In case of a population-wide infectious disease outbreak, such as the novel coronavirus disease (COVID-19), people’s online activities could significantly affect public concerns and health behaviors due to difficulty in accessing credible information from reliable sources, which in turn causes people to seek necessary information on the web. Therefore, measuring and analyzing online health communication and public sentiment is essential for establishing effective and efficient disease control policies, especially in the early stage of an outbreak.This study aimed to investigate the trends of online health communication, analyze the focus of people’s anxiety in the early stages of COVID-19, and evaluate the appropriateness of online information.We collected 13,148 questions and 29,040 answers related to COVID-19 from Naver, the most popular Korean web portal . Three main methods were used in this study: (1) the structural topic model was used to examine the topics in the online questions; (2) word network analysis was conducted to analyze the focus of people’s anxiety and worry in the questions; and (3) two medical doctors assessed the appropriateness of the answers to the questions, which were primarily related to people’s anxiety.A total of 50 topics and 6 cohesive topic communities were identified from the questions. Among them, topic community 4 (suspecting COVID-19 infection after developing a particular symptom) accounted for the largest portion of the questions. As the number of confirmed patients increased, the proportion of topics belonging to topic community 4 also increased. Additionally, the prolonged situation led to a slight increase in the proportion of topics related to job issues. People’s anxieties and worries were closely related with physical symptoms and self-protection methods. Although relatively appropriate to suspect physical symptoms, a high proportion of answers related to self-protection methods were assessed as misinformation or advertisements.Search activity for online information regarding the COVID-19 outbreak has been active. Many of the online questions were related to people’s anxieties and worries. A considerable portion of corresponding answers had false information or were advertisements. The study results could contribute reference information to various countries that need to monitor public anxiety and provide appropriate information in the early stage of an infectious disease outbreak, including COVID-19. Our research also contributes to developing methods for measuring public opinion and sentiment in an epidemic situation based on natural language data on the internet. The recent appearance of the novel coronavirus disease COVID-19) has been devastating worldwide. In South Korea, hundreds of new cases have been diagnosed daily since late February 2020. The cumulative number of confirmed cases at the time of writing  exceeded 9000. Internationally, over 800,000 cases have been confirmed in more than 200 countries, areas, and territories  and [바이러스 or 폐렴]) or (코로나19 or 코로나 19 or 신종코로나 or 신종코로나 or COVID19 or COVID 19 or COVID-19). English and Korean words were mixed in the search criteria because Koreans use both languages commonly. The English translations of the Korean words used here are as follows: 코로나=corona, 우한=Wuhan, 바이러스=virus, 폐렴=pneumonia, 신종코로나=novel corona. Therefore, we included biological words such as virus or pneumonia, or a relatively formal name referring to this disease, such as COVID19 or corona19, in the search criteria. These criteria were used to identify questions and answers that were related to COVID-19 and contained at least a fraction of biological perspective, as we assumed that the biological words and formal name reflect the perspective at least a little. Since COVID-19 is a controversial issue in domestic politics, we searched for posts that contained at least some biological perspective and excluded posts written purely from a political viewpoint.Third, we isolated the questions from the selected data and again selected the questions satisfying the following search criteria: (코로나 or corona or 우한 or COVID). Questions including irrelevant words  were removed. Since dogs or cats could be infected with a different type of coronavirus than COVID-19, there were questions about it. We excluded the questions related to pets. Questions related to “corona,” the guitar-producing company in Korea, were also excluded. The advanced criteria were applied only to the questions because some users supplied answers without considering the questions’ contents. In other words, although rare, there were cases in which answers related to COVID-19 were attached to questions unrelated to COVID-19. This ensured that both questions and answers were related to COVID-19.Fourth, the duplicate questions were deleted. Q&A forum users sometimes reposted the same question or posted a similar question with a slight change in the wording, which were unhelpful. The criteria used to find duplicate questions were whether the first 50 or the last 50 characters of the question, including blank spaces, were duplicated.Fifth, the few questions (n=14) posted before January 20, 2020, were deleted, as the data in this period cannot represent public concern properly. As a result, 13,148 questions and 29,040 answers, which were assumed to be related to COVID-19, were collected. Several text-mining techniques, including structural topic modeling and word network analysis, were used to analyze public concerns from 13,148 questions. Language data analyses have often used human interpretation capability . These sAlthough text mining allows us to examine a huge amount of data, these techniques usually cannot capture delicate nuances. For example, using basic text mining techniques, determining whether the answer is correct information or a rumor is somewhat difficult. This poses a challenge to the researcher because rumors, especially convincing rumors, use similar words and connection of words with valid information. To compensate for this, we also used a method that allows medical doctors  to categorize answers to questions on a particular topic and then analyze the characteristics of those answers.In summary, three main methods were used for analysis: the structural topic model (STM), network analysis, and professional qualitative classification. Each method is described in the following sections.The STM, a type of topic modeling method, was selected to extract the overall themes or focus of 13,148 questions and examine how the theme or focus changed over time.Like most topic modeling methods developed after the latent Dirichlet allocation (LDA), the STM can extract multiple topics and the topics’ probability distribution in each document from a large number of documents. The extracted topics and their distribution are information that summarizes the given documents ,18.The topic estimation process is based on several assumptions. Topic modeling methods assume that a document is a simple set of words and a topic is a probability distribution of words . Each document contains multiple topics with specific probability distributions . It is then assumed that individual documents were randomly generated from the topics and their distribution per document, and were not directly written by humans; thus, the most probable topics and their distributions are estimated considering the given data -19.Naturally, the probability distribution of words itself does not have intuitive meaning; however, we can interpret the meaning of the topic from the probability distribution of words. When a topic is expressed qualitatively, it mainly appears as an unequal use of words. For example, suppose a topic of “cancer screening test” exists in the language materials. Certain words like “screen” or “mammography” would be used more frequently in this material than other words. Therefore, if we can deduce the word probability distributions, which are likely to produce the given documents, we can also deduce the topics’ meanings by noting the high probability words in the corresponding probability distributions.Distributions of topics in each document are also important information for interpreting the topics because they can be used to identify how each topic is realized into language material. We can also identify documents that have the highest proportion on each individual topic. For example, we can identify the top ten documents with the highest proportion of topic 2 among all documents. After reading the ten documents, we can understand the detailed context and intuitive meaning of topic 2 more accurately.In short, the topic modeling method estimates topics and their probability distributions per document that explain the given documents appropriately. Although the probability distribution itself does not provide intuitive meaning, researchers could interpret the topics’ meaning.Besides this general function of topic modeling, the STM estimates how much of the document’s meta information affects the topics’ proportion or content ,21. MetaThe application of the STM to the questions is described as follows. Of the 13,148 questions, 12 questions were additionally eliminated in the preprocessing for the STM. We only used the words that appeared in at least 2 questions and questions that contained at least 2 words, as a word that only appears in a single document or a question that contains only 1 word carries little information for topic modeling. We estimated 50 topics from the remaining 13,136 questions. The number of topics was set at 50 because there was no significant improvement in topic modeling performance after 50 as measured by the held-out likelihood  when chaAll the topics were interpreted and labeled by considering three kinds of information: the words given high probability in each topic, the words with a high frequency and exclusivity (FREX) score in each topic, and the documents with a high proportion of each topic. The importance of the high probability words and the documents estimated to have a high proportion of each topic in interpreting topics has been explained previously. The words with a high FREX score supplement the high probability words by considering exclusivity and frequency together . That isWe also used the STM to sample representative questions containing subjects related to anxiety and worry. To analyze the appropriateness of the answers to the questions related to the public’s anxiety and worry, most representative questions needed to be reselected from the entire batch of questions. Since it is impossible for a small group of human researchers to review 13,148 questions directly, the STM results were used to select questions that contained anxiety- and worry-related topics. We extracted questions that contained a high proportion of topics discussing physical symptoms and self-protection methods against COVID-19 because they were revealed as the main targets of anxiety and worry.Topic modeling is useful for identifying broad topics in a large volume of documents; however, a researcher cannot control the model to see results on specific subjects. Therefore, analyzing the relationship between particular words of interest is important in achieving our research goals.One of our research objectives was to identify the objects and contexts of anxiety and worry expressed by people. To identify the source of anxiety and worry, we extracted the top 20 words that appeared most frequently in the questions including the words “불안” or “걱정,” which are Korean words for “anxiety” and “worry,” respectively. We considered both words appearing in the same question as a linkage or an association between the words.Additionally, we created a word network using the top 50 words linked to the two Korean words referring to anxiety and worry to analyze the context of people’s anxiety and worry comprehensively. Observing individual words associated with anxiety and worry cannot accurately analyze the full context of anxiety and worry. A network of words linked to anxiety and worry allowed us to further analyze the context of anxiety and worry. Therefore, the top 50 words associated with the two Korean words referring to anxiety and worry were gathered, and the network was created. Connection