WO2005040455A1

WO2005040455A1 - Nanowire and nanoarray composed of tusnsten, molybdenum and the oxide thereof which have a large area and the preparation and the application

Info

Publication number: WO2005040455A1
Application number: PCT/CN2004/000992
Authority: WO
Inventors: Ningsheng Xu; Juncong She; Shaozhi Deng; Jun Chen; Jun Zhou
Original assignee: Zhongshan University
Priority date: 2003-08-29
Filing date: 2004-08-27
Publication date: 2005-05-06
Also published as: CN1492076A; CN1283835C

Abstract

The present invention discloses a nanowire and nanoarray composed of tungsten, molybdenum and the oxide thereof which have a large area. The present invention also discloses the method for preparating the nanowire and nanoarray, as well as the application.The method according to the present invention is simple and direct, the demand of the equipment and the cost is low. At the saure time, the nanowire and nanoarray which have a large area prepared according to the invention have a excellent field electron emmision property and a extensive future of application, especially in the field of electron emmision FPD, cold cathode flaring tube, cold light illuminator etc.

Description

Large-area tungsten, molybdenum and its oxide nanowires and arrays, and preparation and application thereof

TECHNICAL FIELD

The present invention relates to a large area of nanowires of tungsten, molybdenum, and oxides thereof, an array thereof, a preparation method thereof, and applications thereof.

Prior art prior to the present invention

Tungsten and molybdenum have relatively low work functions in metals, good mechanical properties, especially high temperature performance, and low evaporation rate. They were first used as field emission materials. As field electron emission materials, they also have the most significant advantage of being able to output a large emission current density, which is very important for applications in field electron emission devices. Tungsten dioxide and molybdenum dioxide are both metal conductive oxides. They are also widely used as memory materials, catalysts and sensors. Tungsten trioxide and molybdenum trioxide are both n-type wide bandgap semiconductor materials. They are widely used in displays, sensors, solar cells, and as catalysts.

Prior to our invention, there were only reports on the electrochemical synthesis of molybdenum nanowires and the use of inorganic substances as precursors to synthesize tungsten nanowires. However, their preparation method has high cost, low yield, complicated process, and cannot prepare large-area nanowire films, especially the ordered nanowire arrays of the above materials. These greatly restrict their application.

Object of the invention

An object of the present invention is to provide a nanowire and an array of tungsten, molybdenum, and oxides thereof prepared in a large area. Another object of the present invention is to provide a method for preparing a nanowire of tungsten, molybdenum simple substance and its oxide, and an array thereof.

Another object of the present invention is to provide application of a nanowire of tungsten, molybdenum, and its oxide, and an array thereof. Technical solution adopted by the present invention

In our invention, we first prepare a large area of nanowires or arrays of tungsten dioxide and molybdenum dioxide, and then obtain tungsten and molybdenum simple nanowires or arrays by reduction, respectively, and use the oxidation method Nanowires or arrays of tungsten trioxide and molybdenum trioxide are obtained.

In order to prepare nanowires or arrays of tungsten, molybdenum and their oxides, the present invention adopts the following process steps: 1. Preparation of nanowires or arrays of tungsten dioxide and molybdenum dioxide:

1 Clean the substrate to remove impurities from the substrate.

2 Place the tungsten (molybdenum) source and the substrate in a vacuum heating device. The substrate is placed directly above the tungsten (molybdenum) source or on the same plane (the distance between them is adjustable). Evacuate, then

1

Confirm this After that, an inert gas is passed in as a protective gas, and a constant current is maintained.

3 Heat the tungsten (molybdenum) source and substrate separately. When preparing tungsten dioxide, the tungsten source is heated to 1000 ~ 2000 ° C, and the substrate is heated to 900 ~ 1400 ° C _{; when} preparing molybdenum dioxide, the molybdenum source is heated to 1000 ~ 2000 ° C, and the substrate is heated to 80 (10O ° C. Holding time is 1 minute to 120 minutes.

