Japan Science and Technology Agency (JST) (Saitama, JP) received U.S. Patent 7,662,731 for a quantum dot manipulating method and a generation/manipulation apparatus which can control the size of a large number of generated quantum dots on or below the order of percent which is required for optical applications of the dots. The method directly generates quantum dots in superfluid helium and manipulates the generated quantum dots by shining light onto the quantum dots.
Since the manipulation is carried out in a low temperature environment (in superfluid helium) in this manner, resonance changes are prevented from occurring due to a rise in temperature of the quantum dot. Furthermore, the surroundings are in a superfluid state, the target quantum dot can move hardly being affected by diffusion and meeting little resistance.
The quantum dot production/manipulation apparatus is adapted to generate quantum dots with a generation laser and manipulate the quantum dots with a manipulation laser in a housing containing superfluid helium in an internal space. Thus, the quantum dot generation and manipulation can be carried out in superfluid helium which has extremely low temperature (2 K or below) and very high thermal conductivity.
By directly generating quantum dots and manipulating the quantum dots with light in superfluid helium, the size and layout of the quantum dots can be controlled by a method that never existed before, according to inventors Tadashi Itoh, Masaaki Ashida, Hajime Ishihara and Takuya Iida.
By directly generating quantum dots and manipulating the quantum dots with light in superfluid helium, the size and layout of the quantum dots can be controlled by a method that never existed before, according to inventors Tadashi Itoh, Masaaki Ashida, Hajime Ishihara and Takuya Iida.
Quantum dots are generated by shining a dot production laser (4a) onto a solid object (3) in a quantum dot production/manipulation apparatus (1) containing superfluid helium (7) therein. A dot manipulation laser (5a) is shone onto the generated quantum dots to manipulate the quantum dots. FIG. 2 is a see-through illustration of features of a quantum dot production/manipulation apparatus used in the present example.
FIG. 3 is a scanning electron microscope image of CuCl quantum dots produced and manipulated with the quantum dot production/manipulation apparatus in FIG. 2.
The quantum dot is any structure of a semiconductor, metal, organic compound, or like material, typically a few to a few hundred nanometers in size, which is a system where quantum mechanical effects can happen. In the embodiment detailed later, a semiconductor is used. Semiconductors are suitable because, among other reasons, they have inside thereof electronic systems such as excitons with very sharp resonant structure from which strong radiation force is presumably obtainable under a laser at corresponding frequencies.
Examples of such semiconductors include I-VII compound semiconductors, II-VI compound semiconductors, III-V compound semiconductors, and silicon (Si). However, any semiconductor may be used. The I-VII compound semiconductor is, for example, a copper compound, such as CuCl, CuBr, or Cul (especially, copper halide). The II-VI compound semiconductor is, for example, a cadmium compound, such as CdS or CdSe, or a zinc compound, such as ZnO. The III-V compound semiconductor is, for example, a gallium compound, such as GaAs.
Preferred among these compounds are I-VII and II-VI compounds. I-VII compounds are thought to exhibit strong effects. Generally, in the semiconductor, a hole combines with an electron to produce an exciton, an example of the resonance energy level. The unique energy of an exciton is dependent on a quantum dot size. This effect is exploitable: by selecting a laser which has a resonant wavelength with quantum dots with a particular size, one can select only quantum dots of that size.
Examples of such semiconductors include I-VII compound semiconductors, II-VI compound semiconductors, III-V compound semiconductors, and silicon (Si). However, any semiconductor may be used. The I-VII compound semiconductor is, for example, a copper compound, such as CuCl, CuBr, or Cul (especially, copper halide). The II-VI compound semiconductor is, for example, a cadmium compound, such as CdS or CdSe, or a zinc compound, such as ZnO. The III-V compound semiconductor is, for example, a gallium compound, such as GaAs.
Preferred among these compounds are I-VII and II-VI compounds. I-VII compounds are thought to exhibit strong effects. Generally, in the semiconductor, a hole combines with an electron to produce an exciton, an example of the resonance energy level. The unique energy of an exciton is dependent on a quantum dot size. This effect is exploitable: by selecting a laser which has a resonant wavelength with quantum dots with a particular size, one can select only quantum dots of that size.
A group of researchers, which includes the inventors, made a theoretical proposal that quantum dots with different quantum mechanical uniqueness become manipulable with light by exploiting that (1) radiation force is much more intense (difference can reach three to four orders of magnitude) when light is resonant with the transition energy of an electron in nanosubstance than when it is out of resonance and (2) individual quantum dots (especially, semiconductor quantum dots) experience different radiation forces from light because of different quantum mechanical uniqueness of the dots.
A patent application has been already filed for theory (2) as Japanese Unexamined Patent Publication (Tokukai) 2003-200399 (published on Jul. 15, 2003). The idea behind theory (2) is indeed unique and never existed before. To realize it, the nanosubstance is ideally placed in a free space in a low temperature environment where resonance structure does not change.
Accordingly, in the JST apparatus, quantum dots are directly produced in an extremely low-temperature (2 K or lower), very high-thermal-conductivity environment (superfluid helium). The generated quantum dots are then exposed to light to enable manipulation of the quantum dots. Hence, resonance changes are prevented which would otherwise occur due to a rise in temperature of the quantum dot. Furthermore, the dot is surrounded by a superfluid state. The quantum dot can move hardly being affected by diffusion and meeting little resistance. Therefore, say the inventors, the apparatus provides a method which never existed before that enables manipulation of substance (e.g., control of nano particle size and arrangement) at the nanoscale level.
Accordingly, in the JST apparatus, quantum dots are directly produced in an extremely low-temperature (2 K or lower), very high-thermal-conductivity environment (superfluid helium). The generated quantum dots are then exposed to light to enable manipulation of the quantum dots. Hence, resonance changes are prevented which would otherwise occur due to a rise in temperature of the quantum dot. Furthermore, the dot is surrounded by a superfluid state. The quantum dot can move hardly being affected by diffusion and meeting little resistance. Therefore, say the inventors, the apparatus provides a method which never existed before that enables manipulation of substance (e.g., control of nano particle size and arrangement) at the nanoscale level.
No comments:
Post a Comment