Growth of non-layered 2D transition metal nitrides enabled by transient chloride templates

Domain: physics
Published: 2026-01-14
Editorial outcome: minor_revision

Abstract
2D transition metal nitrides (TMNs) have attracted significant attention due to their magnetic, electrical, and chemical properties at atomic thickness. However, the synthesis of 2D TMNs is still challenging, due to their strong isotropic metal-nitrogen bonding networks. Here, we report a universal synthesis of non-layered 2D TMN family by using corresponding metastable metal chlorides as transient templates. This approach takes advantage of the layered structures and low conversion energy barriers of transition metal chlorides (TMCls) to grow 2D TMNs. Fifteen types of 2D TMNs and their alloys were synthesized, demonstrating the versatility of this method. The 2D TMN family exhibits tunable magnetic characteristics ranging from antiferromagnet to hard magnet, which can be modulated by their composition. This work overcomes previous synthesis limitations, thus offering a pathway to explore fundamental properties of 2D TMNs and accelerate their applications.

Introduction
Transition metal nitrides (TMNs) represent a class of materials with impressive properties, including ultrahigh mechanical strength, remarkable thermal stability, tunable magnetism, and superconductivity1–4. Recent advances in two-dimensional (2D) materials have spurred interest in reshaping TMNs into ultrathin 2D forms to unlock enhanced functionalities5–8. For instance, owing to unsaturated dangling bonds and low-coordination atoms, the exposed surfaces endowing 2D TMNs with excellent catalytic performance and chemisorption capabilities in energy-related applications4,9–13. Notably, under electron and phonon confinement at the 2D limit, these ultrathin TMNs exhibit properties distinct from their bulk counterparts, offering opportunities for fundamental studies in magnetism5,14–16, electronic transport5,8, optical properties8, etc. Additionally, due to their atomic-level thickness, 2D TMNs could exhibit high flexibility, making them promising building blocks for future 2D electronic, spintronics, and optoelectronic devices17–21. To achieve these property explorations and applications, the prerequisite is the universal and controllable synthesis of 2D TMNs.

Different from other nonlayered materials such as transition metal oxides (TMOs, e.g., Fe2O3) and transition metal chalcogenides (e.g., FeS), TMNs shows special isotropic hybrid metallic-covalent interactions between metal and nitrogen atoms in three dimensions22–26. This isotropy impedes the formation of thin 2D TMNs by using the established method in synthesizing other non-layered 2D materials2,3,27–29. Currently, approaches such as selective etching of MAX phases17,30,31, salt-templated growth32,33, and 2D template conversion34,35, have been developed to produce certain free-standing 2D TMN materials. For example, Urbankowski et al have fabricated 2D Ti4N3-based MXene by using the molten fluoride salts to etch Al atoms from Ti4AlN3 powder precursor30. Note that the produced materials contain unavoidable surface terminal groups, which influence the understanding of the intrinsic properties of pure 2D Ti4N3. In another work, Jin et al have obtained layered W2N3 nanosheets by ammonization of 2D Na2W2O4 salt-templates with similar lattice symmetry, while this method remains limited to a few 2D TMNs since the lattice matching requirement between salt and target materials10. Although the 2D template conversion approach shows promise for the universal growth of high-quality pristine 2D TMNs, selecting suitable template materials to avoid the long nitriding time caused by etching is critical34,35. Transition metal chlorides (TMCls) therefore is a potential choice since their low conversion energy, while their high-temperature instability makes this process practically unachievable36,37. How to stabilize and nitrogenize these metastable templates is critical for the successful growth of 2D TMNs.

Here, we develop a transient chloride template assisted reverse-thermal-field (RTF) strategy for the universal synthesis of a library of 2D TMNs and their alloys. We use TMCls as templates, taking advantage of their layered structure and low conversion energy barriers to corresponding nitrides. By applying a spatially RTF method during nitridation in a short time, we directly transform metastable TMCls templates into ultrathin TMNs with preserved integrity and single-crystallinity. Through changing the type of precursor and growth temperature, we have grown 7 types of 2D TMNs and 8 types of 2D TMN alloys. The high-resolution transmission electron microscopy (HRTEM) images confirm the structure and composition of materials. Magnetic measurements show that the 2D TMNs exhibit magnetic behaviors different from their bulk counterparts, and alloying is proven to be an effective way to modulate their magnetism.

Results
Growth of 2D TMNs by the reverse-thermal-field CVD method
As shown in Fig. 1a, compared to common transition metal compounds like oxides and sulfides, TMCls possess two key advantages which make them promising templates to grow 2D TMN. First, TMCls show the lowest solid-to-solid conversion energy to TMNs at high temperatures, which reduces the conversion time and thus inhibits the crystal etching caused by NH3 and H2 during the conversion process. Second, unlike the transition metal oxides and sulfides which mainly shown on layered structures, most of the TMCls exhibit a layered vdW structure (Supplementary Fig. 1). However, due to their high volatility and hygroscopicity, the 2D TMCl templates cannot exist stably at high temperatures, making the direct use of their chloride template unapplicable. Indeed, Supplementary Fig. 2 shows the optical microscopy (OM) images of a 2D TMCl flake exposed in air for 10 s, 20 s, 30 s, 40 s, and 50 s, and Supplementary Fig. 3 shows the OM images of deposited TMCl heated at 650 °C in an Ar atmosphere. The quick fading of the flake demonstrates its poor stability. In addition, as shown in the thermal gravimetric analysis (TGA) curves (Supplementary Fig. 4a), all the sublimation temperatures of TMCls (i.e., VCl3, CrCl3, MnCl2, FeCl3, CoCl2, and NiCl2) are below 200 °C, revealing that the 2D TMCl templates cannot maintain as solid crystal at high temperature. However, the thermodynamically supported conversion temperature from chlorides to nitrides is above their sublimation temperature, which indicates that the solid-to-solid conversion from 2D TMCls to 2D TMNs is difficult (Supplementary Fig. 4b), making the traditional CVD method unapplicable (Fig. 1b, c). Interestingly, we found that the sublimation rate of TMCl in NH3 was greater than its growth rate to nitride when the growth temperature was <700 °C, while it was smaller when the temperature was >700 °C (Supplementary Fig. 5). Therefore, the key is how to heat the metastable TMCl templates to the required high temperature in a short time.

Based on this, we develop an RTF method in which the fast switching of the thermal field makes it possible to satisfy the above requirements. Fig. 1d and Supplementary Figs. 6–9 illustrate the setup of the furnace and the growth process of RTF method and traditional CVD method (see details in Methods and Supplementary Information). The step 1 stands for the growth of 2D TMCl templates, and the step 2 represents their conversion to the corresponding 2D TMNs. In the step 1, the TMCl precursors were placed at the upstream of the growth tube (Field I), where the growth temperature was 600-800 °C. At the same time, the mica substrates were placed at the downstream of the tube (Field II), where the temperature was about 100-200 °C to grow a 2D TMCl template under Ar. Subsequently, in the step 2, the temperature of the Field I and Field II was reversed in a short time (<2 s) by moving the furnace while keeping the position of the quartz tube fixed, together with the introduction of NH3. In this step, the 2D TMCl templates were in situ converted to corresponding 2D TMNs when the temperature of Field II quickly reached up to 600-800 °C. At the same time, the temperature of Field I was quickly cooled down to 100-200 °C, inhibiting the extra evaporation of precursors induced contamination. After growth, the temperature of the furnace was cooled down to room temperature (R.T.). Notably, since the TMCls show similar physical and chemical properties, various 2D TMNs were fabricated by changing the type of precursor and tuning the growth temperature. Moreover, through simply mixing the precursors, a variety of 2D TMN alloys have been fabricated, further confirming the universality of this method.

