We suggest an information-theoretic approach for measuring stylistic coordination in dialogues. The proposed measure has a simple predictive interpretation and can account for various confounding factors through proper conditioning. We revisit some of the previous studies that reported strong signatures of stylistic accommodation, and find that a significant part of the observed coordination can be attributed to a simple confounding effect—length coordination. Specifically, longer utterances tend to be followed by longer responses, which gives rise to spurious correlations in the other stylistic features. We propose a test to distinguish correlations in length due to contextual factors  and turn-by-turn coordination. We also suggest a test to identify whether stylistic coordination persists even after accounting for length coordination and contextual factors. Thus, such claims are susceptible to various confounding effects. For instance, it is known that there is significant length coordination in dialogues, in the sense that a longer utterance from user m user X . Thus, itime-shifted mutual information. The proposed coordination measure characterizes the dependence between the stylistic features of the original post and the response. In addition, we provide a computational framework to account for confounders when measuring stylistic coordination.Here we attempt to remedy the problem and propose an information-theoretic framework for characterizing stylistic coordination in dialogues. Namely, given a temporally ordered sequence of utterances  by two individuals, we characterize their stylistic coordination with We revisit some of the case studies where linguistic coordination was reported and demonstrate that a significant part of the observed correlations in linguistic features can indeed be explained by length coordination rather than stylistic accommodation. In particular, most stylistic features that exhibit statistically significant correlation exhibit little to no correlation after length coordination has been taken into account.We also focus on the observed length correlations, and examine whether it is due to turn-by-turn coordination between the participants, or can be attributed to other contextual factors. We construct a statistical permutation test and demonstrate unequivocally that turn-by-turn length coordination in dialogues indeed takes place. Finally, we develop a similar test for stylistic features, and demonstrate that at least for one of the datasets, the remnant coordination (after conditioning on length) cannot be explained by contextual factors alone and has to be due to turn-by-turn level coordination between the speakers.To represent stylistic features in utterances, we use Linguistic Inquiry Word Count (LIWC) , which im, and K is the total number of exchanges in a dialogue. Since we focus on coordination between the same stylistic markers, we will drop the superscript m from now on. We use the convention O to represent the originator—the person who is producing the original utterance in a single exchange, R to represent the respondent—the person who is replying to the originator.Each dialogue is a sequence of utterance exchanges between two participants. Following , 5 we bip be the joint distribution of the random variables O and R. We characterize the amount of stylistic coordination using Mutual Information (MI) [H(O) = −∑p(o) log p(o) is the Shannon entropy of O, and H(O∣R) is the entropy of O conditioned on R. Note that in our case the arguments are temporarily ordered: O is always the initial utterance, and R is the response, so that Let ion (MI) ; see S1 m in an utterance of O’s can help to predict R’s usage of m in the immediate response. In contrast to linear correlation measures, mutual information is well suited for handling strongly non-linear dependencies.Recall that mutual information between two variables measures the average reduction in the uncertainty of one variable, if we know the other variable. Thus, in essence, the proposed measure of stylistic coordination quantifies how the use of a marker after conditioning on a third variable, Z, via Conditional Mutual Information, defined asI(O : R∣LR), where LR is the length of the utterance by user R.We measure the correlation between two variables O and R. We could do this by first calculating the empirical distribution p and then using plug-in estimator tends to underestimate the entropy of a system. Instead, here we use the statistical bootstrap method introduced by DeDeo et al. [Given a set of samples o et al. , which ao et al.  for morek-nearest neighbors to each point, and then average the mutual information estimated from the neighborhood of each point. It has been shown that this estimator is asymptotically unbiased and consistent. Discussion of different entropy estimators can be found in [While the above discrete estimator works well for evaluating mutual information between discrete stylistic variables, it is not very useful for evaluating mutual information between two length variables, due to limited number of samples we have. Instead, we will use a continuous estimator introduced by Kraskov et al. . This nofound in  and refenon-Admins. All of the users interact with each other on Wikipedia talk pages, where they discuss issues about specific Wikipedia pages. We focus on dialogues where each participant make at least two exchanges within a dialogue, which results in over 30,000 utterances.We applied our coordination measures to two datasets previously studied in : oral trO and R who have participated in a dialogue. Unfortunately, most pair-wise exchanges are rather short and do not produce sufficient samples for evaluating mutual information or conditional mutual information. Instead, we group the individuals according to their roles, and then use aggregated samples to calculate stylistic coordination between the groups. The groups correspond to Judges and Lawyers for the Supreme Court data, and Admins and non-Admins for the Wikipedia data.Ideally, we would like to calculate linguistic accommodation between any pair of individuals I(O : R) and I(O : R∣LR). The bias in estimators for conditional mutual information and mutual information are generally different. Therefore, rather than estimating mutual information directly, we use a conditional mutual information estimator where we condition on randomly permuted values for LR. We repeat this procedure for four hundred times to produce 99% confidence intervals for I(O : R) (blue bars). The green bars give the 99% confidence intervals in case there is no stylistic coordination by estimating CMI with R’s utterances permuted (erasing any stylistic coordination).Impersonal Pronoun, Article, and Auxiliary Verb are reduced by factors of ∼ 6.7, ∼ 4.8, and 5.3, respectively, after conditioning on length. For the feature Conjunction, the 99% confidence interval of coordination score is above the confidence interval of zero information before conditioning, and falls into the confidence interval of zero information after conditioning. Similarly, in Impersonal Pronoun, Article, Adverb, Preposition, Quantifier) become practically zero after conditioning, suggesting that the observed coordination in those stylistic features are due to length correlations.The blue dots show the mutual information between the corresponding stylistic features, and suggest strong linguistic correlations between the groups. This effect, however, is strongly diminished after conditioning on the length of utterances (red dots). For instance, the coordination scores on features A similar picture holds for the Wikipedia dataset shown in directionality, in stylistic coordination. For instance, by comparing Fig Another interesting observation is that there is significant asymmetry, or To conclude this section, we note that some of the correlations in stylistic features persist even after conditioning on length. One can ask whether this remnant correlation is due to turn-by-turn level linguistic coordination, or can be attributed to other confounding factors. We address this question in detail later in the text.Alice and Bob are always conversing using short statements, while in another conversation they exclusively use long statements, perhaps due to different topics of conversation. Length coordination is found if data from these two conversation is aggregated, however, this coordination only reflects Alice’s and Bob’s response to the topic of conversation. More generally, aggregating data might lead to effects similar to Simpson’s paradox [As discussed in the previous section, the observed correlations in linguistic features can be attributed to coordination in the length of utterances. Here we analyze this phenomenon in more detail. In particular, we are interested whether the observed length correlations are due to turn-by-turn coordination, or can be attributed to other contextual factors. For instance, consider a scenario that in one conversation,  paradox .contextual factors), consider the Bayesian network model that incorporates both contextual factors and length coordination, as shown in LO and LR are random variables representing the length of an utterance by the originator O and the respondent R, respectively. In the model with both solid and dashed lines in LO explicitly influences LR. While if we only have the soild lines in LR is independent of LO after conditioning on the context C. Thus, the model in C can vary within a single conversation, for example, the theme of a conversation may change as time goes by. But for simplicity, we will assume that the contextual factor C does not change within the dialogue or conversation.To understand the possible extent of various confounding factors  is given by the following conditional mutual information:OLC) asOLC captures not only the length coordination in a turn-by-turn level, but also the confounding behaviors between LO, LR and C. In fact, OLC can be decomposed into two items:interaction information [co-information [LO, LR and C.A direct measure of Turn-by-turn Length Coordination (ormation  or co-inormation ), and chTLC described in LO and LR are conditionally independent of C if and only if TLC = 0. However, direct evaluation of TLC is not possible due to the lack of sufficient number of samples, e.g., the number of exchanges within a specific dialogue. Nevertheless, it is possible to test the turn-by-turn length coordination by a non-parametric statistical test as shown below.A straightforward method to test for turn-by-turn coordination is to evaluate Our null hypothesis is that there is no turn-by-turn coordination, so that all observed correlations are due to contextual factors. We now describe a procedure for testing this hypothesis.c from originator o and respondent r as:kth exchange (two utterances) by the originator o and respondent r in dialogue c, and Kc represents the total number of exchanges in c. We also define the aggregated set of exchanges of user o ∊ O and user r ∊ R as:Co,r represents all the dialogues that involved user o and r. We can rewrite SO ← R element-wise asN = ∣SO ← R∣ representing number of samples. For each triplet of right hand side in Rk is the reply utterance to Ok in the dialogue Ck. Finally, from SO ← R we obtain the setlen (⋅) is a function representing the length of an utterance.We denote the pairwise set of exchanges in a specific dialogue r’s utterances in the set So ← r,c:LO and LR are conditionally independent from each other given C. Then, it is easy to see that under this null model, the samples L(SO ← R) and p. This observation suggests the following test: We first estimate OLC from the sample L(SO ← R) (denoted as OLC0) and then using the within-dialogue shuffled samples OLC1). Under the null hypothesis, these two estimates should coincide. Conversely, if OLC0 ≠ OLC1, then