The obtained responsivity is about two orders of magnitude higher than that of the commercial mid-infrared photodetectors. Our work opens a route towards achieving high-performance optoelectronics operating in the mid-infrared regime.The pursuit of optoelectronic devices operating in the mid-infrared regime is driven by both fundamental interests and envisioned applications ranging from imaging, sensing to communications. Despite continued achievements in traditional semiconductors, notorious obstacles such as the complicated growth processes and cryogenic operation preclude the usage of infrared detectors. As an alternative path towards high-performance photodetectors, hybrid semiconductor/graphene structures have been intensively explored. However, the operation bandwidth of such photodetectors has been limited to visible and near-infrared regimes. Here we demonstrate a mid-infrared hybrid photodetector enabled by coupling graphene with a narrow bandgap semiconductor, Ti 2O3 nanoparticles can enable efficient mid-infrared photodetection. Here, the authors report a graphene-Ti2O3 based hybrid photodetector with high responsivity of ~300 A W-1 up to 10 μm by varying the number of graphene layers and size of Ti2O3 nanoparticles.Coupling graphene with narrow band-gap Ti Practically, long-wavelength infrared (LWIR) detectors are expected to have features of high photon-carrier conversion efficiency, low noise level at room temperature and fast response speed in a broadband wavelength range. It still remains as a challenge to realize high performance LWIR photodetection with the conventional narrow-bandgap semiconductors such as mercury cadmium telluride (HgCdTe) thin films, indium antimonide (InSb) and artificial semiconductor superlattices via inter/intraband transitions4. Recently, significant efforts have been devoted to colloidal quantum dots (CQDs) based photodetectors due to their high absorption efficiency and facile manufacturing processes5. However, CQDs-based photodetectors suffer from limited operation spectral bandwidth because of their relatively large bandgaps7. Alternatively, two-dimensional materials appear to be promising candidates and provide unique properties such as ultrahigh carrier mobility, easy-integrability and broadband light absorption8. Graphene has been successfully demonstrated as a broadband photodetector from visible to the terahertz wavelength regimes14. Unfortunately, the intrinsic low absorption and fast carrier recombination rate of graphene hinder its application in photodetection, and such devices suffer from low responsivity as well as poor detectivity15.High-performance infrared photodetectors that can convert light into electrical signals lead to a wide range of applications ranging from imaging sensors to optical communications17. In such hybrid structures, one type of carrier (either electron or hole) is trapped in the CQD while the other type rapidly circulates in the graphene channel driven by the external source-drain voltage. Similar designs were also employed in the photodetectors with hybrid graphene-TiO218, graphene-ZnO19, graphene-dye20, and graphene-perovskite structures21. However, the operation wavelength of such hybrid photodetectors are limited in the visible and the near-infrared regimes owing to the relatively large intrinsic bandgap of the light absorbers9. Although black phosphorene25 and noble metal dichalcogenides have been recently demonstrated as a near-infrared/mid-infrared semiconductor26, it still remains as a challenge to further improve the performance of photodetectors in terms of photon absorption efficiency, responsivity, and response speed in the important mid-infrared regime.Several pioneering works have been devoted to improving the performance of graphene-based photodetectors through constructing hybrid structures. Ultrahigh optical gain was achieved in hybrid graphene-CQD structures, where graphene serves as the ultrahigh speed carrier transport channel and CQD serves as light absorber with high absorption efficiency2O3) nanoparticles. Ti2O3, a stable semiconductor with extraordinary broadband photoresponse characteristics, has a narrow-band gap of 0.09 eV, corresponding to a cut-off absorption wavelength of 13.3 μm27. The working mechanism is as follows: when the incident light is absorbed by the Ti2O3 nanoparticles, the photo-excited electrons are trapped in the Ti2O3 nanoparticles, while the holes are transferred into the graphene channel, leading to a conspicuous photocurrent measured in a field effect transistor configuration. In addition, we also systematically investigated the photo-generated carrier transfer processes at the interface of graphene and Ti2O3 in this hybrid photodetector. The developed graphene/Ti2O3 photodetector is demonstrated to be capable of operating in both accessible atmospheric windows, the mid-wavelength infrared (MWIR: 3–5 μm) and the LWIR (8–12 μm) regimes. The broadband mid-infrared operation bandwidth, high responsivity and detectivity make the graphene/Ti2O3 a promising candidate for mid-infrared photodetection, providing a novel paradigm for mid-infrared photonics and optoelectronics.Here we demonstrate room-temperature mid-infrared photodetectors with high responsivity, detectivity and high speed, realized by hybridizing graphene with a novel narrow bandgap semiconductor, titanium sesquioxide . Ti2O3 is chosen in this hybrid structure as the light absorber owing to its unique narrow bandgap (0.09 eV) that covers the mid-infrared regime27. Ti2O3 is very different from the well-studied wide bandgap semiconductor TiO2, as shown in Supplementary Figure 2O3, density functional theory (DFT) calculations with a plane-wave basis set were performed. The calculation details are given in the Supplementary Note 2O3 due to its unpaired 3d electrons, which contributes to the states just below the conduction band and forms an upper valence band, as shown in Fig. 2O3 is located between the lower and the upper Hubbard band31, which is estimated to be about 0.09 eV according to the absorption spectrum in Fig. 2 is about 3.3 eV and originated from the separation between O 2p and Ti 3d orbitals. The unique and wide-band light absorption of Ti2O3 as shown in Fig. The schematic diagram of the proposed hybrid graphene/Tiace Fig. , leading2O3 nanoparticles with relatively uniform nanoparticle sizes were prepared by a simple ball milling process followed by ultrasound process and purification in ether solution. Then they were spin-coated on the channel surface of a graphene field effect transistor (FET). As shown in the X-ray diffraction (XRD) pattern in Fig. 2O3 nanoparticles exhibit the corundum phase, which is consistent with the previous reports31. As shown in Fig. 2O3 nanoparticles have an average diameter of ~50–200 nm, characterized by scanning electron microscopy (SEM). Furthermore, high-resolution transmission electron microscopy (HR-TEM) and selected-area electron diffraction (SAED) were performed to characterize the structure of the fabricated Ti2O3 nanoparticles. As shown in Fig. 2O3 lattice. Moreover, the corresponding SAED pattern shown in Fig. 2O3 nanoparticles. The Raman spectrum of the Ti2O3 nanoparticles shows seven active Raman modes . X-ray photoelectron spectroscopy (XPS) was used to characterize the electronic states of Ti and O in the Ti2O3 nanoparticles. As shown in Fig. p3/2 peaks with binding energies of 456.8 and 462.5 eV arise from spin-orbit splitting, corresponding to Ti3+ in Ti2O332. In addition, the peak with a binding energy of 529.6 eV in the O 1s spectrum  from Ti2O3 to graphene in the hybrid structure34. Notably, as fabricated Ti2O3 is a p-type semiconductor36, and our fabricated pristine graphene is also p-type due to the absorbed hydrocarbon molecules or humidity. As a result, the charge transfer in this hybrid structure remains inefficient because of the band misalignment between graphene and Ti2O3, which contributes to the weak shift of the G peak shown in Fig. To examine the interaction between graphene and Ti2O3 to investigate the charge transfer process in the hybrid structure. Figure 2O3 interface39. The 2D peak is derived from a second-order, double-resonant Raman scattering mechanism and its frequency decreases with increasing gate voltage that up-shifts the Fermi level of graphene34. Theoretically, it is proven that with the increase of gate voltage, the G peak which is originated from the coupling between G-phonon lattice vibrations and Dirac fermions should present first blue-shift in the p-type doping regime (Vg < VD) for graphene and then red-shift in the n-type doping regime (Vg > VD) for graphene38. This is contrary to the experimentally observed trend of G peak shown in Fig. 2O3 interface. In the p-type doped regime of graphene (Vg < VD), the gating effect on graphene is the dominant contribution to the red-shifts of both G peak and 2D peak as the charge transfer process is suppressed, as shown in Fig. 2O3 to graphene channel begins to dominate in the n-type doped regime of graphene (Vg > VD) when the Fermi level is upshifted.We thus applied gate voltages to modulate the Fermi level of graphene and align the band structure between graphene and Ti2O3 nanoparticles in the mid-infrared regime and the efficient charge transfer in the hybrid graphene/Ti2O3 structure modulated by proper gate voltage, the mid-infrared photodetection performance of such hybrid photodetectors was demonstrated. The fabrication details of the photodetector can be found in the Id−Vd curves are generally linear and symmetric for small source-drain voltages, indicating ohmic-like electrode contacts. An obvious decrease of channel current is observed with laser irradiation, which is contributed by the photocurrent as shown in Fig. 2O3 structure, which is defined as the absolute value of the source-drain current under the laser illumination subtracted by the dark current, is shown in Fig. p-doped), which is consistent with the inefficient charge transfer due to the band misalignment between graphene and Ti2O3 in the hybrid structure, as shown in Fig. 2O3 into graphene.With the strong optical absorption of the Ti2O3 photodetector shows a broadband photoresponse in the mid-infrared regime as shown in Fig. −1 under a source-drain bias of 2 mV, was achieved with 10 μm laser illumination. This indicates that our hybrid photodetector offers low electrical power consumption. The obtained responsivity here vastly surpasses those in the previous reports on graphene- and other 2D-based mid-infrared photodetectors43, which is about two orders of magnitude higher than that of commercial mid-infrared photodetectors based on MCT, InSb and so on46. Figure 2O3 interface introduced during the device fabrication process47. The device also demonstrated good stability during the on/off measurements, and the performance remains stable after several weeks if the device is properly kept. Furthermore, the hybrid graphene/Ti2O3 photodetector shows versatile photoresponse in a broad spectrum range from 4.5 µm to 10 µm as shown in Fig. The hybrid graphene/Ti2O3 photodetector presents a noteworthy enhancement when the graphene channel increases from monolayer to trilayer as shown in Fig. 2O3 nanoparticles and the graphene layer as explained in