Thick Gold Layer Research Articles

An atomic force microscope nanoscalpel for nanolithography and biological applications

We present the fabrication of specialized nanotools, termed nanoscalpels, and their applicationfor nanolithography and nanomechanical manipulation of biological objects. Fabricatednanoscalpels have the shape of a thin blade with the controlled thickness of 20–30 nm andwidth of 100–200 nm. They were fabricated using electron beam induced deposition at theapex of atomic force microscope probes and are hard enough for a single cut to penetrate a∼45 nm thick gold layer; and thus can be used for making narrow electrode gaps required forfabrication of nanoelectronic devices. As an atomic force microscope-based technique thenanoscalpel provides simultaneous control of the applied cutting force and the depth of thecut. Using mammalian cells as an example, we demonstrated their ability to make narrowincisions and measurements of local elastic and inelastic characteristics of a cell, makingnanoscalpels also useful as a nanosurgical tool in cell biology. Therefore, we believe that thenanoscalpel could serve as an important tool for nanofabrication and nanosurgery onbiological objects.

Influence of an Electric Field on Oriented Films of DMPC/Gramicidin Bilayers: A Circular Dichroism Study

A film of oriented bilayers containing a mixture of gramicidin and dimyristoylphosphatidylcholine (DMPC) has been deposited on a fused-silica window coated with a 10 nm thick gold layer. The thin layer of gold allows the application of an electric potential across the film and the study of its influence on the structure and integrity of the bilayers. Electrochemical measurements, ellipsometry, and far-UV circular dichroism (CD) were employed to characterize the properties of the film of bilayers as a function of the potential applied to the gold electrode. For potentials across the film that are within the range approximately +300 to -150 mV the oriented film of bilayers is stable, and no change in the CD spectra of gramicidin molecule is observed. At more negative potentials, an increase in the film thickness and water content measured by ellipsometry indicated that the film swells and incorporates water, which causes a change in the circular dichroism spectrum of gramicidin molecules in the film. This transformation was interpreted as a change in the average orientation of gramicidin molecules within the film due to a decrease in the ordering of the molecules upon swelling.

Construction of simultaneous SPR and QCM sensing platform

To construct a novel simultaneous SPR and QCM sensing system, an AT-cut quartz crystal is fabricated by sputtering 250 nm of ITO on one side of the quartz plate over a 5-nm thick underlay of titanium, while a 50-nm thick layer of gold is sputter-deposited on the other side to induce a total light reflection of an incident laser beam on the thin gold layer. The signals of the sensing system are detected using a Handy-SPR and QCA922 when dropping 200 microL of Milli-Q water into the sensing cell. A decrease in the SPR reflected light intensity is clearly identified. In the same experiment, the changes in the resonant frequency and resistance are about 2 kHz and 200 Omega, respectively. Furthermore, the oscillation stabilities of the resonant frequency and resistance are about 50 Hz and 2 Omega, respectively, which are sufficient to detect a large mass change on the QCM/SPR chip.

Optical properties of chalcogenide multilayer deposited on Au layer

The chalcogenide multilayers were prepared as dielectric mirrors having the first order stop bands in the near infrared region ∼1.55 μm. The 7.5 layer pairs of the alternating amorphous Sb–Se and As–S layers were deposited on glass substrates using a conventional thermal evaporation method. To center the stop bands of the 15-layer dielectric mirrors at 1.55 μm, the layer thicknesses 117 nm for Sb–Se and 169 nm for As–S single layers were calculated from the quarter wave stack condition. The optical reflection and transmission spectra of the prepared mirrors were measured using a UV/VIS/NIR and FT-IR spectroscopy at the ambient and elevated temperatures. The optical reflection of the annealed 15-layer chalcogenide mirror was found higher than 99% in the range of 1440–1600 nm. As the 200 nm thick gold layer was added between the substrate and the chalcogenide mirror, the stop band of the annealed Au/multilayer system broadened to 1360–1740 nm simultaneously with an appearance of the ∼15% transmission peak at 1.55 μm. A preparation of similar metal/multilayer systems is one of the possible ways how to design the dielectric filters for near infrared region exploiting the good optical quality of the chalcogenide films and their simple deposition.

