It was the prevalent cause of the significant decrease in the reverse current and short-circuit current. No photovoltaic effect dependence on the graphene roughness and work function could be observed.Graphene was synthesized directly on Si(100) substrates by microwave plasma-enhanced chemical vapor deposition (MW-PECVD). The effects of the graphene structure on the electrical and photovoltaic properties of graphene/n-Si(100) were studied. The samples were investigated using Raman spectroscopy, atomic force microscopy, and by measuring current–voltage (I-V) graphs. The temperature of the hydrogen plasma annealing prior to graphene synthesis was an essential parameter regarding the graphene/Si contact I-V characteristics and photovoltaic parameters. Graphene n-type self-doping was found to occur due to the native SiO In most studies, graphene is synthesized by chemical vapor deposition (CVD) on copper foil and then transferred to the silicon substrate ,13,14,15The abovementioned problems can be solved using graphene directly grown on silicon by plasma-enhanced chemical vapor deposition , althougTherefore, the present study investigates the effects of the directly synthesized graphene structure on current–voltage characteristics and photovoltaic properties of the graphene/n-Si photovoltaic devices. Various synthesis conditions were used to grow graphene samples of different structures and surface morphologies. Only a small influence or no influence of the graphene thickness, defect density, surface morphology, and work function was found. The impact of substrate-induced self-doping and silicon surface pretreatment on the graphene/n-Si device’s current-voltage and photovoltaics characteristics was revealed.Samples were produced using a microwave PECVD system Cyrannus (Innovative Plasma Systems (Iplas) GmbH, Troisdorf, Germany). Monocrystalline, double-side polished, n-type Si(100) , with a resistivity of 1–10 Ω·cm, was used as a substrate. A precursor gas mixture of hydrogen and methane was used for graphene synthesis. Before the growth of graphene, hydrogen plasma was ignited, and methane gas was only introduced when the target temperature was reached. In some cases, the silicon substrates were plasma pre-annealed at higher temperatures than the temperature of the subsequent graphene synthesis. A special enclosure was used to protect from direct plasma that results in high etching rates of the sample . Synthes4OH + H2O2 + H2O), impurity removal (1:50 solution of HF + H2O), and RCA 2 (1:1:6 solution of HCl + H2O2 + H2O) treatments [2 [After graphene synthesis was carried out, diode fabrication began with Al back contact formation (on the uncoated Si side) using e-beam technology. The DMF + acetone boiling and RCA 1  being at 1620 cm−1. The Lorentzian function was used for the best peak fit, considering Merlen et al. [D/IG ratio was used to reveal the defectiveness of our produced samples [2D/IG ratio contributed to the graphene thickness evaluation [Thickness and defect characterization was carried out via Raman scattering spectroscopy using a Raman spectrometer, InVia . The measurement was done just after the graphene synthesis and before the graphene/Si(100) diode fabrication. We acquired Raman spectra at several different places on each sample, considering possible differences in the graphene structure across the specimen. The beam power was set to 1.5 mW, and the excitation wavelength was 532 nm. Several peaks were analyzed for in-depth characterization and defect estimation . The G peak was separated into two components, with the actual G peak being at 1600 cmn et al.  who made samples . In contaluation   was employed to detect any structural peculiarities of the graphene surface. The surface morphology was investigated at room temperature and ambient air conditions using a NanoWizard III atomic force microscope . The measurements were done in tapping mode. The silicon probes  with a thin layer (25 ± 5 nm) of Pt/Ir coating on both re-ex and tip sides of the probes were used. The probe parameters were as follows: spring constant 2.7 N/m; 60 kHz frequency; 30 nm tip ROC; pyramidal shape. Images of 2 µm × 2 µm size were acquired from the measured data using JPKSPM Data Processing software . Kelvin probe measurements were carried out using the same instrumental setup to evaluate graphene work function.R(0.3 V)), forward current vs. reverse current at ±0.1V (IR(0.1 V)/IF(0.1 V)), forward current vs. reverse current at ±0.3 V (IR(0.3 V)/IF(0.3 V))). The photovoltaic parameters (short-circuit current (ISC) and open-circuit voltage (UOC)) were derived from current–voltage characteristics measured under illumination. The I-V characteristic’s dependence on temperature was measured using a similar setup to the photovoltaic parameter measurements. The same Keithley 6487 picoampere meter/voltage source was employed, with thermal operational conditions being changed by a custom-made Peltier element configuration. The temperature varied from −20 to 40 °C. Each measurement was made after the temperature value had settled down.The current-voltage (I-V) characteristics were measured using a Keithley 6487 picoampere meter/voltage source. The measurements were done at several points on the sample to evaluate the possible dispersion of the characteristics. Characteristics were investigated in three different regimes to study the photovoltaic properties of the fabricated devices. These were dark mode (sample was not illuminated), UV mode (when the sample was illuminated by 406 nm wavelength light-emitting diode (LED)), and IR mode (when the sample was illuminated by 800 nm wavelength light-emitting diode). In all instances, the voltage range was from −2 to +2 V. To ensure the same optical power (5.2 mW) between different measurement modes, currents supplied to the LEDs were selected accordingly. The measurements were done at several different places on the samples to evaluate the dispersion of the results. Diode behavior was studied by examining the I-V characteristic parameters in the dark  characteristics of the produced photodiodes can be seen in 2D/IG ratio values indicated the presence of few-layer graphene. The thickness of the one graphene layer was ~0.4 nm [The graphene AFM images and topography parameters were studied to supplement our Raman spectroscopy findings , Table 2 ~0.4 nm ,58. Thus ~0.4 nm . Sample In most cases, graphene Raman scattering spectra were investigated for defect-free or few-defect graphene (no Raman D peak). However, directly synthesized graphene usually contains a significant number of defects . This ca2D/IG ratio with ID/IG ratio was found  [2D decrease with the I2D/IG ratio increase in 2D values can be found for graphene samples of the same thickness. Thus, FWHM2D depends on some other factors. The Pos2D, in our case, was upshifted with the I2D/IG ratio  . One canIG ratio c. In con samples ,63,64,65G is related to the ID/IG ratio of defective graphene [G dependence on ID/IG ratio was found in our case  pre-annealed at 900 °C. For the samples synthesized on the silicon pre-annealed at 700 °C temperature, the tendency of the FWHM2D to decrease with increased FWHMG was found  characteristics of the graphene/Si(100) heterojunctions and graphene structure were studied. The initial surface preparation