Field emission is a cornerstone phenomenon for advanced vacuum microelectronic devices, enabling next-generation applications. Achieving efficient, low-turn-on electron emission with a high field enhancement factor critically depends on the development of nanostructured materials with optimized morphology and electronic properties. In this study, we demonstrate how gallium (Ga) doping serves as an effective strategy to tune and boost the field emission characteristics of zinc oxide (ZnO) nanowire (NW) arrays. Ga-doped ZnO NWs with varying concentrations (0-4 at. %) were synthesized via a low-cost and facile combined two-step spin-coating and hydrothermal method and systematically characterized by complementary experimental analyses. The 2 at. % Ga-doped sample exhibited the most favorable performance, achieving the lowest turn-on (1.50 V/μm) and threshold (3.75 V/μm) fields and a significantly improved field enhancement factor (β = 8577). These improvements arise from the synergistic effects of increased electrical conductivity and optimized NW geometry at this ideal doping level. Finite element simulations further elucidated these findings by revealing how reduced NW diameter, improved alignment, and increased surface charge density (carrier concentration) associated with Ga doping collectively enhance the field enhancement factor. The computational results show excellent agreement with the experimental trends, confirming that controlled doping and structural optimization are key determinants of emission efficiency. This integrated experimental-theoretical simulation framework provides a mechanistic insight into the interplay between structural, electronic, and electrostatic factors and establishes Ga-doped ZnO NWs as a promising platform for high-performance field emission applications.

Providing a contamination-free silicon surface remains a challenge in semiconductor technology, atomically precise manufacturing, and atomic-scale electronics. Plasma cleaning shows promise in eliminating contaminants with minimal surface damage, yet an in-depth understanding of the different plasma gases' effects on silicon surface at both atomic and submicron levels is lacking. This research utilized scanning tunneling microscopy (STM) to explore the surface cleaning of Si(100) substrates by remote hydrogen, oxygen, and air plasma pre-treatments, combined with 1050 degrees C thermal flashes. STM imaging was conducted on both 20 nm and 500 nm regions to bridge microscopic and macroscopic observations. Our findings indicate that a combination of remote hydrogen plasma with thermal flashes most effectively cleans the Si(100) surface. Specifically, hydrogen plasma selectively cleans the underlying silicon without removing the thin native oxide layer, which is subsequently eliminated by thermal flashing, while oxygen plasma also cleans effectively but leaves few localized contaminations.

The effects of annealing on chemical vapor deposited graphene are investigated via a weak localization magnetoresistance measurement. Annealing at 300 degrees C in inert gases, a common cleaning procedure for graphene devices, is found to raise the dephasing rate significantly above the rate from electron-electron interactions, which would otherwise be expected to dominate dephasing at 4 K and below. This extra dephasing is apparently induced by local magnetic moments activated by the annealing process, and depends strongly on the backgate voltage applied.

We used multiprobe scanning tunneling microscope (STM) to fabricate and electrically characterize nanostructures on Si surfaces. We overcame resistive contacts by using field evaporation to clean tip apexes in order to create Ohmic contact with the Si surface states on a Si substrate. A two-probe (2P-) STM with Ohmic contact allowed for measurement at very low bias, limiting conduction through space-charge layer and bulk states. The Ohmic 2P-STM measurement clarified the surface conductivity of the Si(111)-(7 × 7) surface. We also confirmed that Ohmic 2P-STM can be replaced with more convenient Ohmic one-probe STM for the conductance measurements on the Si surface. We prepared nanostructures using STM lithography to define electronically isolated two-dimensional (2D) regions with various aspect ratios. Their surface conduction properties are described well by the conventional sheet model, proving the diffusive 2D conduction on the Si surface. Constrictions and breaks in 2D structures were also evaluated. Ohmic 2P-STM will be helpful for the investigation of exploratory atomic-scale circuitry or cutting-edge materials sciences.

Effects of annealing on chemical vapor deposited graphene are investigated via a weak localization magnetoresistance measurement. Annealing at 300 in inert gases, a common cleaning procedure for graphene devices, is found to raise the dephasing rate significantly above the rate from electron-electron interactions, which would otherwise be expected to dominate dephasing at 4 K and below. This extra dephasing is apparently induced by local magnetic moments activated by the annealing process, and depends strongly on the backgate voltage applied.

