SEED LAYER, HETEROSTRUCTURE COMPRISING A SEED LAYER, AND METHOD FOR FORMING A MATERIAL LAYER USING A SEED LAYER - Patent application

Abstract

A seed layer 102 is described for inducing nucleation to form a material layer 106. In one embodiment, the seed layer 102 comprises a layer of two-dimensional (2D) monolayer amorphous material having a disordered atomic structure adapted to create localized electronic states and form potential wells that couple adatoms to the surface of the seed layer 102 by van der Waals (vdW) interactions to form the material layer, each of the potential wells having a potential energy greater than the ambient thermal energy to trap adatoms on the surface of the seed layer. Also described are embodiments related to methods of forming the seed layer, a heterostructure 100 comprising the seed layer 102, a method 300 of forming a heterostructure comprising the seed layer, a device comprising the heterostructure, and a method of enhancing the vdW interaction between adatoms and the surface of the seed layer.

Description

[Technical field]

[0001] The present disclosure relates to seed layers, heterostructures comprising seed layers, and methods of forming material layers using seed layers. [Background technology]

[0002] The integration of heterogeneous materials is an important aspect for making high performance semiconductor devices. For example, high speed and high efficiency optoelectronic devices such as light emitting diodes, infrared (IR) sensors, photodetectors, and solar cells generally involve multi-layer heterostructures that require the integration of III-V semiconductors (GaAs, GaN, InP, and others) and II-VI semiconductors (CdTe, CdS, ZnS, oxides, and others) with silicon (Si) microelectronics. The advantages of such integration lie in the excellent optoelectronic properties available from III-V or II-VI materials, as well as the economy and compatibility of Si with complementary metal oxide semiconductor (CMOS) technology.

[0003] The conventional technique used to form such multi-layer heterostructures is epitaxial growth, where an epilayer of material grown on a substrate is covalently bonded to the underlying substrate material. However, stringent requirements must be met to achieve suitable quality of such multi-layer heterostructures, thereby limiting their versatility. For example, direct heteroepitaxy of III-V or II-VI materials on Si using conventional epitaxial growth methods is generally not possible due to thermal expansion, polarity, and lattice mismatch between III-V or II-VI materials and Si.

[0004] One way to overcome this is by using van der Waals epitaxy (vdWE) techniques. The van der Waals epitaxy (vdWE) technique is based on non-covalent interactions between adatoms and the substrate surface. Non-covalent interactions relax the requirement for lattice matching, allowing materials with relatively large mismatches to be grown on top of each other. Due to its suitability for the growth of two-dimensional (2D) materials, the vdWE technique has become an attractive material growth method in recent years to facilitate the fabrication of semiconductor devices. Unfortunately, crystalline 2D materials generally do not have dangling bonds on the surface, thus resulting in very low surface and adsorption energies of adatoms during subsequent epitaxial growth. This makes it difficult to grow heterostructures using the vdWE technique to obtain uniform and strain-free films, often resulting in island-like growth, low growth rates, and poor films for subsequent epitaxial growth. This unintentionally impacts the device performance of the resulting devices. The integration of three-dimensional (3D) materials onto 2D materials is even more challenging given the weak vdW interactions used in this vdWE technique, which results in very poor wetting of the 2D material surface by common 3D materials, resulting in the formation of inhomogeneous, distorted, and clustered 3D material films instead of uniform, flat films.

[0005] It would therefore be desirable to provide a seed layer, a telostructure comprising a seed layer, and a method of forming a material layer using a seed layer that addresses the above-mentioned problems and / or provides a useful alternative. Furthermore, other desirable features and characteristics will become apparent from the following detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure. Summary of the Invention

[0006] Aspects of the present application relate to seed layers, methods of forming seed layers, heterostructures comprising seed layers, devices comprising heterostructures, methods of forming material layers using seed layers, and methods of enhancing van der Waals (vdW) interactions between adatoms and a surface of a seed layer.

[0007] According to a first aspect, there is provided a seed layer for inducing nucleation to form a material layer, the seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure adapted to create localized electronic states to form potential wells that couple adatoms to a surface of the seed layer by van der Waals (vdW) interactions to form the material layer, each potential well having a potential energy greater than the surrounding thermal energy to trap adatoms on the surface of the seed layer.

[0008] By using a seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material with a disordered atomic structure, the disordered atomic structure creates localized electronic states that form potential wells that act as high energy sites for adsorption of adatoms during growth of the material layer via vdW interactions. This results in stronger interactions between the adatoms and the surface of the seed layer (e.g., compared to conventional vdW epitaxy) and a higher nucleation density of adatoms on the surface of the seed layer, which together work to improve the wetting of adatoms on the surface of the seed layer to achieve a uniform and flat material layer growth. Furthermore, the disordered atomic structure of the seed layer can also be tailored from a fully amorphous phase to a nanocrystalline phase to tailor the interaction between the underlying substrate and the material layer, thereby providing a useful handling for remotely controlling the growth of the material layer. Furthermore, since the growth of the material layer is obtained from the vdW interactions between the adatoms and the seed layer, the seed layer serves as a universal seed layer that allows any material layer to be grown on any substrate. Furthermore, the stronger vdW interaction between the surface of the seed layer and the material layer allows the grown material layer to be separated from the underlying substrate to create a free-standing film, which can be advantageous in the design of heterostructure electronic devices.

[0009] The layer of 2D monolayer amorphous material may comprise 2D monolayer amorphous carbon.

[0010] The seed layer may have an optical transparency of greater than 98% at optical wavelengths between 550 nm and 800 nm.

[0011] The seed layer may be thermally stable at temperatures from room temperature to 700°C, from room temperature to 600°C, from room temperature to 500°C, from room temperature to 400°C, from room temperature to 300°C, from room temperature to 200°C, from room temperature to 100°C, or from 600°C to 700°C, 500°C to 700°C, 400°C to 700°C, 300°C to 700°C, 200°C to 700°C, 100°C to 700°C, 20°C to 700°C, or 700°C.

[0012] The seed layer may comprise one or more additional layers of 2D monolayer amorphous material deposited on a layer of 2D monolayer amorphous material to form a multi-layer structure of the seed layer.

[0013] According to a second aspect, there is provided a method of forming a seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure adapted to create localized electronic states to form potential wells that couple adatoms to a surface of the seed layer by van der Waals (vdW) interactions to form a material layer, each of the potential wells having a potential energy greater than the surrounding thermal energy to trap adatoms on the surface of the seed layer, the method comprising growing the seed layer on a substrate using laser-assisted chemical vapor deposition (LCVD).

[0014] LCVD allows for non-catalytic growth of seed layers directly on a variety of substrates (metals, semiconductors, insulators, glasses, and polymers) at low temperatures by utilizing a photolysis process. Photolysis refers to the use of one or more photons to induce chemical reactions in molecules to break them down into simpler particles. This provides a number of advantages. First, the use of laser-assisted CVD allows for the direct growth of a seed layer on the substrate of interest, thus avoiding the time-consuming transfer methods typically practiced when the seed layer or the material of interest can only be grown on a specific base substrate. Second, the ability to grow a seed layer on the substrate of interest and avoid transfer methods provides a cleaner seed layer for the growth of subsequent material layers, since the growth of the material layer can be formed in situ in the same CVD or growth process. This allows for the formation of defect-free, uniform, and flat material layers on the seed layer, since potential impurities on the surface of the seed layer are reduced. For clarity, it should be recognized that the growth of subsequent material layers is not limited to LCVD. Other suitable growth processes for forming material layers (e.g., 2D, 3D, or oxide materials) can be used if the growth process can be realized in situ. Third, the LCVD process allows the seed layer to be grown on the base substrate at lower temperatures, particularly when the material of the base substrate has low thermal stability (e.g., is thermally stable at temperatures below 300° C. or 400° C.), thereby preserving the pristine surface and crystallinity of the material of the base substrate for subsequent growth. Fourth, the low-temperature laser-assisted CVD process is also compatible with conventional semiconductor processing techniques.

