Introduction: Backchannels, i.e., short interjections by an interlocutor to indicate attention, understanding or agreement regarding utterances by another conversation participant, are fundamental in human-human interaction. Lack of backchannels or if they have unexpected timing or formulation may influence the conversation negatively, as misinterpretations regarding attention, understanding or agreement may occur. However, several studies over the years have shown that there may be cultural differences in how backchannels are provided and perceived and that these differences may affect intercultural conversations. Culturally aware robots must hence be endowed with the capability to detect and adapt to the way these conversational markers are used across different cultures. Traditionally, culture has been defined in terms of nationality, but this is more and more considered to be a stereotypic simplification. We therefore investigate several socio-cultural factors, such as the participants’ gender, age, first language, extroversion and familiarity with robots, that may be relevant for the perception of backchannels.Methods: We first cover existing research on cultural influence on backchannel formulation and perception in human-human interaction and on backchannel implementation in Human-Robot Interaction. We then present an experiment on second language spoken practice, in which we investigate how backchannels from the social robot Furhat influence interaction  and impression of the robot (measured by post-session ratings). The experiment, made in a triad word game setting, is focused on if activity-adaptive robot backchannels may redistribute the participants’ speaking time ratio, and/or if the participants’ assessment of the robot is influenced by the backchannel strategy. The goal is to explore how robot backchannels should be adapted to different language learners to encourage their participation while being perceived as socio-culturally appropriate.Results: We find that a strategy that displays more backchannels towards a less active speaker may substantially decrease the difference in speaking time between the two speakers, that different socio-cultural groups respond differently to the robot’s backchannel strategy and that they also perceive the robot differently after the session.Discussion: We conclude that the robot may need different backchanneling strategies towards speakers from different socio-cultural groups in order to encourage them to speak and have a positive perception of the robot. Backchannels often come very natural in human-human conversations  and visual —or negative displays of non-understanding or disagreement—verbal  and visual .Backchannels may be described based on their functions, as displays of understanding, agreement, emphatic support, emotion, encouragement to continue or request for information or confirmation . The funmhm) or lexical  and if they are simple (mono- or bisyllabic expressions), double  or complex (combinations of different backchannel types)  . For themmhm 43%; yeah 19%, uh-huh 18%, oh 14% and hm 6%). These backchannels, which can be used generically, are hence the attentive listener’s bread and butter. However, Backchannels may be formulated in a great variety of ways, but it is often the case that a small number of backchannels dominate. For example, How frequently backchannels are uttered will naturally depend on the topic of the conversation, the speaker’s offers of backchannel opportunities and the individual listener, depending on factors such as degree of extroversion or socio-cultural traits , i.e., frequency and timing of backchannels and, more seldom, backchannel category prediction (BCP), i.e., backchannel formulation. In addition, human provision of, reaction to and perception of backchannels in HRI have also been studied.Different backchannel formulation methods have been implemented and tested in HRI, from copying the actual backchannels of a human listener in the same conversation , over leAs we will investigate the interlocutors’ perception of the robot, it is relevant to consider the study by Finally, as conversations are bidirectional exchange of information, it is also important how human interlocutors backchannel towards robots. Traditionally in research on backchannels, culture has been synonym with nationality and/or language, and most work has focused on differences between languages, related to how frequently backchannels are expected, how they are formulated and speaker cues signalling that a backchannel is welcome. The role of backchannels, and hence the distribution between different backchannel functions, clearly differs between different languages. yes, si, oui in English, Spanish, French) and non-lexical acknowledgement , other types are found in much fewer languages, such as lexically negative backchannels to support a negative speaker utterance , backchannels that express surprise  or laughter . It is clear that such differences can affect intercultural conversations, e.g., if the speaker interprets a lexically negative backchannel as disagreement or expressions of surprise as non-understanding. Moreover, the same forms may not convey the same functional meaning, as shown by Wardvs. 40.3% of backchannels being non-vocal, 25% vs. 30.9% being vocal and 52.5% vs. 28.7% being combined vocal and non-vocal.When it comes to the multimodal nature of backchannels, As already described in Other studies, with different types of language families have shown that Pakeha listeners produce more backchannels than Maori listeners  and thatoh, ha, hmm yea, umm, yea aah, yeah, yeap, aha aha, and lexical items such as okay, right, all right exactly, okay, yes, which are hence quite similar to the L1 speakers’ use of backchannels.It has been emphasized that second language learners need to master backchanneling in the second language  and Li eSince conversations are a two-way interaction, L1 speakers may also adapt backchannels when interacting with L2 speakers. Related to the below study, which includes the human interlocutors’ perception of the robot, it is worth noting that There is evidence that other factors, such as gender and age, may also influence backchannels. Many studies see , that thvs. 40%), whereas the women’s were consistently more frequently supportive than neutral (65% vs. 35%). When it comes to perception of backchannels, Using an analysis of large radio dataset of 1800 listener backchannels in 22 conversations The experiment setup and focus follows closely on the one presented by Do socio-cultural factors—specifically gender, age, extroversion level and familiarity with robots—influence how L1 and L2 speakers respond to robot backchannels aimed at balancing the activity in multiparty interaction?Based on the findings in previous work, described in H1. The adpative robot backchanneling behaviour will, in general, make the participation more balanced than if the same backchannel strategy is used towards both speakers; H2. Socio-cultural characteristics of the speakers will influence, quantitatively, in the form of speaking time, and qualitatively, in the form of interaction responses, how effective the adaptive robot backchannel strategy is; and H3. Socio-cultural characteristics of the speakers will also influence how they perceive the robot’s interaction.The question is analysed in an experiment where a social robot provides relatively more, and more expressive, backchannels towards the least speaking participant in an interaction pair. Our hypotheses are that The user experiment was conducted by two researchers, one with the main responsibility of interacting with the participants and one in charge of launching and monitoring the hardware and software for the experiment.Titan face mask, as shown in The first researcher welcomed the participants, distributed and collected the informed consent form—which described the experiment, the data collection, the handling and analysis of the recorded data and the subject’s rights to withdraw from the study during or after the experiment—and checked that the participants had filled in the pre-study questionnaire , which wThe robot introduced itself, asked the participants some icebreaker questions and then repeated the rules of the game see . This waThe human-robot interaction was centered around the word guessing game Taboo, in that the human players should describe a word—without saying the word or part of it—shown to them, in writing and with a picture, on a computer screen. The screen was placed behind the robot, as shown in Two sets of robot backchannel behaviour were used in this experiment, the rule-based static (for the control group) and the activity-adapted . The two sets are equal in terms of backchannel verbal formulation and timing, and to the extent that it is possible to control, target for total frequency of feedback during the session (note that the amount of backchannels depends on the subjects’ speaking activity and therefore differs between sessions). The two sets are therefore regarded to be equally valid robot backchanneling strategies in general . The difference between the two sets primarily lies in how they are distributed between the two human interlocutors.The robot used the “interested” and “understanding” backchannels in the Acapela text-to-speech synthesis for Swedish with the Elin voice. A large variation of predefined non-verbal  and verbal  in different prosodic renditions are available. For the control group backchannels, a low intonation and a neutral emotion expression was used and no additional visual backchannel cues were provided.Backchannels were provided at approximately 35% of all backchannel opportunities, which where defined heuristically during pilot testing so that they occurred during the human speaker utterances with a minimum interval of 2.9 s between backchannels and only for utterances longer than 1.5 s, but without any linguistic analysis of the semantics of the speaker’s utterances. Since the robot automatically turns its head towards the active speaker, backchannels are clearly addressed towards that speaker.This control condition hence corresponds to a backchanneling behaviour that has been found to be preferred over completely random or no backchannels in previous HRI studies. The average number of backchannels per speaker in the Control condition was M = 11.7 (SD = 13.6), corresponding to 3.7 backchannels per minute of active speaking time.The adaptive robot backchanneling for the experiment group used the same formulation and identification of backchanneling opportunities as for the control group, but provided backchannels inversely proportional to the interlocutor’s accumulated relative speaking time. That is, the interlocutor that has spoken the least should receive more frequent and more expressive backchannels, with the aim of increasing the speaking share for that interlocutor by displaying a boosted listener interest by the robot. Since the accumulated speaking time is used to determine the more and less active interlocutors, the robot’s backchannel strategy is initially attuned and its decision regarding which interlocutor should receive more backchannels may hence change during the interaction. On average, the least active speakers received 2.1 as many backchannels per speaking time in the Experimental condition compared to the Control, whereas the more active speakers received fewer (0.85 times) backchannels per speaking time in the Experimental condition. The encouraging backchannels were selected to be more expressive and energetic and were accompanied by a smile or an affirmative nod.The average number of backchannels per speaker in the Experimental condition was M = 13.3 (SD = 11.6), corresponding to 5.3 backchannels per minute of active speaking time.The pre-session questionnaire gathered demographic information , determined the subject’s extroversion level using eight questions from the Big Five Inventory scale  and charI am using the following voice assistants on a regular basis” , “Describe your previous experience of interacting with a speaking robot”; and attitudes: “Describe your general attitude towards interacting with a speaking robot”; “In my opinion, robots should be developed to be as human-like as possible when it comes to … appearance/…interaction/…voice and spoken utterances/…understanding speech,/…emotions” and “I think that it would be a good idea to employ robots (now or in the future) in ” . Unless other answer alternative are stated above, all questions were to be answered on a five-point Likert-scale 1–5 with guiding descriptions for each level and 1 being very low, 3 neutral and 5 very high.The questions about robots were; regarding experience: “I felt that the robot understood what I was saying”, “The robot was paying attention when I was speaking”, “The robot was friendly towards me”, “The robot was introvert/extrovert”, “The robot was balancing its attention between me and my partner” and “The robot behaved like a human listener”. All questions were answered on a five-point Likert scale 1–5 with guiding descriptions for each level, with 1 and 5 respectively signifying very low and very high levels and 3 neutral.The post-session questions focused on the subject’s impression of the robot in the interaction: “Participants were recruited on