the null hypothesis is rejected, suggesting that there is turn-by-turn length coordination.Consider now another sample, which is obtained by randomly permuting the respondent The above procedure, which we call Turn-by-Turn Length Coordination Test, is a conditional Monte Carlo test . The maiOLC0) before permutation. The Turn-by-Turn Length Coordination test shows that the mutual information decreases significantly after permutation, rejecting the null hypothesis that LO and LR are independent after conditioning on the contextual factor C. In other words, the contagion of length exists from the original utterance to the reply on a turn-by-turn level.The results of this test are shown in OLC is higher for Wikipedia than for the Supreme Court. However, one cannot make a general conclusion about the exact magnitude of turn-by-turn length coordination (TLC) simply by calculating the loss, i.e., OLC0 − OLC1.For the results on the Wikipedia discussion board in Personal Pronoun in Fig We demonstrated in the previous section that strong correlations in utterance length explain most of the observed stylistic coordination. However, in some situations, there are statistically significant non-zero signals even after conditioning on length, e.g., the first feature dimension LO and LR; stylistic variables m, and the contextual  variable C. The solid arrow from LO to LR reflects our findings from the last section about the existence of turn-by-turn length coordination. The dashed arc between the features C, C, Toward this goal, consider the Bayesian network in m:m appears or not in an utterance. Also, the Overall Stylistic Coordination(OSC) is defined asOSC is exactly the conditional mutual information introduced in C.  with respect to a specific style feature  path in )TSC in TSC is hard to evaluate due to lack of sufficient samples. Furthermore, the shuffling test from the previous sections is not directly applicable here either, because it needs to be done in way that keeps the correlations between LO and LR intact: In other words, one can exchange utterances that have the same lengths. Since most dialogues are rather short, this type of shuffling test is not feasible, and one needs an alternative approach.Again, a direct measure of turn-by-turn stylistic coordination corresponds to non-zero OSC = TSC. Thus, the null hypothesis is that there is contextual level coordination in stylistic features. We emphasize that by contextual coordination, we are actually referring to the links from C to FO and C to FR in Our proposed test is based on the following idea: if we can rule out the influence of the contextual factors on stylistic correlations, then any non-zero conditional mutual information can be only explained by turn-by-turn stylistic coordination, i.e., SO ← R as:fm (⋅) is a binary function represents whether the style feature m in an utterance appears or not.We follow the same notation and methodology used in previous sections. By OSC1 using the shuffled sample OSC1 is larger than zero, then there is necessarily contextual coordination. On the other hand, if OSC1 = 0, then all the observed stylistic correlations  must be due to turn-by-turn stylistic coordination.Consider now the shuffling procedure: we randomly permute respondent’s utterances within a dialogue and obtain the set OSC1 are within the zero-information confidence intervals, indicating that non-zero conditional mutual information (OSC before shuffling) cannot be attributed to contextual factors. In other words, the remnant correlations that are not explained by length coordination must be due to turn-by-turn level coordination.Let us first consider the results of the above test for the Supreme Court data. From Fig OSC), the results of the above permutation tests are rather inconclusive. Namely, although the confidence intervals of OSC1 do overlap with the zero information confidence intervals, one cannot state unequivocally that they are zero. In other words, one cannot rule out the null hypothesis that the remnant stylistic coordination is due to the contextual factors rather than turn-by-turn coordination.The situation is different for Wikipedia data. Indeed, Fig Mutual Information(MI) as a theoretically motivated measure of dependence to characterize the amount of stylistic coordination between the originator and the respondent in the dialogue. Moreover, by introducing Conditional Mutual Information(CMI), which allows us to measure the correlation between two variables after conditioning on a third variable, we are able to more accurately gauge stylistic accommodation by controlling for confounding effects like length coordination.In conclusion, we have suggested an information theoretic framework for measuring and analyzing stylistic coordination in dialogues. We first extracted the stylistic features from the dialogue of two participants and then used We then used the proposed method to revisit some of the previous studies that had reported strong stylistic coordination. While the suggestion that one person’s use of, e.g., prepositions will (perhaps unconsciously) lead the other to use more prepositions is fascinating, our results indicate that previous studies have vastly overstated the extent of stylistic coordination. In particular, we showed that a significant part of the observed stylistic coordination can be attributed to the confounding effect of length coordination. We find that for both Supreme Court and Wikipedia data, the coordination score is greatly diminished after conditioning on length. We also find that the significant asymmetry in stylistic coordination shown in the previous study  is drastLO, LR and C, the mutual information I(LO : LR) > 0, while I(LO : LR∣C) = 0. If we only look at the aggregated data, averaging over all contexts, C, i.e., I(LO : LR), there will be artificial mutual information between LO and LR. Ideally, we could calculate I(LO : LR∣C) directly, however, there may not be enough samples for us to calculate the conditional mutual information for all values of C. How can we still determine whether I(LO : LR∣C) is zero or not while using all the data? We thus designed non-parametric statistical tests to solve this problem in general while making full use of the available data. More importantly, because these information-theoretic quantities directly reflect constraints on graphical models, the mystery of Simpson-like paradoxes is replaced with concrete alternatives for generative stories as depicted in Figs Simpson’s paradox provides a famous example of how correlations observed in a population can disappear or even be reversed after conditioning on sub-populations. In an information-theoretic framework setting, a similar “paradox” can be seen in the example illustrated by We also observed that for some of the stylistic markers, there was diminished but still statistically significant correlations even after conditioning on length. We again designed a non-parametric statistical test for analyzing this remnant coordination more thoroughly. Our findings suggest that for the Supreme Court data, the remnant coordination cannot be fully explained by other contextual factors. Instead, we postulate that the remnant correlations in the Supreme Court data is due to turn-by-turn level coordination. For the Wikipedia data, however, our results are less conclusive, and we cannot draw any conclusion about turn-by-turn stylistic coordination. Thus, caution must be taken when making general claims about the possible origin of stylistic coordination in different settings.It is possible to develop alternative tests based on a more fine-grained, token-level generative models. The main idea behind such a test is to shuffle the word tokens uttered by an individual within each dialogue, which should destroy turn-by-turn coordination. Our preliminary results based on this test suggest that most of the remnant correlations are indeed due to turn-by-turn coordination. However, we emphasize that this test requires an additional assumption whose validity needs to be verified, namely that the words used by a given speaker within a conversation are independent and identically distributed (i.i.d.). Furthermore, the test assumes stationarity, i.e., that the contextual factors do not vary within the course of the dialogue. While this assumption seems reasonable in the dialogue settings considered here, it is important to note that deviations from stationarity might be yet another serious obstacle for identifying stylistic influences , 20. Indhistorical and ahistorical mechanisms of lexical entrainment [While our work focuses on linguistic style matching, we believe that the information-theoretic method proposed can be useful for studying more general types of linguistic coordination in dialogues, such as structural priming , 22, or rainment . Indeed,In a broader context, we note that sociolinguistic analysis has been used for assessing and predicting societally important outcomes such as health behaviors, suicidal intent, and emotional well-being, to name a few examples –29. ThusS1 File(PDF)Click here for additional data file.S2 File(PDF)Click here for additional data file.


LINE-1 (L1) is the most abundant mammalian transposable element that comprises nearly 20% of the genome, and nearly half of the mammalian genome has stemmed from L1-mediated mobilization. Expression and retrotransposition of L1 are suppressed by complex mechanisms, where the key role belongs to DNA methylation. Alterations in L1 methylation may lead to aberrant expression of L1 and have been described in numerous diseases. Accumulating evidence clearly indicates that loss of global DNA methylation observed in cancer development and progression is tightly associated with hypomethylation of L1 elements. Significant progress achieved in the last several years suggests that such parameters as L1 methylation status can be potentially utilized as clinical biomarkers for determination of the disease stage and in predicting the disease-free survival in cancer patients. In this paper, we summarize the current knowledge on L1 methylation, with specific emphasis given to success and challenges on the way of introduction of L1 into clinical practice.  