 vP- or ΣP-ellipsis on their L2 Chinese oral production of utterances with vP- and ΣP-ellipsis in the current study.If the analysis above is on the right track, it is reasonable to assume that, with improved L2 Chinese language proficiency and their increased automaticity in L2 Chinese oral production, and with more exposure to vP- and ΣP-ellipsis in their L2 Chinese input, they are more likely to produce utterances with vP- and ΣP-ellipsis, and this tendency is indeed observed in our intermediate and advanced learners’ data. At the same time, L1 influences are detected at intermediate and advanced levels as well, where English speakers are found to produce more utterances with vP-ellipsis in their L2 Chinese oral production than Korean speakers, and in contrast, Korean speakers produce more utterances with ΣP-ellipsis than English speakers. This finding is on a par with what is reported in The absence of L1 influence at beginner levels found in the present study is also in conformity with the finding concerning beginner learners’ L2 Chinese oral production of utterances with object-ellipsis in It should be acknowledged that with the data from and the design of our experiment, we are not in a position to pinpoint whether and to what extent the breakdown at the syntax-stylistics interface or the operations of checking and deleting is the main reason behind the absences of L1 transfer in beginner learners’ L2 Chinese oral production of utterances with vP- and ΣP-ellipsis. It is likely to be a joint effect of the two. We have to leave this issue for future research.+ β”  in “Cross-linguistic differences of verb-phrase ellipsis in Chinese, Korean and English”. We believe that what is elided can be measured on the basis of computational complexity involved, which, in turn, can affect early or late disappearance of L1 influence. The asymmetry in the disappearance of L1 influence in speech production of vP- and ΣP-ellipsis at advanced levels can be accounted for with the help of the measurement of computation complexity in feature checking, as in + β” , p.8. WeAccording to this metric, the more items a verbal identity checking operation involves, the more computational complexity the operation has. L2 structures with less computational complexity are expected to be acquired more easily than those with more computational complexity. In the current case, the operations on the vP-ellipsis are computationally less complex than the ΣP-ellipsis, because the former involves identity checking and deleting of only a vP and an NP object, but the latter requires identity checking and deleting of not only a vP and an NP object, but also a model and a negator. Although Korean does not have the vP-ellipsis, L1 Korean learners are able to overcome the disadvantage of not having vP-ellipsis in their L1 and acquire the less complex vP-ellipsis construction at a relatively early stage in their L2 Chinese acquisition. In contrast, L1 English learners do not allow the ΣP-ellipsis in their L1. In addition, the ΣP-ellipsis in the target language Chinese is computationally more complex than the vP-ellipsis, requiring identity checking and deleting of more items than vP-ellipsis, and as a result, their L1 English grammar is relied upon more when Chinese sentences with ΣP-ellipsis is dealt with, delaying the disappearance of L1 influence in their L2 Chinese oral production of utterances with ΣP-ellipsis. This explains why L1 influence is shorter-lived in L2 Chinese oral production of vP-ellipsis than ΣP-ellipsis.The current study tracks the role of L1 in L2 speech production of Chinese verb phrase-ellipsis structures at different stages of L2 development. One finding of the study is the absence of L1 influence on L2 Chinese speech production until intermediate and advanced levels. Both L1 English and L1 Korean learners of L2 Chinese at beginner levels tend to produce complete responses with no ellipsis, in spite of the fact that vP-ellipsis is allowed in English and that ΣP-ellipsis in Korean. This finding provides us with evidence against the FT Hypothesis proposed by FTFA, , 1996, wThe original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.LZ did the data collection and statistical analyses. BY made substantial contributions to the theoretical framework for the findings of the study. LZ and BY made equal contributions to the design of the experiment, data interpretation, and the writing of the manuscript. Both authors contributed to the article and approved the submitted version.The work was supported by Shanghai Planning Office of Philosophy and Social Science (Grant No. 2022EYY009).The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Motor imagery (MI) has emerged as an individual factor that may modulate the effects of attentional focus on motor skill performance. In this study, we investigated whether