Diffuse-interface model for nanopatterning induced by self-sustained ion etch masking

We construct a simple phenomenological diffuse-interface model for composition-induced nanopatterning during ion sputtering of alloys. In simulations, this model reproduces without difficulties the high-aspect ratio structures and tilted pillars observed in experiments. We investigate the time evolution of the pillar height, both by simulations and by {\it in situ} ellipsometry. The analysis of the simulation results yields a good understanding of the transitions between different growth regimes and supports the role of segregation in the pattern-formation process.Comment: 10 pages, 3 figures; minor revisions with respect to first version; figures nicened; journal ref. adde

Optical properties of silicon carbide polytypes below and around bandgap

The optical properties of SiC polytypes are discussed with relation to the structure of SiC. The main part of the paper review the detailed measurements of the uniaxial dielectric function below and around the minimum band gap, using phase-modulated spectroscopic ellipsometry, polarised light transmission measurements or crossed polariser variable angle of incidence interferometry. In particular, the oscillations in the recorded ellipsometric intensities, due to interference between the ordinary and extraordinary modes, specific to thick uniaxial wafers, are used to accurately measure the below band gap dielectric difference. It is focused on the differences in optical properties among the polytypes, in order to investigate SE and closely related techniques as a candidate for bulk-material wafer inspection and characterisation. (37 refs)

Breakdown and field emission conditioning of Cu, Mo and W

The ultra-high-vacuum electrical breakdown characteristics of copper, molybdenum and tungsten have been explored in a setup based on a capacitor discharge. Upon repeated sparking, tungsten and molybdenum showed improvement of the maximum applicable field before breakdown (conditioning) in contrast to copper, which experienced alternate improvement and degrading. After conditioning, tungsten withstood the highest applied field followed by molybdenum and copper. This behaviour was correlated with that of the field enhancement factor extracted from measurements of the field emission current. These results are compared with the tests performed on 30 GHz test accelerating structures for the future Compact Linear Collider

Breakdown resistance of refractory metals compared to copper

The behaviour of Mo, W and Cu with respect to electrical breakdown in ultra high vacuum has been investigated by means of a capacitor discharge method. The maximum stable electric field without breakdown and the field enhancement factor, beta have been measured between electrodes of the same material in a sphere/plane geometry for anode and cathode, respectively. The maximum stable field increases as a function of the number of breakdown events for W and Mo. In contrast, no systematic increase is observed for Cu. The highest values obtained are typically 500 MV/m for W, 350 MV/m for Mo and only 180 MV/m for Cu. This conditioning, found for the refractory metals, corresponds to a simultaneous decrease of beta and is therefore related to the field emission properties of the surface and their modification upon sparking. Accordingly, high beta values and no applicable field increase occur for Cu even after repeated breakdown. The results are compared with RF breakdown experiments [1] performed on prototype 30 GHz accelerating structures for the CLIC accelerator

Real-time control by multiwavelength ellipsometry of plasma-deposited multilayers on glass by use of an incoherent-reflection model

International audienc

Fast near infra-red ferroelectric liquid crystal based Mueller matrix system for imaging and spectroscopy

The science and optical engineering of imaging Mueller Matrix Ellipsometry (MME) and Spectroscopic MME is currently being revitalized based on an efficient optimal design method, and through the use of the so-called Eig envalue Calibration Technique (ECT). Through the ECT one may efficiently measure the details of the polarization state generator (PSG) matrix, and the polarization state analyzer (PSA) matrix, and hence avoid modeling of any unknown polarizing components in the system, and in particular the exact response of complex polarizing elements such as liquid crystal retarders. We here start up with presenting a detailed an alysis of the dynamic response of a near infrared Ferroelectric Liquid Crystal based Mueller matrix ellipsometer (NIR FLC- MME) [1] . A time dependent simulation model, using the measured time response of the individual FLCs, is used to describe the measured temporal response. Furthermore, the impulse response of the detector and the pre-amplifier is characterized and in cluded in the simulation model. The measured time dependent intensity response of the MME is well explained by simulations. A FLC based NIRMME system is here shown to be able to operate accurately at the maximum speed of approximately 16 ms per Mueller matrix measurement (steady state response). We demonstrate here time dependent Mueller Matrix measurements of a dynamically changing sample, with even down to 8 ms sampling time of each complete Mueller Matrix (with some loss of accuracy). We secondly briefly present the NIR-FLC- MME imaging system, and show applications to strain imaging of a crystal subjected to an external pressure. Furthermore, we present near-infra-red Mueller matrix images and corresponding polar decomposition images of thin slices of bio-tissue [2]

Real time control of plasma deposited multilayers by multiwavelength ellipsometry

International audienc

Real time control of the growth of silicon alloy multilayers by multiwavelength ellipsometry

International audienc

Staircase and saw-tooth field emission steps from nanopatterned GaSb surfaces

International audienceHigh resolution field emission experiments from nanopatterned GaSb surfaces consisting of densely packed nanocones prepared by low ion-beam-energy sputtering is presented. Both uncovered and metal-covered nanopatterned surfaces were studied. The field emission surprisingly takes place by regular steps in the field emitted current. Depending on field, the steps are either regular flat plateaus or saw-tooth shaped. To our knowledge this is the first time that such results have been reported. Each discrete jump may be understood either as a resonant tunnelling effect causing the abrupt emission of a high aspect ratio single cone, or as a cascading effect where nearby cones switch on upon the on-set of the primary emitting cone with the highest field enhancement factor. The staircase shape may in both cases be understood from the spatial distribution of the aspect ratio of the cones. We find no evidence for a strong enhancement of the average field enhancement factor