N graphene layers interacting with conducting substrate. We derive a dispersion function that incorporates the polarization function of both the graphene monolayers and the semi-infinite electron liquid at whose surface the electrons scatter specularly. We find a surface plasmon-polariton that is not damped by particle-hole excitations or the bulk modes and which separates below the continuum mini-band of bulk plasmon modes. The surface plasmon frequency of the hybrid structure always lies below We predict the existence of low-frequency nonlocal plasmons at the vacuum-surface interface of a superlattice of  N-layered superlattice of free-standing monolayer graphene sheets (MGLs)89101112Several years ago, there was considerable activity in the study of the electronic properties of layered semiconductor superlattices1234N graphene layers interact with a conducting substrate may be adjusted by changing the layer-substrate separation, the energy band gap or the number of 2D layers. It has been shown that such an energy gap may be produced by circularly polarized light17meV being modified with intensity of the light2021Here, we demonstrate how the intensity of the response of the surface plasmon arising when et al.9101112qc which marks the onset of damping by bulk modes in the miniband continuum. If the distance between the layer and the surface is decreased to several nanometers, our model faithfully reproduces the finding recently reported experimentally for nonlocal plasmon branches. Consequently, this successful agreement between our theory and the experimental data for one layer motivated us to consider a superlattice of graphene layers and the effect of the plasmon continuum on each separate mode.We employ our model to determine the plasmon excitation dispersion relation for a single layer on a conducting substrate and show how our results may simulate the experimental data recently reported by Politano hybrid optical tools. Consequently, it is of the highest importance to obtain full information about the behavior  of the plasmon modes interfaced with the substrates of a different material242628There is a number of important real-world modern applications of plasmons in graphene-based heterostructures which definitely should be pointed out. A comprehensive review describing these applications could be found in ref. N 2D graphene layers whose planes are perpendicular to the z-axis at z < 0. Each graphene layer will be described by an energy band structure for Dirac fermions and may be intrinsic, gapped or doped. This model does not allow inter-layer hopping and hence it differs from the one we employed to describe the anisotropy of π-plasmon dispersion in AA-stacked graphiteN = 1 gapless MLG, when the conductor surface-MLG separation exceeds a critical distance dc, the intensity of the surface plasmon in the long wavelength regime is sufficiently high to be observable up to some cut-off wave vector qc of the surface plasmon frequency. Beyond qc, the intensity of ωc is very weak until the plasmon wave vector reaches some value dc, the surface plasmon intensity in the long wavelength regime is weak and the mode only appears at shorter wavelengths when the in-plane wave vector ωc is completely suppressed when the surface-layer separation is less than dc. We then make some concluding remarks in Section 4 regarding the inspiration for our work, a summary and significance of our findings, and what new theoretical formalism is presented in our paper.The model we use for a superlattice consists of r, r′ and frequency ω or its inverse K satisfying In our formalism, we consider a nano-scale system consisting of an arbitrary number of 2D layers and a thick conducting material. The layer may be monolayer graphene or a 2DEL such as a semiconductor inversion layer or HEMT (high electron mobility transistor). The graphene layer may have a gap, thereby extending the flexibility of the composite system that also incorporates a thick layer of dielectric material. The excitation spectra of allowable modes will be determined from a knowledge of the nonlocal dielectric function N 2D layers and a semi-infinite structure is given by31In operator notation, the dielectric function for the where xy-plane and suppressing the in-plane wave number q|| and frequency ω, we obtainIn integral form, after Fourier transforming parallel to the Here, the polarization function for the 2D structure is given bywhere the 2D response function obeyswith g = 4 takes account of valley and spin degeneracy. At T = 0, the Fermi-Dirac distribution function is reduced to the Heaviside step function where and the imaginary part byB in ref. γ ≪ ω in Eq. q4 of the corresponding results in ref. ω > vFq.We clarify that our long wavelength approximation of q − ω domain. The point is that we have written the expression for a region where the plasmon is not damped. If a plasmon branch is located below the diagonal ω = vFq, the plasmon is strongly damped because of the singularity γ ≪ ω is not satisfied. We provide the long-wave limit approximation for the polarization function only in the region where the plasmon is undamped or almost undamped. We again emphasize that we employed the full expression for the one-loop electron polarization function, which is valid at arbitrary wave vector and chemical potential for both gapless and gapped graphene to obtain all our numerical results and graphs. Both intra- and inter- band transitions have been taken into account.It is crucial to highlight the fact that our numerical simulations were based on the full nonlocal polarization function. It is well-known that for graphene, and especially for gapped graphene, the polarization function is determined as a piecewise function with different expressions for the regions of Our model does not include effects due to plasmon-plasmon scattering, a higher order effect. Also we employed Dirac electrons for both gapped and gapless graphene, since the doping is not high enough to be considered in the anisotropic region. These approximations are applicable for low energy plasma excitations and sufficiently clean samples. All relevant theoretical papers on plasmons in graphene and two-dimensional electron liquid, such as refs Upon substituting this form of the polarization function for the monolayer into the integral equation for the inverse dielectric function, we havez1 = ai in Eq. We now set These linear algebraic equations may be solved simultaneously and their solutions expressed in matrix form aswhere and In mean-field theory, we have37whereand andMaking use of these results in Eq. ωp, then we useIf the bulk plasma within the semi-infinite slab is fully local in the sense that from which the corresponding local inverse dielectric function qz-integrations in Eqs qz-nonlocality dependence, eliminating the possibility of an unrestricted limit qz → 0 and modifying the plasmon dependence on q||. Additionally, the imaginary part of qz-integrations, which consequently contributes to damping of the surface plasmon modes even in the low-q|| limit. The “nonlocal” q||-correction to the surface plasmon, and its imaginary part involving damping, depend on the properties of the bounding surface. But, there is a range of applicability. This can be seen by examining the parameter measuring the importance of nonlocality in the bulk dielectric function Ethemal = μ is the Fermi energy in the degenerate substrate with electron effective mass While Eq. N = 1, 2, 4 layers of graphene as shown in Figs 1a is less than a critical value In this section, we present numerical results for the plasmon dispersion for a system consisting of a semi-infinite conducting medium which is Coulomb-coupled to dc, both symmetric and antisymmetric modes become damped, for different ranges of wave vector. We emphasize that the upper plasmon branch (symmetric mode) remains almost unchanged for all cases, either with one or two graphene layers.Similar conclusions for a pair of graphene layers electrostatically coupled to a semi-infinite conducting material are presented in eV. Indeed, very recently, Politano and collaborators have published a joint experimental-theory paper on Bi2Se3 which is a heavily doped topological insulator, where it seems that the surface plasmon energy is 104 meV, around 0.1 eV. High-resolution electron energy loss spectroscopy has provided evidence of mutual interaction between the surface plasmon and the Dirac plasmon of Bi2Se3Bi2Se3 interface, which was recently experimentally realized by Kepaptsoglou et al.Bi2Se3 should hybridize with plasmons in graphene.In order to observe the plasmon coupling we must ensure that the surface mode is not damped due to the inter-band single particle excitation, i.e., the surface plasmon frequency is comparable with the Fermi energy in graphene. The latter is in the range of the graphene 2D plasmon energy, i.e., let’s say below 1 On the other hand, the zero-temperature doping Fermi energy in graphene can also vary significantly depending on the electron density and may be estimated asa0 = 6 nm (nanometers) and the estimated critical distance at which the lower plasmon branch no longer exists in the long-wavelength limits is acr = 2 nm (nanometers) or ~101 Å. However, these distances could easily vary by an order of magnitude, or even more, by changing the electron density in graphene, which gives enough flexibility for experimental arrangements. For this reason, we chose to set our scale in terms of kF in all our graphs. Comparison with analytical results for a single layer of graphene on a metal surface is helpful. The spectra of plasma waves in gated graphene heterostructures were addressed for various voltages and temperaturesγ (inverse lifetime) with the use ofRegarding the units we used to set our length scale by, we would like to make the following remarks. Presenting the inter-layer distances in Angstroms or nanometers would immediately allow an experimentalist length scales to work with. The Fermi wave vector in graphene is determined directly from the electron density and for a standard value ω = Ωp(q) is a prerequisite for calculating γ. This is basically obtained by having where the evaluation of the plasmon dispersion As far as the presentation of the plasmon peaks is concerned, it is important to note that each density plot with a peak corresponding to a plasma mode is accompanied by a line plot in which an exact numerical solution of the dispersion equation is obtained for each branch, either damped  and the other branch is associated with the surface plasmon, originating at dc, the surface plasmon may not exist in the long wavelength limit. We obtain a surface plasmon at both intermediate as well as long wavelengths as this layer-surface separation is increased. For this hybrid structure, the surface plasmon frequency lies below the surface plasmon frequency for the semi-infinite substrate. Experimental verification of these simulated results may be achieved using high-resolution electron-energy-loss spectroscopy (EELS)9The important conclusions of our work are as follows. We formulated and exploited a newly derived expression for plasmon dispersion in a superlattice of 2D layers which are Coulomb-coupled to a metallic substrate by taking into account the full nonlocality of the layers as well as the underlying conductor. We predict the existence of low-frequency nonlocal plasmon excitations at the vacuum-surface interface for various conditions of surface-layer separation as well as the energy gap. When the separation between the conducting surface and the nearest layer is less than some critical distance How to cite this article: Gumbs, G. et al. Plasmon Excitations of Multi-layer Graphene on a Conducting Substrate. Sci. Rep. 6, 21063; doi: 10.1038/srep21063 (2016).