It is often assumed that adding losses to a resonant system necessarily broadens the width of the resonance. Here, the scattering spectrum of gold nanoparticles in P3HT (strongly absorbing) and PMMA (low loss) were measured using dark field microscopy and surprisingly, the linewidth was halved in the lossy medium. To gain physical insight into this unusual result, a Green function analysis was employed, and the roles of the permittivity, both magnitude and dispersion, in reducing the linewidth when material losses are increased were made clear. This surprising route to narrower linewidths is intriguing for nanoplasmonic applications including sensing, spectroscopy, imaging and nanolasing and also more generally for resonant systems where loss is conventionally avoided.

Narrow plasmon linewidths are often desirable for plasmonic devices such as biosensors. Loss is often associated with broad linewidths, and much effort is spent in reducing losses in metals. Although losses can be effectively reduced by a variety of methods such as, reducing surface roughness, and including optical gain to counter the loss, losses will never be fully eliminated from a system [1]. Rather than avoiding loss, we focus on how the linewidth can be reduced in the presence of loss. In this paper, we show how a dispersive lossy surrounding dielectric can narrow the plasmon linewidth. We support this claim with experimental scattering measurements using a dark field microscope, as well as with Green function calculations.

The effects of loss on the plasmon resonance peak in dispersive absorbing media are investigated. We find that dispersive loss can lead to narrower plasmon resonances. We also measure the plasmon peak for gold nanospheres embedded in P3HT, poly(3-hexylthiophene), using a dark field microscope.

This chapter focuses on applications of nanoparticles in enhanced optical nonlinearities. The role of acoustic resonance of nanoparticles in nonlinear optical response, where the electrostrictive force excites the acoustic modes of nanoparticles and produces a traveling periodic variation in refractive index of the sample, is investigated. In these measurements, even a weak laser can produce extraordinarily strong four-wave mixing signal above a critical threshold intensity, which means extremely high-quality factors for the nanoparticle vibrations, as if the water damping disappears entirely. Interestingly, it can be seen in the measurement that a smaller bandwidth corresponds to smaller polystyrene nanoparticles due to the fact that larger particles have the resonances approaching to the collision rate for water of 20 GHz , leading to the higher damping and a larger bandwidth. Acousto-optics is a branch of physics that deals with the interaction of sound and light. The diffraction of light by acoustic waves of short wavelengths was first postulated by Leon Brillouin in 1922.

In "Modeling and observation of mid-infrared nonlocality in effective epsilon-near-zero ultranarrow coaxial apertures" the authors perform infrared transmission measurements on coaxial aperture arrays in metal films. They claim that the blue-shift of the resonances is the result of nonlocality. They claim that roughness will not produce a shift. This is contrary to past results in plasmonics, to our simulations and to past published claims from some of the same authors. Furthermore, the effect of planarization that occurs for atomic layer deposition, as has been reported elsewhere, will produce a blue-shift. Finally, discrepancies between different nonlocal models, time-dependent density functional theory and other experimental observations all call into question the accuracy of the particular nonlocal model chosen for this regime.

Lossy materials can be used in nanoplasmonic systems to narrow plasmon linewidths, which is desirable for biosensing applications. A scattering cross section linewidth of about 30 nm is found for gold nanoparticles in the lossy P3HT.

Early experiments on alkali-doped graphene demonstrated that the dopant adatoms modify the conductivity of graphene significantly, as extra carriers enhance conductivity while Coulomb scattering off the adatoms suppresses it. However, conductivity probes the overall scattering rate, so a dominant channel associated with long-range Coulomb scattering will mask weaker short-range channels. We present weak localization measurements of epitaxial graphene with lithium adatoms that separately quantify intra- and intervalley scattering rates, then compare the measurements to tight-binding calculations of expected rates for this system. The intravalley rate is strongly enhanced by Li deposition, consistent with Coulomb scattering off the Li adatoms. A simultaneous enhancement of intervalley scattering is partially explained by extra carriers in the graphene interacting with residual disorder. But differences between measured and calculated rates at high Li coverage may indicate adatom-induced modifications to the band structure that go beyond the applied model. Similar adatom-induced modifications of the graphene bands have recently been observed in ARPES, but a full theoretical understanding of these effects is still in development.

Optical trapping and characterization of 10 base pairs (bp) hairpin DNA as well as its interaction with tumor suppressing protein (p53), wild and mutant types, using a Double Nano-Hole (DNH) optical tweezer have been previously reported. This paper discusses the application of the above technique in characterizing potential tumor suppressing activators from their interactions with a p53 mutant variant and 10bp hairpin DNA while establishing a comparison with the wild protein-DNA interaction.