[0015] According to a third aspect, there is provided a heterostructure comprising a substrate and a seed layer formed on the substrate, the seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure adapted to create localized electronic states to form potential wells that couple adatoms to a surface of the seed layer by van der Waals (vdW) interactions, each potential well having a potential energy greater than the surrounding thermal energy to trap adatoms on the surface of the seed layer.

[0016] The substrate may include one of a metal, a semiconductor, an insulator, a glass, a polymer, silicon, silicon carbide, sapphire, a III-V substrate, a II-VI substrate, or an oxide.

[0017] If the substrate is a crystalline substrate, the seed layer may be adapted to screen effects caused by the crystallinity of the crystalline substrate.

[0018] The heterostructure may comprise a layer of material formed on a seed layer, the layer of material being formed by bonding adatoms of the material to a surface of the seed layer by van der Waals (vdW) interactions.

[0019] The material layer may comprise one or more layers of a 2D material, the 2D material including one of graphene, borophene, boron nitride, perovskite, transition metal dichalcogenide, or black phosphorene.

[0020] The material layer may include one or more layers of III-V semiconductor materials.

[0021] The III-V semiconductor material may include one of GaAs, GaN, AlN, InP, and InN.

[0022] The material layer may include one or more layers of II-VI semiconductor materials.

[0023] The II-VI semiconductor material may include one of CdTe, CdS, and ZnS.

[0024] The material layer may include one or more layers of an oxide.

[0025] The oxide may include one of hafnium oxide, aluminum oxide, manganese oxide, a perovskite, or a spinel.

[0026] The seed layer may comprise 2D single layer amorphous carbon.

[0027] According to a fourth aspect, there is provided a device comprising any of the above-mentioned heterostructures.

[0028] According to a fifth aspect, there is provided a method of forming a material layer on a substrate, the method including forming a seed layer on the substrate, the seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure adapted to create localized electronic states to form potential wells that couple adatoms to a surface of the seed layer by van der Waals (vdW) interactions, the potential wells each having a potential energy greater than the thermal energy of the surroundings to trap adatoms on the surface of the seed layer, and forming the material layer on the seed layer by coupling adatoms of the material to the surface of the seed layer by van der Waals (vdW) interactions.

[0029] The method may include tailoring the strength of vdW interactions between adatoms of the material and a surface of the seed layer by varying a disordered atomic structure of the layer of the 2D monolayer amorphous material.

[0030] The method may include forming a handling layer on the material layer and separating the seed layer from the substrate to form a free-standing film comprising the seed layer and the material layer.

[0031] Forming the seed layer on the substrate may include growing the seed layer on the substrate using laser assisted chemical vapor deposition (LCVD).

[0032] Laser-assisted CVD may be carried out at temperatures between room temperature (e.g., 20°C) and 400°C, between 20°C and 50°C, between 20°C and 100°C, between 20°C and 150°C, between 20°C and 200°C, between 20°C and 300°C, between 100°C and 200°C, between 100°C and 300°C, between 200°C and 300°C, between 200°C and 400°C, or between 300°C and 400°C. In some embodiments, a temperature range of 20°C to 300°C or 20°C to 400°C may be advantageous because it is complementary to industrial processes, considering that complementary metal oxide semiconductor (CMOS) technologies generally have temperature limitations within these temperature ranges. For example, nanometer-sized domains in thin film materials may be damaged when exposed to high temperatures exceeding 300°C or 400°C. In some embodiments, it may be advantageous to grow the seed layer at room temperature using LCVD, since the LCVD growth process does not require heating, and therefore the growth equipment used may not need to include heaters or suitable thermal isolation / containment. Furthermore, eliminating heating for the LCVD growth of the seed layer also reduces energy consumption and therefore the overall cost of material growth.

[0033] According to a sixth aspect, there is provided a method for forming a material layer on a seed layer, the method comprising creating a disordered atomic structure in the seed layer, the disordered atomic structure of the seed layer adapted to create localized electronic states to form potential wells that couple the adatoms to the surface of the seed layer by vdW interactions to form the material layer, the potential wells each having a potential energy greater than the surrounding thermal energy to trap the adatoms on the surface of the seed layer.

[0034] It should be appreciated that features related to one aspect may be applicable to other aspects. Thus, the embodiments provide a seed layer comprising a layer of two-dimensional (2D) monolayer amorphous material having a disordered atomic structure, which creates localized electronic states to form potential wells that act as high energy sites for adsorbing adatoms during growth of the material layer via vdW interactions. This leads to stronger interactions between the adatoms and the surface of the seed layer, leading to a higher nucleation density of adatoms on the surface of the seed layer, which together work to improve the wettability of the adatoms on the surface of the seed layer to achieve a uniform and flat material layer growth. Furthermore, the disordered atomic structure of the seed layer can also be tailored from a fully amorphous phase to a nanocrystalline phase to adjust the interaction between the underlying substrate and the material layer, which provides useful handling to remotely control the growth of the material layer. Furthermore, the stronger vdW interactions between the surface of the seed layer and the material layer allow the grown material layer to be separated from the underlying substrate to create a free-standing film, which may be advantageous in the design of heterostructure electronic devices.

[0035] Embodiments will now be described, by way of example only, with reference to the following drawings, in which: [Brief description of the drawings]