criterion is a coappearance of words in the same question. This network is extremely dense because the network is made of words that are used in a similar context. Only the most prominent links were required to be selected to extract particularly prominent meanings. For this, only the links with the highest weight,  were extracted to create a subnetwork. This subnetwork was assumed to contain the most prominent contexts related to people’s anxiety and worry.The network community detection algorithm was applied to this subnetwork to extract distinguished themes from the network. This algorithm identifies relatively more cohesive communities of nodes within a network -25. WhenWalktrap was selected from the various network community detection algorithms because of its excellent performance while overcoming the “resolution problem” ,26. A reThe Walktrap algorithm was also used to identify cohesive communities of topics related to each other. The STM estimates the correlation between topics ,27. A poThat is, after estimating 50 topics from 13,136 questions, these topics were summarized into 6 topic communities using the Walktrap algorithm and then interpreted. This additional step was employed due to the fact that, although 50 topics is a great summary, it is still a lot of information for a person to grasp intuitively.Using the results of the aforementioned methods, we assessed the appropriateness of the answers to questions dealing with the main targets of anxiety and worry, and found that the main themes were physical symptoms and self-protection methods. We selected sample questions and answers that addressed these two subjects. Two medical doctors, who are family medicine specialists and the authors of this paper, classified the answers into 5 independent categories: appropriate answers, unrelated answers, wrong answers, advertisement, and other. If there was a disagreement on an answer’s category, they discussed until they reached an agreement and recorded the agreed result.The sample questions were selected by considering the proportion of topics in each question that resulted from using the STM. The themes of physical symptom and self-protection correlated with the fourth and fifth topic communities, respectively. Choosing high proportion questions from each community of topics could form good sample questions that appropriately represent each theme. Therefore, the proportion of the topic communities 4 and 5 was calculated for each question based on the topic proportion information per question. It was created by adding up the proportion of topics belonging to each topic community. The top 100 questions were selected for both topic communities 4 and 5, and the answers to each question were identified. The number of answers was 250 and 306, respectively.For the previously mentioned methods, especially STM and network analysis, to function properly, morphemes need to be extracted from our language data. That is, we need information about what kinds of words appeared from where and at what frequency. The program used to determine this is called a morphological analyzer. From the many types of morphological analyzers applicable to Korean, Komoran was used because it is resilient to the spacing problem in Korean and is sufficiently qualified, as it won awards from the National Institute of Korean Language in 2016.We would like to mention in advance a caveat regarding the words extracted from the data by Komoran; Korean and English do not respond 1:1. For example, there are several Korean words that can be translated as fever (“열” and “발열”). When translating such words into English, we numbered them .Our data included a total of 13,148 questions. Of the words that appeared in the questions, About 50 topics were estimated from 13,136 questions using the STM and were interpreted by the authors. Most topics had an apparent subject or consistent contents that allowed a precise interpretation. Some topics, however, were extracted because of expressions that appeared repeatedly in various questions, regardless of the content of the question. This is because topic modeling captures the coappearance patterns of multiple words observed in documents without considering the meanings of words. For example, if many questions on different subjects contain similar expressions, like “please answer my question or you could be cursed,” the topic model would capture that pattern and estimate the topic based on the pattern. In our model, several topics were extracted because of unique Korean language usages. In this case, we unified the interpretation of the topic as “Questions involving particular Korean language expressions without a common subject.” Additionally, we presented the most prominent Korean expression in these topics in Korean in parentheses and translated its meaning into English.The third column in The STM calculates the proportions of topics on a per-document basis. This allowed us to calculate the proportion of each topic in the entire document, which could also be used to calculate the proportion of the topic communities in the entire document. We aggregated proportions of topics belonging to the same community. Additionally, the STM calculated the proportion variation of all topics over time because the time variable was set as a covariate in our STM. The estimates of topics’ proportion changes over time could also be aggregated to produce the proportion change of the topic communities over time. Topic community 4 (questions suspecting possible COVID-19 infection after developing a particular symptom) occupied the largest proportion of all the questions. It increased sharply in late February when the number of infections had begun to increase earnestly in Korea. In We extracted 20 words that were most frequently connected with words referring to anxiety and worry  from the questions posted from January 20 to March 1, 2020. We also checked whether the list of words associated with anxiety and worry would vary with time. The period  was divided into 6 weeks, and the top words associated with anxiety and worry was extracted from the data of the 6 subperiods . During We formed a word network using the top 50 words linked to anxiety and worry and extracted its subnetwork based on the most prominent 500 links. By applying the Walktrap algorithm to the subnetwork, we could extract three cohesive word communities or three distinct themes. The answers to questions about physical symptoms were often appropriate and relatively less distorted. On the other hand, there were many advertising answers to questions related to self-protection measures.In the event of a novel infectious disease outbreak, the general population cannot easily assess the accuracy of the information regarding the disease, and there is increased reliance on online information. Obtaining appropriate and accurate information is extremely difficult, especially in the early stage of an outbreak, due to the uncertainty about the disease. There may be a delay before the governance body, such as health authorities, announces official statements regarding the disease, including symptoms, treatment, or preventive measures. However, it is unlikely that the public would refrain from seeking information and patiently wait until the accurate information becomes publicly available. In this scenario, it is more probable that the members of the populace would seek to acquire the much-needed information from other sources such as the internet.anxiety and worry in the word network analysis. This implies that the people were mainly concerned about whether developing a particular physical symptom was relevant to COVID-19 and ways to protect them from COVID-19.Consistent with previous studies, our data showed that people sought information regarding COVID-19 on the web. The analysis of 13,136 questions revealed that the largest proportion of topics was regarding anxiety and worries about possible COVID-19 infection after developing a particular symptom. The proportion of topics regarding concerns over working conditions also slightly increased as the COVID-19 outbreak became prolonged. Physical symptoms such as cough, throat pain, and sputum as well as self-protective measures such as wearing a mask were some top key words that simultaneously appeared with the words We also analyzed the appropriateness of the answers that replied to the questions. About 63% of the total answers to questions on suspecting possible COVID-19 infection after developing particular symptoms were evaluated as appropriate, while 15.6% of the answers were incorrect, implying a potential dissemination of misinformation. For questions regarding self-protective measures, such as questions asking how to wear masks properly, as much as 66.3% of the answers were advertisements. Thus, it can be assumed that the general population may have difficulty in obtaining appropriate information on self-protective measures.This study contributes to the establishment of early health communication about public concerns and anxiety observed at the early stage of COVID-19. The initial stage of the epidemic is when neither the health authorities’ policies nor people’s understanding of the epidemic has stabilized. Under these circumstances, people’s online exchange of information and emotion can have a great influence. Governments should implement proper measures to establish online health communication in the early stage of an outbreak to provide appropriate and accurate information. Considering that web data-based studies related to COVID-19 are rare at present, our research’s policy and academic value is more pronounced. Although there are studies that use web data to analyze various characteristics of public psychology for other infectious diseases, there are few studies related to COVID-19. Given that numerous countries have been affected recently and are in the initial stage of the COVID-19 outbreak, our study on South Korea, which experienced COVID-19 relatively early, could be a reference point for policy making in other countries.This study also contributes to devising methods of measuring public psychology using language data in the circumstance of an infectious disease outbreak. Understanding public psychology and culture is essential when dealing with infectious diseases  because Additionally, this study is differentiated from other studies in how we used text mining techniques. Previously, papers using health-related text data often used frequency as the main information, such as the number of Twitter mentions , or applVarious advanced analyses are possible using the data and results of this study. One of the notable results in our study is that the proportion of topic community 4 (questions suspecting possible COVID-19 infection after developing a particular symptom) seems to be linked to the actual number of confirmed patients. Considering that the symptoms observed in topic community 4  were reported as common symptoms of COVID-19 in other clinical reports, this linkage might not be a coincidence. This suggests that information extracted from web data may help identify and even predict the actual trend of infectious diseases. Future research could use sophisticated time series analyses to scrutinize this possibility. Additionally, it is noteworthy that a certain kind of question could have a high proportion of answers written from commercial motivations . This imThis study has limitations concerning the range of data. Although Naver is the most popular portal website in Korea, people are not just using this one service. For further comprehensive analysis of information and emotion exchange in online spaces, various sources of web data, including various social network services, need to be incorporated. Furthermore, since the internet user population does not appropriately represent the entire population, it is necessary to consider using the data produced through traditional methods such as surveys and the internet natural language data together.Nevertheless, this study showed how health information exchanged based on the disease transmission related to people’s anxiety and commercial interest in new infectious disease outbreak via a novel approach using online data analysis and topic modeling.