Submicron Gold Coating Measurements for Hohlraum Development

A thin gold layer is deposited as a liner on the interior of a uranium hohlraum to protect from oxidation of uranium. X-ray fluorescence (XRF) spectrometry was chosen as the liner thickness measurement method for its accuracy, speed, and ease of measurement. The process is noncontact and nondestructive. The thicknesses were determined using a micro-XRF spectrometer unit with analysis software. The accuracy of the measurements was verified against qualified standards. The method was used to accurately measure gold liner thicknesses of cylindrical hohlraums, and it gave initial promising results for measuring the thickness of a boron-doped gold layer when corrected for the gold atom fraction.

Characterization of a broadband all-optical ultrasound transducer-from optical and acoustical properties to imaging

A broadband all-optical ultrasound transducer has been designed, fabricated, and evaluated for high- frequency ultrasound imaging. The device consists of a 2-D gold nanostructure imprinted on top of a glass substrate, followed by a 3 microm PDMS layer and a 30 nm gold layer. A laser pulse at the resonance wavelength of the gold nanostructure is focused onto the surface for ultrasound generation, while the gold nanostructure, together with the 30 nm thick gold layer and the PDMS layer in between, forms an etalon for ultrasound detection, which uses a CW laser at a wavelength far from resonance as the probing beam. The center frequency of a pulse-echo signal recorded in the far field of the transducer is 40 MHz with -6 dB bandwidth of 57 MHz. The signal to noise ratio (SNR) from a 70 microm diameter transmit element combined with a 20 microm diameter receive element probing a near perfect reflector positioned 1.5 mm from the transducer surface is more than 10 dB and has the potential to be improved by at least another 40 dB. A high-frequency ultrasound array has been emulated using multiple measurements from the transducer while mechanically scanning an imaging target. Characterization of the device's optical and acoustical properties, as well as preliminary imaging results, strongly suggest that all-optical ultrasound transducers can be used to build high-frequency arrays for real-time high-resolution ultrasound imaging.

Laser energy transformation to shock waves in multi-layer flyers

Investigations of powerful laser pulse action on planar flyer targets consisting of the layers of different materials are of importance from the basic as well as the applied physics point of view. One important aspect of this research deals with optimization of inertial fusion targets design. Here, the role of a thin heavy metal layer as a protector against preliminary heating of compressed thermonuclear fuel by thermal X-ray radiation can be mentioned as one particular topic to be properly understood. In this paper, the results of our studies of such a thin layer influence on the laser-produced energy deposition in the flyer foils as well as on the hydrodynamic motion of the foils as a hole will be reported. A 0.4 μ m thick gold layer was located between an aluminum layer of 6 μ m thickness and mylar layer with thickness of 2.5 μ m, used here as an ablator. For comparison, the flyer target without the gold layer but of the same area density was employed. Two different target constructions were used: (1) with a 2 mm gap separating the foil and the massive targets for measuring the foil velocity and (2) with gaps of 50, 100 and 200 μ m for laser energy transfer efficiency measurements. Targets were irradiated by laser beam energies of ∼100 J in the case of the first harmonic, and by laser beam energies ∼120 J in the case of the third one using the Prague Asterix Laser System iodine laser. The interaction spot radius of 200 μ m and the laser pulse duration of ∼250 ps were employed in these experiments. A three-frame interferometric and shadowgraphic system was set-up as to measure velocities of the rear side of the foils and to determine electron density distributions at different stages of plasma evolution. Volumes of craters produced by collisions of accelerated foils with a massive aluminum block were used as an indicator of the laser energy transfer efficiency into the foils of both types. These experiments have shown that the presence of the thin gold layer causes a decrease of the flyer velocity by a factor of ∼1.2 for both the harmonics. However, in the case of the first harmonic, the energy transfer into the flyer with the gold layer is higher (compared with the flyers without the gold layer) only for the targets with smaller gaps. In the case of the third harmonic, about 10% decrease in the amount of energy transferred into the foil with the gold layer was observed.

