The properties of two-dimensional (2D) materials are readily affected by their surroundings. Therefore, the underlying substrates and surrounding materials always disturb the pristine properties of 2D materials. Herein, we describe how the pristine properties of suspended 2D materials can be precisely extracted from Raman and photoluminescence (PL) spectra with great signal enhancements by taking advantage of both air gap suspension and nanocavity enhancement effects. The modes of the Raman emission lines were enhanced to almost the same degree when the 2D materials were positioned over the nanocavity: the 2D/G peaks of suspended single-layer graphene (SLG) and the E 1 2g /A 1g peaks of MoS 2 were significantly enhanced almost equally. Moreover, recording Raman and PL spectra at different positions of the suspended 2D materials was a very powerful tool for observing charge transfer between the pristine 2D materials and the surrounding materials. We also found that the residual holes of the suspended SLG could be neutralized by aluminum (Al) at certain positions. By employing the air cavity structure, we could readily locate the charge neutrality point of the suspended 2D materials. In addition, the PL intensity of MoS 2 could be greatly enhanced when using the same nanocavity. The great enhancements in the PL signals from the suspended 2D materials allowed us to further investigate the spectral weights of both the A 0 exciton and A − trion peaks when MoS 2 was suspended or supported upon various metal films. This approach may open up new doors for techniques allowing precise characterization of abundant information from pristine and suspended 2D materials.
We have used a carbothermal process in the absence of a catalyst or template to prepare two-dimensional (2D) platinum (Pt) nanoplatelets and one-dimensional (1D) Pt nanobelts on sapphire surfaces. This paper describes the first examples of the growth of Pt nanobelts and mesobelts. It appears that the presence of adequate quantities of diamond and Y 2 O 3 powder at a molar ratio was a critical factor controlling the Pt gas species to form nanobelts at a relative low level of supersaturation. When the growth time was 15 h, we obtained ultralong (0.5 mm) mesobelts and microsheets. Electrical measurements indicated that the single-crystal Pt nanobelt had an extremely low resistivity of 16.8 µΩ cm and a failure current density of greater than 1 × 10 7 A cm -2 . These unique Pt nanobelts are potentially attractive nanoscale building blocks for use as interconnects in nanoelectronic devices.Research into noble-metal nanostructures is stimulated by the fascinating size-and shape-dependent properties of these nanomaterials. Because of their unique and tunable properties, they hold promise for various applications in optics, electronics, information storage, biological labeling, and imaging. 1 Platinum (Pt) is one of the most important noble metals, 2-4 especially for its application in the fields of molecular scale electronic devices, 5 biosensors, 6 and catalysts. 7,8 For example, because platinum is inert, highly thermally stable in air, and does not cause contamination of the integrated circuit, it is the most common choice for use in integrated circuit repair and modification and bottom electrode. 9 Also, because of its nice performance toward the detection of hydrogen peroxide, a typical enzymatic product, platinum electrodes, and platinum nanostructure modified electrodes have been widely used for fabrication of biosensors. 10 Because Pt has a face-centered cubic (fcc) structure, there is no crystallographic driving force for anisotropic growth. As a result, Pt atoms generally assemble to form faceted spheres (e.g., singlecrystal cuboctahedrons) 11 and, in particular, few reports exist describing the growth of two-dimensional (2D) and one-dimensional (1D) Pt nanostructures. In spite of that, it is common for other fcc metals (like Ag, Au) to form 2D nanostructures, such as triangular and hexagonal platelets, when transition-metal colloids are prepared in solution through the reduction of metal salts. 12-14 Most reports on the preparation of Pt nanostructures have been limited to the synthesis of nanoparticles (NPs) or polycrystalline nanorods using either solution-phase techniques 15 or template-directed synthesis 16 for examples of synthesized 2D and 1D Pt nanostructures, respectively. Tan et al. prepared 2D Pt NPs by the reduction of their salts with a weak reductant -potassium bitartrate. In their study, Pt NPs have two dominant shape distributions, triangular and square. 17 For an instance of synthesized 1D Pt nanostructures, Zhao et al. synthesized polycrystalline Pt nanowire array electrode by dc electrodeposi...
Ceramic-to-metal heterojunctions have been established to improve high-temperature stability for applications in aerospace and harsh environments. In this work, we employed low-temperature diffusion bonding to realize an alumina/Cu heterogeneous joint. Using a thin layer of lanthanum-doped titanium (La-doped Ti) to metallize the alumina surface, we achieved the bonding at a temperature range of 250–350 °C. We produced a uniform, thermally stable, and high-strength alumina/Cu joint after a hot-press process in vacuum. Signals from X-ray diffraction (XRD) suggested the successful diffusion of Ti and La into the alumina substrate, as Ti can easily substitute Al in alumina, and La has a better oxygen affinity than that of Al. The transmission electron microscopy and XRD results also showed the existence of CuxTiyO phases without CuxTiy or LaOx. In addition, the bonding strength of alumina/copper hot-pressed at 250, 300, and 350 °C were 7.5, 9.8 and 15.0 MPa, respectively. The process developed in this study successfully lowered the bonding temperature for the alumina/copper joint.
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