Only about 1% of the genome is comprised of genes while the vast majority is comprised of repetitive elements—retrotransposons, transposons, satellite, and tandem repeats. The first two are also known as mobile or transposable elements, since they are capable of moving within the genome. While the more ancient class—transposons—uses the “cut-and-paste” mechanisms, retrotransposons relocate via an RNA intermediate in a “copy-and-paste” mechanism.It is becoming increasingly evident that transposable elements are tightly associated with the generation of genetic diversity and can influence the expression of numerous genes. Specifically, transposable elements can affect the integrity of the genome by retrotransposition, resulting in potential insertions and deletions within the coding sequences, as well as genomic rearrangements—by shuffling genomic fragments by 5′ and 3′ transduction and recombination between the homologous elements. Additionally, transposable elements have capacity to affect gene expression by numerous mechanisms, such as providing alternative promoters, silencing by transcriptional or RNA interference (RNAi), and creating cryptic splice sites and polyadenylation signals –4.Two major classes of retrotransposons are long-terminal repeats (LTR) and non-LTR elements. The former are named for their long-terminal repeats flanking the internal proviral sequence on both sides. LTRs are structurally related to exogenous retroviruses, although lacking the ability to move from one cell to another. Two families of these endogenous retroviruses are known to be currently active in mice . ActivitThere are about 516,000 copies of LINE-1 (L1) in the human genome prevalently located within its gene-poor regions, reaching up to 20% of the human genome . HoweverPropagation of L1 in mammalian genomes occurs via the process of autonomous retrotransposition. Current endogenous retrotransposition activity of some recent L1 elements determines the widespread genomic structural variations within and between populations and variations in normal development, neuronal differentiation, and human cancers , 19–22. cis-preference followed by the entrance of RNP into the nucleus [Transcription of the L1 full-length mRNA from the internal promoter, mediated by the RNA polymerase II, initiates L1 retrotransposition. This mRNA then is transported to the cytoplasm, where it is translated to ORF1p and ORF2p—L1-encoded proteins that preferentially associate with their encoding RNA . The L1  nucleus . Next, aMobilization of L1, thus, occurring via a “copy-paste” mechanism is associated with a number of events, including the development of novel gene promoters, splice sites, polyadenylation signals, dispersing transcription binding splice sites, linking genes in transcriptional networks, and facilitating the evolution of novel traits (reviewed in ).DNA methylation is one of the most important mechanisms for the regulation of genetic information and one of the key mechanisms for silencing repetitive elements (reviewed in ). It is Silent transcriptional status of L1 has been associated with DNA methylation, specifically within the 5′-UTR, that contains both L1 promoters and is rich in CpG sites. Demethylation of L1 by exogenous stressors, DNA demethylating agents (5-azacytidine), or in disease has been associated with its aberrant transcription –29. DNA Other epigenetic mechanisms have also been reported to be involved in the regulation of L1 expression. For example, acetylation and methylation of histones have been implicated in silencing of L1 retrotransposition in embryonic carcinoma cell lines . Accumul Factor VIII gene that prevented synthesis of functional coagulation factor [β-thalassemia, and diabetes [When the regulation of normal L1 activity is impaired, retrotransposition events may result in numerous deleterious effects. For instance, it can result in disruption of the ORF of the functional gene, genome amplification, and the development of genomic instability. The first human disease associated with L1 retrotransposition was haemophilia A, stemmed from the independent mutagenic L1 insertions into exon 14 of then factor . To datediabetes , 35, 36. APC gene, leading to the disruption of its function [ APC in colorectal cancer [It has also been hypothesized for a long time that L1 retrotransposition may be associated with cancer development and progression, but the lack of tools needed to detect novel retrotransposition events in human cancers did not allow the support of this hypothesis. The first L1 retrotransposition in cancer was reported by Miki et al. in colorectal cancer and was characterized by insertion of the 3′ portion of L1 into the last exon of thefunction . A numbefunction , 39. Howl cancer , can be l cancer  reportedLoss of global DNA methylation was the first epigenetic alteration demonstrated in human cancers , 42. SubThis hypomethylation can result in a number of unwanted effects associated with aberrant L1 activity and retrotransposition. Also, while L1 is interspersed primarily within gene-poor regions of the genome, its presence within or neighboring the coding sequences can be detrimental. For instance, loss of L1 methylation within its 5′-UTR may result in its aberrant activation and affect the expression of neighboring genes. Hypomethylation of L1 element insertions within the promoters and introns of coding genes may result in aberrant expression of these genes . On the Significant alterations of L1 in human cancers, associated primarily with its increased expression, elevated protein levels, and hypomethylation, together with the very high copy numbers of L1 in the genome, suggest that L1 can be potentially utilized as a diagnostic modality. It is becoming increasingly evident that the methylation status of L1 can be utilized as a prognostic marker in cancer. Indeed, loss of L1 methylation is usually found to be more pronounced in advanced stages of cancer and in metastasis than in the early stages of cancer, or in primary tumors, respectively. c-MET oncogene, the gene that contains an L1 insertion within its intron [Growing evidence clearly demonstrates that hypomethylation of L1 is usually associated with poor prognosis and shorter disease-free survival. For instance, a study of 211 lung adenocarcinoma patients concluded that disease-free survival in the group with hypomethylated L1 was significantly shorter than that of the nonhypomethylated group . The ress intron .Importantly, the study by Benard et al.  shows thWhile, for the vast majority of human cancers, L1 demethylation was associated with poor prognosis, some controversial results exist for melanoma, where L1 hypomethylation was associated with favorable prognosis in stage IIIc patients . HoweverAccumulating evidence suggests that the methylation status of L1 cannot only be utilized as a prognostic marker but also discriminate between the earlier and later stages of cancer. Extensive research performed in several cohorts of colorectal cancer (CRC) patients indicates that methylation of L1 not only is considerably lower in the tumor compared to adjacent stromal and normal mucosal epithelial cells , 58 but  ERBB2(HER2) amplification, and p53 overexpression [Another study by Park et al. , performpression . Similarpression .Field for cancerization is the phenomenon characterized by “the occurrence of multifocal and recurrent epithelial tumors that are preceded by and associated with widespread changes of surrounding tissue or organ fields .” The ro APC and RASSF1 were significant prognostic factors only in univariate analysis in non-small cell lung cancer, the methylation status of L1 remained significant prognostic factor in multivariate analysis that included age, gender, smoking history, histologic type, and pathologic stage. Moreover, in the same study, L1 methylation also revealed a significant prognostic value for stage IA NSCLC patients in multivariate analysis [It is becoming increasingly evident that the prognostic value of the L1 methylation status might exhibit higher potential than the methylation status of individual tumor-suppressor genes characteristic of a specific cancer. In the recent study, Saito et al.  reportedanalysis . MGMT and MLH1 genes was not associated with patient prognosis [Similar findings were reported from the cohort of 217 patients with curatively resected esophageal squamous cell carcinoma, where L1 hypomethylation was significantly associated with shorter survival, while the methylation status ofrognosis . MET, RAB3IP, and CHRMP results in their reactivation and aberrant expression in CRC metastasis. The recent study by Ikeda et al. [The role of L1 in tumor's metastatic potential is becoming increasingly recognized . Severala et al.  reportedIdeal biomarkers should be low-invasive and reflect the pathomorphological changes in the target organs. In this regard, determination of L1 methylation status in biological fluids, such as blood and saliva, is of particular interest. Up to date, a number of studies have attempted to determine the association between the methylation of L1 in leukocytes, peripheral blood mononuclear cells, and buccal DNA and the risk for certain cancers –73. DespWhile normal adult human tissues usually do not express L1 (or express at very low levels), considerable levels of L1 RNA and protein are found in cancerous tissues . ImportaOne of the major challenges is the high degree of variability in L1 methylation between the evaluated samples . InteresAnother challenge is variability and certain discrepancies between the studies. For instance, while some studies report L1 hypomethylation in leukemia patients , others In the last two decades, L1, the most abundant repetitive element in the human genome, experienced a dramatic switch from being “junk DNA” to being “an important player in the mammalian genomes .” Its in


Surfactant proteins SP-A and SP-D are useful biomarkers in diagnosis, monitoring, and prognosis of idiopathic pulmonary fibrosis (IPF). Despite their high structural homology, their serum concentrations often vary in IPF patients. This retrospective study aimed to investigate distinct compartmentalization of SP-A and SP-D in the vasculature and lungs by bronchoalveolar lavage fluid (BALF)/serum analysis, hydrophilicity and immunohistochemistry.We included 36 IPF patients, 18 sarcoidosis (SAR) patients and 20 healthy subjects. Low-speed centrifugal supernatants of BALF (Sup-1) were obtained from each subject. Sera were also collected from each patient. Furthermore, we separated Sup-1 of IPF patients into hydrophilic supernatant (Sup-2) and hydrophobic precipitate (Ppt) by high-speed centrifugation. We measured SP-A and SP-D levels of each sample with the sandwich ELISA technique. We analyzed the change of the BALF/serum level ratios of the two proteins in IPF patients and their hydrophilicity in BALF. The distribution in the IPF lungs was also examined by immunohistochemical staining.In BALF, SP-A levels were comparable between the groups; however, SP-D levels were significantly lower in IPF patients than in others. Although IPF reduced the BALF/serum level ratios of the two proteins, the change in concentration of SP-D was more evident than SP-A. This suggests a higher disease impact for SP-D. Regarding hydrophilicity, although more than half of the SP-D remained in hydrophilic fractions (Sup-2), almost all of the SP-A sedimented in the Ppt with phospholipids. Hydrophilicity suggests that SP-D migrates into the blood more easily than SP-A in IPF lungs. Immunohistochemistry revealed that SP-A was confined to thick mucus-filling alveolar space, whereas SP-D was often intravascular. This data also suggests that SP-D easily leaks into the bloodstream, whereas SP-A remains bound to surfactant lipids in the alveolar space.The current study investigated distinct compartmentalization of SP-A and SP-D in the vasculature and lungs. Our results suggest that serum levels of SP-D could reflect pathological changes of the IPF lungs more incisively than those of SP-A. The pulmonary surfactant consists of phospholipids, mainly dipalmitoyl phosphatidylcholine (DPPC), surfactant protein (SP)-A, SP-B, SP-C, and SP-D. Both SP-A and SP-D are produced by type II alveolar epithelial cells and Clara cells, and are secreted into the alveolar space, 2. UnliLCO), chronological changes in respiratory functions, and desaturation during the 6-min walk test who had a bronchoalveolar lavage (BAL) performed at the Sapporo Medical University Hospital from December 2003 to May 2012. SAR patients were used as disease controls because, in Japan, they seldom show fibrotic changes in the lung, even with pulmonary lesions, 24. TheTo compare BALF concentration of the two proteins, this study also included a control group consisting of 20 healthy subjects from our previous study in which BAL was conducted under the same conditions. They hag) to remove cell components, and this Sup-1 was cryopreserved at -80°C until use.Each participant received an intramuscular injection of atropine sulfate and hydroxyzine or pethidine, followed by local anesthesia with lidocaine. A flexible bronchofiberscope  was inserted orally to pour 50 mL of 0.9% saline (37°C) into the bronchus of the right middle lobe or the left lingula, and the BALF was recovered. This process was repeated three times and the fractions pooled together. BALF was centrifuged , named SP-A Test/Kokusai-F , as previously described. A standg; 4°C; 16 