global MI, as well as its components  moderate the effect of attentional focus on performance in a group of ninety-two young adult novice air-pistol shooters . After completing the movement imagery questionnaire-3 (MIQ-3), participants were asked to complete a pistol shooting experiment in three different attentional focus conditions: (1) No focus instruction condition  (2) an internal focus instruction condition, and (3) an external focus condition. Shot accuracy, performance time, and aiming trace speed  were measured as the performance variables. Results revealed that shot accuracy was significantly poorer during internal relative to control focus condition. In addition, performance time was significantly higher during external relative to both control and internal condition. However, neither global MI, nor its subscales, moderated the effects of attentional focus on performance. This study supports the importance of attentional focus for perceptual and motor performance, yet global MI and its modalities/perspectives did not moderate pistol shooting performance. This study suggests that perception and action are cognitively controlled by attentional mechanisms, but not motor imagery. Future research with complementary assessment modalities is warranted to extend the present findings.The online version contains supplementary material available at 10.1186/s40359-023-01047-z. Individuals perform motor tasks with differing levels of attention. Traditional views considered attention as a passive spotlight or gatekeeper, acting prior to perceptual processing to merely filter out undesirable inputs in favor of others  –6. In co“representations … of sensory information without a direct external stimulus” [perceptual processing, in the absence of immediate sensory input from a relevant sense-modality [Aside from attentional focus, mental imagery is another cognitive mechanism that may affect individuals’ perceptual-motor performance. Given the mental imagery definition as timulus”  or percemodality , 25, sommodality . Studiesmodality . In othemodality , 27. Premodality . That ismodality  as both modality  and percmodality , 31 and modality , 33. Furmodality  and convmodality . Based omotor imagery  [perspectives  have potential unique contributions to outcomes. To the best of our knowledge, only one recent study in children distinguished between MI perspectives , showing that while high levels of kinesthetic MI deteriorated overhand ball throwing learning in children adopting an external focus, external visual MI dominance resulted in superior motor learning for children adopting an external focus [or attentional focus, and also given the existence of some inconsistencies regarding the role of kinesthetic MI on attentional focus effects, we employed additional tasks and outcome variables to complement traditional performance indicators related to end-point accuracy. To this end, we measured performance time, aiming point stability , and performance accuracy during shooting performance of a group of young novice 10-m air-pistol shooters.A number of previous works have attempted to provide evidence regarding the modulating roles of ecution)  on motorecution) , and MI ecution)  during decution) –41. Furtecution) , 42, 43.ecution) . In addiecution) , 42, 43 ecution) . TherefoNinety-two young adult university students  with normal or corrected to normal vision, and with no self-reported musculoskeletal or postural disorders voluntarily participated in the study. Of note, a few incomplete datasets were excluded from the final analyses due to general optical system failure.The MIQ-3 is a 12-item questionnaire  to measuThe participants were asked to shoot an air-pistol as accurately and as quickly as possible at an electronic target 10 m away in an indoor environment. The SCATT shooting system  was used to quantify pistol shooting performance, congruent with prior work . The SCAFollowing completion of the MIQ-3, participants began the shooting task. After a short familiarization period, participants were asked to shoot at the target in three different attentional focus conditions: (1) control condition, (2) IF, and (3) EF. Participants completed their shooting performance under control (no focus instruction) conditions first, then ordering of internal and EF conditions was counterbalanced between participants. Similar to previous attentional focus studies, we issued participants the control focus condition first, followed by the counterbalancing of attentional focus conditions, to ensure one condition could be used as a stable control that was not biased by previous attentional focus instruction  , 50. WhiFirst, repeated measure analyses of variance were performed to investigate if shot accuracy was different among the attentional focus conditions. Similar analyses were done for performance time and aiming