Characterizations of 2D TMNs and their alloys
By using the above RTF method, 7 types of mono-metal non-layered 2D TMNs (i.e., CrN, MnN, VN, FeN, CoN, h-NiN, r-NiN, WN, and ZrN) as well as 8 types of 2D TMN alloys (i.e., r-Co0.6Ni0.4N, h-Co0.6Ni0.4N, Co0.3Fe0.7N, Cr0.2Fe0.1Co0.7N, Co0.2Ni0.1Fe0.7N, Cr0.2Fe0.1Co0.7N, Cr0.2Fe0.1Co0.7Mn0.1N, Cr0.2Fe0.1Co0.7Ni0.1N) are grown (Fig. 2a, b). Taking CoN as an example, the lateral size and thickness of the 2D flakes are determined by the growth temperature and duration of step 1 (Supplementary Fig. 10 and Supplementary Fig 11). The lateral size exhibits a volcano-like relationship with both increasing temperature and time, whereas the thickness generally increases. The largest CoN flake obtained thus far has a lateral size of 51 μm (Supplementary Fig. 12a), achieved at a growth temperature of 750 °C with a 5 min growth time, while the thinnest flakes (~1.03 nm, Supplementary Fig. 12b) are obtained at 600 °C with a 2 min growth time. We performed systematic studies and found that the morphology of the samples is decided by both their crystal symmetry and growth temperature. Most 2D TMNs and alloys show hexagonal morphology, which is similar to their corresponding TMCls with six- or three-fold symmetry. Note that MnN, r-NiN, and r-Co0.6Ni0.4N show rectangular morphology, which is decided by the morphology of the template. For instance, as shown in Supplementary Fig. 13, 2D NiN exhibits a hexagonal morphology when synthesized at 650 °C, which corresponds to the hexagonal shape of the 2D template formed at that temperature. Conversely, when the step 1 temperature is increased to 800 °C, a rectangular shape 2D template forms, resulting in rectangular 2D NiN flakes. And this result maybe attributed to their different composition of nickel chloride grown under different temperature. Taken together, we have grown 15 types of non-layered 2D TMNs and their alloys by using the RTF method.

We then investigated the crystal structure and composition of the 2D TMNs. Fig. 3a shows the crystal structure of Fe2N (PDF#97-002-0390). The HRTEM image and selected area electron diffraction (SAED) pattern (Fig. 3b and its inset) reveal that the 2D Fe2N has a lattice spacing of 0.138 nm, which is assigned to the (110) plane. Low magnification image and the corresponding energy-dispersive spectroscopy (EDS) mapping indicate that Fe and N atoms are uniformly distributed (Fig. 3c). The corresponding EDS result shows the characteristic peaks of Fe and N atoms (Fig. 3d) with an atomic ratio of ~2:1, suggesting the composition of Fe2N. Similarly, we obtained HRTEM images of 2D VN and 2D MnN and their corresponding SAED patterns (Fig. 3f, j). The 2D VN shows a lattice spacing of 0.146 nm, and the 2D MnN shows a lattice spacing of 0.247 nm, which are consistent with their atomic structures (VN: PDF#97-016-9819; MnN: PDF#97-023-6828). The corresponding EDS mapping (Fig. 3g, k) and EDS results (Fig. 3h, l) show that all the elements are uniformly distributed and both the V:N and Mn:N atomic ratios are 1:1, which are in consistent with their corresponding crystal structures (Fig. 3e, i). The detailed HRTEM images and SAED patterns of the other 2D TMNs are shown in Supplementary Figs. 14–17, and the h-NiN and r-NiN belong to the same atomic structure (PDF#97-016-1755). These results suggest the high quality of the obtained 2D TMNs.

We also characterized the structure and composition of the 2D TMN alloys. HRTEM image and SAED pattern of the 2D Co0.6Ni0.4N alloy are shown in Fig. 4a, revealing a lattice spacing of 0.151 nm, which is similar to the CoN (d220 = 0.151 nm) and NiN (d220 = 0.152 nm). Highly uniform elemental distribution is also confirmed by EDS mapping in Fig. 4b, and the corresponding EDS result (Fig. 4c) shows the characteristic peaks of Co, Ni and N atoms, with the atomic ratio of Co:Ni:N is about 0.6:0.4:1. For Co0.3Fe0.7N, the HRTEM and SAED results in Fig. 4d reveal a lattice spacing of 0.142 nm, which is similar to the CoN (d220 = 0.151 nm) and FeN (d220 = 0.141 nm, PDF#97-023-6810). Interestingly, the FeN here belongs to the cubic structure rather than the previously fabricated 2D Fe2N. The EDS mapping (Fig. 4e) exhibits the highly uniform elemental distribution of Co0.3Fe0.7N alloy. The corresponding EDS result in Fig. 4f shows the characteristic peaks of Fe, Ni, and N atoms, with the atomic ratio of Fe:Co:N is about 0.7:0.3:1. Moreover, the HRTEM image of 2D Co0.2Ni0.1Fe0.7N and its corresponding SAED pattern (Fig. 4g) show a lattice spacing of 0.072 nm, which is almost half of NiN (d220 = 0.152 nm), CoN (d220 = 0.151 nm), and FeN (d220 = 0.141 nm, PDF#97-023-6810). This should be attributed to the lattice distortion caused by the different lattice constants of the three materials. Additionally, the corresponding EDS mapping (Fig. 4h) and EDS result (Fig. 4i) demonstrate the uniformly distribution of Ni, Co and Fe in the flakes with an approximate atomic ratio of Co:Ni:Fe:N = 0.2:0.1:0.7:1. The detailed HRTEM image and EDS mapping of 2D r-Co0.6Ni0.4N are shown in Supplementary Fig. 18. The above results suggest that the RTF synthesized 2D TMN alloys exhibit high crystallinity and uniformity.

Magnetic properties of 2D TMNs and their alloys
Finally, we investigated the magnetic properties of 2D TMNs and their alloys by magnetic force microscopy (MFM) and superconducting quantum interference device (SQUID). Fig. 5a-f show the MFM phase contrasts of the 2D TMNs (i.e., VN, CrN, MnN, Fe2N, CoN, and NiN) at R.T. The results show that CoN has the largest saturation magnetization among these materials, which is consistent with their M-H loops measured by SQUID (Fig. 5g). The M-H loops of 2D TMN alloys were also characterized and summarized in Fig. 5h. In detail, the 2D Co0.3Fe0.7N alloy shows an antiferromagnetic behavior, with lower saturation magnetization (Ms) and coercive force (Hc) than both 2D CoN and 2D Fe2N. While 2D Cr0.3Fe0.7N alloy exhibits a ferromagnetic behavior (2D Fe2N: antiferromagnetic, 2D CrN: ferromagnetic) and moderate magnetism (Ms = 0.208 emu, Hc = 250 Oe) compared with 2D CrN (Ms = 0.068 emu, Hc = 188 Oe) and 2D Fe2N (Ms = 0.377 emu, Hc = 252 Oe). The magnetic properties of all the 2D TMNs and their alloys are summarized in Fig. 5i and Supplementary Table 1. Taken together, we can either enhance or weaken the magnetic response of 2D TMNs by selecting appropriate metals or alloying, thereby expanding the performance range of 2D magnets to meet diverse application requirements.

Discussion
In this work, we developed a RTF CVD method to convert 2D TMCls and obtained fifteen types of non-layered 2D TMNs and their alloys. The key of the method is using metastable TMCls as transient templates, with features of their 2D layered structure and low conversion energy barrier to TMNs. Combined HRTEM images, SAED patterns and EDS spectra results reveal the single-crystalline structure and composition uniformity of these 2D materials. Magnetism characterizations show rich and tunable magnetic behaviors of 2D TMN by alloying. The general growth method for non-layered materials could enrich the 2D material family with exotic properties and applications.

