Buried Nanostructures Research Articles

Vibrational near-field mapping of planar and buried three-dimensional plasmonic nanostructures

Nanoantennas confine electromagnetic fields at visible and infrared wavelengths to volumes of only a few cubic nanometres. Assessing their near-field distribution offers fundamental insight into light–matter coupling and is of special interest for applications such as radiation engineering, attomolar sensing and nonlinear optics. Most experimental approaches to measure near-fields employ either diffraction-limited far-field methods or intricate near-field scanning techniques. Here, using diffraction-unlimited far-field spectroscopy in the infrared, we directly map the intensity of the electric field close to plasmonic nanoantennas. We place a patch of probe molecules with 10 nm accuracy at different locations in the near-field of a resonant antenna and extract the molecular vibrational excitation. We map the field intensity along a dipole antenna and gap-type antennas. Moreover, this method is able to assess the near-field intensity of complex buried plasmonic structures. We demonstrate this by measuring for the first time the near-field intensity of a three-dimensional plasmonic electromagnetically induced transparency structure.

Subsurface measurement of nanostructures on GaAs by electrostatic force microscopy

The size of surface buried oxide nanostructures are measured by electrostatic force microscopy (EFM). In contrast to atomic force microscopy that cannot probe subsurface structures and thickness, we show that EFM data include information about the thickness of individual nanostructures, consequently allowing us to determine the thickness of buried nanostructures on semiconductor substrates. We further show that this measurement can be performed simultaneously with AFM using EFM modulation spectroscopy.

Back Cover: Ann. Phys. 11/2012

Annalen der PhysikVolume 524, Issue 11 Back CoverFree Access Back Cover: Ann. Phys. 11/2012 First published: 19 November 2012 https://doi.org/10.1002/andp.201290017AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract A new plasmonic biosensing device based on ultrasmooth metallic surfaces with buried plasmonic nanostructures is presented. Using template stripping, ultrathin gold films with less than 5 Å surface roughness are optically coupled to buried plasmonic gratings. Because of this arrangement, light only need illuminate the buried gratings, and sensing with opaque or highly scattering liquids is possible. Picture: N. C. Lindquist et al., pp. 687, in this issue. Volume524, Issue11Special Issue: Plasmonic SensorsNovember 2012 RelatedInformation

Ultrasmooth metallic films with buried nanostructures for backside reflection-mode plasmonic biosensing.

We present a new plasmonic device architecture based on ultrasmooth metallic surfaces with buried plasmonic nanostructures. Using template-stripping techniques, ultrathin gold films with less than 5 Å surface roughness are optically coupled to an arbitrary arrangement of buried metallic gratings, rings, and nanodots. As a prototypical example, we present linear plasmonic gratings buried under an ultrasmooth 20 nm thick gold surface for biosensing. The optical illumination and collection are completely decoupled from the microfluidic delivery of liquid samples due to the backside, reflection-mode geometry. This allows for sensing with opaque or highly scattering liquids. With the buried nanostructure design, we maintain high sensitivity and decoupled backside (reflective) optical access as with traditional prism-based surface plasmon resonance (SPR) sensors. In addition, we also gain the benefits offered by nanoplasmonic sensors such as spectral tunability and high-resolution, wide-field SPR imaging with normal-incidence epi-illumination that is simple to construct and align. Beyond sensing, our buried plasmonic nanostructures with ultrasmooth metallic surfaces can benefit nanophotonic waveguides, surface-enhanced spectroscopy, nanolithography, and optical trapping.

Engineering surface waves in flat phononic plates

Surface acoustic-wave phenomena span a wide range of length scales going from the devastation of earthquakes down to image reconstruction of buried nanostructures. In solid-fluid systems, the so-called Scholte-Stoneley waves (SSWs) dominate the scene at the interface with their evanescent fields decaying away into both media. Understanding and manipulating these waves in patterned surfaces would enable new applications of sound to be devised for imaging and acoustic signal processing, although this task has so far remained elusive. Here, we report SSW modes displaying directional gaps and band folding in fluid-loaded solid phononic plates. The plates are inhomogeneously patterned with in-plane periodic modulations of the elastic constants, but present flat surfaces free of corrugations. We experimentally demonstrate control of SSWs, which opens a promising route toward acoustic fluid sensing, microscopy, and signal processing.