trace speed between attentional focus conditions. An alpha level of p < .05 was set a priori, and post-hoc analyses were performed using Bonferroni adjustments as appropriate. In addition, we ran simple regression analyses to investigate potential associations between each MI measure and each air-pistol shooting performance measure in different attentional focus conditions . Also, the association between performance time and shot accuracy, and between aiming trace speed and shot accuracy during each attentional focus condition were examined to help interpret findings. Finally, using MEMORE process macro , we ran Descriptive statistics of participants’ internal visual MI, external visual MI, and kinesthetic MI scores are shown in Table F  = 4.45, p = .015, η = 0.046). Pairwise comparisons using Bonferroni adjustments revealed that while accuracy during external focus  was not significantly different than other attentional focus conditions, participants were more accurate during control  relative to internal focus  condition (p = .017). Performance time was different between conditions  = 21.47, p = .019, η = 0.21). Pairwise comparisons revealed that participants had higher performance time during external  relative to both control  and internal focus , and performance time during internal focus was also significantly higher than during the control focus condition (p = .03). Finally, the effect of attentional focus conditions on aiming trace speed was significant  = 3.38, p = .046, η = 0.041), although pairwise comparisons failed to identify the location of effect. Mean and standard error of shot accuracy, performance time, and aiming trace speed during different attentional focus conditions have been shown in Figs. Results indicated a significant difference in participants’ performance accuracy between attentional focus conditions . There were no associations between MI total score or its subscales with performance time during any focus conditions . There were no associations between MI total score or its MI subscales with aiming trace speed during any focus conditions .There were no associations between MI total score or its subscales with shot accuracy during any focus conditions  nor any of the three subscales  moderated differences in shot accuracy between attentional focus condition.Neither total MI score (p range = 0.33 − 0.91) nor any of the three subscales  moderated differences between foci of attention and performance time.Neither total MI score (p range = 0.69 − 0.70) nor any of the three subscales  moderated differences between foci of attention and aiming trace speed.Neither total MI score  during different attentional focus conditions. Based on several lines of research, we expected that individual differences in MI would play a crucial modulating role in cognitive control of both perceptual and motor performance. Our findings however failed to show any modulating role for MI. We nevertheless observed that attentional focus affected perceptual and motor outcomes measured in this study. More particularly, an internal focus resulted in less accurate shots than control focus. In addition, movement time was shorter during control relative to both internal and external focus, whereas an external focus resulted in longer movement times than other attentional foci.too difficult for our inexperienced individuals as they had to shoot towards a standard, yet relatively small bulls-eye (11.5 mm diameter) from a distance of 10 m. Prior literature proposed a hypothesis that suggests overly difficult tasks  do not allow for beneficial adoption of superior cognitive strategies such as an external attentional focus [Several attentional focus hypotheses, including the constrained-action hypothesis and self-invoking trigger hypothesis, have previously suggested that an internal focus hinders perceptual and motor functions due to controlled processing that interferes with automatic performance , 53, 54.al focus , possiblal focus . Althougal focus –60. Our Given an external focus did not facilitate our participants’ accuracy while increasing their performance time, alternative explanations are warranted given the extant literature on this topic . For instance, during control processes of goal-directed aiming tasks, successful visual processing is necessary to achieve desired movement accuracy . Future First, despite including a relatively large number of participants in the study, our participants were not particularly poor at motor imagery, as our participants had self-reported MI scores that were relatively higher than a score that can be deemed as poor imagery ability. In the MIQ-3, a score of 4 is neutral (neither easy nor hard), and individuals that score 3 or lower are those who report difficulty in MI ability. As our descriptive results show, our participants had mean MI scores  that are