High Nucleation Density Research Articles

Premelted-Substrate-Promoted Selective Etching Strategy Realizing CVD Growth of High-Quality Graphene on Dielectric Substrates.

Direct chemical vapor deposition growth of high-quality graphene on dielectric substrates is a great challenge. Graphene growth on dielectrics always suffers from the issues of a high nucleation density and poor quality. Herein, a premelted-substrate-promoted selective etching (PSE) strategy was proposed. The premelted substrate can promote charge transfer from the substrate to the nuclei near graphene domains, thus facilitating the reaction between the CO2 etchant and the nuclei. Consequently, the PSE strategy can realize selective etching of nuclei formed near graphene domains to evolve high-quality graphene with a uniform domain size of ∼1 μm and an ID/IG ratio of ∼0.13 on glass fiber, achieving the largest domain size and the lowest defect density in graphene grown on a noncatalytic substrate without metal assistance. The largely improved quality of graphene significantly increases the electrical conductivity by 3 times and improves the working life by 7 times when applied as an electric heater compared with that fabricated without the PSE strategy.

High-Performance Boiling Surfaces Enabled by an Electrode-Transpose All-Electrochemical Strategy.

High-performance boiling surfaces are in great demand for efficient cooling of high-heat-flux devices. Although various micro-/nano-structured surfaces have been engineered toward higher surface wettability and wickability for enhanced boiling, the design and fabrication of surface structures for realizing both high critical heat flux (CHF) and high heat transfer coefficient (HTC) remain a key challenge. Here, a novel "electrode-transpose" all-electrochemical strategy is proposed to create superhydrophilic microporous surfaces with higher dendrites and larger pores by simply adding an electrochemical etching step prior to the multiple electrochemical deposition steps. Enabled by the high nucleation density and high wicking capability, a high boiling performance is shown on such "etching-then-deposition" surfaces with simultaneously high CHF of 2,641±10kWm-2 and high HTC of 214±6kW(m2 K)-1, which are more than 2.5 and 4.3-fold enhanced from those on smooth surfaces, respectively. A very stable morphology and boiling performance of such surfaces subject to consecutive tests are also shown. Using this strategy, such superhydrophilic microporous layers are fabricated on curved surfaces with larger areas, both on spheres and slender cylinders, and demonstrate excellent boiling performance in quenching tests. This facile, geometry-adaptive, durable, and scalable strategy is very promising for making high-performance boiling surfaces for large-scale industrial applications.

Edge Electron Effect Induced High-Entropy SEI for Durable Anode-Free Sodium Batteries.

Anode-free sodium metal batteries represent great promising as high-energy-density and resource-rich electrochemical energy storage systems. However, the savage growth of sodium metal and continuous consumption hinder its stable capacity output. Herein, ordered flower-edges of zinc on Al substrate can induce high-entropy solid electrolyte interphase (SEI) to adjust sodium uniform deposition and extremely reduce electrolyte consumption with ultrahigh initial Coulombic efficiency (97.05%) for prolong batteries cycling life. Theoretical and experimental studies have demonstrated that the electron-donating property and exposed edge sites between (100) and (101) facets in zinc flower enhance anion adsorption onto the inner Helmholtz plane accelerating its interface decomposition. Additionally, the ordered zinc edges serve as homogeneous-nucleating template, leading to thin and inorganic-rich SEI layer (18 nm, ZnF2, NaZn13, NaF, and Na2CO3) with high-entropy discrete multicomponent distribution, so that fast and high-flux Na ions transport field, thereby reducing the critical nucleation barrier and promoting sodium high density nucleation (7.36 × 1013 N cm-2) and pyknotic growth (3 mAh cm-2, 22µm). The assembled anode-free sodium batteries exhibit high stability (86%, 90 cycles) under ultrahigh cathode loading (32 mg cm-2). Moreover, the anode-less single-layer pouch batteries exhibit a durable capacity retention of 99% after 600 cycles.

Synthesis of submillimeter-size two-dimensional metal iodides single crystal via undercooling control strategy

Two-dimensional (2D) metal iodides have attracted significant attention in recent years due to their superior optoelectronic properties. However, the current synthesis methods for 2D metal iodides are either time-consuming or not able to synthesize large size crystal. Here we develop an undercooling control strategy based on hot plate assisted vertical vapor deposition for the synthesis of submillimeter-size 2D bismuth iodide (BiI3) single crystal. The whole synthesis process is efficient and only takes one minute in atmosphere. The problem of high nucleation density can be addressed by undercooling control, avoiding the collide of crystals before they grow into large size. This general approach is versatility and can be expanding to synthesize other 2D metal iodides. In addition, nonlinear optical property investigation of BiI3 crystal reveals a thickness-dependent and power-dependent second harmonic response. Our strategy presents a new solution for facile preparation of large-size 2D metal iodides, facilitating their fundamental physics studies and next-generation optoelectronics development.