4 Reduce the temperature in an inert gas atmosphere until it cools to room temperature.

In the above process, thorium uses tungsten powder, tungsten flakes, or tungsten boats as the tungsten source (molybdenum powder, molybdenum flakes, or molybdenum boats as the molybdenum source). The substrates used are single crystal silicon wafers, silicon pinpoint arrays, metal wafers, glass, ceramics, and other high-temperature resistant materials, and the geometry is not limited.

2. Preparation of nanowires or arrays of elemental tungsten and molybdenum:

1 Put a sample of tungsten dioxide (molybdenum dioxide) nanowires or arrays into a vacuum heating device, pre-evacuate the vacuum heating device, and then pass in hydrogen as a reducing gas, and maintain a constant current.

2 Warm up the sample to 5O0 ~ 1000 ° C and keep it for 3 to 15 hours.

3 Reduce the temperature in a hydrogen atmosphere until it cools to room temperature.

3. Preparation of Nanowires or Arrays of Tungsten Trioxide and Molybdenum Trioxide-1 Place tungsten dioxide (Molybdenum Dioxide) nanowires or arrays into a vacuum heating device, pre-evacuate the vacuum heating device, and then pass argon A mixture of gas and oxygen, and maintain a constant current.

2 During the preparation of tungsten trioxide, the temperature of the sample is raised to 500-1000 ° C, and the temperature is maintained for 2-60 minutes; when preparing the molybdenum trioxide, the temperature of the sample is raised to 300-600 ° C, and the temperature is maintained for 2-60 minutes.

3 Reduce the temperature in a mixed gas atmosphere of argon and oxygen until it cools to room temperature.

The invention provides a method for preparing nanowires of tungsten, molybdenum, and their oxides, and arrays thereof, by using large flours. The preparation method is simple and straightforward, does not require high equipment, and has low cost. At the same time, it has been proved through experiments that they have excellent field electron emission properties and have great application prospects as cold cathode electron sources, especially in field electron emission flat panel displays, cold cathode light emitting tubes, and cold light sources.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la is the XRD spectrum of the MoO2 nanowire film.

Figure lb is a SEM photograph of a MoO nanowire film.

Figure lc is a high-resolution TEM and corresponding electron diffraction pattern of a Mo 2 nanowire film.

Figure _2a is an XRD spectrum of a simple molybdenum nanowire film.

Figure _2b is a morphology of a simple molybdenum nanowire film. Fig. _2c is a high-resolution TEM and corresponding electron diffraction pattern of a simple molybdenum nanowire film. Fig. 3a is an XRD spectrum of a molybdenum trioxide nanowire film.

Figure 3b is a morphology of a MoO3 nanowire film.

Figure 3c is a high-resolution TEM and corresponding electron diffraction pattern of a MoO3 nanowire film. Figure 4a is the XRD spectrum of the tungsten dioxide nanowire film.

Figure 4b is a SEM photograph of a tungsten dioxide nanowire film.

Figure 4c is a high-resolution TEM and corresponding electron diffraction pattern of a tungsten dioxide nanowire film. Figure 5a is the IXRD spectrum of a simple tungsten nanowire film.

Figure 5b is an SEM image of a simple tungsten nanowire film.

Figure 5c is a high-resolution TEM and corresponding electron diffraction pattern of a simple tungsten nanowire film. Figure 6a is an XRD spectrum of a tungsten trioxide nanowire film.

Figure 6b is a SEM image of a tungsten trioxide nanowire film.

Figure 6c is a high-resolution TEM and corresponding electron diffraction pattern of a tungsten trioxide nanowire film. Figure 7a is a field emission image of a molybdenum dioxide nanowire film.

Figure 8a is a field emission image of a simple molybdenum nanowire film.

Figure 9a is a field emission image of a molybdenum trioxide nanowire film.