h) into a supernatant (Sup-2) and precipitate (Ppt). The Ppt was resuspended in 1.2 mL of 0.9% saline. The concentrations of SP-A and SP-D in Sup-2 and Ppt were measured by ELISA as stated above. Following which, the phospholipids were extracted from Sup-2 and Ppt by the method of Bligh and Dyer[The hydrophilicity of SP-A and SP-D in the BALF of IPF patients (N = 19) were measured after centrifugation of 1.2 mL of Sup-1  and embedded in paraffin. Then, 3-μm thick sections were deparaffinized and stained using the following protocols. The primary antibodies were mouse anti-human SP-A monoclonal antibodies , and mouse anti-human SP-D monoclonal antibodies . Thereafter, the sections were incubated with biotin-labeled secondary antibody , and stained using the DAB Peroxidase Substrate Kit . For SP-D, samples were pretreated in 10 mM citric acid solution  before being incubated with the primary antibody.Furthermore, the stained sections were boiled in 10 mM citric acid solution  to remove antibodies, and stained again with monoclonal CD34  or monoclonal D2-40  as primary antibodies. Double immunostaining was performed using the Vectastain ABC-AP Mouse IgG Kit  and the alkaline phosphatase substrate kit . CD34 stains vascular endothelium, particularly in small capillaries, whereasThe semi-qualitative analysis of immunohistochemistry was performed with concordance of three well-trained pulmonologists who had knowledge of the pathologic features of interstitial pulmonary diseases. We defined immunohistochemical intensities of normal type II epithelial cells as positive; “+”, and expressed those of each area using five grades: “-”, none; “±”, more or less; “+”, positive; “++”, more intense; and “+++”, very intense.U–test (between the two groups) or the Kruskal Wallis test (among three groups). The differences between each pair of the three groups were tested using the Mann–Whitney U–test with Bonferroni correction. The differences in sex and the smoking status were tested using the chi-square test. The correlations between the two variables were evaluated using the Spearman’s rank correlation coefficient. All P values < 0.05 were considered statistically significant.All analyses were performed using the SPSS Statistics 21 (IBM Inc.). The data of age and the BALF recovery rate with symmetric distribution are expressed as mean ± standard deviation, and the differences between the three groups were tested using one-way ANOVA. The differences between each pair of the three groups were tested using Tukey’s HSD test. The data of SP-A and SP-D levels in the serum and BALF, the BALF/serum level ratios of the two proteins, and the percentages of surfactant proteins and phospholipids fragmentation in Sup-2 or Ppt showed asymmetric distributions. These data are expressed as median (interquartile range), and tested using the Mann–Whitney The basic characteristics and recovery rates of BALF of each subject group are summarized in Table The data of SP-A and SP-D levels of each subject group are summarized in Table Measurements of SP-A in BALF revealed comparable concentrations between the three groups P = 0.245): IPF patients (median 1275.0 ng/mL), healthy subjects (median 1978.0 ng/mL), and SAR patients (median 1600.0 ng/mL)  of SP-A and SP-D were median 19.1 (SP-A) and 1.3 (SP-D) in IPF patients, and median 51.2 (SP-A) and 7.8 (SP-D) in SAR patients. These gaps were significantly smaller in IPF patients than in SAR patients (SP-A: P = 0.01 and SP-D: P < 0.001)   to generate a hydrophobic precipitate (Ppt) and hydrophilic supernatant (Sup-2). Nearly all the SP-A sedimented in the Ppt (median 97.9%), indicating high hydrophobicity. In contrast, SP-D partitioned into the two phases, but significantly more in Sup-2 (median 52.4%). Finally, nearly all surfactant phospholipids were collected in the Ppt (median 100.0%). Together, these data suggest that hydrophilicity of SP-A is weakened by binding with phospholipids in BALF. The results of centrifugation of BALF are summarized in Table The BALF supernatant fractions from IPF patients centrifuged to remove cellular components (Sup-1) were centrifuged again 33,000 3,000 g tThe tissue distribution of SP-A and SP-D was analyzed by immunostaining of surgical lung biopsies from IPF patients and peripheral noncancerous control lung tissue from lung cancer patients. Type II alveolar epithelial cells, which are known to produce pulmonary surfactant, were positive for both surfactant proteins in normal peripheral lungs Figures A, B and Semi-qualitative analysis of the immunohistochemical distribution comparing SP-A and SP-D is presented in Table It has been reported that serum SP-A and SP-D concentrations are elevated in IPF and other interstitial lung diseases, and that they can predict the progression of respiratory failure and prognosis in IPF, 6. HoweWe previously reported BALF concentrations of SP-D equivalent or lower in IPF patients than in healthy subjects. Likewis99mTc-DTPA) aerosol was exacerbated among IPF patients and suggested that the migration of substances from the alveolar space into the bloodstream was accelerated[According to the current study, the BALF/serum level ratio of SP-A was reduced from 51:1 in the sarcoidosis group to 19:1 in the IPF group. In contrast, IPF caused a 6-fold decrease in BALF/serum level ratio for SP-D, with 7.8:1 in the sarcoidosis group compared with 1.3:1 in the IPF group. These data suggest that IPF caused a preferential leakage of SP-D from the alveolar space into the bloodstream. Moreover, in this study, the SP-D concentrations in sera were correlated with those in BALF, but such a correlation was not found for SP-A. This result may be due to the higher permeability of SP-D, implying that not only BALF concentration but also serum concentration can be easily altered according to the amount of secretion of SP-D from productive cells. Mogulkoc et al. reported that the clearance of inhaled technetium 99 m-labelled diethylenetriamine penta-acetic acid (elerated. One of elerated, 38. ThiThe present study revealed dissociation between SP-A and SP-D in IPF lungs, suggesting that different protein–lipid interactions may affect their leakage into the bloodstream. Most of the SP-A found in the alveolar space is bound to DPPC, which is the main component of pulmonary surfactant. In contCD34 is known as a marker of vascular endothelium, 40. EbiThis study has some limitations. We should interpret the concentrations in BALF not only from the viewpoint of the leakage and clearance but also from that of the alterations in the production amount in IPF lungs. Because both proteins have the important function to regulate the inflammatory cell response, their productions may be altered in IPF lungs. Further examinations are required regarding these issues. We used the data of BALF from healthy volunteers who were investigated in our previous study. BecauseThe histopathological features of IPF indicate a heterogeneous appearance. Honeycombing, in which type II cells are replaced with regenerated ciliated epithelial cells, is a finding that represents the end stage of fibrotic change, and this finding seldom regresses. In contrast, alveolitis is a potentially reversible and treatable parenchymal abnormality. In such a lesion, type II alveolar epithelial cells are extremely hyperplastic. These variable features may reflect dynamic differences between SP-A and SP-D because of their hyprophilicity. If serum SP-D levels mirror the severities of moderate and reversible damage to the epithelium due to their ready leakage into the bloodstream, these levels can be used as a biomarker to predict therapeutic response. We need to assess the utilities of these biomarkers with regard to the therapeutic effects of drugs such as antifibrotic agents. Currently, KL-6, MMP-7 and CCL-18 have been also reported as blood biomarkers of IPF–22. WherAlthough SP-A and SP-D are serum biomarkers of IPF having high homology, the current study suggests that the difference in hydrophilicity of the two proteins could be the cause of their difference in migration from the air space into the bloodstream. Because SP-D leaks into the circulation more easily, serum levels of SP-D may reflect pathological changes of the disease more sharply than those of SP-A.Written informed consent was obtained from the patient for the publication of this report and any accompanying images.


Furthermore, the magnitude of the elastic deformations can be controlled by changing the relative rotation angle between two layers. Magnitude of the out-of-plane displacements in graphene agrees well with those observed in experiments and can explain the experimentally observed bandgap opening in graphene. Upon increasing the relative rotation angle between the two lattices from 0° to 10°, the magnitude of the out-of-plane displacements decrease while in-plane strains peaks when the angle is ~6°. For large misorientation angles (>10°), the out-of-plane displacements become negligible. We further predict the deformation fields for MoS2-WS2 and MoSe2-WSe2 heterostructures that have been recently synthesized experimentally and estimate the effect of these deformation fields on near-gap states.Recent technological advances in the isolation and transfer of different 2-dimensional (2D) materials have led to renewed interest in stacked Van der Waals (vdW) heterostructures. Interlayer interactions and lattice mismatch between two different monolayers cause elastic strains, which significantly affects their electronic properties. Using a multiscale computational method, we demonstrate that significant in-plane strains and the out-of-plane displacements are introduced in three different bilayer structures, namely graphene-hBN, MoS Recent technological advancements in the isolation and transfer of different 2D materials without loss of material quality have led to the renewed interest in stacked/layered materials and heterostructures12345et al.2-graphene and graphene-MoS2-metal junctions can be tuned to obtain photocurrent with quantum efficiency as high as 55%. Similarly, graphene stacked on hBN has been shown to possess electron mobilities that are at least two orders of magnitudes higher compared to graphene on the conventional substrates such as silica or silicon9102D materials such as graphene, hexagonal boron nitride (h-BN), phosphorene, MoSet al.22 on WS215162  per percent of applied strain has been recently confirmed by photoluminescence experiments2 bilayer DFT calculations shows that the interlayer coupling varies with the twist angle and distance between two layers which increases the bandgap from 1.2 eV to 1.7 eV when interlayer distance is increased by 1 Å.Recently Woods ab-initio computational methods. Length scales associated with the Moiré patterns require consideration of large system sizes that are currently not possible using ab-initio simulations. Molecular dynamics simulation studies are also limited due to the difficulty in developing empirical force fields for many of the new materials. Recent attempts to study deformations of Moiré patterns are based on various poorly controlled approximations, whose validity is difficult to quantify. For example, Neek-Amal et al.et al.It is clear from the above discussion that elastic deformations play a crucial role in determining the electronic properties of vdW heterostructures. However, current theoretical studies to investigate such interlayer interaction induced deformations are limited in their predictive power mainly due to the large mismatch between the length scales of deformations (ten to hundred nanometers) and the length scales accessible to accurate i.e., continuum finite-deformation simulations informed by ab-initio calculations and infer possible consequences of these deformations on the electronic properties of these materials. vdW-corrected