considered relatively high (range from 5.81 to 5.87). However, rather than considering this as a methodological limitation of the present work, we consider this a unique finding as individuals in our study had less difficulty imagining their action from different modalities and perspectives, compared with previous works reporting relatively high MI abilities [Second, although, like many previously published pistol-shooting-related work [Third, We should also note that our participants were novices, and therefore their little experience of physically executing the imagined action may have resulted in inefficient (unorganized) neurocognitive processing [Fourth, the MIQ-3 used in our current study does not measure some important aspects of mental imagery such as mental imagery vividness- a diagnosis tool for identifying individuals with extreme imagery conditions [Fifth, and finally, while MI may be action specific [Our study failed to provide support for the suggestion that perception is cognitively controlled by means of mental imagery . Therefobilities , 63–65. bilities  conductebilities  exhibit bilities  considerbilities . Therefoted work , 67, 68,ocessing , that asnditions –72 whichnditions –77. Furtspecific , the MIQOur study has some limitations that should be acknowledged. We used a laboratory-based task that may reduce the complexity of what occurs during real situations ; therefoIn conclusion, this study showed that participants’ self-reported baseline MI and its subscales do not moderate attentional focus effects on novices’ air-pistol shooting performance accuracy, performance time, and aiming trace speeds. These findings may suggest that individuals’ MI does not affect cognitive control of perceptual and motor functions. However, an internal focus may reduce shot accuracy relative to control focus. Importantly, an external focus may result in an increased performance time to ensure the task goal. The study highlights the importance of future studies to enhance our theoretical and practical knowledge regarding mental imagery, and attentional focus in sport science and rehabilitation.Additiona file 1.Supplementary materials. Secondary data analysis using motor imagery dominance.


The band structure of the monolayer and the armchair ribbons of different widths are discussed with illustrations. The time-dependent wavefunctions of the systems and the expectation values of interest are determined by solving the coupled equations of the band amplitudes “exactly” . First, simulations are made for the population excitation in the conduction band (CB) from the valence band (BV), the VB-CB interband correlation (or “coherence”), the intraband, the interband and the total currents in the monolayer graphene. The graphene currents are compared with the corresponding currents induced in an armchair ribbon . The change from the 2D monolayer to the 1D ribbon shows a remarkable transition of the dominance of the intraband current that leads to a near steady total current in the monolayer, to a dominance of the interband current in the ribbon that induces an oscillatory current in the ribbon beyond the pulse duration. The difference observed might be a combined effect of the “confinement” in one dimention and a finite band-gap minimum in the case of the ribbon. However, this transition should be further investigated for better clarity. A brief comparison of the radiation spectra emitted from the monolayer and from the ribbon is also made. They show a grossly similar structure and a relative insensitivity with respect to the detailed structure of the targets chosen. This might be due to the dominance of virtual continuum-continuum transitions, to and from the bands states, that lie behind the fundamental quantum process of high harmonic emissions. Lastly, the dependence of the charge currents, induced in a ribbon of unit width (N = 1), on the carrier-envelope-phase (CEP) of the incident laser pulse is investigated. It is seen that the shape of the main part of the current produced in the ribbon can be fully reversed by changing the CEP of the ultrashort laser pulse from 0 to π. More generally, it is suggested that the pulse shape of the charge carriers in the ribbon could be designed by similarly tailoring the form of the vector potential of the incident laser pulse.In this work we investigate quantum mechanically the interaction of an intense ultrashort laser pulse with the graphene monolayer as well as with the armchair graphene ribbons of different widths. We consider a tight binding (TB) Hamiltonian of the monolayer graphene and give two rules for deriving the dispersion relations of the armchair graphene  Their method makes use of the side walls of 6H-SiC mesa structures to epitaxially grow the armchair ribbons of different widths on them, while the ARPES technique was used to investigate the