The quenching of fluorescence (FL) at the vicinity of conductive surfaces and, in particular, near a 2-D graphene layer has become an important biochemical sensing tool. The quenching is attributed to fast non-radiative energy transfer between a chromophore  and the lossy graphene layer. Increased emission rate is also observed when the QD is coupled to a resonator. Here, we combine the two effects in order to control the emission lifetime of the QD. In our case, the resonator was defined by an array of nano-holes in the oxide substrate underneath a graphene surface guide. At resonance, the surface mode of the emitted radiation is concentrated at the nano-holes. Thus, the radiation of QD at or near the holes is spatially correlated through the hole-array’s symmetry. We demonstrated an emission rate change by more than 50% as the sample was azimuthally rotated with respect to the polarization of the excitation laser. In addition to an electrical control, such control over the emission lifetime could be used to control Resonance Energy Transfer (RET) between two chromophores. The quenching of fluorescence in the vicinity of metals ,2 and itIntensity studies need to be complemented by time-resolved emission rates . ConcentScreening near the Dirac point by charged carriers depends on the amount of charge placed within a small distance away from the graphene . Again, Our ultimate goal is to explore energy transfer from one QD to another via a surface guide as a mediator. To do so effectively, we first need to control the lifetime of the energy donating QD through a simple mechanism; in our case, this will be an azimuthal rotation of the substrate.The Coupling Process and its Theoretical Considerations: the coupling process may be broken into several steps . A surface mode is sustained due to the large refractive index of graphene (ngraphene~2.6), QDs and hafnia, but not necessarily through a plasmonic mode for which the dielectric constant of graphene needs to be negative [Excitation of the chromophore  by a pump laser at frequency ωnegative .i1→f1 with i1—the initial, excited state of QD and f1—the final state, the excited dipole in the graphene. The final state, f1 may transfer its energy to another QD nearby or thermally relax. If the graphene is coupled to a resonator , then the QD may relax at a rate of Γi1→f2 with i1—the initial, excited state of the QD and f2—the final electromagnetic state within the surface resonator. That mode may propagate back and forth along the surface resonator and eventually be coupled to free space modes or back to the lossy graphene film. Coherence in our case is achieved when the surface mode is at resonance with the local periodic perturbations.The excited QD dipole is coupled non-radiatively to a charge dipole in the graphene via energy transfer ,10,11 atA third interaction channel between the standing surface mode and the dipole generated in the graphene may be possible. Its mutual coupling may be sensitive to nonlinear photonic, or phononic effects  and coulThe surface mode is coupled to free-space radiation modes and detected by a faraway detector.Furthermore,(a)when all the other parameters are kept the same, the emission rate of a chromophore coupled to a 2-D system is smaller than a chromophore coupled to a 3-D system;(b)the conductive graphene increases the emission rate through non-radiative energy transfer process, which is enabled by charge screening;(c)ET = Γi1→f1 + Γi1→f2 in the absence of other nonlinear processes (see ET/(ΓET + ΓD), where ΓET and ΓD are, respectively, the non-radiative rate of energy transfer and the radiative decay rate of a stand-alone donor. Thus, increasing or decreasing of ΓET provides an active control over the entire process. Long lifetime donors  are preferred;the effect of a resonating spatial perturbation is to further increase the emission rate of the chromophore due to an increase in the DOS near resonance . The measses see . The pro(d)the efficiency of the coupling between the QDs and the surface mode is enhanced because the resonating electromagnetic mode is mostly confined to the structure holes as we shall see below. A photon travelling back and forth within a resonating structure  forms a standing wave at resonance conditions. The resonance conditions result in enhanced intensity at some particular tilt and azimuthal rotation angles with respect to the nano-hole array ,26.see also :Excitatiβs. A standing wave is formed if a Bragg condition is met: |βs-G| = βs; G is the reciprocal wave vector of the spatial square array of holes with a pitch. The wavenumber of the surface mode may be written as, βs~k0neff = (2π/λ0) × neff. Here, λ0 is the free-space emission wavelength and neff is the effective refractive index of the surface mode .Following , once coβs = oksinθ + qG with q integer (positive or negative). At normal incidence, we may pick up the x and y coordinate along the square hole-array coordinates, βscos(φ) = q1Gx and βssin(φ) = q2Gy with q1,2–integers and for square array, Gx = Gy = G  and the coupling to the surface guide is made with every other hole-plane q = 1/2. When excited by an s-polarizations  there is a non-zero z-component (perpendicular to the guide surface) mostly in the air pillars. This implies that excited QDs, situated in, or nearby holes, are spatially correlated.The simulations indicate that the propagation along the x-direction in the surface guide may be polarized along either the y-direction  or z-direction (perpendicular to the guide surface) for excitation and emission modes. For the emission wavelength, λPolarization and dephasing: At normal incidence, the incident laser beam is polarized parallel to the guide’s surface. Simulations suggest that the pillar-interfaced, graphene surface guide supports Transverse Electric (TE) modes for the excitation and emitted wavelengths . At normal incidence and through momentum conservation, this s-polarized excitation mode is coupled to two counter-propagating TE guided modes. The de-polarization [βsL, βse are the surface wavevectors for the incident (laser) and emitted (fluorescence) modes, then, for a co-linear case, βsL + βse + G = 2π × neffcos(φ)/λL + 2π × neff/λe − 2π/Λ = 0 within 1% if we assume neff = 1.15 (see below). For a square array, we expect the transition rate to have a 90° rotation symmetry, considering two orthogonal Bragg reflectors along the x- and y-directions. Discussion on the fitting curve to the azimuthal data is provided in the rization  through Since the energy transfer depends on the distance between the graphene and chromophore, a spacer may be used to control their mutual interaction. While very thin, this spacer—a 10 nm hafnia film on the graphene—in addition to the QDs and the graphene itself, may construct a surface optical waveguide. Coupling the excitation laser to this guide, or coupling the emission to free-space radiation modes may be conveniently made through a periodic array of nano-holes in the oxide substrate under the graphene layer. The array of holes provides for spatial confinement of the surface mode, effectively increasing its propagation lifetime but also increasing the emission rate of a nearby QD via an increase in the emission’s density of states (DOS) (Purcell effect).2. A square hole-array, with a pitch of 250 nm, a hole-diameter of 30 nm and a hole-depth of ca 30 nm was defined by e-beam lithography and etched into the SiO2 layer by using CHF3. The wafer was coated with ZEP diluted 1:4 anisole, spun at 4 krpm for 30 s and baked at 150 °C. A JEOL 8100 was used to write the pattern using 2 nA current and a dose of 300 μC/cm2. The sample was developed in n-amyl acetate for 60 s, rinsed in Isopropyl Alcohol (IPA) for 30 s and then dried with N2. The devices were etched for 2 min in DC reactive ion etching (50 sccm CHF3 2 sccm O2) 50 W power at 10 mTorrAll samples were made on a 500-micron-thick p-Si wafers coated with 150 nm SiOA monolayer graphene was grown by the Chmical Vapor Deposition (CVD) method as described in . The graThe QDs  were pu2. The dots, suspended in toluene were either dip-coated or spun at 2500 RPM for 30 s.Raman spectra were taken with a 633 nm HeNe laser (above the excitation and emission wavelengths of the QD) at an intensity of 2 mW as an excitation source and a × 20 objective. Stresses in the graphene from the hafnia and the QDs may affect its 2-D line, albeit its position remained in the vicinity of 2650 1/cm. The QD emitting in the wavelength of ca 575 nm were pumped with a 90 ps, 250 μW, 405 nm laser at a pulse rate of 25 MHz. The fluence was 1000 W/cm2 spot onto a well-defined spot that was visible through the set of filters and could be visited time and again. The sample area could be viewed using a home built optical microscope that could be separated from the measurement system by a prism and which was equipped with a white light illuminator and a Charge Coupled Device (CCD) camera while viewing through the same objective. An error in repeating the measurement of the same spot was estimated as less than 10%. Uncertainties in the exact spot position may have contributed to coefficient variations. For the fluorescence data, the detector was equipped with a cut-off low-pass filter whose cut-off wavelength was 450 nm. For the time-resolved measurements, a bandpass filter between 500 and 700 nm was used (with a different detector than the one used for the fluorescence measurements).For the time-resolved and fluoresce measurements, the laser beam at 405 nm was focused by an × 5 objective to a ca 25 micron−1. It is attributed to dots that are in close proximity to the graphene guide. The medium rate is of the order of 0.2 ns−1 and is attributed to dots that are less impacted by the graphene layer. The smallest decay rate is of the order of 0.05 ns−1 and serves as a background component and could be also attributed to the photon lifetime in the waveguide. As the focal point moves away from the graphene surface, the weight of the three ensembles is shifted towards dots that are less impacted by the graphene surface.The FL curves exhibited multiple decay rates and could be properly fitted with three decay constants. In each case, the entire curve (from the stating pulse at ca 6 ns to 200 ns) was used for fitting. The largest decay rate is of the order of 2 nsHere are some considerations to the fit process that led to the evaluation of the emission rates.(1).The geometrical effect of the laser spot on the overall emission rate assessment is not straight forward. The Gaussian beam has features of a plane wave only at the focal point; yet, excitations of the dots with varying degrees of efficiency occur with the unfocused beam as well.(2).Limiting the fit to mainly one time component that is prevalent in a finite time range  runs the risk that the solution will be affected by the boundaries of the time window.(3).Having too many time constants may blur the physics of the processes.