Abstract:
The present invention provides a system and a method of detecting a sublimation point, preferably applied to organic molecules. The system of detecting a sublimation point comprises: a heater, a capillary device, a vacuum pump, an ultraviolet light source, a photography device, a digital vacuum meter and a needle valve. The system of detecting a sublimation point is suitable for detecting the sublimation point of an organic light emitting molecule such as tris(8-hydroxyquinolinato) aluminum (Alq 3 ) and tris(phenylpyridine) iridium (Ir(ppy) 3 ). The needle valve can be used for controlling air pressure to measure the sublimation point under different pressures. Advantageously, the required quantity of organic molecules can be below 1 mg, thus not only saving the organic molecules, but also detecting the sublimation point without contaminating apparatuses.

Description:
FIELD OF THE INVENTION 
       [0001]    This application claims priority from Taiwan Patent Application No. 100138554, filed on Oct. 24, 2011, in Taiwan Intellectual Property Office, the contents of which are hereby incorporated by reference in their entirety for all purposes. 
       BACKGROUND OF THE INVENTION 
       [0002]    In recent years, science and technology advance, so that the quality requirements for semiconductors and optoelectronic materials become increasingly higher, and the sublimation method and method for detecting sublimation points of semiconductors and optoelectronic materials becomes increasingly more important than ever. At present, existing methods for measuring sublimation points require a relative large quantity of samples. For example, a thermogravimetric analyzer (TGA) is an instrument used for detecting and measuring a sample material at a specific temperature. The principle of the thermogravimetric analyzer (TGA) primarily puts a sample into a furnace capable of increasing, decreasing or maintaining temperature through programs, and a fixed ambient gas (such as nitrogen or oxygen) is passed through the furnace, such that when the temperature rises to an evaporation temperature, a decomposition temperature or an oxidation temperature of a certain material composite, the sample will be evaporated, decomposed and oxidized to result in a loss of weight, and the change of weight of the sample varied with temperature or time is recorded, so as to determine the decomposition temperature, thermal stability, composition proportion, sample purity, water content, reduction temperature, sublimation temperature and anti-oxidation property of the material can be determined. Therefore, two major elements in TGA are a temperature control element and a weight measuring element. With a combination of the two, the change of weight at different temperatures is recorded. However, the required quantity of the sample is approximately equal to 3 mg. Since the quantity of the sample is very small, a larger waste of the sample will result. In addition, the sample may contaminate the instrument, thus causing tremendous inconvenience to users. 
         [0003]    Wherein, the method of detecting a sublimation point of an organic molecule gains increasingly more attention, and the organic molecule includes an organic light emitting diode (OLED) material such as Alq 3  and Ir(ppy) 3 . Particularly, The method and system only requiring a trace amount of sample for detecting the sublimation point not only reduces the waste of the sample, but also lower the cost. 
         [0004]    However, conventional methods and systems for detecting a sublimation point of an organic molecule sublimation point as disclosed in R.O.C. Pat. No. TWI242463 provides both vertical and horizontal high-performance vacuum sublimation apparatus and method, which are only applicable for mass producing high-purity chemicals. R.O.C. Pat. Application No. TW200934576 discloses a quantitative sublimation and purification apparatus that fills a raw material and collects a product precisely, and different models of sublimation devices can be used to efficiently purify a special chemical by sublimation. U.S. Pat. No. 4,407,488 discloses an apparatus to solidify and deposit a gas, and then heat to sublimate the gas. The apparatus is primarily used for partitioning and purifying sample materials in different containers to achieve the separation and purification effects. 
         [0005]    Obviously, the application of present existing sublimation apparatuses and methods thereof mainly adopt the separation and purification methods, but there is no disclosure of the method and apparatus for detecting the sublimation point of the organic molecule by a trace amount of the sample. 
       SUMMARY OF THE INVENTION 
       [0006]    It is a primary objective of the present invention to provide a system and method of detecting a sublimation point, particularly the system and method of detecting a sublimation point of a trace amount of organic molecules at different vacuum levels. 
         [0007]    Another objective of the present invention is to detect a sublimation point and a heat of sublimation of an organic molecule at different vacuum levels quickly without contaminating apparatuses. 
         [0008]    To achieve the aforementioned objectives, the present invention provides a system of detecting a sublimation point comprising: a heater, for heating an organic molecule, and the heater including a temperature display for displaying a temperature; a capillary device, installed on the heater, and including a plurality of capillaries, for carrying the organic molecule; a vacuum pump, coupled to the capillary device, for pumping air from the capillary device to lower an air pressure in the capillary device; an ultraviolet light source, for irradiating an ultraviolet light onto the capillary device, such that when the organic molecule is sublimed, a color change of the plurality of capillaries occurred after irradiating the ultraviolet light indicates that the organic molecule has reached a sublimation point. 
         [0009]    Preferably, the system of detecting a sublimation point in accordance with the present invention further comprises: a digital vacuum meter, coupled to the vacuum pump and the capillary device, for displaying a vacuum level inside the capillary device; a needle valve, coupled to the digital vacuum meter, and the capillary device and the vacuum pump being used for regulating the air pressure in the capillary device; and a photography device, for recording a color change and a corresponding temperature of the plurality of capillaries during a heating process. 
