Aluminum Grating Research Articles

Features of Light Transmission and Stark Effect in a Plasmonic Nanostructure Comprising Organic Semiconductor and Subwavelength Aluminum Grating

Specific features of light transmission and electroabsorption in a plasmonic nanostructure with organic semiconductor (zinc phthalocyanine, ZnPc) and subwavelength aluminum grating (AlGr) have been experimentally investigated. The glass–AlGr–ZnPc–Al nanostructure was prepared using layer-by-layer deposition. First, only a part of the structure has been analyzed to check the grating quality. After deposition of an organic semiconductor (ZnPc) layer on the grating, the transmission of TE and TM polarized light through AlGr and ZnPc layers upon excitation of plasmon resonances has been studied. Afterwards, a semitransparent aluminum layer has been deposited on the ZnPc layer (an additional electrode for measuring the electroabsorption effect). For TM polarized light, a multiple increase in the electroabsorption effect has been found (in comparison with a structure without subwavelength grating). This result can be explained by the Stark effect on exciton transitions and the presence of two cavities in the structure, which are related to the excitation of plasmonic states and the Fabry–Perot effect between aluminum electrodes. The presence of the cavities leads to a decrease in the group velocity of light and, accordingly, increases the density of exciton states, which are characterized by a large difference between polarizabilities in the excited and ground states.

Plasmonic Enhancement of Photocurrent in a Hybrid Structure with a Subwavelength Aluminum Grating

Strong anisotropy of photocurrent excitation is observed in a hybrid photovoltaic structure comprising a film of organic-semiconductor blend and a subwavelength metal grating at one of the electrodes. The results are explained in the context of a numerical model demonstrating different characters of localization of optical fields with different polarizations and, correspondingly, the polarization-selective excitation of plasmons.

Resonance of surface-localized plasmons in a system of periodically arranged gold and silver nanowires on a dielectric substrate

The plasmon resonance of nanogratings consisted of periodically arranged square cross-section nanowires of a copper and aluminum on the dielectric substrate was studied by the rigorous coupled-wave analysis. The cross-sections of the nanowires are 30 × 30 nm2 and 50 × 50 nm2. The period was equal to 0.06 μm and 0.1 μm. The spectral dependences of the absorption, reflection and transmission coefficients of the nanograting in the wavelengths range from 0.1 to 1.0 μm were calculated. The field distribution at the interfaces of grating-air and grating-substrate was simulated. The maximum absorption is calculated at the wavelengths of 0.555 μm for copper and wide absorption band from 0.12 to 0.22 μm for aluminum gratings. The resonance peak for aluminum nanowires splits into two or more peaks. Spectral characteristics of the copper nanowires are similar to the corresponding characteristics of the gold nanowires; however, the maximum absorption is shifted to the long-wave region from 0.525 μm for gold nanowires to 0.555 μm for copper. It is necessary to use more number of coupled waves for the aluminum grating than for copper. That is from the point of view of the calculation convergence. Therefore, the electromagnetic fields at the resonance wavelengths which occur in the aluminum nanowires are stronger than in comparison to the copper nanowires.

Design Analysis of Refractive Index Sensor with High Quality Factor Using Au-Al2O3 Grating on Aluminum

We propose a surface plasmon resonance (SPR)-based refractive index sensor using gold-alumina grating over aluminum film for biosensing. Conventional SPR sensor based on gold grating exhibits broader SPR dips whereas that based on aluminum grating exhibits narrow reflection dip. A narrow reflection dip is desirable as it provides good resolution and improves the accuracy of measurement. Aluminum is less stable and generally is not preferred for an SPR-based sensor. It is more prone to being oxidized, which reduces the sensitivity and increases the width of the reflection dip of the sensor. While gold cannot provide narrow SPR reflection dips, but is used as an SPR active metal due to its more chemical stability. In order to improve the accuracy of gold grating-based sensor while taking care of oxidation problem of aluminum, in this paper, we propose a gold grating over aluminum film for SPR-based sensor and show that this configuration improves the sensitivity and the detection accuracy of the conventional sensor. Moreover, the oxidation problem is reduced to some extent as a part of aluminum is covered with gold. In order to completely avoid the oxidation of aluminum, we further propose to cover the exposed part of the aluminum with alumina and show that this configuration further improves the accuracy by reducing the width of the SPR reflection dip without affecting the sensitivity significantly. Numerical simulations show that sensitivity of proposed sensor is 270.33°/RIU with quality factor of more than 267.65 RIU−1.

