Introduction
Massless Dirac fermions in graphene
The reciprocal lattice vectors are 𝒃𝒃1 =2𝜋𝜋. The first Brillouin zone is a hexagon and has two non-equivalent points K and K' at the corner of the graphene:. Using the tight-binding model and considering only nearest-neighbor hopping, the tight-binding Hamiltonian is described by the 2 × 2 matrix. where 𝒌𝒌 is the wave vector and. energy bands have the form.4,5.
Landau quantization in single layer graphene
In addition to applying a real magnetic field in graphene, it is well known that structural deformations of the graphene lattice can result in local stresses and induce pseudo-magnetic fields and Landau levels. It has also been theoretically proposed that a certain controlled voltage can induce a nearly uniform pseudo-magnetic field and cause a pseudo-magnetic quantum Hall effect.6 Fig.
Synthesis of graphene and graphene-based nanostructures by
The Scope of This Thesis
Schematic of the PECVD setup for the synthesis of graphene sheets and VG-GN without active heating. 7.1 (b) we show the AFM images of the region marked by the blue box in Fig. 1b.
Strain-engineering the Gauge Potential of Graphene and
Introduction
It is well known that the Berry phase of electronic wave functions can have a profound effect on the physical properties of materials.8–10 For example, the Berry phase is known to be responsible for various effects (quantum, anomalous, spin and valley ) of Halli. ,10–. In this section, we introduce the basic concepts of Berry phase and Berry curvature.
Berry phase effects on graphene
6.9(b) is an AFM cross-section of the image along the blue line in the SEM image of Fig. The time evolution of the Raman spectral characteristic of the 2D, G and D bands of graphene is shown in Fig.
Theory for strain-induced modifications to Dirac fermions in
Raman spectroscopy of graphene
A three-dimensional representation of the tunneling spectra taken along the same line cut is shown in Fig. Here, r denotes the distance measured from the lower left end to the upper left end of the black arrow in Figure 2.
Single-step Growth of Graphene by Plasma-enhanced
Introduction
If the direction of the vibrational modes is perpendicular to the carbon-carbon bonds, the modes are known as longitudinal (L). Because the interaction between each layer is weaker, the Raman spectrum of turbostratic graphene is very similar to the single-layer graphene.
Current techniques used for the synthesis of graphene
In this chapter we discuss recent developments in PECVD techniques for the synthesis of graphene on various metal substrates. This environment enables graphene growth on various surfaces at relatively lower temperatures and faster growth than T-CVD.29,36 Furthermore, PECVD techniques can be used for rapid and large-scale functionality of graphene and related materials, which is a versatile approach that further broadens the scope of graphene-based applications. These advantages make PECVD growth of graphene and graphene-related nanostructures very attractive and are considered a promising technique to improve the compatibility of graphene growth with semiconductor manufacturing processes.
Reviews of PECVD growth of graphene sheets on
In the following years, the growth of graphene by the PECVD methods faced two major challenges. One was to produce continuous and large areas of graphene films, and the other was to improve the quality of the PECVD-grown graphene. Meanwhile, many research groups have experimented with different PECVD systems and growth conditions to improve the quality of graphene grown on Cu substrates.
Single-step deposition of high-mobility graphene at
Here r denotes the distance measured from the lower left edge to the upper left edge of the black arrow shown in (c). We have also monitored the optical emission spectra (OES) of the plasma during the growth process as a function of the 1,2-DCB/CH4 partial pressure ratio, as shown in Fig. Shorter lengths than those of grown GNSPs (as shown by the histogram in Fig.
Nanoscale Strain Engineering of Graphene
Introduction
Proper strain engineering at the nanoscale can also produce tunable electronic density of states for nanoelectronic devices such as electrons. The objective of this chapter is to demonstrate the feasibility of nanoscale strain engineering of graphene by means of theoretical simulations and empirical development of PECVD-grown graphene on nanostructured substrates. Empirical proof of concept for nanoscale strain engineering via nanostructured substrates for graphene is also demonstrated and compared to theoretical simulations.