         [0010]    Preferably, the capillary device further includes a rubber cap and a capillary frame, wherein the rubber cap has a plurality of holes formed at positions corresponding to the plurality of capillaries respectively, and end opposite to the plurality of holes is coupled to the vacuum pump, and the rubber cap and the capillary frame are jointly provided for fixing the plurality of capillaries. 
         [0011]    Preferably, the organic molecule includes an organic light emitting molecule. 
         [0012]    Preferably, the organic light emitting molecule includes tris(8-hydroxyquinolinato) aluminum (Alq 3 ) or tris(phenylpyridine) iridium (Ir(ppy) 3 ). 
         [0013]    Preferably, the system of detecting a sublimation point in accordance with the present invention can detect the heat of sublimation (ΔHsub) and the heat of melting (ΔHmelt) of the organic molecule. 
         [0014]    The present invention further provides a method of detecting a sublimation point, and the method comprises the steps of: filling an organic molecule into a capillary of a capillary device; putting the capillary filled with the organic molecule on a heater; turning on a vacuum pump to pump air out of the capillary device; turning on the heater to heat the organic molecule; and irradiating an ultraviolet light source onto the capillary device, thereby a color change of the capillary indicates that the organic molecule has reached a sublimation point. 
         [0015]    Preferably, the heater has a heating speed falling within a range of 5˜15° C. per minute. 
         [0016]    Preferably, a needle valve is used for regulating the pressure within a range of 20 mmHg˜760 mmHg 
         [0017]    In summation, the system and method of detecting a sublimation point in accordance with the present invention have one or more of the following advantages: 
         [0018]    (1) The quantity of the organic molecule filled into the capillary can be less than 1 mg, not only saving the organic molecules, but also avoid contaminating the system of detecting a sublimation point in accordance with the present invention. 
         [0019]    (2) The present invention uses less amount of sample to detect the sublimation point and the heat of sublimation (ΔHsub) in a shorter time, so that the invention can lower the costs. 
         [0020]    (3) The present invention compares the difference of the sublimation points of the organic molecule at different vacuum levels, and such data become very important for evaporation devices. 
         [0021]    The contents disclosed in the aforementioned prior art are provided for readers to understand the technical background of the present invention, but the contents do not obstruct this invention, and the contents are prior arts familiar to persons ordinarily skilled in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic view of a system of detecting a sublimation point of the present invention; 
           [0023]      FIG. 2  is a flow chart of a method of detecting a sublimation point of the present invention; 
           [0024]      FIG. 3A  shows Alq3 attached to the capillary wall of the optical microscope diagram; 
           [0025]      FIG. 3B  is a weight percentage versus temperature loss graph of Alq 3  measured by a thermogravimetric analyzer (TGA); 
           [0026]      FIG. 4  shows the results of ln P versus 1/T of a system of detecting a sublimation point of Alq 3  in accordance with the present invention; and 
           [0027]      FIG. 5  is a curve showing the heat of sublimation (ΔHsub) and the heat of melting (ΔHmelt) of Alq 3  by using a differential scanning calorimeter (DSC). 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    The technical characteristics of the present invention will become apparent with the detailed description of the preferred embodiments accompanied with the illustration of related drawings as follows. It is noteworthy to point out that same numerals are used for representing respective elements for the description of the preferred embodiments and the illustration of the drawings. 
         [0029]    With reference to  FIG. 1  for a schematic view of a system of detecting a sublimation point  100  in accordance with the present invention, the system of detecting a sublimation point  100  comprises a heater  101 , a capillary device  103 , a vacuum pump  104  and an ultraviolet light source  105 . 
         [0030]    The heater  101  for heating the organic molecule whose sublimation point is to be detected, and the heater  101  comprises a temperature display device  102  for displaying the temperature of a heating process. When the organic molecule is sublimed, the temperature display device  102  informs us about the temperature. The capillary device  103  is installed on the heater  101  and includes a plurality of capillaries for carrying the organic molecule to be heated. The vacuum pump  104  is coupled to the capillary device  103  through a Teflon tube for pumping air out of the capillary device  103  to reduce the air pressure in the capillary device  103 . The ultraviolet light source  105  is provided for irradiate an ultraviolet light to the capillary device  103 . When the organic molecule is sublimed, the ultraviolet light source  105  irradiates to discover any color change of the capillary, and the color change indicates that the organic molecule has reached a sublimation point. 
         [0031]    In addition, the system of the present invention selectively adds a photography device  106 , a digital vacuum meter  107  and a needle valve  108 . The photography device  106  can record the color change of the capillary during the heating process and the corresponding temperature displayed by the temperature display device  102 . Even if a user is not observing the color change at site, the user still can know that the organic molecule has reached the sublimation point. The digital vacuum meter  107  can be installed between the capillary device  103  and the vacuum pump  104  and coupled by the Teflon pipe for displaying the vacuum level. The needle valve  108  can be installed between the capillary device  103 , the digital vacuum meter  107  and the vacuum pump  104  by the Teflon pipe for regulating the air pressure in the capillary device  103  after the vacuum pump  104  pumps the air out of the capillary device  103 . 
         [0032]    The weight of the organic molecules used for detection by the system of the present invention can be less than 1 mg, or a less amount of sample can be used for detecting the sublimation point to avoid wasting the sample or contaminating the system  100  of the present invention. 