Electro-Optic Effect in Thin Films of a Dielectric and a Ferroelectric with Subwavelength Aluminum Grating

The electro-optic effect in three nanoscale heterostructures, in each of which a thin layer of dielectric or ferroelectric material is inserted between two planar metal electrodes, has been studied. Each structure has one aluminum layer, containing a subwavelength grating with a period of 400 nm, contacting with either the glass substrate or air. The light transmission spectra of structures with subwavelength grating contain characteristic plasmon dips. Short external-voltage pulses affect the change in the refractive index of the corresponding active layer. Significant values of these changes may be useful for designing optical modulators.

Design of long-wavelength infrared polarizer based on sub-wavelength aluminum-ZnSe grating

A dual-layered sub-wavelength grating consisting of two kinds of materials, aluminum and ZnSe, is developed to improve the performance of polarimetric elements in long-wavelength infrared (LWIR) polarization imaging system. Parameters of the designed grating’s morphological structure are optimized on the basis of analyzing the effects on the polarization performance through the rigorous coupled wave theory, which helpfully calculates the diffraction efficiency. With a rectangular profile, the grating designed for applications in LWIR band has periods of 1 μm and 50%-fill-factor. The depths of aluminum and ZnSe in the grating region are 0.6 μm and 0.4 μm respectively. A TM transmission greater than 87.54% with an extinction ratio exceeding 47 dB is achieved in the 7~15 μm band when the angle of incidence is from zero to sixty degree. The grating maintains an extinction ratio better than 50 dB and TM transmission over 90.80% above 10.6 μm incident wavelength, which is superior to single-layered aluminum gratings with the same depth in the transmission performance in comparison. The simulation results show that this grating has excellent polarization performance in the broad LWIR band.

Light transmission coefficients by subwavelength aluminum gratings with dielectric layers

Spectral positions of plasmon resonances related to boundaries between a thin aluminum layer and dielectrics (air, glass, VDF–TrFE 65/35 ferroelectric copolymer, and indium tin oxide (ITO)) have been determined in the transmission spectra of aluminum gratings of three types with 30 × 30 μm2 dimensions and 350-, 400-, and 450-nm line periods. Experimental results agree well with spectral positions of plasmon resonances calculated for the normal incidence of TM-polarized light. In addition, maximum values of transmission coefficients in the region of λ ≈ 900–950 nm have been determined for glass–Al–copolymer and glass–ITO–Al–copolymer structures. These values are close to 100%, which shows that the effective optical aperture is two times greater than the geometric areas of slits.

Mueller Matrix of Specular Reflection Using an Aluminum Grating Surface with Oxide Nanofilm.

The accurate nondestructive and real-time determination of the critical dimensions of oxide nanofilms on periodic nanostructures has potential applications in nanofabrication techniques. Mueller ellipsometry is fast, accurate, nondestructive, and can be used in the ambient air. This study used the elements of a Mueller matrix of specular reflection, which is based on a Mueller ellipsometry method, to evaluate the thickness of an oxide nanofilm on an aluminum grating surface. By using non-traditional rigorous coupled-wave analysis (RCWA), we decomposed the Mueller matrix to obtain the relationship between the evaluated polarization properties of reflected light and the dimensions of oxide nanofilms on aluminum grating surfaces. We also quantitatively analyzed the Mueller matrix elements' variation due to the thicknesses of top, sidewall, and bottom oxides. We consider these oxide films are naturally formed and of nonuniform thickness on grating structures. The results show that the elements of Mueller matrix shift with the increasing of the uniform thickness of oxide at a fixed wavelength. Moreover, as oxide nanofilms on grating structures are nonuniform, the impact of the thickness of side wall oxide on the Mueller matrix elements is more obvious than that of top and bottom oxides at the relative larger incidence wavelength range. The finding of this work may facilitate the nondestructive and real-time measurement of the thickness of oxide nanofilms on metal gratings where the metal is easily oxidized.