the campuses of KTH and Stockholm University, using flyers and electronic invitations. In total, 38 adult subjects, 15 men, 22 women and 1 not disclosed were recruited, with the demographic details indicated in Most subjects had no (13) or little (11) experience of interacting with robots, while 12 had some experience and 2 were regular users . The L2 speakers were slightly more familiar with robots  than the L1 speakers . Further, most (24) did not use any voice assistant, and of those who did, Apple’s Siri was the most used (4 subjects), followed by Google Assistant (3), Google Home (3) and Amazon Alexa (2). The subjects were rather neutral regarding general attitude towards interacting with robots .p = 0.02) related to the previous experience of interacting with robots, with the younger and male participants having more experience  than, respectively, the older and the female .With two exceptions, no significant differences were found, using non-parametric Mann-Whitney U-tests, in the pre-session responses between L1 and L2 speakers, between men and women, between “younger” (below the average of 34 years) and “older”  or between subjects who had less  and more (above 2.0) experience of robots. The only significant differences . Extroversion , familiarity with robots  and attitudes towards robots  were not controlled for, since the pre-session questionnaire data was analysed after the experiment, but were nevertheless rather balanced between the two conditions.The participants were paired so that one L2 Swedish speaker played the game together with either an L1 speaker of Swedish (15 interactions) or another L2 speaker (one interaction with two C1 level subjects and one B2-C1 interaction). Three sessions, two in the Experimental condition and one in the Control, were with two L1 speakers. The pairing was balanced as much as possible between the two experiment groups when it comes to gender , proficiency  and age , but this was still appropriate for the purpose of the interaction .Secondly, the modular text-to-speech synthesis component, which here used a female voice from Acapela, is automatically supplemented by accompanying realistic lip movements, which are an important support for L2 learners’ speech perception. Furhat software further supports natural language understanding using real-time cloud-based automatic speech recognition for its interaction with users. However, due to generally poor automatic speech recognition performance for L2 speakers of Swedish , its gueThe game interaction, in which the robot was fully autonomous, may be illustrated through the examples in Shure Model WH20 professional microphones that were calibrated to avoid detecting non-speech content like sudden movements, breathing, or general noise. The accumulated speaking time was measured continuously during the experiment in order to adjust the robot’s backchannels towards the least active speaker in the Experimental condition. For the post-session analysis, the speaking times were used to investigate the influence the robot’s backchannel strategy had on the balance of the interaction  and the distribution ratio rs of the two subjects’ share of the speaking time , while rs is a more direct measure of the balance between the two subjects.Three measures of speaking activity were used: the subject’s total speaking time In addition, the post-session questionnaire was used to identify how socio-cultural factors, identified through the pre-session questionnaire, influenced the participants’ reactions to robot backchannels . For thevs. L2 speakers in this study), gender, age, extroversion and familiarity with robots. We investigated the influence of these socio-cultural factors on the balancing effect of the robot’s adjusted backchannel strategy  was very similar between the Experimental condition and the Control . Secondly, that the mean speaking time of the less active speaker in each pair was 26.8% higher in the Experimental condition than in the Control . Thirdly, that the speaking time of the more active speaker was 14.8% lower in the Experimental condition than in the Control .The aspect of how the robot’s vocal and visual backchannels influence the balance in the speakers’ participation is the specific focus of the study by R between the dominant and the non-dominant participant in the pair in the Experimental condition was almost half of that in the Control , but this difference was not significant . We ensured that the difference between the two conditions is not due to lower speaking ratio differences for the L1–L1 interactions by calculating the mean difference in speech ratio when excluding the three L1–L1 interactions . Overall, there was almost no difference in speaking ratio Rs between L1 and L2 speakers for the subset of 15 L1–L2 interactions in the Experimental condition . The reason for this difference being lower than that for dominant vs. non-dominant speakers, is that the L2 speaker was more active than the L1 speaker in three interactions in the Experimental condition and one in the Control.The difference in speaking time ratio Δrs depending on gender, age, extroversion and familiarity with robots in combination with if the subjects are L1 or L2 speakers, as shown in vs. L2 is considered as the main factor, since it, in addition to being a cultural feature in itself, corresponds to a difference in linguistic proficiency for 15 out of 19 interactions. We hypothesise that this difference leads to unbalanced speaking time, and hence difference in robot backchannel strategy in the experimental condition. As the subjects are then divided into eight sub-groups, they are too few per group to expect that statistical significance could be found . Since this is a between-subject experiment, comparisons between the Experimental and Control conditions are moreover made on the group level, and do hence not show actual changes in response for individual subjects.These results demonstrate that the robot’s adaptive backchannel strategy reshaped the interaction, as it encouraged the non-dominant speaker to talk more and the dominant to talk less. However, hypothesis H1 was not formally confirmed, as the difference in speaker ratio imbalance was not significant. A main reason for this, illustrated by the high standard deviation in speaking time for the less active speaker in the Experimental condition, is that the encouraging effect was very different for different speakers. For this study, we therefore explore the data further by considering the differences in speaking time ratio r between the non-dominant and dominant speaker in the pair points to possible relationships that are interesting to investigate further, both qualitatively , whereas female L2 speakers (as well as the L1 speakers) have a very similar speaking ratio in the two conditions (p = 0.93).The Younger L2 subjects in the Experimental condition are substantially more active than in the control (p = 0.11) and the opposite is to some extent true for younger L1 subjects (p = 0.17). Older L2 subjects have a lower speaking ratio in the Experimental condition than in the control (p = 0.26) and the opposite is true for older L1 subjects (p = 0.40).The more Extrovert L2 subjects in the Experimental condition are substantially more active than in the Control (p = 0.29), whereas the more introvert L2 subjects are slightly less active (p = 0.69).The more Introvert L1 subjects in the Experimental condition have a lower speaking ratio than in the Control (p = 0.10), whereas the group of extrovert L1 speakers have a slightly higher speaking ratio in the Experimental condition than in the Control (p = 0.63).Familiarity with robots may influence the reaction to adaptive robot backchannels, as L1 and L2 speakers who are more familiar with robots have a higher speaking ratio in the Experimental condition than those who are less familiar (p = 0.17). The L1 speakers who are less familiar with robots have a lower speaking ratio in the Experimental condition than in the Control (p = 0.17), whereas L2 speakers have a slightly higher speaking ratio (p = 0.80) if they are more familiar with robots, but no difference if they are less familiar with robots (p = 1.0).Nevertheless, the observed mean decrease in speaking ratio difference Δtatively  and quanWhat we observe would hence suggest that of the L2 speakers, the male, the younger, the more extrovert and the ones more familiar with robots are more encouraged by the additional backchannel attention from the robot, while the female, older and more introvert L2 speakers are not as encouraged to speak more, or may even speak less. For the L1 speakers, the younger, the more introvert and the ones less familiar with robots may be more susceptible to speaking less if the robot focuses its backchannels more towards the other interlocutor. Without a larger subject group, for which statistical relationships might appear, these observations are rather speculative, but it does seem plausible that extrovert subjects become more active when receiving more attention and that introvert subjects become less active when receiving less. Familiarity with robots could influence in terms of speakers who are more familiar with robots firstly are speaking relatively more in general  positive linear relationship between age and speaking time in the Control , i.e., older L2 speakers spoke more. A linear relationship was also identified for extroversion level , but the effect size was too weak (R2 ≈ 0.1) to be considered.Multiple linear regression analyses were performed to investigate how the socio-cultural factors influenced speaking time. For the L2 speakers, there was a statistically significant , excluding the conversations in which one or both participants spoke so little that no backchannels were generated.Mid-turn, (close-to-) Turn-final and After-turn. To exemplify these timings, in the utterance describing lightning: “It thunders in the dark(MT)and then it suddenly(TF)becomes light.(AT)”, (MT) is Mid-turn, (TF) is Turn-final and (AT) is After-turn. The latter could be with or without a preceding pause. The robot vocal backchannels were annotated as being of three different types, “uhum”, “mm” and “aa”, but as “uhum” dominated heavily , differences in vocal backchannel formulation were not considered.A three-level backchannel timing annotation scheme was used: vs. 48.1% in Control) and After-turn backchannels (42.2% Hold vs. 80.0%). The turn is hence yielded almost twice as frequently in the Experimental condition than in the Control for After-turn backchannels and 25% more frequently for Turn-final backchannels.For speaker reactions, four different alternatives (two each for hold and yield) were annotated: Hold, when the speaker continued without or after a hesitation/pause and Yield, when either the other speaker or Furhat took the turn. This high-level annotation is summarised in vs. 44% without for the After-turn backchannels).The total bar heights in The result that speakers more often yield the turn than holding it after an After-turn backchannel may seem quite non-intuitive, since backchannels in one-to-one interactions usually encourage the active speaker to continue, but it seems that, in this three-party (game) setting, the Turn-final and After-turn backchannels may instead be perceived as an acknowledgement that the robot has understood the utterance and that it is hence the other participant’s turn. The reason that this happens to a larger extent in the Experimental condition would then be that the emphasised backchannels more clearly signals understanding and encourages three-party interaction . Considering the 13 L1–L2 interactions , we first corroborate that the mean number of yielded speaker turns, for all timings, is much higher in the Experimental condition (M = 5.14) than in the Control (M = 0.83) also for this subset , and then find that the proportion of L2 speakers taking the turn is the same in the Experimental condition (M = 0.22) and in the Control (M = 0.2). Hence, the effect of the adaptive emphasized backchannels in the Experimental condition is that both L1 and L2 speakers take the turn more frequently than in the Control, but with the L1 speakers being substantially more active at taking the turn in both conditions.yeah, right, correct, exactly etc.To further investigate turn holding and yielding, a more detailed conversation analysis was performed of the sequences containing Turn-final and After-turn backchannels. The annotation protocol was that every backchannel occurrence was labeled in a separate text file with type , time in the video recording, speaker (left or right), turn-taking , Furhat’s action , the speaker’s verbal reaction  and non-verbal reaction . We found that the generation of backchannels interconnects with the level of collaboration between the two human participants. Collaboration was analysed in terms of concrete practices in interaction, in particular (1) help-seeking, through asking the conversational partner directly or indirectly and with or without accompanying head-turns; (2) bodily orienting towards the partner and directing gaze toward the other, particularly during hesitations or problem of turn completion or continuation; (3) completing each other’s turns without any display of interruption; (4) conducting joint actions, e.g., laughing or