We investigate the effect of the electron wave function producing permittivity (epsilon) near zero in sub-nanometer gaps and at surfaces. The field enhancement is calculated for gaps and nanoparticles, as well as the absorption from nanoparticles. Our modified quantum corrected model shows reduced absorption for nanoparticles due to "cloaking" of the epsilon near zero region, which has lower loss than the bulk region. We demonstrate that a modified quantum corrected model finite-difference time-domain simulation of metal slits with sub-nanometer gaps are in good agreement with the analytic expression for the quantum corrected plasmonic resonance wavelength as a function of gap size coming from Re{ε} = 0.

Sub-nanometer gaps can cause extreme local field enhancements, and therefore they are used in surface enhanced raman spectroscopy (SERS). However, the fabrication of this kind of substrates presents a challenge due to lack of a reliable technology that would produce consistent and uniform nanogaps. Currently, one of the ways to fabricate nanogaps is atomic layer deposition, followed by glancing angle ion miller or tape peeling method for planarization [1]. In this work, nanogaps were fabricated by using self-assembled monolayer (SAM) whose thickness is determined by the length of carbon chain. Focused ion beam was used to mill an array of squares on Au sample with a glass substrate. Then, after deposition of SAM, more Au was sputtered. Finally, the whole structure was stripped off using adhesive epoxy, exposing nanogaps whose thickness was determined by SAM. SERS mapping of these substrates showed extreme field enhancement along the gaps.

Upconversion is a promising route to absorb photons below the bandgap energy of Si and GaAs solar cells. Here we report upconversion from two prominent IR solar bands around 1210 nm and 1520 nm using plasmon enhanced upconversion in 2% doped NaYF4 : Er3+ nanoparticles with gold nanorods. Gold nanorods with resonances at 808 nm and 980 nm were used to selectively increase the upconverted emission at those wavelengths. Erbium doped nanoparticles demonstrate no upconversion under 1210 nm excitation alone; however, in the presence of 1520 nm excitation, an intermediate state is populated and the 1210 nm light contributes to the upconversion as well. The selective plasmon-enhanced emission at 980 nm and at 808 nm are close to the bandgaps of Si and of GaAs; this makes them promising candidates for improving efficiency of Si-based and GaAs-based solar cells.

We investigate the electrical response of a device with sub-nanometer gaps, which potentially can be used as an ultrafast optical switch. In todays electronics, semiconductor devices at best have a picosecond response time. Making structural change is one way to achieve faster electronics. The Coulomb blockade effect in tunnel junctions can reproduce a highly nonlinear response current, which is required for a switch. However, a tiny capacitance is necessary for a femtosecond time constant. A sub-nanometer gap with a small surface area can satisfy both of these conditions. The nonlinear optical switching behavior of a sub-nanometer gap has been observed experimentally [1]. It is a potential candidate for an effective and low-cost switch with high speed operation. We fabricated a gold on silicon sample with sub-nanometer gaps filled by self-assembled monolayer and then we illuminated it with a femtosecond pulsed laser. We recorded the dark current and photocurrents of the sample with different incident powers. This experimental report can pave the way for harnessing high-speed switching in nanodevices with sub-nanometer gaps.

We demonstrate dual-wavelength (1210 and 1520 nm) excitation of upconverter nanoparticles (Er-doped nanoparticles) with plasmon-enhanced emission. Gold nanorods of 25 nm diameter with resonances at 808 nm and at 980 nm selectively enhance the upconversion emission of 2% erbium-doped NaYF4 nanoparticles at 808 nm and at 980 nm. No upconversion is seen for 1210 nm excitation alone, and 1520 nm excitation alone provides lower upconversion. The sequential 1520 and 1210 nm absorption yields the most upconversion, and the power dependence of emission supports the sequential absorption mechanism. This provides a promising avenue for harvesting from the two strongest infrared bands of the solar spectrum with selective emission tuned to either the Si or GaAs band gap.

We report the optical trapping of single Er3+/Yb3+ co-doped up-converting fluorescent nanoparticle with rectangle aperture on gold sample using a continuous wave 980 nm single-beam laser. The laser also excites visible luminescence from the nanoparticles. This feature enables us to analyze the number of individual nanoparticles loading into a trap stage. We record the number of trapped nanoparticles using a CCD camera which also can be confirmed by measuring the variation in the laser intensity transmitted through the rectangle aperture. The rectangle aperture enhances the local field that serve in enabling trapping and enhancing the emission of up-converting nanoparticles. In addition, we investigate the impact of rectangle dimensions on the ratio of emitted upconversion in the 544 nm to 655 nm range. Results show a change in ratio of upconversion peaks in the range of 544 nm to 655 nm while sweeping through different lengths of rectangular aperture. This study could help improve the understanding of lanthanide upconversion nanoparticle interaction with plasmonic gold nanoapertures at the nanoscale level.