Figure 7b shows the field emission J-E and F-N characteristics of the MoO2 nanowire film. Figure 8b shows the field emission J-E and F-N characteristics of the elemental molybdenum nanowire film. Figure 9b shows the field emission J-E and F-N characteristics of the MoO3 nanowire film. Figure 7c is the field emission stability curve of the MoO2 nanowire film.

Figure 8c is the field emission stability curve of the elemental molybdenum nanowire film.

Fig. 9c is the field emission stability curve of the molybdenum trioxide nanowire film.

Fig. 10 is a graph of field emission J-E and F-N characteristics of a tungsten dioxide nanowire film. Figure 11a is a field emission image of a tungsten dioxide nanowire film. '

Figure lib is a graph of field emission J-E and F-N characteristics of elemental tungsten nanowire films. Fig. 11c is a graph of field emission stability of a thin film of tungsten dioxide nanowires.

Figure 12a is a field emission image of a tungsten trioxide nanowire film.

Figure 12b is a graph of field emission JE and FN characteristics of a tungsten trioxide nanowire film. FIG. 12c is a field emission stability graph of a tungsten trioxide nanowire film. FIG. 13a shows a case where a molybdenum oxide nanowire film is applied to a cold cathode light emitting tube, and the light emitting tube is working. FIG. 13b is an IV characteristic curve of a molybdenum oxide nanowire film applied to a cold cathode light-emitting tube when the anode voltage is 7 kV, and the anode voltage is 7 kV.

Examples

1. Prepare a nanowire film of molybdenum dioxide.

1 Using a (100) plane single crystal silicon wafer as the substrate, first ultrasonically clean it in acetone for 5 minutes, and then ultrasonically clean it in absolute ethanol for 5 minutes.

2 Select a molybdenum boat as the molybdenum source, place the molybdenum boat in a vacuum heating device (c |) 350x400mm), and place the silicon wafer directly above the source of the molybdenum boat with a distance of 1mm between them. Pre-evacuate the vacuum heating device to 1.0xlO- ² Torr, and then pass in argon as a protective gas with a gas flow rate of 200 standard cubic centimeters per second and maintain a constant current.

3 Increase the temperature of the molybdenum boat at a rate of 100 ° C / minute, and finally raise the temperature to 1200 ° C and keep it for 30 minutes.

4 Reduce the temperature in an argon atmosphere until it cools to room temperature.

2. Prepare a nanowire film of elemental molybdenum.

1 Place a sample of Mo 2 nanowire film in a vacuum heating device (φ350 × 400ηιπι). Pre-evacuate the vacuum heating device to 1.0 × l (T ² Torr), and then pass in high-purity hydrogen with a hydrogen gas flow rate of 200 standard cubic centimeters per second.

2 Warm up the sample at a rate of 100 ° C / minute, and finally raise the temperature to 800 ° C and keep it for 10 hours.

3. Preparation of nanowire films of molybdenum trioxide.

1 Place a sample of Mo 2 nanowire film in a vacuum heating device (φ350 × 400πιη). The vacuum heating device was pre-evacuated to 1.0 × 10 · ² ΤΟΓΓ, and then a mixed gas of argon and oxygen was introduced, and the gas flow rates were 100 standard cubic centimeters per second.

2 Increase the temperature of the sample at a rate of 100 ° C / minute, and finally increase the temperature to 400 ° C and hold for 30 minutes.

4. Prepare a nanowire film of tungsten dioxide.

1 Using a (100) plane single crystal cassia wafer as the substrate, first ultrasonically clean it in acetone for 5 minutes, and then ultrasonically clean it in absolute ethanol for 5 minutes. 2 Select a tungsten boat as the tungsten source, place the tungsten boat in a vacuum heating device ((|) 350><400mm), and place the silicon wafer on the tungsten boat. Pre-evacuate the vacuum heating device to 1.0xl 0_ ² Torr, and then introduce argon as a protective gas with a gas flow rate of 200 standard cubic centimeters per second and maintain a constant current.