Supplementary Figure −1 for hybrid trilayer graphene/Ti2O3 photodetector under 10 µm laser illumination. Another prominent feature of the hybrid photodetector is its high detectivity as obtained from the low noise spectrum as shown in Fig. 48. The detectives, D*, are calculated to be ~2 × 108 cm Hz1/2 W−1, 3 × 108 cm Hz1/2 W−1, and 7 × 108 cm Hz1/2 W−1 for monolayer, bilayer and trilayer graphene according to Supplementary Equation 45. Graphene layer dependent photoresponse properties are shown in Supplementary Note 46. The results here provide hints towards optimizing the 0D-2D hybrid infrared optoelectronic devices.The photoresponse of the hybrid graphene/Ti2O3 nanoparticles on the optoelectronic properties of the hybrid graphene/Ti2O3 structure. As shown in Fig. 2O3 nanoparticles from 200 to 80 nm . Ethanol was added during milling, and the milling speed was fixed at 300 rpm for 48 h. The size distribution of the obtained nanoparticles is shown in the Supplementary Figure Ti2O3 nanoparticles spin-coated on KBr substrate were measured using a Fourier Transform Infrared Spectrometer . The measurements were all performed in the ambient conditions.The absorption spectra of the Ti2 layer. The location and quality of graphene were characterized by optical contrast using an optical microscope and Raman spectroscopy, respectively. Then, graphene-based FETs with the heavily doped silicon substrate as the backgate electrode were fabricated by standard photolithography and e-beam evaporation. Subsequently, the Ti2O3 nanoparticles were dispersed in ethanol solution  and spin-coated (4000 rpm) on the surface of the graphene channel. The devices were then dried in an oven under 100 °C for 12 h.Graphene flakes were mechanically exfoliated from a crystal of highly oriented pyrolytic graphite (HOPG) using adhesive 3M-tape and deposited on a silicon wafer with a 285-nm thermalized SiOThe electrical characteristics were examined by a semiconductor parameter analyzer . The responsivity measurement was performed in a digital deep level transient spectroscopy (BIORAD) system with mid-infrared lasers  to illuminate the whole devices, as shown in Supplementary Figure Supplementary Information


Graphene is a nanomaterial with many promising and innovative applications, yet early studies indicate that graphene may pose risks to humans and the environment. According to ideas of responsible research and innovation, all relevant actors should strive to reduce risks related to technological innovations. Through semi-structured interviews, we investigated the idea of graphene as a risk (or not) held by two types of key actors: graphene researchers and innovation advisors at universities, where the latter are facilitating the movement of graphene from the laboratory to the marketplace. The most common idea found is that graphene is not a risk due to, e.g., low toxicity, low amounts produced/used, and its similarity to harmless materials (being “just carbon”). However, some researchers and advisors also say that graphene is a risk, e.g., under certain conditions or due to a lack of risk-related information. We explain the co-existence of these seemingly contradictory ideas through (1) the semantic ambiguity of the word risk and (2) a risk/no-risk rhetoric, where risks are mentioned rhetorically only to be disregarded as manageable or negligible. We suggest that some of the ideas held by the researchers and innovation advisors constitute a challenge to responsible research and innovation regarding graphene. At the same time, we acknowledge the dilemma that the discourse of responsible innovation creates for the actors: denying graphene risks makes them irresponsible due to a lack of risk awareness, while affirming graphene risks makes them irresponsible due to their everyday engagement in graphene development. We therefore recommend more research into what researchers and innovation advisors should do in practice in order to qualify as responsible. In 2010, Andre Geim and Konstantin Novoselov were awarded the Nobel Prize for their “groundbreaking experiments” regarding the carbon-based nanomaterial graphene , high stThe Flagship, launched in 2013, involves more than 150 academic and industrial research groups in 23 countries and is coordinated by Chalmers University of Technology in Gothenburg, Sweden. Given the impact that graphene research “is expected to exert on tomorrow’s technologies and world economy,” among the objectives of the Graphene Flagship are “to build a pathway for the newly accumulated strategic knowledge to impact European industries and society” and “to secure a major role [of the EU] in this ongoing technological revolution” ?”The interviews of the graphene researchers and innovation advisors were transcribed and the material coded into categories in an iterative process. The primary focus was the categorization of the respondents’ main ideas about graphene risks, i.e., the respondents’ risk associations with graphene. By risk association, an actor establishes a connection between something and the notion of risk –47. In oThe notion of risk is multifaceted and has received theoretical interest from a variety of disciplines . Many deIn supposed contrast to this subjective understanding of risk, claims are sometimes made that risk is objective , 53, 54.x is a risk” presuppose a perspective from which some value is at stake. Still, such statements may be motivated by objective reasons, including evidence that human exposure to x can cause cancer  seems to be safe,” “there are no risks with graphene,” “I trust my colleagues who say that there is no risk with graphene,” “it is a safe material,” “graphene is not really a problem in nature,” “we see nothing alarming,” “the consumer has minimal risk,” and “graphene […] is environmentally friendly”. One researcher said:“If we replaced all electronic screens in the world, 2 billion touchscreens per year, there would be 60 kilograms emissions of graphene. This is not much.”This quote suggests that the absence of risk is easily achieved, e.g., by chemical modifications or simply by not (consciously) inserting it into the human body. More specific statements provide graphene’s lack of toxicity as a rationale for its lack of risk: “graphene will not attack cells” and “it is not toxic”. Other claims provide the lack of exposure to graphene as rationale, referring to the presence of safety equipment in labs (masks and fume hoods), the fast excretion of graphene from the body, and graphene being encapsulated in products. Another rationale stated for a lack of risk is the small amounts of manufactured graphene currently existing and anticipated in the future. One researcher said:“Since the 1850s all schoolchildren have used [lead] pencils, they have ingested graphene. Since we learned to make fire we have ingested graphene from the ashes.”Another frequent rationale for graphene not being risky is its similarity to other harmless substances, in particular the graphite carbon in lead pencils. Quotes include “carbon is not dangerous,” “I have no worries touching it, it is like pencils, graphite,” “it does not pollute as it is just carbon,” “regarding risks, graphene should not be that dangerous, it is graphite,” and “graphene is carbon; it is not dangerous for nature”. One researcher said:The basis for this rationale is that the carbon form graphite found in lead pencils and ashes consist of graphene sheets, although separate graphene sheets are considered to be another carbon form  than graphite.“To manufacture graphene you use Scotch tape, it is the same procedure to produce silicon. There is no danger. Not worse than silicon.”A similar rationale is that graphene is not a risk because of its similarity to the presumed harmless material silicon, as exemplified by this quote:“So far we haven’t seen any larger risks, on the contrary, those who are researching the risks […] think that their work is very boring, as they can only publish when they find risks. The toxicologists look for problems and when they can’t find any they can’t publish, so it’s too bad for them – but it’s good, of course that they don’t find anything. So far there are no studies that indicate danger.”The ideas about graphene risk voiced by innovation advisors echoed those of the scientists in many respects. All pointed out that graphene likely poses no risk, in particular due to lack of toxicity: “at the moment it seems that there’s no risk, at least this far we haven’t found any specific risk,” “if it’s handled in a proper way, nothing too worrying has come out,” “one can say that it’s not poisonous, there’s no danger that it is a toxin,” and “no risks that I know of,” “at this time it’s not problematic because we haven’t found anything yet.” One advisor elaborated:This lack of discovered toxicity in graphene by toxicologists was also pointed out by a second advisor. Yet, another advisor said that while there were some doubts about the long-term effects of its use in the human body or with other living creatures, he saw no risks in industrial applications, and that risks had not been discussed—they, the advisors, depended on the common sense of the researchers they worked with, and on the reviews that the research had undergone.“Graphene is a new area and there are no large amounts bought today, and very little is needed. If all mobile phones’ displays were to be covered with graphene, you would only need five kilos or something.”The claim that graphene is not a risk if proper procedures are followed came up. For example, one advisor noted that graphene samples sent within the Graphene Flagship were tracked and that one always has to be careful in handling materials, in the event that they could have a deleterious effect on one’s health. Here too, the small amount of graphene in use was pointed out: “It will be at least ten to fifteen years before graphene will be involved in the large processes.” One advisor said:“[G]raphite has existed all the time – and graphene is basically graphite in many layers, and mixed. People use pencils and children eat the pencils, so you know that it’s probably not supertoxic or anything like that, it’s just carbon.”Like the scientists, some of the advisors pointed out that graphene is simply carbon: “it’s carbon molecules and we have plenty of carbon, “no (risk involved) – we’re talking about carbon atoms, basically” and “graphene oxidizes at 400 degrees, it burns and becomes carbon dioxide.” One advisor explained:Like the scientists, then, these advisors link graphene’s lack of risk to its basis as a common element found throughout nature and currently in common domestic use, such as in pencils.dissimilar to the presumed more dangerous carbon-containing material carbon nanotubes:“You can compare it with the carbon nanotubes. They had some problems a few years back because a few studies appeared which showed that these coal nanotubes weren’t at all beneficial, but rather dangerous, similarly to asbestos […] They are long, and sharp. But graphene doesn’t have that form factor, so to speak.”One advisor brought forward the argument that graphene is not a risk since it is is a risk, or at least that risks cannot be excluded, saying for example that “there must be some dangers with graphene” and that “there are risks with graphene therefore we have protection.” Several mention the lack of knowledge as a rationale for graphene being risky, as shown by these quotes: “[…] risk research is at the beginning, you should not eat it [graphene],” “no one knows if graphene is toxic, some say it is other it isn’t,” “there might be health issues but we don’t know yet,” and “it is not clear how toxic graphene can be.” Some mention as rationales that specific conditions must be fulfilled in order for graphene to constitute a risk, in particular related to exposure probability, saying for example “possibly graphene can be dangerous as nano particles, if you breath them in,” “if you insert graphene into your body it might hurt you,” and “it is important to distinguish between flakes that you can breathe in and powder graphene you do not want to inhale.”Several researchers also expressed that graphene “The risks vary depending on where the material is in the life cycle. In the manufacturing of graphene in tennis rackets there is a risk of inhaling flake at the beginning. […] [W]hat happens when you throw away electronics? This is looked upon at the moment.”