significantly influences the Schottky and ohmic contact I-V characteristics ,79,80,81R(0.3 V), IR(0.1 V)/IF(0.1 V), IR(0.3 V)/IF(0.3 V)) on the main Raman peak ratios was found , when the Si(100) substrate was hydrogen plasma pre-annealed at 700 °C /IF(0.3 V) ratio, it is seen that values of the reverse current and IR(0.3 V)/IF(0.3 V) of the samples grown after annealing in 700 °C gradually decrease when FWHM2D decreases  decrease (IR(0.3V)/IF(0.3 V) increase) with increasing surface roughness can be observed, although the plot’s strange “branching out” is seen. Due to this, it is impossible to conclude whether this magnitude of roughness impacts device performance.Inclusions of the non-planar graphene, such as wrinkles, can significantly influence charge transport properties ,89. HoweTypical I-V curves of produced photovoltaic devices under illumination can be seen in SC and UOC were investigated concerning Raman parameters   samples, Irameters . Figure creases) a,b. The function . In the function ,30. In ofunction ,27,28,38d FWHM2D c when sarelation d, with sSC correlation with Pos2D and PosG   , and datrameters . It shouain size  after anoughness . The mosterlayer . At the terlayer .R(0.3V) was analyzed. An increase in the ISC following a rise in IR(0.3V) can be seen at least in two groups of samples (SC can be seen when IR(0.1 V)/IF(0.1 V) increases (R(0.3 V)/IF(0.3 V) is taken into account  plot was employed to show that UOC tends to increase with a short-circuit and reverse current ratio increase, although it branches out when the ratio reaches a value of ~1 (SC/IR(0.3V), which tends to be minimal (<0.183 V) when annealing was carried out at 900 °C, different illumination regimes show that IR irradiation yields higher UOC and ISC. As in many discussed relations, samples that were annealed at 700 °C also had the most significant spread of ISC/IR(0.3 V), with values situated in a range of 0.336–3.375. UOC in samples that had been annealed at 800 °C before graphene growth tended to increase with ISC/IR(0.3V), although moderate dispersion of values was observed.The photovoltaic parameter’s relation with I samples a. Curve ncreases b, with o account c, the dispersive . The UOCue of ~1 d. While 2 surface [The electron transfer from the n-Si(100) to the graphene should result in decreased graphene/Si contact barrier and, hence, increased reverse current ,96. In o surface ,98.2 interface results in a dipole formation, and charge redistribution imposes n doping in the graphene [2 interface [2 can also be n-type doped [The charge exchange at the graphene/SiOgraphene , althougnterface . The grape doped .2D  with graphene dopant concentration is significantly suppressed by increasing the graphene layer number [2 to the graphene and subsequent charge redistribution within the graphene [Graphene work-function shift with doping significantly decreased when the graphene layer number increased . The mair number . This isgraphene . The chagraphene . Numerougraphene .2D should downshift and the FWHM2D should increase with an increase in doping and, hence, increased native oxide surface positive charge density. Thus, the reverse current and IR/IF ratios decrease with the graphene substrate-induced self-doping seen in SC increase with IR/IF ratio and with IR can be explained by the flow of the tunneling photocurrent similarly to the quantum dot and superlattice solar cells where the tunneling effect was used to raise the short-circuit current [The analysis of samples’ I-V characteristics measured at different temperatures revealed the flow of the tunneling and thermionic emission currents . At lowe current ,106. It  current . In addi current ,108.It was revealed that the silicon substrate hydrogen plasma pre-annealing was a very important technological parameter regarding the photovoltaic parameters. An increase in the annealing temperature to 900 °C resulted in suppression of the photovoltaic effect. The AFM study revealed no clear morphology and phase changes due to the silicon surface treatment by hydrogen plasma at both 700 and 900 °C . Si(100)OC did not depend on the ISC and increased with ISC/IR ratio for ratios up to 1–1.5  photovoltaic devices properties were revealed.2 interlayer to the graphene was the main reason for the notable reverse current (IR) and short-circuit current (ISC) decrease. Due to the tunneling photocurrent flow, the UOC increased with a short-circuit current, and the reverse current ratio increased. Significant hydrogen plasma pre-treatment effects on the current-voltage characteristics and photovoltaic parameters were observed, revealing the importance of the graphene/silicon interface.The graphene n-type self-doping due to the charge transfer from the native SiOIt was found that the graphene samples’ work functions were nearly the same (4.820–4.826 eV), even though the graphene structure and properties of the photovoltaic devices varied dramatically. No effects of graphene surface morphology and defects on the electrical and photovoltaic characteristics were found. The short-circuit current and open-circuit voltage only slightly increased with graphene layer number.Thus, directly synthesized graphene/n-Si solar cells can be improved by preventing n-type self-doping and optimizing the graphene/silicon interface, whereas graphene defects, layer number, work function, and morphology are much less critical.


N-halosuccinimides as the halogen source under neat grinding or liquid-assisted grinding conditions in a ball mill has been described. Depending on the azobenzene substrate used, halogenation of the C–H bonds occurs in the absence or only in the presence of PdII catalysts. Insight into the reaction dynamics and characterization of the products was achieved by in situ Raman and ex situ NMR spectroscopy and PXRD analysis. A strong influence of the different 4,4’-substituents of azobenzene on the halogenation time and mechanism was found.The direct and selective mechanochemical halogenation of C–H bonds in unsymmetrically substituted azobenzenes using  Electrophilic aromatic substitution –3 and liThe need for green and sustainable chemistry  has led 2]2 in combination with AgSbF6 as catalyst and N-halosuccinimide  as halogen source [N-bromosuccinimide (NBS) and MCM-41-SO3H catalyst and no liquid additives [ortho-halogenation of acetanilide with NXS  using Pd(OAc)2 as precatalyst in the presence of p-toluenesulfonic acid (TsOH) as an additive under solvent-free conditions [In 2015, Bolm and Hernandez reported the halogenation of 2-phenylpyridine in a ball mill using [Cp*RhCln source . Two yeadditives . In 2018nditions . Recentlnditions .II-catalyzed bromination of unsubstituted azobenzene (L1) by N-bromosuccinimide (NBS) under neat grinding (NG) and liquid-assisted grinding (LAG) conditions in a ball mill [II species, cyclopalladated intermediates, and products 2 as precatalyst in the presence of TsOH and MeCN as solid and liquid additives, respectively, led to the ortho-halogenated products relative to the azo group of the azobenzenes. In situ Raman monitoring of these reactions confirmed that the most favorable reaction pathway is via the monomeric cyclopalladated intermediate, as in the halogenation reaction of unsubstituted L1 [L1 and its para-halogenated derivatives were unsuccessful