3 Increase the temperature of the tungsten boat to 100 ° C per minute, and finally raise the temperature to 1200 ° C and keep it for 30 minutes. 4 Reduce the temperature in an argon atmosphere until it cools to room temperature.

5. Preparation of nanowire thin film of elemental tungsten.

1 Place a sample of tungsten dioxide nanowire film in a vacuum heating device ((() 350x400mm). Pre-evacuate the vacuum heating device to 1.0xlO_ ² Torr, and then pass in high-purity hydrogen, and the hydrogen gas flow rate is 200 standard cubic centimeters. Every second.

6. Prepare a nanowire film of tungsten trioxide.

1 Place a sample of tungsten dioxide nanowire film in a vacuum heating device (φ350 × 400ιηη). The vacuum heating device was pre-evacuated to 1.0xl O- ² Torr, and then a mixed gas of argon and oxygen was passed in, and the gas flow rates were 100 standard cubic centimeters per second.

2 Raise the temperature of the sample at 100 ° C / minute, and finally increase the temperature to 800. C and incubate for 30 minutes.

For the nanowire thin films of tungsten, molybdenum and their oxides prepared in the above examples, we used X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy spectroscopy (EDS), and Raman spectroscopy (RAMAN), etc. for observation and analysis. Their field electron emission characteristics have also been studied and applied to cold cathode light emitting tubes. The present invention is further described below with reference to the accompanying drawings and the attached table.

Figure 1 (a) is the XRD spectrum of the molybdenum dioxide sodium noodle film. By analyzing the spectrum, we can know that the nanowire film is a molybdenum dioxide nanowire with a monoclinic structure. From the SEM photos of typical samples (Figure 1 (b)), it can be seen that the nanowires are grown perpendicular to the substrate. The diameter of the nanowires is about 150 nanometers and the length is about 3 micrometers. Through high-resolution TEM (Figure 1 (c)) and corresponding electron diffraction (inset in the upper right corner of Figure 1 (c)) analysis, we can also confirm that the nanowire has a crystal structure. Figure 2 (a) is the XRD spectrum of the elemental molybdenum nanowire film. By analyzing the spectrum, we can confirm that the nanowire film is a very pure molybdenum nanowire with a body-centered cubic structure. The morphology of molybdenum nanowires is similar to that of molybdenum dioxide nanowires. The diameter is slightly smaller, about 100 nm [Fig. 2 (b)]. By high-resolution TEM [Fig. 2 (c)] and the corresponding electron diffraction (inset in the upper right corner of Fig. 2 (c)) analysis, we can confirm that the molybdenum nanowires also have a crystal structure. Figure 3 (a) is the XRD spectrum of the trioxide nanowire film. Through analysis, we can confirm that the nanowire film is a very pure molybdenum trioxide nanowire with an orthogonal structure. Molybdenum trioxide nanowires are also grown on a vertical substrate, and their morphology is basically similar to that of molybdenum dioxide nanowires, with a diameter of about 200 nm [Fig. 3 (b)]. By high-resolution TEM [Figure 3 (c)] and corresponding electron diffraction analysis (inset in the upper right corner of Figure 3 (c)), we can know that the nanowire has a crystal structure. Figure 4 (a) is the XRD spectrum of the tungsten dioxide nanowire film. By analyzing the spectrum, we can know that the nanowire film is a tungsten dioxide nanowire with a monoclinic structure. From the SEM photos of typical samples (Figure 4 (b)), it can be seen that the diameter of the nanowires is about 100 nanometers and the length is about 2 micrometers. Through high-resolution TEM (Figure 4 (c)) and corresponding electron diffraction (inset in the upper right corner of Figure 1 (c)) analysis, we can also confirm that the nanowire has a crystal structure, but there are many defects. Figure 5 (a) is the XRD spectrum of the elemental tungsten nanowire film. By analyzing the spectrum, we can confirm that the nanowire film is a very pure tungsten nanowire with a body-centered cubic structure. FIG. 5 (b) is an SEM image of tungsten nanowires. Through the analysis of ytterbium-resolved TEM [Fig. 5 (c)] and the corresponding electron diffraction (inset in the upper right corner of Fig. 2 (c)), we can confirm that the noodles in tungsten also have a crystal structure. Figure 6 (a) is the XRD spectrum of the tungsten trioxide nanowire film. Through analysis, we can confirm that the nanowire thin film is a very pure tungsten trioxide nanowire with a monoclinic structure. FIG. 6 (b) is a SEM image of a tungsten trioxide nanowire film. From high-resolution TEM [Figure 6 (c)] and the corresponding electron line analysis (inset in the upper right corner of Figure 6 (c)), we can know that the nanowire has a single crystal structure.

