Patterned thin films have had an enormous impact on modern technology, and though semiconducting elements typically grab the spotlight, metal surfaces have played a crucial role in various advanced applications such as materials characterization, biosensors, chemical sensors and microelectro-mechanical systems (MEMS).
Surface patterning describes fabrication methods which modify substrates with extreme precision.
The need for detailed surface structures is becoming increasingly common for scientists across a range of disciplines and there are many means with which these surface patterns can be created.
In this blog, we discuss surface patterning with shadow masks, an important tool for fabricating thin film components for microelectronics in a rapid and repeatable manner.
Surface patterning is the general term used to describe any fabrication method for modifying a substrate with extremely fine precision. Producing detailed surface structures with microscale features is now a matter of course for scientists and engineers in a wide range of application areas. As with any new manufacturing paradigm, there are various technical routes for creating precision surface patterns. Selecting the best surface patterning method can subsequently be a difficult choice.
One of the main problems in microscopy is the movement of the specimen from beam irradiation during imaging which can lead to low-resolution images which are blurred. Carbon films on metal grids can cause this specimen drift. Using gold thin films instead of carbon can stop the drift as they are chemically inert and biocompatible, less fragile, extremely conductive and non-oxidizing. Gold thin metal films are often seen as the most significant signal amplification components in electrochemical and optical sensor applications. In surface plasmon resonance (SPR) applications, gold thin metal film has electron densities which have the plasmon frequencies in the visible light range.
Photolithography is an important microfabrication technique used to pattern substrates for modern electronics, sensors, and microfluidics. It is a precise form of custom surface fabrication where the interface of a wafer is coated with a light-sensitive polymer known as a photoresist. The coated wafer is then exposed to light which is selectively attenuated by a mask, leaving behind a latent image which is chemically, physically, or optically etched to provide a permanent micro-structured pattern on the wafer’s surface. Coupled with metal deposition and etching techniques, photolithography is a versatile method for fabricating microstructures for optics, chemical and bio-sensors, and microfluidic devices.
Small-scale patterned electrodes for scientific micro-electromechanical systems (MEMS) are intricate parts usually created by additive manufacturing (AM). At Platypus Technologies, we generate patterned gold thin films on glass created via e-beam metal evaporation using a titanium adhesion layer to enhance the mechanical stability of the film.
A field effect transistor (FET) is a key electronic component that is used throughout numerous areas of the electronics industry. FETs are largely used within integrated circuits, consuming much lower levels of power than integrated circuits using bipolar transistor technology meaning they can be used on a much larger scale.
A scanning electron microscope (SEM) scans a focused electron beam over a surface to produce an image. The electrons in the beam interact with the sample, creating differing signals that can be employed to gain information about the surface topography and composition.
A biosensor is an analytical device which is usually used to detect a chemical substance. They combine a biological component with a physicochemical conductor and are usually constructed of three segments; sensor, transducer and associated electrons.
Additive manufacturing (AM) is a growing engineering paradigm that enables technicians to produce a wide range of intricate, prototypical parts. Among these are small-scale patterned electrodes for scientific micro-electromechanical systems (MEMS).
Infrared spectroscopy, typically infrared reflection absorption spectroscopy (IRRAS), is the favoured method used to characterise ultrathin layers like self-assembled monolayers. When infrared moves through a sample, some radiation is absorbed and some is transmitted. IR detectors acquire these characteristic signals to generate a spectrum which represents the sample’s molecular fingerprint. This highlights the inherent value of IR spectroscopy; it can be used to elucidate molecular compositions as a function of characteristic absorption/transmission spectra.
What can we use to probe sample surfaces beyond visible light? Electron beams are ideal for powerful magnifications many orders of magnitude greater than that of optical microscopy. But when we are dealing with resolutions of nanometre (nm) and sub-nm proportions, resolving power isn’t the final word. This is partly because researchers are spoilt for choice when it comes to molecular-scale imaging solutions.
Nanostructured thin films have been instrumental in pushing the boundaries of modern electronics and technology. They form one of the cornerstones of key devices in virtually any market that comes to mind, from consumer electronics to ultra-resolution microscopy.
Surface science covers a multitude of chemical and physical interactions occurring at the boundary between one phase and another. Wherever a substrate is deployed, it has been engineered with some consideration for the unique dynamics occurring at its uppermost surface layers in end-use conditions. At Platypus Technologies, we provide custom metal coatings for precision surface engineering and sub-microscopic investigations.
Gold-coated surfaces play an increasingly important role in precision imaging of various biochemical phenomena. There are many unique qualities that make gold surfaces ideal for atomic-scale observations, including near-total (>99%) reflectivity in the infrared (IR) region and useful adsorption properties with bioactive implications. This has proven pivotal in various forms of IR spectroscopy, where gold-coated glass is used as a substrate for biomolecules of interest. But glass and mica are not the only substrates used for microscopy-grade gold thin films.
Platypus Technologies currently offers coatings of gold, silver, and platinum and now we are launching a new product: Copper coatings.
Gold-coated glass is extremely valuable in high-resolution imaging applications. We talked about this at length recently, extolling the unique adsorption mechanics and infrared (IR) reflectivity of gold thin films as critical virtues for niche areas of experimentation. The key takeaway from that article was this: Provided your thin film is extremely high purity and topographically uniform at the atomic scale, your gold-coated substrate should provide a flawless surface for detailed microscopic or spectroscopic observations.
Since the 1960s, silicon technology has been revolutionizing the way we think about electronic devices and digital communications. Gold-coated silicon wafers represent another step on that exponential trajectory of innovation in semiconductor technology, combining the inherent electrical properties of silicon with the unique optical and physicochemical characteristics of gold. Provided the composite is engineered with absolute precision, gold-coated silicon wafers can be used in critical nanophotonic applications.
It goes without saying that gold is an incredibly valuable material, but its value in the combined fields of microscopy and spectroscopy extend far beyond the superficial. Gold thin films deposited uniformly onto transparent glass or mica have useful optical properties, including selective reflectivity and transmissivity. Provided that gold-coated glass can be engineered with extremely precise planarity at, or approaching, the atomic range, it can be readily leveraged in a range of high-resolution imaging techniques that push conventional optical limits.
Nanotechnology is a rapidly growing area of research and development (R&D) focussing on materials and structures with sub-microscale dimensions. The nanoscale can be difficult to visualize given that is a couple of orders of magnitude below anything that is visible with the human eye.