(4).Considering the fit quality by only its R-square value is insufficient. One needs to consider the distribution of the residuals about the fitting parameter see . The res2, the graphene film was much larger, approximately 5 × 5 mm2. The maps are overlaid on an image of the substrate; some cracks formed in the hafnia during the transfer of the hafnia/graphene film are noted.In A typical full fluorescence (FL) curve for sample S7 (with 10-hafnia layer on top of the graphene) exhibits a 470 nm line that is attributed to color centers of the 10 nm hafnia on graphene a. The liThe effect of focusing the laser beam on the measured time rates is shown in A more detailed description is provided below for sample S7. The QDs were deposited on the hafnia/graphene layer by use of dip-coating. Plotting the maximum count vs. azimuthal angle, φ, between the laser polarization and the hole-array orientation yields mainly two peaks, at 0° and at 180°, that allude to the stability and repeatability of the measurements  but do n−1) and the medium (of ca 0.2 ns−1) rates. The medium decay rate distribution as a function of the azimuthal rotation angle φ is shown in We concentrate on the first two major decay rates: the largest (of ca 2 nsThe error in the decay rate fit is less than 1% (and hence is contained within a data point); the error in the azimuthal angle is 0.5°. We attempted to maintain the same spot position during sample rotation. The error of maintaining that spot is estimated at less than 10%. Yet, uncertainties in the exact spot position may have contributed to coefficient variations.eff = 1.15. The largest decay rate coefficient as a function of azimuthal angle φ for samples S8 (QD under the graphene) and S9 (QD on top of graphene) are shown in If surface guide is interfaced with a relatively top thick polymer instead of air the surface guide becomes more symmetric. The 250 nm PMMA layer, used during the transfer stage of graphene was retained and no oxide was deposited on top of the graphene. Sample S2 was made of spun QD in the nano-hole array and under the graphene layer. Judged by the emission rates, the dots resides away from the graphene. As exhibited by There are a few more questions that need to be addressed:What is the role of the graphene thickness? As the graphene thickness increases so does its conductivity and thus its screening effect. If the QD are placed above the surface guide, their interaction with the hole-array would be decreased. An increase in the graphene thickness will also increase its electromagnetic losses. The effect of multilayer graphene on the lifetime of the QDs was studied by us  and otheWhat is the effect of temperature? It has been shown that the specific conductance of graphene decreases with an increase in temperature in the range 0–180 K and increases with an increase in temperature in the range 180–800 K ,34. ThisFinally, what about QDs at longer wavelengths? The effects described here are scalable up to λ~10 μm when the graphene becomes plasmonics . Beyond that wavelength, the surface guide becomes much more effective  and highWe observed variations in the quenched fluorescence’s lifetime of QDs embedded with patterned quasi two-dimensional graphene surface guides upon azimuthal rotations. These variations were as large as 50%. Since coupling to spatially resonating surface modes is also associated with large emission rates for nearby chromophore, one, in principle, could control an energy transfer from one type of dot to another via the graphene surface guide. In addition to an electrical control ,35, spat


Transparent conducting electrodes (TCEs) have attracted considerable attention towards the development of flexible optoelectronic devices. In this study, mixed-dimensional TCEs are fabricated based on the two-dimensional graphene and one-dimensional electrospun metal fiber that can address the shortcomings of each electrode. In comparison with other TCEs, the Ag fiber/graphene hybrid electrodes exhibited a highly stable morphology , low sheet resistance (approximately 11 Ω/sq), high transmittance (approximately 94%), high oxidation stability with excellent flexibility, and outstanding chemical stability. The multiple functionalities of the transparent and flexible hybrid structure highlight its potential for applications in emerging electronics and highly stable optoelectronics. As interest in these flexible optoelectronic devices increases, researches on TCEs for implementing such devices are being actively conducted. Conventional indium tin oxide (ITO) electrode has been applied in optoelectronic devices owing to high transmittance and conductivity5. However, the ITO electrode has fatal shortcomings, and its strain values are significantly low (approximately 1.1%), rendering it unsuitable for use as an electrode for emerging optoelectronic devices. Additionally, it has a high refractive index, and it requires a high vacuum and high-temperature deposition which makes ITO unsuitable for roll-to-roll manufacturing6. In this regard, various alternatives, such as carbon nanotubes (CNTs)7, graphene9, metal nanowires11, metal nanogrids12, and thin films13, that can replace ITO have been investigated in TCEs.Recently, as the demand for wearable devices increases, optoelectronic devices, such as, liquid-crystal displays (LCD)15 have been stimulated owing to their excellent electrical properties (10 Ω/sq), high optical transmittance (approximately 90%), and high strain value (approximately 11%), compared to ITO. Furthermore, these 1D metal networks do not require a high vacuum and high-temperature deposition process, which could be implemented in a roll-to-roll manufacturing16. Among the metal-network–based electrodes, the electrospun Ag fiber has attracted considerable interest because of its lower percolation threshold, as a result of its longer length (a few cm), compared to that of Ag nanowires (AgNWs), and thus has been applied in various optoelectronic devices17. Moreover, the surface roughness of the junction-free electrospun Ag fiber can be simply controlled by modifying the thickness of its Ag thin-film deposition, which is a critical problem for AgNWs.Among these alternatives, one-dimensional (1D) metal networks, such as metal nanowires and metal fiber electrodes, have been studied extensively as promising substitutes for ITO. Numerous studies on metal networks have been conducted and their applications18. Therefore, an OLED with Ag fiber electrodes exhibits non-uniform emissions at a low luminance because the current only flows through the fiber electrodes19. Thus, the fabrication of an ultrathin, gas- and thermal-stable, conductive, and flexible buffer layer for the Ag fiber electrodes is required, which can improve the non-uniform current flow caused by the network structure while maintaining the durability of the Ag fiber electrodes.However, because Ag fiber electrodes are also made of metal, their electrical characteristics are deteriorated by heat and chemical treatments when applied in device fabrication. Furthermore, owing to the nature of the metal when exposed to air and moisture, the Ag fiber electrodes are oxidized easily, which leads to a significant increase in resistance and haziness. Therefore, an additional buffer layer is required that can prevent the oxidation of the Ag fiber electrodes while maintaining their electrical characteristics. Additionally, because the Ag fiber electrodes are fabricated in a network form, current only flows through the Ag fiber, and no current flows into the empty space between the Ag fiber electrodes21. Graphene, a two-dimensional (2D) graphite structure, is considered the most promising material with outstanding electrical, optical, and thermal properties23. Particularly, graphene has excellent mechanical strength as it has surprisingly high strain values (approximately 25%). Furthermore, graphene has its unique honeycomb structure as a result of its single atomic carbon layer, which prevents small molecules such as hydrogen and water from passing through and keeps it stable against chemical agents24. Therefore, several studies have used graphene as a protection layer to prevent the oxidation of metals such as copper and nickel25. Additionally, graphene exhibits absorption of only 2.3% in the NIR range to visible light wavelengths, which minimizes the loss of transparency from the Ag fiber electrodes26.In recent studies, hybrid structures of graphene and metal nanowires have been considered alternatives to existing electrodes such as ITO for emerging electronicsIn this study, highly stable and flexible mixed-dimensional TCEs were fabricated by wet-transferring graphene manufactured by the chemical vapor deposition (CVD) method onto junction-free Ag fiber electrodes for applications in optoelectronic devices. The new nanomaterial derived from the 1D Ag fiber and 2D graphene features excellent electrode properties by complementing each other’s disadvantages while highlighting their advantages. By raising the graphene buffer layer on top of the Ag fiber electrodes, additional current flowed through the graphene, and the percolation threshold was decreased accordingly, thereby improving the overall current characteristics. Furthermore, graphene’s properties markedly improved the thermal and chemical durability of the electrodes. These Ag-fiber/graphene hybrid electrodes are expected to be applied to emerging optoelectronic devices that can feature excellent characteristics while replacing the existing electrodes.Figure −1 and 2D peak, showing the number of layers of graphene at 2,700 cm−1. Here the 2D-to-G intensity ratio was larger than 1 and there was no D band, showing the presence of disordered structure, around 1,350 cm−1. This result confirms that the wet-transfer of CVD monolayer graphene onto the Ag fiber electrodes was successful without any damage27.A Raman spectrum was acquired directly from the Ag-fiber/graphene hybrid electrodes to confirm the presence of graphene on the hybrid electrodes. Figure 28. High peak-to-valley ratio can cause electrical shorts and current leakage, which can degrade the performance of the device. 1D metal networks are not suitable for many device applications owing to their intrinsic roughness, and this causes a high leakage of currents, which leads to severe device failures30. Hence, even if the surface roughness is lower than that of AgNW, the highly porous surface morphology of the single Ag fiber is not appropriate for applications in thin-film devices. In this regard, the surface roughness of the Ag fiber can be controlled by simply modifying the thickness of its Ag thin-film deposition. A Ag thickness of 40 nm was used to fabricate the Ag fiber electrodes. Figure Rrms) with the larger width of the Ag fiber electrodes. The average RMS surface roughnesses and average peak-to-valley ratio for the Ag fiber and Ag-fiber/graphene electrodes are summarized in Table Rrms values of the Ag fiber and Ag-fiber/graphene electrodes were 32.719 and 15.676, respectively. These results demonstrate that the Ag-fiber/graphene hybrid electrodes are suitable for applications in emerging thin-film optoelectronic devices.Morphological images of the Ag fiber and Ag-fiber/graphene hybrid electrodes were acquired by using AFM. A lower surface roughness enables strong bonding and easier post-processing, and it improves the device performanceThe optical and electrical properties of the Ag fiber and Ag-fiber/graphene hybrid electrodes were investigated. First of all, Fig. 30. On the contrary, as the surface coverage increased, the network of the Ag fiber also increased, and the overall conductivity improved. Figure For both Ag fiber electrodes and Ag-fiber/graphene hybrid electrodes, the transmittance of the substrate decreased as the spinning time of PS fiber increased owing to the increase in surface coverage with increase in the spinning time. The surface coverage of Ag fiber electrodes, as a function of spinning time, is discussed in our previous paperCompared to those of the Ag fiber electrodes, the transmittance and sheet resistance of the Ag-fiber/graphene hybrid electrodes were higher and lower, respectively, which suggests that the Ag-fiber/graphene hybrid electrodes delivered better optical and electrical performances than the Ag fiber electrodes. This is because, as mentioned earlier, since the Ag fiber electrodes feature a network form, there are empty spaces where the electrodes are not present, which eventually leads to an open-circuit fault. In other words, the sheet resistance increased as the connection between the Ag fiber electrodes and the conductive probe was partially broken, and for the Ag-fiber/graphene hybrid electrodes, the CVD graphene layer covered the entire Ag fiber electrodes, which means that the current could flow through