JP3908654B2 - Surface micro-area mass spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for ionizing atoms and molecules constituting a substance and mass-analyzing them, and more particularly to an apparatus for analyzing the mass of atoms and molecules present in a minute region of a sample surface. .
[0002]
[Prior art]
Conventionally, there are secondary ion mass spectrometry and laser desorption ionization as methods for measuring the mass number of atoms and the molecular weight of molecules constituting a substance on a solid surface.
[0003]
In these methods, a sample is irradiated with ions or a laser, the constituent atoms or molecules of the sample are desorbed from the surface by the physical effect or chemical effect, and a partially ionized product is measured by a mass spectrometer.
[0004]
In that case, since ions and lasers have a size of about μm even if they are condensed, the spatial resolution of information obtained by mass spectrometry is at most a region having a diameter of μm.
[0005]
In order to improve the spatial resolution, a technique combining a scanning tunnel microscope and a pulsed laser has been developed.
[0006]
In this method, the sample surface atoms are irradiated with a nanosecond pulse Nd: YAG laser (266 nm), and a pulse voltage of several volts to several tens of volts is applied to a metal probe such as tungsten to desorb and ionize sample surface atoms. is there.
[0007]
Although this method has limitations on the samples that can be applied, it achieves a spatial resolution of several tens of nanometers in diameter.
[0008]
[Problems to be solved by the invention]
In the surface mass spectrometry with the spatial resolution of the linear diameter of several tens nm, although realized desorption ionization using a pulse voltage in addition to the laser excitation, can not be applied to macromolecules and non-conductive specimen There is a problem that it is poor in versatility because it is restricted by the target sample.
[0009]
For example, when the molecular weight is several hundred thousand, such as a protein, ionization of molecules does not occur only by excitation with ions and lasers and support of a pulse voltage.
[0010]
Further, since excitation is performed with a voltage pulse, the sample itself is required to be a conductor, and it is difficult to measure an insulator such as a semiconductor or an organic substance typified by silicon.
[0011]
In view of the above situation, the present invention is a surface micrometer capable of mass spectrometry of atoms and molecules existing on the outermost surface of a sample with a spatial resolution of several tens of nanometers, even for a macromolecule or a non-conductive sample. An object of the present invention is to provide a region mass spectrometer.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] A surface micro-area mass spectrometer comprising an organic matrix material applied to the tip of a probe, means for controlling the position of the sample, and means for irradiating an ultraviolet pulse laser, and the probe is disposed in the vicinity of the sample surface The sample is close to the tip , and the ultraviolet pulse laser is irradiated onto the sample approaching the probe , and sample atoms and molecules in a minute region are desorbed and ionized from the sample surface, and mass spectrometry is performed.
[0013]
[2] The surface microregion mass spectrometer according to [1], wherein the probe is made of silicon or tungsten.
[0014]
[3] The surface microregion mass spectrometer according to [1] above, wherein the organic matrix substance is 2,5-dihydroxybenzoic acid or 3,5-dimethoxy-4-hydroxycinnamic acid. .
[0015]
[4] The surface microregion mass spectrometer according to [1], wherein the ultraviolet pulse laser has a pulse width of picoseconds to nanoseconds.
[0016]
[5] In the surface microregion mass spectrometer described in [4] above, the ultraviolet pulse laser having a pulse width of picoseconds to nanoseconds is a nitrogen laser (337 nm) or an Nd: YAG laser (355 nm, 266 nm). It is characterized by that.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0018]
FIG. 1 is a schematic diagram of a surface microregion mass spectrometer showing an embodiment of the present invention.
[0019]
In this figure, 1 is a probe, 2 is an organic matrix material, 3 is an ultraviolet pulse laser, 4 is a time-of-flight mass analyzer, 5 is a sample, 6 is a vacuum vessel made of glass or stainless steel, 7 is a vacuum pump is there.
[0020]
The components are installed in a vacuum vessel 6 made of glass or stainless steel, and the pressure is reduced by a vacuum pump 7.
[0021]
An organic matrix material 2 such as 2,5-dihydroxybenzoic acid or 3,5-dimethoxy-4-hydroxycinnamic acid is applied to the tip of the probe 1 having a needle shape made of a material such as silicon or tungsten. .
[0022]
The probe 1 is brought close to just above the sample 5 and the sample 5 is irradiated with an ultraviolet pulse laser 3 having a pulse width of picoseconds to nanoseconds such as a nitrogen laser.
[0023]
Ions generated from the surface of the sample 5 by irradiation with the ultraviolet pulse laser 3 are subjected to mass analysis by a mass analyzer such as a time-of-flight mass analyzer 4 and a mass spectrum is measured.
[0024]
A probe 1 as used in an atomic force microscope or a scanning tunneling microscope approaches the surface of the sample 5 to the vicinity of the surface pole, and 2,5-dihydroxybenzoic acid or 3,5-dimethoxy is approached on the probe 1 surface. An organic matrix material 2 such as -4-hydroxycinnamic acid is applied. The organic matrix material 2 absorbs the ultraviolet pulse laser 3, and then the interaction between the organic matrix material 2 and atoms and molecules on the surface of the sample 5 (so-called matrix-assisted ionization) causes the atoms and molecules on the surface of the sample 5 to Desorbed and ionized from the surface. The generated ions are measured by a mass analyzer such as a time-of-flight mass analyzer 4 to obtain a mass spectrum.
[0025]
Based on the above principle, it is possible to measure the mass spectrum of atoms and molecules on the outermost surface of the sample with a spatial resolution of several tens of nm in diameter.
