Patent Publication Number: US-2016236192-A1

Title: Raman sample cell

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional patent application Ser. No. 62/116,689, filed Feb. 16, 2015 entitled “Raman Sample Cell,” which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally directed to a sample cell. 
     BACKGROUND 
     Spectrographs (sometimes referred to as spectrometers) are common instruments used to measure the properties of input light across the component wavelengths of the input light, e.g., the intensity of the light at some or all of the component wavelengths of the input light. They are particularly useful in the fields of material and chemical analysis, where light of different types (infrared, visible, and/or ultraviolet) may be directed onto a sample, and the resulting light reflected by, emitted by, and/or transmitted through the sample can then be supplied to and analyzed by the spectrograph. The resulting readings can provide information about the properties of the sample. 
     When illuminating light, such as a laser beam, is incident upon a sample material, molecular bonds in the material can be excited by the incident light and can emit radiation which can be detected as scattered light. The Rayleigh component of the scattered light corresponds to the light emitted when the molecule relaxes from the excited state to the ground state. Infrequently, the molecule relaxes to a different vibrational or rotational level in the ground state. This produces Raman scattering components at Stokes and anti-Stokes frequencies. A sample composed of multiple molecular species will produce a spectrum of such Raman scattering. The Raman scattering components can be detected and analyzed to help determine the composition of the sample. 
     Various instruments have been developed for analyzing Raman spectra including Raman microscopes in which a very small area on a sample can be analyzed to determine characteristics of the composition of the sample at that area. In a typical Raman microscope, narrow band or monochromatic illuminating light, such as laser light, is passed along a beam path through the objective lens of the microscope where it is focused at a focal point on a sample. The Raman scattering from the sample collected by the microscope objective is passed back on a beam path to a spectrograph which typically separates the Raman scattering radiation by wavelength and detects it. 
     Some sample materials can deteriorate rapidly in air, and therefore require handling in an inert (e.g., argon or nitrogen) atmosphere in a controlled-atmosphere chamber (sometimes referred to as a glove box). Examples of such air-sensitive sample materials include lithium ion battery components, such as electrode and separator materials. It is also often useful to analyze the same sample by different techniques, such as scanning electron microscopy (SEM) and Raman microscopy, while maintaining the sample in the same controlled-atmosphere environment. SEM analysis typically employs a variety of sample holders of different shapes and sizes, depending on whether, for example, an edge or a flat surface of the sample is being analyzed. 
     Therefore, there is a need for a sample cell for air-sensitive sample materials mounted on a variety of sample holders. 
     SUMMARY 
     In one embodiment, a sample cell includes a cell body having a proximal end, a distal end, a circumference, and a sample holding surface on the proximal end. The sample cell further includes an o-ring around the circumference, a cap disposed over the proximal end of the cell body, the cap forming a seal with the o-ring, and a window in the cap located at an adjustable distance from the sample holding surface. The sample holding surface can include a recess adapted for a sample holder, and, optionally, a locking pin that secures the sample holder in the recess. In some embodiments, the window can be one of a calcium fluoride, quartz, glass, or magnesium oxide window. The sample cell can include a cell mounting plate connected to the distal end of the cell body. In certain embodiments, the cell body and cap can include matching threads. The cap can have a diameter in a range of between 1.6 inches and 2.0 inches, such as 1.83 inches. The adjustable distance can be in a range of between 0.0 inches and 0.26 inches, such as 0.01 inches. 
     In another embodiment, a method of holding a sample includes mounting a sample holder on a sample holding surface located on a proximal end of a cell body having a circumference, and an o-ring around the circumference, disposing a cap over the proximal end of the cell body, forming a seal with the o-ring, the cap including a window, and adjusting the distance between the window and the sample holding surface. The method can further include securing the sample holder with a locking pin, which can be located in a recess in the cell body. In some embodiments, the method can further include mounting the cell onto a cell mounting plate. In certain embodiments, adjusting the distance between the window and the sample holding surface can include threading the cap over the proximal end of the cell body. 
     The invention has many advantages, including enabling analysis of air-sensitive sample materials mounted on a variety of sample holders. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-section of the sample cell. 
         FIG. 2A  illustrates a perspective view of the sample cell. 
         FIG. 2B  illustrates a perspective view of a cross-section of the sample cell. 
         FIG. 3  illustrates a cross-section of the sample cell including a sample holder. 
         FIG. 4  illustrates the sample cell on a sample stage of a Raman microscope. 
         FIG. 5  is a photograph of an embodiment of the sample cell on a sample stage of a Raman microscope. 
         FIG. 6  is a flow chart of an exemplary method of holding a sample. 
