Applications of the Nanofilm Product Line

ABSTRACT
The main feature of tin-doped-indium oxide In2O3:Sn is the combination of electrical conductivity and optical transparency. ITO is mainly used to make transparent conductive coatings for liquid crystal displays, flat panel displays, plasma displays, touch panels, electronic ink applications, organic light-emitting diodes, solar cells, and antistatic coatings. Different deposition processes can be used to produce ITO layer. The lateral distribution of thickness and optical properties of films locally grown out of plasma flow on a base from magnetron sputtering was detected with the nanofilm_ep3se. Spectra of Delta and Psi were measured for regions of interest for a general inspection and a large scale investigation. The high resolution investigation on a smaler scale was based on a spectra of Delta maps at different wave length. In the optical model the dispersion function of the ITO layer was describt by a constant background refractive index and and a Lorenz oscillator. The calculated optical properties were the frequency of the UV absorption line, the refractive index, the extinction and the thickness of the ITO layer.

Andreas Janshoff, Maja Geidig, Simon Faiss

ABSTRACT
The phase transition of individually addressable microstructured lipid bilayers was investigated by means of non-contact imaging ellipsometry. 2-D membrane compartments were created on silicon substrates by micromolding in capillaries and the thermotropic behavior of various saturated diacyl phosphatidylcholines (DPPC, diC15PC, DMPC) as well as mixed DMPC/cholesterol membranes was determined measuring area expansion and thickness of the bilayer as a function of temperature. We found an increase in the phase transition temperature of 2 – 6 °C as compared with liposomes and a reduced melting cooperativity. Individually addressable microstructured lipid bilayers are clearly advantageous over conventional bilayer preparation techniques if precise measurements are needed.

Matthias Vaupel, Ulrich Stöberl

ABSTRACT
Graphene and graphene oxide layers are localized and charcterized on different substrate materials by means of the spectroscopic imaging ellipsometer nanofilm ep3se. The thickness and the dispersion functions of the refractive index n and of the extinction k of a few μm-wide layers are obtained. The results of imaging ellipsometry agree with the results obtained by the combination of AFM and confocal microscopy within the error margins. By contrast to the latter methods the measurement time is much shorter with imaging ellipsometry.

ABSTRACT
Graphene and graphene oxide layers are localized and charcterized on different substrate materials by means of the spectroscopic imaging ellipsometer nanofilm ep3se. The thickness and the dispersion functions of the refractive index n and of the extinction k of a few μm-wide layers are obtained. The results of imaging ellipsometry agree with the results obtained by the combination of AFM and confocal microscopy within the error margins. By contrast to the latter methods the measurement time is much shorter with imaging ellipsometry.

Laser Diodes (LD) consist of semiconducting materials e.g. GaAs or Si, which are doped with electron donors and electron acceptors in different layers. Doping atoms can be Al and In among many others. At the interface between layers with electron depletion and electron excess, electrons and holes can recombine and emit light if a voltage is applied between these layers. Coherent light emission out of the LD is obtained if more light is amplified by recombination than lost through the reflecting outer surfaces of the LD (facets) and by absorption in the LD. The properties of the LD i.e. emission wavelength, linewidth, power, stability, lifetime depend on the dispersion functions of refractive index n and extinction k of all materials of the LD and on the thickness of each layer on the LD. In order to control the quality of the LD those dispersion functions and thickness shall be measured. Especially important for the function of the LD are the optical properties of the anti-reflection coating on the emitting surface of the LD. In a quantum well laser the interface of the light emission is only a few nm thin. Spectroscopic ellipsometry is the ordinary method to measure these optical properties on large semiconducting wafers. Imaging ellipsometry is needed to measure on those tiny LDs, because high lateral resolution of a few μm is necessary.

Ellipsometric Platform EP³ SPR
Multi-Channel and Imaging Surface Plasmon Resonance Analyser

Optical anisotropy of a material means that the refractive index depends on the propagation direction of light. The anisotropy is caused by a net macroscopic orientation of the microscopic constituents, e.g. molecules or crystal domains of the anisotropic material. Anisotropy appears in many thin polymer films, liquid crystals, lightemitting organic devices (OLEDs), and non linear optical materials. These thin anisotropic films appear structured as a matrix in many different types of displays.