[0026]
Since the surface microregion mass spectrometer of the present invention uses a probe in the same manner as an atomic force microscope or a scanning tunneling microscope, in principle, a spatial resolution of a few nanometers in diameter or less and a depth of less than Å. It is possible to measure atomic / molecular images and uneven images on the sample surface with resolution.
[0027]
As an application example, FIG. 2 shows the analysis results of protein molecules (molecular weight 112,534) adsorbed on the silicon surface. In FIG. 2 (a), the adsorption of three protein molecules is observed as an atomic force microscope image. When one molecule is desorbed and ionized by the surface microregion mass spectrometer of the present invention, as a result, the adsorbed portion of the molecule is scraped into a crater, and the atomic force microscope image is shown in FIG. ) As shown. Note that one side of the atomic force microscope image shown in FIG. 2 is 300 nm.
[0028]
From this, it can be seen that the desorption is successful only in the region of several tens of nm in diameter. Next, FIG. 3 shows the mass spectral characteristics of the molecules desorbed from the crater part of FIG.
[0029]
As is apparent from FIG. 3, molecular ions having molecular weights 112 and 534 corresponding to the molecular weight of the adsorbed protein are detected. From these results, it can be seen that mass analysis of atoms and molecules existing on the surface with a spatial resolution of several tens of nm in diameter is achieved by the surface microregion mass spectrometer of the present invention.
[0030]
In the above-mentioned examples, two examples of 2,5-dihydroxybenzoic acid and 3,5-dimethoxy-4-hydroxycinnamic acid were shown as the organic matrix material. They may be used.
[0031]
Thus, according to the present invention, even a macromolecule having a molecular weight of 100,000 or more such as a protein can be desorbed and ionized, and the spatial resolution of mass spectrometry has a high resolution of several tens of nm in diameter.
[0032]
In other words, since mass spectra of atoms and molecules can be obtained with a spatial resolution of several tens of nanometers, it becomes possible to identify atoms and molecules in a minute region, and the present invention is difficult for measurement using a scanning probe microscope or a near-field optical microscope. Can solve the problem of simple molecular identification.
[0033]
In addition, since an electric field or the like is not used, application to a non-conductor is possible.
[0034]
These characteristics contribute not only to the identification of adsorbed molecules on metal surfaces, but also to the identification of molecules adsorbed on semiconductor surfaces, the identification of atoms constituting semiconductor surfaces, and the identification of macromolecules such as proteins in biological cell membranes and their behavior elucidation. be able to.
[0035]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0036]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained.
[0037]
(A) Since the organic matrix support effect is used for ionization of the surface constituent material, ionization of macromolecules becomes possible.
[0038]
(B) Since the organic matrix substance is applied to the probe, a spatial resolution with a diameter of several tens of nanometers can be achieved.
[0039]
(C) By realizing desorption ionization without using a pulse voltage, the present invention can be applied to semiconductor samples and insulator samples.
[0040]
Thus, since the organic matrix support effect is used for ionization of the surface constituent material, and the organic matrix material used for the ionization is applied to the probe, the influence is a region of several tens of nanometers in contact with the probe. Therefore, it is possible to mass-analyze atoms / molecules existing on the outermost surface of the sample with a spatial resolution of several tens of nanometers. In addition, desorption and ionization of macromolecules with a molecular weight of 100,000 or more and mass analysis with spatial resolution of several tens of nanometers are possible, so that they can be applied to ionization of macromolecules such as proteins and insulator samples. It is also possible to observe an atomic order uneven image.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a surface microregion mass spectrometer showing an embodiment of the present invention.
FIG. 2 is an atomic force microscope image in place of a drawing showing the analysis results of protein molecules adsorbed on the silicon surface according to an embodiment of the present invention.
3 is a diagram showing mass spectral characteristics of molecules desorbed from the crater portion in FIG. 2. FIG.
[Explanation of symbols]
1 Probe 2 Organic Matrix Material 3 Ultraviolet Pulse Laser 4 Time-of-Flight Mass Analyzer 5 Sample 6 Vacuum Container 7 Vacuum Pump

Claims (5)

(A) an organic matrix material applied to the tip of the probe;
(B) means for controlling the position of the sample;
(C) an ultraviolet pulse laser irradiation means;
(D) The probe is brought close to the vicinity of the sample surface, the ultraviolet pulse laser is irradiated to the sample approaching the probe , and sample atoms and molecules in a minute region are desorbed and ionized from the sample surface, and mass spectrometry is performed. A surface micro-area mass spectrometer characterized by performing. 2. The surface microregion mass spectrometer according to claim 1, wherein the probe is made of silicon or tungsten. 2. The surface microregion mass analyzer according to claim 1, wherein the organic matrix substance is 2,5-dihydroxybenzoic acid or 3,5-dimethoxy-4-hydroxycinnamic acid. Analysis equipment. 2. The surface microregion mass spectrometer according to claim 1, wherein the ultraviolet pulse laser has a pulse width of picoseconds to nanoseconds. 5. The surface microregion mass spectrometer according to claim 4, wherein the ultraviolet pulse laser having a pulse width of picoseconds to nanoseconds is a nitrogen laser (337 nm) or an Nd: YAG laser (355 nm, 266 nm). Surface micro-area mass spectrometer.

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