electronic structure of the sub-bands of armchair ribbons that revealed the presence of band gaps in most ribbons as well as a gapless pair of bands for ribbons of certain widths . This development opens up new prospects of further research on the effect of quantum confinement and of potential applications of the ribbons in semiconductor electronics, specially, where the monolayer graphene is not directly usable due to its missing band gap.Graphene is a two dimensional hexagonal one-atom-thin monolayer of carbon atoms that shows remarkable material, electrical and optical properties e.g.  with mucand with armchair graphene ribbons. To this end first we consider an analytical TB (tight binding) Hamiltonian in the reciprocal lattice space, determine its eigenvalues and eigenfunctions, give two simple rules for constructing the band-system of armchair ribbons (of any width) from the graphene bands and, briefly illustrate the lattice structure of the monolayer graphene and of the armchair ribbons. Next, the current and the transition dipole operators (relevant for the study of laser interactions) are constructed analytically from the TB Hamiltonian. The laser interaction is introduced using the minimal coupling prescription in the reciprocal lattice space and the time-dependent Schrödinger equation of the interacting system is obtained in the adiabatic representation  the interactions of an intense ultrashort laser pulse with the monolayer graphene tion cf. . To solvtion cf.  for the a = |a1| = |a2| is the lattice constant. The nearest neighbour (nn) distances from one atom (red) of the cell are d1| = |d2| = |d2| = aCC, the carbon-carbon bond length, and, K± = ±{4π/(3a), 0} are the two non-equivalent “Dirac points” of band degeneracy . Note that the lattice constant M, as well as the Dirac points . The “armchair” structure of the horizontal edge and the zik-zak structure of the vertical edge of the monolayer graphene sheet are to be noted here.The lattice structure of a two dimensional graphene monolayer is illustrated schematically in 2, as used in this work, we tested (following the suggestion of an anonymous referee) and found no significant effect of the band asymmetry with non-zero overlap integral s0 = 0.129, as in this work, and s0 = 0 for the symmetric bands. This is apparently due to the high values of the dipole operator in the vicinity of the Dirac points  interactions, the stationary wavefunction ψ(k) of the graphene monolayer can be written as a linear combination of the two Bloch functions associated with the two pz orbitals (per cell). We may then apply the variational principle as usual to construct the expectation value of the energy operator H0, and arrive at the following 2 × 2 variational matrix equation (e.g. ψ(k) = {ψ1(k), ψ2(k)} as well as the energy of the least bound pz orbital, ϵp2:H0(k) is a 2 × 2 matrix with elementsAssuming two carbon atoms per unit cell (red and black dots in the rhombus of ion e.g.  with resh(k) can be expressed by its real amplitude f and phase χ as:g0 is the “hopping” integral (the nearest neighbour interaction matrix element); the lattice constant aCC is the carbon-carbon bond length. The 2 × 2 overlap matrix S is defined by its elementss0 is the dimensionless overlap integral. In this work we have followed the convention ; we also adopt the parameter values g0 = 3.033 eV, s0 = 0.129, and the C-C bond length aCC = 0.142 nm, quoted therein  is the 2D lattice-momentum in the -plane of the monolayer graphene. The corresponding normalised eigenvectors are,The eigenvalues and the eigenvectors of s0 = 0.129 is small compared to 1, it appears in the first order in the denominators in the eigenvalues  then, one obtains a pair of symmetric energy bands. This is particularly so near the Dirac points where the interaction with the laser field is dominant. One may note that with s0 = 0.129 the energy bands are generally asymmetric and the VB and CB have different band widths .We note that although for graphene the square of envalues  and so ienvalues ). Note acf. e.g. . The Hamminimal coupling prescription  is the vector potential associated with the laser electric pulse F(t), and is given by the definition Introduction of the laser-graphene interaction in the system is readily implemented within the present theory by the iltonian  by the sk(t) in terms of the adiabatic  basis states ψ1 (kt) and ψ2 (kt) of H (kt) and write:To solve it, we may first expand the total wavefunction Ψψ1 (kt) and |2⟩ ≡ ψ2 (kt) from the left to get the pair of coupled equations for the time-dependent occupation amplitudes of the valence and the conduction bands, c1  and c2 , respectively:We substitute it in V11 and V22 above, can be transformed away by a unitary transformation of the amplitudes without affecting the probabilities and the expectation values calculated with respect