[0036] [Figure 1] FIG. 2 is a structural diagram that illustrates a schematic representation of a heterostructure with a seed layer according to one embodiment. [Diagram 2] FIG. 2 is a schematic plan view illustrating a seed layer including monolayer amorphous carbon (MAC), according to one embodiment. [Diagram 3] 2 is a flow chart illustrating the steps of a method for forming the heterostructure of FIG. 1. [Figure 4] 2 is a flow chart illustrating steps in a method of forming a free-standing film comprising a seed layer and a material layer using the heterostructure of FIG. 1 . [Diagram 5] 5 is a schematic diagram showing steps in a method for forming a free-standing film associated with FIG. 4. [Figure 6] 1 shows photographs of MAC films grown on three separate substrates: titanium, glass, and copper, according to one embodiment. [Figure 7] FIG. 7 shows the Raman spectrum of the grown MAC film of FIG. 6. [Figure 8] FIG. 1 illustrates a theoretical simulation of out-of-plane structural relaxation in a MAC film, inducing localized strain in the lattice structure of the MAC film, according to one embodiment. [Figure 9] FIG. 9 shows the model used for the theoretical simulations of FIG. 8 with the modulus of the wave function squared overlaid, showing the localized electron distribution in the atomic structure of the MAC. [Figure 10] FIG. 2 illustrates a plot of the optical transmission spectrum of a MAC, according to one embodiment. [Figure 11A] 11A-11C show scanning transmission electron microscope (STEM) images of a seed layer having two different structural variations according to one embodiment; FIG. 11A shows a STEM image of a MAC film. [Figure 11B] FIG. 11B shows a STEM image of a nanocrystalline graphene film. [Figure 12A] 12A shows Raman spectra of a MAC before and after temperature treatment at about 700° C., according to one embodiment; FIG. 12A shows the Raman spectrum of a MAC before temperature treatment; [Figure 12B] FIG. 12B shows the Raman spectrum of the MAC after the temperature treatment. [Figure 13] FIG. 12C shows a transmission electron microscope (TEM) image of the MAC of FIG. 12B after temperature treatment. [Figure 14] FIG. 1 is a schematic diagram illustrating a heterostructure comprising a two-dimensional (2D) material grown on a seed layer on a substrate, according to one embodiment. [Figure 15] FIG. 1 is a schematic diagram illustrating a heterostructure comprising a three-dimensional (3D) material grown on a seed layer on a substrate, according to one embodiment. [Figure 16A]FIG. 16A shows optical images of MoS 2 grown on three different surfaces, according to one embodiment; FIG. 16B shows an optical image of MoS 2 grown on silicon dioxide (SiO 2 ). [Figure 16B] FIG. 16B shows an optical image of MoS2 grown on a monolayer MAC on SiO2. [Figure 16C] FIG. 16C shows an optical image of MoS2 grown on a few-layer MAC on SiO2. [Figure 17A] FIG. 17A shows scanning electron microscope (SEM) images of MoS2 grown using a sapphire substrate, according to one embodiment; FIG. 17B shows SEM images of MoS2 grown directly on a sapphire substrate and on a monolayer of MAC on a sapphire substrate. [Figure 17B] FIG. 17B shows a magnified SEM image of MoS2 grown on a monolayer of MAC on a sapphire substrate. [Figure 18A] FIG. 18A shows scanning electron microscope (SEM) images of MoS2 grown using a sapphire substrate, according to one embodiment; FIG. 18B shows SEM images of MoS2 grown directly on a sapphire substrate and on a few-layer MAC on a sapphire substrate. [Figure 18B] FIG. 18B shows a magnified SEM image of MoS2 grown on a few-layer MAC on a sapphire substrate. [Figure 19] FIG. 2 shows an atomic force microscope (AFM) image of In2Se3 grown on a monolayer MAC on a SiO2 substrate according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Exemplary embodiments relate to seed layers, methods of forming seed layers, heterostructures comprising seed layers, devices comprising heterostructures, methods of forming material layers using seed layers, and methods of enhancing vdW interactions between adatoms and a surface of a seed layer.

[0038] In this application, it is recognized that the use of the singular includes the plural unless specifically stated otherwise. It should be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include the plural unless the context clearly dictates otherwise. Furthermore, the use of the terms "including," "comprising," and "having," as well as other forms such as "include," "comprise," and "have," are not to be considered limiting.

[0039] In the present application, it should be understood that devices and / or heterostructures as described herein may be operable in a variety of orientations, and therefore terms such as "top", "base", "underlying", etc., as used in the following description, are used for convenience to aid in understanding relative positions or orientations, and are not intended to limit the orientation of the devices and / or heterostructures.

[0040] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0041] In an embodiment of the present invention, a seed layer is used that comprises a layer of a two-dimensional (2D) monolayer amorphous material with a disordered atomic structure, which creates localized electronic states to form potential wells, thereby providing the seed layer with high energy sites for adsorbing adatoms during the growth of the material layer by vdW interactions. Localized electronic states refer to the distribution of electronic states in the 2D monolayer amorphous material that are not extended to overlap each other. In particular, in a disordered material system, these localized electronic states are sufficiently isolated from each other, which may lead to the elimination of electrical conduction of the 2D monolayer amorphous material. The potential wells formed by the localized electronic states of the 2D monolayer amorphous material refer to trap sites that have a potential energy greater than the available ambient thermal energy, thereby trapping adatoms on the surface of the seed layer, preferably at the locations of these potential wells. These potential wells formed by the localized electronic states created by the disordered atomic structure of the 2D monolayer amorphous material lead to a strong interaction between the adatoms and the surface of the seed layer and a high nucleation density of the adatoms on the surface of the seed layer, which together work to enhance the wettability of the adatoms on the surface of the seed layer to achieve a subsequent uniform and flat material layer growth. In this example, enhancing the wettability of the adatoms refers to improving the attractive force between the adatoms and the surface of the seed layer so that this attractive force is stronger than the attractive interaction force between the adatoms. By enhancing the wettability of the adatoms, a uniform distribution of the adatoms is formed on the surface of the seed layer instead of the formation of clusters of the adatoms on the surface. Furthermore, the disordered atomic structure of the seed layer can also be adjusted from a fully amorphous phase to a nanocrystalline phase to tune the interaction between the underlying substrate and the material layer, which provides a useful handling to remotely control the growth of the material layer. Furthermore, the strong vdW interaction between the surface of the seed layer and the material layer allows the grown material layer to be separated from the underlying substrate to create a free-standing film, which may be advantageous in the design of heterostructure electronic devices. In the present context, the term "amorphous material" refers to a material that lacks the long-range order that is typical of crystalline materials.The term "monolayer" refers to a layer one atom thick, which may range in thickness from a few angstroms (Å) to a few nanometers.

[0042] FIG. 1 shows a schematic structure of a heterostructure 100 according to one embodiment. The heterostructure 100 comprises a seed layer 102 formed on a substrate 104. As shown in FIG. 1, the seed layer 102 is formed directly on the substrate 104 (i.e., the seed layer 102 is formed adjacent to and on top of the substrate 104). The substrate 104 provides structural support for the seed layer 102. The heterostructure 100 also includes a material layer 106 formed on the seed layer 102. The material layer 106 may include any material of interest, which will be further described in connection with FIGS. 14 and 15 below. The seed layer 102 includes a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure. The disordered atomic structure is adapted to create localized electronic states and form potential wells for binding adatoms to the surface of the seed layer 102 via van der Waals (vdW) interactions to form the material layer 106. The seed layer 102, which includes a layer of 2D monolayer amorphous material, may be formed from any 2D material so long as the seed layer 102 has a disordered atomic structure that creates localized electronic states to form potential wells that enhance the vdW interaction between adatoms and the surface of the seed layer 102.

[0043] In the embodiments described below, monolayer amorphous carbon (MAC) is used as an exemplary 2D monolayer amorphous material for the seed layer 102. Figures 2-19 are described with reference to using one or more layers of MAC as the seed layer 102. MAC is a sp 2It comprises a bonded carbon lattice, which retains similar vdW interactions as a graphene monolayer, but provides additional vdW interactions from its disordered atomic structure, which creates localized electronic states that can act as a driving force for aligning adatoms in-plane with the surface of the MAC. When used as a seed layer 102, this results in higher surface wettability of adatoms on the surface of the seed layer 102 (e.g., compared to graphene or other crystalline 2D materials), which allows for uniform and flat growth of the material layer 106. This makes the MAC an ideal candidate for a seed layer 102 for epitaxial and / or non-epitaxial growth of various material films, as opposed to, for example, graphene.