         [0033]    The organic molecule includes an organic light emitting molecule, and the organic light emitting molecule can be tris(8-hydroxyquinolinato) aluminum (Alq 3 ) or tris(phenylpyridine) iridium (Ir(ppy) 3 ), and whose light emitting property is used for observing the color change when the sublimation point is reached. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0034]    In addition, the capillary device  103  further includes a rubber cap  1031  and a capillary frame  1032 , and an end of the rubber cap  1031  has a plurality of holes formed thereon and corresponding to the plurality of capillaries respectively, and the other end of the plurality of holes is coupled to the vacuum pump  104 , and both ends of the rubber cap  1031  are interconnected, such that air can be pumped from the capillary by the vacuum pump  104 . The capillary frame  1032  and the rubber cap  1031  are jointly provided for fixing the plurality of capillaries. 
         [0035]    With reference to  FIG. 2  for a flow chart of a method of detecting a sublimation point in accordance with the present invention, the method comprises the following steps: 
         [0036]    S 21 : Fill organic molecules into a capillary of a capillary device. 
         [0037]    S 22 : Put the capillary device filled with the organic molecules on a heater. 
         [0038]    S 23 : Turn on a vacuum pump to pump air out of the capillary device. 
         [0039]    S 24 : Turn on the heater to heat the organic molecules; and 
         [0040]    S 25 : Use an ultraviolet light source to irradiate a capillary wall of the capillary device, wherein a color change of the capillary wall indicates that the organic molecule has reached a sublimation point. 
         [0041]    After the step S 21  takes place, a syringe needle is used to rinse a capillary wall by distilled water after the step of filling the organic molecule into the capillary of the capillary device takes place. The syringe needle can be used for rinsing the capillary wall by distilled water, so that the powder of the organic molecules will not remain on the capillary wall. After the step S 23  takes place, if the digital vacuum meter reads 10 −7  atm, the needle valve is shut, and then the vacuum pump is turned off. To improve the convenience of the observation, the photography device is provided for recording the color change of the capillary and its corresponding temperature during the heating process. 
         [0042]    The organic molecule includes an organic light emitting molecule which can be Alq 3  or Ir(ppy) 3 , and the heater is provided for heating the organic light emitting molecule at a speed of 5˜15° C. per minute, preferably 10° C. per minute. 
         [0043]    Preferably, the needle valve is turned on to regulate the pressure of the capillary device to a pressure range of 20 mmHg˜760 mmHg. The weight of the organic molecule is less than 1 mg. If the organic molecule is heated to the sublimation point at different pressures, a misty organic molecule attached onto the capillary or a color change of the capillary indicates the sublimation points at different pressures. The present invention can compare the difference of the sublimation points of the organic molecule at different vacuum levels. For evaporation elements, these are necessary data. 
         [0044]    To verify the data of the sublimation points measured by the system and method of detecting a sublimation point in accordance with the present invention, this embodiment uses Alq 3  as the organic molecule sample to measure the sublimation point and the heat of sublimation (ΔHsub), and a thermogravimetric analyzer (TGA) and a differential scanning calorimeter (DSC) to compare the measured data. It is noteworthy to point out that this embodiment adopts Alq 3  for the organic molecule, but the invention is not limited to Alq 3  only, and the sublimation point and the heat of sublimation (ΔHsub) of other organic molecules such as Ir(ppy) 3  can be used as well. 
         [0045]    With reference to  FIG. 3A  for optical microscopic photos of a system of detecting a sublimation point in accordance with the present invention, a capillary of the system is provided for carrying the Alq 3 . In the first capillary ( 1 ), the Alq 3  at an atmospheric pressure is filled into the capillary. In the second capillary ( 2 ), the Alq 3  at the atmospheric pressure is filled into the capillary, and then the syringe needle is used for rinsing the capillary wall by distilled water to clean any Alq 3  powder attached on the capillary wall. In the third capillary ( 3 ), the Alq 3  at the atmospheric pressure is filled into the capillary, and then heated to the sublimation point, until the Alq 3  is attached onto the capillary wall. The Alq 3  is an organic light emitting molecule at the atmospheric air pressure (760 mmHg). The method as shown in  FIG. 2  is adopted, and it is found that the Alq 3  obviously reaches the sublimation point. The optical microscope shows that condensed particles of Alq 3  are attached onto the capillary wall of the third capillary ( 3 ) as shown in P 1  of the figure. The sublimation point of the Alq 3  measured by the system of detecting a sublimation point of the present invention is approximately equal to 308° C.  FIG. 3  shows a weight loss temperature of Alq 3  measured by the thermogravimetric analyzer (TGA), and  FIG. 3B  shows that the weight loss temperature of the Alq 3  is approximately equal to 310° C., so that the sublimation point of the Alq 3  measured by the system and method of detecting a sublimation point in accordance with the present invention is approximately equal to 310° C., which is very close to the sublimation point measured by the thermogravimetric analyzer (TGA), but the invention further has the advantage of using a sample with the quantity of less 1 mg to obtain the sublimation point. 
         [0046]    In addition, the sublimation point temperatures of the Alq 3  measured at the pressures of 20 mmHg, 110 mmHg, 210 mmHg, 300 mmHg, 310 mmHg, 410 mmHg, 500 mmHg and 760 mmHg are equal to 282° C., 285° C., 291° C., 293° C., 294° C., 297° C., 299° C. and 308° C. respectively, and then the pressure (P), the temperature (T), ln P and 1/T are used to create a table as shown in Table 1, and then a graph of ln P versus 1/T is plotted as shown in  FIG. 4 . From the figure, the slope is found to be equal to −40694.9058, and finally the data are substituted into the Clausius-Clapeyron equation (as shown in Equation (1)) to obtain the heat of sublimation (ΔHsub) which is equal to 736.4 J/g. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Sublimation  
                   