to the total wavefunction of the system .Note that a common term, x and y components of the velocity operator are obtained in the present theory analytically from the Hamiltonian 6) by differentiation with respect to the components of the lattice-momentum k = ,The Jop = euop and the transition dipole operator can be obtained from the velocity operator using the Heisenberg equation of motion:The quantum mechanical current operator defined as ψ1 > and |ψ2 >, with the respective eigenvalues, E1 and E2, of H  may be defined generally in the form x and y axes, respectively; the associated vector potential is given by For the applications, the incident laser field V12 (kt) and V21 (kt) in χ(kt) that appears in We point out in passing that the coupled dynamical expectation value of the “current” along the x and y axes, using the interacting total wavefunction of the system, Ψ, and summing over the k-states of the first Brillouin zone (BZ) including the 2-fold spin- and valley-degeneracy of graphene, respectively gs = 2, and gv = 2:k-space and LD, for the “volume” in the lattice-space (with D = 2 for the monolayer graphene and D = 1 for the armchair graphene ribbons).Finally, we give the expressions for the quantum mechanical intraband current, while the third sum that depends on the VB-CB correlation (or “coherence”) term is referred to as the interband current. It is convenient for most purposes to deal with the corresponding normalised currents  and the conduction band (CB = |2⟩), is often referred to as the We note that the normalised currents are in a. u., with To complete the definitions we also give the matrix elements appearing above, explicitly:c1  and c2 . They are used to determine the total wavefunction of the interacting system and to construct the expectation values to investigate first the excitation of the CB population and the interband correlation (or “coherence”). Next, the intraband and the interband currents as well as the total current are simulated for the case of graphene monolayer and an armchair ribbon . Also simulated are the spectra of the radiation emitted from the monolayer and the ribbon currents. Lastly, the effect of the so-called carrier-envelope-phase  on the shape or symmetry of the current produced in a ribbon  is studied. It is suggested that ultrashort charge-current pulses of desired shape or symmetry might be possible to design by tailoring the vector potential of the laser pulse similarly. The results of the simulations carried out are illustrated graphically, and are compared, and discussed in the next section.For the simulations made in this work, we have solved the coupled e = m = ℏ = 1, c = α−1 = 137.036. We note also that [1 a. u.] of length = a0 = 1Bohr = 0.0519 nm [1 a. u.] of time = t0 = a0/(αc) = 24.19 as, and [1. a. u.] of e = 1.602 × 10–19 C.Unless stated explicitly otherwise, for the convenience of writing and the numerical simulations, in the rest of the work we have used the Hartree atomic units: kx-axis (for ky = 0). The energy degeneracy of the two bands are seen to occurr at the Dirac points  in the -plane where one can also readily recognise the hexagonal structure of the Brillouin zone of the monolayer graphene. In this work, as indicated earlier, we also consider the armchair graphene ribbons cut along the armchair edge (y-axis) with a finite number of cell widths, N, along the transverse direction (x-axis)  while the ribbon’s length is assumed to extend freely along the armchair axis (y-axis).In xis) cf. . The conWe give below two simple, yet general, rules for obtaining the entire system of energy band dispersion relations of the sub-bands of the armchair graphene ribbons (of any width N):Rule 1: An armchair ribbon of width N has N VB-CB band-pairs, r = 1, 2, … , up to N.Rule 2: The N pairs of dispersion relations of the bands can be obtained from the eigenvalues of the monolayer graphene by the simple substitution: kx → kx  = (2/a) (rπ/(N + 1)), where a is the graphene lattice constant).K). Thus, for the Dirac fermion model of armchair ribbons we get the following simple dispersion relations of the rth pair of bands of a ribbon of width N:vF ≈ c/300. It is also worth observing  in a robust and compact form of an armchair ribbon. This might be of interest for potential applications in digital/optical systems. In qy = 0, as they should (but differ elsewhere). The system of VB-CB band pairs are colour coded as follows:  → blue;  →  and,  → . For example, for N = 3, there are three VB-CB pairs of bands none of which is degenerate. However, one pair (red) shows a band-gap minimum, as in a 1D semiconductor. The “m-rules” 1) and 2) given above can be easily verified  for the three ribbons of widths N = 1, 2, and 3, shown in the figure. , does not maintain the parallel separation away from the band centre, qy = 0, unlike the “flat” bands