Modes Manipulation Within Subwavelength Metallic Gratings

Surface plasmon polariton (SPP) and cavity modes supported by the plasmonic gratings are often of hybrid nature in ruling light-nanostructure interactions. The coupling of incident light to SPP waves through the excitation of SPP modes usually traps the light at the air-metal interface, while the coupling to standing waves through cavity modes confines the light within the cavities. However, in a specific application, the highly selective coupling of incident light to either SPP or cavity mode is always required. We present here, for a single metal-insulator-metal (MIM) groove, the coupling strength of incident light to a certain mode can be engineered by varying the groove width and depth. To further enhance the coupling selectivity, the periodicity was introduced to the MIM grooves: When the period approaches (deviates from) the wavelength of SPPs, the incident light highly couples to SPP (cavity) mode, due to the constructive (destructive) interference between the propagating SPPs at metal-air interfaces. Two types of metallic gratings, aluminum grating with its period approaching the λSPP and iridium grating with its period far away deviating from the λSPP, were fabricated and measured. The almost null TM transmission through aluminum grating and detection of surface enhanced Raman scattering (SERS) signal from iridium grating solidly guarantee the validity of the proposed method in manipulating the modes, through which the energy flow can be guided to its supposed-to-appear regions.

Liquid crystal on subwavelength metal gratings

Optical and electrooptical properties of a system consisting of subwavelength metal gratings and nematic liquid crystal layer are studied. Aluminium gratings that also act as interdigitated electrodes are produced by focused ion beam lithography. It is found that a liquid crystal layer strongly influences both the resonance and light polarization properties characteristic of the gratings. Enhanced transmittance is observed not only for the TM-polarized light in the near infrared spectral range but also for the TE-polarized light in the visible range. Although the electrodes are separated by nanosized slits, and the electric field is strongly localized near the surface, a pronounced electrooptical effect is registered. The effect is explained in terms of local reorientation of liquid crystal molecules at the grating surface and propagation of the orientational deformation from the surface into the bulk of the liquid crystal layer.

Time-resolved detection of propagating Lamb waves in thin silicon membranes with frequencies up to 197 GHz

Guided acoustic waves are generated in nanopatterned silicon membranes with aluminum gratings by optical excitation with a femtosecond laser. The spatial modulation of the photoacoustic excitation leads to Lamb waves with wavelengths determined by the grating period. The excited Lamb waves are optically detected for different grating periods and at distances up to several μm between pump and probe spot. The measured frequencies are compared to the theoretical dispersion relation for Lamb waves in thin silicon membranes. Compared to surface acoustic waves in bulk silicon twice higher frequencies for Lamb waves (197 GHz with a 100 nm grating) are generated in a membrane at equal grating periods.

Bilayer lift-off process for aluminum metallization

Recently published reports in the literature for bilayer lift-off processes have described recipes for the patterning of metals that have recommended metal-ion-free developers, which do etch aluminum. We report the first measurement of the dissolution rate of a commercial lift-off resist (LOR) in a sodium-based buffered commercial developer that does not etch aluminum. We describe a reliable lift-off recipe that is safe for multiple process steps in patterning thin (<100 nm) and thick aluminum devices with micron-feature sizes. Our patterning recipe consists of an acid cleaning of the substrate, the bilayer (positive photoresist/LOR) deposition and development, the sputtering of the aluminum film along with a palladium capping layer and finally, the lift-off of the metal film by immersion in the LOR solvent. The insertion into the recipe of postexposure and sequential develop-bake-develop process steps are necessary for an acceptable undercut. Our recipe also eliminates any need for accompanying sonication during lift-off that could lead to delamination of the metal pattern from the substrate. Fine patterns were achieved for both 100-nm-thick granular aluminum/palladium bilayer bolometers and 500-nm-thick aluminum gratings with 6-μm lines and 4-μm spaces.

Research on the polarization and temperature characteristics of subwavelength aluminum gratings

An aluminum grating with period of 152 nm is designed and manufactured based on rigorous coupled wave analysis. Its transmissions of TM and TE waves are measured at 532 nm, 632.8 nm and 810 nm, respectively. From the agreement between the experimental results and simulations, a grating thickness of 80 ± 5 nm can be determined. The analysis of and experiments on the grating temperature dependence reveal its thermal stability in ambient conditions.

A New Test Device for Mechanical Ruling Process of Aluminum Grating

The study of the mechanical ruling process of aluminum grating needs a new test device. And a program controlled test device for mechanical ruling was analyzed, designed, manufactured and tested in this paper. The developed mechanical ruling techniques of this device to fabricate micropatterns are introduced with the characteristics of multiple degrees of freedom, openness, visualization, and operability. After some primary tests, assessment of microgrooves was performed with mini video microscopy, which confirmed the validity of the new device for mechanical ruling process investigation.