without the PdII catalyst and TsOH, the halogenation of azobenzenes with the strong electron-donating substituents in the para position occurred in the absence of the added PdII catalyst and additives, in the ortho position to the substituent, which is typical for the products of electrophilic aromatic substitution.Here we present the mechanochemical selective halogenation of unsymmetrically substituted azobenzenes by NXS . The liquid-assisted grinding of tuted L1 . While tII catalyst was developed for the selective imidation of azobenzenes containing a dimethylamino group as substituent in the para position to the azo group.In addition, an additive- and solvent-free protocol without the added PdL1 [Inspired by our findings on the mechanochemical halogenation of L1  and the L1 , we inveL1 [L2), 4-aminoazobenzene (L3), 4-dimethylaminoazobenzene (L4), and 4-(dimethylamino)-4'-nitroazobenzene (L5)) with NXS (X = Cl and Br) occurred in the absence of the added PdII catalyst and additives. These reactions in most cases produced electrophilic substitution products that were halogenated in the ortho position(s) relative to the electron-donating substituent  relative to the electron-donating substituent, which may be attributed to competition between PdII-catalyzed reactions and uncatalyzed electrophilic substitution.In contrast to the reactions of L1 , the halstituent , as confstituent  and NMR stituent . All expII catalyst [Our results are consistent with those reported by Sanford's group for the halogenation of various substrates by NXS with and without Pdcatalyst . Most ofcatalyst , resulteL3 and L4 with NCS produced the monochlorinated products L3Cl-I and L4Cl-I as single isomers within one hour (L5 with NCS resulted in a mixture of mono- and dichlorinated regioisomers (L5Cl-I and L5Cl-II) , the chlorination of L5 proceeded much more slowly (Neat grinding of L5Cl-II) , entry 4L2 (L2 with NBS gave the monobrominated product L2Br-I in 96% yield after 15 hours of milling (L2 confirmed its conversion to the product L2Br-I (L2Br-I was accompanied by the intensity decrease of L2ν(N=N) and ν(C–N) bands in the range 1400–1450 and 1080–1200 cm−1, respectively. Compounds L2 and L2Br-I were identified in the reaction mixture by the Raman spectra of isolated L2 and L2Br-I  at the para position of the second phenyl ring in L5 significantly slowed the halogenation reaction and impaired the reactivity of the azobenzene. This result suggests that NO2 has a long-range effect that spreads through the azobenzene skeleton. Compared to the bromination of substrates L3–5 containing amino substituents, the analogous reaction of L2 is slower because the methoxy substituent has weaker donor strength than amino substituents [The reactivity trend of electron-rich azobenzenes tituents .II catalysts for the halogenation of Csp2–H and imidation of Csp3–H bonds of azobenzenes with electron-donating substituents by electrophilic activation with NXS.The protocols described above provide a solvent- and additive-free approach without added PdL1 [para position relative to the azo group: 4-chloroazobenzene (L6), 4-bromoazobenzene (L7), and 4-iodoazobenzene (L8)  .Ln/NXS/TsOH 1:1.2:0.5 equiv, 5 mol % Pd(OAc)2 precatalyst, and 15 µL MeCN as liquid additive. Under these conditions, the reactions of L6–8 with NBS resulted in moderate to good yields of monobrominated products LnBr-IV 2(MeCN)2 was identified as the active catalyst, formed in situ, in the bromination reaction of L1 [L6–8 were carried out using Pd(OTs)2(MeCN)2 as the catalyst instead of Pd(OAc)2. As expected, the yields of LnBr-IV products were comparable to those obtained in the reactions with the Pd(OAc)2 precatalyst.The bromination of on of L1 , the anaII-catalyzed iodination of L6–8 was conducted with N-iodosuccinimide (NIS) as the iodine source. The reaction time for the iodination of L6 was the same as for the analogous bromination reaction  gave no chlorinated product, which was also observed in the reaction of L1 with NCS  data  data , are simL6–8 in the presence of 30 mol % PdII catalyst revealed a new band around 1380 cm−1 (ν(N=N) bands of the In-I intermediates, confirming that the bromination of L6–8 proceeds via monopalladated In-I intermediates as in the reactions of L1 2 with L6–8 and TsOH were performed using 25 µL of MeCN as a liquid additive in a molar ratio of 1:1:1 (Ln/Pd(OAc)2/TsOH). In situ Raman monitoring of C–H bond activation was possible for L6 and L7, while in the case of L8, fluorescence prevented a more detailed insight into this reaction. The monitoring results confirmed the complete conversion of azobenzenes L6 and L7 to their monopalladated products after about one hour of milling, as well as a reaction course similar to that of the analogous reaction of L1 [To gain insight into the dynamics of the formation of cyclopalladated intermediates on of L1  2 as precatalyst, as confirmed by NMR spectroscopy.The isolated cyclopalladated intermediates L1 [L6–8 begins with the formation of the catalytically active PdII species, Pd(OTs)2(MeCN)2, from Pd(OAc)2, TsOH, and MeCN. It is followed by the formation of monomeric cyclopalladated intermediates In-I, at which halogenation occurs. Based on the similarities between the halogenation of L6–8 and the bromination of L1 [I1-I are also possible for the halogenation of I6-I, I7-I, and I8-I [The results of in situ and ex situ spectroscopic monitoring along with the structural characterization of the intermediates have shown that the mechanism of the halogenation of azobenzenes with electron-accepting substituents is consistent with the proposed mechanistic schemes for the bromination of the unsubstituted azobenzene L1 . Thus, ton of L1 , we assuand I8-I .L1 and its para-halogenated derivatives L6–8 toward NBS or NIS. The competition experiments showed that the azobenzenes with electron-withdrawing substituents are much less reactive to halogenation than L1. The reactivity of azobenzenes in the case of NBS decreases in this order: L1 >> L6 > L7 ≈ L8  as the halogen source.II catalyst. These transformations, which take place via electrophilic aromatic substitution, resulted in products halogenated in the ortho position to the electron-donating groups. The reactions of azobenzenes containing a dimethylamino group as substituent with NIS led to imidation products. A different reactivity of the dimethylamino group compared to the other substituents was also observed in these reactions.Halogenation of azobenzenes with strong electron-donating groups was carried out without an added Pdpara-halogenated azobenzenes required the presence of the PdII catalyst and TsOH as additive. In situ spectroscopic monitoring of these reactions revealed that the PdII-catalyzed halogenation proceeds via monomeric cyclopalladated intermediates formed by activation of the C–H bond in azobenzenes with the in situ generated Pd(OTs)2(MeCN)2 catalyst. The described results indicate a strong dependence of the halogenation outcome of C–H bonds in 4,4’-functionalized azobenzenes on the nature of their substituents.On the other hand, the halogenation of File 1Detailed experimental procedures, complete characterization data for new compounds, X-ray structures of compounds, and the results of in situ Raman monitoring.File 2X-ray crystallographic data.


