Svetlana Dligatch

Hot Carrier Extraction with Plasmonic Broadband Absorbers

Hot charge carrier extraction from metallic nanostructures is a very promising approach for applications in photocatalysis, photovoltaics, and photodetection. One limitation is that many metallic nanostructures support a single plasmon resonance thus restricting the light-to-charge-carrier activity to a spectral band. Here we demonstrate that a monolayer of plasmonic nanoparticles can be assembled on a multistack layered configuration to achieve broadband, near-unit light absorption, which is spatially localized on the nanoparticle layer. We show that this enhanced light absorbance leads to ∼40-fold increases in the photon-to-electron conversion efficiency by the plasmonic nanostructures. We developed a model that successfully captures the essential physics of the plasmonic hot electron charge generation and separation in these structures. This model also allowed us to establish that efficient hot carrier extraction is limited to spectral regions where (i) the photons have energies higher than the Schottky junctions and (ii) the absorption of light is localized on the metal nanoparticles.

Mechanical characteristics of optical coatings prepared by various techniques: a comparative study.

Good performance of optical coatings depends on the appropriate combination of optical and mechanical properties. Therefore, successful applications require good understanding of the relationship between optical microstructural and mechanical characteristics and film stability. In addition, there is a lack of standard mechanical tests that allow one to compare film properties measured in different laboratories. We give an overview of the methodology of mechanical measurements suitable for optical coatings; this includes depth-sensing indentation, scratch resistance, friction, abrasion and wear testing, and stress and adhesion evaluation. We used the techniques mentioned above in the same laboratory to systematically compare the mechanical behavior of frequently used high- and low-index materials, namely, TiO2, Ta2O5, and SiO2, prepared by different complementary techniques. They include ion-beam-assisted deposition by electron-beam evaporation, magnetron sputtering, dual-ion-beam sputtering, plasma-enhanced chemical-vapor deposition, and filtered cathodic arc deposition. The mechanical properties are correlated with the film microstructure that is inherently related to energetic conditions during film growth.

The design and construction of a prototype lateral-transfer retro-reflector for inter-satellite laser ranging

The Gravity Recovery and Climate Experiment (GRACE) mission, launched in 2002, is nearing an end, and a continuation mission (GRACE Followon) is on a fast-tracked development. GRACE Follow-on will include a laser ranging interferometer technology demonstrator, which will perform the first laser interferometric ranging measurement between separate spacecraft. This necessitates the development of lightweight precision optics that can operate in this demanding environment. In particular, this beam routing system, called the triple mirror assembly, for the GRACE Follow-on mission presents a significant manufacturing challenge. Here we report on the design and construction of a prototype triple mirror assembly for the GRACE Follow-on mission. Our constructed prototype has a co-alignment error between the incoming and

Role of the spacer layer in plasmonic antireflection coatings comprised of gold or silver nanoparticles

Abstract. Metal nanoparticles (NPs) can increase the absorption of light within semiconductors and hence improve the efficiency of solar cells. We experimentally investigate the effect that gold and silver NPs have on the reflectance of silicon wafers. The NPs are fabricated using the low cost, large area technique of thermal dewetting. We show that a dielectric spacer layer between the NPs and the semiconductor is required to achieve a net reduction of reflection. Furthermore, the optimum thickness of the spacer layer is found to be independent of NP size and metal type.

Optimization of coating uniformity in an ion beam sputtering system using a modified planetary rotation method

A modified planetary rotation system has been developed to obtain high uniformity optical coatings on large substrates in an ion beam sputter coater. The system allows the normally fixed sun gear to rotate, thus allowing an extra degree of freedom and permitting more complex motions to be used. By moving the substrate platen between two fixed positions around the sun axis, averaging of the distributions at these two positions takes place and improved uniformity can be achieved. A peak-to-valley radial uniformity of ∼0.15% (∼0.07% rms) on a single layer film on a 400 mm diameter substrate has been achieved without the aid of masking.

Development of precision double corner cubes for the Space Interferometer Mission

NASAs Space Interferometer Mission (SIM) PlanetQuest requires, among other things, very precise retroreflectors. The CSIRO Australian Centre for Precision Optics (ACPO) has developed Double Corner Cubes (DCCs) to meet the requirements. The DCC consists of an assembly of three 30o wedged prisms optically contacted to a 132 mm diameter flat base plate. The material for all components was Zerodur. The specifications for the DCC were extremely challenging and posed considerable difficulties in the fabrication, coating, assembly, alignment and metrology. Some of the key specifications included: flatness of all reflecting surfaces to be ~ 10 nm peak to valley (P-V); dihedral angle errors < 0.5 arc seconds; collocation of the vertices of the two corner cubes within a circle of 5 um radius; all reflecting surfaces to be gold coated for a final microroughness < 0.5 nm rms; the clear or working aperture extended to within 0.2 mm of all physical edges; and the assembly had to withstand large vibrational forces. CSIRO delivered to JPL a DCC that was used as the primary unit in the so-called Kite testbed to satisfactorily meet the demonstration requirements of the SIM Milestone 8. This paper will discuss some of the procedures used to realize the DCCs and will show examples of results achieved.