every space tightly, leading to a seamless physical contact with the conductive probe. Furthermore, the CVD graphene layer is known to be a highly stable and efficient electron transport layer. Thus, the current measurement between the Ag-fiber/graphene hybrid electrodes and the conductive probe could be highly effective, which means that the Ag-fiber/graphene hybrid electrodes are expected to provide stable electric signals and power supply. An improved electrical connection increases the potential of the Ag-fiber/graphene hybrid electrodes for application as an alternative to the existing electrodes for practical optoelectronic devices.rb) or rolled around and subsequently unrolled under a 5 mm bending radius at a speed of 3 mm s−1. The sheet resistance of each electrode was compared to its initial value . The tensile strain applied to the bent substrate was estimated by31The Ag-fiber/graphene hybrid electrodes exhibited superior mechanical flexibilities, essential for emerging flexible optoelectronic devices such as OLEDs and OSCs. A repetitive bending test was performed to investigate their mechanical durability. During the test, pieces of the Ag-fiber/PEN and Ag-fiber/graphene/PEN were rounded at various bending radius (rb). It is well known that the ITO is made of brittle materials, so it cracks upon exposure to a minimal strain. Therefore, the resistance of the ITO film rapidly increased up to 100% above rb = 5 mm. Both Ag fiber film and Ag-fiber/graphene film exhibited changes in resistance approximately smaller than 15% at difference rb values, although the resistance change of the Ag fiber film was 5% larger than that of the Ag-fiber/graphene film. Figure In Fig. To further evaluate whether the graphene layer acted as a chemically protective layer against the Ag fiber electrodes, various solutions with different pH values of 2 to 12 were prepared. The Ag fiber and Ag-fiber/graphene electrodes were then covered in each pH solution for 20 min, respectively. As shown in Fig. 33. As shown in Fig. 32. It is well known that Ag electrodes, such as the Ag nanowires and the Ag fiber, quickly oxidize when exposed to air. While the Ag electrodes are oxidized, the silver oxides are formed on the Ag fiber electrodes surface, which leads to an increase in the electrical resistivity and junction resistance of the Ag fiber34, as shown in Fig. To further evaluate the thermal stability of the Ag-fiber/graphene hybrid electrodes through the thermal-stable property of the graphene protection layer, the Ag fiber and Ag-fiber/graphene electrodes on the PEN substrates were annealed on a hot plate at 85 °C for 120 h. Their variations in resistance were measured after every 24 h. The melting point of the Ag fiber was significantly low (85 °C), even though the melting point of silver is approximately 962 °C, owing to the increased influence of the loosely bounded surface atoms of the nanostructureThe performances of Ag fiber electrodes and Ag-fiber/graphene hybrid electrodes are summarized in Table The highly transparent, flexible and stable Ag-fiber/graphene hybrid electrodes were fabricated by wet-transferring the CVD graphene onto the Ag fiber electrodes. The Ag-fiber/graphene hybrid electrodes featured excellent optical and electrical properties, chemical stability, and mechanical flexibility, and they exhibited very low surface roughnesses, as the CVD graphene layer simultaneously served as an efficient current pathway by filling the voids. Furthermore, the Ag-fiber/graphene hybrid electrodes exhibited superior long-term stability under harsh environments, such as high temperature or chemical disturbances. Overall, the use of graphene as the buffer layer in the Ag fiber electrodes ensures high stretchability, low surface roughness, and high chemical and thermal stabilities while retaining the properties of the Ag fiber electrodes. The proposed unconventional approach can advance the development of transparent electrodes for emerging electronics.2) plasma under a pressure of 500 mTorr at 90 W during 5 min to oxidize the Ag thin film not covered with the PS fiber mask. Then the substrate was immersed in an H2O2 solution to etch the oxidized Ag thin film (AgOX) and then immersed in deionized (DI) water for 30 s for complete removal of AgOX. Finally, it was left for 5 min in chloroform to remove the remaining PS fiber. The fabrication is also presented in detail in our previous report30.First, The Ag-fiber/graphene hybrid electrodes were fabricated by wet-transferring CVD graphene layer on top of the Ag fiber electrodes. A graphene monolayer was transferred by using the poly (methyl methacrylate) (PMMA)-based technique . A PMMA layer was spin-coated on a graphene/copper foil at 500 rpm for 15 s and 2,000 rpm for 30 s. The PMMA layer could act as a support layer for the graphene. After the coating, the sample was annealed at 100 °C for 60 s and dried in air. The sample was floated on an ammonium persulfate etchant (0.1 M in DI water) for 12 h until the copper foil was fully etched away. A PEN substrate with electro-spun Ag fiber electrodes was used to lift off the PMMA/graphene and then dried in air for 8 h to remove water residues trapped between the graphene and PET substrate. The sample was then immersed in acetone, isopropyl alcohol, and DI water (for 15 min in each of them) to remove the PMMA layer.A four-probe system was used to measure the sheet resistance over randomly selected points of each sample to estimate the electrical properties of the Ag-fiber/graphene hybrid electrodes. The Ag-fiber/graphene hybrid electrodes were analysed by field-emission scanning electron microscopy . Their optical properties were measured by using a Cary 5000 UV–visible spectrophotometer (Varian/Agilent). The surface topography and profiles of the hybrid electrodes were measured by using atomic force microscopy . A bending tester  with a digital multimetre was used to perform a cyclic bending test. Raman spectroscopy  at a laser excitation wavelength of 532 nm was employed to measure the graphene quality. pH solutions were prepared by mixing a solution of hydrochloric acid (HCl) and sodium hydroxide (NaOH) with DI water to test the chemical stabilities.


In recent decades we have seen an exponential growth in the amount of data gathered within psychological research without a corresponding growth of theory that could meaningfully organize these research findings. For this reason, considerable attention today is given to discussions of such broader, higher-order concepts as theory and paradigm. However, another area important to consider is the nature of the questions psychologists are asking. Key to any discussion about the scientific status of psychology or about progress in the field (scientific or otherwise) is the nature of the questions that inspire psychological research. Psychologists concerned about scientific progress and the growth of theory in the field would be well served by more robust conversations about the nature of the questions being asked. Honest, curiosity-driven questions—questions that admit to our ignorance and that express an active and optimistic yearning for what we do not yet know—can help to propel psychology forward in a manner similar to the development of theory or paradigm. However, existing as it does in the “twilight zone” between the natural sciences and the humanities, psychology is fertile ground for questions of wide-ranging natures, and thus the nature of progress in the field can be variously understood, not all of which will be “scientific.” Recent psychological research in three areas  are discussed as examples of how curiosity-driven questions being asked from a position of informed ignorance can lead to progress in the field. It is “the right question, asked the right way, rather than the accumulation of more data, that allows a field to progress.” , psychology is considered a “soft science” relative to the natural sciences . More recently, it has come to be seen as a linear, collective-level accumulation of external, objective data from a mechanistic world. The philosopher Charles Taylor . What is more, the limitations or suggestions for future research are often actually backhanded suggestions in support of the given claims . Such practices in effect anchor psychological questions to the past and to the already-known, rather than projecting them into the future and the as-yet-unknown. In as far as we root for a hypothesis, and do so at the expense of genuine, curiosity-driven questions, we run the risk of silencing the data and ignoring the subject. This can also happen when our constructs are too rigidly defined, indicating that a lack of universal agreement about even core constructs in the field is not necessarily a bad thing, that is, as long as this flexibility allows us to turn meaningfully to the data, or rather, to the subject under study. In fact, intentionally loosening up on widely held definitions can shift priority from the researcher and the past (the known), to the subject and the future (the as-yet-unknown), and yet, “That principle is one that is difficult for many scientists to swallow, because it relaxes control, gets the experimenter out of the driver’s seat, and leaves it up to the subjects […] to produce the results”  in particular. What is more, given the nature of curiosity-driven questions arising from informed ignorance, it is impossible to identify such questions on face value . In other words, while we have been referring to this as a “question,” or rather a type of question, it is in reality more of an approach or practice. Just as the question “Why am I sick?” can be scientific, moral, rhetorical, etc. Sehon , any parAn example of such a process can be seen in psychological research on consciousness. The notion of consciousness is of fundamental importance within psychology, but also in broader, non-academic discussions. It is also one of those often used, but incredibly “fuzzy,” concepts within the field . DSD should not be confused with what is known as “gender dysphoria” APA , that isnecessarily those that lead to scientific progress. In fact, psychological work in this area is often clearly non-scientific. There also remains considerable disagreement regarding just what the science is supposed to say beyond the realms of method. Taken together, this is an example of the “twilight zone” of which Ichheiser spoke and with which he was both comfortable and confident.Scientific knowledge regarding various DSDs has increased over the past several decades . As discussed above, within discussions of the scientific status of psychology it is worth reflecting on the assumptions contained in the questions posed, the degree to which they are future-oriented, and the degree to which they are responsive to, and receptive of, the subject. At the same time, not all meaningful and valuable questions need to lay the foundations for scientific progress, or any kind of progress for that matter . In our concern for the progress of “psychological science,” it is worth reflecting on the potentially progressive quality of our questions. Do they reflect an honest curiosity about the world? Are they boldly expressive and humbly receptive? To the extent that they balance between the known and the unknown, and between the “trivial order” and the “barbaric vagueness” of the given field, it is important that we recognize that not all questions are equal. Questions come in a wide range of types and they serve all sorts of ends, not all of which bespeak the possibility of scientific progress as currently understood. This is not in itself problematic, far from it. Yet, for psychologists concerned with the scientific status of the field or with the possibility of its progress as an empirical science, it is worth asking if our questions provide fertile ground for the notion of such progress in the first place.