of the full TB model, that do.) We may add that the band structure of the armchair ribbons of width N may be also viewed as possessing N “conduction channels”. They apply to the full TB dispersion relations as well as to the Dirac fermion model (applicable near the Dirac points ving cf.  that 1) Jop = euop . It is clear from the figure that the strength of the transition moment is particularly strong near the corners of the hexagonal BZ (or the Dirac points) in both positive (upper part in the figure) and negative (lower part of the figure) signs of the strength.As we have seen above, the availability of the TB Hamiltonian in the analytic form  below,  and the 2 , polarised linearly and parallel to the “armchair edge” of graphene (the y-axis):F0 is the peak electric field strength, tp is the pulse duration, ω is the circular frequency and ϕ0 is the carrier-envelope-phase (or CEP). The corresponding vector potential is given by,For the simulations in this work we have generally restricted ourselves to an intensity of 1 TW/cm2, tp = 1.5 cycles or, 4 fs).The pulse is illustrated graphically in after the pulse has ended. Simulations are made for the following quantities: 1) CB population, 2) “VB-CB correlation”, and 3) “band currents”, and the results are presented graphically below. They are normalised, as discussed above per unit “volume” . As indicated above, the units of the quantities represented are in Hartree atomic units (a.u.) . The normalised population transfer to the CB and the VB-CB correlation are computed assuming an initially fully occupied VB and an empty CB. Similar initial conditions are assumed for the simulations of the normalised band currents. They are computed from the following normalised formulas .Note that the duration of the simulation times are extended mostly up to twice the pulse duration (up to three cycles) with no field present in the last 1.5 cycles. This allows one to observe the residual response of the system 1) Normalised CB population:2) Normalised VB-CB correlation:The units for 1) and 2): a.u.] = 3) The normalised Currents: They are simulated from the y-component of the formulas, interband correlation—or the VB-CB “coherence”—(middle panel), as well as the interband current (bottom panel). The simulation duration is extended to twice the pulse duration (1.5 cycles) to 3.0 cycles. This allows one to observe the behaviour of the response after the pulse is over. The CB population is seen to increase considerably with the passage of the pulse and attains essentially a steady state superimposed by a mild modulation that persists after the end of the pulse. This is to be contrasted with the oscillatory behaviour of the interband correlation (or the VB-CB “coherence”) that shows a sub-cycle oscillation at the end of the pulse and beyond. We point out that sub-cycle oscillations and ballistic currents have been studied and observed experimentally earlier by Hommelhoff and collaborators  and the interband current (middle panel). Conceptually, the intraband current is associated directly with the sum of the electron-current in the CB and the “hole”-current in the VB. The interband current (middle panel) is associated with the interband correlation or the VB-CB “coherence” (discussed above with respect to intraband current (top panel) and reaches essentially a steady state with a mild modulation. Note that the mild modulation of the interband current causes the mild modulation of the total current beyond the duration of the 1.5 cycle laser pulse.In borators . Note th2, and a pulse duration of 1.5 cycles. In comparison with the monolayer case  in the monolayer current to the strong oscillation of the current in the ribbon does not hold universally for the ribbons  We show in 2, 800 nm, 1.5 cycle laser pulse (as in y-axis). It can be seen that both the spectra have similar qualitative characteristics—namely, a high signal for the low photon orders with a rapid fall in intensity followed by a low and broad plateau that extends to large orders (over a hundred) of the incident photon energy. They show a relative insensitivity to the detailed structure of the target chosen. This is reminiscent of the relative insensitivity also of the gross structure of the so-called “HHG” spectra of atoms/molecules. From the quantum point of view, this insensitivity of the gross structure of the spectra seen here might be due to the dominance of the virtual continuum-continuum transitions between the two band-continua, like that in the ionisation continuum of atoms/molecules that lie behind the fundamental HHG emission process [cf. e.g., review (Section 4.7), The normalised emission spectra computed here are defined by the frequency transform of the normalised currents as follows:se as in . The lasribbon by tailoring the laser pulse. It has been found recently by Hommelhoff and