[0044] FIG. 2 shows a schematic top view 200 of a seed layer including a MAC. As shown in FIG. 2, a MAC is a two-dimensional (2D) disordered sp 2 It has a disordered atomic arrangement with a continuous network of carbon (C) atoms. This is in contrast to conventional polycrystalline graphene, which contains (heterogeneous) ordered crystalline domains separated by grain boundaries. The absence of grain boundaries in the MAC seed layer 102 makes the disclosed MAC seed layer 102 ultra-strong and suitable for applications that may require deformation, such as bending and stretching. In a MAC, the ratio of hexagonal carbon rings to the total number of carbon rings (i.e., the total number of hexagonal and non-hexagonal carbon rings) may be less than 1.

[0045] FIG. 3 shows a flow chart illustrating steps of a method 300 for forming the heterostructure 100 of FIG.

[0046] In step 302, a seed layer 102 is formed on a substrate 104. In this embodiment, the seed layer 102 comprises single layer amorphous carbon (MAC) and the substrate 104 comprises a sapphire substrate. In this embodiment, the MAC is formed using a laser assisted chemical vapor deposition (LCVD) process at room temperature using hydrocarbons as precursors (e.g., CH4, C2H2, etc.). Hydrogen gas (H2) and argon gas (Ar) may also be mixed with the precursors. In this LCVD process, a laser acts as both an energy source to decompose the precursor gases in a process called photolysis and as a localized heat source. In this embodiment, the LCVD process for creating the MAC seed layer 102 uses the following parameters: (i) process gas: C2H2; (ii) chamber pressure: 2×10 -2 mbar; (iii) laser fluence: 70 mJ / cm; (iv) growth time: 1 min; (v) plasma power: 5 W. In this embodiment, an LCVD process is used to form the MAC, however, it will be appreciated that in other embodiments, an LCVD process can also be used to form the non-carbon based seed layer 102.

[0047] The exemplary process described above employs the use of acetylene (C2H2) in the growth chamber for the growth process. The gas pressure in the chamber during growth is 2×10 -2 The gas is controlled at 1000 psi and 1000 psi mbar in the presence of a plasma generator operating at a power of 5 W. The growth begins with the exposure of a 248 nm excimer laser on the surface of the sapphire substrate 104 with a fluence of 70 mJ / cm and a pulse frequency of 50 Hz. The laser exposure time (i.e., growth duration) is set to 1 min to obtain a continuous MAC seed layer 102 on the substrate 104. No stage heater is used in this growth. Several parameters disclosed herein include hydrocarbons as precursors, precursor mixtures, adjustments to the photolysis process and equipment, temperature adjustments, substrate temperature adjustments, alteration of the C value, alteration of the number of atomic layers, sp 2 vs sp 3may be adjusted to control and / or modify properties of the disclosed MAC seed layer 102, including but not limited to, modifying the ratio of, and modifying adhesion to the substrate 104. In this embodiment, the thickness of the MAC seed layer 102 is designed to be about one atomic layer thick.

[0048] Furthermore, it should be appreciated that the use of a photolysis approach to form the seed layer 102 as described above is separate from common approaches to forming 2D material films, for example, using thermal CVD (TCVD). In particular, TCVD requires a hot substrate to cause adatom bond-breaking and bond-forming chemical reactions on the surface of the substrate. However, the temperature required to cause such reactions is typically much higher than the crystallization temperature of the 2D material. This means that at the minimum growth temperature required to form a 2D material film on the surface of the substrate, the atoms of the 2D material deposited on the substrate surface are highly mobile (e.g., surface diffusion) and rearrange to become crystallized to some extent during the formation of the 2D material. As a result, the formed 2D material film will have a variable degree of crystallinity and may not be completely or entirely amorphous. In contrast, by using a photolysis approach, energy from a laser breaks the bonds of the precursor gases and provides additional energy for the subsequent formation of the 2D material film when the atoms of the 2D material are deposited on the substrate surface at low temperatures (e.g., at room temperature or at a temperature below the crystallization temperature). Therefore, by using the strategy of photolysis at low temperature, the deposited atoms of the 2D material have lower mobility and are less likely to move after reaching the surface of the substrate. This restriction of the atomic motion (surface diffusion) of the atoms prevents the formation of crystals in the 2D material. Thus, a monolayer amorphous film can be formed.

[0049] The use of the photolysis method for forming the MAC seed layer 102 as described above can provide a number of advantages. First, the MAC seed layer 102 as synthesized by LCVD can be integrated with existing semiconductor processing techniques. In particular, LCVD is an industrially scalable process that can achieve high throughput of large area films. Thus, the LCVD process for seed layer formation can be easily integrated with current semiconductor processing techniques to make the process industrially compatible and scalable. In addition, LCVD is an ultra-fast deposition technique that can coat the entire surface of the substrate 104 with a MAC film in less than 60 seconds. Thus, LCVD is more efficient than the widely used atomic layer deposition (ALD) process.

[0050] Secondly, the use of LCVD means that the MAC seed layer 102 can be synthesized at low temperatures below 300° C. (e.g., as low as 200° C. or even at room temperature), which is compatible with silicon-based technologies. Also, in contrast to the growth of graphene, the cost of growing MAC using LCVD is significantly lower, since less energy is required for LCVD growth compared to conventional thermal chemical vapor deposition of graphene, which requires temperatures of about 1000° C. Furthermore, the reduced synthesis temperature (e.g., temperatures between 20° C. and 150° C.) may enable direct MAC growth on polymeric substrates used in OLEDs and flexible electronics. The low temperature growth of MAC as a seed layer 102 is also advantageous in that it preserves a pristine and smooth interface between the seed layer 102 and the substrate 104, with minimal disruption of the lattice or surface reconstruction of the single crystal substrate.

[0051] Third, low-temperature photolytic growth of MAC by LCVD can be used to perform direct growth of MAC seed layer 102 on a variety of substrates, including Si, monocrystalline, polycrystalline, metal, glass, polymer, and others. Furthermore, the subsequent growth of material layer 106 on seed layer 102 is dominated by vdW interactions between the surface of the MAC seed layer and the adsorbing adatoms, thereby minimizing the role of substrate 104 on this subsequent material growth. In particular, one or more layers of MAC can be tailored to screen information of the crystalline material underlying substrate 104 and thus govern the subsequent growth mechanism.

[0052] In step 304, a material layer 106 is formed or deposited on the seed layer 102. Considering the stronger vdW interactions between adatoms and the surface of the seed layer 102, as provided by the disordered atomic structure of the seed layer 102, various materials can be used to form the material layer 106. This will be further described in relation to Figs. 14 and 15. Thus, it will be appreciated that depending on the material used for the material layer 106, a number of growth or deposition techniques can be used to form the material layer 106. Examples of deposition techniques that may be applied include molecular beam epitaxy (MBE), atmospheric pressure CVD (APCVD), metal organic CVD (MOCVD), plasma enhanced CVD (PECVD), thermal CVD (TCVD), and atomic layer deposition (ALD). Embodiments of different materials used to form the material layer 106 will be discussed in relation to Figs. 16A-19.

[0053] FIG. 4 shows a flow chart illustrating steps of a method 400 for forming a free-standing film comprising a seed layer 102 and a material layer 106 using the heterostructure 100 of FIG.

[0054] At step 402, a handling layer is formed on the material layer 106. In other words, the handling layer is formed adjacent to and on the material layer 106. The handling layer may include a metal stressor layer, a flexible tape layer, or a layer of an adhesive material that may have a stronger adhesion to the underlying material layer 106 compared to the adhesion between the seed layer 102 and the substrate 104.