“Perhaps there are some hazardous chemicals in the manufacturing process. The problem is that the production will be in India and other countries where they are not as thorough. But this is the same for all electronic products. It is during the production and during the recycling there could be risks. We never talk about risk at work.”Several researchers also say that there are risks related to graphene during production and other product life cycle stages. These are not necessarily related to graphene itself, but possibly to other substances used: “there is a risk with acids that are used in making graphene, but that is easily controlled” and “we use some dangerous chemicals in the process, but they are all approved in the lab.” Two researchers elaborate further:“We haven’t seen any large risks… But at the same time, one can’t yet say that there aren’t any risks because it’s too large an area, there are too many types of material and too many different systems we have to look at, brain cells, intestinal cells, yes, you know, one has to have done so many studies before one can say that something is bad, or good.”Some advisors are also reluctant to conclusively say that graphene is not a risk. The lack of conclusive knowledge about possible risks of graphene is what makes them doubtful, much in the same way as the researchers. They refer to this gap in knowledge in one way or another, while at the same time, maintaining that graphene probably does not constitute a risk:“If a company has a product, they have to class their materials, they have to account whether it contains ‘hazardous materials’ or such. And then they ask if graphene is a dangerous material, of course they ask. And we have to answer, like, ‘a little, well, maybe, maybe a little, or maybe not’… it’s not poisonous, they haven’t been able to prove that it’s toxic… but it’s just this, there is a lot left to do. That’s what one can say. One has to be pretty honest, and say that it’s not poisonous, but there are many studies left to do.”Another advisor points out:“A large flake that is several micrometers in size, for example, probably has completely different health aspects than a flake which is only, say, 10 or 20 nanometers large. So it’s about size, and how they interact with cells, and other things.”Several advisors also adhere to the rationale that graphene constitutes a risk under certain conditions. One advisor points out that although it is composed of carbon atoms, it is not beneficial to inhale. Another notes that difference in health risks are to be expected from different sizes of graphene molecules:Later in the interview, this advisor added that research regarding risks should be carried out in parallel with the development of materials and that it was possible that mistakes might be made with graphene, which is why one has to be careful, carry out evaluations, and be vigilant all the time.“It’s always included in any business plan. One mandatory part of the business plan is having the risk analysis… So it’s just a table that has the description of the risk. The probability of the risk, the severity of the risk if it happens, and the actions to prevent the risk happening. So that’s in it, always. But risk as an element is a really important factor of course… when you think about the risk you have to be thinking about the external ones and the internal ones and the ecological ones and the commercial ones, so... because that’s part of the things that are telling you if this is worth doing, but also telling others that you have at least been thinking about these things. So. It’s just not just a list, it’s important.”One tool that innovation advisors can use to exercise vigilance regarding the possible risks of materials used in new products is the risk assessment carried out routinely when new projects and products are evaluated. In the conversations about risk, four of the six interviewees brought up the importance of these assessments in considering potential problems. One noted:This risk assessment is, then, the currently existing means for detecting human and environmental risks implicated by a future widespread use of graphene. Another advisor noted: “We try to include the concept of sustainability in all our ideas, to think about ‘is this environmentally sustainable?’” He continued, however, to say that it is the economic risks that are the most central in the risk assessment. To consider risk and sustainability “is part of the process,” a third advisor said, but noted that if the researcher presenting the proposal did not know of any risks, it was not followed up. This was echoed by his colleague who claimed that they had not thought about the possible risks of graphene, but rather that they had faith in the researchers’ good judgment considering the reviews their research had undergone. As the risk assessment focuses primarily on commercial risks, and the innovators themselves—together with researchers—are the primary providers of the information used in the assessment, it appears the possibility of detecting novel health and environmental risks in the assessments is limited. The advisors are thus constrained to repeating that to date, no dangers have been discovered and adding that more research is needed.Two ideas expressed by the researchers refer to fundamentally different kinds of risks than the health and environmental risks mentioned above, more related to research and innovation. One said that “the major risk of the graphene is that there is too much money in graphene, other 2D materials are ignored.” The researcher thus suggests that overly high investments in graphene research is hampering important research into other interesting materials and that this is more problematic than any human health- and environmentally related risks. Another researcher said that “the biggest risk is that we will not fulfill the promises around graphene.” This researcher refers to the many promises that graphene brings in terms of innovations see “” sectionis not a risk and that it is a risk. We see two possible reasons for this seemingly contradictory finding: one rhetorical and one semantic. These are explored below.It might seem strange that several researchers and advisors expressed both that graphene As can be seen in Table Considering the semantic explanation, we can first note the conceptual distinction between risk and hazard that is often made in the risk research literature. Hazard then refers to potential loss, while risk refers to exposure to a hazard , 62. “RiHowever useful and clear this theoretical distinction between risk and hazard might be, the word risk has a less narrow and precise meaning in common usage . In factresponsible if they associate graphene with risk, which they partly do. However, the respondents are at the same time irresponsible to associate graphene with risk, since they clearly engage in the then-risky activity of graphene development and innovation on an everyday basis. Demands for responsibility thus also motivate the respondents to dissociate graphene from risk and to downplay risks, which they also do. Given this dilemma-like situation, it is perhaps no wonder that the respondents express a mixed understanding of graphene as a possible risk. Existing research policy on RRI from the European Commission [The semantic explanation does not necessarily point to the respondents being irresponsible from an RRI point of view, but rather to the semantic difficulty  of the risk concept in common language . Howevermmission  providesmmission , 68.Which role should scientists and innovation advisors have in the early anticipation and avoidance of risks?Do scientists and innovation advisors experience a ‘damned if you do, damned if you don’t’ dilemma when it comes to acknowledging technological risks?Can individual-level criteria for RRI be formalized?We therefore recommend further research into how RRI should be approached in practice, in particular what actors such as researchers and innovation advisors should do (or think) to qualify as responsible. Potentially interesting research questions include:Our recommendation is in line with Frankel , who wriWe have found that the main idea held by graphene researchers and innovation advisors is that graphene is not a risk. Rationales provided for this are that graphene is not toxic, that exposure is low, that small amounts are expected to be produced and used, that graphene can be made safe, that graphene is similar to harmless materials , and that graphene is different from hazardous materials such as carbon nanotubes. A less frequent but still common idea is that graphene is a risk. This is motivated by the current lack of risk-related information for graphene, as well as that it can be risky under certain conditions and in different stages during its product life cycle . We suggest that these two seemingly contradictory ideas can be explained through (1) the semantic ambiguity of the word risk, which can denote both actual and potential losses, or (2) a risk/no-risk rhetoric, during which risks are first rhetorically mentioned only to be disregarded as manageable or negligible later. We also note that some researchers mentioned as main risks that the focus on graphene could hamper research and development of other interesting two-dimensional materials, and that the high promises of graphene may not become fulfilled. Given the second explanation, we suggest that some of these ideas held by the graphene researchers and innovation advisors constitute challenges for RRI in the graphene field and for graphene technology. At the same time, we acknowledge that the uncertainty of graphene risks and the RRI discourse put the respondents in a dilemma-like situation. If they deny that graphene is a risk, they become irresponsible because of their lack of risk awareness. If they affirm that graphene is a risk, they also become irresponsible because of the engagement in graphene development that their work constitutes. More research regarding what researchers and innovation advisors should do in practice in order to qualify as responsible is therefore recommended.