Unique features of the Boudouard reaction coupled with CO‐driven catalyst engineering ensure not only suppression of the second layer growth but also provide a simple and reliable technique for surface cleaning. Aside from being a novel carbon source, carbon monoxide ensures peculiar modification of catalyst and in general opens avenues for breakthrough graphene‐catalyst composite production.Following the game‐changing high‐pressure CO (HiPco) process that established the first facile route toward large‐scale production of single‐walled carbon nanotubes, CO synthesis of cm‐sized graphene crystals of ultra‐high purity grown during tens of minutes is proposed. The Boudouard reaction serves for the first time to produce individual monolayer structures on the surface of a metal catalyst, thereby providing a chemical vapor deposition technique free from molecular and atomic hydrogen as well as vacuum conditions. This approach facilitates inhibition of the graphene nucleation from the CO/CO Unique features of Boudouard reaction facilitate high‐purity, wafer‐scale single‐crystal graphene on metal catalysts. Nevertheless, the method for the state‐of‐the‐art graphene, i.e., “natural” exfoliation, is strictly limited in terms of the sample size and geometry. Therefore, a large‐scale graphene synthesis is a challenge to bring lab‐scale prototypes to a wide range of applications. One of the most advanced approaches to graphene preparation is chemical vapor deposition (CVD). This method comprises catalytic decomposition of gaseous carbon sources  on metallic substrates. The CVD synthesis of single‐crystal monolayer graphene is an unprecedented challenge for catalysis: the cycle of carbon precipitation should be terminated after the first graphitic layer, and carbon‐, hydrogen‐, and oxygen‐based intermediates should control the nucleation of new seeds.Graphene has become a milestone discovery in contemporary solid‐state physics and materials science.1 Prop4 and C2H4 on the surface of metallic  and semiconducting (Ge) substrates. One of the strategies to obtain single‐crystal graphene is the alignment of the graphene nuclei that prevents defect formations caused by grain boundaries. This method demands a single‐crystalline metallic foil, which requires additional technological steps. Another strategy relies on the inhibition of graphene nucleus density so that each seed grows up into a large graphene crystal. Such an approach requires a balance between nucleation control and the growth rate of a single grain. In this case, the pressure within the reactor plays a dominant role to control the nucleation process. Remarkable progress in obtaining large graphene samples with outstanding electronic properties and superior crystallinity was achieved using molten and resolidified substrates. However, according to the recent review, rapid synthesis technique facilitating single grain growth is still a challenge.During the past decade, wafer‐scale single‐crystal graphene synthesis was achieved using hydrocarbons such as CH and “graphene‐like structures” were recently observed, CO has never been used for the CVD synthesis of monolayer graphene on a metallic substrate. Carbon monoxide is truly a unique carbon source. Unlike the conventional methods based on pyrolysis of hydrocarbons requiring hydrogen to control carbon intermediates, the unique thermodynamics of the Boudouard reaction, 2CO ⇆ C + CO2, under high temperatures favors CO, not the carbon precipitation. The high stability of CO molecule restricts noncatalytic pyrolysis, and, thereby, formation of amorphous deposits or second graphitic layer. Moreover, carbon monoxide appears to have a peculiar interaction with the surface of transition metals, especially with copper.A carbon source with specific stability to prevent nucleation of multiple grains by both pyrolysis and surface decomposition may help to overcome the abovementioned problems. Surprisingly, one of the simplest carbon sources, carbon monoxide, has acquired little attention. Though the first multilayer graphitic structures were reported as early as in the 1950s17 and and single‐walled carbon nanotubes (SWCNTs) both on lab‐ and industrial scales. Indeed, HiPco (high‐pressure CO) was one of the very first technologies to deliver a high yield SWCNT synthesis, while the combination of the aerosol CVD method with CO provides state‐of‐the‐art transparent conducting films. It should be mentioned that SWCNT growth based on the Boudouard reaction allows nucleation control by the addition of CO2. At the same time, CO2 is also a superior pre‐treatment “cleaning” tool during the graphene synthesis. However, the utilization of CO2 with hydrocarbons to control nucleation and growth processes during graphene synthesis is limited. In contrast, the Boudouard reaction allows the implementation of both nucleation control and perfect cleaning by CO2. Finally, the CO‐based synthesis route is completely hydrogen‐free, favorable in atmospheric or high‐pressure CVD implementations.Taking into account all benefits of CO utilization, the absence of the method for monolayer graphene synthesis is even more interesting, since the well‐studied Boudouard reaction has been actively used for the synthesis of graphite26 and2Figure 2 rich atmosphere at 1135 °C . We have constructed a horizontal tubular hot‐wall reactor equipped with a fast load‐in∖out ceramic manipulator Figure 1a–d. AftC Figure , a CO/COC Figure . After aC Figure . The sysFigureI2D/IG greater than 2 over the entire area of the sample. Dendritic boundaries are likely formed due to high growth rates, while the produced domains still preserve hexagonal shape that suggests a single‐crystal nature of the layer. X‐ray photoelectron spectroscopy (XPS) data collected from the graphene‐coated copper surface reveal the outstanding purity of both the graphene and the copper substrate  in Figure LMM lines  measurements performed on the same sample. These data reveal classical electronic landscape and graphene Dirac cone with a common electron doping shift. It is worth noting that a Shockley surface state can be clearly observed near the Fermi level (0.285 eV). This electronic state is another evidence of pure reduced copper, which surface is protected by a graphene layer. Such an observation is rather unusual for a CVD graphene on a copper catalyst. Note that this state, intrinsic to Cu (111) surface, has never been observed for as‐grown samples when non‐single‐crystal substrates were used.Catalytic disproportionation of carbon monoxide leads to the formation of graphene grains of up to several mm in size Figure . These ae Figure . Obtainel Figure , indicatFigure  Such an unprecedented alignment facilitates the formation of single‐crystal grains of graphene, which is also confirmed by LEED obtained from individual graphene crystals of ≈4 mm in size  plane Figure  alone spFigure 24 Suce Figure . The twoÅ Figure  and reve] Figure . For mor copper pellet on top of a molybdenum foil (acting as a wetting layer by heating to 1135 °C and cooling to 1085 °C) and added a procedure of CO2 annealing during the melting phase for additional copper cleaning. It should be stressed that we observed no traces of carbon species on Cu after CO2 annealing with XPS and Raman spectroscopy. Thereby, the rate of graphene nucleation was reduced by recrystallization of copper by several orders of magnitude reaching 102–103 cm−2s−1 while no impurities leading to multilayer graphene were observed as well.A single crystal graphene synthesis is a result of a thorough kinetic study for the mechanisms of grain nucleation and growth. When working with copper foils, we have observed the graphene nucleation to be extremely sensitive to the surface roughness or impurities; we even observed the formation of the multilayer graphene  and nuclei surface density (N)  graphene synthesis terminates. The dependence of the growth rate on the average grain perimeter , diffusion (Ed = 1 eV), catalytic decomposition of CO molecule (Edec = 2–4 eV), and attachment