[0055] In step 404, the seed layer 102 is separated from the substrate 104 to form a free-standing film. This is accomplished by exfoliating or peeling the material layer 106 and seed layer 102 from the substrate 104 to form a free-standing film, followed by removal of a handling layer that was formed or attached to the material layer 106. The exfoliation is governed by a stronger interaction between the seed layer 102 and the material layer 106 compared to the substrate 104. The stronger interface between the seed layer 102 and the material layer 106, and the non-covalent bond between the seed layer 102 and the underlying substrate 104, aid in exfoliating the free-standing film from the substrate 104. This is advantageous because the free-standing film comprising the seed layer 102 and the material layer 106 can be isolated for use, for example, in a flexible transparent optoelectronic device, and the substrate 104 can be reused.

[0056] Figure 5 shows a schematic diagram 500 illustrating steps of the method 400 of forming the free-standing film of Figure 4. In this embodiment, a bi-layer MAC is formed on a substrate 510 and used as a seed layer 512. A bi-layer 2D material is formed on the seed layer 512 as a material layer 514.

[0057] As illustrated by schematic diagram 502, a handling layer 516 is formed over material layer 514. This corresponds to step 402 described above.

[0058] As illustrated by schematic diagram 504, peeling or delamination of material layer 514 and seed layer 512 from substrate 510 is performed using handling layer 516. A separated free-standing layer 518 comprises material layer 514 and seed layer 512.

[0059] As shown by schematic diagram 506, the handling layer 516 is then removed from the free-standing layer 518. The handling layer 516 may be removed, for example, by the following techniques: If the handling layer 516 is a metal stressor layer, it may be removed by immersing the handling layer 516 in a metal etchant. If the handling layer 516 is a flexible tape layer, the flexible tape layer may include a thermal or UV release adhesive that can be removed by heating the tape or exposing it to UV light, respectively.

[0060] Figure 6 shows photographs 600 taken of MAC films grown on three separate substrates: titanium, glass, and copper. As shown in Figure 6, photograph 602 shows a MAC film grown on a titanium substrate, photograph 604 shows a MAC film grown on a glass substrate, and photograph 606 shows a MAC film grown on a copper substrate. From at least photograph 604, it is apparent that the deposited MAC film is transparent in visible light.

[0061] FIG. 7 shows the Raman spectra of the grown MAC films of FIG. 6. Raman spectrum 702 was obtained using a MAC film grown on a glass substrate, Raman spectrum 704 was obtained using a MAC film grown on a titanium substrate, and Raman spectrum 706 was obtained using a MAC film grown on a copper substrate. As shown in all of the Raman spectra 702, 704, 706 in FIG. 7, the Raman spectra are typical of a crystalline graphene monolayer (approximately 2700 cm). -1 In contrast, the Raman spectra 702, 704, 706 all have a broad (approximately 1600 cm) 2D peak. -1 G peak at 708 and (at about 1350 cm -1The Raman spectra 702, 704, 706 also reveal a D / G ratio in the range of about 0.5 to 1. This D / G ratio, combined with the absence of a 2D peak, distinguishes the disordered atomic structure of MAC from that of 2D graphene and diamond. The Raman spectra 702, 704, 706 also verify the growth of the MAC films grown on these three separate substrates.

[0062] FIG. 8 shows a diagram 800 illustrating a theoretical simulation of out-of-plane structural relaxation in a MAC film 802, which induces localized strains in the lattice structure of the MAC film 802. In this theoretical simulation, the atomic coordinates of the atoms of the MAC film 802 in the model are initially positioned in a planar 2D plane. By taking into account the interaction forces between these atoms, atomic rearrangements of these atoms are performed in 3D space, and the atomic coordinates of the atoms of the MAC film 802 occupy their new equilibrium positions, where the structure of the MAC film 802 is in the most stable configuration with the lowest internal energy. As shown in diagram 800, the simulated MAC film 802 is of a single layer and has a thickness 804 of about 6.5 Å. The amorphous or disordered atomic structure of the MAC film 802 creates a distorted 2D lattice with localized electron distribution, which results in a surface with a relatively high energy. Such a surface initiates strong interactions with adsorbing adatoms, resulting in higher surface wettability required for uniform planar 2D and / or 3D material film formation. This helps overcome the poor wetting of 3D material films on 2D surfaces for vdW epitaxy due to the inherent low surface energy at the surfaces of 2D crystalline materials.

[0063] Furthermore, the higher surface energy of the MAC 802 due to the disordered atomic arrangement and enhanced vdW interactions provides a large number of nucleation sites for the adsorbed adatoms on the MAC seed layer. The large number of nucleation sites (or higher nucleation density) can substantially reduce the growth rate and temperature requirements for the subsequent material layer growth, thereby making the growth process more energy and cost-effective. Furthermore, the enhanced vdW interactions between the MAC 802 (i.e., seed layer) and the material layer (or epilayer) provide a stronger interface that is stable even during the subsequent high temperature growth process. This ensures uniformity in the subsequent planar material layer formation and prevents or reduces the formation of islands and / or clusters during this subsequent growth of the material layer. It is noted that the formation of islands and / or clusters in the material layer results in a non-planar active layer material film that is detrimental to the device performance of subsequent devices formed using such non-planar material layers.

[0064] Figure 9 shows the model 900 used for the theoretical simulation of Figure 8. The wave function squared coefficients are superimposed on the model 900 to show the localized electron distribution 902 in the atomic structure of the MAC 802.

[0065] As shown in model 900 of FIG. 9, a MAC film is a one atom thick carbon film with a mixture of hexagonal and non-hexagonal rings in its structure. The rings are fully connected to each other to form a polygonal network in large area films of at least micron size. The ratio of the number of hexagonal rings to the total number of carbon rings (i.e., the total number of hexagonal and non-hexagonal rings) is an indication of the crystalline (or amorphous) C. The non-hexagons are in the form of 4, 5, 6, 7, 8, and 9 membered rings. Five membered rings 904 and seven membered rings 906 are shown in FIG. 9 in contrast to the regular six membered rings 908 that are typical of crystalline graphene. Disclosed embodiments may correspond to a range of C values ​​from 0.5 to 0.8 inclusive. This differs from graphene where C=1 for a pure hexagonal network.

[0066] FIG. 10 shows a plot 1000 of the optical transmission spectrum of a MAC 1002, according to one embodiment.

[0067] Plot 1000 shows the optical transparency of MAC1002 over a range of optical wavelengths. As shown in FIG. 10, the optical transparency is about 98.1% at an optical wavelength of 550 nm, and the transparency increases with increasing optical wavelength. Thus, the present embodiment provides a MAC with optical transparency of 98% or more at wavelengths of 550 nm or more. The disclosed MAC is different from graphene. Line 1004 shows the theoretical limit of 97.7% for the optical transparency of graphene. Thus, at least from plot 1000, it is demonstrated that MAC1002 of the present embodiment exhibits higher optical transparency than graphene at wavelengths of about 550 nm or more. In particular, the transparency of MAC1002 does not decrease rapidly at short wavelengths (<400 nm). This may be due in part to less contamination in the growth process of MAC1002, since MAC1002 can be grown on any substrate without using a transfer method. The high optical transparency of MAC in the visible range (approximately 98.1% at 550 nm, with increasing optical transparency at higher wavelengths) makes it an ideal candidate for a seed layer on a transparent substrate (e.g., glass or a suitable polymer) for forming subsequent active semiconductor films for transparent devices.