Theoretical simulations of strain-induced pseudo-magnetic fields
MD simulations of the strain effects on a nm2 graphene sheet induced by a nanoparticle with a diameter of 2.4 nm and a maximum height h0 = 2.4 nm: (a). The orientation of the threefold symmetry pattern coincides with the zigzag direction of the graphene lattice structure. 4.1(f)), suggesting significant changes in the electronic properties of graphene under such a nanostructure with comparable lateral and vertical dimensions.
Engineering arrays of nanodots on silicon substrates by
Overall, the spatial map of the 2D band across the region of graphene above the nanostructures clearly revealed significant inhomogeneity (Fig. 4.3(a)), which was in sharp contrast to the spatial homogeneity of the 2D band map of a controlled region of graphene on top of a flat region of the BN/Si substrate (Fig. A more quantitative comparison of the spatial distributions of the 2D band frequency in these two regions is illustrated by the histograms in Fig.
Engineering nanodots on silicon by self-assembly of
Finally, a monolayer PECVD-grown graphene was placed on top of the BN/Au nanoparticles/silicon, which induced wrinkles on the graphene, as illustrated in Fig. In particular, we note a general preferred wrinkle alignment along approx. 150º direction relative to the x-axis of the plot. A monolayer of h-BN on top of the same quasi-periodic gold nanoparticles in (a) over a (500
Engineering nanodots on silicon by Pd tetrahedron nanocrystals
4.7(d) corresponds to the bias, the vertical axis corresponds to the spatial dimension along the black line (from lower left to upper right) in Fig. To further verify the correlation between the magnitude of the determined pseudomagnetic field from topography and from spectroscopy, we compare in Fig. We found that the maximum magnitude of the pseudomagnetic field calculated from the structural distortion was ~600 Tesla (Fig.
Conclusion
Trajectories of K and K' valley fermions for an angle of incidence at θ = 15° with respect to the normal vector of the parallel channels. Upon further increasing the 1,2- DCB/CH4 partial pressure ratio to ∼2.4, a highly branched, flower-like nanostructure developed. This scenario is consistent with ultraviolet photoelectron spectroscopy (UPS), TEM, and energy dispersive X-ray spectroscopy (EDS) studies of GNSPs as a function of the 1,2-DCB/CH4 partial pressure ratio, which will be elaborated below.
Graphene Transport Measurement and Graphene Valleytronics
Introduction
A transverse valley current can be induced due to the anomalous velocity, which is called the Valley Hall effect (VHE). In single-layer graphene, the inversion symmetry can be broken by atomically aligning a single layer of graphene on top of h-BN.67 Moreover, gigantic non-local resistance on the order of quantum resistance can be observed without a magnetic field at low temperature, indicating that the occurrence of the quantum valley Hall state.70 In double-layer graphene, an electric field perpendicular to the graphene can break the inversion symmetry. Valley Hall transport has been demonstrated using non-local transport measurements in a Hall bar geometry with back-gated voltages.71,72 Furthermore, one-dimensional valley-polarized conducting channels associated with the protected chiral edge states of quantum valley Hall insulators have been demonstrated on the domain walls between AB- and BA-stacked bilayer graphene73.
Formation of periodic parallel graphene wrinkles for
Upper panel: Trajectories of K and K' fermions for an incident angle perpendicular to the parallel channels (θ = 0°). Top panel: Simulated trajectories of K and K' fermions for an incident angle perpendicular to the realistic strain-induced parallel pseudomagnetic fields (θ = 0°) shown in the figure. Bottom panel: trajectories of K-valley fermions incident at an angle θ = 75° with respect to the normal vector of the parallel channels.
Valley Hall effect of strained graphene
5.3(a), strong non-local resistance and valley-Hall effects can be detected under appropriate back-gated voltages, leading to a valley-Hall transistor similar to the previous observation of the valley-Hall effect in exfoliated single-layer graphene-on-h-BN flakes.67 It is also conceivable to obtain strongly valley-polarized currents through the combination of valley splitters (Fig.). We found that peaks in the RNL are associated with the pseudo-magnetic field-induced Landau levels in a single valley. Here 𝑙𝑙𝐵𝐵 denotes the magnetic length associated with an average pseudomagnetic field B and is given by 𝑙𝑙𝐵𝐵 =�ħ⁄(𝑒𝑒𝐵𝐵).
