| 1. |
- Dong, Y. B., et al.
(författare)
-
The growth of graphene on Ni–Cu alloy thin films at a low temperature and its carbon diffusion mechanism
- 2019
-
Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:11
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2 /Si substrate at a low temperature (~600◦ C).
|
|
| 2. |
- Guo, W., et al.
(författare)
-
Rapid chemical vapor deposition of graphene on liquid copper
- 2016
-
Ingår i: Synthetic Metals. - : Elsevier BV. - 0379-6779. ; 216, s. 93-97
-
Tidskriftsartikel (refereegranskat)abstract
- Molten copper is used to catalyze the graphene synthesis by chemical vapor deposition. The Cu has no grains above melting temperature, which is favorable for graphene growth. Using a vertical cold wall system, the deposition rate is drastically increased as compared with common hot-wall tube furnaces, pushing the method one step forward towards applications. A molybdenum-graphite Joule heater is used to avoid mechanical deformation of the carrier foil for the catalyst to ease the subsequent processes. The rapid deposition makes it possible to observe graphene growth on liquid Cu even at low pressure, where severe Cu evaporation simultaneously occurs.
|
|
| 3. |
- Liu, Lihui, 1985, et al.
(författare)
-
A Mechanism for Highly Efficient Electrochemical Bubbling Delamination of CVD-Grown Graphene from Metal Substrates
- 2016
-
Ingår i: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 3:8
-
Tidskriftsartikel (refereegranskat)abstract
- In most cases, transfer of chemical-vapor-deposited 2D materials from metallic foil catalysts onto a target substrate is the most necessary step for their promising fundamental studies and applications. Recently, a highly efficient and nondestructive electrochemical delamination method has been proposed as an alternative to the conventional etching transfer method, which alleviates the problem of cost and environment pollution because it eliminates the need to etch away the metals. Here, the mechanism of the electrochemical bubbling delamination process is elucidated by studying the effect of the various electrolytes on the delamination rate. A capacitor-based circuit model is proposed and confirmed by the electrochemical impedance spectroscopy results. A factor of 27 decrease in the time required for complete graphene delamination from the platinum cathodes is found when increasing the NaOH ratio in the electrolyte solution. The opposite trend is observed for delamination at the anode. The surface screening effect induced by nonreactive ions in the vicinity of the electrodes plays a key role in the delamination efficiency. The analysis is generic and can be used as a guideline to describe and design the electrochemical delamination of other 2D materials from their metal catalysts as well.
|
|
| 4. |
- Liu, Q., et al.
(författare)
-
High responsivity sensing of unfocused laser and white light using graphene photodetectors grown by chemical vapor deposition
- 2016
-
Ingår i: Optical Materials Express. - 2159-3930. ; 6:7, s. 2158-2164
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene photodetectors grown by chemical vapor deposition are fabricated for unfocused laser and white light sensing. The unfocused light enlarges the illuminated graphene area and mimics the real-life sensing conditions, yielding a responsivity of 104 mA/W at room temperature without enhancing absorbance by waveguide and plasmonics. The devices are based on positive photoconductivity from the electron-hole photocarrier pairs and the bolometric-effect-induced negative photoconductivity. The buried off-center local gate induces a net internal potential in the graphene. The relative strength of the two photoconductivities depends on the gate voltage. The technology is scalable, which is a step ahead toward real applications.
|
|
| 5. |
- Pan, G. Z., et al.
(författare)
-
Analysis of optical coupling behavior in two-dimensional implant-defined coherently coupled vertical-cavity surface-emitting laser arrays
- 2018
-
Ingår i: Photonics Research. - 2327-9125. ; 6:11, s. 1048-1055
-
Tidskriftsartikel (refereegranskat)abstract
- Optical coupling behavior and associated effects in two-dimensional implant-defined coherently coupled vertical-cavity surface-emitting laser (VCSEL) arrays are studied via both experiments and theoretical calculations. Experiments show that optical coupling between array elements can enhance the array’s output power. Additionally, optical coupling via leaky optical fields can provide extra optical gain for the array elements, which can then reduce the thresholds of these elements. Elements can even be pumped without current injection to emit light by receiving a strong leaky optical field from other array elements. Optical coupling can also cause unusual phenomena: the central elements in large-area coherently coupled VCSEL arrays that lase prior to the outer elements when the arrays are biased, or the average injection current required for each element to lase, which is much lower than the threshold for a single VCSEL. Theoretical calculations are performed to explain the experimental results.
|
|
| 6. |
- Sun, Jie, 1977, et al.