Waveguide-enhanced grazing-incidence small-angle x-ray scattering of buried nanostructures in thin films

X-ray standing waves generated by the interference of the scattered x rays from parallel surfaces of a thin film, the so-called waveguide effect, can be used to enhance or reduce the scatterings from certain depths of the film. Used in combination with grazing-incidence small-angle x-ray scattering, this resonance effect provides depth sensitivity to extract buried structures in thin films of polymer and polymer/nanoparticle nanocomposite, which are not readily accessible by most surface techniques, such as scanning probe microscopy. We developed a rigorous theory of the diffuse scattering in the framework of the distorted-wave Born approximation using a discretization method analogous to Parratt's recursive formalism. In such a case, the distortion of the electric field of the unperturbed state from the nanostructures of interest is considered in a self-consistent manner. This theory allows a quantitative determination of the buried nanostructures when the x-ray waveguide enhancement is present or the size of the nanostructures of interest is comparable to or larger than the spatial frequency of electric-field intensity modulation. A unique capability afforded by this theory is that a nanometer or even subnanometer spatial resolution can be achieved in the depth information of the buried nanostructures, along with the in-plane correlation of the structures.

Scanning-Gate Microscopy of Semiconductor Nanostructures: An Overview

This paper presents an overview of scanning-gate microscopy applied to the imaging of electron transport through buried semiconductor nanostructures. After a brief description of the technique and of its possible artifacts, we give a summary of some of its most instructive achievements found in the literature and we present an updated review of our own research. It focuses on the imaging of GaInAs-based quantum rings both in the low magnetic field Aharonov-Bohm regime and in the high-field quantum Hall regime. In all of the given examples, we emphasize how a local-probe approach is able to shed new, or complementary, light on transport phenomena which are usually studied by means of macroscopic conductance measurements.

A single-step electron beam lithography of buried nanostructures using cathodoluminescenceimaging and low temperature

We report a new electron beam lithography process using the cathodoluminescenceproperties of semiconductors to visualize nanostructures buried underneath the resist andto subsequently write the pattern associated with these nanostructures. This single-stepprocess could be used, for example, to make electrical contacts to nanowires (asillustrated in this work) or to design a photonic crystal resonator centered on asingle quantum dot. Fabrication speed and positioning accuracy are significantlyincreased as compared to the standard process since no alignment marks andthe mapping step of the nanostructures with respect to these marks are needed.We show also that low temperature (down to 5 K) could be used to improve theobservation of the nanostructures through the resist while keeping very good spatialresolution.

Probing the magnetism of nanostructures buried in metallic surfaces and their possible utilization

AbstractWe discuss the possibility to probe magnetic properties of nanostructures buried beneath a metallic surface by means of local probe techniques. We prove, that those properties can be deduced from the spin‐resolved local density of states (LDOS) above the surface. In‐plane polarization maps in vacuum above the surface are shown to allow one to simultaneously detect electronic, magnetic, and even geometric properties of subsurface structures. It is argued, that the coupling of buried nanostructures to each other can be deduced from the symmetry of the polarization map. To underline the importance of studying buried nanostructures several possible applications of buried magnetic impurities are pointed out. The exchange coupling of an adatom to a nanostructure or a monolayer (ML) across a paramagnetic spacer is shown to oscillate with the thickness of the latter. This could provide one with reliable means to stabilize the spin of a magnetic adatom in either a ferromagnetic or an antiferromagnetic configuration with respect to the magnetic orientation of the monolayer or nanostructure. The possibility to tailor the exchange coupling between single magnetic impurities on a surface through the adjustment of the overlayer thickness and the interatomic separation in a dimer, is discussed.