sighing together, and finally, (5) generating backchannels on each other’s utterances and even giving (positive) feedback to each other, e.g., vs. 4.8) and also a higher hold ratio for these backchannels (averages of 0.39 vs. 0.25).In general, collaboration firstly leads to more speaking activity for the human speakers and less pauses and silences in interaction, which results in a higher number of generated robot backchannels for participant pairs who collaborate more. Secondly, even if we found this interconnectedness between higher collaboration and higher number of backchannels in both the Experimental and Control condition, it was more prominent in the Experimental condition. Due to the relatively low number of interactions in each setting, it is not possible to determine with certainty that the higher level of collaboration in the Experimental condition is a result of the different robot backchannel strategy, but the findings do suggest that there is a direct relation between a higher frequency of backchannel-productions by the robot and increased collaboration. The four interactions that were assessed to be most collaborative had a higher number of turn-final and after-turn backchannels than the other sessions , but soon yields the turn, which is immediately taken over by L (#09), who produce a clue, but also seeks confirmation from R who confirms it (#11). During this negotiation, the robot produces two backchannels (#10 and #13), which are followed by further collaboration between the human interlocutors (#15–16).tsk”), smacking the lips, and drumming with their fingers on their legs. As the robot is set to respond to descriptions with guesses or backchannels, rather than taking own initiatives, this lack of collaboration also leads to less production of backchannels.In contrast, in vs. 10.4), potentially indicating age-related difference in social conventions for interaction. The collaborating pairs further self-assessed to be less extrovert than the less collaborating pairs . The reason that the less extrovert subjects collaborate more, which might seem counter-intuitive as extroversion is usually considered to promote inter-personal interaction, may be that the individuals in the more extrovert pairs were instead competing more to be dominant, which is also a trait of extroversion.The collaboration between human subjects is dependent on the rapport that they form with each other, which in turn is influenced by socio-cultural factors, such as if the pair is matched in lingusitic level, gender, age and personality (extraversion) and how familiar, and hence comfortable, they are with interacting with a robot. The language proficiency did not affect the level of collaboration, which is also illustrated by the collaborative interaction in An additional factor that influences the rapport is the prior level of acquaintance between the subjects. The L1 and L2 speakers were recruited through separate systems and assigned to sessions independently to avoid that closer acquaintances were paired, but some pairs may nevertheless have had some familiarity with each other. Finally, we are interested also in if socio-cultural factors influence how the participants perceived the robot, which we explore in the next section.p = 0.02) difference was found, i.e., that the L2 speakers found that the robot’s interaction was slightly unbalanced towards them (M = 3.4), while the L1 speakers found that the robot’s interaction was balanced (M = 3.0). From an application point of view, this is interesting, since it could indicate that the L2 speakers became aware that the robot was trying to encourage their interaction, but that this was achieved without the L1 speakers feeling neglected.gender, male L1 speakers rated the robot’s friendliness substantially higher, female L2 speakers the extroversion higher, female L1 speakers the human-likeness lower and both male and female L1 speakers the understanding lower. Female subjects overall rated the robot significantly (p = 0.01) higher regarding attentiveness (M = 4.4) than the male did (M = 3.7), but otherwise there were no statistical differences in the ratings from the two genders.For age, older speakers rated the robot’s friendliness substantially lower in the Experimental condition, whereas the younger speakers rated it higher, and the difference between the age groups was significant (p = 0.02) for the Experimental condition. The older L1 speakers in addition rated the understanding and the human-likeness lower; in agreement with younger L2 speakers in the latter case. The younger subjects overall rated the robot’s extroversion significantly higher (p = 0.03) in the Experimental condition (M = 4.3) than in the Control (M = 3.6), whereas the older subject rated its friendliness significantly (p = 0.04) lower in the Experimental condition (M = 3.2) than in the Control (M = 4.2).For extroversion, the introvert speakers rated the robot’s understanding and attentiveness lower and extroversion higher, regardless of condition. For the Experimental condition, extrovert subjects also rated the robot’s extroversion higher (but less so than the introvert) but the human-likeness and understanding lower. The difference for understanding (M = 2.6 vs. M = 3.9) was significantly (p = 0.01) lower than in the Control and this rating was also significantly (p = 0.04) lower than from the introvert subjects (M = 3.7). For familiarity with robots, the subjects with below-mean familiarity rated the robot’s understanding, attentiveness, friendliness and human-likeness lower and extroversion higher in the Experimental condition, often in contrast to the subjects with above-mean familiarity, who had the opposite view for understanding (L2 subjects), attentiveness and human-likeness (both L1 and L2 subjects) and friendliness (L1 subjects). The rating of human-likeness by the subjects with below-mean familiarity with robots was significantly (p = 0.01) lower in the Experimental condition than in the Control (M = 2.8 vs. M = 4.0). The latter rating was further significantly (p = 0.01) higher than the rating from the subjects with above-mean familiarity (M = 2.7).The set of L1s was too heterogeneous to make any statistical analysis of post-session survey differences between L1s or L1 language groups. Further, we initially hypothesised that educational level, as a proxy for sociolect, could influence the perception of robot backchannels, but since all recruited subjects were at university undergraduate or graduate level, the group was too homogeneous to explore this.p = 0.01) relationship found was for the rating of the robot’s friendliness, for which the male subjects’ rating increased with age, regardless of condition and regardless of if they were L1 and L2, and the female subjects’ rating decreased with age in the Experimental condition for both L1 and L2 subjects, while it was close to constant in the Control.A multilinear regression analysis was performed for each of the post-survey categories to investigate how experimental condition, gender, L1/L2 speaker and age plus their interactions influenced the ratings. The only statistically significant . Attentiveness was affected by gender, in line with earlier findings  and short (60 s per game word) interactions, whereas another measure would be required for longer and less structured conversations, in which different speakers may dominate sequentially. For the latter case, it may be more appropriate to estimate the dominating speaker based on a sliding time window.It should finally be noted that the nature of backchannels is such that they can only be delivered towards someone who is speaking. This signifies that the absolute number of backchannels will be low for subjects who speak very little, even in the Experimental condition when the robot provided relatively more backchannels towards the least speaking subject . Moreover, the adaptive backchannel strategy in the Experimental condition has the side effect that if one of the speakers is very inactive, then the more active speaker will also receive few backchannels, since the robot aims to display a higher relative proportion of backchannels towards the other speaker . An improved adaptive backchanneling strategy, when the time limit is less strict, would be to ensure a minimum level of backchannels towards an active speaker, even if the other participant is silent.This study has investigated how users of different socio-cultural backgrounds perceive and react to robot backchannels as a first step towards creating culturally aware robots. The next step would be to use the information to adapt the robot’s behaviour and interaction to suit the present users. Based on the results above, we suggest that the robot’s backchannels may be adapted in the following ways:The experiment showed that Participation-adjustment, i.e., to display relatively more backchannels towards the least-speaking participant, contribute to a more balanced interaction, but is—at least with the current formulation and timing—more effective for male, younger and extrovert speakers, compared to female, older and introvert speakers. The formulation, timing and frequency of backchannels may therefore have to differ for different socio-cultural groups in order for them to have the same function.Further, the conversation analysis showed that the social rapport between the participants influences how the robot backchannels are perceived, as speakers in collaborative pairs are more likely to hold the turn after a turn-final or after-turn backchannel than non-collaborative speakers. The intended function of the robot back channels—e.g., to promote collaboration or to specifically encourage the current speaker to continue—should hence influence timing, frequency and formulation of backchannels.Gender and/or age influence expectations on the interplay between interlocutors in a conversation, regarding what constitutes a friendly, attentive listening behaviour. The backchannel strategy in the present study was the same towards all subjects in the same condition, but observations from the reactions  suggest that female and older subjects may expect more and more explicit backchannels that are also more equally distributed between interlocutors in order to perceive the robot to be polite and encouraging speaking activity.In addition to the above differences in perceiving backchannels, it should be noted that previous studies have shown that there are gender differences in producing them, and the robot backchannels may need to be adapted if a male voice is used for the robot. Similarly, the Furhat robot used in this study is more anthropomorphic in appearance and interaction signals than most other commercially available robots. It remains to be shown if similar effects would be obtained also with less anthopomorphic robots.Introvert speakers should receive more explicit verbal backchannels, formulated to clearly encourage them to continue, when this is the robot’s intention. This may in particular be required for subjects with low familiarity with robots, as they seem to perceive robot backchannels differently than more experienced subjects. It should also be considered that there may differences in the subjects’ responses to robot backchannels depending on if they are formulated to encourage the less active speaker (as in this study) or to restrain the more active speaker (in order to provide the peer with more opportunities to speak).The multimodal analysis further suggests that the timing and formulation of the backchannels influence how the interlocutors perceive their function, as Turn-final and After-turn backchannels often encouraged speakers to yield the turn rather than to hold it. Backchannel formulation should hence correspond to its intended function for the timing when it is issued.The EMCA analysis identified a number of age-gender-extroversion related differences, which could be used if a rule-based backchannel strategy is employed, but a data-driven approach may hold larger potentials to learn formulation, timing and frequency of backchannels for different interlocutor categories  from a multimodal spoken interaction database, e.g., Spontal .Starting from the findings in previous research that backchannel production and perception differ between different socio-cultural groups and that robot backchannels may shape HRI, we have shown, in a multi-party experiment, that the robot’s backchanneling strategy has a substantial impact on how two speakers distribute their speaking time (H1) and that both the distribution of speaking time (H2) and the perception (H3) of the robot are influenced by several socio-cultural factors. These influenced the effectiveness of the encouraging backchannels and we have therefore proposed a number of adjustments to different socio-cultural factors that should be made if a rule-based backchanneling strategy is used. The proposed changes should be evaluated in future user studies, but may also be calibrated with and compared to observed backchannel strategies in existing multimodal databases of human-human interaction. Backchannels play a very important role in natural spoken interactions between humans and based on findings such as the ones from this study, robots may be endowed with backchannel capabilities that make them more culturally aware.