               
               
                   
                 Pressure (P) 
                 lnP(atm) 
                 Point (T) 
                 1/T (k-1) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  20 mmHg 
                 −3.63759 
                 555k 
                 0.001802 
               
               
                   
                 110 mmHg 
                 −1.93284 
                 558k 
                 0.001792 
               
               
                   
                 210 mmHg 
                 −1.28621 
                 564k 
                 0.001773 
               
               
                   
                 300 mmHg 
                 −0.92954 
                 566k 
                 0.001767 
               
               
                   
                 310 mmHg 
                 −0.89675 
                 567k 
                 0.001764 
               
               
                   
                 410 mmHg 
                 −0.61716 
                 570k 
                 0.001754 
               
               
                   
                 500 mmHg 
                 −0.41871  
                 572k 
                 0.001748 
               
               
                   
                 760 mmHg 
                 0 
                 581k 
                 0.001721 
               
               
                   
                   
               
             
          
         
       
     
         [0000]      ln  P =(Δ H sub/ R )×1 /T   (1)
 
         [0047]    With reference to  FIG. 5  for the heat of sublimation (ΔHsub) and the heat of melting (ΔHmelt) of Alq 3  by using a differential scanning calorimeter (DSC), the DSC is an instrument used for measuring an energy change of a sample material at a specific temperature condition. The main principle of the DSC is to put a sample into a heating furnace to increase, decrease or maintain the temperature through a program, and an ambient gas such as nitrogen or oxygen is passed. If the sample is evaporated, melted or crystallized to cause a phase change, the energy absorbed or discharged will vary accordingly, so that the energy varied with temperature or time can be used as a basis for determining the heat of reaction, melting point, glass transition temperature, crystallization temperature, specific heat, thermal stability, oxidation stability, crosslinking heat of reaction, and kinetic analysis of a material. In a detection, the heat of sublimation (ΔHsub) measured by the differential scanning calorimeter (DSC) is equal to 634.2597 J/g as shown in  FIG. 5 . Compared with the reading obtained from the system of detecting a sublimation point in accordance with the present invention, the error falls within an acceptable range. The detected peak as shown in  FIG. 5  indicates that the melting point of the Alq 3  is equal to 418.83° C., and the heat of melting (ΔHmelt) is equal to 128.9523 J/g. 
         [0048]    In summation, the sublimation point detected by the system and method of detecting a sublimation point in accordance with the present invention is close to the sublimation point detected by the thermogravimetric analyzer (TGA), and the amount used for the detection in the present invention is less. For a trace amount of the sample, a waste of sample can be avoided, and the system of detecting a sublimation point in accordance with the present invention will not be contaminated. In addition, the present invention can measure the sublimation points of the organic molecule at different pressures. For evaporation elements, each sublimation point serves as a necessary datum. 
         [0049]    While the invention has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.