     
    
    
     Like reference numerals refer to corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the description of the invention herein, it is understood that a word appearing in the singular encompasses its plural counterpart, and a word appearing in the plural encompasses its singular counterpart, unless implicitly or explicitly understood or stated otherwise. Furthermore, it is understood that for any given component or embodiment described herein, any of the possible candidates or alternatives listed for that component may generally be used individually or in combination with one another, unless implicitly or explicitly understood or stated otherwise. Moreover, it is to be appreciated that the figures, as shown herein, are not necessarily drawn to scale, wherein some of the elements may be drawn merely for clarity of the invention. Also, reference numerals may be repeated among the various figures to show corresponding or analogous elements. Additionally, it will be understood that any list of such candidates or alternatives is merely illustrative, not limiting, unless implicitly or explicitly understood or stated otherwise. In addition, unless otherwise indicated, numbers expressing quantities of ingredients, constituents, reaction conditions and so forth used in the specification and claims are to be understood as being modified by the term “about.” 
     Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the subject matter presented herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the subject matter presented herein are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. 
     In some embodiments, the sample cell described herein can be used, for example, for ex-situ battery studies of materials that will be deteriorated rapidly in open air. The sealed cap design enables the use of the sample cell in inert gas conditions to transfer sample material in and out of the cell. The design accepts standard SEM pin mounts, which have a variety of sizes and shapes. A user is able to mount a sample flat, for surface study, or mount the sample with one side facing up for cross section study. The SEM pin mount will facilitate transfer of samples between a Raman microscope and an SEM. The adjustable cap design allows for focus adjustment for different types of samples and different working distances from objectives, while maintaining the seal during the adjustment, because the air-tight adjustable seal allows the window, which is sealed into the cap, to move up and down for focus and working distance adjustment while still maintaining the seal during the adjustment. The sample cell is designed to be used with a standard Raman microscope stage or any microscope stage which accepts one or more (e.g., two) standard slides, which are typically 3 inches (7.6 cm) long and 1 inch (2.54 cm) wide. The replaceable cap enables multiple window material options for the sealed window, such as quartz, CaF 2 , MgO, glass, or sapphire, or any other window materials which provide a clean Raman background for different samples. 
     In one embodiment, as shown in  FIG. 1 , a sample cell  100  includes a cell body  110  having a proximal end  120 , a distal end  130 , a circumference  140 , and a sample holding surface  145  on the proximal end  120 , an o-ring  160  around the circumference  140 , a cap  170  disposed over the proximal end  120  of the cell body  110 , the cap  170  forming a seal with the o-ring  160 , and therefore maintaining a controlled atmosphere around sample holding surface  145  such as an inert (e.g., argon or nitrogen) atmosphere established by assembling the cell in a glove box. The sample cell  100  also includes a window  180  that is sealed in the cap  170  and located at an adjustable distance  185  from the sample holding surface  145 . In one aspect, the distance  185  is adjustable due to the cap  170  and cell body  110  being configured with threads (shown in  FIG. 3 ), so that the cap  170  can be lowered onto the cell body  110  while maintaining the seal with the o-ring  160 . The sample holding surface  145  can include a recess  190  adapted for a sample holder (shown in  FIG. 3 ). In one exemplary embodiment, the diameter of the cap  170  is in a range of between 1.6 inches (4.1 cm) and 2.0 inches (5.1 cm), such as 1.8 inches (4.6 cm). 
     The sample cell  100  can be made of a variety of materials. The cell body  110 , cap  170 , and mounting plate  195  can be made of metal, polymer, or composite materials. The window  180  is made of a material (e.g, calcium fluoride, quartz, magnesium oxide, glass, or sapphire) that is transparent (i.e., having an absorbance of less than about 10%) to the wavelengths of light used for the experiment. The o-ring  160  is made of any suitable polymeric material, such as Buna N, neoprene, silicone rubber, or the like. In one aspect, as shown in  FIG. 1 , the sample cell  100  includes a cell mounting plate  195  connected to the distal end  130  of the cell body  110 . 
     In another embodiment, as shown in perspective in  FIG. 2A  and in cross-section in  FIG. 2B , a sample cell  200  includes a cell body  210  having a proximal end  220 , a distal end  230 , a circumference  240 , and a sample holding surface  245  on the proximal end  220 , an o-ring  260  around the circumference  240 , a cap  270  disposed over the proximal end  220  of the cell body  210 , the cap  270  forming a seal with the o-ring  260 , and therefore maintaining a controlled atmosphere around sample holding surface  245 . The sample cell  200  also includes a window  280  in the cap  270  located at an adjustable distance  285  from the sample holding surface  245 . The window  280  is made of a material (e.g, calcium fluoride, quartz, magnesium oxide, glass, or sapphire) that is transparent (i.e., having an absorbance of less than about 10%) to the wavelengths of light used for the experiment. 
     In one aspect, as shown in  FIG. 2B , the sample cell  200  includes a cell mounting plate  295  connected to the distal end  230  of the cell body  210  by bolts  225 . The sample holding surface  245  can include a recess  290  adapted for a sample holder  250 . Examples of SEM sample holders are shown in  FIG. 2B  as sample holders  250 A,  250 B, and  250 C. The post  255  (also called a stub) of sample holders  250 A,  250 B, and  250 C has a diameter adapted to fit into recess  290 . In one aspect, the post  255  is secured in recess  290  by locking pin  215 . If the sample holders  250 A,  250 B, and  250 C are made of metal, such as stainless steel or aluminum, then they are typically coated with an insulating material to prevent electrical short circuits during SEM analysis. Sample holders  250 B and  250 C are examples of sample holders for analyzing cross-sections of a sample, by mounting a sample with the edge perpendicular to the flat surface of the holder and parallel to the pin  255 . Sample materials can be disposed on sample holders  250 A,  250 B, or  250 C and placed in sample cell  200  either before or after SEM analysis. 
