Chemical vapor deposition growth of continuous monolayer antiferromagnetic CrOCl films

Domain: physics
Published: 2025-12-17
Editorial outcome: minor_revision

Abstract
The discovery of two-dimensional magnetic materials has provided an ideal platform for exploring physical phenomena in the two-dimensional limit. However, intrinsic two-dimensional antiferromagnetic materials have been rarely reported, limiting systematic studies of their electronic properties. The discovery of novel intrinsic two-dimensional antiferromagnets and the development of robust synthesis strategies, therefore, remain significant challenges. Here, we report the chemical vapor deposition synthesis of CrOCl monolayer films and nanosheets that exhibit excellent air stability. The CrOCl morphology is tunable, ranging from two-dimensional nanosheets to three-dimensional flower-like structures, with lateral sizes ranging from several microns to continuous monolayer films. Structural characterization confirms the material’s composition and high crystalline quality. Furthermore, magnetic measurements, supported by theoretical calculations, reveal a Néel temperature for CrOCl of ≈14 K. This work provides a reliable route for preparing two-dimensional antiferromagnetic materials.

Introduction
Two-dimensional (2D) magnetic materials have recently become a focus of intense research, driven by their intriguing magnetic properties and potential applications in next-generation electronics and optoelectronics1–5. For example, CrI3 and Cr2Ge2Te6 nanosheets exhibit layer-correlated ferromagnetism at low temperatures6,7. Chemical vapor deposition (CVD)-grown Cr5Te8 exhibits a high Curie temperature, excellent ferromagnetic properties, and a colossal anomalous Hall effect8–11. Furthermore, CrCl3 is an A-type antiferromagnet with in-plane magnetic anisotropy12–14. Similarly, the magnetic order and anisotropy of related chromium trihalides, such as CrBr3 and CrI3, can be tuned by strain and doping15–18, making them a versatile platform for studying magnetic quantum phase transitions and designing novel spintronic devices. Additionally, interactions between graphene and antiferromagnetic materials can open a band gap at the Dirac point of graphene and induce phenomena such as the quantum anomalous Hall effect19,20 and the magnetic proximity effect21,22.

Although researchers have made great progress in growing thin films of 2D van der Waals materials and 2D magnets, achieving the monolayer limit remains challenging. For instance, rapid, scalable synthesis of epitaxially aligned ferromagnetic ternary metal chalcogenide (Cr2Ge2Te6, Cr2Si2Te6, MnSi2Te6) thin films has been reported23. Monolayer and few-layer Cr5Te8 ultrathin films have been synthesized on bilayer graphene by molecular beam epitaxy24. However, films obtained by this method are typically several layers thick, greatly hindering the exploration of intrinsic 2D magnetic properties and device applications. CrOCl, an important member of the MOX (M=Sc, Ti, V, Cr, Mn, Fe, Ni, Bi; X=F, Cl, Br) family, is a recently discovered, structurally anisotropic stable 2D ternary compound25–28, with a Néel temperature of 13.6 K29, making it a promising antiferromagnet. Previous studies of CrOCl and its heterostructures have relied mainly on mechanical exfoliation30–34 and chemical vapor transport29,35. These methods are complex, time-consuming, unsuited to large-scale production, and cannot guarantee repeatable and consistent sample preparation. In addition, mechanical stacking can degrade crystal quality or leave chemical residue contamination, resulting in weak interfacial coupling3. Although CVD-grown CrOCl nanosheets have been demonstrated recently, their thickness and lateral dimensions remain limited28. The controllable synthesis of 2D CrOCl monolayer films is therefore of fundamental and technological importance, but to date it has been explored only theoretically36 and has not yet been realized at a large scale. CVD offers simplicity, high throughput, wafer-scale uniformity, high crystal quality, and is readily scalable37–42, making it an attractive route to high-quality 2D CrOCl.

In this work, we synthesize high-quality continuous antiferromagnetic CrOCl monolayer films and nanosheets using a CVD method featuring rapid heating and cooling, achieved by moving the furnace, which is crucial for the growth of the CrOCl monolayer films. By adjusting the growth temperature (500–800 °C) and time (1–15 min), the thickness and size of CrOCl samples can be precisely controlled, and the morphology of CrOCl shows a clear transition from 2D nanosheets to three-dimensional (3D) flower-like structures. Notably, a continuous CrOCl monolayer film is obtained at 600 °C with a growth of 5 min. Annular dark-field aberration-corrected scanning transmission electron microscopy (ADF-STEM) images confirm the high crystalline quality of the as-grown CrOCl samples, demonstrating a structure consistent with the theoretical simulations. Angle-resolved polarized Raman spectroscopy (ARPRS) and temperature-dependent Raman scattering reveal the structural anisotropy and phase transition behavior of the 2D CrOCl nanosheets. Magnetic measurements, performed using a superconducting quantum interference device (SQUID), show a clear transition in the magnetic susceptibility of CrOCl at 13.9 K. The hysteresis loop of CrOCl gradually diminishes from 3 K to 14 K and eventually disappears, indicating the Néel temperature of CrOCl is approximately 14 K. These experimental findings are supported by density functional theory (DFT) calculations, which predict an antiferromagnetic ground state with a Néel temperature of 13.6 K. Finally, aging experiments on CrOCl nanosheets in an ambient atmosphere demonstrate their excellent environmental stability.