Methods
Synthesis of 2D TMNs and their alloys
The 2D TMNs and their alloys were fabricated using the RTF method. The typical fabrication process was carried out in a movable furnace, as shown in Supplementary Fig. 6. The precursors were placed in a quartz boat located in the upstream region of the quartz tube (Field I), and the mica substrates were positioned in the downstream region (Field II). Argon (100 sccm) was used as the carrier gas throughout the process. The growth involved two distinct steps: Step 1 involved the deposition of the 2D TMCl templates. In this step, Field I (precursor zone) was moved to the heating center and heated to the target temperature (600-800 °C) from room temperature in 30 min and maintained for 2 min. During this step, Field II (substrate zone), situated approximately 10 cm away from the heating center, remained at a lower temperature (100-200 °C). At the end of Step 1, the furnace was swiftly translated along the rail to position Field II (substrate zone) at the heating center, initiating Step 2 (the conversion step). Simultaneously with this movement, a mixture of NH3 and H2 was introduced and maintained for 10 min. Consequently, the temperature of Field II was rapidly increased to 600-800 °C and held for 5 min, while Field I was cooled down to approximately 100-200 °C. Finally, the furnace was cooled to room temperature under an Ar atmosphere.

Traditional CVD growth of 2D TMN: the precursor was placed in the upstream section of a one-zone furnace (Field I), while the substrate was positioned at the furnace center (Field II, the heating center). In step 1, the precursor was heated to 300-400 °C (above its sublimation temperature) and carried by 100 sccm Ar to deposit onto the substrate. In step 2, the substrate was heated to 600-800 °C under a flow of H2 and NH3 to facilitate the nitridation of the deposited TMCl. The corresponding temperature profile is illustrated in Supplementary Fig. 9.

Transfer of 2D TMNs and their alloys: The 2D flakes grown on the mica substrates were transferred onto the TEM grid by a common method using Polystyrene (PS) as a sacrificial transfer film. PS was spin-coated on the sample at 2000 rpm for 60 s. The sample was then heated on a hot plate at 90 °C for 5 min. After baking, the sample was loaded in deionized water and then the peeled-off samples were transferred onto TEM grids. Finally, the PS was removed with methylbenzene.

Material characterizations and magnetic measurements: The morphology of the samples was observed by an optical microscope (Carl Zeiss Microscopy, Germany). The microstructure of the samples was investigated by high-resolution TEM at an acceleration voltage of 300 kV (FEI Tecnai F30, USA). SQUID (MPMS3, Quantum Design, USA) was used to measure the M-H hysteresis loops and M-T curves of the samples. AFM (Cypher ES, Asylum Research, USA) was used to measure the thickness of the samples. MFM (Cypher ES, Asylum Research, USA) was used to measure the magnetic properties of the nanoflakes.