Weak hydrogen bonds formed between the hydroxylated sapphire surface and the π-electron system of SLG result in a clean interface. The charge injection induces a band gap in the adsorbed graphene layer of about (73 ± 3) meV at the Dirac point. The good agreement with the predictions of a theoretical analysis underlines the potential of this hybrid system for emerging electronic applications.Metal-free chemical vapor deposition (CVD) of single-layer graphene (SLG) on c-plane sapphire has recently been demonstrated for wafer diameters of up to 300 mm, and the high quality of the SLG layers is generally characterized by integral methods. By applying a comprehensive analysis approach, distinct interactions at the graphene-sapphire interface and local variations caused by the substrate topography are revealed. Regions near the sapphire step edges show tiny wrinkles with a height of about 0.2 nm, framed by delaminated graphene as identified by the typical Dirac cone of free graphene. In contrast, adsorption of CVD SLG on the hydroxyl-terminated α-Al The excellent structural, thermal, and chemical stability combined with mechanical flexibility and electrical robustness may be of particular interest for memristive devices, which are considered key components for next-generation edge computing6. Recently, Wang et al. demonstrated a graphene/MoS2−xOx/graphene device that exhibits excellent resistive switching performance with an endurance of up to 107 at an operation temperature of 340 °C7. However, further research is needed for a deeper understanding of the role of interfacial properties and defects, especially, those formed during growth and exfoliation8. To fully exploit the exceptional properties of 2DMs for new neuromorphic computing concepts, a scalable process compatible with semiconductor technology is needed to obtain high-quality material on technologically relevant wafer sizes9.Two-dimensional materials (2DMs) are considered as prime candidates for significantly extending the functionality of silicon chips, referred to as ‘CMOS + X’. Co-integration of 2DMs with silicon technology raises the prospect of substantial performance and functional gains in areas like ‘More than Moore’, photonic integrated circuits, neuromorphic computing, and quantum technologies13. However, impurities resulting from imperfect removal of metal catalysts and the PMMA (poly(methyl 2-methylpropenoate)), which is required for the transfer processes, hinder the use of this material for high-volume production while meeting semiconductor standards15. Therefore, current research interest is focused on direct graphene growth on insulating substrates compatible with silicon technology such as α-Al2O3 (0001)20. This standard substrate in compound semiconductor technology guarantees large-volume availability of large-diameter wafers with the required quality at reasonable cost21. Moreover, the lattice constant of the c-plane of sapphire, 0.476 nm, is almost twice that of graphene (2 × 0.247 nm)22. Recent studies have demonstrated the suitability of c-plane sapphire wafers for direct CVD of high-quality SLG24 and the up-scaling to 150 mm diameter substrates using a production scale reactor (AIXTRON CCS 2D)25. Since the first reports of direct growth of SLG on sapphire, the alignment of the SLG on different sapphire surfaces has been the subject of several investigations. Entani et al. and Dou et al. reported a strong interfacial interaction between graphene and α-Al2O3 (0001) dominated by electrostatic forces in the graphene π-system and unsaturated electrons of the oxygen layer of the α-Al2O3 (0001) surface forming a C–O–Al interfacial bond27. In contrast, Saito et al. and Ueda et al. found that graphene growth on c-plane sapphire starts from etch pits formed during the CVD process. The Al-rich surface within the pits plays a central role in the catalytic activity for SLG growth29. This assertion is also supported by the work of Mishra et al. and Chen et al., who obtained high quality CVD SLG for α-Al2O3 (0001) treated in a hydrogen atmosphere prior to the graphene deposition at high temperatures of 1180 °C and 1400 °C, respectively25. Room temperature carrier mobility values of over 2000 cm2/Vs and 6000 cm2/Vs were reported. In contrast to SLG grown on untreated wafers, these films exhibited a lower density of ridges, well defined atomic terraces, and improved crystalline quality with an averaged full width at half maximum (FWHM) of the 2D Raman mode of about 30 cm-1 to 35 cm−1. The low D/G and high 2D/G intensity ratios of about 0.15 and well above 2, respectively, indicate low defect density and carrier concentration in the lower 1012 cm−2 range25. However, the increasing interest in using CVD SLG on hydrated α-Al2O3 (0001) to realize nanoscale electronic devices for next-generation electronics, optoelectronics, quantum and neuromorphic computing, requires a more detailed physicochemical understanding of the electronic properties of the SLG/sapphire system down to the atomic scale32. In particular, the potential energy surface of the SLG on sapphire stack affects both the interface with subsequently deposited layers of sp2-hybridized 2DMs such as h-BN and transition metal dichalcogenides and the characteristic properties of functional devices such as reliability, endurance and retention.Chemical vapor deposition (CVD) has proven to be a reliable, reproducible, and technologically viable synthesis route to wafer-scale SLG films characterised by good crystallinity, low impurity densities and full compatibility with large-scale back-end-of-line (BEOL) integration. Large-area SLG were initially fabricated by CVD on Cu, which serves as a catalyst for the decomposition of hydrocarbon sources2O3 (0001) provided by AIXTRON SE. Raman spectroscopy and Raman mapping were combined with scanning electron microscopy (SEM), conductive atomic force microscopy (c-AFM) and Hall measurements in van der Pauw geometry realized by vapor deposited gold contacts. Surface chemical characterization was performed by X-ray photoelectron spectroscopy (XPS). Atomic level electronic properties were analyzed by scanning tunneling microscopy (STM) and spectroscopy (STS). The combination of micro- and nanoscale analyses provided a deeper understanding of local variations in the SLG/sapphire interactions and the weak electrostatic bonding that controls the electronic properties of the system. A comparison with previously published results from advanced-principles calculations33 complements the study.Therefore, this study focuses on the analysis of local electronic transport properties of CVD SLG on α-Al2O3 (0001)) in an AIXTRON CCS 2D system in 19 × 2″ configuration. The deposition process was essentially similar to the one described in Ref.25. In a pre-bake step, the sapphire substrates were etched in H2 atmosphere at 1400 °C for 10 min. This was followed by graphene deposition at 1460 °C for 500 s using a CH4/H2 mixture in N2 atmosphere at 700 mbar. The SLG/α-Al2O3 (0001) wafers were cleaved into smaller pieces and subsequently, stored in vacuum or under inert gas for further analysis. The transport of the samples or cleaved pieces between the different measurement or storage facilities was done in closed boxes. No further treatment was performed prior to measurement.SLG was deposited on c-plane sapphire with an offcut of 0.2°  GL (20) while all other components were fitted by symmetric peak shapes as GL (30). Samples were stored in nitrogen to minimize atmospheric exposure. Carrier type, mobility and sheet density were obtained from Hall effect measurements at room temperature and a magnetic field of 0.2 T using a LakeShore 8404 AC/DC Hall effect measurement system. The SLG/sapphire samples were cleaved into 10 mm × 10 mm pieces and contacted by Pt metal pads in conventional van der Pauw geometry. SEM images were acquired using a Hitachi SU8000 operating at an acceleration voltage of 0.5 kV and a chamber pressure around 10–7 mbar. The SLG was grounded during these SEM measurements. For c-AFM and STM measurements a smaller piece of the sample (max. 10 × 10 mm2) was placed on an Omicron sample holder. Two small metal sheets were used to fix the sample and make a conductive contact to the SLG which served as a back contact. AFM and c-AFM measurements were executed under ambient conditions. AFM and c-AFM measurements were performed in tapping and contact modes in a Cypher AFM (Asylum Research) with commercial AFM probes (Nanosensors™). STM and STS measurements were performed using a low-temperature (LT) STM from CreaTec Fischer. The STM was operated under ultra-high vacuum (UHV) with a chamber pressure below 10–10 mbar at 4.2 K using custom-made electrochemically etched W tips. Unless otherwise specified, the following systems’ settings were used: STM measurements were performed with an applied bias voltage of 2.3 V and a set-point current of 0.23 nA in constant-current mode. STS measurements were made in the range of + 1.0 to − 1.0 V with feedback loop turned off. The differential tunnel current was determined using an internal lock-in amplifier operating at 473 Hz and an amplitude of 80 mV. The STM images were plane-corrected using the SPIP™ analytical software of Image Metrology A/S, with an optional noise filter.