Thin Films for the physical and life sciences in high-technology applications.

Study of Self-Assembled Monolayers

Au111 thin films are used for studies of ultrathin overlayers such as self-assembled monolayers (SAMs) taking advantage of the large flat gold terraces. SAMs are the most elementary form of a nanometer-scale organic thin film material and are prepared by immersing the gold substrates in solutions containing the relevant molecules. The adsorbates organize then spontaneously into crystalline or semicrystalline structures. See for example M. Wanunu et al., Journal of the American Chemical Society (2004), 126(17), 5569-5576.

An example of a scanning tunnelling microscopy study of SAMs of short carboxyl-terminated molecules on Au(111) thin films can be found under the following reference: C. Dubois and F. Stellacci, J. Phys. Chem. C, 112, 7431 (2008).

An example of a study of the reaction of O(3P) atoms with Alkylthiol Self-assembled Monolayers can be found under the following reference: Carla Waring, Paul A. J. Bagot, Minna T. Räisänen, Matthew L. Costen, and Kenneth G. McKendrick, J. Phys. Chem. A, 113, 4320 (2009).

Instrument Calibration

Au(111) thin films are very useful for scanning probe microscopy (SPM) calibration purposes using the gold terraces unit cell steps of 2.36 Å.

Teaching and Presentations

Au(111) thin films are used for scanning probe microscopy (SPM) studies for educational purposes. Gold on mica samples are ideal for letting students learn about SPM. It is indeed relatively easy to get nice atomic force microscopy (AFM) or scanning tunnelling microscopy (STM) images with those substrates. For ideas and informations on educational news and events in nanotechnology, visit the website of Nanoscience.

 

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Our activities are concentrated on the production and distribution of gold substrates thin films for the physical and life sciences.

Surrounded with excellent know-how and research expertise, PHASIS has also a strong commitment to applied research and device development.

Covering applications from microscopy to chemical sensors, PHASIS offers tailored expertise for high-tech applications using new materials, micro- and nanometric surface modifications, and thin film technology.

  • How can I cut the gold on mica products?


    Phasis provides special scissors with a titanium nitride-coating so that you can cut the mica between the gold region without damaging the gold surface. With these scissors, you will minimise edge-fracturing on the mica compared to cutting with standard scissors.This operation has to be done with precaution to avoid touching or bending the gold surface and minimising the number of particles falling on the substrate during the cutting process. However, it can be done relatively easily and should not present major problems.

  • Do I need to perform a flame annealing with gold on mica from Phasis?


    No, and that is a clear advantage for our customers! You do not need to flame anneal the Au111 on mica substrates before using them. Phasis films are freshly grown just before being sent to the customer. The surface is thus of good quality and there is no need for a second annealing process. However, the substrates have to be used in a short time scale after reception.

  • If I want to flame anneal the substrates anyway, how can I do it?


    If you want to anneal the gold surface using an hydrogen annealing procedure, you first place the substrate on a quartz plate and place another quartz piece on the edge of the sample to hold it down. It takes about a minute with a hydrogen flame sweeping back and forth at a rate of approximately 1 Hz. The flame (approximately 4 cm long) should slightly touch the surface. The gold surface becomes a little bit orange and you have to pay attention not to overheat it - that is, when the film glows! Best do it in the dark to have better visual control. Also make sure that all the safety requirements are met. This procedure is under your own responsibility.

  • Can you grow thicker or thinner gold films on mica?


    Phasis has grown films with thicknesses up to 500nm and lower than 200nm. For very thin film, however, the gold surface will present islands with holes in-between, the film being not thick enough to allow a better covering. Films with thicknesses different from 200nm are non-standard products and price and delivery time have to be determined on a case to case basis.

  • What is epitaxy?


    Epitaxy refers to extended single-crystal film formation on top of a crystalline substrate.

  • Do the BioNano substrates achieve atomically flat regions?


    If you need atomically flat region, you might better consider our gold on mica products. The Bionano gold substrates present very smooth surfaces too with a typical mean surface roughness Sa lower than 1 nm. However, the main difference is that the BioNano gold coating is polycrystalline while the gold on mica has a (111) crystallographic orientation and atomically flat terraces.

  • How is film thickness verified?


    The gold film on mica thickness is controlled using X-ray diffraction analysis. The finite number of diffracting planes leads to oscillations of diffracted intensities whose period is related to the layer thickness. We use the oscillations of diffracted intensities around the 001 peak of gold 111. These oscillations are simulated numerically to estimate the film thickness. The occurrence of finite size oscillations indicates a high degree of crystallinity of the samples. To control the thickness of the Bionano gold, we use the X-ray in the reflectometry mode. Reflectometry is performed in the low angle mode with the x-ray radiation in grazing incidence with respect to the sample. In this configuration, the beam is both reflected by the film surface and by the film-substrate interface, giving an interference pattern observable through oscillations in the reflected intensity. The period of these oscillations only depends on the different refractive indices and on the film thickness, irrespective of whether the film is crystalline or not. The film thickness is the only adjustable parameter to fit the observed oscillations.

  • Can you provide gold-coated glass slides without a titanium adhesion layer?


    Yes, we can coat glass with gold alone.

  • What is the thickness of the mica substrates?


    The mica sheets are freshly cleaved just before the deposition process. The thickness of the final cleaved mica sheets may vary from 80μm to 130μm. The cleaving process is random and the final thickness of the mica sheets cannot be better controlled.

  • How do I contact the bottom electrode (Nb:STO substrate) ?


    The easiest way to contact the bottom electrode is to use a bonding machine (for instance, FEK Delvotec 5430). It welds a wire on the Nb-doped STO substrate through the PZT films using an ultrasonic generator. If you do not have a bonding machine available in your facilities, you can use silver paste to contact the side of the substrate. It is better to scratch a little bit one corner of the substrate with a scalpel before applying the sliver paste. If possible use a paste that is not too liquid and wait approximately 15 minutes for the paste to dry. The drying time may depend on the type of silver paste that you are using. Before performing any PFM measurements, it is a good idea to verify that you have a good electrical contact using a standard Ohmmeter. Since the substrate is conducting, you can simply touch the side or the bottom of the substrate with your probe.

  • Can you briefly describe the procedure to write and image ferroelectric domains using an AFM?


    To write the ferroelectric domains, the tip is in contact with the sample surface and the voltage, +10V or -10V, is applied to the tip through the program (using for instance an AFM Digital Instrument (1996) MMAFM-2). Typically a 0.2 Hz scan rates is used. To image the ferroelectric domains the tip is in contact with the sample surface while applying, between the tip and the grounded substrate, an AC bias. Typically, a 1.5V AC voltage at 10kHz is used for the measurement. The AFM tip excites a local piezoresponse, which can be detected using a lock-in technique (Stanford Research Systems lock-in amplifier). The two polarization states respond 180° out of phase with each other, thus allowing a phase contrast image of the domains to be obtained. 

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