Testing the GRACE follow-on triple mirror assembly

We report on the successful testing of the GRACE follow-on triple mirror assembly (TMA) prototype. This component serves to route the laser beam in a proposed follow-on mission to the Gravity Recovery and Climate Explorer (GRACE) mission, containing an optical instrument for space-based distance measurement between satellites. As part of this, the TMA has to meet a set of stringent requirements on both the optical and mechanical properties. The purpose of the TMA prototype testing is to establish the feasibility of the design, materials choice and fabrication techniques. Here we report on co-alignment testing of this device to the arc second (5 μrad) level and thermal alignment stability testing to 1 .

In situ ellipsometric monitoring of complex multilayer designs

Current developments in optical multilayer design and computation make it possible to calculate filters that satisfy the most demanding optical specifications. Some of the designs are highly sensitive to manufacturing errors and require accurate monitoring and control during thin film deposition. Ellipsometric monitoring enables the accurate deposition of any thickness, including very thin layers, and in situ measurement of both refractive index and thickness of the layers during deposition, which facilitate the subsequent real-time design reoptimisation. In this letter, a number of complex multilayer designs with the aid of ellipsometric monitoring are presented, including a laser notch plus band-blocker filter, dichroic filter, beamsplitter, and a wide-range broadband multiplayer antireflection coating. OCIS codes: 240.2130, 310.1860, 120.2130. doi: 10.3788/COL201008Sl.0044. In recent years, significant progress has been made in the field of multilayer optical coating design [1−5] . Nearly any optical filter specification can be designed theoretically, and a number of solutions have become available for very complex and challenging structures. Unfortunately, the required accuracy and reproducibility of the properties of a material for such structures are sometimes so high that mass production may be impossible, even in state-of-theart deposition systems. Hence, the accuracy of in situ monitoring and effective feedback control of the deposition process remain significant issues to be addressed. A number of well-established optical and non-optical techniques allow the monitoring and control of the layer deposition process [6] . The applicability of a particular method is dependent on the deposition technique and

Large area optical mapping of surface contact angle

Top-down contact angle measurements have been validated and confirmed to be as good if not more reliable than side-based measurements. A range of samples, including industrially relevant materials for roofing and printing, has been compared. Using the top-down approach, mapping in both 1-D and 2-D has been demonstrated. The method was applied to study the change in contact angle as a function of change in silver (Ag) nanoparticle size controlled by thermal evaporation. Large area mapping reveals good uniformity for commercial Aspen paper coated with black laser printer ink. A demonstration of the forensic and chemical analysis potential in 2-D is shown by uncovering the hidden CsF initials made with mineral oil on the coated Aspen paper. The method promises to revolutionize nanoscale characterization and industrial monitoring as well as chemical analyses by allowing rapid contact angle measurements over large areas or large numbers of samples in ways and times that have not been possible before.

Ultra-low-reflectance, high-uniformity, multilayer-antireflection coatings on large substrates deposited using an ion-beam sputtering system with a customized planetary rotation stage

A customized planetary rotation stage has been fitted to a commercial ion beam sputter coater to enable the deposition of high uniformity, multilayer optical coatings on large substrates without the use of masks. Uniformity in this system achieved by sequentially depositing each layer in two fixed locations in the sputtered particle plume where the geometry of the natural thickness distributions on a rotating substrate in these locations are of complementary shape and add to produce an overall uniform layer. The modified planetary stage allows substrate rotation about its own axis at any fixed position of the substrate centre about the axis of the planetary system. The suitable locations in the plume of each material that allow maximum uniformity are found by trial and error refinement of locations obtained by modelling of the plume distribution and expected thickness distributions. Ellipsometric monitoring of the thickness of the layer in each fixed position is used to determine the precise ratio of thicknesses in each location needed to obtain the correct total layer thickness simultaneously with high uniformity. The system has thus far enabled single wavelength antireflection coatings of less than 0.001% reflectance to be fabricated over 270 mm diameter substrates. This requires the film thickness uniformity on all layers to be less than ± 0.2%. In addition, 4-layer, dual wavelength antireflection coatings have been fabricated with less than 0.01% reflectance on both wavelengths over similar substrate dimensions.