µ-Raman spectroscopy in mapping mode was performed at room temperature utilizing the confocal Raman microscope XploRA™ Plus of Horiba equipped with a solid-state laser with a wavelength of 532 nm at 8 mW. The laser line was focused on the sample by a 100 × microscope objective lens resulting in a spot size of about 0.5 µm. The collected light was scattered through a grating with 1200 grooves/mm. Mappings were performed with an exposure time of 2 s, an accumulation time of 2 s and a step size of 0.4 µm. The data were processed using LabSpec 6 spectroscopic suite software from HORIBA. First, a baseline subtraction is performed, then the peak position is determined by the peak maximum. Intensity ratios are calculated from the maximum intensity values and FWHM-values are determined at half maximum intensity. Comparison with the Lorentzian fit of the peaks provides comparable values considering the error ranges. XPS measurements were performed with a VersaProbe 5000 from Physical Electronics. Monochromatic Al K35. Characteristic values such as the positions of the G and the 2D peaks, ΔωG and Δω2D, respectively, the full width at half maximum (FWHMG and FWHM2D), and the intensity ratios I2D/IG and ID/IG are shown in Table I2D/IG can be used to qualitatively estimate whether the analysed graphene film is SLG or multilayer graphene. It is noticeable that the intensity ratio depends on the Raman setup, especially on the laser wave length and the chosen grating36. Peak positions and FWHM depend on the number of layers, but also on the density of defects and on strain effects37.The sample structure is outlined in the inset of Fig. 38. ID/IG values in the range of 0.2 indicate moderate defect density in our samples39. The thin vertical lines in Fig. −1 and 2673 cm−1, respectively40. A slight shift of the peaks to higher values, corresponding to a blue shift, indicates minor compressive strain, probably induced during cooling from the deposition temperature37. Since coefficients of thermal expansion of graphene and sapphire are different over the entire temperature range - negative for graphene and positive for sapphire - a lateral compressive stress is induced in the graphene layer during cooling43.Moreover, the D/G intensity ratio is reciprocally related to the defect concentration of SLG and also correlates with the grain size37. Figure I2D/IG < 2. Moreover, the linewidth of the 2D peak is very broad in the 53 cm−1 region, but the peak positions almost orrespond to the free-standing graphene. (2) The red spectrum meets the SLG criteria considering I2D/IG > 2 and shows the smallest peak widths of all curves with FWHM values of about 16 cm−1 and 35 cm−1 for the G and 2D peaks, respectively. (3) The blue spectrum also meets the SLG criteria, but shows a significant blue shift in the G and 2 -peak positions compared to free-standing graphene, which can be attributed to a compressive stress effect. The ID/IG ratio of the blue curve is slightly increased compared to the red curve consistent with an influence of strain in addition to defects from the growth process. Compared to the results of Tsoukleri et al.44, who subjected a graphene monolayer to tensile and compressive strain, the obtained peak shift of the blue curve could be attributed to a local compressive strain of about 0.3%. Despite the limited lateral resolution of the Raman measurements, the mapping gives evidence of local differences in the quality of the graphene layer, predominantly SLG, grown on the sapphire substrate by CVD. Van der Pauw measurements performed on samples of about 10 mm × 10 mm in size show an overall slight p-type conduction of the SLG with a mobility at room temperature of (1500 ± 100) cm2/Vs and a sheet carrier concentration of about 2.22 × 1012 cm−2, which are in a reasonable range compared to the range in the literature, from outstanding values of about 6000 cm2/Vs20 to values commonly reported for CVD graphene on dielectric substrates, typically below 1000 cm2/Vs45. It appears that the H2-etched α-Al2O3 (0001) surface has a smaller effect on the electronic properties of SLG than other dielectric substrates.Although the lateral resolution of the mapping is still moderate at less than 500 nm, there is a clear local inhomogeneity in the quality of the graphene layer, in agreement with the report of Neumann et al.2O3 (0001) sample after prebaking in hydrogen at 1400 °C for 10 min, and for the SLG/sapphire sample. For the analysis of the untreated and the prebaked sapphire substrates, the energy scale was calibrated using the C 1s signal of adsorbed carbon at 285.0 eV. Due to the overlap of the C 1s signals from adsorbed carbon species and the graphene layer for the SLG/sapphire samples, the energy scale was calibrated with respect to the Al 2p peak of Al2O3 at a binding energy of 74.1 eV46. Figure 2O3 (0001), the sapphire surface prebaked with H2, and the SLG/sapphire samples as black, blue, and red lines, respectively. For all scans, only peaks attributable to oxygen, carbon and aluminium are observed. Other peaks such as those from impurities, are not seen. The Al 2p, O 1s, and C 1s core level spectra of the sapphire substrate in the untretaed and H2-prebaked state are shown in Fig. 2 peak which was fitted with an asymmetric peak shape as A  GL(20)47. The peak energies and widths (FWHM) of the chemical components fitted to the spectra are listed in Table 2O348. After prebaking at 1400 °C in H2 additional peaks appear in the Al 2p and O 1s spectra at about 74.8 eV and 531.5 eV, respectively * are determined to be 75.9 eV and 532.5 eV for Al 2p and O 1s, respectively. Again, the ratio of the peak intensities [(Al–OH)*]/[Al2O3] for the two core level spectra is constant with a value of about 0.55 at 45° take-off angle. The appearance of two interface components, Al–OH and (Al–OH)*, with different binding energies could indicate local inhomogeneities in the SLG/sapphire interaction. The increased binding energy of the (Al–OH)* component ompared to the literature values for Al–OH indicates the formation of hydrogen bonds. The C=O signal is strongest at an analyser angle of 63°, indicating surface species. The C 1s core level spectrum in Fig. 3 and C sp2 signals as the major species. The C sp2 species and the clear signature of the π–π* (shake-up) peak at a binding energy of about 290.5 eV , regardless of the analyzer angle.The spectra of Al 2p and O 1s core levels are also considered as indicators of the chemical state of the H2O3 (0001) exhibits two types of step edges, smaller ones with a step height of 0.21 nm ± 0.01 nm, characteristic of monoatomic α-Al2O3 (0001) steps (1/6 c = 0.217 nm) between two oxygen layers, and larger ones with a step height of 1.30 nm ± 0.01 nm corresponding to the height of the unit cell (c = 1.299 nm) or a multiple thereof52. A unit cell step is marked in the height profile of Fig. 54. The height of the observed wrinkles ranges from 0.2 nm to 0.6 nm, and a root mean square (RMS) roughness of (38 ± 2) pm was obtained for areas of 1 µm2 including the step edges of sapphire.Large-area AFM images Fig. a show a 2O3 (0001) measured in the enter of flat sapphire terraces  emerges. The height of these step edges can be as low as 0.22 nm but can rise to more than 4.0 nm  in the terrace region, is energetically favourable compared to the delaminated graphene/sapphire structure near the step edges (G-II). However, the latter allows the release of stresses and is necessary to enable the formation of the preferred G-I structure also on the next terraces. This issue will be further discussed together with the results from STM/STS analysis.Another feature that appears in the high-resolution AFM images is a variation in the height of the SLG surface with respect to the sapphire surface Fig. b,c. It s nm Fig. b. Thus, 55, suggesting that SLG regions G-II along the step edges have higher carrier density than SLG regions G-I, which are more tightly bound in the enter of the sapphire terraces. In addition, SEM analysis allowed us to image these specific morphological features at larger length scales and at multiple positions on the wafer  surface have been reported in the literature, resulting in an interlayer spacing of 0.26 nm26. On the other hand, theoretical studies of SLG on the Al-terminated α-Al2O3 (0001) surface show weaker dispersion interactions and an interlayer spacing of 0.31 nm26. Importantly, a vertical spacing of 0.338 nm for the SLG/Ir(111) system and of 0.215 nm for SLG/Ni(111) indicates weak van der Waals and covalent interactions, respectively57. Strong electrostatic interactions between SLG and α-Al2O3 (0001) result from the delocalized π-electron system of SLG interacting with the dangling bonds of the α-Al2O3 (0001) surface. These dangling bonds, located at the topmost oxygen atoms, induce p-type doping of SLG26. Due to this interaction  between the layers, a decrease in electron mobility is expected. However, we found that the vertical SLG/α-Al2O3 (0001) distance is increased by 0.12 nm near the step edges of the sapphire. Assuming a minimal value of 0.26 nm for the interfacial distance on terraces, this would result in a distance of 0.38 nm (= 0.26 nm + 0.12 nm) at the step edges. This is significantly larger than the interlayer spacing of graphite (0.336 nm), indicating delamination of the SLG in this region. Delamination also explains the fourfold higher conductivity in the sapphire edge regions compared to the terrace regions of α-Al2O3, where the electron mobility is reduced due to interlayer interactions. Consequently, SLG in regime G-II is considered as ‘nearly free-standing’ graphene in the following.Relatively strong electrostatic interactions between SLG and the oxygen terminated α-Al58. The resulting charge inhomogeneity is randomly distributed. The left side of Fig. 60. The superstructure of SLG in the G-I regime has a period between 2.64 nm  and 2.68 nm, with the majority of buckles having an apparent height of about 45 pm and only a few buckles, shown as brighter regions in Fig. 25. The buckle structure is rotated by 27° ± 1° compared to the atomic honeycomb structure of SLG  surface, is onsistent with the supercells proposed for Al-terminated sapphire and, in particular, with the data reported by Mishra et al. who used a comparable deposition method for SLG25.More detailed information about the surface structure of our samples was derived from LT-UHV-STM measurements. The right side of Fig. 2O3 (0001) in the two regions, are also visible in the STM analysis. While G-II exhibits the features of a free-standing graphene layer, a honeycomb pattern, and random contrast fluctuations, G-I shows the signs of interlayer coupling, i. e., a triangular appearance of the graphene pattern and a superstructure  interface were investigated in more detail using STS /(I/V) spectra is plotted to show the main features. The STS curves in Fig. We clearly observed