Results
Structure and synthesis strategy for 2D CrOCl nanosheets.
To achieve controlled preparation of continuous CrOCl monolayer films and 2D CrOCl nanosheets with high crystallinity, we used the CVD growth method (Fig. 1a). In this approach, naturally oxidized CrCl3 powder served as the sole source of Cr and O throughout the growth process, thereby simplifying process control and reducing impurities relative to protocols that introduce additional O sources. Importantly, our method exhibits excellent reproducibility and yield in growing CrOCl monolayer films and nanosheets (see “Methods” for details). CrOCl adopts an orthorhombic layered structure in the D2h (Pmmn) space group, with the Cr–O bilayers sandwiched between two Cl layers stacked along the c-axis (Supplementary Fig. 1). Fig. 1b shows a typical optical-microscopy (OM) image of the as-grown CrOCl monolayer film transferred onto a 300-nm-thick SiO2/Si substrate. The flat, continuous film uniformly covers the substrate surface, extending over several hundred microns. Notably, growth time critically determines the film thickness and lateral dimensions of CrOCl, particularly during the formation of monolayer films (Supplementary Fig. 2).

When the growth time was increased from 1 to 5 min, isolated CrOCl monolayer domains gradually expanded and coalesced, forming a continuous monolayer film that uniformly covered the substrate (Supplementary Fig. 2a–c). Subsequently, thicker CrOCl nanosheets nucleated on the underlying monolayer and evolved into 3D flower-like CrOCl structures as the growth time was extended from 8 to 15 min (Supplementary Fig. 2d–f). To demonstrate the reproducibility, ten growth runs (Supplementary Fig. 3) carried out under optimal conditions (600 °C, 5 min) yielded continuous monolayer films with >90% repeatability. Fig. 1c shows a representative optical microscopic (OM) image of CrOCl nanosheets grown on mica, which display a rhombic morphology and a monolayer thickness of 1.2 nm (inset in Fig. 1c). The as-grown nanosheets can also be readily transferred onto a 300-nm-thick SiO2/Si substrate (Fig. 1d), facilitating subsequent characterization. CrOCl grown on c-cut sapphire or SiO2/Si likewise exhibits a 3D flower-like morphology (Supplementary Fig. 4). We attribute this morphology to the number of dangling bonds on these substrates (Supplementary Fig. 5d–f); in contrast, the atomically flat surface of mica (Supplementary Fig. 5a–c) is more favorable for the epitaxial growth of 2D CrOCl nanosheets. The atomic force microscopy (AFM) images of CrOCl samples transferred to SiO2/Si (Supplementary Fig. 6) demonstrate a thickness of 1.5 nm, slightly larger than 1.2 nm measured on mica, further supporting the presence of dangling bonds on SiO2.

Growth temperature also strongly influences the morphology, thickness, and lateral dimensions of CrOCl. With increasing temperature, the material evolves from 2D shuttle-shaped domains to 2D rhombic flakes and finally to 3D flower-like shapes, accompanied by pronounced lateral growth (Supplementary Fig. 7). AFM measurements (Supplementary Fig. 8) confirm the corresponding thicknesses of nanosheets grown at 550–650 °C. Because the optical signal of a monolayer is strongly substrate-dependent on mica and SiO2/Si substrates, subsequent analyses focus on few- to thick-layer CrOCl to facilitate interpretation.

Next, the Raman spectra for CVD-grown CrOCl nanosheets of four different thicknesses are presented in Fig. 1e. Three major peaks appear at 207, 414, and 457 cm−1, corresponding to Ag1, Ag2, and Ag3 vibrational modes. As the nanosheet thickness increases, the intensity of each peak steadily increases. Calculated Ag-mode frequencies differences for monolayer and bulk CrOCl match experiment within 4% (Supplementary Fig. 9). X-ray diffraction (XRD) (Fig. 1f) shows prominent reflections at 11.3°, 34.7°, 46.9°, and 59.6°, indexed to the (001), (003), (200), and (021) planes in agreement with the standard pattern (PDF#28-0371)29. The pronounced (001) reflection indicates preferred growth along the [001] direction. X-ray photoelectron spectroscopy (XPS) (Fig. 1g–j) further confirms the bonding environment and composition of the nanosheets. The XPS survey spectrum (Fig. 1g) reveals Cr, O, and Cl species originating from the nanosheets. High-resolution spectra show Cr 2p3/2 and Cr 2p1/2 peaks (Fig. 1h) at 577.7 and 587.3 eV and an O 1s peak at 531.5 eV, respectively (Fig. 1i). Cl 2p3/2 and Cl 2p1/2 peaks appear at 201.4 and 199.8 eV, respectively (Fig. 1j). Collectively, these data demonstrate that the CVD-grown CrOCl nanosheets possess high crystalline quality, stoichiometric composition, and scalable synthesis, providing a robust platform for subsequent studies.

