Giant Kerr response of ultrathin gold films from quantum size effect

Qian, Haoliang; Xiao, Yuzhe; Liu, Zhaowei

doi:10.1038/ncomms13153

Cited by 105 publications

(96 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…As the thickness of films approach just a few monolayers, the strong confinement could lead to quantum effects that could greatly enhance light–matter interactions . For example, it has recently been reported that the Kerr nonlinear optical response in thin Au films is several orders of magnitude larger than the bulk counterpart . In addition, these films are expected to be more sensitive to external electrical and optical perturbations, making them an attractive material platform for realizing dynamic nanophotonic and plasmonic applications.…”

Section: Introductionmentioning

confidence: 99%

Optical Properties of Plasmonic Ultrathin TiN Films

Shah

Reddy

Kinsey

et al. 2017

Advanced Optical Materials

100

101

View full text Add to dashboard Cite

Theoretical studies have been conducted to comprehend these characteristics in ultrathin gold films. [6,7] However, the fabrication of such thin films is generally quite difficult. For conventional plasmonic metals, such as silver and gold, continuous, smooth films with thicknesses lower than 10 nm are challenging to produce because of island formation and large defect concentrations which result from their high surface energy. [8][9][10] On the other hand, transition metal nitrides (TiN, ZrN, etc.) can be grown epitaxially on substrates such as c-sapphire and MgO, [11] enabling the formation of continuous ultrathin films down to 2 nm while maintaining high quality. [12] These materials have gained much interest for plasmonic applications for the visible and near-infrared region due to their tailorable optical properties and refractory quality. [13] TiN has already been shown to have potential applications in photovoltaics, [14,15] waveguiding, [16] modulators, [17,18] and nonlinear optical devices. [3,19] Although some of these devices use films of ≈10 nm, there is additional interest in the formation of ultrathin metallic films (<10 nm) which may facilitate additional applications. To support this, there have been efforts to grow ultrathin TiN films using atomic layer deposition (ALD). However, these films become dielectric below 5 nm and may not be useful for nanophotonic applications. [20] This is because TiN thin films grown using ALD with a TiCl 4 precursor are more prone to Cl impurities, which could result in a degradation of the metallic properties in thinner films. [21][22][23] In the present study, we have grown continuous, epitaxial, ultrathin TiN films that remain plasmonic in the optical range via DC reactive magnetron sputtering. Using sputtering to grow the film decreases the chance of contamination since only Ti, N, and Ar are introduced into the system, which helps maintain the metallic properties in ultrathin films. The dielectric permittivity of these films was extracted using spectroscopic ellipsometry, while Hall measurements give further insight into the optical behavior of the films. Results and DiscussionUltrathin TiN films with thicknesses of 2, 4, 6, 8, and 10 nm were grown on MgO using DC reactive magnetron sputtering. Due to the lattice matching between TiN (4.24 Å) and substrates such as MgO (4.21 Å) and sapphire (4.76 Å), high quality,Overcoming the challenge of growing ultrathin metallic films is of great importance for practical applications of nanoplasmonic structures. In the present work, epitaxial, ultrathin (<10 nm) films of plasmonic TiN are grown on MgO using DC reactive magnetron sputtering. The optical properties of the films are studied through variable angle spectroscopic ellipsometry and Hall measurements. As the film thickness decreases, they become less metallic and exhibit higher loss while still remaining plasmonic in the optical range. These trends are related to the decreasing carrier concentration in the thinner films and increased scattering, respectively. Howev...

show abstract

Section: Introductionmentioning

confidence: 99%

Optical Properties of Plasmonic Ultrathin TiN Films

Shah

Reddy

Kinsey

et al. 2017

Advanced Optical Materials

100

101

View full text Add to dashboard Cite

show abstract

“…Nowadays thin gold films are an important component of highly efficient photonic and plasmonic devices . Ultrathin gold films (thickness < 10 nm) have recently attracted a great deal of interest both for the development of flexible transparent electrodes for optoelectronic devices including thin‐film solar cells, displays and touchscreens, photodetector and light emitting diodes, and for studying quantum‐size effects in metal films . Certainly, high‐quality ultrathin films are also the key element of plasmonic waveguides and hyperbolic metamaterials …”