of the carbon atom to the growing front of the nucleus (Eatt = 2 eV). The last process is more likely to contribute the most to the limiting process.The temperature dependences of the growth rate WG and nuc2 removal shows the highest barrier in the sequence  surface using density functional theory (DFT) methods  allows to significantly reduce the time (down to 10 min) required for millimeter size crystals , a smooth balance between CO2 concentration and total pressure value is the key for facile synthesis of single‐crystal graphene.Small amounts of COreaction.29 As e Figure  while ths Figure . Thus, sFigure dθx/dt):θx, θCO, θCO2, θ—surface coverages for carbon nuclei, CO, CO2, and free surface, respectively; W2+—the rate for decomposition of an adsorbed CO, kdiff, kdes—kinetic constants for diffusion and desorption of carbon intermediates; β—arbitrary constant for the diffusion of carbon intermediates and carbon dimers and nuclei, which can be estimated experimentally; k7 + , k7 − —kinetic constants for CO2 surface assembly from CO and O and decomposition, respectively, k8—kinetic constants for CO2 etching of carbon intermediates.To reveal the graphene nucleation mechanism for the process based on the Boudouard reaction, we developed a model following Donohoe and Robins formalism.55FigAs for the experiments on nucleation temperature dependence, the carbon dioxide concentration was zero, we can omit corresponding terms to describe two cases denoted as “high” and “low” temperature by Donohoe and Robins.55k we did not observe in experiment two distinct regimes for nucleation, only “high temperature one.” We attribute this to the high stability of CO molecule that prevents decomposition at conditions where diffusion controls the nucleation. Moreover, depending on CO2 concentration, we observe two distinct regimes meeting the experimental findings: CO2‐independent  does not lead to the complete termination of the growth, but rather to a self‐etching of individual crystals. Even more, the critical concentration of CO2 . Above 500 cm−1 the spectra practically coincide, while the difference below ≈500 cm−1 is due to free charge carriers in the graphene layer  = σDC × [1 − iωτ]−1, where σDC = neμ = ne2/ɣme* is the direct current conductivity, n is charge carrier concentration, ɣ = 1/(2πτ) is charge carriers scattering frequency (inverse scattering time τ), me* is the electron effective mass, and μ is the electron mobility. The calculated parameters of the Drude‐model fit for the samples grown with different CO2 concentrations are shown in Figure 2 concentration (the red curve), as one would expect, since adding CO2 promotes the growth of greater graphene crystals. At the same time, the conductivity value decreases (the black curve), which suggests a decreasing charge carrier concentration. The obtained UV‐vis‐NIR spectra of the samples are consistent with the single‐layer nature of graphene: indeed, the π plasmon is located at ≈270 nm, and the transmittance is close to 97.7%  × 104 cm2V−1s−1, likely indicating that the graphene transfer on PF affected its intrinsic properties. Subsequent transfer to Si/SiO2 substrate most likely caused more cracks and further decrease in the mobility. Clearly observable Dirac cone with vf = 106 m s−1 also indicates high quality of as‐grown graphene electronic properties.Next, we investigated the charge carrier transport in the transferred graphene by means of contactless Fourier‐transform far‐infrared (FIR) and time‐domain terahertz (THz) spectroscopy and measurements of the field‐effect transistors (FETs) based on graphene with Au/Cr side‐contacts in a Hall‐bar geometry. In the latter devices, the graphene single crystal is encapsulated in parylene‐N, and the heavily doped Si substrate is used as a back gate. To obtain electrodynamic properties of synthesized graphene, we have measured transmission coefficient spectra of graphene supported by a parafilm (PF) substrate and that of a substrate alone  is reduced. Furthermore, the proposed procedure shows significant reduction in duration of heating and cooling procedures to a few tens of minutes. The catalyst preparation step, which might take 7–18 h, is reduced to 15 min. At the same time, high and competitive quality of the produced graphene can be easily achieved.From the engineering point of view, the utilization of CO simplifies the synthesis procedure: there is no need in vacuum12 or 2 allows synthesis of patterned graphene full of holes with perfect boundaries. The presented approach also allows further investigation of transition metal's electronic surface states protected by the graphene layer from degradation. Specific chemistry of various elements with carbon monoxide may allow formation of transfer‐free graphene, e.g. Ti + 2CO ⇆ TiO2 + 2C, TiCl4 + 2CO ⇆ TiO2 + 2C + 2Cl2 or Al2S3 + 3CO ⇆ Al2O3 + 3C + 3S which has been demonstrated for aluminum sulfide powder and can be extended to an atomic layer deposition or CVD films of aluminum sulfide.Future development of the proposed technique might include the design of one‐time‐fill operation under elevated pressure in the autoclave‐bomb of a cold‐wall reactor in order to reach extreme growth rates, which potentially can be upscaled to the wafer size graphene grown in a matter of several minutes. Aside from the well‐known applications of graphene in optoelectronic devices (assuming optimized transfer protocol), the reported novel synthesis opens several new avenues for the scientific community to explore. To name a few, the self‐etching mechanism of Boudouard reaction equilibrium shifting by COundaries.58 The32 concentration) altogether make the system safe and easy‐to‐build when compared to the hydrocarbon‐derived routes.To sum up, we show carbon monoxide to be a promising carbon source for the naturally self‐limiting synthesis of graphene on metallic substrates with low carbon solubility. High temperature annealing of the Cu surface in CO facilitates both a high degree of crystallinity of the formed graphene and modifies the catalyst resulting in the single‐crystal formation. The experimental design and thorough engineering of the growth governed by the Boudouard reaction allowed us to dramatically inhibit the nucleation rate reaching the regime of single‐crystal graphene growth highlighting the route toward the high pressure CO process—HiPco‐G. Besides, it also significantly streamlines the reactor design—operation at ambient or elevated pressures, absence of hydrogen, tuning a smaller set of parameters  to anneal, melt, and clean the surface. Subsequently, the furnace was cooled down to 1085 °C within 4 min and the atmosphere was changed to a combination of CO and CO2, depending on the desired sample type. Next, the sample was rapidly pulled out to a water‐cooled flange zone and kept for 10 min under the synthesis atmosphere . Finally, the chamber was purged with the inert gas and the sample was taken out for further analysis.Chemical vapor deposition hot‐wall reactor was implemented in the form of a horizontal tube furnace with corundum tubular chamber. One of the tube flanges is connected to the set of mass flow controllers to introduce high purity Ar, CO, N2, during 3 h.Ambient pressure: 1085 °C, 3000 sccm CO, 8 sccm CO2, during 12 min at 3500 mbar reactor pressure.Elevated pressure: 1085 °C, 3000 sccm CO, 18 sccm COAmbient pressure: 1085 °C, 3000 sccm CO for 12 min.Elevated pressure: 1085 °C, 1000 sccm CO, for less than 1 min at 3500 mbar reactor pressure.2 during 3 h. The Raman spectra and mapping in Figures 2 substrate. XPS spectra in Figure 2 within 1 h. NEXAFS and ARPES data in Figure 2 within 1 h was used, while for synchrotron studies in Figure 2 for 2 h was used. For LEED measurements  per point were captured by SEM or optical microscope. For high pressure experiments the CO2 concentration was fixed at 0.5% vol and at least 20 grains were collected. These measurements were complicated for lower CO2 concentration by the fact of extremely high growth rates and inability to capture the time required