Compositional and structural characterization of CrOCl nanosheets
To further evaluate the crystal microstructure of CVD-grown CrOCl nanosheets, energy-dispersive X-ray spectroscopy (EDS) and annular dark-field aberration-corrected scanning transmission electron microscopy (ADF-STEM) analyses were performed. From the EDS mapping in Fig. 2a–e, the Cr, O, and Cl signals are uniformly distributed across the sample. The EDS spectrum also confirms the atomic ratio of Cr:O:Cl ≈ 1:1:1 (Fig. 2f). Fig. 2g displays a typical atomic resolution ADF-STEM image of a CrOCl nanosheet, revealing a uniform atomic arrangement with no local discontinuities or defects, thereby demonstrating its high crystal quality. In ADF-STEM mode, the intensity of a nuclear column is approximately proportional to Z2 (where Z is the atomic number), resulting in brighter contrast for Cr columns than for Cl/O columns43. We also observe lattice spacings of 0.158 nm for the (020) plane and 0.196 nm for the (200) plane, indicating a highly ordered periodic atomic arrangement. Bulk CrOCl crystallizes in the orthorhombic space group Pmmn (No. 59), in which each Cr column alternates vertically with overlapping Cl/O columns, as illustrated in the structural model (Fig. 2h). A comparable result is obtained for the CrOCl monolayer film (Supplementary Fig. 10), further verifying its high crystal quality. To more precisely elucidate the composition and phase of as-grown nanosheets, we combined quantitative STEM with selected area electron diffraction (SAED) and corresponding structural simulation. Comparing the experimental STEM image (Fig. 2i) with the simulated STEM image (Fig. 2j) shows that the intensities and positions of the Cr, O, and Cl columns coincide. Similarly, SAED patterns from experiment (Fig. 2k) and simulation (Fig. 2l) display an identical single set of quadrilateral diffraction spots, confirming that the nanosheets are single crystals with an orthorhombic structure. Together with the XRD and XPS results, these findings demonstrate that the CVD-grown CrOCl nanosheets possess well-defined composition and crystal structure.

Orientation distribution and anisotropy of 2D CrOCl
It is well established that the lattice orientation of 2D materials is strongly dependent on the growth substrate44,45. According to previous work, the mica substrate possesses a six-fold symmetrical structure (Fig. 3a)46, which guides the oriented growth of 2D materials. Fig. 3b displays an OM image of CVD-grown CrOCl nanosheets on mica. As expected, the CrOCl nanosheets are preferentially oriented at three principal angles (0°, 120°, −120°), as confirmed by the statistical results in Fig. 3c. Another notable factor is that the vdW interaction between CrOCl and mica substrate plays a critical role in the growth process. The crystal orientation and anisotropy of 2D CrOCl were investigated using angle-resolved polarization Raman spectroscopy (ARPRS). Fig. 3d shows an OM image of a CrOCl nanosheet used for ARPRS measurements. The results demonstrate pronounced intensity differences among the three Raman modes (Ag1, Ag2, and Ag3) of CrOCl nanosheets under parallel (XX) and perpendicular (XY) configurations (Fig. 3e). All three modes show periodic variations from 0° to 180° (Supplementary Fig. 11). In the XX configuration, the Ag1, Ag2, and Ag3 modes exhibit two-fold symmetry with a 180° period (Fig. 3f–h). In this configuration, Ag1 and Ag3 reach maxima at 60° and 240°, while Ag2 mode shows maxima at 150° and 330°. This behavior may reflect phonon-induced modulation of electronic states. The x-polarized photon-electron interaction appears to be dominated by Ag2, whereas Ag1 and Ag3 couple more strongly under y-polarization29. In the XY configuration, all Ag modes display four-fold symmetry with a 90° period, peaking at 15°, 105°, 195°, and 285° (Fig. 3i–k). These findings reveal a close correlation between the crystal orientation of CrOCl and its Raman response.

Temperature-dependent Raman properties of 2D CrOCl nanosheets
To further explore the phase transition behavior of 2D CrOCl nanosheets, we performed temperature-dependent Raman scattering measurements on samples supported by a 300-nm-thick SiO2/Si substrate. Fig. 4a shows three distinct peaks at ~207, 414, and 457 cm−1, corresponding to Ag1, Ag2, and Ag3 modes, respectively, that persist throughout 8.3–300 K. When the temperature is lowered from 300 K to 8.3 K, all three peaks exhibit a blue shift, more clearly visible in their magnified spectra (Supplementary Fig. 12a–c). To clarify the evolution of peak intensity, we plotted Raman spectra from 8.3 K to 300 K using a common baseline (Fig. 4b) and extracted the temperature dependence of the Ag1, Ag2, and Ag3 intensities (Fig. 4c–e). Above 27 K, the intensity first increases and then decreases, whereas below 27 K it remains nearly constant. The temperature dependence of the corresponding frequency shifts likewise and shows a pronounced inflection near 27 K (Supplementary Fig. 12d–f). Taken together, these observations indicate that CrOCl undergoes a phase transition at ~27 K.

