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From femtosecond spectroscopy (fs-spectroscopy) of metals, electrons and phonons reequilibrate nearly independently, which contrasts with models of heat transfer at ordinary temperatures ($T>100$ K). These electronic transfer models only agree with thermal conductivity $(k)$ data at a single temperature, but do not agree with thermal diffusivity $(D)$ data. To address the discrepancies, which are important to problems in solid state physics, we separately measured electronic (ele) and phononic (lat) components of $D$ in many metals and alloys over $\sim$290–1100 K by varying measurement duration and sample length in laser-flash experiments. These mechanisms produce distinct diffusive responses in temperature versus time acquisitions because carrier speeds $(u)$ and heat capacities $(C)$ differ greatly. Electronic transport of heat only operates for a brief time after heat is applied because $u$ is high. High $D_{\mathrm{\text{ele}}}$ is associated with moderate $T$, long lengths, low electrical resistivity, and loss of ferromagnetism. Relationships of $D_{\mathrm{\text{ele}}}$ and $D_{\mathrm{\text{lat}}}$ with physical properties support our assignments. Although $k_{\mathrm{\text{ele}}}$ reaches $\sim 20\times k_{\mathrm{\text{lat}}}$ near 470 K, it is transient. Combining previous data on $u$ with each $D$ provides mean free paths and lifetimes that are consistent with $\sim 298$ K fs-spectroscopy, and new values at high $T$. Our findings are consistent with nearly-free electrons absorbing and transmitting a small fraction of the incoming heat, whereas phonons absorb and transmit the majority. We model time-dependent, parallel heat transfer under adiabatic conditions which is one-dimensional in solids, as required by thermodynamic law. For noninteracting mechanisms, $k\cong \mathrm{\Sigma }{C}_i{k}_i\mathrm{\Sigma }{C}_i/(\mathrm{\Sigma }{C}_i^2)$. For metals, this reduces to $k=k_{\mathrm{\text{lat}}}$ above $\sim$20 K, consistent with our measurements, and shows that Meissner’s equation $(k\cong k_{\mathrm{\text{lat}}}+k_{\mathrm{\text{ele}}})$ is invalid above $\sim$20 K. For one mechanism with multiple, interacting carriers, $k\cong \mathrm{\Sigma }{C}_i{k}_i/(\mathrm{\Sigma }{C}_i)$. Thus, certain dynamic behaviors of electrons and phonons in metals have been misunderstood. Implications for theoretical models and technological advancements are briefly discussed.

In this paper, we have theoretically investigated the effect of built-in-polarization field on various phonon scattering mechanisms in Al${}_x$Ga${}_{1-x}$N/GaN heterostructure. The built-in-polarization field enhances the elastic constant, phonon velocity and Debye frequency of Al${}_x$Ga${}_{1-x}$N alloy. As a result, various phonon scattering mechanisms are modified. Important phonon scattering mechanisms such as normal scattering, Umklapp scattering, point defect scattering, dislocation scattering and phonon–electron scattering processes have been considered. The combined relaxation time due to above scattering mechanisms has also been computed as a function of phonon frequency for various Al contents at room temperature. Our result shows that built-in-polarization field suppresses scattering rates leading to enhanced combined relaxation time. Increased relaxation time implies longer phonon mean free path and enhanced optical and thermal transport properties. The result can be used to determine the effect of built-in-polarization field on optical and thermal properties of Al${}_x$Ga${}_{1-x}$N/GaN heterostructure and will be useful, particularly, for improvement of thermoelectric performance of Al${}_x$Ga${}_{1-x}$N/GaN heterostructure through polarization engineering.

One of the most chemically adaptable elements is boron which is found in the periodic table between two groups, i.e., metals and nonmetals and may create more than 16 polymorphs that are bulk and made of connected boron polyhedra. Given that boron and carbon are comparable elements, it has been questioned whether two-dimensional (2D) boron could serve as a conceptual starting point for the construction of other boron nanostructures. Using boron as fundamental building blocks, boron nanosheets were synthesized known as borophenes. Borophene is found to be a crystalline form of atomic monolayer boron which was theoretically first predicted in mid-1990s and experimentally synthesized very recently in 2015. In this work, we studied both armchair and zigzag formation of borophene and presented a comparative analysis of their minimum sub-band energy, effective mean free path $E_n$, number of conduction channels $N_{\mathrm{\text{ch}}}$, scattering resistance per unit length. The $N_{\mathrm{\text{ch}}}$ for armchair BNR is 3,2,1 for 22nm, 13nm, 7nm, respectively, which is comparatively more than zigzag BNR. We later proposed Top-Contact BNR (TC-BNR) and Side-Contact BNR (SC-BNR). Our analysis shows that SC-BNR offers $96\%$ less resistance compared to TC-BNR and it is of the order of SC-GNR. Further, if we compare with copper interconnects, BNR is better in terms of performance and copper can be replaced with BNR due to high bulk mean free paths 300nm and 400nm compared to copper’s 40nm.

Electron beam (EB) lithography has been mainly used for patterning on masks and reticles in the semiconductor industry and has progressed according to the scaling up of circuit integration and the miniaturization of patterns. Among the various techniques in EB lithography, EB direct writing has played an important role in developing advanced devices because it offers higher resolutions and shorter turn-around time, though its patterning speed has not been high enough for mass-production use. Cutting-edge applications in advanced fields have always been investigated and developed using EB direct writing, and future devices and devices for scientific research, such as various quantum devices, which of course require high resolutions, have also been investigated using the technique.

In this chapter, interactions between electrons and materials, EB direct writing apparatuses, and calculation/measurement of EB diameter are discussed in Section 2. The accuracies of patterning dimensions and positioning in EB lithography are discussed in Section 3. The former includes roughness on pattern edges, and the proximity effect due to electron scatterings and its correction, and the latter is for mainly overlay accuracy. Resist materials, fine patterning, and some applications, including the creation of three-dimensional structures are discussed in Section 4.