for the synthesis regime when individual grains are observable.For the kinetics investigation, samples synthesized on the copper foil were used. For each temperature point on the graph Figure  foil wasα radiation with wavelength of 0.7136 A was used. Further X‐ray diffraction experiments were executed at beamlines No. 2 and No. 4 of VEPP‐3 storage ring at Siberian Synchrotron and Terahertz Radiation Centre, Budker Institute of Nuclear Physics of Siberian Branch of RAS, Novosibirsk, Russian Federation. The beamline No. 2 is dedicated for powder diffraction experiments with high instrumental resolution and is equipped with Si(111) channel‐cut monochromator, sample holder moving along theta angle, and Ge(111) crystal‐analyzer mounted in front of scintillation detector on the 2θ arm of the diffractometer. The working wavelength is 0.154 nm. The beamline No. 4 operates with a wavelength of 0.03685 nm and the diffracted radiation is registered by 2D image plate detector MAR345. The sample is set in transmission mode and can be rotated around the axis perpendicular to the incident beam.Diffraction experiments in reflection geometry have been performed at Institute of Solid State Physics of Russian Academy of Sciences (RAS) using monocrystal diffractometer Oxford Diffraction Gemini equipped by charge coupled device detector with resolution of 0.35 A. MoKand No. 460 of θ–2θ scanning, 2θ scanning at fixed theta angle of 4°, θ scanning at fixed 2θ positions corresponding to Cu(111) and Cu(200) reflections, scanning with sample spinned around normal to the surface. The diffraction patterns of the sample were obtained at beamline No. 4 both in conventional transmission mode with no sample movement and with the sample rotated around the horizontal axis within the range of 30°.The experiment at beamline No. 2 was carried out in different modes including conventional −10–3 × 10−9 Torr using the irradiation of AlKα (mono) 1486.69 eV . Binding energy of Cu 2p3/2 at 932.7 eV is typical of metallic copper, while spin‐orbit splitting with Δ = 19.7 eV, minor satellite features at ≈943 eV, and finally the position of Auger line CuLMM at kinetic energy of 918.7 eV limit the possibility of any chemical modification of the substrate during synthesis.XPS spectra were collected by XPS spectrometer Kratos Axis Ultra DLD with spherical sector analyser, ion gun, ultraviolet and x‐ray sources. Experiments were conducted under ultra‐high vacuum 5 × 10Raman spectroscopy was performed with the DXRxi Raman Imaging Microscope equipped with ×50 objective and a 532 nm excitation laser operating at 1 mW output power. Raman spectra were measured at several points along with the sample with the exposure timeLEED embodied in Kratos Ultra DLD was used for tracking the crystallinity of the samples. The distortion of the image, clearly seen from the imperfection of the hexagons formed in the diffraction pattern of the graphene, is caused by the form of the lens, non‐flat samples’ surface and edge effects of the signal capturing camera.−10 mbar. The angular and energy resolutions of the photoemission experiments were 0.1° and 10 meV, respectively. The sample was introduced to the ultra‐high vacuum UHV chamber from the atmosphere, and before measurements, it was annealed at 300 °C for 20 min. During the measurements, the sample was kept at 20 K.ARPES measurements were carried out using linearly polarized undulator radiation at the U112‐2‐PGM beamline of BESSY‐II in Berlin. Photoelectrons were detected with a Scienta R8000 analyzer at the “One square” ARPES instrument, and the base pressure of the experimental setup was better than 1 × 10 NEXAFS spectra were recorded in total electron yield mode. The measurements were performed for the as‐loaded as well as for the annealed (≈300 °C) samples of graphene on copper.Room temperature NEXAFS measurements were performed at Russian‐German dipole beamline of BESSY‐II electron storage ring operated by Helmholtz–Zentrum Berlin für Materialien und Energie.61 NEX−6 mbar pressure. Spectroscopic data were collected with Opus and TPS Spectra software and processed using least‐square fitting procedure with the home‐made WASF software. Deep minima at higher frequencies correspond to absorption lines of PF . The spectrum of the PF was processed using a well‐known expression for transmissivity of the plane‐parallel layer with the absorption minima modeled with Lorentzians. The obtained electrodynamic parameters of PF were employed for least‐square fitting of the transmission coefficient of graphene on PF using corresponding expression for two‐layered systems  under the conditions of secondary electrons detection mode (ETD detector) and 10 kV electron beam accelerating voltage. For larger grains and various catalyst substrates, Jeol JSM‐7001F at acceleration voltages from 10 to 30 kV, as well as optical microscope Leica with copper oxidation contrasting  were used. Dual beam scanning electron microscope Helios G4  was used to capture EBSD maps. Low‐temperature JT‐SPM SPECS was used for atomic reoslution imaging of graphene samples.Bruker Multimode V8 atomic force microscope was used for graphene grains visualization on early stages employing the difference in adhesion force, young modulus, and sample deformation maps obtained in Quantitative NanoMechanical Mapping PeakForce tapping mode. Bruker RTESPA300 cantilevers with FIJI software with a built‐in function was used for particle size distribution measurements. All images were converted to 16‐bit and the contrast was thresholded so that the background stays white, and the particles are black. After processing the obtained perimeters and areas of the particles were averaged. For processing of Raman, UV‐vis, IR, and XPS were processed using python lmfit, rampy, pandas, matplotlib, and numpy packages.CVD parylene deposition was performed in a home‐built set‐up. A quartz tube was heated by two individual horizontal tube furnaces. One zone was kept at 175 °C, where the parylene‐N dimer was kept in a quartz boat. The second zone was heated to 700 °C. Passing through the tube, sublimed parylene dimer undergoes the pyrolysis in the hot zone and polymerization (at a rate of ≈20 nm/min) in the room‐temperature zone holding the samples. The room‐temperature zone can be isolated by a valve, allowing precise control of the final parylene thickness. The system is pumped by an Edwards scroll pump via a liquid nitrogen cold trap. Silicon wafers coated with the parylene were used as a substrate for graphene FETs and subsequent additional deposition of parylene on top of graphene for encapsulation.3PO4, 18 mL HNO3, 10 mL CH3COOH, 65 mL H2O). After the etching was complete, the sample was transferred to pure water to remove the etchant residuals and scooped it with Si/SiO2 wafer in case of cellulose acetate or PMMA or the PF was taken out by tweezers with graphene for air drying. Following removal of the sacrificial layer was performed in cold acetone for PMMA and CA within 12 h. For the case of PF, the polymer film with graphene was applied to the surface of substrate under mild pressure by a rubber roller and heated to 120 °C on a hotplate to ensure uniform coverage. Subsequently, the substrate was placed in o‐xylene and kept overnight at room temperature, transferred to cyclohexane at 70 °C for 2 more hours and again to o‐xylene at 120° for 2 h. Afterwards, the sample was rinsed by isopropanol, deionized water, and vacuum dried.Poly(methyl methacrylate) (PMMA), cellulose acetate (CA), and parafilm M were employed as sacrificial layers during the transfer. Due to large adhesion between graphene and copper substrate, most probably caused by van der Waals interactions, this work failed to tune the electrochemical delamination and SpEED peeling of the graphene. However, able to use a combination of electrochemical etching of the Molybdenum‐Copper substrate in “Hell”‐etchant (30 mL H4He cryostat (4.2 K) where a sample was in the vapor of 3He (exchange gas). Before cooling down an insert with the sample was pumped during >5 h with residual pressure <5 × 10−4 mbar. Either standard four‐probe low‐frequency lock‐in or DC techniques were used for electrical transport measurements.Under ambient conditions transfer curves have been captured with the help of a probe station and Keysight B1500A Semiconductor Analyser. Low temperature measurements were carried out in a  with the Perdew‐Burke‐Ernzerhof (PBE) approximation for the Exchange and Correlation energy. For most calculations only one k‐point was used; nevertheless, some results were tested with (2 × 2 × 1) k‐points and the relative energies changed only around 0.1 eV verifying the proposed procedure. Climbing Image Nudged Elastic Band (CI‐NEB) methods were implemented in atomic simulation environment module in GPAW. All NEB calculations need the initial and final geometries while an estimation of the transition state (TS) is also beneficial. Linear initial trajectory interpolation usually with initial, TS, and final geometries was used. In some cases, the reacting molecules moved significantly and the reaction path could have two barriers, the NEB calculations were restarted so that it would contain only one transition state. As the process occurs at the temperatures slightly above the melting point for copper, the surface is likely liquefied. Since the accuracy of DFT models for the liquid metal surface is substantially lower than that for the solid structure, for the DFT studies Cu(110) surface was employed. Even though the exact values for the activation energies might slightly differ for the different surfaces, the main trend would remain the same.DFT calculations were performed to assess the reaction pathway for the graphene synthesis based on Boudouard reaction on a copper surface. A periodic 3 × 3 surface unit cell for Cu surface was used and the Cu slab was 7 layers thick. All the calculations were done with the grid‐based projector‐augmented wave (GPAW) code64 witThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.Supporting InformationClick here for additional data file.Supporting InformationClick here for additional data file.


Take-Home Naloxone (THN) is a core intervention aimed at addressing the toxic illicit opioid drug supply crisis. Although THN programs are available in all provinces and territories throughout Canada, there are currently no standardized guidelines for THN programs. The Delphi method is a tool for consensus building often used in policy development that allows for engagement of stakeholders.We used an adapted anonymous online Delphi method to elicit priorities for a Canadian guideline on THN as a means of facilitating meaningful stakeholder engagement. A guideline development group generated a series of key questions that were then brought to a 15-member voting panel. The voting panel was comprised of people with lived and living experience of substance use, academics specializing in harm reduction, and clinicians and public health professionals from across Canada. Two rounds of voting were undertaken to score questions on importance for inclusion in the guideline.Nine questions that were identified as most important include what equipment should be in THN kits, whether there are important differences between intramuscular and intranasal naloxone administration, how stigma impacts access to distribution programs, how effective THN programs are at saving lives, what distribution models are most effective and equitable, storage considerations for naloxone in a community setting, the role of CPR and rescue breathing in overdose response, client preference of naloxone distribution program type, and what aftercare should be provided for people who respond to overdoses.The Delphi method is an equitable consensus building process that generated priorities to guide guideline development.The online version contains supplementary material available at 10.1186/s12954-022-00650-4. A total of 26,690 people died from opioid toxicity between January 2016 and September 2021 in Canada due to the toxic drug supply [Naloxone is a µ-opioid receptor antagonist that reverses opioid overdose and aids in preventing death with minimal adverse effects , 3. In CThe Canadian THN Guideline development project was funded through the Canadian Research Initiative in Substance Misuse Emerging Health Threat Implementation Science program in response to escalating mortality associated with opioid toxicity. THN programs are widely recognized as an important response to the to toxic drug supply yet there are discrepancies within THN programs in Canada, such as whether intranasal THN kits are available and the number of ampoules/vials of naloxone included in THN kits .Guidelines are based on current evidence and used to optimize consistent service provision and administration . There aWhile past THN guidelines offer valuable information, we identified a gap in guidelines developed specifically for community THN distribution programs, which have different informational needs and challenges compared to professional groups. The Canadian harm reduction context may differ from other countries as there is regional variation regarding the scope and quantity of harm reduction policies , availabThe Delphi method is a consensus building approach used to inform policy decisions , 18. ThrGuideline development groups should be multi-disciplinary and represent diverse views, involving a variety of methodological experts and clinicians, as well as any population affected by the guidelines . The DelThe aim of the adapted online Delphi method was to investigate which research questions stakeholders believed should be prioritized in a Canadian THN guideline.All meetings and data collection were conducted online in order to get perspectives of stakeholders from across Canada and to respect physical distancing measures during the COVID-19 pandemic. Author MF facilitated all subcommittee meetings with support from author JN. Authors AM, CS, KR, TDR sat on the Guideline Steering Committee.Guideline Development Group recruitment was an iterative process aiming for pan-Canadian membership and diverse perspectives. Four Guideline Development Group subcommittees participated in the Delphi method.Recruitment occurred between November 2020 and January 2021. The study principal investigators and the affiliated Canadian Research Initiative in Substance Misuse (CRISM) working group members nominated members for the Guideline Development Group. These initial members nominated other potential stakeholders to expand and diversify recruitment using a snowball sampling approach.PWLLE were explicitly invited via the snowball sampling process. PWLLE who were connected or unconnected to advocacy, research, or frontline harm reduction organizations were eligible for participation. We recruited from existing communities of PWLLE such as the Canadian Association of People who Use Drugs, the People with Lived and Living Expertise of Drug Use National Working Group, and Professionals for Ethical Engagement of Peers, from our professional networks, and sought feedback from identified PWLLE to ensure diversity of experiences and cross-country representation.We invited participants from all subcommittees to introduce themselves in whatever manner made them feel comfortable, including lived and living experience, but did not explicitly ask all group members whether they identify as people who use drugs. We recruited sufficient self-identified PWLLE to ensure representation in all subcommittees. PWLLE in the Guideline Development Group who were not being compensated for participation through their workplace were provided $25/hr honoraria .Effort was made to find representation across Canadian provinces and territories through the local and national networks of existing members. Indigenous, Black, and People of Color and 2S/LGBTQ group members were explicitly invited in the snowball sampling process.The Guideline Steering Committee (composed of eight members) steered discussions, encouraged constructive debate, summarized main points and key