Pleural effusion induced by sarcoidosis is rare, and pleural sarcoidosis is often diagnosed by thoracoscopic surgery. The diagnosis of pleural sarcoidosis using thoracentesis may be less invasive when sarcoidosis is already diagnosed histologically in more than one organ specimen. Here we report the case of a 64-year-old woman with pleural sarcoidosis diagnosed on the basis of an increased CD4/CD8 lymphocyte ratio in pleural effusion fluid obtained by thoracentesis. This case report is important because it highlights the usefulness of the CD4/CD8 lymphocyte ratio in pleural effusion as an indicator of pleural involvement of sarcoidosis.A 64-year-old Japanese woman visited our hospital with an initial symptom of dyspnea on exertion for a period of 4 months. Chest computed tomography showed bilateral hilar and multiple mediastinal lymphadenopathy, multiple small nodular shadows in her bilateral lungs, small nodular shadows along the interlobar pleura, and bilateral pleural effusion. Her serum angiotensin-converting enzyme and soluble interleukin-2 receptor levels were elevated. Histological analysis of a resected subcutaneous nodule, and biopsy specimens from a right mediastinal lymph node and from her right lung revealed non-caseous epithelioid granulomas. Her bronchoalveolar lavage fluid exhibited a predominance of lymphocytes together with an increase in the CD4/CD8 lymphocyte ratio. The lymphocytic predominance and the increased CD4/CD8 lymphocyte ratio were also detected in the right-sided pleural effusion fluid obtained by thoracentesis. We diagnosed sarcoidosis with pleural involvement. Because pleural effusion did not resolve spontaneously and her symptom of dyspnea on exertion worsened, corticosteroid therapy was initiated, which ameliorated the sarcoidosis and the pleuritis.Analysis of the CD4/CD8 lymphocyte ratio in pleural effusion fluid obtained by thoracentesis may be helpful for the diagnosis of pleural sarcoidosis when the diagnosis is already made by histological examination of more than one organ specimen. Sarcoidosis is a systemic granulomatous disease of an unknown cause that may involve the lungs, lymph nodes, eyes, salivary glands, skin, liver, spleen, heart, nervous system, muscles, bone, and other organs . A cliniExclusion of tuberculosis and fungal disease is important for an accurate diagnosis . ThoracoA 64-year-old Japanese woman visited our hospital with an initial symptom of dyspnea on exertion. For the past 4 months she had shortness of breath when she walked approximately 100 meters or went up 10 to 20 steps of a staircase. She visited her neighboring hospital 1 month before visiting our hospital where she received a diagnosis of bilateral pleural effusions and seven sessions of thoracentesis; however, no clinical diagnosis could be made although her dyspnea on exertion was slightly improved by the frequent thoracentesis. When she visited our hospital for the first time, she felt dyspnea on exertion on the ground level after several hundred meters. Before she had dyspnea on exertion, she had not had any diseases including sarcoidosis nor had she received any continuous medications such as immunosuppressive drugs. She had no previous history relating pleural effusion, and no family history of sarcoidosis. She did not have any past history for opportunistic infections. A chest radiograph showed the enlargement of bilateral hilar shadows, reticulonodular shadows in bilateral lung fields, and dullness at the right costophrenic angle Fig. . Her ser2) of 93%, maximum pulse of 126 beats per minute and the worst modified Borg scale of perceived dyspnea of 1. Chest computed tomography (CT) showed multiple skin nodules, bilateral hilar and mediastinal lymphadenopathy, bilateral pleural effusion, and multiple small nodules in both lungs and along the interlobar pleura , under a daily dosage of 25mg of prednisolone, a chest radiograph showed decreased pleural effusion (Fig. She was discharged 5 weeks after the first visit and was followed up for the spontaneous resolution of the bilateral pleural effusion. However, no improvement was observed and pleural effusion increased Fig. . The 6-mion Fig. , and CT ion Fig. . The cliet al. reported that 2.8% of out-patients showed pleural effusion, although a histological diagnosis was made only in 1.1% [Mycobacterium cultures, and PCR analyses did not support tuberculosis. Fungal infection was also ruled out by histological examination and bacterial culture of both BALF and pleural effusion fluid. We thought that thoracoscopy was too invasive for the patient as we regarded this case met the diagnosis criteria of sarcoidosis. We also excluded malignant lymphoma by histological examination of a EBUS-TBNA specimen because her serum sIL2R level was elevated at the first visit. sIL2R is not only a marker of malignant lymphoma but is also elevated when a T-cell is activated [et al. reported the elevation of sIL2R in sarcoidosis with active alveolitis [et al. [Pleural sarcoidosis is believed to be rare. Huggins  in 1.1% . In seve in 1.1% , 8. Alth in 1.1% , 9, it i in 1.1% . In our  in 1.1% . When th in 1.1% . We thouctivated . Miyoshiveolitis . The CD4 [et al. . CorticoPleural involvement of sarcoidosis is considered to be an indication for corticosteroid therapy in recurrent or symptomatic cases , 11. AsyIn conclusion, we report a case in which pleural sarcoidosis was diagnosed on the basis of lymphocytic predominance and an increased CD4/CD8 lymphocyte ratio in pleural effusion fluid obtained by thoracentesis. This technique may be useful for the diagnosis of pleural sarcoidosis when sarcoidosis is already diagnosed histologically in biopsy specimens from more than one organ.Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.