[0068] 11A and 11B show scanning transmission electron microscope (STEM) images 1100, 1110 of a seed layer having two different structural variations, according to one embodiment, where FIG 11A shows a STEM image 1100 of a MAC film and FIG 11B shows a STEM image 1110 of a nanocrystalline graphene film. The "white" clusters 1112 as shown in FIG 11B are associated with contamination absorbed on the surface of the nanocrystalline graphene film and not with the crystallinity of its atomic structure.

[0069] Depending on the synthesis conditions, the phase transitions can vary from completely amorphous (e.g., MAC) to nanocrystalline sp 2There can be a wide range of atomic structural variations in the carbon-based seed layer, ranging from a single layer to a nanocrystalline graphene layer. Furthermore, the seed layer can also be formed on the substrate, ranging from a single layer to a multilayer stack. Such structural variations can tune the vdW interactions between the seed layer and the material layer (or epilayer), and can remotely tune the interactions between the substrate and the adatoms forming the material layer during growth. For example, by tuning the crystallinity of the seed layer from completely amorphous to nanocrystalline, more interactions between the substrate and the adatoms can be achieved, since screening of the crystalline effect of the substrate is provided by the potential well of the disordered atomic structure of the 2D amorphous seed layer.

[0070] An example of crystallinity tuning of a carbon-based seed layer can be performed by using similar laser-based growth conditions as described in connection with step 302, but using, for example, a methane precursor gas and a copper foil substrate. For example, when forming a nanocrystalline carbon film, such as that shown in FIG. 11B, the copper foil temperature can be set in the range of 500° C. to 600° C., and when forming a totally amorphous film, such as that shown in FIG. 11A, the copper foil temperature can be set below 400° C. This is because a higher substrate temperature during growth leads to a more crystalline material.

[0071] 12A and 12B show Raman spectra 1200, 1210 of a MAC before and after temperature treatment at about 700° C., according to one embodiment, where FIG. 12A shows the Raman spectrum 1200 of the MAC before temperature treatment and FIG. 12B shows the Raman spectrum 1210 of the MAC after temperature treatment.

[0072] FIG. 12A shows raw data 1202 from Raman spectroscopy of the MAC before temperature treatment, with D band 1204 and G band 1206 fitted, and FIG. 12B shows raw data 1212 from Raman spectroscopy of the MAC after temperature treatment, with D band 1214 and G band 1216 fitted. As shown in the Raman spectra 1200, 1210, the shapes of the D bands 1204, 1214 and G bands 1206, 1216, as well as their D / G ratios, are similar. This verifies that there is no observable change in the crystallinity or grain size of the MAC after thermal treatment at about 700° C. Thus, the MAC is thermally stable at high temperatures of about 700° C., making it a stable seed layer for subsequent high temperature growth of material layers. It will be appreciated that because the MAC is thermally stable at temperatures of about 700° C., it is also thermally stable at any temperature below 700° C.

[0073] FIG. 13 shows a transmission electron microscope (TEM) image 1300 of the MAC of FIG. 12B after temperature treatment. The TEM image 1300 of the MAC is 10×10 nm 2 where cluster 1302 as shown in Figure 13 is contamination covering some area of ​​the MAC. Contamination cluster 1302 may be formed by the transfer process from the substrate (e.g., copper foil) to the TEM grid to obtain this TEM image 1300 and is not related to the crystallinity of the MAC. Inset 1304 in Figure 13 is a Fourier transform of TEM image 1300 and shows the diffraction pattern of TEM image 1300. Notably, inset 1304 shows amorphous halo rings instead of sharp rings or individual dots that would indicate nanocrystalline or polycrystalline graphene, respectively.

[0074] In addition to being a thermally stable layer, the MAC also has high thermal conductivity, allowing it to act as a heat spreading layer in heterostructures with active semiconductor epilayers to transfer heat to a heat sink. This is advantageous since thermal management is an essential aspect of thin film devices such as LEDs. The ability of the MAC to spread heat quickly helps to avoid overheating and degradation of device performance.

[0075] 14 shows a schematic diagram of a heterostructure 1400 comprising a two-dimensional (2D) material layer 1402 grown on a seed layer 1404 on a substrate 1406, according to one embodiment. The heterostructure 1400 has a similar structure to the heterostructure 100 as shown in FIG 1 and can be formed or fabricated using the method 300 of FIG 3.

[0076] The seed layer 1404 comprises a single layer of amorphous 2D material (e.g., MAC in this embodiment, although other single layer 2D amorphous materials can be used) grown directly on a substrate 1406. The substrate 1406 in this embodiment includes SiO2, but other substrates such as Si, SiC, sapphire, III-V materials, II-VI materials, oxides, etc. can be used. The seed layer 1404 grown on the substrate 1406 serves to stabilize the subsequent growth of the 2D material layer 1402 using strong vdW interactions between adatoms of the 2D material layer 1402 and the surface of the seed layer 1404. This advantageously helps to avoid the stringent requirement of using a dedicated substrate to stabilize the growth of the 2D material layer 1402.

[0077] 14 shows a single layer amorphous carbon (MAC) as the seed layer 1404, but multiple layers of MAC can also be used, either by direct growth or transfer methods. The grown 2D material layer 1402 includes one or more layers of a single layer 2D amorphous film, a 2D crystalline film, graphene, black phosphorene, borophene, hexagonal boron nitride (hBN) or boron nitride, transition metal dichalcogenides (TMDs), perovskites, and / or boron phosphides (BPs). The 2D material layer 1402 can be grown on the seed layer 1404 using deposition techniques such as metalorganic chemical vapor deposition (MOCVD), thermal chemical vapor deposition (TCVD), plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), and the like. The 2D-2D composite structure (i.e., a free-standing structure comprising layers 1402, 1404) can be separated from the substrate 1406 after growth to form a free-standing stack, which can be further integrated in the fabrication process of thin film and flexible optoelectronic devices.

[0078] Figure 15 illustrates a structure of a heterostructure 1500 comprising a three-dimensional (3D) material layer 1502 grown on a seed layer 1504 on a substrate 1506, according to one embodiment. Heterostructure 1500 has a similar structure to heterostructure 100 as shown in Figure 1 and can be formed or fabricated using method 300 of Figure 3. The difference between heterostructure 1500 and heterostructure 1400 is that material layer 1502 grown on seed layer 1504 is a 3D material layer, as opposed to 2D material layer 1402 included in heterostructure 1400.

[0079] Different embodiments are described below, including different types of 3D materials and substrates used.

[0080] (i) Integration of CMOS compatible substrates (e.g., Si or Ge) with flat thin films of III-V semiconductors In this embodiment, the MAC layer is formed on a Si or Ge substrate 1506. The MAC serves as a seed layer 1504 for subsequent epitaxial or non-epitaxial growth of one or more layers 1502 of III-V semiconductors (GaAs, GaN, AlN, InP, InN, etc.) using conventional deposition techniques (MOCVD, TCVD, PECVD, ALD, etc.). III-V semiconductor materials can be used as active layers for applications such as light emitting diodes (LEDs), infrared (IR) sensors, photodetectors, and other optoelectronic devices.