Magnetic properties of CrOCl nanosheets
Next, we investigated the magnetic properties of CVD-grown CrOCl nanosheets using a superconducting quantum interference device vibrating-sample magnetometer (SQUID-VSM). Because SQUID measurements require a large mass, we stacked multiple nanosheets on a single SiO2/Si substrate to obtain a sufficiently strong antiferromagnetic signal. Fig. 5a shows a schematic of the SQUID measurement, with the magnetic field aligned parallel to the c-axis. Out-of-plane hysteresis loops recorded at various temperatures (Fig. 5b) reveal switchings between ±3~6 T at 3 K, characteristic of antiferromagnetism. With increasing temperature, the hysteresis loop progressively tightens and disappears at 20 K. The temperature dependence of Δmoment = (momentmax − momentmin) and Δmagnetic field = (magnetic fieldmax − magnetic fieldmin) (Supplementary Fig. 13) likewise decreases monotonically, vanishing at 20 K. Fig. 5c plots the magnetic susceptibility of CrOCl versus temperature at 0.1 T field applied parallel and perpendicular to the c-axis, yielding a Néel temperature of 13.9 K, in excellent agreement with the theoretical calculation (Fig. 5d). Fig. 5e presents a top view of the CrOCl crystal structure, and Fig. 5f depicts the antiferromagnetic spin arrangement calculated on an unshifted k mesh of 13×15×7 at 0 K. Finally, the Raman spectra collected immediately after growth and after eight months of air exposure are nearly identical (Supplementary Fig. 14), confirming the outstanding air stability of CrOCl and underscoring its promise for studies and applications under ambient conditions.

Methods
Growth and transfer of CrOCl monolayer film and CrOCl nanosheets
High-quality, continuous CrOCl monolayer films and CrOCl nanosheets were synthesized on mica substrates via a conventional CVD method. Naturally oxidized CrCl3 powders (5 mg, Alfa, 99.9%) as the sole precursor were placed in a quartz boat positioned at the center of the hot zone, maintained at temperatures between 500–800 °C. A freshly peeled 1 cm × 1 cm mica (KMg3AlSi3O10F2) substrate was placed face-down over the CrCl3 powder. Before growth, the reaction chamber was purged with 500 sccm of argon (Ar, 99.999%) for 10 min. Subsequently, the furnace was heated to the growth temperature under a 100 sccm Ar flow and maintained for 1–15 min to grow the CrOCl monolayer films and CrOCl nanosheets. Here, the growth time, growth temperature, and the temperature gradient during the cooling process are crucial for growing the CrOCl samples. Through regulating the growth parameters, optimal growth conditions and a CrOCl monolayer film with a maximum size of approximately 0.5 cm² can be obtained (see Supplementary Tables 1–4). For further characterization, the as-synthesized CrOCl samples were transferred onto SiO2/Si (300 nm) substrates or copper grids by a polymethyl methacrylate (PMMA)-assisted transfer method.

Structure and composition characterization
The morphology, phase structure, and thickness of CVD-grown CrOCl samples were characterized by optical microscopy (OM) (ECLIPSE LV150N, Nikon), scanning electron microscopy (SEM) (Carl Zeiss, GeminiSEM 500), X-ray diffraction (XRD) (Rigaku D/MAX-Ultima Ⅲ, Japan), and atomic force microscopy (AFM) (Bruker Dimension Fastscan system). Room-temperature Raman spectra were obtained on a WITec/alpha300R confocal microscope with a 532 nm laser excitation source. Angle-resolved polarization Raman spectroscopy (ARPRS) and temperature-dependent Raman spectra were collected using an Acton SpectraPro SP-2300 coupled with a CRYOSTATION C2 system, employing an 1800 grooves/mm grating. For ARPRS measurements, the incident polarization was varied by rotating a half-wave plate. Two polarization configurations were recorded by aligning the scattering light polarization parallel or perpendicular to the incident polarization direction. The X-ray photoelectron spectroscopy (XPS) analysis was performed on a PHI 5000 VersaProbe spectrometer using a monochromatic Al K(alpha) X-ray source. The atomic structure and element distribution of CrOCl were evaluated via high-angle annular dark-field scanning transmission electron microscopy (ADF-STEM) imaging and energy-dispersive X-ray spectroscopy (EDS) mapping using a probe aberration-corrected STEM (Titan cube G2 60-300) at 300 kV.

Magnetic property measurements
SQUID-VSM measurements were conducted using a Quantum Design magnetic property measurement system. CrOCl samples on SiO2/Si (300 nm) substrates were tested at temperatures ranging from 3 to 20 K under an out-of-plane magnetic field varying from −6.3 to 6.3 T. The temperature-dependent magnetic susceptibility of CrOCl samples on SiO2/Si (300 nm) substrates was tested at temperatures ranging from 3 to 300 K under a 0.1 T out-of-plane and in-plane magnetic field.