DFT simulations can be used to determine the interlayer interaction for any bilayer structures while the continuum model based on the non-linear theory of elastic plates can be used to study the deformation at larger length scales associated with the Moiré patterns. Continuum models have been successfully used to study the micrometer scale deformations such as rippling, scrolling and warping of single and multilayer graphene sheets and nanoribbons22232, WS2 and MoSe2 and estimate the change in bandgaps due to these elastic deformations. Furthermore, we also obtain analytical solutions to estimate in-plane strains and the out-of-plane displacements in 2D materials as a function of material and interaction parameters obtained from DFT calculations. These closed-form solutions can serve as a useful guide in determining appropriate material combinations to engineer strain at 2D interfaces.In this article, we develop a general framework to estimate the deformations in heterostructured bilayers with arbitrary misorientation angle using a multi-scale modeling approach, Determine the interaction energy of the unit cell of layer A as a function of its position relative to the unit cell of the substrate, layer B.Based on the above interaction energy, derive a continuum description of the spatial variation  of the interactions energy between the layer A and the substrate by inverse Fourier transformation.Obtain in-plane and out-of-plane forces acting on layer A from the spatial variation of the interlayer interaction energy.Use the forces in a non-linear elastic plate model to predict in-plane and out-of-plane deformations in layer A.Our DFT informed continuum approach involves the following steps  is the average energy of the unit cell, u1(z) is the magnitude of the energy modulations and ϕ(z) gives the energy difference between AB and BA stacked configurations and G1 is the magnitude of the reciprocal vector for substrate primitive unit cell. In the case of Graphene on h-BN, EXX + RPA (exact exchange and random phase approximation) level density functional theory energy calculations were used150 = 3.4 Å, this gives u0 (z) = –69.2 meV, u1 (z) = 2.26 meV and ϕ = –50.4°.Spatial variation of the interaction energy of the unit cell of layer A as a function of its position over the layer B unit cell can be written as (Step 1):AB can be written in terms of Moiré reciprocal lattice vectors Based on this functional form of the interaction energy of the primitive cells, spatial variation of the interaction energy of the two layers within a Moiré cell can be computed by calculating the local stacking of the each unit cell in layer A relative to the unit cell in layer B. Note that since the stacking configurations change only appreciably over the length scales of the Moiré patterns, the variations are gradual on the scale of the lattice spacing. Using this fact, spatial variation of the interaction energy between two layers  VAB can The numerical scheme to relate the unknown Fourier coefficients BN = ac (1+δ) and lattice misorientation angle is denoted by θ. Reciprocal lattice vectors Next, we relate the reciprocal lattice vectors of the Moiré cell to the lattice mismatch and the relative rotation of the two layers. For the case of graphene on hBN (with the same lattice symmetry), the lattice mismatch is defined through the a0 between the layers (Step 2)0 . Here, Fourier coefficient All the components of the force acting on layer A can be computed by taking the derivatives of interaction energies computed in the previous step. However, this will require the knowledge of the Fourier coefficients Derivatives of this energy give the components of the forces acting on the top layer due to the substrate (Step 3):αβ are related to the in plane strains by Hooke’s law:p = 2000 eV/nm2 and flexural rigidity to the bending modulus Eh3 /12(1– σ2) = 1eV. We solve these equations to find in-plane and out-of-plane displacements using the finite element methodSince the length scales over which the magnitudes of the forces vary are large (~14 nm) compared to atomic scales, the deformation of the two sheets can be computed using the von-Karman non-linear plate theoryFor a given bilayer combination, interlayer forces depend both on the magnitude of the lattice mismatch δ and the misorientation angle θ. These forces cause strains in both layers, which are partially relaxed through out-of-plane deformations, depending on the elastic properties of the layers and the nature of interlayer forces. For sake of simplicity we consider the case of layer A on a substrate (for example graphene on h-BN) and present the results for the case of free-standing bilayers in the SI.et al.Due to the forces from the substrate, the graphene monolayer deforms and corrugations develop across the sheet. Our calculations show that the out-of-plane displacements form Moiré patterns as shown in 126Forces arising due to weak vdW interaction between two layers are not strong enough to compensate the lattice mismatch strain; therefore domains of non-uniform strain distribution are created. Strain energy associated with such deformations consists of two parts; one due to curvature (bending) and one due to in-plane strains. In-plane displacements cause lowering of vdW energy by moving to more favorable energy configurations. Out-of-plane displacements are caused by buckling instabilities due to compressive in-plane strains as well as due to different equilibrium interlayer separations for different stacking configurations. Critical strain in each domain is determined by the competition between the penalty associated with the straining the layers and the gain in vdW energy.For a given bilayer with lattice mismatch δ, the period of the Moiré superlattice decreases sharply with the misorientation angle θ between two lattices and is given by:et al.As the cost of bending the graphene monolayer increases with the decrease in length scale over which curvature change appreciably, we find that the magnitudes of the out-of-plane displacements decrease with increase in misorientation angles θ between graphene lattice and hBN lattices . For theThe in-plane strains show a non-monotonic behavior with increasing misorientation angle. In the To gain further insight into the interplay between vdW interactions and elastic deformations, we develop an analytical model using elastic plate theory. Our goal is to determine the out-of-plane displacements w and in-plane displacements u for any given bilayer combination depending on the strength of vdW interactions, material properties and the lattice structure of two sheets. From the numerical solutions, we observe that the out- of-plane displacements do not have a strong dependence on the in-plane forces and similarly the contribution of the out-of-plane displacements to the in-plane strains is small in all cases. In this limit, we can decouple in-plane and out-of-plane displacements and independently determine in-plane displacements as a function of in-plane forces and out-of-plane displacements due to the out-of-plane forces. Governing equations for in-plane displacements are:α we get,Using this form of the displacements in Similarly, Fourier coefficient for the out-of-plane displacement can be obtained from Eq. (14)x,y vary as 1/G, out-of-plane displacement coefficients uz vary as 1/G4. This leads to the rapid decay of the magnitude of the out-of-plane displacements with increasing rotation angle between two sheets, as observed in m have been plotted in Replacing these Fourier coefficients in the 2-WS2 and MoSe2-WSe2 and present in Next, we applied the multiscale method on two model systems of vdW TMD heterostructures MoSK point with the conduction band minimum (CBM) derived from K point in the MoS2-WS2 system are nearly a sum of the electronic structures of the individual layers with the VBM in the W layer while the CBM in the Mo layer2 layer can induce a decrease of CBM and therefore, a band gap reduction. Our results show that the in-plane strains vary from 0.07% to 1.27% for the MoS2-WS2 bilayer structure with the misorientation angle changing from 0.5° to 10° and the band gap reduction due to such strains can be as large as ~190 meV , the direct gap opens at ~190 meV . Similar~130 meV . Non-uni2 bilayer. Our results show that the magnitudes of the out-of-plane displacements, for the vdW heterostructures studied here, are considerably large (~0.5 Å) and will significantly change the electronic properties. A simple estimate based on MoS2 bilayer studyIn addition to the in-plane strains, the out-of-plane displacements may also lead to significant change in the electronic properties. Out-of-plane displacements lead to spatially varying interlayer distances that have been theoretically shownMolecular mechanics simulations of graphene over hBN substrate were performed using the Adaptive Intermolecular Reactive Empirical Bond OrderA multiscale method to compute the elastic deformations for general bilayer structures has been established and validated via comparing the deformations with molecular dynamics simulations as well as with experiments for graphene/hBN bilayer heterostructures. This method is a convenient and precise way to predict the deformation and strains in bilayer 2D heterostructures, and hence paves the way of tuning the electronic and optoelectronic properties of these constructs via strain engineering.Closed form analytical solution to predict the in-plane and out-of-plane displacements are in good agreement with finite element results and remains valid for a vast range of interlayer interactions.2-WS2 and MoSe2-WSe2) have also been computed using our multi-scale method. Patterned strains due to these deformations are predicted to induce periodically localized electron states in the upper layer while the hole states remain extended in the substrate layer.Elastic deformation fields for the two newly synthesized vdW heterostructures .


We simulated and analyzed in detail the behavior of ultrashort optical pulses, which are typically used in telecommunications, propagating through graphene-based nanoribbon waveguides. In this work, we showed the changes that occur in the Gaussian and hyperbolic secant input pulses due to the attenuation, high-order dispersive effects and nonlinear effects. We concluded that it is possible to control the shape of the output pulses with the value of the input signal power and the chemical potential of the graphene nanoribbon. We believe that the obtained results will be highly relevant since they can be applied to other nanophotonic devices, for example, filters, modulators, antennas, switches and other devices. The production of smaller yet more simple and efficient electronic and photonic devices is the biggest concern of industry and commerce, given the increase in the user requirements for these devices. Meanwhile, the electrical and optical characteristics of graphene are attracting attention from researchers around the world. The plasmon technology on which this new material is based has enabled the development of nanoscale devices, which are also faster and more efficient than traditional devices found today. The nanoscale dimensions of graphene-based plasmonic devices allow for their integration into electronic and photonic integrated circuits.Since there are many nanophotonic devices based on nanophotonics waveguides, this study was focused on the simulation and analysis of the attenuation, dispersion and nonlinear effects occurring in signals propagating through a graphene-based waveguide. We considered a graphene nanoribbon located between similar dielectric layers, as will be described further. Previous reports illustrated several details regarding these waveguides –7; howevW) strongly influences the mode behavior that propagates through these graphene nanoribbons. In this