Graphene-covering is a promising approach for achieving an acid-stable, non-noble-metal-catalysed hydrogen evolution reaction (HER). Optimization of the number of graphene-covering layers and the density of defects generated by chemical doping is crucial for achieving a balance between corrosion resistance and catalytic activity. Here, we investigate the influence of charge transfer and proton penetration through the graphene layers on the HER mechanisms of the non-noble metals Ni and Cu in an acidic electrolyte. We find that increasing the number of graphene-covering layers significantly alters the HER performances of Ni and Cu. The proton penetration explored through electrochemical experiments and simulations reveals that the HER activity of the graphene-covered catalysts is governed by the degree of proton penetration, as determined by the number of graphene-covering layers. Graphene-covering technology provides a promising approach for achieving a non-noble-metal-catalyst with corrosion protection and catalytic activity under acidic media. Here, the authors unveil that the electrochemical hydrogen evolution mechanism is governed by the proton penetration phenomenon. Among various H2 generation technologies4, the electrolytic production of H2 from water is a promising method5 because it yields high-purity H2 (>95%) and emits no CO2. Polymer electrolyte membrane (PEM) water electrolysis is likely to be the next-generation technology for H2 production; it is more efficient than alkaline water electrolysis because of its H2 gas purity , faster dynamic response, larger current density , and higher discharge H2 pressure 6.Hydrogen  has frequently been employed as the cathode catalyst because it exhibits a high electrochemical activity and is chemically stable even in strongly acidic environments. However, the scarcity and high cost of noble-metal catalysts limit the use of PEM electrolysers. Given this limitation, it is important to develop cost-efficient, acid-stable, noble-metal-free catalysts that possess high hydrogen evolution reaction (HER) activity comparable to Pt and are chemically tolerant to acidic conditions.10. For example, graphene-encapsulated Ni, Fe, and CoNi alloy nanoparticles have been used in acidic electrolytes13. These encapsulated nanoparticles show sufficient tolerance against corrosion yet maintain their HER performance because the outermost graphene layers become HER-active owing to charge transfer from the underlying metal substrate13. However, regardless of the charge transfer effect, the performance of graphene-covered non-noble metal catalysts seems to be strongly dependent on the underlying metal substrate13. Here, a fundamental question is: how can the HER effectively occur with graphene layer covering, where the covering graphene blocks the catalytically active sites on the surfaces of the non-noble metal catalysts? Although the HER mechanism can be understood by the charge transfer13 and proton penetration through graphene15, this has not been evidenced by experiments. Therefore, it is crucial to determine how both the charge transfer and the proton penetration through graphene affect the HER mechanism of the graphene-covered non-noble metal catalysts.The main source of HER catalyst degradation in acidic media is corrosion. This corrosion can be suppressed through passivation or covering of the catalyst surface with chemically stable graphene layers2) penetrate by bypassing the N-dopant-induced defect sites, which makes the catalysts covered by N-doped graphene electrochemically more active than those covered by non-doped graphene. Our results reveal that the charge transfer effect is not a dominant factor, while the ability of protons to penetrate graphene governs the HER activity of graphene-covered non-noble metal catalysts regardless of morphology and composition. This study provides new insights for the development of non-noble metal catalysts for electrochemical hydrogen production through graphene covering by balancing the contrasting properties of corrosion resistance and catalytic activity in acidic media.In this study, we investigate the HER mechanisms of the proton penetration/charge transfer through the graphene-covering layers and their impact on the catalytic activity of graphene-covered non-noble metal catalysts. We find that protons as well as molecular hydrogen  and N-doped graphene layers (NGLs) Fig. . The gra17. The atomic structures of GLs and NGLs with various layer numbers were observed using high-resolution transmission electron microscopy (HRTEM). The HRTEM image of the monolayer GL (1GL) showed a honeycomb structure comprising six carbon atoms with six-fold symmetry spots assigned to monolayer graphene  induced by N-doping  indicated high 2D-band to G-band (I2D/IG) intensity ratios of 3.8–4.9, suggesting that the monolayer graphene is highly crystalline22  intensity ratios of 0.05–0.08. In contrast, the NGLs exhibited relatively high ID/IG ratios (0.7–1.4), which illustrates that N-doping induced many defects. We interrogated the chemical binding state of GLs and NGLs through XPS , graphitic (0.76 at.%), and oxidic structures (0.36 at.%) in the NGLs24. We observed a very tiny amount of residual Cu metal (≤0.01 at.%) , Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS)ene Fig. . The bilene Fig. , b18,19.2SO4 using a three-electrode system and compared them to those of the bare 3–6NGL samples  as well as the bare Cu and Ni sheets (without graphene-covering). The HER polarization curves of the Cu/3–6NGL samples showed that the overpotential (η10) at the current density 10 mA cm−2, normalized by the electrode surface area, increased with an increasing number of NGLs .We subsequently transferred the graphene layers onto the Cu and Ni sheets with trilayer NGL and hexalayer NGL . These graphene-covered Ni and Cu sheets were sandwiched between Nafion films. We measured the HER activities of the Cu/3–6NGL and Ni/3–6NGL samples in 0.5 M HGLs Fig. . The η10η10 values of the Cu/NGL and Ni/NGL samples should be identical regardless of the catalytic activity of the metal substrates. However, the observed η10 values of the Ni/3NGL and Ni/6NGL samples were 53.3% and 29.7% lower than those of the bare 3NGL and 6NGL samples. The reductions in the η10 values due to the Ni substrate (53.3% for the 3NGL and 29.7% for the 6 NGL) are much larger than the reductions due to the Cu substrate  and observed the generation of Hers Fig. . Raman sers Fig. . Overall−1 at 24 °C25) on both sides. The Nafion/graphene layers/Nafion sandwich membrane was placed on the same Si3N4 chip used for the Raman measurements to isolate the anode and cathode chambers of the H-type cell  between the two chambers that were physically separated by graphene in the H-type cell  characteristics in a two-electrode system. The proton current through the graphene layers was proportional to the bias voltage in the +200 to −200 mV range . This manifests that the proton-penetration resistance arises predominantly from the graphene layers rather than the Nafion. The electrochemical resistance of proton penetration through the graphene layers was further investigated by electrochemical impedance spectroscopy. The results also confirmed the correlation of the proton-penetration resistance and the layer number of graphene . The proton currents, which are defined as the limited current of HER by proton diffusion, through the NGLs were observed to be 1.5 times greater than those through the GLs Fig.  and 7. T14. An Arrhenius-type-fit of the data provides the energy barriers of 0.95 ± 0.03 and 0.87 ± 0.03 eV for 1GL and 1NGL, respectively. In addition, the energy barriers for GLs are almost proportional to the number of GLs (2GL: 1.76 ± 0.04 eV) while the energy barriers for NGLs are not simply proportional to the number of NGLs . These results indicate that the nitrogen dopant-induced defects on the graphene lattice accelerate the proton penetration26. Moreover, the I–V curves of 6NGL demonstrated a non-linear behaviour at a wide voltage range from −3.5 to +3.0 V  from 8 h of CA testing as a function of the overpotential (η10-tot) at the current density of 10 mA cmtot−2, normalized by the total surface area (i.e. the Brunauer-Emmett-Teller (BET) surface area of the catalyst), and the current density at −600 mV vs. RHE for fair catalytic ability comparisons , and NiMo alloy nanoparticle (NiMoNP) catalysts . We plotons Fig. . SurprisQuestions that arise here include: how do NGLs enhance proton penetration compared to GLs, and how does a proton penetrate through multiple graphene layers? To address these questions, we computed the energy barriers for proton penetration through a defect-free 1GL lattice, a 1GL lattice with a 5–7 defect, and several types of NGL lattices using the nudged elastic band (NEB) method. Our calculations reveal energy barriers of 3.16 eV and 2.30 eV for a 1GL lattice with no defects and a 1GL lattice with a 5–7 defect, respectively Fig.  and 10. 2O molecules .The pathway for proton penetration through multiple graphene layers to the non-noble metal surface in the presence of H2 molecules through graphene lattices  , but it must only overcome an energy barrier of <1.0 eV when graphene has nanopores (diameter: 2.5–5.8 Å)  and pyridine  as carbon and nitrogen sources24. The Cu foil was loaded on a corundum boat and inserted into the centre of a quartz tube (φ30 × φ27 × 1000 mm) in a furnace. The tube was heated at 1000 °C for 1 h under an atmosphere of H2  and Ar . Then, GL was grown with an additional flow of CH4  for 30 min, while NGL was grown with an additional flow of CH4 (20 sccm) and pyridine (0.5 m bar). The as-synthesized graphene on Cu foils after Cu dissolution in 0.25 M Fe(NO3)3 solution was manually stacked to prepare graphene-covered Cu and Ni sheets and graphene separating membranes  via a conventional CVD method using CH2, Solid angle 0.26 sr). Raman spectra were performed using a Renishaw InVia Reflex with an incident wavelength of 532 nm. X-ray diffraction (XRD) was carried out using a D2 PHASER . Surface chemical states were studied by X-ray photoelectron spectroscopy  with an Al Ka and X-ray monochromator.Morphology and microstructure of as-synthesized graphene were characterized using a scanning electron microscope , transmission electron microscopes , and equipped energy dispersive spectroscopy  = E(Ag/AgCl) + 0.0591 × pH + 0.197. The pH value of the electrolyte was recorded as 0.5–0.55. The Ag/AgCl reference electrode was calibrated using a Pt wire as the working electrode. The polarization curves were obtained using a sweep rate of 5.0 mV s−1. The electrode potential was automatically iR-compensated with the ohmic resistance.An electrochemical workstation  was used for all electrochemical measurements. Catalytic activities of graphene-covered Cu/Ni sheets and Ni/NiMo nanoparticles samples were performed in a three-electrode system. As-prepared graphene-covered catalysts, a graphite rod, an Ag/AgCl electrode, and Ar-saturated 0.5 M HI–V characteristics and electrochemical impedance spectra were performed in a two-electrode system. The schematic of the homemade H-type cell for electrochemical measurements of proton penetration was shown in Fig. 3N4 chip (window size: 10 × 10 μm) fixed in the centre was used to isolate the anode and cathode chambers filled with 0.5 M H2SO4. The distance between the electrode and separator was 1.0 cm. The size of the Pt plate electrode was 1.0 × 1.0 cm. Electrochemical impedance spectra were recorded with the frequency ranging from 106 to 100 Hz. The CA measurements were carried out in a three-electrode system, in which an Ag/AgCl electrode equipped with a salt bridge was used as the reference electrode. Temperature dependence of proton conductivity experiments for graphene layers were performed over a temperature range of 273–328 K to avoid water freezing and membrane damage due to thermal expansion.The 33. The Becke-Lee-Yang-Parr (BLYP)35 exchange-correlation functional was used. We employed double-zeta valence plus polarization (DZVP) basis sets. The core electrons were described by the Goedecker-Teter-Hutter pseudopotential36. The real-space density cut-off was set to 320 Ry. The van der Waals correction was included via Grimme’s D3 method37. The simulation cell lengths in the x-, y-, and z-directions were 25.56, 24.595, and 50 Å39, respectively. The C–C bond lengths of pristine graphene are 1.42 Å. The 5–7 defect was introduced according to the reported literature40. The nudged elastic band method41 was used with three intermediate states. The calculated barrier heights are independent of calculation methods and consistent with previous reports (Supplementary Tables 42.The DFT calculations were performed via the CP2K programSupplementary InformationPeer Review File