Computational details
To theoretically investigate the magnetic properties and Raman spectra of CrOCl, first-principles calculations within the framework of density functional theory (DFT)47 are performed with the Vienna ab initio Simulation Package (VASP)48,49. The Perdew-Burke-Ernzerhof (PBE) parametrized generalized gradient approximation (GGA) is employed to describe the exchange-correlation potentials50,51. The projector-augmented-wave (PAW) pseudopotentials52 are utilized to model the electron-ion interactions. The kinetic energy cutoff and the charge density cutoff are set to 500 eV. The charge densities are determined self-consistently on an unshifted k-mesh of 13×15×7 and 13×15×1 for geometric structures calculations of bulk and monolayer CrOCl, respectively. The convergence criteria were 1×10−6 eV for the energy difference in electronic self-consistent calculation and 1×10−2 eV/Å for the residual forces on atoms. To better describe the strong correlation effect of d electrons in Cr, the DFT+U method is used for all calculations, with the Hubbard’s U and Hund’s J for the Cr d electron setting to 3.0 and 1.0 eV, respectively, which were used in previous studies27, and are comparable to those adopted in modeling CrSCl53 and CrI354. The density functional dispersion correction (D3-Grimme) is adopted for the van der Waals (vdW) interactions55. The Néel temperature is determined from Monte Carlo simulations based on the heat bath algorithms56,57.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript reports Chemical Vapor Deposition Growth of Continuous Monolayer Antiferromagnetic CrOCl Films. The\nCVD growth of 2D magnets is essential for large-scale implementation. Thus, the work is promising, with detailed\ncharacterization and analysis. I have the following comments/queries for the authors.\n1. The introduction is a bit lengthy and in a review style. The authors may consider writing it more focused on the challenge\nof increasing CVD growth in 2D magnetic/antiferromagnetic materials and how their work tackles this key challenge.\n2. The work is very interesting, as the authors have successfully synthesized continuous monolayer CrOCl films over a large\narea, which is a step toward scalability. However, several reports have been published on monolayer growth of 2D vdW\nmaterials and 2D magnets. How does this work differ from other reports on similar classes of materials (perhaps because of\nthe continuous film)? Also, how repeatable is the process of growing continuous antiferromagnetic CrOCl monolayer films?\nThe authors can discuss these earlier efforts, specifically in large-scale growth.\n3. Could the authors tabulate different growth parameters, such as time, temperature gradient during cooling of the samples,\nthe approximate area of films with varying layer thicknesses (monolayer, bilayer, etc.), and what the optimal conditions were\nfor achieving such large-area growth (page 15)? Can this method be applied to grow similar types of other materials, or can\nthis procedure be extended, in principle, to other materials as well?\n4. It has often been reported that disorder induced by stacking multiple layers and slight twisting between layers plays a vital\nrole in 2D materials and can lead to exotic physical phenomena. Since the authors have stacked monolayers to measure the\nmagnetic properties, could this influence the magnetic interactions or properties of these stacks?\n5. Additionally, is it possible to measure the magnetic susceptibility (or magnetization as a function of temperature, for Néel\ntemperature/ordering transitions more accurately) of the reported samples, or are there any experimental difficulties in doing\nso?\n6. It has been predicted that strain/electric field can influence the magnetic nature of CrOCl (Phys. Chem. Chem. Phys.,\n2020, 22, 12806, J. Am. Chem. Soc. 140, 2417-2420 (2018)). Can the authors comment on the strain in their films?\n7. Also, why did the authors measure the M-H curve along the c-axis (out-of-plane)? Could they also measure these curves\nin the in-plane direction, or will the results be essentially the same?", "reviewer_2": "The authors have reported the CVD growth of CrOCl films. This is an area of significant current interest. While the quality of\nwork is good, the conclusions should have been supported by some calculations. There are several results that could have\neasily been computationally verified, for example, Raman spectroscopy peaks, a magnetic model showing the ground state,\nanisotropy, and possibly the transition temperature. That could have made the claims more credible."}, "author_response": "Response to Reviewer #1:\nComments:\nThis manuscript reports Chemical Vapor Deposition Growth of Continuous\nMonolayer Antiferromagnetic CrOCl Films. The CVD growth of 2D magnets is\nessential for large-scale implementation. Thus, the work is promising, with detailed\ncharacterization and analysis. I have the following comments/queries for the authors.\nReply:\nWe are highly grateful for your professional review and constructive comments on\nour manuscript. According to your comments and suggestions, we have carefully\nrevised the manuscript and provided a point-by-point response. The reviewers’\ncomments are in blue, and our responses are in black, and all critical changes in the\nrevised manuscript have been marked in yellow.\n1. The introduction is a bit lengthy and in a review style. The authors may consider\nwriting it more focused on the challenge of increasing CVD growth in 2D\nmagnetic/antiferromagnetic materials and how their work tackles this key challenge.\nReply:\nWe sincerely appreciate your suggestion. We have carefully revised relevant content\nbased on your recommendation, which can be found in the revised manuscript (please\nsee the highlighted text on Pages 3-4).\n2. The work is very interesting, as the authors have successfully synthesized\ncontinuous monolayer CrOCl films over a large area, which is a step toward scalability.