differences in the binding mechanism on the flat terraces and near the step-edges of the same sample leading to different electronic properties in the respective regions. These results are of obvious significance for the design of devices using SLG/sapphire as the bottom electrode/substrate stack. Therefore, the local electronic properties of our SLG/α-AlSTS Fig. . In partSTS Fig. a. They wSTS Fig. , while i62. All these effects an lead to peculiarities in the bias dependence of the differential conductance, which is directly related to the local DOS. In the (dI/dV)/(I/V) curves obtained for G-II  at (− 0.52 ± 0.03) V and (+ 0.36 ± 0.04) V, respectively. They correspond to tip-graphene interactions that increase in intensity with rising set point current, i. e., with decreasing tip-sample distance63. In Fig. VDII = (15 ± 7) mV (Iset = 0.22 nA) indicating weak p-doping, which is consistent with the results of our van der Pauw measurements. However, this Dirac point shift strongly depends on the tip material, in particular the difference in work function between the tip material and the graphene, the tip geometry, and the distance between the tip and the sample64. As the tip approaches the sample, we observe a shift of the Dirac point and the whole STS spectrum to negative values, ΔVDII = (-155 ± 13) mV  in graphene is very sensitive to even small environmental pertubations such as electrostatic coupling to the underlying substrate, the effects of ripples and defects, or simply an approaching tip2 or on graphite65. The coupling of tunneling electrons with substrate inherent phonons, here presumably the out-of-plane acoustic phonon of graphene with an energy of about 65 meV65 leads to features in the LDOS at EF ± 65 meV that explain our observations. e–ph coupling is characteristic for free-standing graphene and therefore suggests that at most a small interaction of SLG and sapphire may be present in G-II65. It should be noted that as the distance between the tip and the samples decreases, the pertubations of the LDOS become more pronounced, thus affecting the shape as well as the observation of the Dirac cone.The two shoulders flanking the Dirac point with a separation of about (134 ± 24) mV, observed for G-II in Figs. 2O3 (0001). These defect states are reported to show a separation of about 1.5 eV and vary locally as expected for non-uniform surfaces66. Thus, the main features in the differential conductance spectra on G-I and G-II are due to different causes: SLG π-band/α-Al2O3 defect state and SLG/tip interaction, respectively. This is also reflected in the changed distance between the main features of 1.60 V on G-I and only 0.88 V on G-II , a shift of the Dirac point of only ΔVDI = (− 34 ± 14) mV (to negative voltages) is observed, which is significantly smaller compared to that on G-II. This is a consequence of the enhanced coupling of SLG to the α-Al2O3 (0001) substrate. It should be noted that at Iset = 0.22 nA the Dirac point is at VDI = (16 ± 7) mV, indicating weak p-type doping, while at Iset = 0.51 nA the value VDI = (− 18 ± 9) mV is the result of interactions of the G-I layer with the W-tip and the α-Al2O3 (0001) substrate. The Dirac points of the G-I and G-II regimes for large tip/substrate distances both show comparable slight p-doping.The normalized differential conductance data measured on G-I, Fig. c show si-II Fig. b indicat2O3 (0001) in an epitaxial manner causes a periodic superstructure accompanied by a pronounced influence on the electronic structure of G-I. The periodic interlayer coupling leads to a breaking of the graphene sublattice symmetry and the twist angle between the SLG and α-Al2O3 (0001) discussed above probably leads to Van Hove singularities (VHS), i. e., maxima, in the LDOS of graphene61. These appear in our STS measurements on G-I as peaks at both sides of the Dirac point  surface, since VHS as well as all other pertubations of graphene DOS with respect to the substrate can be observed only in the case of interlayer coupling .The electrostatic binding of SLG on the enter of the terraces of α-AlI/dV)/(I/V) curves depicted in Fig. Iset = 0.35 nA shows a band gap opening at the Dirac point of (87 ± 5) meV  surface67. Such band gap openings can be as large as 90 meV or 260 meV, as reported for SiO2 or SiC substrates, respectively69. However, here the band gap is only visible at certain current set points used for STS and disappears at larger and smaller values68. We observe this dependence on the current set point, and, in addition, a local dependence. The band gap opening is best resolved at the last measurement point on G-I, where the periodic modulation of the π-band ends but the sublattice symmetry is still broken. As a result, the intensity of the VHS decreases and the interference with the remaining band gap is smaller. The magnitude of the band gap opening determined in this work is rather small and indicates a minor interaction between G-I and α-Al2O3 (0001). However, it agrees well with the value of 84 meV derived from advanced first-principle calculations performed by Huang et al. on the graphene/α-Al2O3 (0001) system33. Based on their calculations, the authors proposed two structures with clean interfaces. These are graphene on Al-terminated α-Al2O3 (0001) and graphene on fully hydroxylated α-Al2O3 (0001) with an open band gap of about 182 meV and 84 meV, respectively. On the other hand, the calculations of Huang et al. predict a strong interaction between an O-terminated sapphire surface and the graphene layer, leading to gap states resulting from hybridization between graphene and the oxygen orbitals of the surface33. Strong Al–O–C bonds, as described in Refs. can be excluded for our system.The (dI/dV)/(I/V) curves for the 0.22 nA and 0.35 nA set point currents, indicated by red and blue colours, respectively. The abrupt change of the main peak positions in the transition region between G-II and G-I can be clearly observed. In addition, the clear Dirac point dependence of G-II and G-I on the tip-to-surface distance is evident. Another interesting feature, best inferred from Fig. VD in G-I and G-II is clearly different and directly supports the assumption that G-I corresponds to coupled graphene, while G-II is almost free-standing.The changes in the local electronic properties of the graphene that occur along the line from one SLG region to the other are summarized in Fig. 2O3 (0001) system obtained from a scalable CVD process by means of chemical surface characterization and quantitative analysis of the local topography and electronic structure in comparison with studies of graphene on graphite and SiO2 and structure simulations derived from first principle calculations70 allow us to unambiguously identify the interlayer coupling of the SLG/α-Al2O3 (0001) interface. Based on the results of XPS and (dI/dV)/(I/V) analysis, we can exclude the O-terminated α-Al2O3 (0001) surface and strong Al-O-C bonds for our system. A more detailed comparison identifies the SLG/hydroxylated α-Al2O3 (0001) as the most likely interface. This is also supported by the flat topography observed for the SLG on the sapphire terraces and by the experimental evidence of a band gap opening in the SLG of about (73 ± 3) meV at the Dirac point. This is very close to the value of about 84 meV calculated for the interface of graphene and the hydroxylated α-Al2O3 (0001) surface33.The results of the comprehensive analysis of the SLG/α-Al2O3 (0001) structures for the two regimes in agreement with the chemical and topographic results described so far. The partial hydroxy -termination of the sapphire surface derived from XPS analysis is included in the schematics. The SLG regime G-I shown in Fig. 71. In the G-II region near the step edges, the interlayer spacing is further increased, resulting in nearly free-standing SLG, as shown in Fig. 2O3 (0001) interface in the G-I and G-II regions explain our experimental topographic and electronic observations. The basic model shown in Fig. In summary, the schematic drawings in Fig. 2-etched α-Al2O3 (0001) applying various surface sensitive methods such as SEM, AFM, c-AFM in combination with XPS and Raman spectroscopy. The homogeneous wafer-size SLG which originates from a commercial CVD process, shows inhomogeneity at the local level at intermediate defect concentration. In addition, we have identified two regions of our SLG films with significantly different SLG/α-Al2O3 (0001) interfacial interactions. Characteristically, these regions are located either on sapphire terraces or along step edges. Based on an atomically resolved topographic and electronic characterisation using STM/STS methods, weak but distinct interfacial interactions were found on the sapphire terraces, which can be attributed to weak hydrogen bonds between the hydroxyl terminated sapphire and the SLG. These to moiré structures  formed by a twist angle between the hexagonal α-Al2O3 (0001) and the hexagonal graphene structure. A band gap opening in the SLG of about (73 ± 3) meV at the Dirac point, which is a consequence of charge injection into the graphene layer, could be experimentally detected. The absolute value is in good agreement with a prediction from first-principle calculations. In contrast, SLG near the step edges is considered to be almost free-standing. This situation can be described as conductive paths formed by the free-standing SLG along the sapphire step edges and the SLG on the sapphire terraces, which is less conductive by a factor of 4. The weak interfacial interaction between SLG and H2-etched sapphire allows for high charge carrier mobility leading to high conductivity of SLG/α-Al2O3 (0001). We believe that these results contribute to further understanding of the SLG/α-Al2O3 (0001) interface and are of particular interest for future device concepts based on graphene as conducting electrode layer with epitaxial relationship to the supporting insulating substrate.In summary, we have investigated local correlations between morphological, topographical and electronic properties of SLG deposited on HSupplementary Information.