Calculations of temperature-dependent Gibbs formation energy of compounds: Enthalpy data of compounds in this work were extracted from Lange’s handbook of chemistry38 (CrN, CrCl3, Cr2O3, FeCl3, Fe2O3, FeS, MnCl2, MnO2, NiCl2, NiO, NiS, CoO), FactSage39 (CrS, CoCl2, CoS, Fe2N, MnS, VCl3, V2O3, VS), and DFT calculation (CoN, NiN, MnN, VN). All the compound data were extracted only at 298 K. The chemical potentials of the elements were obtained with the minimum Gibbs energy at a given temperature.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Non-layered 2D materials have attracted much attention recently and is a new research frontier in the 2D materials field. Among all non-layered 2D materials, transition metal nitrides TMNs are particularly interesting but is rather difficult to grow into 2D thin forms due to their isotropic covalent/ionic bonding, which is a well-known challenge in the field. In this paper, He et al. have established a very innovative method, by using metal chloride as a “Transient Template”, to grow a large variety of metal nitrides and their alloys into large and thin 2D forms. This seems to be the first report about universal synthesis of such large amount of different kinds of 2D TMNs. The authors have performed systematical investigations regarding material growth mechanism, material characterization, structural and chemical analysis, as well as magnetism properties. Overall, the quality of research is high and the conclusions are supported by their experiments. This work has solved a long-standing problem in the field, and the referee recommends its publication in Nature Communications after minor revisions to further strengthen the work, noted below.\n1). What’s the largest size of 2D TMN flakes you can grow? What are the factors that limit the sizes of the 2D TMNs? Please show some experimental results or add discussions.\n2). The figure 1 reflects the design concept of the new growth strategy which is nice. There seems a display typo, i.e., “metastable layered TMCl template?” Please check. In addition, what are the molecules in Figure 1c? It is not very clear to see, nor were explained or illustrated in the figure. Please make this point clear. Also, what’s the temperature profile for traditional CVD? Please write it clearly.\n3). Different 2D TMN materials seem have different shape or morphology, is that correct? Is it purely determined by the symmetry of the crystals, or also been affected by the growth parameters like growth temperature? Please discuss this point.\n4). For the methods part, please describe more details about the growth furnace. Is it a one-zone or three-zone furnace? What’s the position/temperature where you put the precursors? What’s the detailed shape of the container? It would be helpful to add these details, preferably a photo of the set-up, so that others can use the growth recipe for these kinds of 2D TMN synthesis.\n5). The English writing should be further polished. For example, in Abstract, “15 types of 2D TMNs and their alloys…” can be changed to “Fifteen types of 2D TMNs and their alloys…” for clarity. Figure 2 caption, “Number of Metal Elements”, the letter M and E may not be capitalized. Please keep consistent with other places throughout the manuscript. The authors should polish these details before publication.", "reviewer_2": "This work reports a novel and universal synthesis method, reverse-thermal-field (RTF) CVD strategy, for growing a wide range of non-layered 2D TMNs and their alloys. The key innovation is the use of metastable, layered TMCls as transient templates, which are first grown at a low-temperature zone and then rapidly converted into TMNs by quickly moving to a high-temperature zone in the presence of ammonia. The authors successfully demonstrate the growth of 15 different 2D TMNs (7 mono-metal nitrides and 8 alloys) and show that their magnetic properties (e.g., saturation magnetization, coercive field) can be effectively tuned through composition. In general, this work is interesting and has good novelty. I can recommend the publication after addressing the following concerns:\n1. The claimed mechanism is the “solid-to-solid” conversion of a 2D TMCl template. However, it is important to provide direct evidence that the layered structure of the initial TMCl flake is converted to TMN during the rapid heating step and acts as a true template, other than the direct deposition of TMN under the environment of precursor gas, NH3, and H2. Therefore, providing an optical image of TMCl flakes after step 1 (30 min heating + 2 waiting time) and before step 2 is necessary. Alternatively, it is also acceptable to perform the TEM characterization of the intermediate flakes during step 2, that should contain both Cl and N atoms.\n2. It is hard to imagine how the TMCls with six- or three-fold symmetry transform into the rectangular-shaped TMNs. If it is a solid-to-solid transition, the metal atoms need to move freely on the mica substrate, and an intermediate shape between the triangle (or hexagon) and rectangle can be captured if step 2 is stopped at around 2.5 min.\n3. It would be beneficial to include references for the sentence in lines 66-69.\n4. In Fig. 5a-f, the thicknesses are not directly displayed; line cuts are necessary.", "reviewer_3": "The authors report a universal reverse-thermal-field CVD strategy for synthesizing two-dimensional transition metal nitrides (TMNs). In this approach, metastable metal chloride crystal templates are first deposited on mica substrates and then converted to TMNs by high-temperature nitridation, before the chloride templates are lost. Using this method, the authors demonstrate the growth of VN, CrN, MnN, Fe₂N, CoN, NiN, and their alloys. Structural and compositional characterizations (TEM, EDS, AFM) are presented, while magnetic properties are probed by MFM and SQUID. Overall, the technique represents a potentially viable route toward 2D TMNs and is therefore an important contribution to the 2D materials community. However, additional details and clarifications are needed:\n1. A more detailed parametric study of the different materials should be conducted. For example, how was the temperature for Field 1 and 2 selected? Was any optimization performed in selecting these values? Can the crystal quality/defect density of the as-grown TMN be quantified? Such as using Raman peak width/position, and corroborated with XRD/XPS if feasible.\n2. Can the CVD parameters, such as precursor loading or growth duration, be used to systematically control layer thickness, nucleation density, and flake size? Since the authors describe these TMNs as 2D materials, please report the thickness statistics, which should typically be in the range of a few nm. Further optimization would be necessary to probe genuine 2D characteristics rather than bulk-like properties.\n3.Figure S2 shows the rapid loss of metastable CrCl₃ crystal within 40 s. For the RTF-CVD process, please provide the time-temperature profile. How rapid is the heating/cooling transition from 100–200 °C up to 600–800 °C? This is important for researchers to replicate the method.\n4.For the alloyed TMNs, are the metal elements randomly incorporated in a single phase, or is there any short-range ordering/phase segregation? Can the elemental composition be tuned by adjusting precursor ratios?\n5.The AFM and MFM images of the alloyed TMN, along with the corresponding thickness measurements, should be included in Figure 5. Does the magnetic property change with thickness?"}, "author_response": "List of changes (blue in the revised manuscript and SI):\n(1) Some sentences have been added or revised on Pages 2, 4, 7, 10, 18, 19 and 20 in the\nrevised manuscript.\n(2) Figure 1b, Figure 2 and Figures 5a-5f have been updated in the revised manuscript\naccording to the suggestions of reviewers.\n(3) The in-situ observation of deposited TMCl evolution under high temperature has been\nadded as Figure S3 in the revised SI.\n(4) A photo of the setup used to achieve RTF process has been added as Figure S6 in the revised\nSI.\n(5) Temperature profile of the growth process of RTF method has been added as Figure S8 in\nthe revised SI.\n(6) Temperature profile of the traditional CVD method has been added as Figure S9 in the revised SI\n(7) The relationship between morphology of CoN and growth temperature has been added as\nFigure S10 in the revised SI.\n(8) The relationship between morphology of CoN and growth time has been added as Figure\nS11 in the revised SI.\n(9) OM and AFM images of 2D CoN have been added as Figure S12 in the revised SI.\n(10) OM images of 2D nickel chloride templates with different morphologies have been added\nas Figure S13 in the revised SI.\n(11) Typos have been corrected in the revised manuscript.\n(12) Two new references have been added in the revised manuscript.