Blooming microflowers: Shaping TiO2 nanostructures via anodization in metal chloride-based electrolytes

TiO2 microflowers, consisting of nanotubes, were generated via potentiostatic anodization in fluoride-free electrolytes infused with metal chlorides. Anodizing titanium foil at 15 V for 10 min in electrolytes containing 0.1 M of FeCl3·6H2O, CrCl3·6H2O, FeCl2·4H2O, and CuCl2·2H2O yielded nanotubes with outer diameters of approximately 30 nm, 45 nm, 50 nm, and 60 nm, respectively. The introduction of metal chloride to the electrolyte significantly altered the anodization kinetics, facilitating the growth of TiO2 microflowers. These structures consist of nanotube bundles that are of few microns in length with tunable diameters, achieved rapidly within the anodization timeframe. Microflowers formed in FeCl3·6H2O electrolyte feature high aspect ratio TiO2 nanotube bundles with smaller diameters and higher nucleation density, whereas those developed in CrCl3·6H2O, FeCl2·4H2O, and CuCl2·2H2O electrolytes exhibit less preferable morphology.

Revealing the Role of Spacer Layer in Domain Dynamics of Hf0.5Zr0.5O2 Thin Films for Ferroelectrics

AbstractHfO2‐based ferroelectrics offer promises for next‐generation nonvolatile nanoscale devices owing to excellent CMOS compatibility and robust ferroelectricity at the nanoscale. However, fundamentally understanding the mechanism of polarization reversal and domain dynamics is challenging because the role of the spacer layer at the domain level in HfO2‐based ferroelectrics remains elusive. Here, it is realized that visualization of time‐resolved dynamics of nanoscale domain configurations in the epitaxial Hf0.5Zr0.5O2 thin films using phase‐field simulations. Scale‐free domain independent switchability (namely, irreducible stable polar domain down to 1 nm lateral size) and sharp domain walls that originate from weak interactions between adjacent domains characterized by the reduced gradient energy coefficient, which unravels the mesoscale mechanism of spacer layer in domain dynamics are demonstrated. Meanwhile, it is revealed that 180° polarization switching is dominated by the nucleation of a new domain with a high nucleation density, well described by the nucleation‐limited switching model. This study not only provides a fundamental mesoscale mechanism of the spacer layer, but also stimulates further studies on the manipulation of ultra‐scaled single domain state for designing high‐density and fast‐speed HfO2‐based ferroelectric memory.

Controllable regulation of diamond nucleation and growth on GaN substrates through pulse bias duty ratio

GaN/AlN/diamond composite structures were prepared by the pulsed-DC bias-enhance nucleation (BEN) technique. Smooth diamond interface on GaN surface obtained for the first time by BEN technique. Different bias duty ratios (30%–70 %) can regulate the nucleation of diamond. The nucleation density increases and then decreases with the increase of duty ratio. The highest nucleation density was 1011 cm−2 which enough to grow a dense diamond layer on GaN. The effect of BEN treatment on the interface was investigated and some positive and negative results were obtained. After diamond deposition, GaN layer was protected by amorphous carbon and dielectric layers from hydrogen plasma, which implies that the BEN technique has the potential to be applied to grow diamond on GaN surfaces. A smooth and complete interfacial structure was obtained after diamond deposition. After the BEN treatment, 10 nm AlN layer was carbonized into an amorphous structure. BEN duty cycle can modulate GaN/AlN/diamond interface structure, which may reduce interfacial thermal conductivity. These results demonstrate the potential of BEN technique for diamond deposition on GaN substrates and provides a reference for further optimization.

Structure and Properties of Polylactide Composites with TiO2-Lignin Hybrid Fillers.