Figures 7 (a), 8 (a), and 9 (a) are the field emission images of molybdenum dioxide, elemental molybdenum, and molybdenum trioxide nanowire thin films. We can find that these nanowire thin films have very uniform field emission and emit light. The morphology of the area is basically the same as the morphology of the film (insets in the upper left corner of Figures 7 (a), 8 (a), and 9 (a)). Figures 7 (b), 8 (b), and 9Cb) and the upper left illustration are the field emission JE and FN characteristic curves of molybdenum dioxide, elemental molybdenum, and molybdenum trioxide nanowire films, respectively. From their JE characteristic diagram, we can find molybdenum dioxide, open field and threshold field elemental molybdenum and molybdenum trioxide nanowire film (turn-on field threshold field are defined required to produce a 10 μ a / cm ² and lOmA / cm ² current density Electric field) are 2MV / m, 2.2MV / m, 3.5MV / m and 4.75MV / m, 6.24MV / m and 7.65MV / m. Their threshold electric field can be comparable to that of carbon nanotubes. Their FN curves are linear, indicating that their field emission meets the classical field emission theory. Figures Ί (c), 8 (c) and 9 (c) are dioxide The field emission stability curves of molybdenum, elemental molybdenum, and molybdenum trioxide nanowire films have only fluctuations, respectively.

± 2.5%, ± 5%, and ± 10%. Figure 11 (a) and Figure 12 (a) are the field emission images of tungsten dioxide and tungsten trioxide nanowire films, respectively. We can find that the nanowire films have very uniform field emission, and the morphology of the light-emitting area and the film morphology ( Figure 11 (a) and Figure 12 (a)) are basically the same. Figure 10, Figure 11 (b) and Figure 12 (b), and the upper left illustration are the field emission JE and FN characteristic curves of tungsten dioxide, elemental tungsten, and tungsten trioxide nanowire films, respectively. From their JE characteristic diagrams We can find the opening electric fields of tungsten dioxide, elemental tungsten and tungsten trioxide nanowire films at 5.2MV / m, 8MV / m and 2.45MV / m. Figure 11 (c) and Figure 12 (c) are the field emission stability curves of tungsten dioxide and tungsten trioxide nanowire films, respectively, and their fluctuations are only ± 4% and ± 2%, respectively. This shows that they have excellent field emission stability, which is of great significance to them in practical applications. Table 1 shows the field emission characteristics of various nanowire films: (see Table 1)

Table 1

It can be seen from the table that the opening electric field and threshold electric field of the nanowire thin films we prepared are higher than the best reported carbon nanotubes and silicon carbide nanowires, but they can be comparable or better than other materials. Figure 13 shows the application of molybdenum dioxide nanowire thin film to a cold cathode light emitting tube. Fig. 13 (a) shows the situation that the arc tube is working. It can be seen that the arc tube emits light very uniformly. 13 (b) shows the IV characteristic curve when the anode voltage is 7 kV. From the curve, we can see that the arc tube At below 500 volts there is an emission current.