decisions, and gave oversight to the guideline development process.The Affected Community Committee (composed of seven members) provided guidance and recommendations based on the values and preferences of people with lived experience related to naloxone distribution and use in opioid overdose.The Clinical Expert Committee (composed of 13 members) provided guidance and recommendations on the use of naloxone in opioid overdose from a clinical perspective.The Guideline Development Panel (composed of 15 members) voted on the key questions to be addressed by the guideline  as part of a Delphi method. Members of the Guideline Steering Committee, Affected Community Committee, and Clinical Expert Committee were invited to participate in voting as part of the Guideline Development Panel.Subcommittees of the Guideline Development Group included:Author AM, a member of the Guideline Steering Committee, introduced meeting facilitation strategies drawing on experiences facilitating with community groups and varied stakeholders on harm reduction topics in British Columbia . MeetingWe identified initial key questions based on a recent scoping review of the literature on the use of naloxone for reversal of opioid overdose in a community setting . Themes Three subcommittees  reviewed these initial questions and suggested new questions before the Guideline Development Panel voted on the importance of each question. The Guideline Development Group discussed whether to include questions on cost-effectiveness due to concern about the potentially stigmatizing effect of comparing lives lost to public health programming cost. However, some Guideline Development Group members described challenges getting funding for services in the absence of evidence on cost-effectiveness. Questions on cost remained in the voting process but were flagged for careful consideration for presentation of evidence.The Guideline Steering Committee, Affected Community Committee, and Clinical Expert Committee recommended that plain language questions rather than academic research questions or statements be developed to guide the process . The GuiA total of 15 Guideline Development Panel members participated in voting on which key questions should be addressed in the guideline. The Guideline Development Group was composed of people that had overlapping lived or living/clinical/academic experience. A table with descriptions of the panel members’ professional and advocacy roles is included as a Additional file Methodology for the Delphi method was drawn from McMillan et al. . Data coThe method was adapted from early literature on the Delphi by moving data collection online to accommodate for the national scope of the project and to avoid limitations related to the ability to meet in-person during the COVID-19 pandemic .All Guideline Development Panel members participated in the first round of voting (15/15) while 80% of members (12/15) participated in the second round of voting.The research team used the CREDES tool to inform reporting of the Delphi method in this manuscript .A total of 17 of the 35 original research questions scored below 2.0 in the first round of voting and so were retained for the second round. Nine of the 17 key questions were rated below 2.0 in the second round of voting and qualified for inclusion in the THN guideline. The mean scores for both rounds are presented in Table The Delphi method was conducted to identify what questions community stakeholders thought important to prioritize in a Canadian guideline on THN. The following key questions were identified as important to address: What equipment should be in THN kits, whether there are important differences between intramuscular and intranasal naloxone administration, how stigma impacts access to distribution programs, how effective are THN programs at saving lives, what distribution models are most effective and equitable, storage considerations for naloxone in a community setting, the role of CPR and rescue breathing in overdose response, client preference of naloxone distribution program type, and what aftercare should be provided for people who assist with overdoses.Group heterogeneity among those making decisions can lead to more thorough consideration of all relevant aspects of a topic including applicability; by including a diversity of stakeholders, we were able to thoroughly weigh the pros and cons of key questions from different perspectives . The DelPrior Delphi studies in harm reduction report including people from advocacy groups  or advocWe found the online Delphi method to be especially beneficial in the context of a pan-Canadian project occurring during dual public health emergencies of drug toxicity and the COVID-19 pandemic. Public health and community health organizations reported feeling increasingly burdened trying to respond to the pandemic while concurrently seeing increases in overdose-related mortality , 35. TheThe Delphi method is the first step in community engagement for a Canadian THN guideline and will inform the next stage of the guideline development project. Three of the highly ranked key questions will be translated to research questions for systematic reviews and the evidence will be evaluated using the GRADE approach . EvidencDespite targeted recruitment, Newfoundland and Labrador, the Northwest Territories, Nunavut, and Prince Edward Island were not represented in the Guideline Development Group. Some of the nominees from these provinces and territories reported a higher than usual workload due to the COVID-19 pandemic as a barrier to participation. While two of the three territories were not represented, perspectives from the Yukon were included. Conclusions drawn through this Delphi method may not be generalizable to the provinces and territories not represented.A key limitation is reliance on online meetings. While use of online meetings and data collection allowed us to engage people from across Canada, it could present barriers to engagement especially for those with limited access to technology or limited technological knowledge including PWLLE. Additionally, our project relied on participants’ comfort with sharing ideas. While data collection was conducted using survey software, other meetings occurred over ZOOM video conferencing software. Prior qualitative research shows that while participants may feel able to express ideas during online focus groups, they also felt less engaged with other participants and less able to have a conversation that flowed compared to face-to-face discussions . We obseThe research team drafted the guideline questions using Population/Problem, Intervention/Exposure, Comparison, Outcome/Findings (PICO) language, then reworded them into accessible language for the Delphi method. However, this created uncertainty with the research team around the interpretation of some of the prioritized questions. The team was unable to ascertain how individuals interpreted the common language questions, which led to challenges in creating the final PICO questions used in the literature searches in the absence of more extensive pilot testing. Capturing comments on the questions or asking the voters to explain their understanding of the questions may have ensured that voters all had similar interpretations. Additionally, key questions included multiple outcomes, but the research team needed to narrow down questions for feasibility of executing the systematic reviews that will generate evidence for the THN guidelines.The Delphi method allowed Guideline Development Group members from across disciplines, life experiences, and geographical space to share insights and help establish priorities for a Canadian guideline. A guideline on Take-Home Naloxone informed by key stakeholders will provide evidence to support consistent, effective, and equitable service delivery across Canada. The evidence on the nine questions identified through this Delphi method study will be explored through systematic review.Additional file 1. Table 1. Guideline Development Panel Breakdown.