Future Electronic device : Molecular device

In recent daily life, human life could not be separated with electronic tools. The role of electronic tools in human life is very important to improve the quality and quantity of their life. Every year, their problems become more complicated, huge, and connected which cause the demands of the systems that could deal with various and big data in more faster way are inevitable. Thus, scientists are driven to realize electronic devices, which are smaller, faster, and more powerful.

Improvements in human life style quality also require the more high-function and user-friendly devices, such as more resolution, bright in any condition, transparent, and or foldable. However, the research in this field is mainly influenced by two factors nowadays. They are demand of electronic devices, which consume low power and use the material which is abundant available and not harmful to living things and ecosystem, and demand of multi-national electronic company to keep their business based on trends on human life style change, as their consumers. Actually, almost of researches are supported by them to create advanced products as money machine.

The former factor made scientists focus on research using polymer and organic material. One of efforts is on creating electronics devices, which have mechanism similar to the organic systems such as photosynthesis system, mimicry, etc. The later factor has lead research on electronic devices with fabulous characteristics, such as high function, transparent, formidable, adaptable, tunable, etc. One of breakthroughs is recent discovery on method how to exploit the long-conjectured bi-stable electrical conductivity of ferroelectric materials. This discovery gave prospect to realize smart, ultra-dense, and low-power memory technology. However, those two factors always show on trade-off relation. Here, the demands need to be compromise each other. The popular example is OLED, which is inferior compare to LED. One of the best ways to compromise those factors is to imitate systems, which have already shown its tremendous function fulfilling those requirements. Now, research on molecular devices especially using polymer and organic material is getting many attentions.

The trend of electronic devices getting miniaturized has shown remarkable progress every year. If this trend is to continue, the size of electronic device will soon need to reach the scale of atoms or molecules. This grew new goal that need a new concept of electronic devices. The idea to embed atoms or molecules between electrodes, which perform basic of digital electronic functions, was already pushed forward at the mid-1970s. Some new promise concepts have been realized for individual function, but the efforts to realize at least a functional small system of molecular devices are still far from its goal. Scientists still have many enormous obstacles, such as economical fabrication, electronics optical characterization of atoms or molecules, and the way to transfer information between molecules.

Molecules and polymers have unique electronic and optical properties suitable for use in electronic devices. These properties, however, are complex and not well understood. Charge transport, for example, is affected by molecule shape, which can change during device operation and is difficult to measure. Now, a new technique is available to characterize the electronic states of molecules. The key characteristic of this technique—called fluorescence yield x-ray absorption spectroscopy—is its ability to probe molecules that are buried underneath other molecules, as well as under metallic electrodes (Fig. 1). First, x-ray photons illuminate a device of interest, causing core electrons inside a particular atom to be promoted to higher energy levels. When these electrons relax, they release their energy either to other electrons, or to photons. Finally, these energetic electrons or photons are emitted from the device, and the researchers can measure their energy. Then, they can determine the properties of the emitting molecule. The ability to select the type of atom that is excited—for example, carbon—aids the analysis.

Fig. 1 A schematic of fluorescence yield x-ray absorption spectroscopy.

A new experimental result has shown the prospect to realize the molecular devices. The result has provided the first experimental determination of the pathways by which electrical charge is transported from molecule-to-molecule in an organic thin film. The results also show how such organic films can be chemically modified to improve conductance. It is shown that when the molecules in organic thin films are aligned in particular directions, there is much better conductance. To date, chemists already know how to fabricate organic thin films in a way that can achieve such an alignment, which means it should be able to use information provided by this methodology to determine the molecular alignment and its role on charge transport across and along the molecules. This will help improve the performances of futures organic electronics devices.

Fig 2. STEM image of an organic thin film deposited on a silicon nitride membrane

Another recent study also has shown success in developing a new transparent solar cell that is an advance of polymer solar cell (PSC) that produces energy by absorbing mainly infrared light, not visible light, making the cells nearly 70% transparent to the human eye. The near-infrared photoactive polymer absorbs more near-infrared light but is less sensitive to visible light, balancing solar cell performance and transparency in the visible wavelength region. Instead of the opaque metal electrode used in the past, the transparent conductor made of a mixture of a silver nanowire and titanium dioxide nanoparticle is used.

These some breakthrough achievements, however, are only few premature steps to realize technology of molecular devices. Still, many steps need to be developed and tested based on scientific method. Understanding of molecular characteristics and developing economical high-throughput fabrication method in molecular scale are required. Many new advanced methods to manipulate and modify the molecular component forming complete electronic systems of molecular components are likely to be invented in future researches. Human effort in facing environmental and climate problems, therefore, will give influences in developing future electronic device, and hybrid combination of molecular device and existing devices is likely will shape our future electronic devices.

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