Infants are known to engage in conversation-like exchanges from the end of the second month after birth. These ‘protoconversations’ involve both turn-taking and overlapping vocalization. Previous research has shown that the temporal organization of adult–infant turn-taking sequences is similar to that of adult verbal conversation. It has also been shown that young infants adjust the quality of their vocalization in response to the quality and timing of adult vocalization. We present new evidence of turn-taking interaction in infants aged between 8 and 21 weeks based on the analysis of 176 samples of naturalistic face-to-face interactions from 51 dyads. We found high levels of latched turns as well as frequent initiation of turn-taking by infants at these ages. Our data do not support the hypothesis that turn-taking ability increases with age between 2 and 5 months but do suggest that infants are active participants in turn-taking from the earliest age and that mothers adjust turn-taking formats to infants. Conversation is a complex communicative process in which visual and auditory signals are combined in a flow of turn taking. An important aspect of the temporal organization of conversation is the fluency between turns. The end of a speaker’s turn needs to be anticipated by the next speaker for the conversation to be fluent . In everYet a number of studies in psychology describe turn-taking interaction occurring between infants and adults as early as in the second month of life, long before any access to lexical information. A recent study conducted by In the first weeks after birth, infants begin to produce vocalizations that are described in the literature as coos and murmurs  and thatThe appearance of these kinds of vocalizations gives rise to vocal exchanges with adult partners that resemble conversations because they are characterized by alternating vocalizations separated by audible pauses . Adults Various approaches have been used to demonstrate the active role of both mothers and infants in the first half year of life in face-to-face interaction. A durational approach reveals stable timing structures in maternal behavior across vocal and kinesic modalities . MothersA related approach to studying protoconversational organization focuses on the match or cross-correlation between temporal patterns of maternal and infant vocalization in spontaneous face-to-face interaction. The fact that mothers and infants engaged in social interaction match each other for vocalization and pause duration suggests a mutual regulation of the turn-taking exchange . In her If infants partake in a truly co-regulated turn-taking, they must have the ability to perceive the contingent relations between their own behavior and that of their partner. These contingent relations hinge on the perception of timing in social interaction. Research has shown that infants’ sensitivity to contingency changes right around the time when protoconversations appear, around the age of 2 months . The stiStarting around the age of 2 months, the cooing stage  is assocOne longitudinal study has reported a quantitative increase in vocal turn-taking with less overlapping vocalization between 12 and 18 weeks of age  suggestiThe most detailed longitudinal study of the timing of turn-taking in infancy was conducted recently by Hilbrink et al. (submitted) on 12 infants aged between 3 and 18 months. These researchers report on the prevalence of turn-taking exchanges throughout the period they studied. They also find that turn-taking organization varies little between 3, 4, and 5 months of age but that turns slow down markedly around the age of 9 months. At this age infants respond to mothers’ utterances with longer gaps whereas maternal turn-timing remains stable over time. Furthermore, this study shows that the amount of overlap in turn-taking remains constant between 3 and 5 months of age but decreases thereafter. The slowing down of turn-taking can be associated with important qualitative changes in social interaction and communicative skills such as joint attention.The present paper assesses developmental change in turn-taking organization between the 3rd and the 5th months of life. We first aimed to explore the hypothesis that turn-taking is, from the first weeks of life, a mutually coordinated effort and then to assess developmental change and stability in the amount of overlap, duration of switching pauses (gap) between turns and length of TTSs. We thus compared spontaneous vocal interactions between mothers and infants ages between 2 and 3 months with those of mothers with 4-to-5-months-old infants.Fifty one MI dyads participated in this study. Infants were aged between 8 and 21 weeks [28 boys and 23 girls aged respectively 12.8 weeks ± 3.77 (range: 8–19) and 13.2 weeks ± 3.73 (range: 8–21)], were born full-term and in good health. Out of the 51 mothers, three mothers were bilingual speakers but spoke to their infants in French. The sample was divided into two age groups: a group of ‘younger’ infants  and a group of ‘older’ infants . The present research was approved by the university ethics committee (CCP n°1450089).All dyads were recorded in naturalistic contexts, in their home, when infants were in a quiet alert state. Before each observation, consent forms were signed by the parents. Mothers and infants were placed in comfortable positions, facing each other. Mothers were asked to talk to their infants in their usual manner for approximately 10 min and to avoid using any toys. Video and audio recordings were made using two camcorders (Sony Handycam HDR-CX190) and a digital audio recorder (Korg Sound on Sound Unlimited Track Recorder) placed near the dyad. Only the audio recordings were used in this study.A total of 176 audio samples were selected [3.5 audio samples on average per infant ± 2.2 (range: 1–9). Audio sample length was on average 106.7 s ± 57.9 (range: 18–252)]. In all 90 min and 41 s of interaction were analyzed. Samples lasted on average 31 s. The samples were taken from a large corpus of audio recordings, they were the first to meet following four selection criteria:(1) Each sample included at least one vocal contribution by the infant and no negative infant vocalizations .(2) In each sample, mothers addressed their infant directly. Sequences including song to infants were discarded.(3) Samples were segmented based on pause duration: pauses between vocalizations that exceeded 3 s marked the end of the selected audio sample.(4) Recording quality was optimal for all samples.We used Sound Analysis Pro  to segmeBased on visualization of spectrograms and audio guidance, each sequence was manually segmented into 4 types of events: maternal vocalization, infant vocalization, overlapping vocalization and pause, according to the following criteria:(1) A vocalization (either by mother or infant) was defined as the production of vocal sound by one partner that was either continuous or included unvoiced segments of less than 300 ms. If the silent pause following an audible vocal sound was greater than 300 ms, two successive vocalizations were coded.(2) Overlapping vocalization was coded when either mother or infant vocalized over the vocalization of the partner. The entire vocalization was coded as overlapping even if it was only partially masked by the partner’s vocalization.(3) Pauses occurred either between two vocalizations by the same partner (within- speaker pause) or between alternating vocalizations (switching pause). Within-speaker pauses had a duration that was necessarily greater than 300 ms and lower than 3000 ms. Switching pauses could range from a few milliseconds to 3000 ms. Two alternating vocalizations were qualified as latched when the switching pause had a duration of less than 50 ms.(4) Vegetative sounds produced by infants such as burps, growls or hiccups, noise from the environment and vegetative sounds produced by mothers, such as coughs, were not coded.A TTS was defined as sequence of vocalizations involving at least one alternation between speakers. Such a sequence could involve alternation between a vocalization of mother and of infant or between a vocalization of mother or infant and an overlapping vocalization. A TTS ended when the same speaker produced at least two vocalizations in succession or the pause following a vocalization was greater than 3000 ms.Sound Analysis Pro  providesTwenty percent of the data set were double-coded. Inter-coder reliability (Pearson product-moment correlations) was 0.87, 0.98, 0.78, and 0.95 respectively for number of infants’ vocalizations, mothers’ vocalizations, vocalizations involving overlap and pauses. Onset positions were considered identical if they occurred within 50 ms, thus measures of vocalization duration had an error tolerance of up to 100 ms. Both coders correctly identified 80.6% of all onset positions within the subset of double-coded sequences.Analysis was done with Stata for Windows (version 12). Multiple regression was used to compute partial regression coefficients and logistic regression to estimate ORs and Wald 95% CIs . Age .Table 1). Infant vocalizations which were not involved in turn taking were produced either after an infant vocalization (12.8%) or were isolated, i.e., were neither preceded nor followed by another vocalization (14.1%). The proportion of infant vocalization occurring within TTSs was higher among younger infants than among older infants .Infant vocalizations occurring within less than 3 s of a maternal vocalization, i.e., involved in turn taking, represented 73.1% of all infant vocalizations , and the remaining were vocalizations that followed a maternal vocalization . These were either latched vocalizations, that is vocalizations occurring without an intervening pause  or vocalizations involving a switching pause . Contingency analysis conducted on type of vocalization revealed a significant age effect : older infants vocalized twice in succession more frequently than younger infants whereas vocalizations occurring after a switching pause were more frequent among the younger infants. No difference was observed between the two groups for frequency of overlapping vocalizations .Among the vocalizations occurring within TTSs, some were overlapping vocalizations (p = 0.49), but a significant gender effect: girls’ vocalizations were on average 108 ms longer than boys’ vocalizations (p = 0.049).Infant vocalizations lasted on average 869.7 ms ± 662.3 (range: 50.2–3640.0). Multiple regression conducted on the durations of vocalizations revealed no effect of age (Table 2). One in five mother vocalizations was consecutive to an infant vocalization , either as a latched turn  or involving a switching pause . Only 13.5% of mother vocalizations were not embedded in a sequence of vocalizations (n = 297) and 51% were preceded by a maternal vocalization (n = 1113).Maternal vocalizations occurring within less than 3 s of an infant vocalization – i.e., involved in turn taking – represented 35.8% of all maternal vocalizations . Mothers vocalized twice in succession more frequently with younger infants but overlap was more frequent for mothers of older infants .Contingency analysis conducted on type of vocalization revealed a significant age effect . A gender effect was also observed, mothers of boys vocalizing on average longer (p = 0.034).Mothers’ vocalizations lasted on average 1144.7 ms ± 904.9 (range: 50–9803). Multiple regression conducted on the durations of the vocalizations showed a significant effect of age: the vocalizations of mothers of younger infants were on average 399 ms longer than those of mothers of older infants (p < 0.0001). No gender effect was found (p = 0.25). Analysis of the number of vocalizations per minute revealed no significant effects, neither for gender (p = 0.96) nor for age (p = 0.92).Vocalizations involving overlap lasted on average 1550.7 ms ± 1090.1 (range: 110–4928). Multiple regression conducted on the durations of the 344 overlapping vocalizations revealed a significant effect of age: overlapping vocalizations involving younger infants were 812 ms longer than those involving older infants (n = 202) were latched, i.e., without a pause between alternating vocalizations. This proportion was quantitatively higher for older infants than for younger ones but not significantly so . Maternal vocalizations preceding a latched turn by the infant were shorter, though not significantly so, than those involved in turns including a switching pause . Among the 441 turns performed by mothers, 41.7% were latched. This proportion was