mentioning

confidence: 99%

Ultrathin and Ultrasmooth Gold Films on Monolayer MoS₂

Yakubovsky

Stebunov

Kirtaev

et al. 2019

Adv Materials Inter

View full text Add to dashboard Cite

films are also the key element of plasmonic waveguides [10,11] and hyperbolic metamaterials. [12,13] Growth of continuous and ultrathin gold films on different substrates, such as glass, silicon oxide, silicon nitride, graphene etc. is notoriously difficult due to the poor wetting of gold to these substrates. [14,15] The growth kinetics of metal films is generally determined by the adsorption and diffusion behavior of metal adatoms on the substrate. A small ratio of the adsorption energy of metal adatoms on the substrate to the bulk cohesive energy of the metal and low diffusion barrier for an adatom favor the 3D island growth behavior also known as the Volmer-Weber growth mode. [16] Within the framework of this growth model, the formation of a metal film is associated with the following stages: nucleation of islands, island growth, island impingement and coalescence, percolation, and channel filling to finally form a continuous thin film. To reduce the percolation threshold of ultrathin gold films, adhesion or seed layers of Ti, Cr, Ni, Pt, or Ge are commonly used. However, these adhesion layers significantly affect the optical and electrical properties of ultrathin metal nanostructures. [17][18][19][20][21][22] Recently, the organosilane-based adhesion layers (mercaptosilanes and aminosilanes) were used for the deposition of sub-10 nm thick continuous Au films on silicon and glass surfaces. [23][24][25][26][27] However, organosilanes are not compatible with nonoxidized silicon surfaces and poorly compatible with standard lift-off procedures, that imposes severe limitations to their use as adhesion layers. [21] Adhesion layers based on organosilanes are also inefficient for the deposition of atomically thin metal films [14] and does not move us closer to the deposition of 2D layers from bulk plasmonic metals. Actually, the latter seems now as impossible as the deposition of atomically thin carbon films had been considered before 2004. [28] In the present paper, we propose the use of MoS 2 monolayer as an entirely new type of "universal" (i.e., it can be transferred to any arbitrary substrate) [29][30][31] adhesion layer for ultrathin (<10 nm) high-quality continuous gold films. To test the feasibility of this idea, we deposited ultrathin gold films of different thicknesses onto monolayer MoS 2 , grown on silicon dioxide substrates (Figure 1a), and studied their structural and optical properties.An electron beam evaporator Nano Master NEE-4000 was used to deposit Au films on top of atmospheric pressure CVD (APCVD)-grown full area coverage MoS 2 monolayers on silicon wafers with a 285 nm thick SiO 2 coating (from 2D semiconductors Inc.). The deposition was performed at Sub-10 nm continuous metal films are promising candidates for flexible and transparent nanophotonics and optoelectronic applications. In this article, it is demonstrated that monolayer MoS 2 is a perspective adhesion layer for the deposition of continuous conductive gold films with a thickness of only 3-4 nm. Optical properties of continuous ultrath...

show abstract

“…The n 2 is (8.9−1.6 i ) × 10 −13 m 2 W −1 , which is several orders of magnitude higher than that of traditional nonlinear materials, [ 20 ] and is the direct evidence of ISBTs, as has been demonstrated in gold MQWs. [ 16 ] The ISBT selection rule, if not broken, gives the n 2 a sin(θ) dependence; for example, the n 2 at θ = 10° is expected to be 27% of that at θ = 40°. However, from the measured wavelength dependence of n 2 at θ = 10° (Figure 4c), we observe that it is about 50% of the amplitude of that at θ = 40°, indicating a significant break of the ISBT selection rule.…”

Section: Resultsmentioning

confidence: 99%

“…It was not until very recently, however, that the optical nonlinearities of MQWs have been experimentally explored, enabled by the success in fabrication of ultrathin continuous metallic films on top of a dielectric substrate. [ 13,16,17 ] Surprisingly, ISBT peaks, the signature of the quantum size effect in QWs, have been observed in the nonlinear coefficient spectra of these MQWs [ 16,17 ] ; the manifestation of the ISBTs is an extraordinary enhancement of these optical nonlinearities which are several orders of magnitude larger than those of traditional nonlinear materials at visible/near‐infrared (NIR) frequencies. However, no systematic study of the ISBT selection rules for optical nonlinearities in MQWs has been made.…”

Section: Introductionmentioning

confidence: 99%

Anomalous Nonlinear Optical Selection Rules in Metallic Quantum Wells

Qian

Liu

2020

Adv Funct Materials

Self Cite

View full text Add to dashboard Cite

Intersubband transitions (ISBTs) in conduction-band quantum wells (QWs) have attracted tremendous attention for their high technological potential, ranging from quantum cascade lasers, quantum well infrared photodetectors, to various nonlinear optical elements. One of the main characteristics of using the ISBTs is their polarization selection rule, which forbids a normalincidence geometry. Here, it is shown that the ISBT selection rule is not strict on optical nonlinearities in metallic QWs (MQWs). The nonlinear process of second harmonic generation nearly follows the selection rule, while the optical Kerr nonlinear process severely deviates from it. The anomalous optical selection rules result from the non-negligible ultrafast electron-electron scattering in these plasmonic systems, and a coupled mode theory is provided to get a physical grasp of the problem. The flexible selection rule in MQWs could bring drastic improvements in efficiency and diversity of ISBT-based devices.

show abstract

Giant Kerr response of ultrathin gold films from quantum size effect

Cited by 105 publications

References 40 publications

Optical Properties of Plasmonic Ultrathin TiN Films

Optical Properties of Plasmonic Ultrathin TiN Films

Ultrathin and Ultrasmooth Gold Films on Monolayer MoS₂

Anomalous Nonlinear Optical Selection Rules in Metallic Quantum Wells

Contact Info

Product

Resources

About

Giant Kerr response of ultrathin gold films from quantum size effect

Cited by 105 publications

References 40 publications

Optical Properties of Plasmonic Ultrathin TiN Films

Optical Properties of Plasmonic Ultrathin TiN Films

Ultrathin and Ultrasmooth Gold Films on Monolayer MoS2

Anomalous Nonlinear Optical Selection Rules in Metallic Quantum Wells

Contact Info

Product

Resources

About

Ultrathin and Ultrasmooth Gold Films on Monolayer MoS₂