Study of ancient Islamic gilded pieces combining PIXE-RBS on external microprobe with sem images

Numerous metallic objects with very aesthetic and technological qualities have been recovered by archaeological excavations. Adequate processes of restoration and conservation treatments require the accurate determination of the elemental composition and distribution within the objects, as well as the identification of the nature and distribution of the corrosion products. Ideally the identification method should cause no alteration in the sample. In this work, different archaeological pieces with a gilded look have been characterized using simultaneously PIXE and RBS at the CMAM external microprobe in order to study the gilding metalworking done in the Iberian Peninsula during the Middle Ages. The gold layer thickness and its elemental concentrations of Ag, Au and Hg were determined by both techniques and compared with the scanning electron microscopy images obtained for some fragments of pieces.

Ellipsometry study of ultra thin layers of evaporated gold

AbstractOptical properties of ultra thin (from 1 to 40 nm) films of gold evaporated on glass and silicon were studied with the method of spectroscopic ellipsometry in both external and internal reflection configurations as well as with the UV‐visible absorption spectroscopy. The results obtained showed a gradual shift of the plasmon peak from 580 nm for 1 nm thick films to more than 1000 nm for thick (40 nm) gold films. Such phenomenon can be interpreted in terms of quantum confinement of surface plasmons in gold islands. The threshold of the metal‐dielectric transition was found at the film thickness between 4 and 5 nm. Thiolation of the surface of glass has resulted in a slight decrease in the effective thickness of gold layer and respective smaller blue shift of n (λ) and k (λ) dispersion curves, however no dramatic changes were observed in the film morphology. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Plating of archaeological metallic objects – studies by differential PIXE

The differential PIXE method using an external proton beam up to 3MeV energy was applied to examine plated layers of tin, silver and gold on bronze, brass, iron and silver objects from Roman and Early Medieval period. The concentration profiles were deduced from the measurements by the method of virtual slicing the target into layers, and minimizing the differences between the measured and calculated X-ray yields. The tinned layers were usually thin (about 1μm), but the thickness of silver and gold layers was in several cases thicker and exceeded the proton range. The plating techniques were identified as application of the molten metal for tinning, and as fire gilding for the gilded objects.

Micromachined plastic W-band bandpass filters

Results are presented for micromachined plastic waveguide bandpass iris filters for W-band applications using a cost-effective polymer micro hot embossing process in conjunction with metallic electroplating and sealing techniques. The prototype filter has an 8-μm thick electroplated gold layer on a polymeric WR-10 waveguide with a 5-cavity Chebyschev-type design. Measurement results show center frequency of 96.77 GHz with a bandwidth of 3.15%, a loaded quality factor 31.73 and an unloaded quality factor for a single cavity resonator is 1210.6, respectively. A minimum insertion loss of −1.22 dB and return loss of better than −9.3 dB have been measured over the entire passband.

F<sub>2</sub>-Laser Angle Nanomodification of PET

This work is focused on laser modification of polymers with different angles of incidence. Periodic surface structures generated by linearly polarized F2 laser light (157 nm) on polyethyleneterephthalate (PET) were studied. Atomic force microscopy was used to study the topological changes induced by the laser irradiation. The laser irradiation induces the formation of periodic ripple structures, the width of and the height being angle dependent. The periodic structures were formed with the laser fluence 4.70 mJ/cm2. The laser modified PET foils were coated with a 50 nm thick gold layer by sputtering. After Au deposition on the laser PET foils with ripple structure, the roughness of surface decreases in comparison to PET with ripples without Au coating.