The dataset shows the relationship and valuation of the coastal dunes of the Araucanía region in Chile. The valuation of the local population was surveyed using a questionnaire applied to 49 subjects belonging to Mapuche communities and local government. The data consists of eight tables that show a list of questions, the number of times per year that visit the dunes, cultural practices carried out in the dunes, valuation of ecosystem services provided by the coastal dunes, and knowledge about flora and fauna. Lastly, the original questionnaire and its responses in Spanish and English are included in supplemantary material. This dataset was generated within the framework of the manuscript “Ecosystem services and uses of dune systems of the coast of the Araucanía Region, Chile: a perception study” where 23 leaders of Mapuche communities and 26 representatives of the local government were interviewed. The dataset can be used to compare the valuation of ecosystems by local communities, especially when quantitative data are scarce or do not exist. It also allows comparing local governance in similar contexts.•Data on perception and local knowledge are especially important when there is no other source of data.1The data consists of eight tables in which the perception and local knowledge are collected from the Mapuche communities and representatives of the local government. 2comunas  of Saavedra, Teodoro Schmidt and Toltén on the coast of the Araucanía Region, Chile. The area covered by dunes is 4,349 ha  and the Queule river in the south .The database was built in the dune systems located in the The coast of the Araucanía Region presents the highest percentages of poverty and rural habitation in Chile (CASEN 2015), resulting from high levels of land division , a farming-based economy, and in recent years the impact of forestry plantations Peña-Cortés et al., as a result of which there are few remnant patches of native forest Pincheira-Ulbrich et al.The subsistence farming economy is associated with Mapuche communities and rural inhabitants Peña-Cortés et al. As with the rest of the country, most major decisions are taken centrally in the national capital, Santiago, although a certain level of decision-making occurs at local government level, in the towns of Saavedra, Toltén and Teodoro Schmidt where most public services are concentrated.http://muniteodoro.cl/portal/), Saavedra (http://municipiodesaavedra.cl/Municipio/), and Toltén (http://www.tolten.cl/web/). The selection strategy for the local government group targeted most of the heads of services directly related with the natural system, namely: the Local Development Unit (UDEL), the Community Development Office (DIDECO), the Planning Secretary (SECPLAC), the Territorial Development Programme (PDTI) and the Environment Department. Initial contact with this group was by e-mail, allowing interviews to be coordinated. Local government actors were selected in this way. The participants of the Mapuche group were selected following a non-probabilistic strategy through a “snow-balling” procedure; the first contact was made with the President of the Association of Lafquen Leufu Communities (Saavedra), and a total sample of 23 people was obtained .The study participants were selected using the official lists of Mapuche communities and local government employees. In the case of the Mapuche group (community presidents), the information was provided by the National Indigenous Development Corporation (CONADI), the Local Development Programme (PRODESAL) and the Intercultural Departments of the respective municipality. The information on local government personnel was obtained from the websites of the municipalities of Teodoro Schmidt , five multiple choice (five or six options per question), seven open questions and three using a Likert-type scale. The Likert scale questions used a scale of one to five , covering the full range of values for the item being assessed. Questions of this type included the classification categories proposed by Castro (2015) which are then presented in results rearranged according to Common International Classification of Ecosystem Services (CISES)  (Questions 10). Each section included an explanation of the main concepts of the theme, to ensure correct assessment by the participants.For multiple-choice question in During the interview, efforts were made to maintain openness and non-judgmentality, treating each interviewee fairly and impartially, regardless of their socio-economic status, social status, race, religion or physical appearance. Potential research participants were asked to read the plain language statements and complete a research consent form if they are willing to participate in this project voluntarily. Potential participants were asked to read the research consent form in order to voluntarily express their willingness to participate in this project.Pablo Arévalo-Valenzuela: Conceptualization, Investigation, Application of method, Data analysis; Fernando Peña-Cortés: Supervision, Data discussion; Jimmy Pincheira-Ulbrich: Writing-Original draft preparation, Visualization, Reviewing and Editing, Data analysis.The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article.


A graphene-PbS quantum dot (QD) composite for application in high-performance near-infrared (NIR) photodetectors (PDs) is proposed in this study. A single-layer graphene flake and oleic acid-capped PbS QD composite is fabricated through the conventional sonication process, in hexane solution. Field emission scanning electron microscopy images of the graphene-PbS QD composite dispersed on a glass substrate confirm that the composite contains both aggregated graphene flakes and single-layer graphene with wrinkles; Transmission electron microscopy images reveal close packing with uniform size. The increased absorbance and quenched photoluminescence intensity of the graphene-PbS QD composite supports enhanced photoinduced charge transfer between graphene and the PbS QDs. Moreover, the specific Raman mode of the PbS QDs, embedded in the spectrum, is enhanced by combination with graphene, which can be interpreted by SERS as relevant to the photoinduced charge transfer between the Pbs QDs and graphene. For device application, a PD structure comprised by graphene-PbS QDs is fabricated. The photocurrent of the PD is measured using a conventional probe station with a 980-nm NIR laser diode. In the fabricated PD comprising graphene-PbS QDs, five-times higher photocurrent, 22% faster rise time, and 47% faster decay time are observed, compared to that comprising PbS QDs alone. This establishes the potential of the graphene-PbS QD composite for application in ultrathin, flexible, high-performance NIR PDs. In particular, two-dimensional layered materials and zero-dimensional quantum dots have attracted significant attention for optoelectronic applications because of their excellent optical and electrical properties11. Graphene is a representative metallic layered material consisting of carbon atoms arranged in a hexagonal lattice with strong inplane chemical bonds14. Although graphene has high electron concentration, weak light absorption and fast carrier recombination limit its application in optoelectronics16. PbS colloidal quantum dots (QDs) are promising semiconductors for application as active material in near-infrared optoelectronics because of their small and tunable direct band gap18. Moreover, PbS QDs have outstanding optical and electrical properties due to which their application can be expanded to photodetectors (PDs), light emitting devices, field effect transistors, and photovoltaics22. The different work function and carrier concentration of graphene and the PbS QD enable photoinduced charge transfer when these two materials are in physical contact25. For application in photoresponsive devices, this phenomenon can enhance the photoresponsivity and improve the response time of the PD.Low-dimensional materials are suitable for application in flexible devices because of their atomic-scale dimensions26. Photoinduced charge transfer can be the dominant contribution to the surface-enhanced Raman signal on the semiconductor substrate27. Therefore, the study of the SERS of graphene and PbS QDs is significant for the analysis of the photoinduced charge transfer and Raman spectroscopy.One of primary mechanisms of surface-enhanced Raman scattering (SERS) is chemical enhancement that involves photoinduced charge transfer between inhomogeneous substancesThe hybrid structure comprising graphene and PbS QDs is atomically thin, forming a flexible and transparent device. Furthermore, the fabrication process of this hybrid structure is simple, inexpensive, and large-scale because it is a solution-based process.Herein, we report the fabrication and characterization of a graphene/PbS QD hybrid structure for application in near-infrared PDs. Graphene flakes were dispersed in butylamine and hexane to achieve uniform distribution on a glass substrate. Hexane solution was used to disperse the PbS QDs. Mixtures of graphene flakes and PbS QDs were deposited on a glass substrate using a spin casting machine. Further, the room-temperature photoluminescence, and the Raman and absorption spectra were measured to confirm the optical properties that can be modified by the photoinduced charge transfer of PbS QDs. The surface morphology was evaluated using scanning electron microscopy. The device performance was assessed using the current–voltage curve, photocurrent measurement, and external quantum efficiency.In this study, single-layer graphene and PbS QD composite was dispersed in hexane solution. (See Method section) The single-layer graphene and PbS QD composite was coated on a glass substrate treated with ultraviolet-ozone surface cleaning for 10 min. Figure 28.Figure For the quantitative examination of the graphene-PbS QD composite, energy dispersive spectroscopy (EDS) was employed. Table 