collaborators that the electron dynamics in monolayer graphene can be controlled by choosing the field strength and the phase of the laser field. Thus, they have observed sub-cycle Stuekelberg oscillations and field dependent change of directions of the ballistic current in monolayer graphene (armchair ribbon. The results of simulations of the currents (LHS column) are shown in π, -π/2, and π/2. Comparing the top two rows of the figure, with CEP = 0 and CEP = π, it can be seen that the symmetry of the ultrashort current pulse is fully reversed on changing the CEP of the incident laser pulse from 0 to π. More generally, the results show that the main part of the currents for different CEPs in the ribbon follow the shape of the vector potential of the incident laser pulse. This suggests the possibility of shaping an ultrashort pulse of charge-carriers in the ribbon to a desired form by tailoring the vector potential of the incident laser pulse to mimic the form.Finally, we consider the possibility of shaping the ultrashort current of charge carriers in an armchair graphene graphene . Here weand with armchair graphene ribbons of different widths is made. A TB model is used for the graphene bands and two simple rules for generating the system of sub-bands of the armchair graphene ribbons of any width, N, are given and the band structures are discussed with illustrations.A quantum mechanical investigation of the interaction of an ultra-short intense laser pulse with a two dimensional monolayer graphene interband “correlation” (or “coherence”) and the currents generated in the monolayer graphene and in an armchair graphene ribbon . It is found that the population transfer from an initially fully occupied valence band (VB) to an empty conduction band (CB), is seen to increase during the pulse and ends with a finite steady population, that persists after the pulse is over. In contrast the excitation of the interband correlation or, the VB-CB “coherence”, shows an oscillatory behaviour both during and after the passage of the pulse.Simulations are carried out to investigate, first, the laser pulse excitation of the CB population, the VB-CB intraband component, that leads to a near steady rest-current with a mild modulation. The transition to the ribbon exhibits a remarkable change from the dominance of the intraband current in the monolayer to the dominance of the oscillatory interband current in the ribbon. The ribbon appears to reduce the possible effect of band dispersion in 1D, compared to the open 2D monolayer. The difference seen could be a combined result of the quantum “confinement” effect to 1D as well as due to the difference in the band structure of the ribbon having a band-gap minimum. However, the transition to the oscillatory ribbon current does not hold universally for the ribbons of different widths and, thus, remains open to further investigations in the future for greater clarity.A comparison of the currents generated in the monolayer graphene with the current in an armchair ribbon (of width N = 3) shows that the former is dominated by the broad plateau that extends over many (over a hundred) orders of the incident photon energy. The form of the spectra are also rather insensitive to the target chosen. This is reminiscent of the gross structure and the relative insensitivity to the target chosen also for the well-known “HHG” spectra of atoms or molecules. From the quantum point of view, this insensitivity might be due to the dominance of the virtual continuum-continuum transitions between the two bands, not unlike the transitions in the ionisation continuum of atoms and molecules, that govern the fundamental HHG emission process.A brief comparison of the radiation emitted by the currents in the monolayer graphene and the ribbon (N = 3) is also made. They show a gross similarity and a relative insensitivity to the detailed structure of the targets used. The emission spectra are found to be virtually continuous in frequency and fall off rapidly in intensity with the initial photon orders and reach a low but π. More generally, the result of the simulations made shows that the main part of the pulse of the charge-carriers in the ribbon follows the shape of the vector potential of the incident laser pulse. This suggests the possibility of shaping the ultrashort pulse of charge carriers in the ribbon to a desired form by tailoring the vector potential of the laser pulse to mimic the form.Finally, the possibility of controlling the shape of the ultrashort current of the charge carriers in an armchair ribbon of unit width (N = 1) by the incident laser field is briefly studied. Simulations with different carrier-envelope-phase (CEP) of the incident laser pulse show, for example, that the symmetry of the current in the ribbon can be fully reversed by changing the CEP of the laser pulse from 0 to