quantitatively higher when mothers responded to older infants than when they responded to younger infants, but again not significantly so . Infant vocalizations preceding a latched turn by the mother had the same duration as those involved in turns including a switching pause (respectively 869 and 870 ms).Among the 454 turns produced by infants 44.5% (p = 0.82) or for mothers (p = 0.60). No gender effect was found.Pauses between vocalizations by the same speaker, which were by definition restricted to the range of 300 to 3000 ms, lasted on average 745.5 ms ± 557.0 (range: 310–2643.6) for infants and 967.3 ms ± 606.4 (range: 300–2994.8) for mothers. Multiple regression analysis revealed that within speaker pauses were not significantly different according to age, neither for infant (p = 0.007). No significant gender effect was found (p = 0.16).The samples comprised 838 switching pauses lasting on average 730 ms ± 543.6 (range: 50–2974). Multiple regression analysis showed that switching pauses were on average 174.0 ms longer in samples involving older infants (p = 0.013) and showed that switching pauses inside an IM pair of vocalizations were on average 135.4 ms shorter than those inside a MI pair of vocalizations (p = 0.014). This difference was not impacted by infant age (p = 0.68).Among the switching pauses, 60.5% concerned pairs of vocalizations that were either between an IM pair of vocalizations (30.1%) or between a MI pair of vocalization (30.4%), i.e., switching pauses which did not involve an overlapping vocalization. Both types of switching pause were analyzed separately. Multiple regression analysis confirmed the overall age effect for all switching pauses  = 30.6, p < 0.0001], both measures were analyzed separately in order to appreciate whether they were likely to be explained by age.In total, 489 TTSs were identified, lasting on average 5.68 s ± 4.39 (range: 0.3–28.2) and ranging from 2 to 18 turns . Because duration and number of turns were highly correlated [p = 0.57) nor of gender (p = 0.56). However, we did observe a significant difference between both age groups regarding the duration of TTSs: TTSs of older infants lasted 1.22 s longer . No significant gender effect was found (p = 0.53).Multiple regression conducted on the number of turns per TTS did not reveal any significant effect, neither of age . No significant gender effect was found (p = 0.30).TTSs were divided into two subgroups depending on which partner initiated the sequence. Sequence initiation was coded when a vocalization occurring after a pause lasting at least 3 s was followed by at least one vocalization by the partner within less than 3 s. Among the 489 TTSs collected, 44.8% were initiated by infants. Logistic regression showed that TTS initiation by infant was most likely to occur in older infants . We also observed a significant gender effect: boys were less likely to end a TTS than girls .Turn-taking sequences were also divided in two subgroups according to which partner terminated the sequence. A sequence termination was coded when a vocalization following at least one vocalization by the partner within less than 3 s was followed by a pause of at least 3 s. Among the 489 TTSs observed, 37 (7.6%) ended with a co-vocalization and were then excluded from analysis. Twenty four percent of the remaining 447 TTSs were ended by infants. Logistic regression showed that TTSs were more likely to be ended by infants in older infants  were collected using acoustic analysis software. The aim of the study was, first, to ascertain whether vocal exchanges involving young infants has a turn-taking format and, second, to investigate developmental change in vocal turn-taking.The first finding was that three out of four infant vocalizations are either followed or preceded by a maternal vocalization. Infants in both age groups vocalize in turn as frequently, and the most common turn-taking format at both ages is one involving three turns . Indeed, infants respond to mothers’ vocalizations as often as mothers respond to infants’ vocalizations at both ages. Although the turn-taking format is observed in vocal interactions of infants aged between 2 and 5 months, the question that needs addressing is whether mothers are responsible for creating these formats or whether infants actively partake in shaping TTSs.One way to investigate infants’ active role in turn-taking is to ask whether they demonstrate anticipation of the mothers’ turns and whether they show initiative in generating a vocal response from the mother. The present study provides partial answers to these questions because it is based on durational measures and does not include other acoustic features such as intonation contour, pitch matching or amplitude modulation. Some of our findings support the hypothesis that, already from the 2nd month of life, infants anticipate turns and initiate TTSs.Infants at both ages used a high proportion of latched turns, that is they began to vocalize within a few milliseconds (less than 50 ms) of the end of the mother’s vocalization, without any overlap. To our knowledge, no study of early MI vocal interaction has reported on the frequency or significance of latched turns. This finding is significant in teasing apart the roles of adults and infants in turn-taking exchanges. Indeed, although latched turns are less frequent than overlapping vocalization, it seems implausible that they would occur randomly at the frequencies we report. The temporal window for initiating vocalization is markedly smaller for latched turns than for turns involving a pause and for overlapping vocalizations. Indeed, the average time frame within which an infant vocalization is described as an ‘overlapping vocalization’ in our study is 1145 ms  and the average time frame within which an infant vocalization is involved in a turn (excluding latched turns) is 730 ms (the average duration of a switching pause). The high frequency of latched infant vocalizations suggests that infants actively shape the turn-taking organization of an exchange and anticipate events within it. Based on a comparison of the probabilities of infants producing different prosodic contours, a previous study showed that 3-months-old selectively match their vocalizations to preceding maternal vocalization . Thus thThe finding that infants in the 3rd months already frequently perform latched turns poses a major challenge. How do young infants project the end of a turn as precisely as adults do in verbal conversation, with ‘no-gap-no-overlap’ , withoutFurthermore, it is interesting to explore the possible functions of latched turns in protoconversational exchange. The experience of a seamless transition between self-expression and other-expression may be highly relevant for a young infant, reinforcing an emerging sense of agency in the 1st months of life. Latched turns may be conceived as joint action, where each individual’s actions are coordinated so as to achieve a joint outcome and where each individual’s action cannot be understood in isolation from the others’ .Overall, comparison of the two age groups revealed both continuity and change in turn-taking organization. We do not find any differences in terms of mean frequency of vocalizations involving overlap between the two ages. Nor do we find that the duration of switching pauses decreases with age. On the contrary in our data they are longer among the older infants. Older infants do not perform proportionately more latched turns than younger infants. We did find that switching pauses were more frequent in younger infants’ interactions. This finding should entail that younger infants partake in a greater number of alternating vocalizations but we did not find that the number of turns within TTSs increases with age. This inconsistency may be explained by the quantification method we used for turn-taking. Overlapping vocalizations and latched vocalizations were taken into account in the quantification of number of turns whereas the frequency of switching pauses was quantified on the basis of non-overlapping vocalizations alone. It is therefore not possible to describe the contribution of each type of vocalization within the TTSs. Future studies should be aimed at more precise description of overlapping vocalization in MI interaction.Turn-taking sequences were found to be longer for older infants despite the fact that infant vocalizations have similar durations in both age groups and that mothers’ vocalizations are shorter in interactions with older infants. Longer TTSs at 4–5 months than at 2–3 months are most likely explained by the increase in switching pause duration between the two ages. Furthermore, a greater number of infant vocalizations were either responded to or were responses to the mother among the younger infants, and older infants vocalized more often twice in succession. These two age-related changes may reflect a transition between the highly social cooing stage and the more solitary exploratory sound play that follows in vocal development . HilbrinOur findings confirm the active role of mothers in adjusting their vocal behavior to infants. Mothers’ vocalizations were found to be longer with younger infants, and they produce more successive vocal utterances when interacting with younger infants. Mothers perform more latched turns with older infants and switching pauses between IM pairs of vocalizations are shorter on average than between MI pairs, suggesting that mothers respond to infants faster than infants respond to mothers. In a previous study, the duration of switching pauses in vocal turn-taking between 2 and 3 months-old infants and mothers was found to vary cross-culturally in relation with parenting styles and cultural representations . SwitchiThe significance of our findings on initiation and termination of TTSs is ambiguous. We found that older infants were more likely to initiate a TTS. However, initiating a sequence does not imply that older infants show greater initiative in turn-taking, as this finding could be explained by mothers responding more often to the vocalizations of older than of younger infants. In fact, a recent study has shown that, without knowledge of infant age, naïve listeners implicitly attribute greater communicative intentionality to vocalizations of 5 months-old infants than to those of 1 month-old . Our data also show that older infants more frequently terminate TTSs than younger infants. This may also be seen to reflect the mother’s stance toward the infant rather than a change in the way infants organize turn-taking because mothers may not respond as often to terminal vocalizations with older infants. It would be interesting to take into account the acoustic characteristics of these initial and terminal infant vocalizations in order to gain insight into the question of infant initiative. Prosodic cues such as intonation contour may signal initiative to mothers, for both initiating and terminating turn-taking. It is also possible that mothers do not respond to terminal vocalizations because the TTS has reached a durational threshold, her unresponsiveness would then serve a regulatory function. It is worth investigating the transformations of the two partners’ roles in turn-taking across ages. Indeed, mothers may progressively give the infant more and more prominence in the interaction, considering her more and more as an active partner with “something to say” while making the rules of turn-taking more salient. Infants may become less interested in a vocal turn-taking and more interested in multimodal turn-taking around object play or shared activities.Overall our findings do not clearly support the hypothesis that infants’ become more competent at turn-taking between the 3rd and 5th months of life. Indeed, we find neither shorter switching pause durations nor less overlap between these ages. Rather, our findings suggest that turn-taking organization is sensitive to changes in infants’ social motives, reflecting a growing involvement in object play and joint activity. Although mothers are clearly highly adaptive and active in vocal exchanges with infants, we have found evidence that already very young infants play an active role in shaping the unfolding of TTSs. This exploratory study on the early development of turn-taking points to the possibility that turn-taking in preverbal interaction adapts to infants’ changing motives for communicating and learning, and paves the road to the crucial socio-cognitive skills that precede and enable language use.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.