From the above analysis results, we can conclude that we have prepared nanowire thin films of tungsten, molybdenum and their oxides. At the same time, the above nanowire films have very good field emission characteristics. Their opening electric fields and threshold electric fields are low, and their stability is relatively good. This shows that they can fully meet the requirements for field electron emission display materials and can be applied to field emission Flat panel display, cold cathode light emitting tube, cold light source, etc.

Claims

Rights request

1. A large-area tungsten, molybdenum, and oxide nanowires and arrays thereof, characterized in that: the tungsten, molybdenum, and oxide nanowires and arrays are grown on a large-area substrate.

2. The large-area tungsten, molybdenum, and oxide nanowires and arrays thereof according to claim 1, wherein the substrate is a single crystal silicon wafer, a metal wafer, glass, ceramic, or other high-temperature resistant Materials are not limited in geometry, and nanowires are grown on the substrate to form nanowire films and arrays.

3. The large-area tungsten, molybdenum and its oxide nanowires and arrays according to claim 1, wherein: the substrate is a silicon pinpoint array, and the nanowires of tungsten, molybdenum and its oxides are grown. An array of nanowires is formed on the silicon tip.

4. The method for preparing tungsten dioxide and molybdenum dioxide nanowires and their arrays in the oxide according to any one of claims 1, 2 or 3, is performed according to the following steps-a) cleaning the substrate, removing the substrate Impurities on

b) The tungsten (molybdenum) source and substrate are placed in a vacuum heating device, the device is pre-evacuated, and then an inert gas is passed as a protective gas, and a constant current is maintained;

c) Heating the tungsten (molybdenum) source and substrate separately. When preparing tungsten dioxide, the tungsten source is heated to

1000 ~ 2000 ° C, the substrate is heated to 900 ~ 1400 ° C; when preparing molybdenum dioxide, the molybdenum source is heated to 1000 ~ 2000 ° C, and the substrate is heated to 800 ~ 1100 ° C. The holding time is from 1 minute to 120 minutes. d) The temperature is lowered in an inert gas atmosphere until it is cooled to room temperature.

5. The method for preparing nanowires and arrays of tungsten dioxide and molybdenum dioxide according to claim 4, wherein: the tungsten source is tungsten powder, tungsten sheet or tungsten boat, and the molybdenum source is molybdenum powder , Molybdenum flakes or Molybdenum boat.

6. The method for preparing elemental tungsten and molybdenum nanowires and their arrays according to claim 1, 2 or 3, is performed according to the following steps-a) growing tungsten dioxide (or molybdenum dioxide) nanowires and The substrate of the array is placed in a vacuum heating device. The vacuum heating device is pre-evacuated, and then hydrogen is passed as a reducing gas, and a constant current is maintained.

b) The substrate is warmed to 500 ~ 1100 ° C and held for 3 to 15 hours.

c) The temperature is lowered in a hydrogen atmosphere until it is cooled to room temperature.

7. The method for preparing the nanowires of tungsten trioxide and aluminum trioxide and the arrays thereof in the oxide according to claim 1, 2 or 3, is performed according to the following steps: a) Placing the substrate with tungsten dioxide (molybdenum dioxide) nanowires and their arrays in a vacuum heating device, pre-evacuating the vacuum heating device, and then passing in a mixed gas of argon and oxygen, and maintaining Constant current

b) The substrate is heated to 500-1000 ° C during the preparation of tungsten trioxide and held for 2-60 minutes; the preparation of molybdenum trioxide is heated to 300-600 ° C for the substrate and held for 2-60 minutes;

c) The temperature is lowered in a mixed gas atmosphere of argon and oxygen until cooled to room temperature;

The nanowires and arrays of tungsten, molybdenum, and their oxides as claimed in claim 1, 2 or 3, for use as a field cathode cold cathode material.

The application according to claim 8, including the application of a cold cathode light emitting tube.