\nComment. Non-layered 2D materials have attracted much attention recently and is a new\nresearch frontier in the 2D materials field. Among all non-layered 2D materials, transition metal\nnitrides TMNs are particularly interesting but is rather difficult to grow into 2D thin forms due\nto their isotropic covalent/ionic bonding, which is a well-known challenge in the field. In this\npaper, He et al. have established a very innovative method, by using metal chloride as a\n“Transient Template”, to grow a large variety of metal nitrides and their alloys into large and\nthin 2D forms. This seems to be the first report about universal synthesis of such large amounts\nof different kinds of 2D TMNs. The authors have performed systematical investigations\nregarding material growth mechanism, material characterization, structural and chemical\nanalysis, as well as magnetism properties. Overall, the quality of research is high and the\nconclusions are supported by their experiments. This work has solved a long-standing problem\nin the field, and the referee recommends its publication in Nature Communications after minor\nrevisions to further strengthen the work, noted below.\nResponse. Thank you very much for your positive and encouraging assessment of our work.\nWe sincerely appreciate the reviewer by writing that our work is “very innovative”,\n“systematical investigations” and pointing out “to be the first report about universal synthesis\nof such large amounts of different kinds of 2D TMNs”.\nComment 1. What’s the largest size of 2D TMN flakes you can grow? What are the factors\nthat affect and limit the sizes of the 2D TMN, our results reveal that the lateral size of the 2D TMNs is\nprimarily determined by the growth temperature and growth time of step 1 (the template\nformation step), as detailed in Figures R1 and R2. Both parameters exhibit a volcano-shaped\nrelationship with the lateral size of the resulting 2D CoN flakes. This trend can be attributed to\nthe nucleation density of the transition metal chloride (TMCl) templates: at lower nucleation\ndensities, increasing the temperature or time promotes lateral growth, leading to larger flakes.\nHowever, beyond an optimal point, excessively high nucleation density restricts the available\n2\nspace for lateral expansion, thereby limiting the final flake size. Under the optimized conditions\n(a growth temperature of 750 ℃ and a growth time of 5 minutes), we have achieved 2D CoN\nflakes with an average lateral size of several tens of micrometers, with the largest flake reaching\n51 μm (Figure R3).\nFigure R1. The relationship between morphology of CoN and growth temperature. (a)\nOM images of CoN with increased temperature from 600 ℃ to 800 ℃, and all the growth time\nwere 5 min. (b) The thicknesses of CoN under different growth temperatures. The thickness\nwas obtained by AFM measurements of 249 flakes. (c) The lateral sizes of CoN under different\ngrowth temperature. The lateral size was obtained by OM characterization.\nof CoN with increased growth time from 2 min to 20 min, and all the growth temperatures were\n650 ℃. (b) The thicknesses of CoN with different growth time. The thickness was obtained by\nAFM measurements of 293 flakes. (c) The lateral sizes of CoN with different growth time. The\nlateral size was obtained by OM characterization.\nChanges to the manuscript.\n Figure R1, Figure R2 and Figure R3 have been added as Figure S10, Figure S11 and Figure\nS12a in the revised SI.\n Several sentences have been added on Page 10. “Taking CoN as an example, the lateral\nsize and thickness of the 2D flakes are determined by the growth temperature and duration\nof step 1 (Figure S10 and S11). The lateral size exhibits a volcano-like relationship with\nboth increasing temperature and time, whereas the thickness generally increases. The\nlargest CoN flake obtained thus far has a lateral size of 51 μm (Figure S12a), achieved at a\ngrowth temperature of 750 ℃ with a 5-minute growth time, while the thinnest flakes (~1.03\nnm, Figure S12b) are obtained at 600 ℃ with a 2-minute growth time.”\nComment 2. The figure 1 reflects the design concept of the new growth strategy which is nice.\nThere seems a display typo, i.e., “metastable layered TMCl template?” Please check. In addition,\nwhat are the molecules in Figure 1c? It is not very clear to see, nor were explained or illustrated\nin the figure. Please make this point clear. Also, what’s the temperature profile for traditional\nCVD? Please write it clearly.\nResponse 2. We sincerely thank the reviewer for pointing out these oversights. We have\ncarefully corrected the typo in the figure. Furthermore, we have revised Figure 1 (now Figure\nR4 in the response) to provide a clearer illustration of the molecular species involved and to\nexplicitly label the temperature profiles. Specifically, the molecules depicted in Figure 1c\n5\nrepresent the sublimated metal chloride species (e.g., MCl ). Regarding the traditional CVD\nx\nprocess, its temperature profile is now provided in the new Figure S8. In a standard one-zone\nCVD setup, the precursor (located upstream, Field I) is typically heated to 300-400 ℃ (above\nits sublimation point) and transported by Ar carrier gas to deposit on the substrate (located at\nthe center, Field II). Subsequently, in step 2, the substrate region is heated to 600-800 °C under\na mixture of H and NH for nitridation. However, due to the instability of the 2D TMCl\n2 3\ntemplates at high temperatures, they often sublimate before the nitridation temperature is\nreached in this configuration, leading to unsuccessful growth.\nFigure R4. Design and growth process of the reverse-thermal-field (RTF) CVD method.\n(a) Calculations of the Gibbs energy barriers of the solid-to-solid conversion from transition\nmetal chlorides, oxides, and sulfides to the TMNs counterparts at 1000 K. The positive energy\n6\nmeans the conversion is theoretically unfavorable, while the negative energy means it is\ntheoretically favorable. (b) Schematic of the metastable 2D TMCl template. (c) Scheme to\nillustrate the temperature program and growth result of the traditional CVD method. The\nnitridation process starts when the temperature reaches the thermodynamically supported\nconversion temperature. And the TMCl is sublimated as MClx molecules before the nitridation\nprocess. (d) Scheme to illustrate the temperature program and growth result of the RTF CVD\nmethod. The dashed and solid lines represent the temperature of the precursor and substrate,\nrespectively. The nitridation process starts when the thermal field is reversed. The detailed\nprocess is shown in the Experimental Section and Supporting Information.\nFigure R5. Photo of the setup used to achieve RTF process.\nthe precursor during growth, and the precursor is located at Field Ⅰ. (b) Temperature profile of\nthe substrate during growth, and the substrate is located at Field Ⅱ.\nChanges to the manuscript.\n Figure R4 has been reproduced as Figure 1 in the revised manuscript to replace the original\nFigure 1.\n Figure R5 and Figure R6 have been added as Figure S6 and Figure S9 in the revised SI\n Several sentences have been added on Pages 19 and 20. “Traditional CVD growth of 2D\nTMN: the precursor was placed in the upstream section of a one-zone furnace (Field I),\nwhile the substrate was positioned at the furnace center (Field II, the heating center). In\nstep 1, the precursor was heated to 300-400 ℃ (above its sublimation temperature) and\ncarried by 100 sccm Ar to deposit onto the substrate. In step 2, the substrate was heated to\n8\n600-800 ℃ under a flow of H and NH to facilitate the nitridation of the deposited TMCl.\n2 3\nThe corresponding temperature profile is illustrated in Figure S9.”\nComment 3. Different 2D TMN materials seem have different shape or morphology, is that\ncorrect? Is it purely determined by the symmetry of the crystals, or also been affected by the\ngrowth parameters like growth temperature? Please discuss this point.\nResponse 3. Thank you for raising this important point regarding morphology control. (1)\nDifferent 2D TMNs indeed show different shapes under different growth conditions. (2) The\nfinal morphology of the 2D TMNs is indeed directly inherited from the morphology of the\nintermediate 2D TMCl template formed during step 1. The growth parameters, particularly\nthe temperature in step 1, critically influence the shape of this initial template. For instance, as\nshown in Figure R7, 2D NiN exhibits a hexagonal morphology when synthesized at 650 ℃,\nwhich corresponds to the hexagonal shape of the 2D template formed at that temperature\n(Figure R7a). Conversely, when the step 1 temperature is increased to 800 °C, a rectangular\nshape 2D template forms (Figure R7b), resulting in rectangular 2D NiN flakes. Therefore, the\nmorphology is predominantly determined by the growth-parameter-dependent morphology of\nthe transient TMCl template.\nFigure R7. OM images of 2D nickel chloride templates obtained at different growth\ntemperatures. (a) OM image of a triangular/hexagonal shape 2D template when the growth\ntemperature is 650 ℃. (b) OM image of a rectangular shape 2D template when the growth\ntemperature is 800 ℃.\nChanges to the manuscript.\n Figure R7 has been added as Figure S13 in the revised SI\n Several sentences have been added on Page 10. “Note that MnN, r-NiN, and r-Co Ni N\nx y\nshow rectangular morphology, which is decided by the morphology of the template. For\ninstance, as shown in Figure S13, 2D NiN exhibits a hexagonal morphology when\nsynthesized at 650 ℃, which corresponds to the hexagonal shape of the 2D template\nformed at that temperature. Conversely, when the step 1 temperature is increased to 800 ℃,\na rectangular shape 2D template forms, resulting in rectangular 2D NiN flakes.”