Visual object recognition is of fundamental importance in our everyday interaction with the environment. Recent models of visual perception emphasize the role of top-down predictions facilitating object recognition via initial guesses that limit the number of object representations that need to be considered. Several results suggest that this rapid and efficient object processing relies on the early extraction and processing of low spatial frequencies (LSF). The present study aimed to investigate the SF content of visual object representations and its modulation by contextual and affective values of the perceived object during a picture-name verification task. Stimuli consisted of pictures of objects equalized in SF content and categorized as having low or high affective and contextual values. To access the SF content of stored visual representations of objects, SFs of each image were then randomly sampled on a trial-by-trial basis. Results reveal that intermediate SFs between 14 and 24 cycles per object (2.3–4 cycles per degree) are correlated with fast and accurate identification for all categories of objects. Moreover, there was a significant interaction between affective and contextual values over the SFs correlating with fast recognition. These results suggest that affective and contextual values of a visual object modulate the SF content of its internal representation, thus highlighting the flexibility of the visual recognition system. Rapid and accurate visual recognition of everyday objects encountered in different orientations, seen under various illumination conditions, and partially occluded by other objects in a visually cluttered environment is necessary for our survival. The first theoretical efforts to explain this feat relied on purely bottom-up mechanisms in the visual system: cells in early visual areas would be sensitive to low-level features and cells in higher areas would integrate this information in order to then match it to a representation in memory , while having little to no effect on basic-level category verification, suggesting that basic-level categorization does not particularly rely on LSFs  and did not suffer from any reading disability. A written informed consent was obtained prior to the experiment, and a monetary compensation was provided upon its completion.Forty-seven healthy participants  with normal or corrected-to-normal visual acuity were recruited on the campus of the Université de Montréal for an object recognition study. Participants were aged between 19 and 31 years  environment, using functions from the Psychophysics Toolbox  and randomly filtered at each trial, according to the SF Bubbles method , participants sat comfortably in front of a computer monitor, in a dim-lighted room. Participants did two 500-trial blocks, with a short break in between. Each trial began with a central fixation cross lasting 300 ms, followed by a blank screen for 100 ms, the SF-filtered random object image for 300 ms, a central fixation cross for 300 ms, a blank screen for 100 ms, and finally a matching or mismatching object name that remained on the screen until the participant had answered or for a maximum of 1000 ms. Subjects were asked to indicate with a keyboard key press as accurately and rapidly as possible whether or not the name matched the object depicted in the image. This picture-name verification task was chosen because it imposes a specific level of categorization to subjects (we chose the basic-level) without focusing attention explicitly on either affective or contextual value of the object. Name and object matched on half the trials.To determine the spatial frequencies that contributed most to fast object recognition for each condition, we performed least-square multiple linear regressions between RTs and corresponding sampling vectors. Only correct positive trials  were included in the analysis. RTs were first z-scored for every object to minimize undesired sources of variability pertaining to psycho-linguistic factors such as word length and lexical frequency (see Stimuli: Control of low-level features). They were further z-scored for each condition in each subject's session to diminish variability due to task learning. Trials associated with z-scores over 3 or below 3 were discarded .p-value is satisfied. We used this test rather than the Pixel test . We report the size k of the significant cluster and its maximum Z-score Zmax. We implemented the Cluster tests as bootstraps . To analyse possible effects of condition on accuracy, without taking SFs into account, we first conducted a 2  × 2  repeated-measures ANOVA on mean accuracies per participant. There was an effect of contextual value : non-contextual objects  were recognized more easily than contextual ones . There also was an effect of emotional value : neutral objects  were recognized slightly more easily than emotional objects .The mean accuracy was 87.49%  = 53.04, p < 0.001, η2p = 0.53]. This interaction was decomposed into simple effects. First, there was an effect of emotion on non-contextual objects . Non-contextual neutral objects  were recognized more easily than non-contextual emotional objects . Second, there was an effect of emotion on contextual objects as well . Contextual emotional objects  were recognized more easily than neutral contextual objects .There was an interaction between emotional and contextual values  whereby non-contextual objects (MdSD = 60) were recognized faster than contextual ones . There was no effect of emotional value [F < 1].The mean RT for correct positive trials was 623 ms  = 18.46, p < 0.001, η2p = 0.29]. This interaction was decomposed into simple effects. First, there was an effect of emotion on non-contextual objects . Non-contextual neutral objects  were identified faster than non-contextual emotional objects . There also was an effect of emotion on contextual objects . Contextual emotional objects  were identified faster than contextual neutral ones .There also was an interaction between emotional value and contextual value [Zmax = 3.94, k = 23, p < 0.01; Figure p > 0.05). Similarly, there was no significant difference between non-contextual and contextual objects (p > 0.05).To determine the spatial frequencies that contributed most to fast object recognition for each condition, we performed least-square multiple linear regressions between z-scored transformed RTs  and corresponding sampling vectors for correct positive trials. All object categories confounded, SFs between 13.71 and 24.31 cycles per object width (cpo) correlated negatively with RTs . We found a significant interaction for SFs between 5.52 and 6.69 cpo . The interaction thus seems to be caused by the significant effect of contextual value on emotional but not on neutral objects, combined with the significant effect of emotional value on contextual but not on non-contextual objects.We subsequently decomposed the interaction into simple effects. There was a significant effect of contextual value on neutral objects between 15.25 and 19.20 cpo; these SFs were correlated more negatively with RTs for contextual neutral objects than for non-contextual neutral objects  are associated with fast RTs for basic-level verification. This suggests that objects are processed particularly rapidly through these SFs. Although this interpretation is the most straightforward, it is also possible that object processing was at least partly completed before the presentation of the words and, therefore, that the RTs reflect remnants of object processing rather than object processing Another unique aspect of our study is the fact that we equalized SF content of the object images prior to their sampling. This allows us to interpret results more confidently in terms of content of internal representations. Indeed, if SF content is not normalized among stimuli, results most likely reflect an interaction of the stored representation with the information available in the stimulus. Unfortunately, few studies have applied this procedure. As a notable exception, Willenbockel et al.  did equaNo main effect of contextual or affective value was observed in the SFs correlating with the objects' fast identification. However, we found a significant interaction between affective and contextual values for SFs centered on 6 cpo (or 1 cpd). This indicates that these LSFs, those usually associated with the magnocellular pathway  also led to longer RTs for contextual emotional objects than for non-contextual emotional objects. The effect of contextual value on SF content of object representations had not been tested before but it had been often proposed that rapidly extracted LSFs are sufficient to activate representations associated with an object Bar, . Our datThe main findings of the present study are (i) that the SF content of object representations in general are in an intermediate band between 14 and 24 cpo (2.3–4 cpd), and (ii) that intrinsic high-level categorical properties of an object influence the SF content of its internally stored representation, more precisely that affective and contextual values interact in their modulation of the SF content of object representations.According to predictive accounts of brain function (e.g., Rao and Ballard, Our study cannot however address directly the issue of temporal dynamics of visual object recognition. While we observed that some SFs are more useful to identify some objects, we cannot conclude that these are extracted first. Further studies should address these issues and their links to potential initiation of top-down mechanisms.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.