The optimal device can detect wide-range RH from 15% to 70% with small incremental changes (0.1–2.2%). X-ray photoelectron spectroscopy reveals the relation between the surface binding condition and sensing response. Finally, the proposed sensor is attached onto the face mask to analyze the real-time human breath pattern in slow, normal, and fast modes, showing potential in wearable electronics or respiration monitoring.Developing ultraflexible sensors using metal oxides is challenging due to the high-temperature annealing step in the fabrication process. Here, we demonstrate the ultraflexible relative humidity (RH) sensor on food plastic wrap by using 808 nm near-infrared (NIR) laser annealing for 1 min at a low temperature (26.2–40.8 °C). The wettability of plastic wraps coated with sol-gel solution is modulated to obtain uniform films. The surface morphology, local temperature, and electrical properties of the SnO Relative humidity (RH) is the measurement of water vapor in air at a specific temperature and pressure . Sensing2/rGO, graphdiyne, and Cellulose NF/Carbon black-based humidity sensors printed on flexible substrates were also demonstrated .,46.45,462, acetone, and NH3 under a fixed background relative humidity (RH 60%). The concentration of the analyte gas was controlled by tuning the flow rate and volume of the syringe pump system. Moreover, the injection time was fixed to be 30 s in the syringe pump system. All the measurements were carried out at room temperature (24 °C), which was controlled by the air conditioner.First, the relative humidity of the sensing chamber must be controlled by the mass flow meters of “dry air” (directly from the air cylinder) and “wet air” (through the water chamber). We modulated the relative humidity to 15%, 20%, 30%, 40%, 50%, 60%, and 70%, and the relative humidity was monitored by a commercial relative humidity sensor (CHY-321 Thermo Hygrometer). After placing the flexible sensor inside the sensing chamber, we needed to wait for a stable electrical signal in real-time measurement using Keysight U2722A at a fixed voltage of 7 V. The current was traced when tuning the RH levels. The flow rate of the total gas flow was fixed at 500 mL/min. To also place an incremental change in the RH level, the syringe pump was used to inject pure nitrogen into the sensing chamber. Tuning the syringe pump can cause a 0.1% to 2.2% RH change in the chamber. When testing the selectivity, the syringe pump then injected various analytes such as NO, NO2 film when using the various solvents  on the three kinds of plastic wrap substrates. The mixing ratios were mentioned above. It is observed that SnO2 on HDPE/resin exhibited the highest current (5 × 10−7 to 4 × 10−6 µA). The current is higher than LDPE (~10−8 µA) and PMP (7 × 10−8 to 2 × 10−7 µA) under a 7 V biasing voltage at 60% RH. It is also noticed that LDPE and PMP substrates took a longer time (~1 h) to dry the film under vacuum. Spin-coating the sol-gel mixture on the HDPE/resin substrate can lead to a dry film within 30 min under vacuum. Note that the commercially available HDPE/resin plastic wrap exhibits roughly 0.01 mm textures on the surface. In the following experiments, we selected the HDPE/resin plastic wrap as the substrate and used the DI water: ethanol (1:1) mixed solution in the sol-gel solution process. When using the solution process to form the semiconductor film, the weak affinity between the substrate and solvent leads to poor thin film uniformity and hence poor device electrical properties and stability. Thus, the exploration of how to find a proper solvent to form a uniform sensing film on various kinds of plastic wraps is important. The hydrophilicity of the plastic wrap substrates was tested by contact angle measurement . The contact angles of solvents on different plastic wraps are shown in 2-covered substrates. The real-time thermal images captured under NIR irradiation for 1 min with powers of 16, 33, and 84 W/cm2  are shown in S−16, S−33, and S−84, respectively. In the following experiments, the NIR laser annealing conditions  did not cause a substrate temperature higher than 41 °C. In To ensure not to damage the substrate, it is also essential to understand the substrate temperature under NIR laser irradiation. A thermal imager (Testo 875i-versatile) was used to understand the local thermal heating of NIR laser annealing of SnO2 film on the HDPE/resin substrate was analyzed. The AFM image of only the HDPE/resin plastic wrap before NIR laser treatment showed a surface roughness  of 3.63 nm in 2 to 84 W/cm2  showed an increased surface roughness of 6.29 nm (S−84 (1.52 nm) is comparable to that of the thermal-annealed sample with 200 °C 1 h annealing (1.22 nm)  analysis has been used to study the morphology of the HDPE/resin substrate before and after different NIR irradiations. Additionally, the morphology of the SnO84 W/cm2 . The sur84 W/cm2 a–c. On t 6.29 nm . This re1.22 nm) . The SnOrding to , coating2 samples on HDPE/resin. A literature survey states that the presence of rich oxygen vacancy in SnO2 metal oxide plays a crucial role in humidity sensors . I. I2 sampnd S−vac . In Figuwide-dynamic-range response and the detection of the incremental change response. The current voltage (I-V) characteristic curves of S−84 under different relative humidities are shown in S−84 may show how the oxygen vacancy promotes the formation of conductive ions such as H+ and H3O+. This increases the current through the hopping of these ions between neighboring hydroxyl groups [2 may be mixed with some remaining byproducts . Hence, the electron-conducting path may be formed by interconnecting the high-level oxygen vacancy network as well as the hydroxyl-rich parts. Hence, in a high relative humidity environment, water molecules cover the hydroxyl-rich parts to promote the hopping-related current. It is plausible that the very sensitive RH response is because the hopping serves as a bottleneck in the conducting path. Thus, the surface current level increases after attaching water molecules to the SnO2 film. To keep a high enough current level when tuning the relative humidity, we chose 7 V to bias the sensors in the following sensing response measurement. In this section, we will discuss relative humidity sensing responses in two ways, such as the l groups . Accordil groups . In our wide-dynamic-range responses to relative humidity, RH (%), of 20%, 30%, 40%, 50%, 60%, and 70% are plotted in the current vs. time plot in T90, (marked in cyan blue color) and the recovery time, RcT90, (marked in yellow color) of the proposed sensor are 90 s and 150 s, respectively. Here, T90 indicates the time taken by the sensor to show 90% of its initial response  in relative humidity. The response is named the ectively . Thus, tincremental change responses as a function of the RH change  are plotted in S−16, S−33, S−84, S−vac, and PMP−84 sensors. It shows that the responses are quite similar for S−16, S−84, and S-vac, whereas the S-33 and PMP−84 sensors exhibit comparatively low responses , so the sample was named PMP−84. The I-V characteristic and the real-time incremental-change responses are shown in 2 sensors can be formed successfully on different plastic wrap substrates and a deliver very sensitive response to a relative humidity change of only 0.1%. The effect of different NIR annealing powers on the RH response of the sensors was investigated. The esponses f. The I-S−84 sensor exhibited high selectivity towards H2O molecules. Specifically, no response to 1 ppm NH3, NO, or NO2 molecules was recorded. Only a small response (1.1%) to 1 ppm acetone was observed. To understand the performance of the flexible humidity sensor at different bending conditions, the response of the sensor was measured at the natural flat and bending conditions (convex and concave) under 60% RH with 2% incremental RH change  to parts per million (ppm), found in the highly humid human exhaled breath . Thus, tH change b. The meS−84 under 1% RH change is shown in the current vs. time plot in S−84 sensors to perform real respiration detection.To enable practical applications, we also evaluated reliability tests including the repeatability and the storage lifetime measurement. The repeated response data of S−84 sensors to detect respiratory patterns. The study protocol was approved by the institutional review board (no. 202101239B0C502). Slow, normal, and fast respiratory patterns were monitored by the real-time current curves given in S−84 sensor was put inside a glass chamber with a fixed background relative humidity of 70%, 60%, and 50%. Continuous slow, normal, and fast nasal breath was released 5 cm away from the substrates (n = 2).In this section, we used the proposed bstrates . Noted tbstrates . The resbstrates a. The opbstrates b–d. The bstrates  and outsbstrates b–d are uS−84 sensor to a conventional face mask for continuous respiratory monitoring (S−84 increases to about 10 µA. The net changes in current (ΔI) are 1.62, 1.34, and 1.03 µA during exhalation/inhalation for slow, normal, and fast breath, respectively. Noted that ΔI can be enlarged by introducing comb-like electrodes in future works. The corresponding gray and cyan-blue rectangles in To show the advantage of easy integration with masks, we attached the nitoring e. Figure2 thin film on plastic wrap was successfully demonstrated by NIR laser annealing at low powers (16–84 W/cm2) at room temperature. To obtain a uniform sol-gel SnO2 thin film, the suitable wetting angle on the plastic wrap needs to be controlled between 25 and 45°. The thermal imager reveals that the equivalent temperature is as low as 26.2–40.8 °C, corresponding to the 1 min irradiated NIR laser power of 16–84 W/cm2. Moreover, the XPS results prove the presence of high-level oxygen vacancies on the surface of the sensor, which may facilitate the absorption of water molecules and allow a fast-enough response and recovery time (<30 s). This sensor exhibits a wide dynamic range to detect relative humidity from 15% to 70%, and it also has high sensitivity to detect 0.1% to 2.2% incremental changes in relative humidity. With the ultra-flexible substrate, the sensor can be easily attached onto a face mask. When placing the proposed sensor in front of the human nose covered by a mask, the sensor can clearly reflect the respiration pattern in slow, normal, and fast breathing. Thus, this sensor can be a good candidate in the field of respiratory disease monitoring. The proposed “sensor on mask” technology may be a comfortable and convenient approach for continuous breath detection.The ultrathin and ultra-flexible relative humidity sensor with SnO


Furthermore, the device was transparent and flexible with the capability of spatially mapping touch stimuli and monitoring real-time temperature. Due to all these unique characteristics, this novel noncontact mechanosensation GSFET active matrix provided a new method for self-powered E-skin with promising potential for self-powered wearable devices and intelligent robots.Owing to highly desired requirements in advanced disease diagnosis, therapy, and health monitoring, noncontact mechanosensation active matrix has drawn considerable attention. To satisfy the practical demands of high energy efficiency, in this report, combining the advantage of multiparameter monitoring, high sensitivity, and high resolution of active matrix field-effect transistor (FET) with triboelectric nanogenerators (TENG), we successfully developed the tribotronic mechanosensation active matrix based on tribotronic ion gel graphene scrolls field-effect transistors (GSFET). The tribopotential produced by TENG served as a gate voltage to modulate carrier transport along the semiconductor channel and realized self-powered ability with considerable decreased energy consumption. To achieve high spatial utilization and more pronounced responsivity of the dielectric of this transistor, ion gel was used to act as a triboelectric layer to conduct friction and contact electrification with external materials directly to produce triboelectric charges to power GFET. This tribopotential-driving device has excellent tactile sensing properties with high sensitivity (1.125 mm The great progress of flexible electronic skins (E-skins), epidermal electronics, and mechanosensation active matrix, with the aim of miming perceptive functions of human skin, has inspired great research interests for potential applications in robotics, prostheses, and wearable healthcare monitoring devices . The aboAs a powerful means to monitor the physiological status of the human body, electronic skins (E-skins) based on the field-effect transistor (FET) active matrix array are capable of mimicking the functions of human skin, monitoring activity and sensing and adjusting, and demonstrating their large development horizon and research value by transducing external stimuli to electronic signals. To realize demands of wearing conformally on human skin, transparent stretchable electronic devices have inspired extensive research interests. Three main available strategies to achieve stretchability for electronic device are (1) fabricating the device matrix with stretchable interconnectors ,21,22,23Given graphene scrolls as the channel of FET and active element for E-skin, self-powering has also been