\nComment 4. For the methods part, please describe more details about the growth furnace. Is it\na one-zone or three-zone furnace? What’s the position/temperature where you put the\nprecursors? What’s the detailed shape of the container? It would be helpful to add these details,\npreferably a photo of the set-up, so that others can use the growth recipe for these kinds of 2D\nTMN synthesis.\nResponse 4. We appreciate the reviewer’s suggestion to enhance the reproducibility of our\nmethod. As requested, we have provided a photograph of our setup (Figure R8) and the detailed\ntemperature profile for the RTF process (Figure R9). The growth was performed in a modified\none-zone tube furnace equipped with a sliding rail system, which allows the furnace to be\nphysically translated between Field I (precursor location) and Field II (substrate location). The\nprecursors were contained in a standard quartz boat. We have thoroughly revised the\n“Experimental Section” in the manuscript to incorporate these crucial experimental details,\nensuring the growth recipe is clear for other researchers.\nFigure R9. Temperature profile of the growth process of RTF method. (a) Temperature profile of\nField Ⅰ, where the precursor located. (b) Temperature profile of Field Ⅱ, where the\nsubstrate located.\n Figure R8 and Figure R9 has been added as Figure S6 and Figure S8 in the revised SI.\n Several sentences have been rewritten on Page 7 in the revised manuscript. “Figures 1d and\nS6-S8 illustrate the set-up of the furnace and the growth process of RTF method and\ntraditional CVD method (see details in Experimental Section and Supporting Information).”\n Several sentences have been added on Page 20 in the revised manuscript. “Synthesis of 2D\nTMNs and their alloys: the 2D TMNs and their alloys were fabricated using the RTF\nmethod. The typical fabrication process was carried out in a movable furnace, as shown in\nFigure S6. The precursors were placed in a quartz boat located in the upstream region of\nthe quartz tube (Field I), and the mica substrates were positioned in the downstream region\n(Field II). Argon (100 sccm) was used as the carrier gas throughout the process. The growth\ninvolved two distinct steps: Step 1 involved the deposition of the 2D TMCl templates. In\nthis step, Field I (precursor zone) was moved to the heating center and heated to the target\ntemperature (600-800 ℃) from room temperature in 30 minutes and maintained for 2\nminutes. During this step, Field II (substrate zone), situated approximately 10 cm away\nfrom the heating center, remained at a lower temperature (100-200 ℃). At the end of Step\n1, the furnace was swiftly translated along the rail to position Field II (substrate zone) at\nthe heating center, initiating Step 2 (the conversion step). Simultaneously with this\nmovement, a mixture of NH and H was introduced and maintained for 10 minutes.\n3 2\nConsequently, the temperature of Field II rapidly increased to 600-800 ℃ and was held for\n5 minutes, while Field I cooled down to approximately 100-200 ℃. Finally, the furnace\nwas cooled to room temperature under an Ar atmosphere.”\nComment 5. The English writing should be further polished. For example, in Abstract, “15\ntypes of 2D TMNs and their alloys…” can be changed to “Fifteen types of 2D TMNs and their\nalloys…” for clarity. Figure 2 caption, “Number of Metal Elements”, the letter M and E may\nnot be capitalized. Please keep consistent with other places throughout the manuscript. The\nauthors should polish these details before publication.\nResponse 5. We sincerely thank the reviewer for this meticulous feedback on language and\nformatting. We have carefully polished the English throughout the entire manuscript.\ncapitalization in the Figure 2 caption has been corrected to “Number of metal elements” for\nconsistency. We have conducted a thorough proofreading to ensure uniformity in terminology,\ncapitalization, and overall language quality.\nFigure R10. Universal growth of 2D TMNs and their alloys by the RTF method. (a) The\nperiodic table of elements shows the transition metal elements involved in this work. (b) Optical\nmicroscopy images of the 15 types of 2D TMNs and alloys. All the scale bars are 5 μm. The\nmaterials have one, two, three, and four types of metal elements are highlighted in yellow, pink,\ngreen, and blue, respectively.\nChanges to the manuscript.\n Figure R10 has been added as Figure 2 in the revised manuscript to replace the original\nFigure 2.\n The sentence on Page 2 has been rewritten. “Fifteen types of 2D TMNs and their alloys\n13\nwere synthesized, demonstrating the versatility of this method.”\n The sentence on Page 18 has been rewritten. “In this work, we developed a reverse-thermal\nfield CVD method to convert 2D TMCl and obtained fifteen types of non-layered 2D TMNs\nand their alloys.”\nComment. This work reports a novel and universal synthesis method, reverse-thermal-field\n(RTF) CVD strategy, for growing a wide range of non-layered 2D TMNs and their alloys. The\nkey innovation is the use of metastable, layered TMCls as transient templates, which are first\ngrown at a low-temperature zone and then rapidly converted into TMNs by quickly moving to\na high-temperature zone in the presence of ammonia. The authors successfully demonstrate the\ngrowth of 15 different 2D TMNs (7 mono-metal nitrides and 8 alloys) and show that their\nmagnetic properties (e.g., saturation magnetization, coercive field) can be effectively tuned\nthrough composition. In general, this work is interesting and has good novelty. I can\nrecommend the publication after addressing the following concerns:\nResponse. Thanks very much to the reviewer for your careful reading and positive\nrecommendations. We appreciate the reviewer for the comments that “novel and universal\nsynthesis method” and “interesting and has good novelty”. And according to the suggestions,\nwe have made extensive revisions to improve the quality of our manuscript.\nComment 1. The claimed mechanism is the “solid-to-solid” conversion of a 2D TMCl template.\nHowever, it is important to provide direct evidence that the layered structure of the initial TMCl\nflake is converted to TMN during the rapid heating step and acts as a true template, other than\nthe direct deposition of TMN under the environment of precursor gas, NH , and H . Therefore,\n3 2\nproviding an optical image of TMCl flakes after step 1 (30 min heating + 2 waiting time) and\nbefore step 2 is necessary. Alternatively, it is also acceptable to perform the TEM\ncharacterization of the intermediate flakes during step 2, that should contain both Cl and N\natoms.\nResponse 1. We sincerely thank the reviewer for this valuable suggestion, which is crucial for\nvalidating the “solid-to-solid” conversion mechanism. Regarding TEM characterization, we\nhave tried multiple times to transfer the “transient” TMCl templates to TEM grids for TEM\ncharacterization, but failed. We found that these transient templates are not stable and disappear\nrapidly at ambient conditions (< 1 min).\nexperiments using a visualization CVD system. Such a setup allows us in-situ monitor of the\nthrough a viewport by optical microscopy. In this setup (Figure R12a), the precursor is located\nin zone A and the substrate in zone B and Figure R11 illustrates the temperature profiles of\nzone A and zone B. As shown in Figure R12b, the TMCl template is first deposited on the\nsubstrate when zone A is heated above the precursor sublimation temperature. Subsequently,\nwe captured the intermediate state during the transition to step 2. When NH is not introduced\n3\n(Figure R12c, Figure R13), the TMCl template sublimes away quickly due to the high\ntemperature, leaving no solid product. In contrast, when NH is introduced (Figure R12d), the\nobservation provides compelling evidence that the conversion is indeed a solid-to-solid\nprocess, rather than a direct deposition from the gas phase.\nprofile of zone A, where the precursor located. (b) The temperature profile of zone B, where\nthe substrate located.\nvisualization two-zone CVD technique. (b) The OM images captured at zone B during step 1,\ndemonstrating the deposition of CoCl . (c) The OM images captured at zone B during the\n2\nintermediate state and step 2 without the introduction of NH , showing sublimation. (d) The\nNH , showing in-situ conversion to CoN. (e) The high-resolution OM image of the growth\n3\nresults without the introduction of NH . (f) The high-resolution OM image of the growth results\n3\nwith the introduction of NH .\n A new figure reproduced from Figure R12 has been added as Figure S3 in the revised SI\n Several sentences have been added on Page 6. “Indeed, Figure S2 shows the optical\nmicroscopy (OM) images of a 2D TMCl flake exposed in air for 10 s, 20 s, 30 s, 40 s, and\n50 s, and Figure S3 shows the OM images of deposited TMCl heated at 650 ℃ in an Ar\natmosphere. The quick fading of the flake demonstrates its poor stability.”\ninto the rectangular-shaped TMNs. If it is a solid-to-solid transition, the metal atoms need to\nmove freely on the mica substrate, and an intermediate shape between the triangle (or hexagon)\nand rectangle can be captured if step 2 is stopped at around 2.5 min.