[0081] ii) II-VI Semiconductor Thin Films The ability to integrate II-VI thin film semiconductors (e.g., CdTe, CdS, ZnS, etc.) on any substrate (e.g., Si, semiconductor materials, glass, metal foils, polymers, etc.) is advantageous for solar, photovoltaic, and aerospace applications. As mentioned above, achieving a uniform and flat material layer by vdW epitaxy is difficult due to poor wettability on the epitaxial surface. In this embodiment, a MAC layer 1504, which serves as a seed layer 1504, can be formed on a substrate 1506 for epitaxial or non-epitaxial growth of a layer 1502 of a 3D flat film of II-VI semiconductors. Examples of 3D II-VI semiconductor material films include CdTe, CdS, ZnS, etc.

[0082] iii) Oxide thin film Oxide thin films, including simple metal oxides (Hf2O3, Al2O3, MnO, etc.) and complex oxides (perovskites, spinels, etc.), play important roles in various electronic, spin-engineering, magnetoelectric, and energy storage devices due to their functional properties. These oxides may function as dielectrics, piezoelectrics, pyroelectrics, etc. Using a scheme similar to that shown in FIG. 15, one or more layers of oxide 1502 can be deposited on a substrate 1506 using MAC as a seed layer 1504. The substrate 1506 in this application can be any substrate, such as Si, semiconductor materials, glass, metal foil, polymer, etc. The deposited layer 1502 of oxide film can also be exfoliated to obtain a free-standing film using the method 400 as described in connection with FIG. 4 and FIG. 5.

[0083] 16A, 16B, and 16C show optical images 1600, 1610, 1620 of MoS2 grown on three different surfaces, according to one embodiment: FIG. 16A shows an optical image 1600 of MoS2 grown on silicon dioxide (SiO2), FIG. 16B shows an optical image 1610 of MoS2 grown on a single layer MAC on SiO2, and FIG. 16C shows an optical image 1620 of MoS2 grown on a few layer MAC on SiO2.

[0084] In this embodiment, the MAC is first grown on a SiO2 substrate using the LCVD method, as described in connection with step 302 of FIG. 3. The growth conditions of the MAC on the SiO2 substrate are the same as those described for the sapphire substrate in connection with step 302, and these are not repeated here for brevity. The MAC layer or layers act as seed layers for the subsequent growth of the MoS2 layer. The MoS2 layer is a 2D material grown on the MAC layer or layers by thermal CVD. The parameters for the thermal CVD growth of the MoS2 layer are as follows: MoO3+S, atmospheric pressure chemical vapor deposition (APCVD), 750° C., 20 sccm Ar, and 10 min growth time.

[0085] As evidenced in Figures 16A, 16B, and 16C, layers of MoS2 grow differently on three different surfaces (i.e., no MAC, single-layer MAC, and few-layer MAC, respectively). As shown in optical image 1600 in Figure 16A, standard MoS2 grown on SiO2 forms triangular crystals 1602. Optical image 1610 in Figure 16B shows that using a single MAC layer as a seed layer results in the growth of MoS2 crystals 1612 with irregular shapes and multi-layer centers. As shown in optical image 1620 in Figure 16C, using few-layer MAC as a seed layer results in dense nucleation of MoS2 crystals.

[0086] 17A and 17B show scanning electron microscope (SEM) images 1720, 1704, 1710 of MoS2 grown using a sapphire substrate, according to one embodiment, where FIG. 17A shows SEM images 1702, 1704 of MoS2 grown directly on a sapphire substrate and on a single layer MAC on a sapphire substrate, respectively, and FIG. 17B shows a magnified SEM image 1710 of MoS2 grown on a single layer MAC on a sapphire substrate. 18A and 18B show scanning electron microscope (SEM) images 1802, 1804, 1810 of MoS2 grown using a sapphire substrate, according to one embodiment, where FIG. 18A shows SEM images 1802, 1804 of MoS2 grown directly on a sapphire substrate and on a few layers of MAC on a sapphire substrate, respectively, and FIG. 18B shows a magnified SEM image 1810 of MoS2 grown on a few layers of MAC on a sapphire substrate.

[0087] In this embodiment, the MAC is first grown on a sapphire substrate using LCVD techniques as described in connection with step 302 of FIG. 3. The MAC layer or layers act as seed layers for the subsequent growth of the MoS2 layer. The growth conditions for the MAC on the sapphire substrate are described above in connection with step 302, and these are not repeated here for brevity. The MoS2 layer is a 2D material grown on the MAC layer or layers by thermal CVD. The parameters for the thermal CVD growth of the MoS2 layer are as follows: MoO3+S, atmospheric pressure chemical vapor deposition (APCVD), 850° C., 20 sccm Ar, and 5 minutes growth time.

[0088] As evidenced in Figures 17A, 17B, 18A, and 18B, layers of MoS2 grow differently on three different surfaces (i.e., no MAC, single-layer MAC, and few-layer MAC, respectively). Standard MoS2 grown on sapphire forms triangular crystals 1706, 1806, as shown in SEM images 1702 and 1802 in Figures 17A and 18A, respectively. SEM image 1710 in Figure 17B shows that using a single MAC layer as a seed layer results in high-density nucleation of MoS2 crystals with triangular shape 1712. Using few-layer MAC as a seed layer results in high-density nucleation of MoS2 crystals with dendritic shape, as shown in SEM image 1810 in Figure 18B.

[0089] FIG. 19 shows an atomic force microscope (AFM) image 1900 of indium selenide (In2Se3) grown on a single layer MAC on a SiO2 substrate, according to one embodiment.

[0090] The MAC is first grown or transferred onto a SiO2 substrate, where it acts as a seed layer for the subsequent growth of In2Se3. In2Se3 is a 2D material that is subsequently grown on the MAC using molecular beam epitaxy (MBE) techniques. In this embodiment, In2Se3 has a base pressure of about 6×10 -10 The growth was performed in an MBE chamber at 10 Torr. Ultra-high purity In2Se3 powder (99.99%) was evaporated from a crucible heated by an electron beam source with the temperature maintained at 150 °C. The chamber pressure during growth was approximately 6 × 10 -9 It was Tor.

[0091] A layer of In2Se3 grows differently when a single layer of MAC is used as a seed layer compared to growing a layer of In2Se3 directly on graphene or on a SiO2 substrate without MAC. As shown in AFM image 1900, the In2Se3 crystals 1902 formed using a single layer of MAC as a seed layer retain triangular facets with thicknesses ranging from a few Å (i.e., monolayer thickness) to about 7 nm thick. On the other hand, when In2Se3 is grown on a layer of graphene on a SiO2 substrate, the grown In2Se3 crystals are of monolayer thickness with triangular shape. When In2Se3 is grown directly on a SiO2 substrate, the grown In2Se3 crystals have a highly disordered bulk (3D) structure.

[0092] Alternative embodiments of the present invention include: (i) the seed layer 102 comprises one or more layers of 2D amorphous materials selected from one or more of amorphous MoS2, amorphous In2Se3, amorphous transition metal dichalcogenides, amorphous black phosphorene, amorphous borophene, amorphous boron nitride; (ii) the substrate 104 is selected from one of Si, SiC, sapphire, III-V materials, II-VI materials, oxide semiconductor materials, glass, metals, and polymers; (iii) the material layer 106 is selected from 2D or 3D materials, examples of 2D and 3D materials are provided in connection with Figures 14 and 15; (iv) the material layer 106 can be formed by various deposition techniques, such as LPCVD, APCVD, MOCVD, TCVD, PECVD, MBE, and ALD.