Through-focal HAADF-STEM of buried nanostructures

High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) in combination with strain mapping techniques provides a powerful tool for quantitative analysis of crystalline semiconductor materials. Due to the complex interaction of a focused probe and a sample in HAADF, the calculation of each pixel in a simulation process requires a complete multislice iteration, making the overall computing process a rather demanding task in time and memory. SICSTEM is a parallel software code recently developed for running on the University of Cadiz Supercomputer (3.75 Tflops) that allows the simulation of images from large nanostructures containing more than one million atoms. The software has been designed to be able to generate not only one dimensional line scans or two dimensional images, but also to perform optical sectioning in the STEM simulation process, providing an easy way to simulate 3D HAADF-STEM images. In this work we consider GaAs capped GaSb nanostructures epitaxially oriented on a GaAs substrate. A methodology has been developed by combining the through-focal series STEM imaging and image analysis to estimate shape and position of buried GaSb nanostructures.

A spin-echo resolved grazing incidence scattering setup for the neutron interrogation of buried nanostructures

We present a dedicated experimental spin-echo resolved grazing incidence scattering (SERGIS) setup for the investigation of surfaces and thin films exhibiting large lateral length scales. This technique uses the neutron spin to encode one in-plane component of the wave-vector transfer in a grazing angle scattering experiment. Instead of the scattering angle, the depolarization of the scattered beam is measured. This allows one to achieve a very high in-plane momentum resolution without collimation of the incident neutron beam in the corresponding direction. SERGIS can therefore offer an alternative or complementary method to conventional grazing incidence neutron scattering experiments. We describe the experimental setup installed at the neutron sources ILL (Grenoble) and FRM II (Garching) and present data obtained with this setup on various samples exhibiting characteristic mesoscopic length scales in the range of several hundred nanometers. We also derive general formulas and error margins for the analysis and interpretation of SERGIS data and apply them to the cases of a one-dimensional structure and of an island morphology.

Probing buried magnetic nanostructures by spin-resolved local density of states at the surface: A density functional study

We demonstrate that it is possible to resolve magnetic properties of small clusters buried up to 1.5 nm deep beneath a metallic surface. The possibility of deducing magnetic properties of buried nanostructures by studying polarization maps of the surface is discussed. Moreover, we show that there is a way to determine the coupling of buried structures to each other by studying the polarization of electrons in vacuum space above the system.

Surface Localization of Buried III–V Semiconductor Nanostructures

In this work, we study the top surface localization of InAs quantum dots once capped by a GaAs layer grown by molecular beam epitaxy. At the used growth conditions, the underneath nanostructures are revealed at the top surface as mounding features that match their density with independence of the cap layer thickness explored (from 25 to 100 nm). The correspondence between these mounds and the buried nanostructures is confirmed by posterior selective strain-driven formation of new nanostructures on top of them, when the distance between the buried and the superficial nanostructures is short enough (d = 25 nm).

Strain in a single ultrathin silicon layer on top of SiGe islands: Raman spectroscopy and simulations

By means of resonant Raman spectroscopy we investigated the strain on a single ultrathin crystalline silicon layer, locally induced by buried SiGe nanostructures. The spectrum of a 5-nm-thick silicon layer on top of SiGe islands shows a single highly strained feature attributed to the out-of-plane phonon. The direct comparison of the experimental results with finite-element methods through spectral simulation shows excellent agreement that clarifies the physical origin of the spectrum. An increase in the silicon layer thickness up to 40 nm results in a progressive reduction in the strain.

Formation of Spatially Addressed Ga(As)Sb Quantum Rings on GaAs(001) Substrates by Droplet Epitaxy

In this work we report on the ability to form low density Ga(As)Sb quantum ring-shaped nanostructures (Q-rings) on GaAs(001) substrates by the droplet epitaxy technique. The Q-rings are formed by crystallization of Ga droplets under antimony flux. After being capped by a GaAs layer, these nanostructures show surface mounding features that are correlated with the buried nanostructures, as demonstrated by TEM analysis, permitting an easy surface location of the optically active Q-rings.