We found and experimentally verified that the bipolar quantum Hall edge transport is drastically affected by the parity of the number of PNJs. This parity effect is universal in bipolar quantum Hall edge transport of not only graphene but also massless Dirac electron systems. These results offer a promising way to design electron interferometers in graphene.Parity effect, which means that even-odd property of an integer physical parameter results in an essential difference, ubiquitously appears and enables us to grasp its physical essence as the microscopic mechanism is less significant in coarse graining. Here we report a new parity effect of quantum Hall edge transport in graphene antidot devices with  Various parity effects, which mean that even-odd property of an integer physical parameter results in an essential difference, has been discovered in many physical systems, especially in mesoscopic physics. For example, the significance of the parity effect regarding the number of electrons is seen in the micron-sized superconducting island24579Since graphene, which is monolayer film of graphite, was first isolated111416171819202122pn junctions (PNJs). We study a graphene device with two types of regions in which the carrier types are n (electrons) and p (holes) which are arranged in series. The number of such regions is M + 1; therefore, the device has M PNJs. Furthermore, we place N antidots on all of the PNJs. The  =  (even case) and  (odd case) are schematically illustrated in N, depending on parity of M. We implemented the proof-of-concept experiments and established the parity effect using a graphene device, whose optical picture is shown in Here we report a new parity effect of QH edge transport in graphene antidot devices with several νtg and νbg as the Landau level filling factors of the two types of regions tuned by both the top- and back-gate voltages and by only the back-gate voltage, respectively. When we calculate the resistance, we obtain the two-terminal conductance using the Landauer-Büttiker formulaνtg) ≠ sgn(νbg), which is unique to graphene  = .).The resistance is obtained as M case. In this case, we obtain the conductance asNext, we discuss the odd R = G−1. The conductance increases as N increases, as found in the even M case. However, the conductance is quantitatively different from that in the even M case (Eq. (1)) in several aspects. First, the conductance dependence on N in the odd M case in Eq. (2) is expressed as a power of N, which is very different from the even M case in Eq. (1). In addition, we can obtain a peculiar result from Eq. (2), νbgνtg/(νbg + νtg) · e2/h, as N approaches infinity. This conductance is the same as that observed in graphene with  = . Furthermore, Eq. (2) is symmetric with regard to the exchange of νbg and νtg. The physical laws possess charge, parity and time (CPT) reversal symmetry. From parity (mirror) symmetry, the conductance in odd M case is demanded to be symmetric about the exchange of νbg and νtg, different from even M case. These unique properties in the bipolar regime originate from the difference in the chirality at the left and right  =  in N, which is only realised in bipolar QH edge transport.The resistance is obtained as M, the number of PNJs. Such fundamental difference, the parity effect, should be useful for not only graphene but also QH devices of massless Dirac electron systems, such as the surface state of topological insulators14These calculated results mean that the resistance formulas as a function of the number of antidots is strongly dependent on the parity of 2. We estimated the thickness of graphene from an analysis of contrast in the optical pictures. Then, we etched the graphene samples using an oxygen plasma and created an antidot in graphene, as observed in the inset of 28α and β in the inset of M, N) = ,, and  by controlling the number of PNJs.We implemented the following proof-of-concept experiments. While there are several reports regarding the transport in graphene PNJs in the QH regime18192021222326M, N) =  case. We applied a top-gate voltage to only the electrode marked as α in νbg and νtg. Vtg and back-gate voltage Vbg at 2 K and 7 T. Cross sections of the image plot at Vbg = 15, 6, −4, and −13 V are shown in pn’ and ‘np’. Several plateaus at which the resistance is almost constant exist in νtg and νbg, in bipolar regime from the resistance in unipolar regime. As shown in h/e2 in  =  =  shown in νtg, νbg) are also consistent with our calculated results. This calculated result for  =  is consistent with the resistance for the  =  case as reported beforeM = 1 case, so that we increase the PNJs to confirm the validity of Eq. (2).We begin with the  =  case (even case), where pnp and npn systems are realised for the condition of sgn(νtg) ≠ sgn(νbg). Experimentally, we applied the top-gate voltage β in Vtg and Vbg in units of h/e2. The image plot is not symmetric with regard to the exchange of the vertical and horizontal axes. This property means that the conductance should be non-symmetric about the exchange of νtg and νbg. Furthermore, we present the cross sections at Vbg = 15, 6, −4, and −13 V of pnp junctions without the antidot1819h/e2 in  =  =  case in νtg, νbg) =  =  case (odd case). We applied the same top-gate voltage to the two top-gate electrodes, α and β, in Vbg and Vtg. The image plot is symmetric with regard to the exchange of the vertical and horizontal axes; therefore, the conductance should be symmetric with regard to the exchange of νtg and νbg. Vtg = 15, 6, −4, and −13 V of νtg, νbg) = /((N + 1) + (1–r)/r), of FPIs arranged in series (not including the interference effect), which are constructed with N + 1 parallel beam splitters arranged in series (see the N = 1 case is shown in r = |νbg|/((M/2 + 1)|νbg| + M/2|νtg|) = Gh/|νtg|e2 and able to calculate the conductance representation without explicitly using the Landauer–Büttiker formula. In the graphene device, the edge states at the left (or right) side marked as ‘Input’, ‘Output1’, and ‘Output2’ in The confirmed parity effect in graphene antidot devices has a good analogy to optical systems, although the interference effect is not explicitly taken into account here. The conductance in the even case can be readily understood by comparing the Fabry-Perot interferometers (FPIs), which are constructed with two parallel beam splitters with reflectivity  see the . A schemνtg| = |νbg| can be viewed as the probability obtained at one port, (1–(1–2t)N + 1)/2, of N  in (1–(1–2t)N + 1)/2 gives Gh/|νtg|e2. A schematic picture of the N = 1 case is shown in In the odd case, we adopted Mach-Zender interferometers (MZIs) arranged in series, where two beams passing through a beam splitter of the MZI enter into the next beam splitter from different sides. This dependence with the condition of | see the . N + 1 aAs we discuss above, there are strong analogy between bipolar QH edge transport in graphene antidot device and optical interferometer. Thus, we believe that this system has a possibility to be a device for investigating interference effect of QH edge state in graphene. We ignored the interference effect between the edge states in our calculation and did not detect any interference pattern experimentally. This is because our device has not enough mobility so that the coherence length in the QH edge state is short. The higher quality graphene devices, such as graphene on h-BN substrate or suspended graphene will enable to measure the interference pattern.M case is a unique transport regime realised on graphene antidot devices or other QH devices of massless Dirac electron systems. Furthermore, we suggest that this difference characterised by the parity can be understood by considering the analogy between the QH edge transport and the optical interferometers. Our results may be available to construct electron interferometer in graphene.In conclusion, we have studied the bipolar QH edge transport phenomena around graphene antidots with several number of PNJs. We derived the formulas to calculate the conductance of graphene with the antidots and PNJs in the QH regime. We experimentally confirmed these formulas with devices having one, two, and three PNJs. Consequently, we have established the parity effect that the conductance dependence on the number of antidots relies on the even--odd parity of the number of the PNJs. In particular, the odd How to cite this article: Matsuo, S. et al. Parity effect of bipolar quantum Hall edge transport around graphene antidots. Sci. Rep.5, 11723; doi: 10.1038/srep11723 (2015).