Different from previous work, in which only DMS was tested and under pure nitrogen conditions, we measured DMS mixed by common air to establish the actual atmospheric measurement environment. Moreover, we used tunable laser absorption spectroscopy with spectral fitting to enable multi-species  measurement simultaneously. Meanwhile, we used empirical mode decomposition and greatly reduced the interference of optical fringes and noise. The sensor performances were evaluated with atmospheric mixture in laboratory conditions. The sensor’s measurement uncertainties of DMS, CH4, and H2O were as low as 80 ppb, 20 ppb, and 0.01% with an integration time 1 s, respectively. The sensor possessed a very low detection limit of 9.6 ppb with an integration time of 164 s for DMS, corresponding to an absorbance of 7.4 × 10−6, which showed a good anti-interference ability and stable performance after optical interference removal. We demonstrated that the sensor can be used for DMS measurement, as well as multi-species atmospheric measurements of DMS, H2O, and CH4 simultaneously.This paper presents a mid-infrared dimethyl sulfide (CH However, it was balanced by pure nitrogen and only DMS was detected, rather than a real air condition. Although spectral interference has been considered comprehensively during spectra investigation, practically, the sensitivity of the sensor is deteriorated by the strong spectral interference from H2O and CH4 when working in practical air condition; there is no other method of data processing for reducing the interference of optical fringes and noise; and the accuracy is affected by internal optical path.Recently, a Mid-Infrared (MIR) spectral DMS sensor was developed by our group . The senν1/ν8-band of DMS, and deduced the concentration of DMS, as well as atmospheric interference CH4 and H2O simultaneously by Multi-Component Spectral Fitting (MCSF). Moreover, we reduced the interference from noise and optical fringes by performing Empirical Mode Decomposition (EMD) and reconstruction to the recorded spectral data. The sensor’s performances were evaluated with common air mixture in laboratory conditions.Moreover, based on our previous investigation, the atmospheric DMS concentration is about 28 ppb around a sewage treatment tower and about 500 ppb near an instant noodle factory. Thus, in this paper, to develop a DMS sensor with strong anti-interference capability and stable performances to detect polluted atmosphere in those factories and the surrounding environment, we utilized another candidate spectrum with wavelength of 3336.7 nm located at the The remainder of this paper is arranged in three sections:  sensor cA < 0.05, according to Beer-Lambert absorption law and optically thin condition, absorption coefficient ωt and can be expanded as a Fourier cosine series:a is the modulation amplitude, which is the wavelength modulation of the laser generated by sinusoidal modulation; ω is the modulation frequency; kH are Fourier series; and k is the harmonic order. Because the second harmonic signal 2f is closely related to the absorption and free of background, typically k = 2 is used in Wavelength Modulation Spectroscopy (WMS). Thus, for the mixed second harmonic signal of n types of gases, they can be expressed as follows:P is the pressure, L is the length of optical path, iχ is the mole fraction of the ith absorbing species, and ijS and ijφ are the line strength and line shape function of the jth line of the ith absorbing species, respectively. Referring to Equation (2), if the pressure and temperature remain constant, we can ignore the variations of line profile, and it can be expressed as:ith absorbing species in per unit volume concentration, and the magnitude of the absorption-based 2f signal, 2fS is the 2f signal that is measured by a lock-in amplifier, G is the electro-optical gain of the measurement system, oI is average intensity of the laser at frequency 2f_i_perS is the 2f signal of ith absorbing species in per unit volume concentration. Therefore, 2fS of a mixture theoretically equals the sum of the product of each component’s concentration and its 2f signal in per unit volume concentration.We developed a DMS sensor based on wavelength modulation spectroscopy, whose theoretical basis is the Beer-Lambert absorption law ,30,31,32ribed as :(4)S2f≈ν14/ν18-bandwidth wavelength of 3367.3 nm was preferred, and the strong absorption made the sensor possess much higher measurement sensitivity than other spectral lines.The MIR fundamental absorption spectra of DMS were investigated in detail in our previous work . By compWe reexamined the spectral line of DMS based on minimum interference principle, including relatively less interference lines and distant interference spectral lines, and the absorbance of absorption line is relatively large. Thus, another spectral range of DMS was preferred based on the Pacific Northwest National Laboratory (PNNL) and High Resolution Transmission (HITRAN) databases. The 5 ppm×m DMS within the range of 3333–3371 nm is presented in ν1/ν8-band to be measured. Detailed analysis is presented in ν1/ν8-band between 3333.7 and 3337.8 nm, and the ν1/ν8-band of 3336.710 nm suffers much lower interference than ν14/ν18-band of 3367.229 nm, including the magnitude of interference and distance between the absorption line and the interference line. Thus, we chose 3333.7–3337.8 nm as our ultimate selection for DMS measurement with comprehensive consideration. Furthermore, although CH4 and H2O have less interference in the absorption of DMS, they are located at the working range of the laser. At the same time, the absorption spectra of methane and water overlap each other, thus it is necessary to obtain the concentration of three gases simultaneously by using the MCSF.The absorption peak wavelength and strength of DMS candidate regions are listed as well as the spectral information of possible interferences from air absorptions. In f signal was processed by MCSF program to obtain the target gas concentration.We developed a DMS gas sensor based on our instrument development platform ,33,34,35f demodulation signal from the data acquisition software.We carefully set all the working parameters of the sensor, including the optical path, gas flow, modulation amplitude, temperature, and so on. The instantaneous line width, dynamic tuning rate, and slope efficiency of ICLs have been reported to be suitable for precision spectroscopy measurements . The lasf signal [f signal, modulation amplitude of 0.27 cm−1 was chose as our optimized selection. Thus, the modulation amplitude of 0.27 cm−1 was preferred to improve the Signal-to-Noise Ratio (SNR) and measurement accuracy.We optimized the modulation amplitude of the DFB-ICL to enable measurement of multi-species spectra without overlap. We optimized the modulation amplitude according to Spectral Discrimination (SD) and normalized amplitude of the DMS WMS-2f signal . Traditif signal  can no lA MCSF algorithm to reduce spectral interference was developed in our previous work , as showAs for the wide-band characteristics of the MIR fingerprint absorption, the measurement sensitivity and accuracy are always deteriorated by overlap with adjacent spectrum, optical fringes, and noise. A solution by EMD and reconstruction to the recorded spectral data was developed in our previous work , as showf signal of each component is normalized, the initialization concentration parameters of each component are estimated, and the 2f signals of single component concentration and mixed concentrations participating in the fitting are produced. If the algorithm converges, the best fitting parameters are obtained. In our simulation, the results of the algorithm basically did not depend on the initial concentration. When the concentration of DMS is within the range of 1–20 ppm, the algorithm always converges.The algorithm includes two parts: (1) EMD is used to decompose and reconstruct the measured spectral data for reducing the optical fringes and noise; and (2) the 2The initialization concentrations of DMS, methane, and water were set as 1 ppm, 1 ppm, and 1%, respectively. Each component used 370 points to participate in fitting, and the program usually cycles fewer than 100 times. Once the algorithm converges, the best fitting parameters are determined.4, and H2O for the MCSF algorithm of the sensor with elaborately planned experiments. The HWG was filled with N2 first and then with a reference gas, therefore, the difference between the 2f signals of the reference gas and N2 could be used as reference signal. The reference signals of DMS and CH4 were obtained using reference gases with concentrations of 20.2 ppm and 3 ppm, respectively. In contrast, the reference signal of H2O was obtained using high humidity air that subtracted air background, and the high humidity air was obtained by a humidifier. With the EMD method [f signal of each component with less optical fringe and noise between 3333.7 and 3337.8 nm of DMS, CH4, and H2O are shown in We obtained superior reference signals of DMS, CHD method , we reduf signals of the mixture and reconstructing them with the EMD method. Take the mixture of H2O (0.14%)-CH4 (0.19 ppm)-DMS (10.1 ppm) as an example: about four IMF components were obtained. Thus, according to the signal characteristics of correlation coefficient, amplitude, and symmetry, the signal was reconstructed, as shown in We reduced the interference from noise and optical fringes by decomposing the measured 2Noise signals usually possess the characteristics of small amplitude and high frequency, while optical fringes are similar to the profile of sinusoidal signal, and all of them have a very low correlation coefficient relative to the absorption signal. Thus, IMF 1 in The detection ability of sensor was usually limited by noise and optical fringes ,37. Thus−6, which is sufficient to satisfy the needs of human health. Although the detection limit is much lower than the 2.8 ppb mentioned in Reference [A comparison was made for the sensitivity and detection limit before and after fringe removal. In eference , it is beference .4 and H2O), prepared with a homemade high-precision gas mixer [4 and H2O in the air were tested beforehand by absolute measurement of direct absorption spectroscopy. The initial concentrations of DMS, CH4, and H2O were 20.2 ppm, 1.9 ppm, and 1.4%, respectively. Thus: (1) in the first group, the concentration of DMS ranged from 2.02 to 10.1 ppm , while the concentration of CH4 and H2O remained at 0.95 ppm and 0.7%, respectively; and (2) the concentration of CH4 ranged from 0.19 to 0.95 ppm (in 0.19 ppm), the concentration of H2O ranged from 0.14% to 0.7% , and the volume of DMS remained at 10.1 ppm in the second group. All of the concentration settings were realized by adjusting the three-channel volumetric flow rate settings in Two groups of DMS concentration gradient experiments with air mixture  for DMS, CH4, and H2O. The measured accuracy of DMS, CH4, and H2O were 0.3%, 1.9%, and 2.8%, respectively. The standard deviations could primarily be attributed to the uncertainty of the mass flow controller and the fluctuation of H2O in the air over time. Although because of the concentration gradient, the O2 and N2 concentrations in the experiment are different from their actual concentrations in air, they have no absorption in the spectrum that we chose and have less influence on our measurement.The concentration of DMS, CH4, and 0.7% H2O. The results are shown in Sixty measurements with 1 s intervals were performed to verify the stability and accuracy of the sensor with the flowing gas mixture of 10.1 ppm DMS, 0.95 ppm CH4, and H2O were 10.10 ± 0.08 ppm, 0.96 ± 0.02 ppm, and 0.7 ± 0.01% with a sampling interval of 1 s, respectively. Therefore, the measurement uncertainties of DMS, CH4, and H2O were 80 ppb, 20 ppb, and 0.01%, respectively, which shows that the sensor has an excellent performance.In 4, and H2O. The sensor’s working wavelength located at 3336.7 nm, i.e., the ν1/ν8-band, was chosen to measure atmospheric DMS, which could avoid serious spectral interference from atmospheric CH4 and H2O. Multiple techniques were specified for wide-band spectra measurement, including modulation amplitude optimization, MCSF, and removal of optical fringes and noise by EMD, which enhanced the performances of the sensor. Experimental results indicate that the measurement accuracy of DMS was raised to 0.3%, and the measurement uncertainties of DMS, CH4, and H2O were improved to 80 ppb, 20 ppb, and 0.01%, respectively. Furthermore, detection limit as low as 9.6 ppb with an integration time of 164 s was obtained, thus the sensor can be applied in monitoring the atmosphere around food processing plants and chemical plants. Future work can concentrate on adjusting the structure of optical path and lengthening the HWG, which will further improve the stability and detection limit of the sensor.In summary, we demonstrated a high-sensitivity and multi-species sensor of atmospheric DMS, CH