\nResponse 2. We thank the reviewer for this insightful question. (1) The key clarification is that\nthe final morphology of the TMN is not transformed from a different initial shape, but is directly\ninherited from the specific morphology of the transient TMCl template formed during step 1.\n(2) Taking nickel chloride as an example, as shown in Figure R13, at a step 1 temperature of\n650 °C, a triangular shape template forms, leading to triangular h-NiN. Conversely, at a higher\nstep 1 temperature of 800 °C, a rectangular shape template is obtained, which subsequently\nconverts into rectangular r-NiN. Therefore, the rectangular morphology originates from a\nrectangular precursor template, not from a restructuring of a triangular one.\nFigure R13. OM images of 2D nickel chloride templates obtained at different growth\ntemperatures. (a) OM image of a triangular/hexagonal shape 2D template when the growth\ntemperature is 650 ℃. (b) OM image of a rectangular shape 2D template when the growth\ntemperature is 800 ℃. These images are\nChanges to the manuscript.\n Figure R13 has been added as Figure S13 in the revised SI\n Several sentences have been added on Page 10. “Note that MnN, r-NiN, and r-Co Ni N\nx y\nshow rectangular morphology, which is decided by the morphology of the template. For\ninstance, as shown in Figure S13, 2D NiN exhibits a triangular morphology when\nsynthesized at 650 °C, which corresponds to the triangular shape of the 2D template formed\nat that temperature. Conversely, when the step 1 temperature is increased to 800 ℃, a\n19\nrectangular shape 2D template forms, resulting in rectangular 2D NiN flakes.”\nComment 3. It would be beneficial to include references for the sentence in lines 66-69.\nWe thank the reviewer for the suggestion, and the related reference (Nat. Commun. 16, 1623\n(2025); CRC Handbook of Chemistry and Physics. 98th edn, (CRC Press, 2017).) has been\nadded in the manuscript.\nChanges to the manuscript.\n The sentence on Page 4 has been rewritten and two new references have been added in the\nrevised manuscript “Transition metal chlorides (TMCls) are therefore a potential choice\ndue to their low conversion energy, while their high-temperature instability caused by their\nlow sublimation temperature makes this process practically difficult.36,37”\nComment 4. In Fig. 5a-f, the thicknesses are not directly displayed; line cuts are necessary.\nResponse 4. We thank the reviewer for this suggestion. We have updated Figure 5 (now Figure\nR14 in the response) to include AFM height profiles (line cuts) for each of the TMN flakes\nshown in panels (a)-(f), directly displaying their thicknesses.\nFigure R14. Magnetism of 2D TMNs and their alloys. (a)-(f) Atomic force microscopy and\nMFM images of individual (a)2D VN, (b) 2D CrN, (c) 2D MnN, (d) 2D Fe N, (e) 2D CoN, and\n2\n(f) 2D NiN flakes measured at 300 K. The scale bar is 2 μm.\nChanges to the manuscript.\n Figure R14 has been reproduced as Figures 5a-5f in the revised manuscript to replace the\noriginal Figures 5a-5f.\nComment. The authors report a universal reverse-thermal-field CVD strategy for synthesizing\ntwo-dimensional transition metal nitrides (TMNs). In this approach, metastable metal chloride\ncrystal templates are first deposited on mica substrates and then converted to TMNs by high-\ntemperature nitridation, before the chloride templates are lost. Using this method, the authors\ndemonstrate the growth of VN, CrN, MnN, Fe₂N, CoN, NiN, and their alloys. Structural and\ncompositional characterizations (TEM, EDS, AFM) are presented, while magnetic properties\nare probed by MFM and SQUID. Overall, the technique represents a potentially viable route\ntoward 2D TMNs and is therefore an important contribution to the 2D materials community.\nHowever, additional details and clarifications are needed:\nResponse. Thank you very much for your positive recommendations. We appreciate the\nreviewer by writing “universal”, “a potentially viable route” and “an important contribution to\nthe 2D materials community”. Additional details and clarifications according to the reviewer\nhave been added to the manuscript to strengthen our work.\nComment 1. A more detailed parametric study of the different materials should be conducted.\nFor example, how was the temperature for Field 1 and 2 selected? Was any optimization\nperformed in selecting these values? Can the crystal quality/defect density of the as-grown\nTMN be quantified? Such as using Raman peak width/position, and corroborated with\nXRD/XPS if feasible.\nResponse 1. We thank the reviewer for these important questions. (1) Regarding temperature\nselection for Field I and II. Taking CoN as an example, the operating high temperatures for\nFields I and II (600-800 ℃) were selected based on two key criteria derived from Figure R15\n(Figure S4 in SI): (i) The thermogravimetric analysis (TGA) curves indicate that these\ntemperatures are sufficient for the sublimation and deposition of the TMCl precursors to form\n2D templates. (ii) The calculated Gibbs free energy (Figure R15b) confirms that the solid-to-\nsolid conversion from TMCl to TMN becomes thermodynamically favorable within this\ntemperature range. Further evolution of the growth results of 2D CoN under different growth\ntemperatures was shown in Figure R16, which shows that when the temperature of Field II was\n21\n600 ℃, some solid-state 2D CoN can be fabricated, while some products showed irregular\nshape, demonstrating that the conversion rate of deposited CoCl might be similar to their\n2\nsublimation rate, leading to incomplete conversion. Conversely, by increasing the temperature\nof the Field II to 750 ℃, almost all the products showed regular triangular/hexagonal shape,\nwhich indicates that the conversion rate of deposited CoCl was much greater than their\n2\nsublimation rate at this temperature for completely solid-to-solid conversion.\n(2) Regarding quantifying defect density in these nonlayered 2D materials. As metallic,\nnon-layered materials with thicknesses typically between 10-20 nm and limited substrate\ncoverage, conventional techniques like Raman spectroscopy (no characteristic peaks for metals),\nXRD, and XPS are ineffective due to the unavoidable substrate effect. Alternatively, we\nconducted HRTEM and EDS to study their structure and composition, to qualitatively reveal\ntheir crystal quality. The clear HRTEM images and SAED patterns of all the 2D TMNs and\ntheir alloys (inserts in Figures 17b, 17f, 17j, 18a, 18d and 18g) shown in the manuscript\ndemonstrate their high crystallinity. As shown in Figures 18b, 18f and 18h, the metal elements\nare uniformly distributed among the flakes, demonstrating the element uniformity in the 2D\nTMN alloys.\nFigure R15. Physical and chemical properties of transition metal chlorides. (a) TGA curves\nof the VCl , CrCl , CoCl , FeCl , MnCl and NiCl . (b) The Gibbs energy barrier of the solid-\n3 3 2 3 2 2\nto-solid conversion from transition metal chlorides to their corresponding nitrides at different\ntemperatures.\nFigure R17. Structural and composition characterization of 2D TMNs. (a) Top-view atomic\nstructure of Fe N. (b) HRTEM image and SAED pattern (inset) of the synthesized 2D Fe N\n2 2\nflake. (c) Low magnification TEM image, EDS element mapping of Fe and N atoms, and (d)\nEDS of the 2D Fe N flake. (e) Atomic structure of VN from the top view. (f) HRTEM image of\n2\nthe synthesized 2D VN flake. The inset is the corresponding SAED pattern. (g) Low\nmagnification TEM image, elemental EDS mapping of V and N atoms, and (h) EDS of the 2D\nVN flake. (i) Atomic structure of MnN from the top view. (j) HRTEM image of the synthesized\n23\n2D MnN flake. The inset is the corresponding SAED pattern. (k) Low magnification TEM\nimage, elemental EDS mapping of Mn and N atoms, and (l) EDS of the 2D MnN flake.\nFigure R18. Structural and composition characterizations of 2D TMN alloys. (a) HRTEM\nimage and SAED pattern of the synthesized 2D Co Ni N flake. (b) Low magnification TEM\n0.6 0.4\nimage, elemental EDS mapping of Co, Ni, and N atoms, and (c) EDS of the 2D Co Ni N\n0.6 0.4\nflake. (d) HRTEM image and SAED pattern of the synthesized 2D Co Fe N flake. (e) Low\n0.3 0.7\nmagnification TEM image, elemental EDS mapping of Co, Fe and N atoms, and (f) EDS of the\nHRTEM image and SAED pattern of the synthesized 2D Co Fe N flake. (g) HRTEM image\n0.3 0.7\nand SAED pattern of the 2D Co Ni Fe N flake. (h) Elemental EDS mapping of Co, Ni, Fe\n0.2 0.1 0.7\nand N atoms and (i) EDS of the 2D Co Ni Fe N flake.\n0.2 0.1 0.7\nto systematically control layer thickness, nucleation density, and flake size? Since the authors\ndescribe these TMNs as 2D materials, please report the thickness statistics, which should\ntypically be in the range of a few nm. Further optimization would be necessary to probe genuine\n2D characteristics rather than bulk-like properties.\nResponse 2. We thank the reviewer for this comment. Regarding the question that whether the\nCVD parameters can control the growth results, we conducted a systematic study and found\nthat the growth temperature and growth time control the lateral size and thickness of the flakes.