Control of Infrared Spectral Absorptance With One-Dimensional Subwavelength Gratings

The wavelength-selective infrared absorptance of a single-layered aluminum subwavelength structure (SWS) is optimized using a hybrid numerical scheme comprising the rigorous coupled-wave analysis method and a genetic algorithm. The results show that the optimized SWS yields a strong absorptance peak (0.99) and a full-width-at-half-maximum (FWHM) of 1.42 μm. In addition, it is shown that the absorptance spectrum of the SWS is insensitive to the angle of incidence of the incoming light and the grating period, but shifts toward a longer (shorter) wavelength as the grating thickness or grating ridge width is increased (decreased). The enhanced absorptance is examined by computing the governing equations of the excitations of Rayleigh-Wood anomaly, surface plasmon polaritons, cavity resonance, and magnetic polaritons. The magnetic field patterns and Poynting vector distribution within the grating structure are also analyzed to support the physical mechanism using the finite-difference time-domain (FDTD) method. The results indicate that the absorptance peak of the SWS is the result of cavity resonance. Also, for a double-layered SWS comprising an aluminum grating and a dielectric layer, a widening of the absorptance spectrum occurs. Overall, the results presented in this study show that SWS gratings which can be easily manufactured using microfabrication technology provide a simple and versatile solution for such applications in tailoring the spectral absorptance used for infrared detection, energy harvesting, and so on.

Enhancement of SOI Photodiode Sensitivity by Aluminum Grating

Aluminum grating was applied to silicon-on-insulator (SOI) pn-junction photodiode to increase the light sensitivity. For 100-nm-thick diode, quantum efficiency (QE) of 26% (x15 enhancement) was attained at the wavelength of 700 nm. Wavelengths of the QE peaks for various grating pitches and light incident angles were examined, and it was confirmed that the coupling between the diffracted light from the grating and the propagation modes in the SOI slab waveguide caused the enhancement.

Enhancement of SOI Photodiode Sensitivity by Aluminum Grating

not Available.

Improved reflectivity and velocity model for aluminum gratings on YZ LiNbO3

Lithium niobate has recently been used for SAW tags and temperature sensors because of its high coupling coefficient and high reflectivity. To increase the device operating frequency for a given electrode line resolution, harmonic operation of the reflector is a very attractive option. When used in conjunction with harmonically operated transducers, the device operating frequency can be increased for a given photolithographic line width resolution. To design and accurately predict the behavior of these devices, it is necessary to model the electrode reflectivity and velocity for both fundamental and second-harmonic operation. The coupling of modes (COM) model has been used to model these devices, however the COM model uses empirically determined coefficients to model reflectivity. In this paper, the reflectivity and velocity of aluminum electrodes is extracted experimentally for fundamental and second-harmonic operation versus metalization ratios ranging from 0.2 to 0.9 and versus normalized metal thickness ranging from 0.4% to 4%. A least-squares fit is then performed on the data using physical terms in the transmission line model to yield equations that can be used in the COM model to predict device behavior over varying metallization ratios and normalized metal thicknesses. Orthogonal frequency-coded (OFC) SAW tags were designed and fabricated and experimentally obtained data are compared with the COM modeled responses for the tags at fundamental and second-harmonic operation to verify the predictions.

Frequency shift and attenuation of hypersonic surface acoustic phonons under metallic gratings

Using aluminum gratings of varying duty cycles, we report picoseconds acoustics measurements of frequency shift and attenuation in surface acoustic phonons in silicon at ∼15 GHz. We observe that the frequency shifts nonlinearly with the duty cycle, particularly in the range of 0.3 to 0.5. The data deviate from the perturbation model as a sinusoidal function of the duty cycle. The attenuation peaks at 0.5 duty cycle which is in good agreement with an eigenmode analysis of the composite structure. This work elucidates the mechanism of surface acoustic phonon scattering at periodic interfaces.

KRIOSBOM101 low-temperature scanning near-field optical microscope

An optical scanning near-field microscope was developed. A cryostat for obtaining low temperatures in the range of 1.8–300 K was designed. The microscope control unit and software were advanced taking into account the temperature range. A room-temperature measurement technique was refined on test aluminum gratings on glass with a period of 4 µm. An optimum size of the scan field, which makes it possible to neglect piezoceramics nonlinearities, was determined.