Our results suggest the adsorption ability of the epitaxial graphene towards divalent Lead ions is concentration-dependent and tends to saturate at higher concentrations. To elucidate the mechanisms responsible for Pb adsorption, we performed DFT calculations and estimated the solvent-mediated interaction between Lead species in different oxidative forms and graphene. Our results provide central information regarding the energetics and structure of Pb-graphene interacting complexes that underlay the adsorption mechanisms of neutral and divalent Lead species. Such a holistic understanding favors design and synthesis of new sensitive materials for water quality monitoring.Deep understanding of binding of toxic Lead (Pb) species on the surface of two-dimensional materials is a required prerequisite for the development of next-generation sensors that can provide fast and real-time detection of critically low concentrations. Here we report atomistic insights into the Lead behavior on epitaxial graphene (Gr) on silicon carbide substrates by thorough complementary study of voltammetry, electrical characterization, Raman spectroscopy, and Density Functional Theory (DFT). It is verified that the epitaxial graphene exhibits quasi-reversible anode reactions in aqueous solutions, providing a well-defined redox peak for Pb species and good linearity over a concentration range from 1 nM to 1 µM. The conductometric approach offers another way to investigate Lead adsorption, which is based on the formations of stable charge-transfer complexes affecting the  The RSD of Pb determination with six repetitions was 3.5%.To monitor the dependence of the analytic signal on the concentration of the Lead ions in solution, we performed more effective SWASV analysis  for Pb in the concentration range between 102+) are initially adsorbed on the inert electrode surface and then they are reduced to neutral Lead species  at a constant potential. At the second stage, Pb0 species are re-oxidized to Pb2+ and desorbed back to the solution in the oxidized state. During the stripping of Lead species accumulated onto the epitaxial graphene surface, Pb0 adatoms lose 2 electrons, thereby contributing to the generation of the stripping current. It is important to note that the resulting stripping current is proportional to the concentration of the adsorbed species. This means that the preconcentration process predominantly defines the sensitivity of the epitaxial graphene towards Pb. Indeed, the more Pb2+ ions will be plated as neutral Pb species on the electrode, the more will be re-oxidized and thus the stronger the striping peak current is expected. Therefore, a knowledge about the interaction between elemental Lead species and graphene in the presence of water is a key to understanding the sensing mechanism at the atomistic level. For this aim we performed comprehensive DFT calculations focusing on the nature of this interaction. Since the van der Waals (vdW) forces are expected to play a fundamental role in the adsorption of elemental metals on graphene [0 on graphene nanofragment are summarized in To gain deep insight into the adsorption mechanism, it is very important to clarify the fundamental principle of generation of the stripping current observed in our experiment. Generally, SWASV comprises two stages: (i) preconcentration step and (ii) stripping step. During the first preconcentration step, Lead divalent ions . According to B3LYP results, binding height of Pb adatom is 4.36 Å see . By consions see  without ions see c. Howeveions see b, we notz-direction (perpendicular to the graphene plane). Therefore, consideration of the vdW correction is a key for gaining insight into the interaction between elemental Pb and graphene and, consequently, for correct explanation of the adsorption mechanism.Furthermore, an important role of London dispersion forces in interaction between Pb and graphene is also evidenced by the spatial redistribution of electron wavefunctions describing frontier molecular orbitals see d. In parD peak, we further investigate the Raman spectra of epitaxial graphene after electrodeposition of the Pb to ensure that adsorption capacity is high enough to provide the appropriate stripping response. Detailed analysis of the Pb electrodeposition on epitaxial graphene was performed in our previous work [D-line. Since the D-mode was not present before electrodeposition process, it is reasonable to assume that its appearance is due to the formation of Pb-C bonds.To gain deeper insight into the interaction between elemental Pb and graphene, we also performed Raman mapping. Bearing in mind that as-grown epitaxial graphene exhibits no defect-related ous work . TherefoD peak intensity distribution suggests that the perturbation related to adsorption of Pb species has local character, most likely restricted to the vicinity of the adsorbed species. Since large Pb clusters are weakly bonded to graphene [D peak. To summarize this section, one can conclude that epitaxial graphene provides enough available electroactive sites for oxidation-reduction reactions during stripping analysis.Furthermore, the observed non-uniform graphene , it is m2+ ions will influence the band structure of graphene and, consequently, the electron transport through graphene. It means that real-time monitoring of the resistance of the epitaxial graphene as a function of time under exposure to injected liquid containing Pb2+ ions will allow estimation of how the epitaxial graphene interacts with divalent Lead ions dissolved in water. As was mentioned before we used epitaxial graphene as a lateral resistor for measurement of the conductometric response. Schematic representation of the device is depicted in 2+ at different molar concentrations within the range from 0.125 μM to 500 μM. The graphene resistor exhibits a good response to Pb2+ and reproducibility even after several repeated cycles. The initial resistance of the epitaxial graphene changed with the Pb2+ solution injected into the flow chamber. It can be understood that the presence of Pb2+ ions dissolved in aqueous solution enhances the conductivity of graphene, as evidenced by the resistance drop during each cycle. The relative variation of the resistance was calculated by equation ΔR = (RPb − REG)/REG, where RPb and REG represent the resistances of the epitaxial graphene after injection of Pb-containing liquid and the initial resistance of the epitaxial graphene, respectively. We noticed that the increase in Lead concentration causes an increase of the differential resistance value, suggesting that the adsorption of Pb2+ metal ions on the epitaxial graphene follows the Langmuir isotherm  in the presence of solvent (water in our case). It was found that the hollow site  is the most favorable adsorption site of Pb2+ ion on graphene  and is very interesting from a practical point of view. As was mentioned before the difference between interaction energy and adsorption energy can be regarded as a degree of deformation of the sp2-plane adsorption event. With this knowledge in mind, we estimated the deformation energy for all considered adsorption geometries. This parameter was found to increase with increasing number of adsorbates, indicating that more energy penalty needs to be paid to accommodate larger number of adsorbates at the graphene surface. Independently of the kind of adsorption configuration, divalent ions always act as typical acceptors, which extract electrons from graphene resulting in the increase in hole concentration. As a result, LUMO is strongly hybridized and shared between graphene and Pb2+ ion b, implyi2+ ion, respectively. As shown in 2+ ions near the adsorption site. Therefore, hole doping effect is caused by the formation of a hybrid charge-transfer complex. It should also be noted that the charge-transfer value obtained using the vdW-corrected functional is very close to that calculated without vdW correction (To visualize the charge-transfer mechanism, we calculated the charge density difference by using the following equation:rrection . This su2+ ion on graphene is very stable and the strong Cation-π interaction helps the Pb2+ ions to remain in the chemisorbed state on the graphene surface. In other words. Pb2+@graphene complex did not collapse with time. Such a dynamical stability will lead to reproducible resistance-time characteristics, which we observed in the experiment.To verify the stability of Cation-π bonding in the presence of water we performed ADMP simulations at room temperature. The potential energy trajectory represented in sp2-bonded carbon network. Our results indicated that Pb2+/Pb0 redox system at the graphene electrode surface is quasi-reversible. The results revealed a strong stripping response of Pb2+ with slope of linear regression of 2.3 × 103 A·cm−2·mole−1·L and good linearity within concentration range between 10−10 M to 10−6 M. The adsorption behavior of Lead was further investigated with Raman spectroscopy. By monitoring of defect-related D-mode of graphene induced by Pb adsorption it was established that epitaxial graphene is an appropriate template providing high adsorption capacity towards Pb. The conductometric approach was found to be an effective tool for monitoring the presence of Lead ions in aqueous solutions, since graphene lateral resistor enables fast response and recovery. It was found that adsorption energy of Lead ions in the regime of low concentrations is higher than that at high concentrations, which is evidenced by the longer recovery time at the nanomolar concentrations. To elucidate the adsorption mechanisms, we also preformed DFT calculations. It was found that the electrochemical response of the epitaxial graphene to Lead is mainly regulated by a van der Waals interaction between neutral Lead atoms and graphene during a redox process, while the conductometric response is governed by the formation of stable charge-transfer complexes, which cause the increase in hole conductivity under Pb accumulation conditions. The current work provides deep insights into the fundamental understanding of the adsorption of Lead in different oxidative forms on epitaxial graphene and is an important step towards development of easy-to-use and portable sensing platform, which enables real-time determination of the toxic Lead in drinking water.In summary, the behavior of Lead species at epitaxial graphene supported by Si-terminated 4H-SiC has been evaluated. By using two independent experimental methods, namely voltammetry and time-resolved electrical characterization we investigate the response of the epitaxial graphene under exposure to Pb-containing aqueous solutions. Raman mapped images provided by confocal Raman spectroscopy confirmed high quality of the epitaxial graphene and low density of point defects, indicating that adsorption events occur at the defect-free