sense, the smaller the nanoribbon width, the lower the number of modes that are present in the waveguide. Previous studies showed that in a graphene nanoribbon of width <50 nm, there exists only a single mode  [W < 10 nm, the classical theory can no longer predict the behavior of GSPPs in a graphene nanoribbon [Given that graphene surface plasmon polaritons (GSPPs) are highly confined in graphene nanoribbons acting as waveguides, it is possible to integrate these waveguides into photonic integrated circuits (PICs). However, the nanoribbon width  . Howevernoribbon .Recent reports showed that it is possible to couple the radiation emitted by a transmitter  with the surface plasmons (SPs) present on a graphene sheet . Other eThe guided TM polarized GSPPs modes were excited through a polarization maintaining single mode fiber, by the use of the end-fire coupling method.This paper is organized as follows: in the following section, we present the characteristics of waveguides composed of a single graphene nanoribbon. After the simulation and analysis is presented, the attenuation, dispersion and nonlinear effects occurring in a graphene-based waveguide are described in the Results and Discussion section. The last section summarizes the conclusions.intra + σinter, can be estimated by the Kubo formula, given by [The local conductivity of graphene, σ = σgiven by :intra is the intraband conductivity (due to electron–photon scattering), μg is the chemical potential of graphene, e is the electron charge, ω is the angular frequency of the light in air and τ is the phenomenological scattering rate. Moreover, the interband conductivity (due to the electron transition) is given by [where σgiven by :g >> kBT and T = 300 K (room temperature), thus, kBT ≈ 26 meV.It is worth noting that The imaginary part of the conductivity determines the type of the polarized modes that can be supported in a graphene nanoribbon. For σ′′ > 0 (where σ′′ is the complex part of the conductivity of graphene), TM modes can be supported, while for σ′′ < 0, TE modes can be supported .T = 0, kBT/μg = 0), the TM modes (s-polarization) and TE modes (p-polarization) are supported in graphene when  and , respectively. By numerical simulations it was proved that energy is absorbed or dissipated when . However, if we consider a fixed graphene chemical potential, the temperature increase causes a finite damping, which is smaller for TM vs TE modes. This is because the real part of the conductivity undergoes more changes in the region where the TE modes are located [In the limit without collision between electrons ( located .t) of the graphene nanoribbon, given as [Starting from Maxwell’s Equations, we arrive at the expression that relates the electric permittivity of a graphene nanoribbon to the angular frequency (ω), conductivity and graphene effective thickness , the equation for the dispersion relation for graphene nanoribbons is given by [In a graphene nanoribbon embedded in a substrate with relative permittivity εgiven by :r is the relative permitivity in which the graphene nanoribbon is embedded.where εThe dispersion relation for graphene nanoribbons for TM modes propagating along a graphene/dielectric interface is also given by :0 = 377 Ω is the air impedance and k0 = 2π/λ0. Similarly, the dispersion relation for the TE modes is given by:where ηSince the wave vectors of the surface plasmons polaritons in a graphene/dielectric surface (GSPPs) have high values, we can conclude that these modes are very well confined in the graphene nanoribbon.W, where W is the width of the graphene nanoribbon [Previous studies have shown that GSPPs can only propagate in graphene nanoribbons when the plasmon energy corresponds to −iσ(ω)/ωnoribbon .W < 10 nm, the classical theory can no longer determine the behavior of GSPPs in the graphene nanoribbon [W < 50 nm for our simulations.As previously mentioned, in a graphene nanoribbon of width <50 nm, only a single mode  exists . On the noribbon . Hence, W = 10 nm and W = 20 nm.W = 20 nm and W = 10 nm (μg = 0.5 eV).However, as we are interested in analyzing the behavior of nanophotonic waveguides with the smallest possible widths, we simulate these waveguides for widths 0 ≈< 1.55 μm in graphene nanoribbons with a width of 10 nm and 20 nm (µg = 0.5 eV). However, to work around this problem, we can increase the value of the graphene chemical potential. Note that the GSPP wavelengths for a graphene nanoribbon of width W = 20 nm are greater than the values for W = 10 nm, that is, the GSPPs modes in a narrower nanoribbons are more confined.From 0 < 2 μm and μg = 0.45 eV are shown in To simplify our calculations, we considered graphene nanoribbons suspended in air. The real and imaginary parts of the GSPP wave vector as a function of the wavelength in air (before coupling to the SPs) for 1 μm < λe of its initial intensity) is given by Lp = Im(q)/2, where q is the wave vector of the GSPP TM modes, we can see from the lower part of Lp remains constant for wavelengths up to 1.7 μm. Also note that in this wavelength range, the value of the ratio Re(q)/Im(q) = ωτ (where τ is the relaxation time) varies very little.Taking into account that the propagation length of the GSPP mode  the SiO2 substrate. Previous studies have defined the value of the mobility in graphene as μg = 60,000 cm2/Vs [2.Hexagonal boron nitride  is a graphite isomorphic insulator in which the boron and nitrogen atoms occupy positions A and B in the Bernal structure. Therefore, the atomic structure of h-BN is similar  to the structure of graphene. It is worth noting that graphene on a layer of h-BN has a charge carrier mobility value and homogeneity of almost an order of magnitude better than on SiO0 cm2/Vs . It is i2, so that a graphene nanoribbon is better positioned on the surface of a h-BN layer. Methods for the deposition of a h-BN layer on SiO2/Si already exist, as detailed in [The surface roughness of the h-BN layer is much smaller than the surface roughness of SiOailed in .The graphene/substrate geometry for a graphene-based waveguide in shown A = A × exp(−(t/τ0)2), where A is the pulse amplitude and τ0 is the temporal half width . To obtain more reliable results, we also considered hyperbolic secant pulses  = A × sech(t/τ0)) in some cases.Since the nanophotonic devices should operate in telecommunication networks, Gaussian pulses should be considered as the input: The GSPP mode wavelengths and the propagation distance can be determined by its wave vectors as given by –25:−1) referring to one propagation length, for λ0 = 1.55 μm and μg > 0.48 eV is illustrated in Using g ≈> 0.68 eV, the mode suffers virtually no attenuation. The attenuation constant values (μm−1) for one propagation length for λ0 = 3 μm and μg > 0.25 eV are given at the bottom of g ≈> 0.43 eV, the mode suffers almost no attenuation. Therefore, since the graphene-based waveguide we are analyzing has a length smaller than 1 Lp, we can neglect the attenuation inside the waveguide. However, we must consider the insertion loss. A schematic view for insertion of an optical signal in a nanophotonic waveguide is shown in Note that for μThe optical signal from an optical source is inserted into a monomode optical fiber via a connector with an insertion loss of 0.5 dB, mainly due to misalignment between the two portions of the optical fibers. The insertion loss of the optical fiber can be neglected due to its short length. The signal output to be coupled to the graphene-based waveguide  suffers I) at the input of the graphene-based waveguide. However, the electromagnetic flux coupled to the SPs (GSPPs) is subject to the electrical and optical graphene parameters. Therefore, the output pulse shape will suffer changes imposed by the graphene parameters.Considering that the modal area of the electromagnetic flux reaching the graphene nanoribbon center is approximately equal to the modal area of a single mode fiber, we can obtain the value of the intensity , as shown in the top of To prove that the attenuation can be neglected when the length of the graphene nanoribbon, It is well known that for short pulses the dispersion and nonlinearity effect should not be considered individually, that is, it is necessary to consider the combined effects of dispersion and nonlinearity.The behavior of the propagation of optical signals in a nonlinear medium can be determined by the following equation :A) is normalized such that represents the intensity (I) of the propagating signal, β1 = 1/Vg is the parameter which determines the group velocity (Vg), β2 is the second order dispersion parameter, β3 is the third order dispersion parameter, γ = n2ω0/cAeff is the nonlinear coefficient , α is the attenuation constant, and Tr ≈ 5 fs is a parameter related to the slope of the Raman gain. The second, third and fourth terms on the left side of where the pulse amplitude , which governs each frequency component with respect to the dispersive broadening, as the pulse propagates a certain distance [In a previous work, the Fourier transform was applied to find the broadening of a pulse that propagates on a nanophotonic metal/dielectric waveguide. Here, a multiplication factor, distance :L is the propagation distance (L < Lp). After applying I is equal to .In We applied n2 ≈ 10−7 cm2/W, which is much higher than the nonlinear refractive index of dielectrics typically used in optical communications (approximately 109 higher) [−7 × λ02 [The advantage of using graphene as a nonlinear medium is the high value of its nonlinear refractive index  higher) . MoreoveLp = 4.146 μm , as a function of time in the top part of L = 500 nm with an input signal power of P0 = 10−10 W, λ0 = 1.55 mm and μg = 0.80 eV) is represented by the solid line.We show the intensity, which was calculated in accordance with L = 500 nm, with an input signal power P0 = 10−10 W, λ0 = 1.55 mm and μg = 0.80 eV. Notice that the shape of the Gaussian pulse in the time domain undergoes a small change, but the output Gaussian pulse in the frequency domain remains unchanged.The intensity as a function of the frequency spectral component is shown at the bottom of 0 = 15 fs at the input (dotted line) and output (solid line) of the nanophotonic waveguide after propagating L = 500 nm, given an input signal power of P0 = 10−9 W . From P0 = 10−9 W suffer a moderate change in the time domain, but they are not changed in the frequency domain.In the upper part of After several simulations, we concluded that given the same propagation length, an increase in the signal power at the input results in strong nonlinear and dispersive effects, which distort the shape of the Gaussian pulses in the time and frequency domain at the output. Additionally, it was found that increasing the value of the chemical potential of the graphene resulted in dispersive effects that distort the shape of the Gaussian pulse in the time domain at the nanophotonic waveguide output.L = 500 nm for the input signal power P0 = 10−9 W . Shown at the bottom of To conclude our simulations regarding graphene-based nanophotonic waveguides, we used a hyperbolic-secant-shaped pulse in the time domain. The results of the intensity (calculated according to In this work we have shown the effects related to the attenuation, high-order dispersion and high-order nonlinearity in graphene-based nanophotonic waveguides. In particular, the changes in the shape of ultrashort Gaussian and hyperbolic secant input pulses due to the attenuation, dispersion and nonlinearities were analyzed. We concluded that it is possible to control the shape of the output pulse as a function of the input signal power and chemical potential of graphene. We believe that the obtained results will be very relevant to the development of graphene-based nanophotonic devices, such as filters, modulators, antennas, switches, and other devices.