     In yet another embodiment, as shown in  FIG. 3 , a sample cell  300  includes a cell body  310  having a proximal end  320 , a distal end  330 , a circumference  340 , and a sample holding surface  345  on the proximal end  320 , adapted for a sample holder  350  disposed on the sample holding surface  345 . The sample cell  300  also includes an o-ring  360  around the circumference  340 , a cap  370  disposed over the proximal end  320  of the cell body  310 , the cap  370  forming a seal with the o-ring  360 , and therefore maintaining a controlled atmosphere around sample holder  350 . The sample cell  300  also includes a window  380  in the cap  370  located at an adjustable distance  385  from the sample holding surface  345 . The distance  385  is adjustable due to the cap  370  and cell body  310  being configured with matching threads  365 , so that the cap  370  can be lowered onto the cell body  310  while maintaining the seal with the o-ring  360 . The window  380  is made of a material (e.g, calcium fluoride, quartz, magnesium oxide, glass, or sapphire) that is transparent (i.e., having an absorbance of less than about 10%) to the wavelengths of light used for the experiment. 
     In one aspect, as shown in  FIG. 3 , the sample cell  300  includes a cell mounting plate  395  disposed on the XYZ sample stage  375  of a Raman microscope (see  FIG. 4 ) Minimization of the adjustable distance  385  enables minimization of the focus distance  383  (also called the working distance) of the microscope objective  305 , which enables higher magnification analysis of the sample on sample holder  350 , because higher magnification microscope objectives  305  typically have shorter working distances  383 . In one exemplary embodiment, the adjustable distance  385  is in a range of between 0.0 inches (0.0 cm) and 0.26 inches (0.66 cm), enabling a sample height in a range of between 0.25 inches (0.64 cm) and 0.01 inches (0.025 cm) to be fully enclosed by the sample cell  300 . A preferred value of the adjustable distance  385  is 0.01 inches, so as to place the window  380  as close as possible to the sample (not shown) without making contact, where contact is an adjustable distance  385  of 0.0 inches. This preferred adjustable distance  385  yields a preferred value of 0.03 inches (0.08 cm) for the minimum working distance  383 . 
     In still another embodiment, as shown in  FIG. 4 , a sample cell  400  includes a cell body  410  having a proximal end  420 , a distal end  430 , a circumference  440 , and a sample holding surface  445  on the proximal end  420 , adapted for a sample holder  450  disposed on the sample holding surface  445 . The sample holding surface  445  can include a recess  490  adapted for a sample holder  450  that includes a post  455 . In one aspect, the post  455  is secured in recess  490  by locking pin  415 . The sample cell  400  also includes an o-ring  460  around the circumference  440 , a cap  470  disposed over the proximal end  420  of the cell body  410 , the cap  470  forming a seal with the o-ring  460 , and therefore maintaining a controlled atmosphere around sample holder  450 . The sample cell  400  also includes a window  480  in the cap  470  located at an adjustable distance  485  from the sample holding surface  445 . The window  480  is made of a material (e.g, calcium fluoride, quartz, magnesium oxide, glass, or sapphire) that is transparent (i.e., having an absorbance of less than about 10%) to the wavelengths of light used for the experiment. In one aspect, as shown in  FIG. 4 , the sample cell  400  includes a cell mounting plate  495  connected to the distal end  430  of the cell body  410  by bolts  425 . The cell mounting plate  495  is disposed on the XYZ sample stage  475  of a Raman microscope  403  that includes Raman microscope objective  405 . A photograph of this embodiment is shown in  FIG. 5 . 
     The sample cell can be used for a variety of sample materials that can deteriorate rapidly in air, and therefore require handling in an inert (e.g., argon or nitrogen) atmosphere. Examples of such air-sensitive materials include lithium-ion battery components, such as electrode, separator, and solid electrolyte materials. Ex-situ lithium-ion battery material studies can include, for example, analysis of electrode materials, separator materials, and the solid electrolyte interphase (SEI) layer. 
     In another embodiment, shown in  FIG. 6 , a method  600  of holding a sample includes mounting at step  610  a sample holder on a sample holding surface located on a proximal end of a cell body having a circumference, and an o-ring around the circumference, disposing at step  620  a cap over the proximal end of the cell body, forming a seal with the o-ring, the cap including a window, and adjusting at step  630  the distance between the window and the sample holding surface. The method can further include securing at step  640  the sample holder with a locking pin, which can be located in a recess in the cell body. In some embodiments, the method can further include mounting the cell onto a cell mounting plate at step  650 . In certain embodiments, adjusting the distance between the window and the sample holding surface at step  630  can include threading the cap over the proximal end of the cell body at step  635 . 
     While the present invention has been illustrated by a description of an exemplary embodiment and while this embodiment has been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.