Gold Nanolayers Prepared on Poly(ethyleneterephtalate)

Ablation, water etching and gold coating were studied on poly(ethyleneterephtalate) (PET) exposed to DC Ar plasma for 240 s at 8.3 W power. Au layers were sputtered on pristine and modified PET and their adhesion and topography were investigated. The roughness and changes of topography after plasma treatment, subsequent water etching and gold coating were followed using AFM microscopy. The thicknesses of ablated layer and water dissolved layer were determined using gravimetry. A nanoindentor was used to perform microstratch tests of sputtered layers. Water dissolving of thin layer after plasma treatment was confirmed by FTIR spectroscopy. We have found that under the present experimental conditions ca 30 nm thick layer of PET is plasma ablated. The surface topography changes dramatically and surface roughness increases. Another ca 16 nm thick layer was removed under present laboratory conditions after 24hour water etching. Subsequent coating with 50 nm thick gold layer increases surface roughness in all cases of surface modification.

Gold coatings on polyethyleneterephthalate nano-patterned by F 2 laser irradiation

In this work we present periodic surface structures generated by linearly polarized F 2 laser light (157 nm) on polyethyleneterephthalate (PET). Atomic force microscopy was used to study the topological changes induced by the laser irradiation. The laser irradiation induces the formation of periodic ripple structures with a width of ca 130 nm and a height of about 15 nm in the fluence range 3.80–4.70 mJ/cm 2 and the roughness of the polymer surface increases due to the presence of these periodic structures. Subsequently, the laser modified PET foils were coated with a 50 nm thick gold layer by sputtering. After Au deposition on the PET foils with ripple structure, the roughness of surface decreases in comparison to PET with ripples without Au coating. For 50 nm thick Au layers, the ripple structure is not directly transferred to the gold coating, but it has an obvious effect on the grain size of the coating. With considerably thinner Au layers, the ripple structures are smoothened but preserved.

Microwave Reflectivity From Gold Sputtered Nanolayer

This paper deals with reflectivity of a gold layer of nanometer-scale thickness sputtered on a dielectric foil at microwave frequencies. A model of nanometer-scale spheres characterizes the behavior of the layer. For short sputtering times, these spheres are separated, and later they touch each other to form a continuous layer. The structure is analyzed in several ways. The first model, as suggested in the literature, replaces the spheres by their electric dipole moments, while the second, newly proposed model replaces them by their mutual capacities. The structure is also being investigated by the CST Microwave Studio software. The data provided by the models is compared with the data obtained from measurements carried out and published by the authors previously. The reduction in effective conductivity of the layer due to microscopic phenomena in thin films is taken into account in the models. The measured conductivity is compared with values taken from the literature, and the differences are discussed.

Fabrication and optical characterization of nano-hole arrays in gold and gold/palladium films on glass

This paper reports on the improved fabrication process and the optical characterization of different nano-hole arrays in thin metal films that are to be integrated into a novel atto-litre titre plate device for high-speed molecular analysis, such as DNA hybridizations and protein immunoassays. The optical detection is based on the enhanced optical transmission that was recently discovered when light passes through periodically distributed sub-wavelength apertures in optically thick metal films. The transmitted light has also small angular diffraction and well-defined spectral features. Using electron-beam (e-beam) lithography (EBL) and lift-off technique, various array structures with hole diameters ranging between 100 nm and 200 nm and different pitches were fabricated in a 200-nm thick layer of gold (Au), palladium (Pd), and gold/palladium (Au/Pd = 60/40) alloy on glass. Introducing Pd to Au, the grain size of the material is decreased, getting a more well-defined shape of the holes. The transmitted spectrum was measured through periodically and randomly distributed nano-holes in Au. Transmitted spectra were compared as well through similar subwavelength hole arrays in Au, Pd, and Au/Pd alloy. Moreover, the fluorescence of Rhodamine G6 (0.05 µM) was measured when using the transmitted light through periodical cavities in Au as the illumination source. It reveals a nine-fold increase in the fluorescent signal.