The research presented in this article focuses on the use of inorganic-organic material, based on titanium dioxide and lignin, as a filler for polylactide (PLA) biocomposites. To date, no research has been conducted to understand the impact of hybrid fillers consisting of TiO2 and lignin on the supermolecular structure and crystallization abilities of polylactide. Polymer composites containing 1, 3 or 5 wt.% of hybrid filler or TiO2 were assessed in terms of their structure, morphology, and thermal properties. Mechanical properties, including tensile testing, bending, impact strength, and hardness, were discussed. The hybrid filler is characterized by a very good electrokinetic stability at pH greater than 3-4. The addition of all fillers led to a small decrease in the glass transition temperature but, most importantly, the addition of 1% of the hybrid filler to the PLA matrix increased the degree of crystallinity of the material by up to 20%. Microscopic studies revealed differences in the crystallization behavior and nucleation ability of fillers. The use of hybrid filler resulted in higher nucleation density and shorter induction time than in unfilled PLA or PLA with only TiO2. The introduction of small amounts of hybrid filler also affected the mechanical properties of the composites, causing an increase in bending strength and hardness. This information may be useful from a technological process standpoint and may also help to increase the range of applicability of biobased materials.

The influence of nitrogen and oxygen on the high nucleation density diamond growth

High nucleation density diamond films were grown on silicon substrates with a high-density nano-diamond suspension crystal seed. By keeping other parameters constant and varying the amounts of oxygen and nitrogen added, diamond films were grown using MPCVD equipment. The composition, structure, and properties of the diamond films were characterized using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results show that the average grain size of samples grown with added oxygen and nitrogen as assisting gases significantly decreased, exhibiting improved crystallinity and fewer defects. However, there was a certain increase in the relative content of graphite, along with the presence of trans-polyacetylene. Furthermore, as the ratio of oxygen to nitrogen increased, the samples exhibited better crystallinity, fewer defects, and overall higher growth quality. The relative content of graphite initially increased, then decreased, and increased again.

Processing temperature-dependent nucleation and growth behaviors of polypropylene nucleated by a bisamide nucleating agent

It has been widely reported that the processing temperature significantly influenced the effectiveness of a β-nucleating agent (β-NA) in polypropylene (PP) and thus leads to variations in the final relative content of β-phase (kβ). To comprehensively understand the changing kβ with processing temperature, PP nucleated by a bisamide β-NA, N,N′-dicyclohexylterephthalamide (DCHT), was heating-treated at different temperatures (Tf) in the range of 200–250 °C, and the impact of Tf on the nucleation and subsequent growth behaviors of the α- and β-phases were separately investigated. Under low Tf, DCHT induced a high relative density of β-nuclei to α-nuclei (Nβ/Nα) with high total nucleation density (N), and both the α- and β-phases grew competitively until the crystallization ended. Under middle Tf, the Nβ/Nα became low with middle N induced by DCHT, and the faster-growing phase dominated the subsequent growth process. Under high Tf, there was a middle Nβ/Nα with low N, and the faster-growing phase became more dominant during the growth process. Based on the observed morphology of DCHT, the decreasing N with Tf could be associated with the specific surface area, the varying Nβ/Nα could be attributed to the variations in both the energy barrier and the surface area of β-nucleation under diverse DCHT morphologies, and the varying growth behavior was probably associated with the outer surface shape of diverse DCHT morphologies. Combining the thorough analysis of the changing nucleation and growth behaviors with Tf, a possible mechanism was proposed to explain the effect of processing temperature on the final polymorphic composition.

Metal Films on Two-Dimensional Materials: van der Waals Contacts and Raman Enhancement.

Electronic devices based on two-dimensional (2D) materials will need ultraclean and defect-free van der Waals (vdW) contacts with three-dimensional (3D) metals. It is therefore important to understand how vdW metal films deposit on 2D surfaces. Here, we study the growth and nucleation of vdW metal films of indium (In) and non-vdW metal films of gold (Au), deposited on 2D MoS2 and graphene. In follows a 2D growth mode in contrast to Au that follows a 3D growth mode. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to image the morphology of metal clusters during growth and quantify the nucleation density. As compared to Au, In atoms exhibit nearly 50 times higher diffusivity (3.65 × 10-6 μm-2 s-1) and half the nucleation density (64.9 ± 2.46 μm-2), leading to larger grain sizes (∼60 nm for 5 nm In on monolayer MoS2). The grain size of In can be further increased by reducing the 2D surface roughness, while the grain size for Au is limited by its high nucleation density due to the creation of interface defects during deposition. The vdW gap between In and MoS2 and graphene leads to strong enhancement (>103) in their Raman signal intensity due to localized surface plasmon resonance. In the absence of a vdW gap, the plasmon-mediated enhancement in Raman does not occur.