Recent emergence of metasurfaces has enabled the development of ultra-thin flat optical components through different wavefront shaping techniques at various wavelengths. However, due to the non-adaptive nature of conventional metasurfaces, the focal point of the resulting optics needs to be fixed at the design stage, thus severely limiting its reconfigurability and applicability. In this paper, we aim to overcome such constraint by presenting a flat reflective component that can be reprogrammed to focus terahertz waves at a desired point in the near-field region. To this end, we first propose a graphene-based unit cell with phase reconfigurability, and then employ the coding metasurface approach to draw the phase profile required to set the focus on the target point. Our results show that the proposed component can operate close to the diffraction limit with high focusing range and low focusing error. We also demonstrate that, through appropriate automation, the reprogrammability of the metamirror could be leveraged to develop compact terahertz scanning and imaging systems, as well as novel reconfigurable components for terahertz wireless communications. They have led to significant breakthroughs in various fields such as imaging, radar, and wireless communications to name a few4. Metasurfaces, the thin-film planar analogue of metamaterials, are composed of an array of subwavelength resonators, and inherit the unique properties of their three-dimensional counterparts while addressing their issues related to bulkiness, losses, and cost. For this, metasurfaces operating at the microwave8, Terahertz12, or optical14 bands have been widely proposed to achieve attractive features such as negative refraction, cloaking, superlensing, or holographic behavior. A large subset of these designs have been based on the generalization of the Snell’s laws of reflection and refraction15, which provided fundamental understanding on how to achieve precise beam manipulation16, vortex creation17, focusing5 through the drawing of specific phase gradients. Another remarkable advance is the proposal of coding metasurfaces, where the device is built (encoded) using a discrete set of unit cell options (bits or words)19. This provides a powerful and intuitive design perspective while drawing a clear parallelism with information theory, which opens new ways to model, compose, and design advanced metasurfaces21. Several works have exemplified such approach mainly for scattering control22.Metamaterials have drawn a great deal of attention since their conception as they enable unprecedented levels of electromagnetic control23. The resulting reconfigurable metasurfaces can be globally or locally tunable, depending on the specific scheme and, with appropriate control means, they become programmable24. Not coincidentally, the programmable metasurface paradigm has found in the aforementioned coding paradigm a natural match to describe and implement reconfigurability. When built using locally switchable elements such as pin diodes, varactors, or switches, coding metasurfaces can be elegantly described as a bit or state matrix and digitally controlled through reconfigurable logic, e.g. a Field-Programmable Gate Array (FPGA)18. Polarization and focusing control5, beam manipulation16, or holograms7 have been demonstrated in the GHz range, whereas fewer proposals have appeared in the THz regime mostly due to the lack of appropriate means for tuning.Two of the main downturns of most metasurfaces are non-adaptivity and non-reconfigurability as, in most cases, the electromagnetic function and its scope are fixed once the unit cell is designed. In response to these drawbacks, metasurface designs with tunable or switchable elements in the unit cell have emerged26. The reasonably low loss of graphene plasmons at THz frequency band has been the main motivation of several wave steering devices27. The plasmon tunability of graphene is achievable through chemical doping or electrostatic biasing. The tunablity of graphene opens the door to globally reconfigurable metasurfaces with fine-grained control of the amplitude-phase response28, or it can provide switching between diverse electromagnetic functionalities in particular setups29. Plasmon tunability can also be leveraged locally, in which case graphene becomes a natural candidate for the implementation of (re)programmable THz metasurfaces. In spite of their potential, graphene-based programmable designs have remained relatively unexplored, and current proposals are mainly limited to dynamic beam manipulation for diffusion30, encryption31, or vorticity control17.Graphene shows great promise for the implementation of THz metasurfaces. This is due to its widely demonstrated plasmonic properties that provide subwavelength behavior required in the unit cell building blockIn this work, a (re)programmable metamirror is proposed as shown in Figure Figure 15. This approach, however, offers no reconfigurability. In this work, instead, we achieve reconfigurability through changes in the electrostatic bias applied to uniformly sized graphene patches. This modifies the complex conductivity of the graphene sheet and, by extension, the phase of the reflected wave.A reflective metasurface operating as a mirror calls for the use of unit cells with a high reflection amplitude and a wide phase range. Fabry-Pérot resonant structures composed of metallic patches over a square grounded substrate can provide such functionality by adjusting the size or position of the metallic patch to achieve the required phaseMethods section.Figure μc,1 and μc,2, respectively). A quick exploration reveals a complete 2π phase range as well as large design space areas with high reflectivity.Compared to the the single-layer graphene structures, our proposed unit cell based on dual-layer graphene enjoys more flexibility to achieve a wide range of phase response and a high reflection amplitude, simultaneously. The dual layer structure, modeled as two parallel RLC cells, provides an additional degree of freedom as each graphene patch can be biased independently. Figure Nbit is the number of bits. We will see that two bits are enough for our purpose. We choose μc,1 = {0.6, 1.3, 0.1, 0.4} eV and μc,2 = {0, 0.6, 0.1, 0.1} eV corresponding to the bit combinations B = {00, 01, 10, 11}, respectively. As observed in Figure π/2 is maintained over the range of 1.9–2.1 THz with an amplitude close to 0.7. This high reflection amplitude for all states guarantees a high focusing efficiency for the designed metamirror.The coding set is built by picking points with as high amplitude as possible, and phases equal to multiples of θi and azimuth angle φi. It is used to focus the energy in a given point defined by x′, y′) at an arbitrary point on the metamirror can be written asλ0 is the wavelength in free space, k0 is the incident wavevector, and r′ =  is the vector position of an arbitrary point on the metasurface.Consider a reflective metasurface under illumination of an incident plane wave at elevation angle θi = ϕi = 0), Equation x′, y′), and rounding off the phase values to those offered by the closest coding states.When the metamirror is illuminated by a normally incident wave  of the reflected field response when the focal point is scanned in space. Differences in the reflected field response due to the scan of focal point creates the confocal image.Figure Charts (a–l) of Figure et al.32, wherein a single graphene layer is laid over the whole metasurface area and tuned using a single bias source. Such approach only allows to control the focal depth with limited range. Focusing with programmable coding metasurfaces has been only demonstrated in the GHz range with devices that use PIN diodes for reconfiguration. This limits the amount of achievable unit cell states, reducing the precision and focusing range.In this work, we have presented for the first time the design of a fully reprogrammable metamirror that can be used in terahertz confocal imaging. The metamirror acts as a focusing reflectarray that leverages the tunability of graphene to achieve the required phase range and programmability at the unit cell level. At the metasurface level, we adopted a coding metasurface approach that allows to dynamically shift the focal point by adjusting the center and slope of a concentric phase gradient. This is in stark contrast to the design by Huang We demonstrated analytically and numerically that the proposed metamirror can shift the focal point both laterally and in depth. With 2 bits per unit cell and assuming a total size of 9λ × 9λ, energy is focused around the desired focal point with less than 6% deviation in the evaluated points. Moreover, the metamirror can operate close to the diffraction limit as long as the focal point is located around the focal depth and centered with respect to the metasurface. We also showed that the programmability of the focal point can be applied to the development of compact devices for 3D terahertz confocal imaging.τ = 0.6 ps, which is well achievable with Chemical Vapor Deposition (CVD) techniques and encapsulated in hexagonal boron nitride (h-BN)34. Those techniques in fact produce significantly higher relaxation times, which would lead to lower loss and better overall performance. Moreover, considering the electrically thin boron nitride layer has a negligible impact in the simulation results. To mention, when the graphene has a lower relaxation time, the plasmonic losses within the structure increase. Therefore, it results in a device with a lower efficiency. Regarding the biasing scheme, different gate-controllable designs have been simulated35 and experimentally validated36, which could be adapted to local addressing of unit cells. Before actually addressing fabrication, a challenge to be addressed in future work would consist on minimizing the interference imposed by the metallic biasing structure on the response of the metasurface. It is worthy to note that bilayer graphene, a material consisting of two layers of graphene, exists in the various forms such as Bernal-stacked form37. Depending on the relative position of layers, different quantum effects can happen in the spacing. But what we have here is different. In our proposed dual-layer structure, the insulating layer (here HDPE) between two graphene patches is sufficiently large for quantum effects to be negligible38. Therefore, crystallographic alignment is not required, and micrometric precision of current lithographic techniques is enough to achieve the results reported in the paper. Therefore, the process of fabrication of dual-layer metasurface structure is generally similar to one-layer structure; and the existing transfer printing methods could be employed39.As a final note, it is worth highlighting that this work brings the concept close to realization by making reasonable assumptions. First, we consider a graphene quality leading to a relaxation time of 40. The length of the unit cell is du = 20 μm and graphene patches are squared with side dg = 12 μm. The operation frequency is set to 2 THz. We consider bulk silicon as the substrate with relative permittivity εr = 11.9, loss tangent tan(δ) = 2.5 × 10−4, and thickness hsi = 10 μm. The extra layer is composed of a layer of HDPE with relative permittivity εr = 2.37, loss tangent tan(δ) = 0.011, and thickness hHDPE = 4 μm.The unit cell structure shown in in Figure σ(ω) is the frequency-dependent complex conductivity of graphene. The conductivity is given bye, kB are constants corresponding to the charge of an electron, the reduced Planck constant and the Boltzmann constant, respectively41. Variables T, τ and μc correspond to the temperature (T = 300 K in this paper), the relaxation time and the chemical potential of the