\nTaking CoN as an example, we performed a detailed study on the effects of growth\ntemperature and growth time during step 1 (Figures R17 and R18). The thicknesses of the flakes\nwas obtained from the AFM characterization, and the lateral size of the flakes were measured\nby the OM characterization. To better study the relationship between the growth\ntemperature/time with the thickness/lateral size, we statistically analyzed more than 500 flakes\ngrown under different growth conditions. As a result, (1) Both growth temperature and growth\ntime exhibit a volcano-shaped relationship with the lateral size of the resulting 2D CoN flakes.\nUnder the optimized conditions (a growth temperature of 750 ℃ and a growth time of 5\nminutes), we have achieved 2D CoN flakes with an average lateral size of several tens of\nmicrometers, with the largest flake reaching 51 μm (Figure R19). (2) By increasing the growth\ntemperature and growth time, the thicknesses of the 2D CoN will increase. Under the optimized\nconditions (a growth temperature of 600 ℃ and a growth time of 2 minutes), we have achieved\n2D CoN flakes with an average thickness of about 10 nm, with the thinnest flake of 1.03 nm\n(Figure R20).\nOM images of CoN with increased temperature from 600 ℃ to 800 ℃, and all the growth time\nwere 5 min. (b) The thicknesses of CoN under different growth temperatures. The thickness\nwas obtained by AFM measurements of 249 flakes. (c) The lateral sizes of CoN under different\ngrowth temperature. The lateral size was obtained by OM characterization.\nimages of CoN with increased growth time from 2 min to 20 min, and all the growth\ntemperatures were 650 ℃. (b) The thicknesses of CoN with different growth time. The\nthickness was obtained by AFM measurements of 293 flakes. (c) The lateral sizes of CoN with\ndifferent growth time. The lateral size was obtained by OM characterization.\nFigure R22. The AFM image of the 2D CoN with the thickness of 1.03 nm.\nChanges to the manuscript.\n Figure R19, Figure R20, Figure R21 and Figure R22 have been added as Figure S10, Figure\nS11, Figure S12a and Figure S12b in the revised SI.\n Several sentences have been added on Page 10. “Taking CoN as an example, the lateral\nsize and thickness of the 2D flakes are determined by the growth temperature and duration\nof step 1 (Figure S10 and S11). The lateral size exhibits a volcano-like relationship with\nboth increasing temperature and time, whereas the thickness generally increases. The\nlargest CoN flake obtained thus far has a lateral size of 51 μm (Figure S12a), achieved at a\ngrowth temperature of 750 ℃ with a 5-minute growth time, while the thinnest flakes (~1.03\nnm, Figure S12b) are obtained at 600 ℃ with a 2-minute growth time.”\nheating/cooling transition from 100-200 °C up to 600-800 °C? This is important for researchers\nto replicate the method.\nResponse 3. We thank the reviewer for emphasizing the importance of this detail. We have\nprovided a photograph of the setup (Figure R23) and the detailed time-temperature profile\n(Figure R24). The key to the RTF process is the physical translation of the furnace on a sliding\nrail, which switches the thermal environments of Field I and Field II within several seconds.\nThis rapid transition is crucial as it instantly brings the substrate (and the TMCl template on it)\nto the high nitridation temperature, preventing the sublimation and enabling the solid-state\nconversion. The detailed process has been illustrated in the Experimental Section in the\nrevised manuscript, as shown below for researchers to replicate the method.\nFigure R23. Photo of the setup used to achieve RTF process.\nof the Field Ⅰ, where the precursor located. (b) Temperature of the Field Ⅱ, where the substrate\nlocated.\nChanges to the manuscript.\n Figure R23and Figure R24 have been added as Figure S6 and Figure S8 in the revised SI.\n Several sentences have been rewritten on Page 7 in the revised manuscript. “Figures 1d and\nS6-S8 illustrate the setup of the furnace and the growth process of RTF method and\ntraditional CVD method (see details in Experimental Section and Supporting Information).”\n Several sentences have been added on Pages 19 and 20 in the revised manuscript.\n“Synthesis of 2D TMNs and their alloys: the 2D TMNs and their alloys were fabricated\nusing the RTF method. The typical fabrication process was carried out in a movable furnace,\nas shown in Figure S6. The precursors were placed in a quartz boat located in the upstream\nregion of the quartz tube (Field I), and the mica substrates were positioned in the\ndownstream region (Field II). Argon (100 sccm) was used as the carrier gas throughout the\nprocess. The growth involved two distinct steps: Step 1 involved the deposition of the 2D\nTMCl templates. In this step, Field I (precursor zone) was moved to the heating center and\n30\nheated to the target temperature (600-800 °C) from room temperature in 30 minutes and\nmaintained for 2 minutes. During this step, Field II (substrate zone), situated approximately\n10 cm away from the heating center, remained at a lower temperature (100-200 °C). At the\nend of Step 1, the furnace was swiftly translated along the rail to position Field II (substrate\nzone) at the heating center, initiating Step 2 (the conversion step). Simultaneously with this\nmovement, a mixture of NH and H was introduced and maintained for 10 minutes.\n3 2\nConsequently, the temperature of Field II rapidly increased to 600-800 °C and was held\nfor 5 minutes, while Field I cooled down to approximately 100-200 °C. Finally, the furnace\nwas cooled to room temperature under an Ar atmosphere.”\nComment 4. For the alloyed TMNs, are the metal elements randomly incorporated in a single\nphase, or is there any short-range ordering/phase segregation? Can the elemental composition\nbe tuned by adjusting precursor ratios?\nResponse 4. We thank the reviewer for these questions. (1) For the elemental distribution: EDS\nmapping (e.g., Figure R25 for Co Ni N) consistently shows a homogeneous distribution of\n0.6 0.4\nthe different metal elements at the nanometer scale, indicating the formation of a uniform alloy\nwithout macroscopic phase segregation. (2) As for the composition tuning: The composition of\nthe alloy is influenced by the relative partial pressures of the different MCl species during step\nx\n1, which is in turn related to the precursor ratios. Taking the Co Ni N as an example (Figures\nx y\nR25 and R26), when the weight ratio of CoCl : NiCl precursor is about 0 : 1, the product is\n2 2\npure 2D CoN; when the weight ratio of CoCl : NiCl precursor is about 1 : 1 the weight ratio\n2 2\nof Co and Ni in the alloys is about 0.6 : 0.4; and when the CoCl : NiCl precursor is about 1 :\n2 2\n0, the product is pure 2D NiN. These results demonstrate that adjusting the weight ratio of the\nprecursor can be used to further tune the element composition, which will be our future work.\n0.6 i0.4\nand SAED pattern of the synthesized 2D Co Ni N flake. (b) Low magnification TEM image,\n0.6 0.4\nelemental EDS mapping of Co, Ni, and N atoms, and (c) EDS of the 2D Co Ni N flake.\n0.6 0.4\nCoCl : NiCl and OM images of products with different precursors.\n2 2\nComment 5. The AFM and MFM images of the alloyed TMN, along with the corresponding\nthickness measurements, should be included in Figure 5. Does the magnetic property change\nwith thickness?\nResponse 5. We thank the reviewer for this suggestion. (1) We have provided the corresponding\nthickness measurements in Figure 5 (Figure R27). (2) Regarding the relationship between the\nmagnetic property and the thickness, we take the CoN as an example and conduct MFM\ncharacterization to reveal its magnetic behavior with different thicknesses. As shown in Figure\nR28, the MFM contrast of 2D CoN changes with thickness, indicating an evolution in magnetic\nproperties from weak signals to strong signals with the increased thickness. Therefore, to ensure\na comparison of intrinsic material properties in the main text, the SQUID measurements in\nFigure R25 (g-i) were performed on flakes with comparable thicknesses (~20 nm).\nMFM images of individual (a)2D VN, (b) 2D CrN, (c) 2D MnN, (d) 2D Fe N, (e) 2D CoN, and\n2\n(f) 2D NiN flakes measured at 300 K. The scale bar is 2 μm. (g) M-H loops of the 2D TMNs\nand (h) their alloys with the magnetic field applied out of plane. The results are measured by\nSQUID at 10 K. The effect of mica substrate has been eliminated (Figure S19). (i) Statistics of\nH , M and Curie temperature (T )/Neel temperature (T ) of the 2D TMNs and their alloys in\nC s C N\n(g) and (h). The T /T of each material is obtained from the M-T curves shown in Figure S20\nC N\nand Figure S21. The materials with one, two, three and four types of metal elements are\nhighlighted in yellow, pink, green and blue, respectively. And increasing H drives the\nC\ntransition from soft to hard magnetic materials.\ncorresponding MFM images of 2D CoN flakes with thicknesses of 14.7 nm, 26.3 nm, 30.3 nm\nand 50.7 nm.\nChanges to the manuscript.\n Figure R27 has been reproduced as Figure 5 in the revised manuscript to replace the\noriginal Figure 5."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have revised the manuscript well, I recommend to accept it for publication.", "reviewer_2": "All of my comments have been thoroughly addressed. Therefore, I recommend the publication.", "reviewer_3": "The authors have addressed all the raised concerns. I find the revised manuscript suitable for publication and recommend acceptance."}, "author_response": ""}]

Decision letter