Effect of thermal-oxidative and mechanical degradation of recycled LDPE on foaming

In this study, we investigated the effect of recycling process on the molecular structure, viscoelasticity and foaming behavior of low density polyethylene (LDPE). A series of LDPE samples with different recycling process was prepared by multiple extrusion using a twin-screw extruder. The molecular weight distribution (MWD) was characterized by gel permeation chromatography (GPC). Wider MWD indicated the generation of higher molecular weight products. Small-amplitude oscillation rheology showed reduced loss factors, indicating that the chain entanglement was more difficult to relax. Moreover, nonlinear viscoelasticity was investigated using elongational rheology and molecular stress function (MSF) model. The results showed a steeper strain hardening exhibited in recycled LDPE. The correlated parameter β in the MSF model indicated that the recycling did not significantly change the branches regularity in LDPE, while the increasing [Formula: see text], the other correlated parameter, indicated that the chain entanglement was enhanced, which was corresponded to the improvement of high molecular weight component. The foaming results revealed that the recycled LDPE had finer cellular structure and higher nucleation density. Moreover, despite adding PP and active CaCO3 to simulate the impurities, the foamability loss of these mixed samples was well restricted and still valuable. Recycled LDPE is instead better than its corresponding virgin one in foaming performance, exhibiting the application potential for further developments.

Melting Behaviors of Bio-Based Poly(propylene 2,5-furan dicarboxylate)-b-poly(ethylene glycol) Co Polymers Related to Their Crystal Morphology.

In this experiment, a series of poly(propylene 2,5-furan dicarboxylate)-b-poly(ethylene glycol) (PPFEG) copolymers with different ratios were synthesized using melt polycondensation of dimethylfuran-2,5-dicarboxylate (DMFD), 1,3-propanediol (PDO) and poly(ethylene glycol) (PEG). The effect of PEG content on the crystallization behavior of the poly(propylene 2,5-furan dicarboxylate) (PPF) copolymers was investigated. For PPF, the nucleation density of the β-crystals was higher than that of α-crystals. As Tc increases, the β crystals are suppressed more, but at Tc = 140 °C, the bulk of PPF has already been converted to α crystals, which crystallize faster at higher nucleation densities, resulting in a difference in polymer properties. For this case, we chose to add a soft segment material, PEG, which led to an early multi-melt crystallization behavior of the PPF. The addition of PEG led to a decrease in the crystallization temperature of PPF, as well as a decrease in the cold crystallization peak of PPF. From the crystalline morphology, it can be seen that the addition of PEG caused the transformation of the PPF crystalline form to occur earlier. From the crystalline morphology of PPF at 155 °C, it can be observed that the ring-banded spherical crystals of the PPF appear slowly with increasing time. With the addition of PEG, spherical crystals of the ring band appeared earlier, and even appeared first, and then disappeared slowly.

AFM, Nano − indentation and TEM characterization study of HFCVD diamond on tantalum and diamond seeded cemented carbide inserts

This research describes an enhanced characterization technique for studying diamond production by hot filament chemical vapor deposition (HFCVD) on cemented carbide (WC − Co) SPUN inserts. The characteristics of diamond (Dia.) and tantalum (Ta) seeded powders used as seeding materials were determined using a variety of microscopic characterizations. Topographic and cross-sectional pictures obtained using field emission scanning electron microscopy (FESEM), respectively, demonstrate that the Ta-seeded substrate had a higher nucleation density, whereas the Dia.-seeded substrate had thicker coatings. Findings from atomic force microscopy (AFM) show that Ta-seeded substrates' mechanical strength is expectedly higher due to the smaller grains and higher apparent density. According to the X-ray diffraction (XRD) results, the Dia. − seeded substrate displayed a lower dislocation density, strain, and Burgers' vector magnitude. The highly crystalline structure of the Ta-seeded sample appeared in the Transmission electron microscopy (TEM) selected area electron diffraction (SAED) images. However, the multi-gradient sample structure of the Dia.-seeded Sample obtained increased its ductility property. The nanoindentation results demonstrated that the Ta-seeded substrate had a higher hardness while the Dia.-seeded substrate had a higher Stiffness and Youngs' modulus value. The findings are crucial for present-day CVD applications since Ta powders offer an alternative option to diamond powders.