The density of states for the gap states are in the range from the latter half of 1012 to 1013 eV−1cm−2. Although the large amount of gap states at the interface of high-k oxide/bilayer graphene limits the current on/off ratio at present, our results suggest that the reduction of gap states below ~1011 eV−1cm−2 by continual improvement of the gate stack makes bilayer graphene a promising candidate for future nanoelectronic device applications.The origin of the low current on/off ratio at room temperature in dual-gated bilayer graphene field-effect transistors is considered to be the variable range hopping in gap states. However, the quantitative estimation of gap states has not been conducted. Here, we report the systematic estimation of the energy gap by both quantum capacitance and transport measurements and the density of states for gap states by the conductance method. An energy gap of ~250 meV is obtained at the maximum displacement field of ~3.1 V/nm, where the current on/off ratio of ~3 × 10 N, εch, εox, tch, and tox are the effective gate number, dielectric constants for the channel and gate insulator, and thickness of the channel and the gate oxide. This perspective attracts great attention to two-dimensional (2D) layered channels in the FET application because of their rigidly controllable atomic thickness (tch < 1 nm), as well as the low dielectric constant (εch = ~4) for typical 2D layered channels35678mBLG = ~0.037mBP = 0.13mMoS2 = ~0.37The main issue of downscaling in the Si field-effect transistors (FETs) is the short channel effect in which the gate control is weakened by the drain bias. Based on an analysis of the electrical potential distribution in the channel region, it is well known that the short channel effect can be neglected when the channel length is ~6 times longer than the scaling length t εch = ~ for typiIon/Ioff) of ~106 is obtained only at the quite low temperature of 300 mK13151718b centers in the SiO2/Si system, assigned by the electron spin resonance measurement2829Dit) and the time constant (τit) for gap states have not been reported.The suppression of conductivity in bilayer graphene has so far been reported by many researchers by applying an external electrical field13141516171819202122231426CQ) through the capacitance measurements (C-V) of bilayer graphene provides direct information on the density of states (DOS) of bilayer graphene, consequently, the energy gap (EG), because it is regarded as the energy cost of inducing the carriers in graphene and is directly related as CQ = e2DOSCQ measurement for bilayer graphene3233EG estimated both from I-V and C-V has not been done yet. Moreover, in principle, the mobile carrier response to a small-signal alternating current voltage at a certain frequency is measured in the C-V measurement. The capture and emission process of mobile carriers at the trap levels distributed throughout the band gap can be extracted as a deviation from the ideal carrier response without any trap levels under the assumption of the equivalent circuit. This technique is known as the conductance methodContrary to the transport measurement, the extraction of the quantum capacitance  by annealing the SiO2/Si substrate in a 100% O2 atmosphere at 1000 °C prior to the graphene transfer2/n+-Si substrates by the mechanical exfoliation of Kish graphite. This device was annealed under Ar/H2 gas flow at 300 °C for 3 hours to remove the resist residue on the bilayer graphene channel. Subsequently, Y2O3, with a thickness of ~6 nm, was deposited on bilayer graphene FETs by the thermal evaporation of Y metal in the O2 atmosphere at PO2 = 10−1 Pa2 atmosphere at ~100 atm and 300 °C. Finally, the top gate electrode was patterned, followed by annealing at 300 °C for 30 s under 0.1% O2 gas flow. The lack of a Raman D band measured through Y2O3 indicated that no detectable defects were introduced into the bilayer graphene by the high-pressure O2 annealing, as shown in To suppress the hysteresis in drain current—gate voltage curves, the SiOEG through the CQ extraction. CTotal) between the source and top gate electrodes, obtained by sweeping VTG at different VBG, which were measured at the frequency of 1 MHz in a vacuum of ~1 × 10−5 Pa at 20 K. CTotal. The CTotal reduction at the Dirac point with increasing VBG indicates the decrease in the DOS by the gap formation because of the strong contribution of CQ. The hysteresis in the bidirectional C-V curves is quite small (~0.1 V for a VTG = ±4 V sweep)CTotal is clearly observed in the gap region, suggesting the existence of trap sites. The gradual saturation of the capacitance with increasing frequency from 200 kHz to 1 MHz suggests that CTotal measured at 1 MHz is close to the ideal capacitance without any response to the trap site. Therefore, the C-V measurement in We first focus on the capacitance measurement to determine CBG/CTG. Using CBG = 0.038 μFcm−2 for SiO2 with dBG = 90 nm and εBG = 3.9, CTG is estimated to be 0.93 μFcm−2. In the course of this study, the typical CTG value is ~1.2 μFcm−2, depending on the Y2O3 thickness. The CTG value is considerably high compared with those reported previously for both monolayer and bilayer graphene, as shown in CTG and CBG, the white dotted lines indicate the constant The slope of the dotted black line at the charge neutrality point of Vch and Cpara are the charging voltage and the parasitic capacitance. The Fermi energy (EF) and the band structure of bilayer graphene are independently controlled by changing VTG and VBG. It should be noted that the contribution of CBG is implicitly involved in CTotal through CQ and Vch, in CQ was extracted along the constant Cpara as a fitting parameter. CQ as a function of EF for different constant CQ is fitted reasonably well with the theoretical value for bilayer graphene calculated by the tight-binding modelCpara = 0.91 μFcm−2. The charging energy required to induce carriers in bilayer graphene is denoted by EF, which is expressed as EF = eVch. Vch can be expressed by the equation for a series combination of capacitors according to CTotal−Cpara and VTG−VDP, respectively. VDP is the Dirac point voltage. The detailed calculation method is explained in CQ value at the Dirac point for DOS for bilayer graphene at the Dirac point is larger than the residual carriers induced externally by the charged impurities at the SiO2 surfaceCQ is clearly observed because the scattering issue, which strongly contributes to the conductivity in I-V, can be neglected in C-V. It should be emphasized that the DOS within the gap region almost reaches zero, which is not observed in the previous report for bilayer graphene with the h-BN top gateEG as a function of absolute value for C-V data. EG was defined as the energy between inflection points for the conduction and valence sides in EG is roughly ~300 mV at The simplified equivalent circuit model of the device is shown in σ) measured as a function of VTG for different VBG at 20 K. The conductivity at the Dirac point decreases with increasing VBG, again indicating the band gap opening. The maximum Ion/Ioff is ~3 × 103 for pnp, ppp, and so on, whose positions are shown in σ = enμ), the carrier density (n) is estimated by the integration of the differential capacitance of CQ. Otherwise, n is overestimated. However, the carrier density at the access region between the source (drain) and topgate is assumed to be consistent with that at the main channel region just below the topgate electrode for the mobility estimation. Shortening this access region by the self-alignment processWe now consider the transport properties for the same device. S) is plotted as a function of temperature, as shown in S value (~600 mV/dec) extrapolated to room temperature is considerably larger than the theoretical lower limit of 60 meV/dec at room temperatureIon/Ioff at 20 K with previously reported data. All the data for Ion/Ioff are selected at 20 K from the literature, while the temperature for the mobility is not limited to 20 K. The mobility in the present study is not very high because it includes the contact resistance. In contrast, Ion/Ioff in the present study is quite high in spite of the direct deposition of high-k oxide on bilayer graphene without any organic buffer layer.Moreover, the subthreshold swing  at the high temperature region, nearest neighbor hopping (NNH) at the intermediate temperature range and variable range hopping (VRH) in a two-dimensional system of localized states at the low temperature region, as follows17To determine E0, T0 and kB are the activation energy, the hopping energy and the Boltzmann constant. Since the lowest temperature in this study is 20 K, the contribution of VRH may not be observed. The conductivity at the Dirac point is plotted as a function of temperature and fitted by two combinations of TA + NNH and TA + VRH, as shown in −1 for TA + NNH, while the plot with respect to T−1/3 does not show clear linear behavior below T = 100 K. The present data can be explained by TA + NNH for the temperature range above 20 K. This is consistent with the previous report where VRH was observed at below 5 K1317EG and E0 are plotted as a function of EG determined by I-V is reasonably consistent with the previous infrared absorption data, while EG determined by C-V is slightly larger. This difference is discussed later. Moreover, E0 increases with where Rit and Cit are the resistance and capacitance associated with the interface traps, their product CitRit is defined as τit, and Rs is the series resistance. It should be noted that Rit and Cit have been neglected due to roughly no electrical communication of carriers with trap sites at 1 MHz in Cp, in parallel with Gp, as shown in the right of Gp and Dit can be given as the followingTo gain insight into the interface properties, the gap states in the electrostatically opened-band gap are quantitatively analyzed using the conductance method. The equivalent circuit of the device is shown in the left of ω = 2πf (f: measured frequency). Finally, Dit and τit can be obtained as f0 is the frequency at Dit is possible because Gp/ω does not include CQ, which is the advantage of the conductance method. However, if there is leakage conductance (Gleak), indicated by the dotted line in the left of Dit quantitatively is the fabrication of a highly reliable top gate insulator on bilayer graphene without any leakage current. This has been achieved by the high-pressure O2 post-deposition annealing of Y2O3.where Gp/ω as a function of f for EF from −74 to −28 meV, where the band structure was fixed as constant at EG = ~150 meV. It should be emphasized that Gp was measured under the constant band structure along the constant VTG and VBG at the same time. To prevent the contribution of a minority carrier response to the conductance, especially for small band gap semiconductors, the measurement temperature was lowered as much as possible, i.e., 20 K (kBT = ~1.7 meV). This quite low temperature is only possible in bilayer graphene because the majority carriers do not freeze due to the doping by the external gate control, unlike substitutionally doped semiconductors. The more detailed measurement conditions are described in the method section. Clear peaks were observed in the Gp/ω-f relation, suggesting the detection of a trap-detrapping sequence of carriers with gap states. The τit value is evaluated to be ~4 μs. In Cit is roughly negligible in CTotal, measured at 1 MHz. According to this τit value, this assumption is roughly, but not completely, reasonable. Therefore, EG estimated by C-V may be slightly overestimated due to the contribution of Cit. Dit as a function of EG for different Dit is in the range from the latter half of 1012 to 1013 eV−1cm−2. The energy dependence of Dit is not so obvious. Although this value is slightly smaller than that for MoS2k oxide/bilayer graphene limits Ion/Ioff at present. The much lower Dit could be achieved for dual-gate bilayer graphene heterostructure with h-BN.Gp in the equivalent circuit. To avoid this, a device with a relatively short channel was used at the expense of the channel area, which increased Cpara in this study compared with typical value of ~0.2 μFcm−2 τit with the channel time constant , suggesting that τit is dominant. Therefore, the present Dit measurement is reliable.In general, the conductance method is applied to the metal-oxide-semiconductor (MOS) capacitor, where the current is injected from the back side through the semiconductor substrate, whose series resistance, including back side contact, can be removed by measuring the impedance at the high-frequency limit (see Method). The interface trap conductance can be precisely measured. In contrast, in the present FET structure, the carriers are injected from the side of the channel through the source and drain43EF stays within EG at some momentum space, while the real states exist at another momentum space, which may macroscopically act as gap states. Here, let us consider the dominant origin of the gap states. From the viewpoint of the time constant, the former origin will be a more time-consuming process than the latter because the rate limiting process is the tunneling between bilayer graphene and trap sites at the oxide surfaceDit should decrease with increasing Dit for different T0 in VRH is extracted at the low temperature region below 5 K, the Dit can be discussed more in detail because T0 is inversely proportional to the density of states for the localized statesDit. Although it is difficult to determine the dominant origin of the gap states at present, the quantitative recognition of the current status for Dit in this study does provide the realistic comparison with other semiconductor channels in terms of the interface quality.Finally, let us discuss the origin of the gap states. As mentioned before, no detectable defects are observed by the Raman D band. Therefore, the trap sites formed by defects are ignored in this discussion. Two possible origins are discussed here, as shown in 47Dit and τit for gap states. At the large displacement field of ~3 V/nm, they are in the range from the latter half of 1012 to 1013 eV−1cm−2 and ~4 μs, respectively. The large amount of gap states at the interface of high-k oxide/bilayer graphene limits the Ion/Ioff ratio at present. Many trials to characterize the interface properties for other 2D layered channels, as well as bilayer graphene, will help in understanding the origin of the gap states. The improvement of gap states below ~1011 eV−1cm−2 is the first step for bilayer graphene devices to be a promising candidate for future nanoelectronic applications.We have succeeded in extracting critical information on the interface quality, that is, −5 Pa. The capacitance measurement and conductance method under the constant Gp should be measured accurately by reducing the contribution of Rs in the equivalent circuit in the right side of Rs was estimated as follows. For the equivalent circuit in Z) is given by Rs at the accumulation side was estimated to be 29.4 kΩ by taking the high-frequency limit (ω→∞), as shown in Gp can be accurately estimated by removing Rs in the equivalent circuit in the right side of Dit measurement at the valence band side, EF is scanned along negative p-type .