Conclusion
6.2(d) ~ (e) show two representative SEM images of the top view of GNSPs grown for 10 minutes with the growth parameters listed in the first row of Table 6.1, and Fig. Using this configuration we could make the most of the UV light and minimize damage to the low-k dielectrics. Following similar ideas, we report the alignment of GNSPs using the AC dielectrophoresis method.
High-yield Single-step Catalytic Growth of Graphene
Introduction
One of the primary challenges to fully realize the technological promises of reduced dimensional graphene nanostructures is to reliably produce large numbers of high quality nanomaterials with large aspect ratios. As a result, they exhibit large aspect ratios (typically from 10:1 to >~130:1) but do not show the effects of quantum confinement. The entire growth process takes place in a single step within less than 20 min at a relatively low plasma power (60 W), and the resulting GNSPs exhibit large aspect ratios and high yields.
Experimental
Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet photoemission spectroscopy (UPS) and electrical conductivity studies all confirm the high quality of the thus obtained GNSPs. During growth, the total pressure of the tube was maintained at 500 mTorr with 2 sccm of hydrogen. For 1,8-DBN, the temperature in the oven varied from 60 °C to 100 °C, corresponding to a variety of precursor partial pressures.
Results and analysis
Representative histogram of aspect ratios of GNSPs obtained from multiple sets of SEM images in their field of view. me). The high growth of GNSPs resulted in a completely darkened substrate surface due to the dense coverage of GNSPs on the metal substrate, as illustrated by the optical micrographs in Fig. We also investigated the electrical properties of standard GNSPs by aligning them on Au electrodes using dielectrophoresis techniques,120,121 as shown in Figs.
Discussion
Conclusions
However, all of these experimental studies involved high-temperature graphene synthesis (>550 °C), which was incompatible with typical CMOS processing temperatures (<450 °C). Synthesis of graphene on polycrystalline Co film by radiofrequency plasma-enhanced chemical vapor deposition. One-step high-yield catalytic growth of graphene nanoribbons by plasma-enhanced chemical vapor deposition.
Selective Growth of PECVD Graphene on Cu Nanostructures
Introduction
Moreover, the impermeability134 and oxidation resistance135 of graphene make it an ideal candidate as a protective barrier material for Cu interconnects to prevent Cu oxidation and diffusion in low-k underlying dielectrics. Mehta et al137,138 investigated the low-temperature (~650 °C) deposition of graphene around Cu nanowires and found that graphene deposition increased the electrical and thermal conductivity. In this chapter, we will discuss how we integrate our PECVD graphene growth technique with realistic industrial wafers and demonstrate the selective growth of graphene on Cu nanostructures.
Optimization of Growth Conditions
The low-k damage in the last column is defined by the height difference of the low-k materials. In Chapter 3, we found that Cu etching always accompanies graphene growth. To mitigate the plasma-induced damage to the low-k dielectric, we introduced a hollow graphite plate as a UV absorber, as shown schematically in the right panel in Fig. Plasma-induced damage of different dielectric materials estimated by the layer thickness before and after PECVD processing using ellipsometry.
Stability Test
Although the positions of the D, G, and 2D bands remain almost unchanged at different temperatures, the FWHM linewidth of the three bands becomes wider as the annealing temperature increases. The increase in ID/IG ratio is generally indicative of the deterioration of the quality of single-layer graphene. Meanwhile, increasing the FWHM linewidth of the 2D band implies a broadening of the phonon modes involved in the double resonance of single-layer graphene.
Future Work
We have developed different methods for the synthesis of graphene and graphene-based nanostructures on a variety of substrates using PECVD techniques. A review of theoretical investigation of graphene chemical vapor deposition synthesis on metals: nucleation, growth and the role of hydrogen and oxygen. Large area coating of graphene at low temperature using a roll-to-roll microwave plasma chemical vapor deposition.
Conclusion
