Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/18—Processes for applying liquids or other fluent materials performed by dipping
  • B05D1/20—Processes for applying liquids or other fluent materials performed by dipping substances to be applied floating on a fluid
  • B05D1/202—Langmuir Blodgett films (LB films)
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y15/00—Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H01L29/76—Unipolar devices, e.g. field effect transistors
  • H01L29/7613—Single electron transistors; Coulomb blockade devices

Definitions

• This invention relates to thin films and structures containing them.
• Ultra small CdS particles were formed by exposing deposited cadmium arachidate Langmuir-Blodgett bilayers to atmosphere of H 2 S. STM images of the resultant films reveals the presence of particles with sizes of about 40 - 60 A. Also voltage-current characteristics were measured by STM on the structure "tip-tunnelling gas - CdS particle - tunnelling gap - graphite substrate". Steps in voltage- current characteristics indicate the appearance of single electron process (Coulomb blockade) at room temperature.
• the process is called monoelectronic because it is possible to distinguish current steps in V/I curve due to unitary increase in the number of electrons in the granule. Step-like behaviour of current was observed in several works at low temperature 1 5
• the value of the temperature is very important for observing such phenomena and the following equation must hold true to allow the monitoring of steps in V/I characteristics 6 e 2 /2C > kT (2)
• the temperature at which monoelectron phenomena can be observed is limited by the capacity of the granule and therefore by its dimensions.
• Rough estimations assuming spherical shape, give 90 A as limiting value of the granule radius: for bigger radii Coulomb blockade cannot take place at room temperature.
• the aim of this work was to investigate by STM a bilayer of cadmium arachidate after exposing it to H 2 S, to find granules of nanometer sizes and to measure with the STM tip local V/I characteristics on "graphite - tunnelling gap - CdS particle - tunnelling gap - tip" structure.
• a bilayer of cadmium arachidate was transferred onto the graphite surface according to standard procedure 10 .
• the sample was placed into a chamber, containing H 2 S, for 30 minutes.
• STM measurements were performed using a device (MM- MDT) , allowing also to measure local V/I characteristics.
• MM- MDT a device
• STM tip was placed over the desired point (CdS particle, identified on previously obtained image) in constant current mode. When the tip was above this point, feedback was switched off and the tip - substrate voltage was swept from -0.5 to 0.5 V.
• the configuration for measurements of V/I characteristics is presented in Figure 1.
• STM image of cadmium arachidate bilayer after exposure to H 2 S atmosphere is presented in Figure 2.
• CdS particles are well distinguishable in the picture. Sizes and shapes of the particles are not equal one another, but, in general, sizes are in the range 40 - 60 A (nevertheless it is possible to find also particles with sizes outside the range) .
• the surface of the particles is rather flat. This fact becomes understandable if we suppose that CdS particles are small monocrystals . The hypothesis is also in agreement with light absorption data, showing the existence of the original CdS band structure in the particles after the reaction with H 2 S 8 , and with electron diffraction data, demonstrating that the lattice spacing value of the particles is the same as in bulk crystal'.
• the surface of LB film after the reaction becomes rough due to the disturbance caused by the particles formation process. This fact is in good agreement with the decrease of the film spacing (bilayer thickness) 5 .
• the decrease implies the declination of hydrocarbon chains from the normal direction to the film plane and so the increase of the area per molecule in the film plane. As a result of it, the total area of the film should increase, while the physical area remains the same (geometrical areas of the substrate) .
• the mentioned contradiction seems to be responsible for the increased roughness of the LB film.
• the value of the particle sizes is less than the one measured by electron diffraction method. The difference is likely due to the fact that in 9 the initial film of cadmium arachidate was 10 - 15 bilayers (growth of CdS crystal can involve atoms also from different film planes) , while here we have only one bilayer.
• Distribution of the particles inside the film is not regular. Some areas contain several particles but there are regions were no particles were observed.
• V/I characteristics of the system "graphite substrate - tunnelling gap - CdS particle - tunnelling gap - STM tip" is presented in Figure 3.
• the characteristic was obtained by placing the tip above the CdS particle, the position of which was determined from previously acquired image. Despite some noise, steps in V/I characteristics are well distinguishable. Steps in the characteristics are equidistant and correspond to the value of voltage of about 0.2 V. Taking into account that the particles have in-plane dimensions of 40 - 60 A and their surface is flat, we can conclude, that the most probable shape of them is disk-like one and the thickness of the disk is a couple of lattice unit cells of CdS.
• nanometer scale CdS particles were formed by exposing Cadmium Arachidate LB film to H 2 S atmosphere. There sizes measured by STM were found to be small enough to allow monoelectron phenomena. These phenomena were observed at room temperature. Rather big noise level points out that measurements were performed near boundary conditions of the validity of equation (2) . Analysis of all experimental data allows to make conclusion about the disk-like shape of the particles as the most probable one. Thus, such treatment of the cadmium arachidate films results in the creation of a new material, where nanometer scale monocrystal semiconductor particles are embedded into insulating LB matrix. This material displays new kinds of phenomena, particularly, but probably not only, - monoelectron ones, which allow to study fundamental properties of systems with decreased number of dimensions and from technological point of view can permit the construction of new types of devices, such as monoelectron transistors.
• Ultra small CdS clusters have been directly synthesised on the very tip of a sharp metal stylus. Voltage-current characteristics measured with such stylus, brought in the proximity of another electrode, display Coulomb blockade and Coulomb staircase pointing out junction capacitances in the 10' 19 F Range.
• the measured characteristics display irrespective the place were the tip was landed, trends like those reported in Figure 5. Such kinds of characteristics have been obtained in about 60% of the prepared samples. These kinds of features are a typical indication of the appearance of single electron phenomena and have been recently reported and discussed both for cryogenic 5,9 and room temperature 9 measurements on different kinds of quantum dots.
• FIG 1 A scheme of the experimental setup for measuring V/I characteristics with STM tip.
• Figure 2 STM image of cadmium arachidate LB film after the reaction with H 2 S. The image was acquired with Pt/Ir (90% - 10%) tip m constant current mode; tunnelling voltage was 2 V, tunnelling current was 0.7 nA. Image sizes are 576 x 576 A 2 . flat regions represent CdS particles.
• Figure 3 Voltage current characteristics of the system

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• 1996
  • 1996-01-15 WO PCT/IB1996/000106 patent/WO1996021952A1/en not_active Application Discontinuation
  • 1996-01-15 EP EP96901090A patent/EP0750795A1/de not_active Withdrawn
  • 1996-01-15 AU AU44951/96A patent/AU4495196A/en not_active Abandoned

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