graphene layer. Note that this expression neglects effects at the graphene edges and considers that the Drude-like intraband contribution dominates, which are experimentally validated assumptions at the sizes and frequencies considered in this work42. In all cases, the relaxation time of graphene τ = 0.6 ps, which is well achievable with current fabrication and encapsulation techniques33. The chemical potential of the top and bottom layers are initially left as parameters for exploration and then fixed to discrete values leading to the adequate amplitude and phase.The graphene layers are modeled as infinitesimally thin sheets with surface impedance 40. For the simulation of unit cells, a Floquet port is applied to excite an x-polarized normal plane wave onto the unit cell and the back-scattered wave is then measured. This way, we obtain the amplitude and phase of the reflection coefficient of the proposed unit cells while taking into consideration mutual coupling between adjacent unit cells. After obtaining the response of individual unit cells, the complete metamirror is modeled as an array of such unit cells with different phases. The metasurface is illuminated by a normal plane wave with x-polarization to obtain the scattered fields above the metasurface and, thus, the field distribution around the focal point. Finally, we simulate the THz imaging device by estimating the scattering response of the spheres in different positions. To this end, we again consider x-polarized normal illumination. To identify the presence of a sphere in the focal point of the metamirror, we compare the far field response of the metamirror with and without the spherical objects. Strong variations indicate the presence of a sphere in the focal point of the metamirror. To note, for the results shown in Figures We implement the unit cells and the complete metasurface in CST Microwave StudioR1, L1, C1; R2, L2, C2) in parallel with equivalent transmission lines representing the HDPE and grounded silicon layers. The values of resistance, inductance, and capacitance of the graphene patches have been extracted from the reflection parameter at the boundary between air and unit cell, which only depend on the chemical potentials of the top and bottom graphene layers for a fixed patch size. For the results shown in Figure R1, L1, C1; R2, L2, C2) are .To gain physical insight into the scattering behavior of the proposed unit cell, an approximate circuit model has been developed. As sketched in Figure Jx on all unit cells. Therefore, we can write the inhomogeneous potential wave equation asr =  and r′ =  are the vector positions of the observation and source points, respectively. The magnetic and electric fields can be found by applying To validate the response of the metamirror around the focal point, we need to use analytical models compatible with near field conditions. Fresnel diffraction theory cannot be used because of the small focal length to lens diameter ratio of our device. Alternatively, we apply the Huygens’ principle to model the currents excited at the metasurface as electrically small sources of radiation. Consider an incident wave polarized along the x-direction that excites an x-directed current density M × N cells asFinally, the metasurface response is obtained by adding the contribution of its


The authors of “The Ready to Reduce Risk (3R) Study for a Group Educational Intervention With Telephone and Text Messaging Support to Improve Medication Adherence for the Primary Prevention of Cardiovascular Disease: Protocol for a Randomized Controlled Trial”  require corrections in relationship to the use of the Morisky Medication Adherence Scale (MMAS-8).The following text was omitted from the Acknowledgements and as a footnote in Table 1 and should be added:Use of the MMAS is protected by US and International copyright laws. Permission for use is required. A license agreement is available from: Donald E Morisky, MMAS Research (MORISKY), 294 Lindura Court, Las Vegas, NV 89138-4632; dmorisky@gmail.com.Two additional references should be cited after reference 37 in the following sentences:In addition, the self-reported 8-item Morisky Medication Adherence Scale (MMAS) was completed at baseline and 12 months. This is an established and validated scale that is commonly used to measure adherence [37].Self-report: 8-item Morisky Medication Adherence Scale (MMAS) [37].Therefore, we have also used a self-reported validated questionnaire (MMAS) [37] and repeat prescription history as supporting outcome measures.The references to be cited are:Berlowitz DR, Foy CG, Kazis LE, Bolin LP, Conroy MB, Fitzpatrick P, SPRINT Research Group. Effect of Intensive Blood-Pressure Treatment on Patient-Reported Outcomes. N Engl J Med 2017 Dec 24;377(8):733-744.Morisky DE, DiMatteo MR. Improving the measurement of self-reported medication nonadherence: Final response. Journal of Clinical Epidemiology 2011 Mar;64(3):262-263.These have become references 50 and 51, respectively, and all subsequent references have been renumbered accordingly.The correction will appear in the online version of the paper on the JMIR website on July 24, 2019, together with the publication of this correction notice. Because this was made after submission to PubMed, PubMed Central, and other full-text repositories, the corrected article also has been resubmitted to those repositories.Authors and journal had to publish this correction due to legal threats by Steven Trubow and Donald Morisky from the company MMAS Research LLC, the copyright holder of the instrument. This is unfortunately not an isolated case, as the developers of this scale are known to comb the literature and ask those who used the scale for research to pay for a retroactive license which may cost thousands or tens of thousands of dollars, and to add references to their work . This isThe Committee on Publication Ethics (COPE) has recently discussed the ethics of this type of behavior by copyright holders of scales (“holding authors to ransom in this way”) and recommends to emphasize “the fact that this is not good for the advancement of scientific knowledge or in the public interest” . As open


Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level. Controllably synthesizing nanocrystals2567Commercially available silicon nitride liquid cell TEM holders have provided the necessary resolution to see and understand a variety of interesting phenomena on the nanoscale91011121314151920Since the thickness of the encapsulating material is one aspect that negatively affects the spatial resolution of the liquid cell experiments, atomically thin, low-Z materials such as graphene would be ideal encapsulating materials222324252628in situ transformations can benefit from employing graphene liquid cell electron microscopy technique. This in situ method is especially valuable for non-equilibrium processes that require visualization during the transformation. One significant drawback of liquid cell TEM techniques is the generation of radiolysis species by the perturbative electron beam3130Figure 1), using an example experiment observing single particle etching of nanocrystals, and hopefully show that graphene liquid cell experiments are possible for almost any group with access to an electron microscope. The protocol will cover graphene coating of grids, liquid cell formation, TEM use for graphene liquid cell etching experiments, and image analysis techniques. Critical steps in making the liquid cells such as the size of the droplet encapsulated, careful consideration of liquid solution contents, and use of only direct transfer graphene will be covered with additional advice on how to avoid repeating the pitfalls of previous researchers. Graphene liquid cell TEM is an emerging technique for nanoscale research, and this article will enable new entrants to begin utilizing this technique.Researchers in chemical, nanomaterial, biological, and other fields desiring spatial resolution of 2 piece of premade graphene-on-copper  which fits around 6 to 8 TEM grids. NOTE: Using 3 - 5-layer graphene instead of single layer graphene encapsulates liquid pockets with higher success rates without losing resolution. Since graphene is an atomically thin, low-Z material, most resolution loss is from liquid thickness for graphene liquid cells.Cut out a roughly 2 cmPlace the graphene-on-copper piece in a glass Petri dish and fill with acetone. NOTE: Acetone is used because PMMA dissolves in acetone.Gently heat the acetone solution (~50 °C) for 5 min, swirling the solution periodically. NOTE: Make sure to watch the acetone and temperature to avoid a fire. This should be done in a fume hood.Remove the graphene-on-copper piece from the acetone wash with tweezers and replace the acetone with new, clean acetone. NOTE: Be careful not to scrape or otherwise damage the graphene surface with the tweezers.Repeat the washing process a total of 3 times.Let the graphene-on-copper air-dry thoroughly before going on to the next step.Clean the graphene using an acetone wash . NOTE: TTable of Materials) are able to properly bond to the graphene surface. Bumps and creases in the graphene-on-copper make it difficult to maintain good contact. Table of Materials) on the bottom glass slide. On top of the wipe, place the graphene-on-copper piece. Finally, place the second glass slide on top. NOTE: Place the graphene-on-copper piece with the graphene side up (touching glass slide) to prevent scratching from the tissue wipe. The folded tissue is used to gradually push out the wrinkles and prevent folding in new creases.Take two clean glass slides and place a folded wipe  down on the graphene with the amorphous carbon in contact with the graphene. NOTE: Be careful not to bend or deform TEM grids when picking them up with the tweezers. Bent TEM grids do not bind properly to the graphene. Picking the grids up by the edge of the grid prevents deformation of the grids. Here, gold TEM grids are used to avoid etching the grids during the step that removes the copper from the graphene-on-copper.Place the holey amorphous carbon support foil-TEM grids  in a second Petri dish. NOTE: The easiest method to transfer the grids involves using a glass slide to pick up the grids and then placing them down in the second Petri dish filled with water. Some grids will fall to the bottom of the Petri dish during the transfer process. This is usually a sign that the graphene on the grid is cracked or otherwise damaged.Remove the floating grids from the solution and place them on top of clean, deionized water ,3 solution in a solution of deionized water with 1.8 µL of HCl per mL water. NOTE: The FeCl3 is the etchant for this etching experiment. Other experiments may add different solutions depending on the experiment being performed.Make a 40 mM FeClMake gold nanorods and concentrate the nanorod sample after cleaning13 in HCl, and 10 µL of nanorods.Mix 0.15 mL of 0.01-0.1 mM Tris Buffer HCl, 0.1 mL of 40 mM FeClPrepare the solution to be encapsulated. NOTE: The solution is specific to the nanocrystal etching experiment. Place ~0.5 µL droplet of solution to be encapsulated on the non-cut graphene-coated TEM grid. Use a tweezers to hold the edge of the TEM grid down while placing the droplet so that the capillary forces do not pick up the TEM grid . NOTE: BQuickly and carefully place the graphene-coated TEM grid with the cut corner on top of the droplet; the goal is to have the second grid come to rest on top of the first grid with no liquid getting squeezed out . NOTE: HWait 5 min to let graphene liquid cell pockets form. NOTE: Some evaporation of the liquid may occur as the pockets are forming, but once a hermetic seal is formed, no additional liquid loss is likely. The relative concentrations of each species in solution should remain constant.Bring the sample to the TEM for imaging. NOTE: The amount of time set aside for sealing varies from researcher to researcher. For etching experiments, less time before bringing the liquid cell to the TEM is desirable to avoid pre-etching.Note:The operation of the Transmission Electron Microscope followed standard procedures found in the user manual. Every TEM will have different alignment procedures.Place the graphene liquid cell in a traditional TEM single tilt holder . NOTE: OLoad the TEM holder into the TEM column. NOTE: Since the graphene liquid cell contains such a small volume of liquid with no reservoir and has separate pockets, there is no need to rigorously check for leaks like silicon nitride liquid cell experiments. Even if a graphene liquid cell pocket burst, only a very small amount of liquid is released and thus would not crash the TEM vacuum system.