29. Note that this increase of absorbance is not mainly induced by absorption of multiple layers of graphene because absorbance of graphene/PbS QD composite is smaller than that of PbS QDs alone in the wavelength range of shorter than 565 nm.  spectroscopies. Figure 30. The PL intensities of the graphene-PbS QD composites with 25% and 50% graphene were lesser by 24.3% and 37.2%, respectively, compared to that of the PbS QDs. The PL intensity represents the number of recombined carriers in the PbS QDs for a unit amount of QDs. These quenched PL intensities are attributed to the enhanced transfer of the photoinduced carriers between graphene and the PbS QDs, which minimizes the charge recombination rate. In addition, Fourier-transform infrared spectroscopy establishes that hexane solution and the glass substrate do not affect the optical properties of the PbS QDs and graphene flakes. . For graphene, three intensive Raman modes are observed at 1,344.8, 1601.3, and 2,701.8 cm−1 , corresponding to the D-band, G-band, and 2D-band, respectively31. In the Raman spectrum of the graphene-PbS QD composite, two Raman modes are observed at 140.3 and 280.8 cm−1, which are associated with the PbS QDs, whereas the Raman spectrum of the PbS QDs does not exhibit a Raman mode32. This is because the specific Raman mode embedded in the spectrum of the PbS QDs is enhanced, which is relevant to the photoinduced charge transfer between the Pbs QDs and graphene, as interpreted by SERS. To verify the enhanced Raman mode of the PbS QDs with graphene, micro-Raman spectroscopy was performed using a 3,000-groove grating for high-spectral resolution, as shown in Fig. −1 is a longitudinal optical (LO) phonon mode corresponding to the 1LO phonon mode of the PbS QD34. The Raman mode at 181.7 cm−1 is attributed to a surface phonon, whose intensity varies depending upon the QD size35. The peak at 140.3 cm−1 is not relevant to the PbS QD. Thus, it can be deduced that the Raman mode of PbS QDs in combination with graphene is enhanced by the photoinduced charge transfer between the two materials.Micro-Raman scattering analysis was performed to examine the photoinduced charge transfer between graphene and the PbS QDs, with a He–Ne laser operating at a wavelength of 632.8 nm. The Raman spectra of the PbS QDs, graphene-PbS QD composite, and glass substrate depicted in Fig. 2 substrate. For a robust metal pad, Au was deposited on the patterned sample using a thermal evaporator  laser diode. In the PD comprising graphene-PbS QD composite, five-times higher photocurrent, 22% shorter rise time, and 47% shorter decay time were observed, compared to that comprising PbS QDs alone. This establishes that the graphene-PbS QD composite has significant potential for application in ultrathin, flexible, high-performance NIR PDs.Single-layer graphene flakes  are fabricated using the modified Hummer’s method. The average diameter and thickness of these graphene flakes ranged between 0.4–0.5 μm and 0.6–1.2 nm, respectively. Single-layer graphene flakes were dispersed in hexane solution (2 mg/ml) through a sonication process for 10 min.37. Subsequently, post-treatment and purification were performed following a published method with some modifications38:All the manipulations for preparing the PbS QDs were performed using the standard Schlenk line technique. Oleic acid-capped PbS QDs (first exciton peak at 950 nm) were prepared as per a previously reported method2 substrate through conventional photolithography and thermal evaporation. A 300-nm thick Au layer was employed as the electrode. Ligand exchanges of the PbS QDs were realized using 1,2-ethanedithiol (EDT) to improve device carrier transportation.Interdigital electrodes were fabricated on an SiOThe absorption spectrum was obtained using a UV–Visible/NIR spectrophotometer (JASCO). PL spectroscopy was performed using a 30-cm monochromator and a charge-coupled device detector excited by a 355-nm diode-pumped solid-state laser. The micro-Raman spectrum was measured with a backscattering geometry using a He–Ne laser (633 nm) for excitation.Supplementary Information.


The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications. The lar.334 nm) . The pre.334 nm) . The mos.334 nm) , which c.334 nm) .+ and OH−. During the process, Li+ entered the layers of the graphite sheets to promote the exfoliation of graphene. OH− was then added to the surface of the graphene to increase its hydrophilicity and dispersion stability in aqueous media. This dispersion theory did not include any surfactants and the entire experimental process was simple, low-cost and environmental-friendly. However, the stable dispersion of the surfactant-free system of graphene in the dispersion was far from that of the surfactant system, and it does not have the potential for the large-scale preparation of graphene [+ salt surfactants have the best wettability for graphene, which can promote the aqueous dispersion of graphene. Therefore, Na+-containing anions and other types of surfactants were selected as dispersants  was purchased from Tsinglube Technology Co., Ltd. , the ionic liquid was obtained from Lanzhou Institute of Chemical Physics , Chinese Academy of Sciences and the other analytical grade reagents were purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd. .The main instruments used in the experiment include: scanning electron microscope (SEM), Carl Zeiss ; atomic force microscope , Oxford Instruments ; Raman, laser model: 532nm, XPOLORA PLUS, JY-HR800 ; Zetasizer Nano ZS .The expanded graphite, which was dried at 80 ± 0.5 °C for 24 h, and a dispersant were added to pure water and magnetically stirred at 60 ± 0.5 °C for 1 h. Subsequently, ultrasonic exfoliation was performed at 60 ± 2.5 °C for 8 h. The mass fraction of the expanded graphite accounts for 0.5 wt.% of the total system mass and that of the dispersant varies at 0.1, 0.3, 0.5 and 1 wt.% of the total system. Except for the NaOH dispersion system, the pH of all dispersant systems was 7.1 ± 0.15. The microscopic mechanism of the 0.5 wt. % dispersant system (SDBS: melamine = 1:1), which was used as a trial basis for the 0.1, 0.3 and 1 wt.% dispersant systems, is shown in The exfoliation grade determines the quality and application value of graphene  in liquid media. The Tyndall phenomenon is a common method for estimating the particle size of the solution in the liquid-phase system after exfoliation. This method relies on the size of the scattering effect of light when parallel light passes through the dispersed phase to evaluate the exfoliation size of graphene in the dispersion. The 0.5 wt.% dispersant system was tested by irradiating parallel light in S value ≤ 0.03). These findings are consistent with the findings of Majid et al. [The volume sedimentation method is one of the simplest and most convenient methods for detecting the stable dispersion of colloids. The smaller the volume ratio of the sediment in the dispersed phase, the higher the concentration of the graphene in the dispersion. The dispersion solution volume ratio is determined as d et al.  and Mated et al. , who repS < 0.05) of the mixed dispersant system (SDBS: melamine = 1:1) was superior to those of single dispersant systems, indicating that the synergistic effect of SDBS and melamine improves the dispersion stability of graphene in pure water. The most excellent dispersion stability was observed when the mass fraction of STAC and CMC in the single dispersant system was 0.3 wt.%. If the mass fraction of the dispersant is excessively high, the dispersant exhibits a micelle phenomenon and loses the ability to stabilize the dispersion. If the mass fraction is extremely low, the dispersion effect cannot be achieved. The solute concentration in each dispersant system was statistically measured in The mass fractions of (SDBS: melamine = 1:1) (PVP: melamine = 1:1) CMC, STAC, SLS and SDBS systems  were varied to further analyzed the graphene dispersion stability in Given the existence of the critical micelle concentrations of the surfactants , the best graphene dispersion effect appears near the micelle concentration. The mass fraction of the dispersants was extremely high due to the intermolecular similarity. The interaction force  shows thAfter the analysis, the chain cationic surfactant STAC was easily electrolyzed to form ammonium ions in the water, which promoted hydrogen bonding with the remaining oxygen-containing groups on the graphene surface after exfoliation . This boThe dispersion stabilities of 0.1 wt.% and 0.3 wt.% SDBS and 0.3 wt.% CMC systems were evident in In non-ionic surfactant systems, although PVP can significantly reduce the surface tension of aqueous dispersion systems, the graphene nanosheets in the water are only affected by the steric hindrance of PVP, which was smaller than the interlayers of the graphene sheets. The van der Waals force cannot promote the stable dispersion of graphene in water. The average zeta potential value was −72.03 mV  and 0.3 wt.% STAC systems in  as seen b,d. Wen The results of the Raman and AFM analyses indicate that the average numbers of graphene nanoflakes in the 0.1 wt.% (SDBS: melamine = 1:1) and 0.3 wt.% STAC systems are approximately 14 and 21, respectively, and a minimum of eight layers of graphene nanoflakes can be exfoliated out.2 hybrid-structured intact expanded graphite. The defect density of graphene in the 0.3 wt.% STAC system is the largest amongst all systems in the experiment (ID/IG = 0.66). The defects, which are generated in the ultrasonic exfoliation process, produce wrinkles. For instance, the point designated by ‘1’ in (1)The electrostatic repulsion force of the charged particles formed by the ionisation of the quaternary ammonium cationic surfactants in water was greater than the steric resistance generated by the non-ionic surfactants. The former also exerts a strong effect on the van der Waals force between the graphene sheets and enhances the exfoliation ability and dispersion stability. The 0.3 wt.% STAC dispersant system exhibited excellent exfoliation ability and dispersion stability and can exfoliate graphene nanosheets with less than eight layers (the average number of layers was less than 14 layers). In addition, the graphene can be stably dispersed in water and no settlement occurred for 13 days.(2)The mixed system of cyclic anionic surfactants and heterocyclic non-ionic surfactants exerts a complex dispersion effect on graphene through electrostatic repulsion and π–π action, which was more stable than that of a single dispersant system. The graphene in the 0.1 wt.% (SDBS: melamine = 1:1) system can remain stable in the storage for 22 days without sedimentation.This study explored the use of a suitable stripping agent in pure water, based on surface energy theory, to overcome the van der Waals force between graphene sheets and prepare graphene. The exfoliation agents must be hydrophilic, heterocyclic and easy to combine with graphene. The graphene surface interacts with a dispersant to prepare few layers of uniformly dispersed aqueous graphene dispersion. The following conclusions were obtained after the experiments:This study used green dispersant to prepare a few layers of stable graphene dispersion in an aqueous system, which is of great significance for the large-scale preparation of such dispersions in practical industrial applications.