Diameter optimization of VLS-synthesized ZnO nanowires, using statistical design ofexperiment

The possibility of diameter optimization of ZnO nanowires by using statistical design ofexperiment (DoE) is investigated. In this study, nanowires were synthesized using avapor–liquid–solid (VLS) growth method in a horizontal reactor. The effects of sixsynthesis parameters (synthesis time, synthesis temperature, thickness of goldlayer, distance between ZnO holder and substrate, mass of ZnO and Ar flow rate)on the average diameter of a ZnO nanowire were examined using the fractionalfactorial design (FFD) coupled with response surface methodology (RSM). Using a2III6−3 FFD, the main effects of the thickness of the gold layer, synthesis temperature andsynthesis time were concluded to be the key factors influencing the diameter.Then Box–Behnken design (BBD) was exploited to create a response surfacefrom the main factors. The total number of required runs for the DoE process is25, 8 runs for FFD parameter screening and 17 runs for the response surfaceobtained by BBD. Three extra runs are done to confirm the predicted results.

Real-Time and Full-Field Detection of Near-Wall Salinity Using Surface Plasmon Resonance Reflectance

An idea of real-time and full-field detection of near-wall salinity is presented to use the surface plasmon resonance (SPR) reflectance that changes with refractive index variations of the tested saline fluid. The laboratory-designed SPR system, based on the Kretschmann's configuration, uses a 47.5 nm thick gold layer as the SPR resonator, coated on a BK7 prism (n=1.515), and requires a one-time system calibration to establish a correlation of the specified saline mass concentration levels to the corresponding CCD (charge-coupled device) pixel gray levels. As a gravity-falling saline drop in water reaches the bottom and diffuses thereafter, the SPR system quantitatively maps the evolution of the salinity distributions in the near-wall region (less than 1 microm). An elaborate uncertainty analysis shows that the overall measurement uncertainties critically depend on the uniformity of the metal film thickness and the accuracy of its dielectric constant.

Effects of Thin-Film Structural Parameters on Laser Desorption/Ionization from Porous Alumina

Nanoporous aluminum oxide layers, grown by anodization of aluminum thin films on glass and then sputter-coated with gold, were used to study the effects of the thin-film structural parameters on laser desorption/ionization (LDI) mass spectrometry (MS) of peptides. Variation of MS signal intensity was examined as a function of alumina pore depth, pore width, and gold layer thickness. Peptide molecular ion intensity was optimal with porous alumina formed from aluminum films of approximately 600-nm thickness; thinner or thicker films gave significantly lower signals. Signals decreased when pore sizes were increased beyond the as-formed width of approximately 100 nm. The MS signal also varied with the thickness of the sputtered gold layer with an optimum thickness being approximately 90 nm. The results of these studies provide values for empirical optimization of LDI MS performance as well as potential clues to the LDI mechanism.

Triggering blue–red transition response in polydiacetylene vesicles: an electrochemical surface plasmon resonance method

Electrochemical surface plasmon resonance (E-SPR) was used to investigate whether the chromic properties of a polydiacetylene (PDA) vesicle films, adsorbed onto an ultra-thin gold electrode, could be triggered by applied potential. This approach constitutes a preliminary model for a novel approach to the use of a triggered chromic transition, as an indicator of biorecognition headgroup binding in these materials. A PDA chromic blue-red transition was identified in E-SPR against the background Deltaepsilon(e) and Deltaepsilon(m). The latter resulted in a ca. 100 mDeg V(-1) shift in the SPR minimum, in the presence of PDA, with the PDA shielding changes in epsilon(e). Electrochemical charge transfer processes in the pre-oxide/oxide anodic region with adsorbed oxygen and hydroxide, involving a change in Au redox state (Au(0)/Au(+)) were visible in the SPR, due to a change in the gold layer thickness and gold oxide layer. However, the cathodic processes, not involving a change in the Au redox state or a increase/decrease in the surface layer dielectric, did not cause a change in the SPR. Based on this, dramatic changes in the optical properties of the adsorbed PDA film could be triggered at an applied cathodic potential, and were identified using SPR. These correlated with a pH-induced chromic transition. Both protonation and ion binding, linked with headgroup environment, were implicated in causing structural transitions in the adsorbed vesicle layer that may also be linked with their bulk optical properties.