\nHowever, several reports have been published on monolayer growth of 2D vdW\nmaterials and 2D magnets (such as “Nano Lett. 2019, 19, 2154; ACS Nano 2020, 14,\n5036; Adv. Funct. Mater. 2020, 30, 2000240”, etc.). The difference between our work\nand other reports on similar classes of materials (taking the above three works as\nexamples) lies in the following: Firstly, previous works mainly focused on the\nmonolayer growth for conventional binary TMDs materials (Cr S , MoS , VS ), while\n2 3 2 2\nwe synthesize a monolayer film of the ternary oxygen halide compound CrOCl.\nSecondly, the controllability of the size and thickness of the two-dimensional materials\nprepared in previous works is relatively limited (see Figure 1a below). The obtained\nsamples are mostly single domains with diameters of several tens of micrometers,\nexcept for high-cost substrate designs (see Figure 1b below) and complex precursors\nand reaction processes (see Figure 1c below). However, our work is the first to prepare\ncontinuous CrOCl monolayer films using the simplest processing equipment and the\nlowest cost, with a sole precursor and stable repeatability. Thirdly, the monolayer two-\ndimensional materials synthesized in previous works mainly focused on semiconductor\nand ferromagnetic materials, while our work is the first to prepare continuous\nmonolayer antiferromagnetic CrOCl films through CVD growth. It has laid a solid\nfoundation for the practical application of antiferromagnetic materials.\nFigure 1. a. Modulation of Cr S nanosheets in size and morphology. b. Schematic illustration\n2 3\nof the Au (111) formation and MoS growth process. c. Schematic illustration of the CVD\n2\nsynthesis process of H-phase VS monolayer.\nfilms include growth time and growth temperature. Our experimental repeatability can\nreach over 90% under 600 ºC with 5 min growth, ten repeated experiments are shown\nin Figure 2. This part has been added to the revised manuscript (please see the\nhighlighted text on Page 6) and Supplementary Fig. 3.\nFigure 2. Ten growth experiments of the CrOCl monolayer film under 600 °C with 5 min\ngrowth.\nMoreover, it must be acknowledged that researchers have made great efforts in the\nlarge-scale growth of two-dimensional van der Waals materials and two-dimensional\nmagnets. For example, Jeong et al. reported a quick and scalable synthesis of epitaxially\naligned ferromagnetic ternary metal chalcogenide (Cr Ge Te , Cr Si Te , Mn Si Te )\n2 2 6 2 2 6 3 2 6\nthin films (Adv. Mater. 2021, 33, 2103609). Xu et al. synthesized monolayer and few-\nlayer CrTe ultrathin films on double-layer graphene by molecular beam epitaxy (Nat.\nmethods is mostly a few layers or even thicker, which significantly hinders the\nproperties and device applications of magnetic materials in the two-dimensional limit.\nGiven this, we successfully synthesized the continuous CrOCl monolayer films by the\nCVD method. In the early stage, we can only grow thick-layer CrOCl nanosheets.\nSubsequently, by adjusting the growth temperature and growth time (as detailed in the\nSupplementary Information), few-layer CrOCl nanosheets were obtained. We found\nthat the growth time is crucial for synthesizing thin-layer CrOCl. Thus, we adopted a\nrapid heating and cooling method to strictly control the growth time. Specifically, the\nfurnace was pushed to the growth position when the temperature was about to reach the\ngrowth temperature. It was then immediately removed after growth and quickly cooled\nby a fan to ensure a precise and stable growth time of 5 minutes. For the remaining time,\nno further growth. Finally, we successfully prepared continuous CrOCl monolayer\nfilms and two-dimensional CrOCl nanosheets.\n3. Could the authors tabulate different growth parameters, such as time, temperature\ngradient during cooling of the samples, the approximate area of films with varying layer\nthicknesses (monolayer, bilayer, etc.), and what the optimal conditions were for\nachieving such large-area growth (page 15)? Can this method be applied to grow similar\ntypes of other materials, or can this procedure be extended, in principle, to other\nmaterials as well?\nReply:\nThank you very much for this meaningful suggestion. Since the parameter changes\nduring our growth process are achieved through the control variate method. For clarity,\nwe will discuss these growth parameters separately. The growth time, growth\ntemperature, and the temperature gradient during the cooling process are crucial for\ngrowing the CrOCl samples (see Table 1-3 below). By regulating the growth\nparameters, optimal growth conditions and a CrOCl monolayer film with a maximum\nsize of approximately 0.5 cm² can be obtained (see Table 4 below). This part has been\nadded to the revised manuscript (please see the highlighted text on Page 14, lines 20-\n24) and Supplementary Tables 1-4.\nRegarding the applicability of our method to other materials, it can be applied to the\ngrowth of other similar materials in principle. Of course, this is related to their\nstructures, especially for layered materials with relatively weak interlayer van der\nWaals forces, such as MoS , WS , etc. By precisely controlling the nucleation density\n2 2\nand growth time, it is very easy to grow them into a single layer. Thus, the exact growth\nconditions, such as precursor selection, growth temperature, and pressure, would need\nto be optimized for each specific material.\n4. It has often been reported that disorder induced by stacking multiple layers and\nslight twisting between layers plays a vital role in 2D materials and can lead to exotic\nphysical phenomena. Since the authors have stacked monolayers to measure the\nmagnetic properties, could this influence the magnetic interactions or properties of these stacks?\nReply:\nThanks for your careful review on this point. The reasons and results for conducting\nstacked measurement are as follows: Firstly, the existing works using the SQUID\nmethod to measure the antiferromagnetism of CrOCl should conduct on their bulk or\npowdery samples (Phys. Rev. B 2009, 80, 144416; ACS Nano 2019, 13, 11353).