Photonic crystals are periodic structures of alternating high/low refractive index domains made of transparent materials. Those crystals can be non-transparent for a particular wavelength range due to multiple reflections and interference in the crystal. Theoretical calculations demonstrate that for fcc (face cubic centred) crystals the ratio between the refractive indices of the different domains must be higher than 2.8 to form a photonic crystal with bandgap. These crystals are used as filters for electro-magnetic radiation, e.g. infrared filters. The filter wavelength depends on the domain size and the refractive index difference between the domains.

Thickness measurement of a layer is a frequent application of ellipsometry. To this end the observables Delta and Psi are simulated with the optical model of the sample. The model contains free parameters, i.e. layer thickness d, which is varied until the difference (mean square error) of measured and observed delta and psi is minimal. The optical model can be used to simulate delta and psi as a function of the thickness d. For a transparent layer (i.e. extinction k = 0, fig. 1) delta and psi are periodic. The period length depends on the angle of incidence and the wavelength. With a single pair of delta and psi the thickness can only be single correctly evaluated up to a multiple of the period length, which is typical 250 nm. In order to evaluate a unique thickness either an angle of incidence or a wavelength spectrum of delta or psi has to be fitted. The imaging ellipsometer EP3-SW can record a delta map of the sample surface at one wavelength instead of single point measurements of delta usually done by nonimaging ellipsometers.

For the production of microstructures Microcontact Printing is a simple an cheap alternative to the rather complicated and expensive Photolithography. By means of Microcontact Printing SAMs (selfassembled monolayers), e.g. a thiol can be printed on a suitable substrate, e.g. gold. The SAM protects the surface from being etched when in a next step the surface is etched to produce a lateral structure. The chemical function of a thiol depends on its functional groups, which can be modified. In that way the surface can be modified to bind particular classes of molecules. Microcontact Printing of SAMs can produce Microarrays carrying thousands of different sensor properties within one cm². Microarrays are applicable in Genomics and Proteomics in biotechnology. Imaging ellipsometry is cheap, fast, and marker-free detection method on Microarrays

Silicon is the basic material for the production of integrated circuits in the semiconductor industry. During the production Si-wafers are doped and coated by functional layers, whose thickness and dispersion functions are measured by Ellipsometry. A silicon chip with SiO2-layer is one of the most frequently measured type of sample in Ellipsometry.

Klaus-Jochen Eichhorn

Sometimes lateral structures of polymer films on solid surfaces prevent a correct estimation of interesting film properties (thickness d, refractive index n). Common ellipsometric techniques give only average values of the thickness and optical constants of the entired illuminated surface region (light spot in mm² range). However, imaging ellipsometry is able to detect the lateral inhomogenities and microstructures in detail, and furthermore, to analyze them by fitting the ellipsometric

Commonly used quality control of DNA arrays employs hybridization, spotting of labeled DNA, and measurement of the Reflection of salt components left from the spotting buffers. Control hybridizations have the disadvantage that the slides used in the control cannot be reused. Spotting of labeled DNA does not guarantee that all other spots are found on the array. Control by measuring residual salt has the disadvantage that the DNA itself is not detected. By contrast to these methods imaging ellipsometry is the only method that allows the direct control of DNA arrays after the final (washing) step in a label-free and non-destructive manner. The images visualize not a ‘carrier’ component as salt but the DNA itself. Each spot is well resolved and can be judged regarding size, shape, homogeneity, positioning within the array. Imaging ellipsometry allows a quality control of DNA arrays without the need for control hybridizations or control spotting of labeled DNA. It measures thickness, refractive index, and (in case of labeling even) extinction of the spotted reaction layer.

In the field of proteomics, one has to deal with a class of molecules with diverging and in several aspects still unpredictable properties. It is quite undesirable to have to modify proteins with labels before being able to characterize them. Obviously, under such circumstances label-free detection methods are strongly favoured.Surface plasmon resonance spectroscopy is the most common label-free technique. However, a gold layer is needed on the solid support which has to be produced under highest standards. Current applications are in most cases restricted to a few regions of interest. Protein arrays on standard glass slides cannot be read out or even be characterized kinetically.