The implementation of imaging techniques with low-energy electrons at synchrotron laboratories allowed for significant advancement in the field of spectromicroscopy. The spectroscopic photoemission and low energy electron microscope, SPELEEM, is a notable example. We summarize the multitechnique capabilities of the SPELEEM instrument, reporting on the instrumental aspects and the latest developments on the technical side. We briefly review applications, which are grouped into two main scientific fields. The first one covers different aspects of graphene physics. In particular, we highlight the recent work on graphene/Ir(100). Here, SPELEEM was employed to monitor the changes in the electronic structure that occur for different film morphologies and during the intercalation of Au. The Au monolayer, which creeps under graphene from the film edges, efficiently decouples the graphene from the substrate lowering the Dirac energy from 0.42 eV to 0.1 eV. The second field combines magnetism studies at the mesoscopic length scale with self-organized systems featuring ordered nanostructures. This example highlights the possibility to monitor growth processes in real time and combine chemical characterization with X-ray magnetic circular dichroism–photoemission electron microscopy (XMCD–PEEM) magnetic imaging by using the variable photon polarization and energy available at the synchrotron source. The cathode lens, or immersion objective lens, is used to image electrons emitted from surfaces . In a miDuring the evolution of PEEM , its firThe following provides an overview on SPELEEM methods along with the recent examples predominantly considering the activity carried out at the Elettra Sincrotrone Trieste. The first part of the paper is organized as an extended introduction to LEEM and XPEEM methodology. Then, we give a detailed account of the instrumental aspects specific to the SPELEEM instrument at Elettra.The bulk of this work is dedicated to applications of the SPELEEM technique. We put special emphasis on graphene, which has been extensively studied by using cathode lens microscopy, LEEM in particular, with numerous studies of epitaxial graphene grown on a variety of transition metal and silicon carbide supports. These microscopy experiments have been carried out by using well-established methodologies, which were formerly developed for the analysis of ultra-thin metal films on single crystal surfaces . These mLow energy electron microscopy (LEEM) is a surface-sensitive method based on the elastic backscattering of low energy electrons ,11. The Contrast mechanism. Among all contrast mechanisms available in LEEM, “diffraction contrast” is the one that is most commonly used. This is derived from the strong energy dependence of electron diffraction intensities, making LEEM suitable for studying crystalline systems  axis, appear gray as they do not produce an XMCD signal. The black and white regions evident in the central wires are the dipolar domains with magnetization parallel and antiparallel to the beam direction, respectively. Note that the strong magnetic contrast in the case of Fe nanowires is visible even in the single XAS image acquired with circular polarization as seen in The XMCD-PEEM imaging is illustrated in Core and valence band spectroscopy. Contrary to XAS-based PEEM, X-ray photoelectron spectroscopy requires a filtering of the kinetic energy of the photoemitted electrons [lectrons . TherefoDark-field PEEM is the analogue of the dark-field method in LEEM, such that the same contrast aperture  is used to filter out everything except the emission along a given angle. From a practical standpoint, the main difference of the dark-field XPEEM operation is the necessity to change the sample tilt angle in order to get the diffraction feature through the aperture [aperture –23. The 6 electron gun and dedicated illumination optics with three condenser lenses, which can deliver a well-collimated e-beam on the sample. In XPEEM operation, instead, the sample is illuminated by the monochromatized X-ray beam produced by the insertion device in the synchrotron ring.Although LEEM and PEEM are widespread, only few instruments that combine both methods can be found in synchrotrons. Some prominent ones are situated at ALBA (Spain), BESSY (Germany), Diamond (UK), MAXLAB (Sweden), NSLS (USA), SOLEIL (France) and SPRING-8 (Japan). Among these, the end station of the Nanospectroscopy beamline at Elettra, the 3rd generation storage ring in Trieste, hosts a spectroscopic photoemission and low energy electron microscope (SPELEEM) . This miA photograph of the experimental apparatus is shown in Electron source. The SPELEEM is equipped with an LaB6 thermionic emission cathode . The emitter is a single crystal cut to a cone angle of 60° exposing a  microfacet of 6 μm diameter as tip, which offers high electron flux at a relatively low temperature of the emitter. In the SPELEEM instrument, the electron beam has a flux density of up to 1 × 1016e−/cm2·sec at the surface. The illumination optics focus the beam on the sample to a slightly elliptical shape with diameter of about 90 μm.6 source is set by its operation temperature, reaching 1900 K at a current of 2.12 A. 6 temperature. By fitting the curve with a Fermi function, we determine a tip temperature of about 1750 K. The sharp rise on the left hand side represents the effect of the instrumental broadening. The broadening obtained from this leading edge is about 65 meV, providing a best estimate for the energy resolution of our electron energy analyzer in LEEM operation. Note that this figure is not limited by the size of the contrast aperture, as the angular spread in LEEM is smaller than the aperture size.The energy spread of the LaB−1. This corresponds to a transfer width of more than 130 Å in real space.The transfer width of the system was measured from the profile of the (00) specular diffraction spot originating from a virtually step-free region of a W(110) crystal, as shown in X-ray source. Two Apple-II type undulators provide an intense X-ray beam with linear horizontal, linear vertical, or circular polarization from below 10 eV up to 1000 eV [2 (H × V), horizontally elongated because of the grazing incidence. A larger area (up to 30 μm) can be illuminated by slightly defocusing the photon beam and by moving it along vertically during image acquisition, although this method usually causes striations in the illumination. The maximum flux is obtained at about 150 eV photon energy and is about 1.8 × 1013 photons/s with the exit slit of the monochromator set to 10 μm and with 200 mA synchrotron ring current [ 1000 eV ,27–28. T current .Energy resolution in XPEEM. The photon source and the SPELEEM operation mode together determine the value of the energy resolution. The resolving power of the VLS400 grating of the beamline monochromator, E/ΔE, is about 3000 for the photon energy range from 700 to 1000 eV. This figure nearly doubles at lower photon energies [μ-spectroscopy operation, in which the dispersive plane of the analyzer is imaged onto the detector. In this way, the resolution is mainly determined by the radius of the analyzer hemisphere (r0 = 10 cm), the pass energy (E = 908 eV), and the angular spread before the analyzer (α = 5 mrad full width) given by the size of the contrast aperture , which also acts as the entrance slit. The energy spread ΔE  is parameterized as [In energy-filtered imaging and diffraction, where images are collected at a well-defined photoelectron kinetic energy, the energy resolution is mainly determined by the size of the analyzer exit slit. Two slits of different width can be used to set the bandpass of the energy filter, corresponding to energy windows of 0.33 eV and 0.79 eV, respectively. Note that the best energy resolution from the instrument can be obtained in the rized as :Inserting the values listed above, the best resolution is estimated to be 101 meV. The experimental energy resolution of the SPELEEM was measured from the W 4f core level of the clean W(110) surface. The dispersive plane spectrum and the corresponding Doniach–Šunjić fit are displayed in Lateral resolution. The SPELEEM spatial resolution is mainly determined by the spherical and chromatic aberrations of the objective lens. LEEM performs better compared to XPEEM. Low energy electron diffraction beams are generally much sharper than the broad photoelectron emission angles. As a result, the angular spread  in LEEM is considerably reduced compared to XPEEM. The same is true also for the energy spread and the chromatic aberrations, which are again reduced in the case of LEEM. The lateral resolution in LEEM mode for the SPELEEM at Nanospectroscopy is demonstrated in 6 cathode providing a much lower current density than the peak photoelectron current in XPEEM.The spatial resolution in XPEEM is about 30 nm . For com−5 mbar, still ensuring a lateral resolution nearing 10 nm. The growth of graphene on a variety of transition metal substrates provide catching examples of the potential of the LEEM method [I(V) curves [LEEM has found ample use in graphene research with its high structural sensitivity and video acquisition rate allowing for dynamic measurements of film growth. In such experiments, graphene is typically obtained by the chemical vapor deposition (CVD) technique. CVD utilizes transition metal catalysts as a means to promote the dissociative adsorption of gases such as ethylene or methane, which can readily deliver the carbon atoms required for island nucleation and growth. LEEM is widely employed to image the growth process; the accessible parameter space is explored by varying the gas pressure and/or sample temperature in a manner compatible with the operation limits of the instrument. In this regard, LEEM permits operation at elevated sample temperatures (approximately up to 1000°C) by using the experimental chamber as a gas flow reactor up to pressures approaching 1 × 10M method –37. For M method –38. In oM method –41. As a) curves .2-supported and suspended exfoliated graphene films [An important aspect is the integration of LEEM with low energy electron diffraction (LEED). Diffraction experiments permit a full characterization of the crystal structure and quality of graphene. For instance, μ-LEED methods have been devised to quantify the short-range roughness of multi-thickness SiOne films . To datene films . On the ne films . The litne films –48, nickne films  and on nne films –51 and Fne films .