Immersion Tin Plating Enabling Reliable Wettable Flanks on QFN Packages

The automotive market increasingly uses bottom-termination IC packages, like Quad-Flat No leads (QFN) packages, for miniaturization, cost reduction and performance. QFN lead frames are electroplated with 8?12 um of tin for PCB soldering, but subsequent singulation exposes the copper-alloy lead frame at the cut edges. On these exposed lead flanks a solder fillet does not form, making Automatic Optical Inspection (AOI) of solder joints on lead-less packages not reliable. A solder fillet on lead flanks also improves the reliability of solder joints. Therefore, the automotive industry strives for a tin plated wettable flank on lead-less packages. Several approaches, e.g. dimpled or step-cut leads, to create a wettable flank are in use or development. Disadvantage of these methods is that only a part of the flank is tin-plated. Immersion tin plating processes are able to fully plate lead flanks. However, the maximum ~1.5um of standard self-limiting displacement immersion tin processes is too thin to comply with the durability requirements of automotive tin solder finishes. This contribution will discuss an immersion tin-plating process, machine concept and test results for a >2 um tin plated wettable flanks. The immersion tin plating process consist of the following process steps: 1. A high-pressure spray rinse prevents incomplete tin coverage by removing copper burrs formed during singulation. 2. A selective descaling process removes the natural copper oxide film on the exposed copper leads. 3. A selective activation process creates a high tin nucleation density to obtain a fine-grained tin layer. 4. The autocatalytic immersion tin process plates a 2 ? 3um tin layer in 45-60 minutes at 70-75oC. 5. An anti-tarnish process protects the tin layer against oxidation. Finally, rinsing and drying remove all traces of the used chemicals from the packages with tin plated flanks. A machine concept for the immersion tin-plating process is currently under development. The lead-less packages are processed directly on Standard singulation tape rings without repacking or manipulation of the packages. This enables a throughput of 20 tape rings per hour with the full package traceability required for the automotive market. Different types of QFN packages mounted on singulation tape were tin plated and subjected to standard (JEDEC J-STD-002E) solderability tests for component lead durability. Fine-grained 2-3 um thick pure tin deposit of good visual quality were obtained on the exposed QFN copper lead sidewalls with the following properties: • 0.5-1.5um residual tin layer after intermetallic formation in 8 h steam aging and 16 h oven bake. • 100% solder wetting after 6h dry bake at 150C • 100% solder wetting after 8h steam aging (93C and 80-90% RH). • 100% solder fillet height after ceramic glass test.

Analysis of phase transformation thermodynamics and kinetics and its relationship to structure-mechanical properties in a medium-Mn high strength steel

The difference in transformation mechanisms between the normal and reverse phase transformation in medium Mn steel was revealed using thermodynamic and kinetic analysis. The results indicate that the austenite formation during the reverse phase transformation is a fast reaction, significant amount of 46.9 vol% retained austenite is obtained after subjected partial reversion at 650 °C × 1 h. At the nucleation stage, the lath-like structure, dislocations, martensitic packet boundaries, and grain boundaries provide high-density nucleation sites for austenite formation. The critical temperature of austenite formation is reduced by the enrichment of Mn and C. However, no ferrite transformation occurred during the normal phase transformation (650 °C × 6 h isothermal treatment and subsequent furnace-cooling process). At the nucleation stage, the undersaturated Mn and C in the prior austenite grain interior provide insufficient concentration fluctuation, leading to a low nucleation rate. At the phase growth stage, the atomic mobility of Mn and C in the parent austenite (control the ferrite growth) is 1/69 and 1/282 than that in ferrite (control the austenite growth) at 650 °C. The differences in nucleation site density, driving force, and element diffusion rate lead to significant variations in phase transformation behaviors. The excellent mechanical property with the product of strength and elongation (PSE) exceeding 20 GPa % is achieved via the sustained transformation-induced plasticity (TRIP) effect by metastable retained austenite over a large strain range.

Effect of mixed wettability surfaces on flow boiling heat transfer at subatmospheric pressures

Subatmospheric flow boiling heat transfer is a promising method for electronics cooling due to lower saturation temperatures. However, pressure is a crucial parameter that affects surface tension and vapor density. In this study, the effect of surface mixed wettability configuration on bubble dynamics and flow boiling was investigated under atmospheric and subatmospheric pressure conditions. Superhydrophilic, superhydrophobic, and mixed-wettability surfaces were prepared and tested at various heat fluxes and three system pressures of 48 kPa, 68 kPa, and 101 kPa. The channel dimensions were 50 mm × 15 mm, and the channel had a depth of 1 mm. The results showed that biphilic surfaces enhanced the performance up to 28% compared to superhydrophilic surfaces at high heat fluxes for subatmospheric boiling. Flow visualization efforts reveal that mixed-wettability surfaces improve heat transfer by extending the efficient slug regime to higher heat fluxes by preventing dried spot formation. These surfaces benefit from high density nucleation sites at low and medium heat fluxes, resulting in a noticeable performance improvement compared to the superhydrophilic surface. The obtained experimental data in this study will be helpful for the development of thermal-fluid systems operating under subatmospheric conditions.

