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A graphene is a one atom thick two dimensional crystal which is one of the allotropic forms of carbon. The graphene has a honeycomb like structure. Due to its magnetic, optical properties, it can be used in various applications. Due to its quantum mechanical behavior, it can be used in electronic applications. Research is going on to develop various prototypes of graphene that could replace silicon based devices. It can be used for developing next generation electronic devices due to its unique properties. But it is difficult to fabricate defect free pure sample. Researchers created nanoscale whispering gallery for electrons in graphene which is inspired by whispering gallery effect.
It is an acoustical effect created in the curved walls of a room. This effect is due to the travelling of sound waves along circular direction rather than straight direction. Due to this effect, the person standing near curved wall can hear any whispering sound produced at other parts of wall. This effect is called whispering gallery. Like this effect, researchers have created whispering gallery effect for light waves.
Nanocrystalline silicon is a photovoltaic material which has high electrical efficiency. The researchers inspired by this whispering gallery effect have fabricated thin nanoscale shells of nanocrystalline silicon. The creation of tiny hollow spheres of photovoltaic nanocrystalline silicon has been described here. First tiny hollow spheres of silica are created which is then coated with silicon. By using hydrofluoric acid, silica is etched away in such a manner it won’t affect the silicon coated over it. It leaves behind the light sensitive shells which are used to form optical whispering galleries. It will capture the light and circulates the light. Thus it forms optical whispering galleries. The light traps inside the nanoshells and travels in round direction. The light circulates round and round causes silicon to absorb more energy. The scanning electron image of single layer of nanocrystalline silicon shell is shown in the below figure. From the figure it can be deciphered the hollow shell structure of silicon. Due to this hollow shell structure the light absorption increases.
More light will get absorbed when the light circulates around circumference of nanoshell for a long time. It has the ability of high efficient light absorption, so it can be used in solar fuels, photo detectors etc. It has a broadband light absorption. In case of single layer nanoshells, more light is absorbed over broader spectrum of light. It can absorb more light than flat layer of silicon deposited side by side with nanoshells. By increasing the layer, the absorption can be increased. The three layers can achieve almost 75 percent absorption of light. The nanoshells allow entering and trapping of light easily so as to increase the absorption. The figure below shows the computer simulation of light which resonates inside the nanoshell.
To create a whispering gallery effect a voltage is applied using scanning tunneling microscope probe which will push the electrons like circular wall of mirrors to the electron from graphene. Thus the whispering gallery is created.
Normally, electrons reflect from potential barrier in a semiconductor material. In graphene, the electrons will tunnel straight through the potential barrier. Graphene is more efficient for producing electronic devices.
Due to whispering gallery effect, the electrons will bounce in the curved walls of barrier, instead of tunneling through it. To create the effect, the system consists of a needle like probe present in the Scanning Tunneling Microscope (STM). It uses voltage from the Scanning Tunneling Microscope (STM) to push some of the electrons in the graphene out of a nano-scale sized area. It controls the location and size of graphene reflecting region. This will create whispering gallery. The size and strength of electronic whispering gallery can be varied by varying the tip voltage of scanning tunneling microscope. The probe can create modes of whispering gallery as well as detection of modes. The sharp tip of scanning tunneling microscope is placed over a sheet of graphene. This will create a circular barrier on the graphene sheet which is act as a perfect curved mirror for electrons. The STM creates a wave like resonance behavior which is known as the modes of whispering gallery. Researchers successfully created whispering gallery effect in electrons in the graphene. This invention will help for the development of new electronic devices, quantum based devices etc.
The whispering gallery is very useful in optics. Due to its high quality cavities and tunability, it can be useful in applications such as sensing, communications etc.
In this case, like p and n regions in transistors two regions are created on the surface of graphene. Below the tip of scanning tunneling microscope, a circular region of graphene with electrons which has one polarity and another polarity on the surrounding regions is created. Between the two regions, a circular junction is created which can be controllable. The graphene sheets consists of electrons which behaves as same as particles in light. i.e, the electrons in graphene behave like photons which is confined in a two dimensional atomic sheet. The circular junction will acts as a curved mirror. It can control and focus the electrons.
The electron resonator has several good features. The new system is based on the existing scanning tunneling microscope (STM) technology; it will create usable devices quickly. The STM creates the whispering gallery effect as well as to observe the results. It can used to study about the phenomenon.
This will lead to the creation of electronic lenses. It enables to observe the object one thousandth size of object. It is entirely different from existing electronic microscopes. In electronic lenses, it is possible to observe ambient low energy electrons within the object. Research is still going on to create graphene devices and whispering gallery theory applied to graphene. In future, it could produce new electro optic devices.
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