[0093] Although only certain embodiments of the invention have been described in detail, many variations are possible in accordance with the scope of the appended claims, for example features described in connection with one embodiment may be incorporated in one or more other embodiments, and vice versa.

Claims

1. a seed layer for inducing nucleation to form a material layer, the seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure; the disordered atomic structure induces a distorted 2D lattice in the layer of two-dimensional (2D) monolayer amorphous material, which undergoes atomic rearrangements in 3D space to create localized electronic states that form potential wells that bind adatoms to the surface of the seed layer via van der Waals (vdW) interactions to form the material layer; The layer of 2D monolayer amorphous material comprises homogeneous 2D monolayer amorphous carbon.

2. The seed layer of claim 1 , wherein the seed layer has an optical transparency of greater than 98% at optical wavelengths between 550 nm and 800 nm.

3. The seed layer of claim 1 or 2, wherein the seed layer is thermally stable at a temperature of 700°C.

4. The seed layer is 4. The seed layer of claim 1, further comprising one or more additional layers of 2D monolayer amorphous carbon deposited on the layer of 2D monolayer amorphous material to form a multilayer structure of the seed layer and tailor van der Waals (vdW) interactions between the seed layer and the material layer.

5. 1. A method of forming a seed layer, the seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure; the disordered atomic structure induces a distorted 2D lattice in the layer of two-dimensional (2D) monolayer amorphous material, which undergoes atomic rearrangements in 3D space to create localized electronic states that form potential wells that bind adatoms to the surface of the seed layer via van der Waals (vdW) interactions to form a material layer; the layer of 2D monolayer amorphous material comprises homogeneous 2D monolayer amorphous carbon; The method further comprising: growing the seed layer on a substrate using laser assisted chemical vapor deposition (LCVD).

6. 6. The method of claim 5, wherein the LCVD is carried out at a temperature in the range of 20°C to 400°C.

7. A substrate; a seed layer formed on the substrate, the seed layer comprising a layer of a two-dimensional (2D) monolayer amorphous material having a disordered atomic structure; the disordered atomic structure induces a distorted 2D lattice in the layer of two-dimensional (2D) monolayer amorphous material, which undergoes atomic rearrangements in 3D space to create localized electronic states that form potential wells that couple adatoms to the surface of the seed layer via van der Waals (vdW) interactions; The layer of 2D monolayer amorphous material comprises homogeneous 2D monolayer amorphous carbon.

8. The heterostructure of claim 7, wherein the substrate comprises one of a metal, a semiconductor, an insulator, a glass, a polymer, silicon, silicon carbide, sapphire, a III-V substrate, a II-VI substrate, or an oxide.

9. 9. The heterostructure of claim 7 or 8, wherein the substrate is a crystalline substrate and the seed layer is adapted to screen effects caused by the crystallinity of the crystalline substrate.

10. 10. The heterostructure of claim 7, further comprising a layer of material formed on the seed layer, the layer of material being formed by bonding adatoms of a material to the surface of the seed layer by the van der Waals (vdW) interactions.

11. 11. The heterostructure of claim 10, wherein the material layer comprises one or more layers of 2D material, the 2D material comprising one of graphene, borophene, boron nitride, perovskite, transition metal dichalcogenides, or black phosphorene.

12. The heterostructure of claim 10, wherein the material layer comprises one or more layers of III-V semiconductor material.

13. The heterostructure of claim 12, wherein the III-V semiconductor material comprises one of GaAs, GaN, AlN, InP, and InN.

14. The heterostructure of claim 10, wherein the material layer comprises one or more layers of II-VI semiconductor materials.

15. The heterostructure of claim 14, wherein the II-VI semiconductor material comprises one of CdTe, CdS, and ZnS.

16. The heterostructure of claim 10 , wherein the material layer comprises one or more layers of an oxide.

17. 17. The heterostructure of claim 16, wherein the oxide comprises one of hafnium oxide, aluminum oxide, manganese oxide, a perovskite, or a spinel.

18. The seed layer is 18. The heterostructure of any one of claims 7 to 17, further comprising one or more additional layers of 2D monolayer amorphous carbon deposited on the layer of 2D monolayer amorphous material to form a multilayer structure of the seed layer and to tailor van der Waals (vdW) interactions between the seed layer and material layer and to tailor interactions between the substrate and the adatoms forming the material layer during growth.

19. A device comprising a heterostructure according to any one of claims 7 to 18.

20. 1. A method of forming a layer of material on a substrate, comprising: forming a seed layer on the substrate, the seed layer comprising a layer of two-dimensional (2D) monolayer amorphous material having a disordered atomic structure, the disordered atomic structure causing the layer of two-dimensional (2D) monolayer amorphous material to have a distorted 2D lattice, the layer of two-dimensional (2D) monolayer amorphous material undergoing atomic rearrangements in 3D space to create localized electronic states that form potential wells that couple adatoms to a surface of the seed layer via van der Waals (vdW) interactions, and the layer of 2D monolayer amorphous material comprising homogenous 2D monolayer amorphous carbon; forming the layer of material on the seed layer by bonding adatoms of a material to the surface of the seed layer through the van der Waals (vdW) interactions.

21. 21. The method of claim 20, further comprising varying the disordered atomic structure of the layer of 2D monolayer amorphous material to tune a strength of the vdW interactions between the adatoms of the material and the surface of the seed layer.

22. To form the multi-layer structure of the seed layer, before forming the material layer on the seed layer, 22. The method of claim 20 or 21, further comprising depositing one or more additional layers of 2D monolayer amorphous carbon on the layer of 2D monolayer amorphous material that tailors the van der Waals (vdW) interactions between the seed layer and the material layer and tailors the interactions between the substrate and the adatoms that form the material layer during growth.

23. forming a handling layer on the material layer; 23. The method of any one of claims 20 to 22, further comprising: separating the seed layer from the substrate to form a free-standing film comprising the seed layer and the material layer.

24. 24. The method of any one of claims 21 to 23, wherein forming the seed layer on the substrate comprises growing the seed layer on the substrate using laser assisted chemical vapor deposition (LCVD).

25. 25. The method of claim 24, wherein the laser-assisted CVD is carried out at a temperature between 20°C and 400°C.

26. 1. A method for forming a material layer on a seed layer by enhancing van der Waals (vdW) interactions between adatoms and a surface of the seed layer, the seed layer comprising a homogeneous two-dimensional (2D) monolayer amorphous carbon layer; forming a disordered atomic structure in the seed layer, the disordered atomic structure of the seed layer causing a rearrangement of the atoms of the seed layer in 3D space to create localized electronic states that create a potential well that couples adatoms to a surface of the seed layer via van der Waals (vdW) interactions that create a distorted 2D lattice in the seed layer and form the material layer.

27. The seed layer formed on a substrate, the seed layer comprising two or more homogeneous two-dimensional (2D) monolayer amorphous carbon layers; The method comprises:

27. The method of claim 26, further comprising controlling a number of layers of homogeneous 2D monolayer amorphous carbon to tailor van der Waals (vdW) interactions between the seed layer and the material layer and tailor interactions between the substrate and the adatoms that form the material layer during growth.

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