\nSecondly, in recent work, the ferromagnetism of the 2D Cr O -CrN heterostructure\n2 3\ngrown by CVD was measured using the SQUID (Adv. Mater. 2024, 36, 2304946).\nThe\narticle states: \"The measured total Ms (3.9 × 10-5 emu) of Cr O -CrN MH (N:Cr = 0.5)\n2 3\nat 300 K was obtained from isolated MHs flakes (thickness: 20 nm) grown on a 3 mm\n× 3 mm sapphire substrate. Assuming 100% coverage of MHs flakes on sapphire (9\nmm2), the estimated average Ms of our sample is no less than 216.7 emu cm-3.\"\nMoreover, a previous work also used the SQUID to measure the ferromagnetism of\nCVD-grown 1T-CrTe (Nat. Commun. 2021, 12, 809). Its Supplementary Information\n2\nindicates: \"It is worth noting that the VSM test can only obtain the averaged signal, and\nthe thickness of the sample will significantly affect the signal obtained. Before\nprocessing the VSM/SQUID test, we statistically analyzed the thickness data of 1T-\nCrTe samples on a large scale, and use the sample thickness with the dominate\n2\npercentage to name the sample.\" Therefore, we speculate that stacking multiple layers\nand slight twisting between layers may occur during their measuring processes. Directly\nCVD-grown thick-layer 2D materials inevitably exhibit stacking phenomena, and our\nresults are no exception (please refer to Sample 11 in Table 3 above). Therefore, since\nthe magnetic property of CVD-grown CrOCl is relatively weak, to utilize SQUID\nmeasurement to characterize its intrinsic magnetism, we believe the sample preparation\nmethod is feasible. Finally, anyway, the hysteresis loop obtained from our CrOCl film\nis highly similar to a previous work (ACS Nano 2019, 13, 11353), despite the different\nsample preparation methods, which demonstrates the key information, such as the\nantiferromagnetic signal and Néel temperature of our CVD-grown CrOCl film. In other\nwords, the influence of the stacked CrOCl on magnetism can be temporarily\ndisregarded in our work, because the more important large-area monolayer growth\nshould be given more attention. Of course, it is extremely necessary to conduct further\nin-depth research on the magnetic interactions for the stacked CrOCl, which has great\nsignificance for exploring the magnetic properties of CrOCl in the two-dimensional\nlimit and potentially uncovering peculiar physical phenomena. We will focus on this\nimportant project in our next work.\n5. Additionally, is it possible to measure the magnetic susceptibility (or magnetization\nas a function of temperature, for Néel temperature/ordering transitions more accurately)\nof the reported samples, or are there any experimental difficulties in doing so?\nReply:\nThanks for your valuable suggestions. We measured the magnetic susceptibility as a\nfunction of temperature for CrOCl in a 0.1 T magnetic field parallel and perpendicular\nto the c-axis (see Figure 3 below), indicating the Néel temperature is 13.9 K, which is\nin agreement with previous work (ACS Nano 2019, 13, 11353). This part has also been\nadded to the revised manuscript (please see Fig. 5c on Page 13, the highlighted text on\nPage 12, lines 11-13, and the highlighted text on Page 14, line 7). Measurement details\nare added in the highlighted text on Page 15 of the revised manuscript.\nFigure 3. The magnetic susceptibility as a function of temperature for CrOCl in a 0.1 T\nmagnetic field parallel and perpendicular to the c-axis.\n6. It has been predicted that strain/electric field can influence the magnetic nature of\nCrOCl (Phys. Chem. Chem. Phys., 2020, 22, 12806, J. Am. Chem. Soc. 140, 2417-\n2420 (2018)). Can the authors comment on the strain in their films?\nReply:\nThanks for your careful review of this point. In our work, strain is likely to exist in\nthe CrOCl films. It primarily arises from the lattice mismatch between the CrOCl films\nand the mica substrates, which may potentially affect the magnetic properties of the\nCrOCl films. Additionally, research shows that the high lattice mismatch may generate\nstrain, further leading to defects and cracks in the CrOCl films. However, the CVD-\ngrown CrOCl films in our work have a very smooth surface and high crystalline quality,\neven after the transfer process. Therefore, we think the strain present in our CrOCl films\nshould be relatively small. In future research, we will also continue to explore the\nstrain\neffect and its influence on the magnetic properties of the CrOCl films.\n7. Also, why did the authors measure the M-H curve along the c-axis (out-of-plane)?\nCould they also measure these curves in the in-plane direction, or will the results be\nessentially the same?\nReply:\nThanks for your kind suggestion. We measured the M-H curve along the out-of-plane\nbecause some previous works reported that the magnetic easy axis of CrOCl is the c-\naxis, meaning the spontaneous magnetization intensity of the material tends to align\nalong the c-axis direction, with a lower magnetization energy, and thus is more easily\nmagnetized. And people always measure M-H curves along the out-of-plane direction\n(Physical Review B 2009, 80; ACS Nano 2019, 13, 11353). Nevertheless, Ye’s group\nmeasured the M-H curves along in-plane and out-of-plane magnetic fields (see Figure\n4 below), which only exhibit some straight lines and no obvious hysteresis loop in the\nin-plane direction (Nano Lett. 2022, 22, 1233). Further indicating the magnetic property\nin-plane of CrOCl is much weaker than the out-of-plane and difficult to detect.\nFigure 4. M-H curves with the applied field parallel or perpendicular to the c-axis at different\ntemperatures.\nFinally, thank you again for your insightful comments and suggestions. They are\nvery helpful for our revision.