The CR line-width is consistent with a high Dirac fermions mobility of ~3000 cm2·V−1·s−1 at 4 K.The van de Waals heterostructure formed by an epitaxial trilayer graphene is of particular interest due to its unique tunable electronic band structure and stacking sequence. However, to date, there has been a lack in the fundamental understanding of the electronic properties of epitaxial trilayer graphene. Here, we investigate the electronic properties of large-area epitaxial trilayer graphene on a 4° off-axis SiC(0001) substrate. Micro-Raman mappings and atomic force microscopy (AFM) confirmed predominantly trilayer on the sample obtained under optimized conditions. We used angle-resolved photoemission spectroscopy (ARPES) and Density Functional Theory (DFT) calculations to study in detail the structure of valence electronic states, in particular the dispersion of π bands in reciprocal space and the exact determination of the number of graphene layers. Using far-infrared magneto-transmission (FIR-MT), we demonstrate, that the electron cyclotron resonance (CR) occurs between Landau levels with a (B) K and K’ points of the Brillouin zone. Low-energy charge carriers therein obey the Dirac-Weyl equation and behave like massless fermionsπ and π* bands near the Fermi level in monolayer graphene are modified in multilayer graphene, showing a strong dependence on the stacking sequence as well as the layer number. Recently multilayer graphene has attracted considerable interest43Monolayer graphene is a two-dimensional materials with linear dispersions near the et al.et al.A viable method for obtaining a large-scale graphene production is the epitaxial approach based on SiC graphitization. The epitaxial growth of graphene on semi-insulating SiC has the potential to enable the next generation of ultra high frequency and low power electronic devices. The main advantage here is the possibility of obtaining a large graphene area directly on semi-insulating substrates which is one of the main requirements for high frequency devices, with a huge control of the number of graphene layers. Moreover, the choice of the appropriate SiC polytype also makes it possible to select for the formation of Bernal or rhombohedral multilayer grapheneThe Si-face 4 H-SiC substrate is preferred to the C-face for the growth of graphene. This is mainly due to the fact that graphene growth is easier to control on the Si-face, and under optimized conditions the thickness of the graphene can be limited to just a mono, bi and few layers over large areas. The off-axis 4H-SiC(0001) substrate could therefore, be a good candidate to obtain trilayer graphene. Although further, experiments are required to obtain large-area and high quality sample with high electron mobility.2·V−1·s−1 at 4 K) for the observation of the electron cyclotron resonance, despite their high doping level. By comparing ARPES measurements and DFT calculations, we show that the ordered trilayer graphene presents an ABA stacking. Using the near-edge X-ray absorption fine structure (NEXAFS) technique, we also measured the unoccupied electronic states (π* and σ*). These observations could be of prime importance, particularly regarding the development of multilayer graphene-based electronic devices.We demonstrate here the successful growth of ordered trilayer graphene layers on off-axis SiC(0001) substrates up to an unprecedentedly large area of hundreds of micrometers. The high quality of the graphene layers was further confirmed by AFM, micro-Raman mappings and X-ray photoelectron spectroscopy (XPS) measurements. Using FIR-MT measurements, we show that trilayer graphene exhibits high electron mobility  at 1550 °C in 800 mbar argon for 10 min . For Si During the graphitization process, graphene growth starts in the vicinity of the nanofacets regions consisting of step edgesfwhm on a 12 × 12 μm2 scan. The different color scale highlights a blue shift of the 2D peak from the terraces to the nanofacets, combined with an increase in the fwhm. This effect was not surprising, as the reduced bonding coordination of the nanofacets led to an easier Si sublimation from the substrate, which as explained before, facilitated graphene growth. This different growth rate between the terraces and the nanofacets may induce the formation of up to a trilayer along the nanofacetsfwhm of the 2D peak. As usual for epitaxial graphene on SiC, several intense peaks were visible in the wavenumber range between 1300–800 cm−1, corresponding to second-order Raman bands originating in the SiC substrate13In addition to AFM imaging, we carried out micro-Raman spectroscopy mapping. −1 (from 2700 to 2750 cm−1), with an increased fwhm of about 60 cm−1 (from 50 to 110 cm−1). At the same time, we also saw a shift in the G peak of about 20 cm−1 (from 1590 to 1610 cm−1). This shift shows a strong correlation between the strain and the charge density on epitaxial graphene. Thus, the observed blue-shift indicates that there is a difference in strain (associated with the shift of the G and the 2D lines) and carrier density (associated with the shift of the G line) between the (0001) terraces and (11–20) nanofacets.This is an indication of the high quality of epitaxial trilayer graphene on off-axis SiC under argon flux. As shown by the Raman maps, the 2D peak from the (11–20) nanofacets had blue-shifted with respect to those of the spectrum obtained for the (0001) terrace of about 50 cms spectra show the conventional deconvolution expected for epitaxial graphene on SiC(0001)12152 hybridized C–C bonds and it this is the signature of the graphene layers. This component was fitted using a Doniach-Sunjic line shape with an asymmetry factor α of 0.1 and a fwhm of 0.5 eV. The two other peaks at binding energies of 283.8 eV (SiC) and 285.3 eV (IL) are attributed to the SiC bulk and to the interfacial layer respectively. Due to the non-metallic nature of these components, the peaks are symmetric (asymmetric factor α = 0 eV). Assuming that the graphene-SiC sample can be modeled as a semi-infinite SiC substrate with a uniform graphene overlayer, the graphene thickness can be calculated from the ratio between the intensity of the G and SiC componentsWe probed the electronic properties of the sample further using XPS and NEXAFS experiments. The C1s spectra  were acq15 cm−2 is about three times of that of the C atoms in the SiC bilayer 15 cm−2. We obtained a thickness For a photon energy of 510 eV, we have an escape depth λ ~ 7.2 Å. In the geometry of our XPS experiment the take-off angle α was 0°, and Unoccupied electronic states of the trilayer graphene were also examined by NEXAFS spectroscopy. The C k-edge spectra were measured for different incidence angles of linear polarized synchrotron light. As shown in the insert of 12F = –1.32 eV. The three peaks observed in the MDC result from the presence of three bands in the ARPES spectrum in 7D) at –320 meV below the Fermi level (EF). This energy shift ΔE (ΔE = ED − EF) is known to be related to the charge transfer from the substrate to the graphene layersn ~ 9 × 1012 cm−2. Considering that the x-ray spot size in the ARPES measurements was about 180 × 80 (H × V) μm2, we can assume that we are able to obtain large areas of mono-domain trilayer with Bernal stacking, in contrast to other works, where the epitaxial graphene showed different domains with different numbers of layers or different stacking10The electronic structure was also probed using ARPES, which is a powerful method for this purpose, as it gives direct access to the spectral function containing the information on electron energy band dispersion. 2) was placed in a 15 T superconducting coil at 4 K and exposed to the radiation from a mercury lamp (Faraday geometry). The transmitted light was analyzed by a Fourier transform spectrometer using a Si composite bolometer directly below the sample for detection. The transmission at a given magnetic field T(B) was normalized by the zero field transmission T(0). Typical transmission spectra are shown in 24th level is the upper populated LL  substrate. Before graphitization, the substrate was hydrogen etched (100% H2) at 1550 °C to produce well-ordered atomic terraces of SiC. The sample was heated to 820 °C and deoxidized at 1100 °C in order to remove the native oxide and a possible surface contamination. The substrate was then heated to 1550 °C in an Ar atmosphere (800 mbar) for 10 min. The samples were cooled down to room temperature and transferred ex-situ to perform the different measurements.The AFM measurements were carried out under ambient conditions and the images recorded in tapping mode. The Micro-Raman mapping was performed at room temperature with a Renishaw spectrometer using 532 nm laser light auto-focusing on the sample by a DMLM Leica microscope with a 100× objective and a power of 5 mW with a spot size of about 1 μm.ν = 60 eV) and sample orientation were set in order to explore the k-space region around the K point in the ΓK direction of the Brillouin zone.The XPS, NEXAFS and ARPES experiments were carried out on the TEMPO beamlineHow to cite this article: Hajlaoui, M. et al. High Electron Mobility in Epitaxial Trilayer Graphene on Off-axis SiC(0001). Sci. Rep.6, 18791; doi: 10.1038/srep18791 (2016).