-/Å2s). In the radiation chemistry community, this is known as the flux density, and dose rate is defined as the amount of energy absorbed per unit area per unit time. Since calculating the amount of energy absorbed by a sample is difficult for complex geometries found in liquid cells, and to maintain consistency with the TEM community, we choose to use dose rate to refer to electrons per unit area per unit time.Turn the TEM filament on at least 20 min prior to calibration to allow it to stabilize for reproducible dose rates; this waiting time may be different depending on the TEM system and electron gun type. NOTE: Election microscopists often use dose rate to refer to the number of electrons delivered per unit area per unit time , and image . Then remove the holder from the beam path and calibrate electron beam dose rate. -/Å2s). NOTE: Keeping the dose rate low prevents the nanoparticles from etching while searching for nanoparticles.Begin searching for nanoparticles in liquid pockets while keeping the dose rate low  to set the condenser lens current for the desired dose rate . NOTE: ABegin collecting a time series of TEM images with metadata of dose rate and time stamps embedded in the image file.After the particle has finished etching, spread the beam and begin looking for other nanoparticles in the liquid pockets.When a sufficient amount of nanoparticle etching videos have been collected, remove the TEM holder from the TEM following standard TEM procedures. Take the graphene liquid cell out of TEM holder. NOTE: A typical imaging session lasts around 2-3 h with approximately 30 videos taken. The number of videos with usable data depends on the quality of the pockets and type of etching experiment.Note: Since TEM videos are 2-dimensional projections of 3-dimensional shapes, careful image analysis needs to be done to extract etching rates or shape changes.Table of Materials).Convert the native DM3 video files to an avi format using ImageJ and import the avi videos into computational software  can be extracted and evaluated further . One ind. Schematic of graphene liquid cell TEM technique. (A) To assemble a graphene liquid cell, a droplet of solution is placed on a graphene-coated holey carbon TEM grid. A second graphene-coated grid is placed on top of the droplet to form a pocket. Note that this image is not to scale and the liquid droplet is about 33% too large. (B) Zoomed-in schematic of a liquid pocket during TEM imaging of gold nanorods. This cartoon is also not to scale. Please click here to view a larger version of this figure.. Process for making graphene coated TEM grids (A) Washing the graphene-on-copper piece in warm acetone (B) Removing macroscopic wrinkles by flattening graphene-on-copper between two glass slides. A tissue is placed beneath the graphene-on-copper piece so as to not fold in new wrinkles. (C) Placing amorphous holey carbon TEM grids on graphene-on-copper with amorphous carbon side of TEM grids touching the graphene. (D) Floating copper/graphene/TEM grids on sodium persulfate etchant. This removes the copper from the grids. (E) Graphene coated TEM grids after etching off copper. The solution is blue and there is no copper left on the graphene-coated grids. For size reference, the diameter of the glass Petri dish is approximately 6 cm and the glass slide is 7.5 cm by 2.5 cm. Please click here to view a larger version of this figure.. Process for making graphene liquid cells (A) Two graphene-coated TEM grids prepared on a glass slide with an edge cut off one of them. The surgical scalpel used to cut the grid is on the top right of the image. (B) Droplet of encapsulating solution on a graphene coated grid. The droplet on the top grid is the right size and has made a nice bead on the graphene. The droplet on the bottom grid has bled through the graphene, possibly due to a crack in the graphene. (C) Second graphene-coated grid placed on top of first grid with droplet of solution. This graphene liquid cell is now ready to load into a TEM. For size reference, the glass slide is 7.5 cm by 2.5 cm. Please click here to view a larger version of this figure.. Loading graphene liquid cell into standard single tilt TEM holder. The graphene liquid cell fits in a standard single-tilt TEM holder in the same way a normal TEM grid fits in the holder. For size reference, the TEM grid has a diameter of 3 mm. Please click here to view a larger version of this figure.. TEM beam control. (A) Condensed electron beam for dose rate calibration viewed using the fluorescent screen. (B) Expanded electron beam for dose rate calibration viewed using fluorescent screen. Intensity decreases as the electrons per area per time decrease which is why the electron beam is very faint. (C) Calibration curve relating the electron beam dose rate to the condenser lens current. This calibration curve is used for controlling the beam dose rate during imaging. (D) Parameters used when collecting TEM videos of nanoparticles in graphene liquid cells. Specific values used for each parameter may change depending on the material being imaged and the resolution needed. Please click here to view a larger version of this figure.. Gold nanorod etching in a graphene liquid cell pocket. Frames of a representative TEM video of a gold nanorod etching under dose rate of 800 e-/Å2s. After an initial period of no etching, the nanorod etches at a constant rate. Please click here to view a larger version of this figure..Method for analyzing frames of video (A) Outlining the nanorod using thresholding in image analysis software.  This separates the nanoparticle from the background and provides a shape for quantitative analysis. (B) Determining the major and minor axes of the nanorod. (C) Extracting each half of the 2-D outline cut along the major axis. Using these outlines, reconstruct the 3-D shape by rotating the outline around the x-axis. Please click here to view a larger version of this figure.Graphene liquid cell electron microscopy can provide mechanistic information about nanocrystal growth and etching with high spatial resolution, but since making graphene liquid cells can be difficult and delicate, the technique requires attention to detail to extract usable data. Even after extensive practice making graphene liquid cells, only about a half to a quarter of made liquid cells successfully encapsulate the liquid solution. The critical step in forming liquid cells is placing the second grid on top of the droplet of liquid. Common errors include getting the tweezers stuck between the two grids, dropping the second grid too far off-center, and starting with a droplet that is too large. Since the assembly of graphene liquid cells is delicate and requires fine motor skills, it usually takes practice to successfully make the liquid pockets. Due to the expense of graphene-coated TEM grids, it is highly recommended that new graphene liquid cell users first practice the liquid cell making process on traditional copper, amorphous carbon TEM grids to save money.Determining the causes of failure for liquid cells can be challenging because a researcher may not know if each step has been successful until imaging the sample at the end, and mistakes, like scratching the graphene, can go unnoticed. The easiest error to identify is an improper assembly because the researcher will immediately see liquid leaking out of the graphene liquid cell. Problems with making the graphene on copper grids, like cracking of the graphene, can be tougher to pinpoint. The quality of the graphene can be checked both before and after coating the TEM grids using Raman spectroscopy, but the graphene usually is unusable after this testing. Additionally, it is important to use direct transfer graphene because the two faces of graphene being put together need to be clean to properly form a seal through Van der Waals forces. Making graphene-coated grids through polymer transfer methods may leave polymer residue on the side of the graphene that is expected to bond together. If the correct procedure is followed using the correct TEM grids, lack of success with the graphene liquid cell is usually due to mishandling of the graphene and grids during assembly and fabrication.Graphene liquid cell TEM advances existing liquid cell TEM techniques by using a much thinner encapsulation material that can used in any traditional TEM holder, making high resolution and facet trajectory tracking experiments much easier. With the resolution of commercial silicon nitride membrane liquid cells, much of the facet and kinetic information that can be attained by etching nanocrystals in the graphene liquid cell would be lost. Graphene liquid cell TEM experiments can also be performed on existing single tilt TEM holders negating the need for expensive new specialized holders. Further, the graphene liquid cell can be put in any holder that accepts standard TEM grid samples allowing for liquid cell experiments to be performed in advanced holders  where silicon nitride liquid cells have not been designed. In addition, graphene liquid cells do not pose the risk of crashing the vacuum of the TEM column if the pockets rupture like other liquid cell TEM techniques. Although the graphene liquid cell is not a ubiquitous technique in nanocrystal fields yet, its ease of use and spatial resolution will make it much more widely used in the future.3, Tris Buffer, and even grapheneex situ reactions in a flask.Even with its many advantages, graphene liquid cell TEM does have limitations on the types of experiments that can be performed. Some liquid does evaporate as pockets form, so it is difficult to exactly determine the concentration of species in solution, even without considering electron beam effects. Graphene liquid cells also have random sizes, heights, and distributions of small pockets, so silicon nitride flow cells have the advantage of more quantifiable pre-beam concentrations and large, uniform liquid layers. As described in this work, only preloaded samples can be viewed using graphene liquid cell in the TEM, so it is not possible to flow in other solutions to trigger chemical reactions. The radiolysis species generated by the interaction of the electron beam with the liquid solution are the only trigger that can be used to start a reaction. Although not demonstrated yet, thermally initiated processes could be triggered in graphene liquid cells using standard heating holders. Electron beam-induced radiolysis effects are still not fully understood and can be difficult to control. Researchers have developed kinetic models to determine the contents of liquid cell pockets after beam interaction31ex situ nanocrystal synthesis and etching experiments will be critical in corroborating the mechanisms seen in liquid cell TEM experiments. Also, researchers have begun working on adding flow capabilities to graphene liquid cell TEMFuture graphene liquid cell experiments will help alleviate some of these concerns while also using new TEM advances to further probe the underlying mysteries of nanocrystals. Correlative The authors have nothing to disclose.