emphasized to address issues of mobility restriction and undesired high energy consumption. That is, harvesting mechanical energy from the human’s body to drive personalized electronics for tactile sensing functions. Fortunately, the triboelectric nanogenerator (TENG), coupling triboelectrifriction and electrostatic induction, has been demonstrated to be a powerful means to convert mechanical energy into electricity. The high voltage output of triboelectric nanogenerators (TENG) facilitates its converting mechanical energy into electrical energy with high productivity ,36,37,38−1); fast response time (~16 ms); and excellent durability (over 1000 cycles test). Combining all these merits, this graphene scrolls mechanosensation active matrix achieved spatial distance and temperature dual-mapping and achieved real-time monitoring. These outstanding performances of graphene scrolls mechanosensation active arrays not only hold great potential for noncontact sensation but also will open an avenue for advanced flexible electronics both the fundamental research and practical applications. In this manuscript, we first report a highly stretchable graphene scrolls field-effect transistor (GSFET) for self-powered tribotronic distance–temperature dual-modes mechanosensation application. In this mechanosensation active matrix, tribopotential stemming from the dielectric layer of ion gel and other friction material acted as the gate voltage. This transparent tribopotential-driven device has extremely stretchable properties  and kept 35% of its original current output) compared to inherent graphene and layer-stacking style graphene sheets; excellent temperature sensitivity (precision as low as 1) and tactile sensing properties including high sensitivity  atmosphere and heating under 1000 °C for 30 min, under a flowing H2 (10 sccm) atmosphere continually; 5 sccm CH4 was introduced to allow graphene growth. After 30 min, the CH4 flow shutoff, and under the same H2 flow conditions, the tube was cooled to room temperature. Thus, large-area (10 × 10 cm2) monolayer graphene was obtained on a Cu foil. According to previous procedures , monolayA layer of Cr/Au as the source/drain electrodes (5 nm/50 nm) was thermal evaporation, which was prior to patterning using UV-photolithography  and etching using Au and Cr etchants, respectively. 2 20 sccm, 150 W, 5 s) of the graphene film.The preparation of graphene patterns involved the following: Poly(methyl methacrylate) (PMMA) supporting layer was spin-coated at 4000 rpm for 5 s onto the graphene patterns on the Cu foil. Prior to being transferred onto a PDMS substrate (thickness of 500 μm), the Cu foil was chemically etched using an aqueous 0.2 M ammonium persulfate solution. Subsequently, the supporting layer was removed by dipping into the hot acetone (~60 °C) for 5 min. To fabricate trilayer graphene scrolls, the above procedure was repeated 3 times, followed by UV-photolithography  and oxygen plasma etching (OIon gel gate dielectrics were patterned by a UV-photolithography. The ion gel consisting of 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ((EMIM) (TFSI)) ion liquid, the poly(ethylene glycol) diacrylate (PEGDA) monomer, and the 2-hydroxy-2methylpropiophenone (HOMPP) photo-initiator (weight ratio of 90:7:3) were cast onto the patterned graphene. Under UV exposure, polymerization of PEGDA was initiated by the reaction between monomers and radicals originated from HOMPP to produce the cross-linked structure. The nonexposed areas that failed to cross-link could be washed away using DI water. The graphene area in contact with the ion gel served as the active channel (L = 300 μm and W = 50 μm), whereas the other region functioned as the source/drain electrodes.The fabricated TENG is based on the contact/separation between a PTFE film  and a cupper film, which was connected to the ground.UV-vis measurements were carried out on an ultraviolet spectrophotometer (HOPBA). The electrical performance and triboelectronic performance of the GFETs were measured by a Keysight B1500A Semiconductor Device analyzer. A displacement motor driven by a computer-controlled stepping motor was connected with a probe station for the triboelectronic performance test. All above measurements were conducted under ambient conditions.4)2S2O8 solution to etch away the Cu foil. The backside graphene without the PMMA coating inescapably had cracks and defects that allowed an etchant to penetrate through [3-treated PDMS, and PMMA was given away by using acetone and repeating the transfer to another layer subsequently. The obtained monolayer graphene scrolls had similar characteristics to the monolayer back-etched graphene  of the symmetric 2D band and the 2D/G intensity ratio (~2.5). As shown in −1) and 2D (2687 cm−1) peaks as the monolayer characteristic of graphene (black curve) but with a distinguishing variation of the 2D/G intensity ratio (~0.22) for the 2D/G intensity ratio of the monolayer characteristic of graphene, which is about (~2.5). It is worth noting that no other surplus peak exists in the Raman spectra of trilayer graphene scrolls, suggesting no newly generated structure besides graphene. Ion gel (composed of 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ((EMIM)(TFSI)) ion liquid, poly(ethylene glycol) diacrylate (PEGDA) monomers, and 2-hydroxy-2-methylpropiophenone (HOMPP) photo-initiator in a weight ratio of 90:7:3), acting as both the gate dielectrics of GSFET and a tribo-electrification layer, was patterned by photolithography above the graphene channel.  (PMMA) was spin-coated to protect the front side of the graphene; followed by that the entire film (PMMA/front graphene/Cu/back graphene) was floated on  and electron–energy loss (EEL) spectroscopy . The atoBesides structure characterization, the electrical properties of graphene scrolls were also investigated by making comparison to monolayer and layer-stacking styles of graphene . Different styles of graphene films, trilayer graphene scrolls, trilayer graphene, bilayer graphene scrolls, and monolayer graphene were transferred onto Ecoflex and patterned into 500 μm-wide and 2000 μm-long channels by photolithography. Two-end resistances as a function of strain deformations and bending deformations were tested under ambient conditions. As shown in To explore the underlying reason behind excellent electrostretchability properties of trilayer graphene scrolls, Raman spectra of trilayer graphene scrolls and monolayer graphene were compared under strain . Figure I–V character and transfer characteristic of trilayer graphene scrolls under variation of relative strain deformation and bending deformation were compared against those of monolayer graphene. As depicted in Report-referred graphene scrolls proposed by Bao et al. are limited to application as the electrode; application as the semiconductor channel has not been reported yet. We, for the first time, investigated properties of GSFET based on trilayer graphene scrolls as a semiconductor channel, demonstrating their superiority. The width and length of graphene channel of the single GFET were 50 µm and 300 µm, respectively, with a 100 µm distance between gate and channel. The I–V character and transfer characteristic of GSFET and GFET under varied relative bending deformation. The case is the same as the strain deformation: trilayer graphene scrolls possess good resistance retention toward deformation. It is worth noting that it was beyond our expectation that the transfer curves turned out to be same as when the monolayer graphene was the channel, with Dirac point being around 0.6.Apart from comparing trilayer graphene scrolls with monolayer graphene, comparison of trilayer graphene scrolls and trilayer stacking graphene  was also conducted.As shown in I–V character of trilayer graphene scrolls under varied temperature were compared with that of monolayer graphene (graphene films transferred on Ecoflex were patterned into 500 μm-wide and 2000 μm-long channels by photolithography). Obviously, the trilayer graphene scrolls displayed more distinct temperature-dependence than that of the counterpart monolayer graphene: every 1 °C induced a 0.7% current variation amount (R − R0)/R0 toward temperature variation of trilayer graphene scrolls  (as the contact distance increased from 0 to 1 mm), suggesting the excellent sensitivity of the triboelectric properties and offering sound fundamentals for the sensor application.On basis of the triboelectric series , electroID variation of 3.63 µA, equivalent to a positive gate voltage of 0.31 V, while for trilayer graphene scrolls FET’s triboelectricity, the 200 μm distance variation of between PTFE and ion gel induced ID variation of 1.1 µA, equivalent to a positive gate voltage of 0.24 V. It was indicated that trilayer graphene scrolls as the channel was less susceptible to triboelectric.This GSFET was compared with our previous work triboelectric GFET based on monolayer graphene  . For GFEC is defined as (1/CG + 1/CQ)−1. CQ and CG in multilayer graphene act as a function of the layer number [CQ increases with increasing layer number because of increasing density of states and saturation as the layer number reaches six. The bilayer and trilayer show anomalies in their transfer curves, which can be ascribed to a second sub-band in presence at approximately 0.5 eV above the Dirac point and is generated by interlayer interactions (the features of multilayer graphene). EDLT analysis can provide deeper insight into the lower susceptibility of trilayer graphene scrolls toward triboelectric than monolayer graphene. According to ion gel EDLT’s equivalent circuit ,57, the r number . The valVG is understood.Compared to monolayer graphene FET, the higher-lying sub-bands are generally unreachable by conventional solid-gated FETs but were reached for the first time by utilizing ion gel (electron double layer effect EDLT), owing to the high-density charge accumulation. Taking the higher-lying sub-band into consideration, a significant capacitance increase with increasing CEDL) and a quantum capacitance of the graphene (CQ) [ћ represents the reduced Planck’s constant, νF is Fermi velocity (1.1106 m/s), e is the electron charge, and n is the charge density. VGmin is the gate voltage corresponding to Dirac point. According to Equation (2), the carrier concentration is closely associated with VG and CEDL. VG is the effective voltage that triboelectric is posed on; according to Equation (2), the value of VG is equal to that of the open voltage of the TENG substrate. The resistance consumption V(R) and open voltage of TENG followed a linear function as distance between two triboelectric materials increased.Because the capacitance of diffuse layer is negligible, the interfacial capacitance of ion gel can be recognized as a serial combination of an electric double layer capacitance (ene (CQ) . With reVG further changes the relationship of VG and triboelectric distance, unambiguously explaining the lower susceptibility of trilayer graphene scrolls toward triboelectric than monolayer graphene.In light of Equation (1), the increment of layer number change The working principle of tribopotential characteristic of this GSFET is the same as our previous work: noncontact mechanosensation active matrix based on tribotronic planar graphene transistors array . There iID response time upon application and release of the triboelectric was only 15 ms, calculated from the vertical rising and dropping of ID. The rapid response time demonstrates the outstanding sensitivity of the device. The ID increased upon the contact–separation cycles commenced between skin and the ion gel (under applied drain voltage of 0.1 V).Our highly stretchable GSFET also possesses excellent rapid dynamic response. As shown in Given that the ultimate goal of triboelectric-driving GFET was applied for noncontact mechanosensation, GSFET array on substrate of PDMS was fabricated with a 4 × 4 GSFETs matrix configuration, as shown in the circuit diagram in The triboelectric distances applied to the active matrix were spatially mapped, as shown in −1), rapid response time (~16 ms), and an endurability operation over thousands of cycles. Owing to all these merits, this graphene scrolls mechanosensation active matrix were spatially distance and temperature dual-mapping and achieved real-time monitoring. We can demonstrate that this device holds promising prospects for self-powered mechanosensation matrix for application of for advanced disease diagnosis, therapy, and health monitoring.In conclusion, we pioneeringly employed trilayer graphene scrolls as FET channel material for a self-powered tribotronics and mechanosensation matrix. This novel structure of trilayer graphene scrolls transistor endowed the triboelectronic FET with extremely stretchable properties  compared to intrinsic graphene and stacking graphene sheet; excellent temperature sensitivity (precision as low as 1); and high transparency. Meanwhile, for tribotronics GSFET, both the output performances powered by distance-dependent tribopotential were in good agreement with applied gate voltage, verifying that tribotronics could serve as an effective power source to drive a mechanosensation active matrix. The mechanosensation matrix possessed tactile sensing properties of high sensitivity (1.125 mm