\nSincerely yours,\nGeliang Yu\nResponse to Reviewer #2:\nComments:\nThe authors have reported the CVD growth of CrOCl films. This is an area of\nsignificant current interest. While the quality of work is good, the conclusions should\nhave been supported by some calculations. There are several results that could have\neasily been computationally verified, for example, Raman spectroscopy peaks, a\nmagnetic model showing the ground state, anisotropy, and possibly the transition\ntemperature. That could have made the claims more credible.\nReply:\nWe are incredibly grateful for your professional review and constructive comments\non our manuscript. We have carefully revised the manuscript, and all the changes in the\nrevised manuscript have been marked in yellow. According to your suggestions, we\nhave calculated the Raman spectroscopy peaks, Néel temperature (T ), and the\nN\nantiferromagnetic (AFM) spin order. The three calculated characteristic A peaks of the\ng\nmonolayer and bulk CrOCl (see Figure 1a, b below) are consistent with the\nexperimental observations, with frequency differences less than 4%. The calculated\nmagnetization as a function of temperature for the bulk CrOCl is shown in Figure 2a,\nfitted T is 13.6 K, which is almost consistent with the 13.9 K measured experimentally.\nN\nMoreover, Figure 2b shows the top view of the CrOCl crystal structure and an AFM\nspin order on an unshifted k-mesh of 13 × 15 × 7 under 0 K (Figure 2c). The above\ncalculation results are in good agreement with previous reports (ACS Nano 2019, 13,\n11353; Nano Lett. 2022, 22, 1233). It also indicates that the experimental results\nobtained from our CrOCl and the theoretical calculations are in excellent agreement.\nAbove calculated Raman spectroscopy peaks have been added to the revised manuscript\n(please see the highlighted text on Page 7) and Supplementary Fig. 9. Calculated T\nN\nand the AFM spin order have been added to the revised manuscript (please see Fig. 5d-\nf on Page 13, the highlighted text on Page 12, lines 14-16, and the highlighted text on\nPage 14, lines 8-9). Computational details please refer to the highlighted text on Page\n16 of the revised manuscript.\nFigure 1. Calculated Raman peaks of the monolayer (a) and bulk CrOCl (b).\nFigure 2. a. Calculated Néel temperature of the bulk CrOCl. b. The top view of CrOCl crystal\nstructure. J refers to the nth neighbor coupling constant. c. The AFM spin order on an unshifted\nn\nk-mesh of 13 × 15 × 7 under 0 K. The up (magenta) and down (blue) arrows represent the spin\ndirection.\nIn addition, regarding the calculations of the magnetic ground state and anisotropy,\nmany works have already been discussed. For instance, Ye’s group (Nano Lett. 2022,\n22, 1233) calculated the antiferromagnetic ground state and anisotropy of the bulk\nCrOCl, the magnetic anisotropy energy (MAE) of the crystalline CrOCl converges on\nthe k-mesh in the sAFM-↑↑↓↓sequence, which also confirms that the c-axis is the easy\naxis (see Table 1 below). Xu’s group calculated the optical anisotropy of 2D CrOCl\nnanosheets (Adv. Mater. 2025, 37, 2405358), the spatial distributions of the VBM (see\nFigure 3a below) and CBM (see Figure 3b below) wave functions show obvious\ndistinctions between the ab- and bc-planes, suggesting the intrinsic in-plane anisotropic\noptical properties of the CrOCl crystal. Furthermore, Han’s group (Phys. Rev. Materials\n2021, 5, 034409) calculated that both the monolayer and the bulk of CrOCl have an\nantiferromagnetic ground state (see Figure 4 and Table 2 below). Since the relatively\nweak interaction between layers, the ground state of the monolayer should be consistent\nwith the bulk, which is AFM. These conclusions are consistent with the anisotropy and\nantiferromagnetic properties of the CrOCl films we have grown, providing strong\nsupport for our experimental results.\nTable 1. k-mesh convergence of magnetic anisotropy energies (MAE) of the bulk CrOCl in\nthe sAFM-↑↑↓↓ order (from Nano Lett. 2022, 22, 1233).\n[REDACTED]\n[FIGURE REDACTED]\nFigure 3. Partial charge density of (a) VBM and (b) CBM of the CrOCl nanosheet (from Adv.\nMater. 2025, 37, 2405358).\n[FIGURE REDACTED]\nFigure 4. a. The top and side view of CrOX crystal structure. Jn refers to the nth neighbor\ncoupling constant. b. Six different AFM spin orders that can be realized within the 2×2×1 and\n1×4×1 supercell (see the black-solid rectangles). The up (light blue) and down (magenta)\narrows represent the spin directions (from Phys. Rev. Materials 2021, 5, 034409).\nTable 2. The calculated relative total energy by GGA+U with the cRPA parameters of U and\nJ . The unit is meV/Cr (from Phys. Rev. Materials 2021, 5, 034409).\nHund\n[REDACTED]\nFinally, we believe that these efforts will make our research results more accurate\nand more precise, meeting high academic standards. We thank you again for your\nfeedback and hope you find the revisions satisfactory.\nSincerely yours,\nGeliang Yu"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have performed calculations and addressed my comments in detail, and the manuscript is now suitable for\npublication.", "reviewer_2": "The revised manuscript can be accepted for publication."}, "author_response": "Response to Reviewer #1:\nComment: The authors have performed calculations and addressed my comments in\ndetail, and the manuscript is now suitable for publication.\nReply: We are very pleased to hear that reviewer found our responses and revisions\nsatisfactory and considers the manuscript now suitable for publication. We thank the\nreviewer once again for his/her constructive and insightful comments, which have\nsignificantly improved the quality of our work.\nResponse to Reviewer #2:\nComment: The revised manuscript can be accepted for publication.\nReply: We sincerely appreciate reviewer’s time and effort to carefully read our\nresponse, revisions and supplementary materials once again. We are delighted to hear\nthat the revised manuscript can be accepted for publication. Reviewer’s constructive\ncomments and suggestions have enabled our work to a higher academic standard."}]

Decision letter