High-strength copper foil prepared with 2-mercaptothiazoline by direct current electrodeposition

A kind of new additive for ultra-thin copper foils with high tensile strength is reported in this work. The highest strength is about 700 MPa with 12 mg/L 2-mercaptothiazoline, and the strengthening effects and mechanisms in different concentrations are studied in detail. 2-Mercaptothiazoline significantly improves the tensile strength of electrolytic copper foils by refining the grains and effectively impeding the slips of dislocations. Fine grains also provide a smooth and flat surface for foils, and weaken the preferred orientation of grains in the cross-section, contributing to the high strength of copper foils at different aspects. The addition of the 2-mercaptothiazoline obviously inhibits the electron transfer process of metal electrodeposition and enhances the electrochemical polarization, resulting in high nucleation density and small nuclei to form fine grains. The high-strength copper foils with a very thin thickness are placed great expectations on the industrial application of lithium-ion batteries.

Additive Molecules Adsorbed on Monolayer PbI2: Atomic Mechanism of Solvent Engineering for Perovskite Solar Cells.

Solvent engineering is highly essential for the upscaling synthesis of high-quality metal halide perovskite materials for solar cells. The complexity in the colloidal containing various residual species poses great difficulty in the design of the formula of the solvent. Knowledge of the energetics of the solvent-lead iodide (PbI2) adduct allows a quantitative evaluation of the coordination ability of the solvent. Herein, first-principles calculations are performed to explore the interaction of various organic solvents (Fa, AC, DMSO, DMF, GBL, THTO, NMP, and DPSO) with PbI2. Our study establishes the energetics hierarchy with an order of interaction as DPSO > THTO > NMP > DMSO > DMF > GBL. Different from the common notion of forming intimate solvent-Pb bonds, our calculations reveal that DMF and GBL cannot form direct solvent-Pb2+ bonding. Other solvent bases, such as DMSO, THTO, NMP, and DPSO, form direct solvent-Pb bonds, which penetrate through the top iodine plane and possess much stronger adsorption than DMF and GBL. A strong solvent-PbI2 adhesion (i.e., DPSO, NMP, and DMSO), associated with a high coordinating ability, explains low volatility, retarded precipitation of the perovskite solute, and tendency of a large grain size in the experiment. In contrast, weakly coupled solvent-PbI2 adducts (i.e., DMF) induces a fast evaporation of the solvent, accordingly a high nucleation density and small grains of perovskites are observed. For the first time, we reveal the promoted absorption above the iodine vacancy, which implies the need for pre-treatment of PbI2 like vacuum annealing to stabilize solvent-PbI2 adducts. Our work establishes a quantitative evaluation of the strength of the solvent-PbI2 adducts from the atomic scale perspective, which allows the selective engineering of the solvent for high-quality perovskite films.

Nucleation and growth of graphene at different temperatures by plasma enhanced chemical vapor deposition

Temperature plays an important role in the synthesis of graphene by chemical vapor deposition. In the low-temperature plasma-enhanced chemical vapor deposition (PECVD) process, although the cleavage of hydrocarbon precursor no longer depends on growth temperature, which can affect the nucleation and growth of graphene by the diffusion and adsorption of active species, the catalytic ability of substrate and other factors, and ultimately lead to various growth of graphene. In this paper, the nucleation and growth of graphene at different temperatures by PECVD were studied. We noted that the nucleation and growth of graphene varied greatly in different temperature zones. Graphene could not be grown at low temperatures (< 600 ℃). At the medium and low temperature (650 ∼ 800 ℃), high nucleation density of graphene with nanometer size were produced. In the middle and high temperature region (850 ∼ 900 ℃), larger grains of graphene grown, and in the high temperature region (> 950 ℃), the coexistence of large and small grains was finally formed. In addition, the models of the nucleation and growth of graphene in different temperature zones were proposed.