Using reflectance anisotropy spectroscopy to characterize capped silver nanostructures grown on silicon

AbstractUsing the single domain Si(111)‐3×1‐Ag surface as a template, room temperature deposition of two or more monolayers of Ag leads to the formation of metallic nanostructures. Reflectance anisotropy spectroscopy (RAS) in the infrared (IR) spectral region is used to analyse the anisotropic conductivity of the structures. The anisotropy is found to be influenced by the offcut angle of the substrate, and hence the terrace width. The Ag nanostructures were capped with Si to form a near‐IR transparent protecting layer. The samples are stable to exposure to ambient conditions for significant periods. The RAS spectra are compared to model calculations, which support the conclusion that the buried metallic Ag nanostructures survive the capping process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrafast acoustics for imaging at the nanoscale

In this paper we present a series of experiments which show that 2-D and possibly 3-D imaging with sub-micron resolution is possible by means of ultrafast acoustic techniques. Optical pulses from a Ti:sapphire laser are used to generate picosecond acoustic pulses on one side of a ~1 mm thick Si wafer. The 1 mm distance is sufficient for the acoustic waves to diffract to the far field before they are detected by time-delayed probe pulses from the Ti:sapphire laser. The acoustic waves are either generated by a surface nanostructure or scattered from a buried nanostructure, and an image of that nanostructure is reconstructed through an analysis of the detected acoustic waves.

Hard X-ray Photoelectron Emission Microscopy (HXPEEM)

Photoelectron emission microscopy (PEEM) excited by hard X-ray photons has been extensively used in recent years by use of highly brilliant synchrotron radiation. In this article, we introduce principles, experimental setup, and some research topics of the hard X-ray PEEM. Especially, a visualization of buried interfacial nanostructures become possible in the use of hard X-ray PEEM, and the hard X-ray PEEM is thought to be a powerful tool for the investigation on surfaces and interfaces. We have also developed a nano-XAFS technique, that is, a microscopic XAFS measurement in 100 nm × 100 nm area using hard X-ray PEEM.

Photo excited scanning probe microscopy for buried nano structure analyses

For buried nano structure analyses, we combined a scanning probe microscope with either a UV laser or x-ray light source. Electron trapping process at Si/SiOx buried interface under UV laser irradiation was investigated with an electrostatic force microscope (EFM). The EFM signal synchronized with optical shutter operation revealed electron trapping process with the time constant of 33 ~ 87 s dependent on laser power. These large values reveal a quasi-stable photoionization state of the trapping site. The EFM with the x-ray source provided an x-ray absorption spectrum of the electron trapping site. The inner-shell excitation and following relaxation of trapped electron into the core-hole result in the quasi-stable photoionization state. Since the photoionization can be detected with EFM easily, nano x-ray absorption spectra can be probed with high efficiency. The trapping site had deeper inner-shell energy level owing to electric field between the sample surface and probing tip, resulting in an energy shift of the absorption spectrum. An estimation of electric field due to the trapped electron reproduced the energy shift. The electric field was dominantly determined by a trapped electron in the nanometer area under the tip, and indicated potential for nano spectroscopy of EFM with an x-ray source.

Evolution of buried semiconductor nanostructures and origin of stepped surface mounds during capping

The authors apply selective wet chemical etching and atomic force microscopy to reveal the three-dimensional shape of SiGe∕Si(001) islands after capping with Si. Although the “self-assembled quantum dots” remain practically unaffected by capping in the temperature range of 300–450°C, significant morphological changes take place on the Si surface. At 450°C, the morphology of the capping layer (Si matrix) evolves toward an intriguing semifacetted structure, which we call a “ziggurat,” giving the misleading impression of a stepped SiGe island shape.