(författare)
-
Electrochemical Bubbling Transfer of Graphene Using a Polymer Support with Encapsulated Air Gap as Permeation Stopping Layer
- 2016
-
Ingår i: Journal of Nanomaterials. - : Hindawi Limited. - 1687-4129 .- 1687-4110. ; 2016
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochemical bubbling transfer of graphene is a technique with high industrial potential due to its scalability, time- and cost-effectiveness, and ecofriendliness. However, the graphene is often damaged due to the turbulence and the trapped bubbles formed by the direct H2O and H+ permeation through the supporting polymer. We invent a graphene mechanical support of polyethylene terephthalate foil/plastic frame/poly(methyl methacrylate) sandwich, with an encapsulated air gap as the permeation stopping layer. The graphene damage is drastically reduced, as confirmed by the morphology and structural and electrical characterization, ultimately improving the controllability/reproducibility of the bubbling transfer of graphene and other two-dimensional materials.
|
|
| 7. |
- Sun, Jie, 1977, et al.
(författare)
-
Mechanism of Electrochemical Delamination of Two-Dimensional Materials from Their Native Substrates by Bubbling
- 2015
-
Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 15:12, s. 31811-31820
-
Tidskriftsartikel (refereegranskat)abstract
- A capacitor-based circuit model is proposed to explain the electrochemical delamination of two-dimensional materials from their native substrates where produced gas bubbles squeeze into the interface. The delamination is actually the electric breakdown of the capacitor formed between the solution and substrate. To facilitate the procedure, the backside of the ubstrate has to be shielded so that the capacitor breakdown voltage can be reached. The screening effect can be induced either by nonreactive ions around the electrode or, more effectively, by an undetachable insulator. This mechanism serves as a guideline for the surface science and applications involving the bubbling delamination.
|
|
| 8. |
- Sun, Jie, 1977, et al.
(författare)
-
Synthesis Methods of Two-Dimensional MoS2: A Brief Review
- 2017
-
Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 7:7, s. Article no 198 -
-
Forskningsöversikt (refereegranskat)abstract
- Molybdenum disulfide (MoS2) is one of the most important two-dimensional materials after graphene. Monolayer MoS2 has a direct bandgap (1.9 eV) and is potentially suitable for post-silicon electronics. Among all atomically thin semiconductors, MoS2's synthesis techniques are more developed. Here, we review the recent developments in the synthesis of hexagonal MoS2, where they are categorized into top-down and bottom-up approaches. Micromechanical exfoliation is convenient for beginners and basic research. Liquid phase exfoliation and solutions for chemical processes are cheap and suitable for large-scale production; yielding materials mostly in powders with different shapes, sizes and layer numbers. MoS2 films on a substrate targeting high-end nanoelectronic applications can be produced by chemical vapor deposition, compatible with the semiconductor industry. Usually, metal catalysts are unnecessary. Unlike graphene, the transfer of atomic layers is omitted. We especially emphasize the recent advances in metalorganic chemical vapor deposition and atomic layer deposition, where gaseous precursors are used. These processes grow MoS2 with the smallest building-blocks, naturally promising higher quality and controllability. Most likely, this will be an important direction in the field. Nevertheless, today none of those methods reproducibly produces MoS2 with competitive quality. There is a long way to go for MoS2 in real-life electronic device applications.
|
|
| 9. |
- Xiong, Fangzhu, et al.
(författare)
-
Transfer-free graphene-like thin films on GaN LED epiwafers grown by PECVD using an ultrathin Pt catalyst for transparent electrode applications
- 2019
-
Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 12:21, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we grew transfer-free graphene-like thin films (GLTFs) directly on gallium nitride (GaN)/sapphire light-emitting diode (LED) substrates. Their electrical, optical and thermal properties were studied for transparent electrode applications. Ultrathin platinum (2 nm) was used as the catalyst in the plasma-enhanced chemical vapor deposition (PECVD). The growth parameters were adjusted such that the high temperature exposure of GaN wafers was reduced to its minimum (deposition temperature as low as 600 °C) to ensure the intactness of GaN epilayers. In a comparison study of the Pt-GLTF GaN LED devices and Pt-only LED devices, the former was found to be superior in most aspects, including surface sheet resistance, power consumption, and temperature distribution, but not in optical transmission. This confirmed that the as-developed GLTF-based transparent electrodes had good current spreading, current injection and thermal spreading functionalities. Most importantly, the technique presented herein does not involve any material transfer, rendering a scalable, controllable, reproducible and semiconductor industry-compatible solution for transparent electrodes in GaN-based optoelectronic devices.
|
|
| 10. |
- Xu, K., et al.
(författare)
-
GaN nanorod light emitting diodes with suspended graphene transparent electrodes grown by rapid chemical vapor deposition
- 2013
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:22, s. 5-
-
Tidskriftsartikel (refereegranskat)abstract
- Ordered and dense GaN light emitting nanorods are studied with polycrystalline graphene grown by rapid chemical vapor deposition as suspended transparent electrodes. As the substitute of indium tin oxide, the graphene avoids complex processing to fill up the gaps between nanorods and subsequent surface flattening and offers high conductivity to improve the carrier injection. The as-fabricated devices have 32% improvement in light output power compared to conventional planar GaN-graphene diodes. The suspended graphene remains electrically stable up to 300 degrees C in air. The graphene can be obtained at low cost and high efficiency, indicating its high potential in future applications.
|
|