* resonance was observed in multilayers and ascribed to specific interlayer states [There is also a growing literature on XPEEM applications in graphene research. In particular, μ-ARPES available in the SPELEEM has been successfully applied to exfoliated –54 as wer states .The intercalation of Au below graphene on Ir(100). Recently investigated by using a wide range of microscopy methods and theory, the graphene/Ir(100) system exhibits unique morphological and electronic properties, which originate from the different film and substrate symmetries [K point of the π-band. These results point to the disruption of the Dirac cones and the formation of a metal-like DOS. Surprisingly, the hybridization of the π-band with Ir states is due to the chemisorption of just 11% of the C atoms in the unit cell of the buckled phase [mmetries . At temped phase .Ir(100) ) per minute at a sample temperature of about 600 °C.In order to modify the graphene–substrate interaction in this system, we have intercalated Au at elevated sample temperature, taking advantage of the fast diffusion of Au adatoms under such conditions. Au is expected to exert a weaker interaction than Ir, hindering the formation of the chemisorption bonds such as those observed in the buckled graphene phase on Ir(100). In our work, the related variations in C–substrate bonding and the electronic structure of graphene were quantified in μ-XPS and μ-ARPES experiments, taking the pristine graphene/Ir(100) system as reference. Experimentally, Au was deposited by using an e-beam evaporator (Elmitec GmbH) at a flux of 0.059 eMLThe evolution of the interface upon increasing Au dose was monitored in situ employing LEEM. Ir(100) [There are two interesting findings that need to be highlighted. First, it appears that Au can intercalate below graphene only after accumulation of a full Au ML at the island edges, and before the nucleation of second or multilayer Au islands. Second, small graphene islands nucleate at the Au-covered surface far from the large graphene crystal, as was verified by μ-LEED analysis. The former observation gives the order of energetics for Au adsorption on Ir versus its intercalation under graphene. The intercalation is facilitated by the lifting of the chemisorbed graphene edges upon Au adsorption at the edges. To explain the appearance of small graphene islands on Au, we must consider that 0.1 ML carbon is chemisorbed to the Ir surface, forming a carbidic c(2 × 2) structure . In suchIr(100) . We noteIr(100) . Due to Upon subsequent cooling to room temperature, the morphology and structure of graphene remain unchanged. In fact, we could not detect any evidence of phase transformation or formation of stripe-shaped domains resembling those of observed on Ir(100). Instead, LEEM imaging at high lateral resolution evidenced the formation of wrinkles in the graphene film, a process which helps relieving the thermal strain, because of the different thermal contraction of film and substrate. Similar features have been previously observed for graphene on Pt(111) and Ir(111) surfaces –62. ImpoThe C 1s μ-XPS spectrum of the graphene/Ir(100) system exhibits two components. The dominant one, at about 283.95 eV binding energy, has been previously ascribed to physisorbed C , consistEF shown in (a) instantly reveals that Au intercalation is manifested by a change in the doping: The circular features identifying the Dirac cones for the graphene/Au system appear narrower than those recorded on pristine graphene, suggesting that the Dirac energy is now closer to the Fermi level. By accurately fitting of momentum distribution curves we could determine a positive doping of just 0.09 ± 0.06 eV for graphene/Au/Ir(100), which has to be compared with the value of 0.42 ± 0.03 eV obtained on graphene/Ir(100) [μ-ARPES data for the graphene/Au/Ni(111) system [π-band moving by approximately 2 eV; the Dirac energy ED is found at just 25 meV above the Fermi level, so that quasi free-standing conditions for the film are claimed. Referring to an analytical model [Clearly, the Au layer induces important variations in the graphene–substrate interaction, which in turn affect the charge transfer processes occurring between substrate and film and, consequently, the doping. /Ir(100) . Our res) system . On the al model –66, the al model .Self-organization may be ascribed the general meaning “spontaneous appearance of a particular form”. Even though the definition may be stretched about to describe nearly all observed shapes in nature, static and dynamic, we assign the term to the formation of regular structures. SPELEEM methods perfectly lend themselves to studies of self-organization phenomena, particularly in the field of nanomagnetism. In a nutshell, LEEM is used to monitor the growth process in real time at high temperatures; spectromicroscopy with XPEEM provides the chemical map of the resulting heterogeneous surface; and finally XMCD-PEEM reveals the magnetization distribution of this nanostructured surface.Stress-induced adsorbate stripes have been recently observed on crystalline surfaces at high temperatures. The mechanism is based on the competition between the cost of a boundary and the gain due to long range elastic interactions between boundaries [undaries . The temundaries .In the case of monolayer Pd stripes on W(110) forming at about 1100 K , it was 3 absorption threshold has confirmed the expected Fe distribution as seen in  direction perpendicular to the stripe axis, as shown in the XMCD map in The stability of the Pd–O stripes on W(110) at lower temperatures allows for a further growth of magnetic wires following the self-organized template. Fe/Pd–O stripes on W(110) have been demonstrated very recently . XPEEM iIron oxides find wide application in several fields of research, among others magnetism and heterogeneous catalysis. In both cases, the heteroepitaxial growth of nanostructured FeOx offers a versatile means to tune the material properties. Recently, SPELEEM techniques were applied to characterize the reactive growth of FeOx on Ru(0001) [−7 mbar) at 900 K resulted in the formation of perfectly triangular micrometer-sized Fe3O4 islands on a FeO wetting layer. The combination of spatially-resolved XPS and XAS spectra, along with μ-LEED patterns, allowed the unequivocal identification of the specific iron-oxide phases.Ru(0001) . Fe growFrom the screening of substrate core-level photoelectrons, the thickness of the micrometer-sized magnetite islands was found to be about 1 nm, which corresponds to two unit cells . XMCD-PE3O4 films on Pt(111) are known to give a (2 × 2) reconstruction with an additional moiré superstructure. Nevertheless, the details of the Fe3O4 surface structure is still under study. The recent work by using an aberration-corrected XPEEM-LEEM setup, SMART , showed distinct differences between LEED I(V) curves obtained from surfaces with differing preparation pathways [3O4(111) surface as summarized in Beyond the self-organized crystal shapes at the micrometer scale, epitaxial iron-oxide films provide a variety of complex surface reconstructions at the atomic scale as usual for oxide surfaces . Fe3O4 fpathways . The rolx growth on Ru(0001), further oxidation by using NO2 as atomic oxygen source resulted in the transformation of the FeO wetting layer to hematite (α-Fe2O3) and the triangular Fe3O4 islands to maghemite (γ-Fe2O3) [Aside structure and magnetism, transformations between different iron-oxide phases were studied by using the SPELEEM methods. In the above example of FeOγ-Fe2O3) . In an iγ-Fe2O3) . In partWe have given a review of SPELEEM methods along with recent applications in the fields of graphene and nanomagnetism. The extensive introduction to LEEM and XPEEM techniques illustrates the basic operation principles, with the intention to serve as a guideline for those unfamiliar with the field. A working example of a SPELEEM instrument is the one available at the Nanospectroscopy beamline at Elettra. Details on the instrumental aspects of the Nanospectroscopy microscope have been given both as an update on the performance of this particular setup, and also as a reference for the typical SPELEEM properties regarding parameters such as energy resolution, lateral resolution, electron beam characteristics and the transfer function of the instrument. After the instrumental part, recent scientific activity in graphene research by using LEEM-PEEM methods have been reviewed. Then, the original example of Au intercalation at the graphene–Ir(100) interface has been presented, showing the effective role of Au in breaking the C–Ir chemisorption bonds and in restoring the neutral Dirac point nearly at the Fermi level. The review has been concluded with examples on self-organized nanomagnetism studies taking advantage of the possibility to perform magnetic imaging with an XPEEM, based on the X-ray magnetic circular dichroism contrast.


Sarcoidosis is a relatively uncommon condition in children. Reports from multiracial societies such as the USA indicate that sarcoidosis is more common in Africans than other racial groups. However, few reports of cases of childhood Sarcoidosis have been published from sub-Saharan Africa to shed light on the burden of sarcoidosis and the demographics and clinical presentation of children diagnosed with sarcoidosis.To describe the occurrence and clinical presentation of Sarcoidosis among children seen at the rheumatology clinics in two referral hospitals in Cape Town, South Africa.We conducted a search for patients with a diagnosis of sarcoidosis in the pediatric rheumatology data base of the two referral hospitals affiliated to the University of Cape Town. The proportion of the patients with a diagnosis of sarcoidosis, their demographic and clinical features was then determined.st child presented with recurrent acute uveitis from the age of 4 years and iris nodules (probable ocular sarcoidosis). The second had acute respiratory distress, lymphadenopathy and hemophagocytic lymphohistiocytosis. Both had raised serum Angiotensin Converting Enzyme (ACE) levels. The 3rd patient had polyarthritis and skin nodules. The 4th, an HIV positive boy, presented with respiratory distress, skin lesions and neuropathy . The second, 3rd and 4th patients had non caseating granulomas on tissue biopsy suggestive of sarcoidosis.A total of 251 Patients were in the data base by the time of the review; 4 (1.6%) had a diagnosis of sarcoidosis. They were aged 10, 4, 17 and 15 years at study time point; 4, 3.5, 11 and 14.5 years at onset of symptoms; and 10, 3.5, 16 and 14.5 years respectively at diagnosis. Three were female. Of the 4 patients, 2 were black and 2 colored. The 1Three of the 4 patients (only 1 of whom had positive tuberculin skin test) were treated for TB in the course of their illness before Sarcoidosis was identified as the cause of the symptoms. This was despite attempts to identify mycobacteria by microscopy, culture and GeneXpert on body fluids and biopsy specimen yielding no evidence of mycobacterial infection. The decision to treat for TB was mainly based on clinical and abnormal chest radiograph findings. Treatment for sarcoidosis was instituted with prednisone and methotrexate in 3 patients and methotrexate alone  in 1 patient. Three of the patients have shown good response to treatment while the patient with polyarthritis and skin nodules has had an unremitting disease course.Though Sarcoidosis is a rare disease in children, it still constitutes a significant proportion of pediatric rheumatology consultations. Children with sarcoidosis may present with clinical and radiological features similar to TB presenting a challenge to clinicians on differentiating them especially in the high TB burden countries in sub Saharan Africa. However, where clinical, laboratory and radiological investigations do not fully support TB infection in TB suspects, Sarcoidosis and other granulomatous inflammatory conditions should be considered and be investigated appropriately.None declared.