Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

Graphene is the two-dimensional crystalline form of carbon whose extraordinary charge carrier mobility and other unique features hold great promise for nanoscale electronics. [ 1 ] Because graphene has no bandgap, however, its electrical conductivity cannot be completely controlled like classical semiconductor. Theoretical and experimental studies on graphene doping show the possibility of opening the bandgap and modulating conducting types by substituting carbon atoms with foreign atoms. [ 2 ] Graphene is easily p-doped by adsorbates like physisorbed oxygen molecules, but complementary doping (both n-type and p-type doping) is essential for functional device applications like complementary metal-oxidesemiconductor (CMOS) circuits. [ 3 ] Recently, a number of approaches have been proposed to synthesize nitrogen-doped graphene (NG), such as chemical vapor deposition (CVD), [ 2 a, 4 ] arc-discharge, [ 2 b, 5 ] and post treatments. [ 6 ] Here, we report a new approach which makes use of embedded nitrogen and carbon atoms in metal substrate to prepare NG. As doping is accompanied with the combination of carbon atoms into graphene during annealing process, N atoms can be substitutionally doped into the graphene lattice. Our method provides not only a better control over the doping density but also a potential advantage to precisely control the solid dopants at desired locations to achieve patterned doping. Our approach for NG synthesis is actually the enthusiastic utilization of the very common segregation phenomenon to turn the trace amount of carbon and nitrogen dissolved in bulk metals into NG. [ 7 ] Metals usually contain a trace amount of carbon impurities, which could be brought into evaporated metal fi lm during the electron beam deposition process. [7a, 8 ]

Synthesis of nitrogen-doped graphene using embedded carbon and nitrogen sources.

The discovery of graphene one decade ago has triggered enormous interest in developing two-dimensional materials (2DMs)—that is 2D allotropes of various elements or compounds (consisting of two or more covalently bonded elements) or molecular frameworks with periodic structures. At present, various synthesis strategies have been exploited to produce 2DMs, such as top-down exfoliation and bottom-up chemical vapor deposition and solution synthesis methods. In this review article, we will highlight the interfacial roles toward the controlled synthesis of inorganic and organic 2DMs with varied structural features. We will summarize the state-of-the-art progress on interfacial synthesis strategies and address their advancements in the structural, morphological, and crystalline control by the direction of the arrangement of the molecules or precursors at a confined 2D space. First, we will provide an overview of the interfaces and introduce their advantages and uniqueness for the synthesis of 2DMs, followed by ...

Interface-Assisted Synthesis of 2D Materials: Trend and Challenges

We report that highly crystalline graphene can be obtained from well-controlled surface morphology of the copper substrate. Flat copper surface was prepared by using a chemical mechanical polishing method. At early growth stage, the density of graphene nucleation seeds from polished Cu film was much lower and the domain sizes of graphene flakes were larger than those from unpolished Cu film. At later growth stage, these domains were stitched together to form monolayer graphene, where the orientation of each domain crystal was unexpectedly not much different from each other. We also found that grain boundaries and intentionally formed scratched area play an important role for nucleation seeds. Although the best monolayer graphene was grown from polished Cu with a low sheet resistance of 260 Ω/sq, a small portion of multilayers were also formed near the impurity particles or locally protruded parts.

Influence of Copper Morphology in Forming Nucleation Seeds for Graphene Growth

Graphene films have been formed by annealing Ni thin films at 800 °C under vacuum conditions. The Ni thin films are deposited on Si/SiO2 and, following annealing, have a polycrystalline morphology with grain sizes on the order of 1 μm. Following growth, the Ni is removed by etching, and the graphene is transferred as a single continuous layer onto a separate surface. The fraction of monolayer graphene is investigated using optical and electron microscopy and Raman spectroscopy and is shown to be >75%.

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Formation of Monolayer Graphene by Annealing Sacrificial Nickel Thin Films

Graphene is formed through the thermally induced decomposition of C60 in combination with a Ni thin film. After transfer to a SiO2 substrate, optical microscopy and Raman spectroscopy confirm the presence of graphene for films of C60 buried under nickel or alternatively for C60 adsorbed on a nickel surface. For buried films the graphene thickness is shown to depend on the fullerene dosage, with evidence of domain growth from nucleation sites separated by tens of micrometers. The adsorption of C60 and the changes arising from annealing are also monitored using scanning tunneling microscopy. We relate our results to previous studies of the decomposition of C60 on nickel and other transition metals.

Graphene Formation by Decomposition of C60

This study gives a simple physics explanation behind the Indian Ocean earthquake, called December 26ths Tsunami The explanation based on physics energy conservation and wave properties have been used to understand this phenomenon

The Physics of Tsunami: Basic understanding of the Indian Ocean disaster

In this work, we investigate by numerical simulation the impact of using standard mobility models versus an inclusion of thin-layer mobility models on 7 nm thin body and 10 nm thin buried oxide (UTBB) SOI MOSFETs of 25 nm gate length (Lg=25 nm). Simulations were performed for both no-ground plane (no-GP) and ground plane (GP) structures for Vds = 20 mV and 1.0 V and substrate biasing of Vsub = 0 V and 0.5 V. Results of on-current (Ion), off-current (Ioff) and linear subthreshold swing (SSlin) only showed marginal differences between the two mobility models used. Significant differences can only be seen in the values of Drain-Induced Barrier Lowering (DIBL) where in this work is extracted as DIBL=(Vthlin - Vthsat)/ΔVd. Moreover, the inclusion of thin layer mobility model gives higher values of transconductance (gm) as compared to standard mobility model.

Impact of Different Mobility Models on 32nm Node UTBB SOI MOSFETs

A Metal-Insulator-Metal (MIM) capacitor with high capacitance, high breakdown voltage, and low leakage current is aspired so that the device can be applied in many electronic applications. The most significant factors that affect the MIM capacitor’s performance is the design and the dielectric materials used. In this study, MIM capacitors are simulated using different dielectric materials and different number of dielectric layers from two layers up to seven layers.  The effect of the different dielectric constants ( k ) to the performance of the MIM capacitors is also studied, whereas this work investigates the effect of using low- k and high- k dielectric materials. The dielectric materials used in this study with high- k are Al 2 O 3 and HfO 2 , while the low- k dielectric materials are SiO 2 and Si 3 N 4 . The results demonstrate that the dielectric materials with high- k produce the highest capacitance. Results also show that metal-Al 2 O 3 interfaces increase the performance of the MIM capacitors. By increasing the number of dielectric layers to seven stacks, the capacitance and breakdown voltage reach its highest value at 0.39 nF and 240 V, respectively.

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S. N. Sabki

Papers

Formation of Monolayer Graphene by Annealing Sacrificial Nickel Thin Films

Graphene Formation by Decomposition of C60

The Physics of Tsunami: Basic understanding of the Indian Ocean disaster

Impact of Different Mobility Models on 32nm Node UTBB SOI MOSFETs

The Effect of Different Dielectric Materials in Designing High-Performance Metal-Insulator-Metal (MIM) Capacitors