RU2660418C1 - Probe for scanning probe microscopy and method of its manufacturing (embodiments) - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to the measurement equipment and can be used in scanning probe microscopy. Probe for the scanning probe microscopy contains cantilever for the atomic force microscopy with the located on the cantilever needle tip optically active region. Active region is the hybrid nanoparticle from the semiconductor material with metal coating of 50–300 nm in diameter. Cantilever material is silicon or silicon nitride, and the nanoparticle consists of the gold-plated silicon. Probe manufacturing method consists in the nanoparticle formation with the close to the spheroid shape on the cantilever needle tip. In one embodiment, the semiconductor material nanoparticle is preliminarily manufactured by the laser ablation method from the deposited on transparent substrate layered metal-semiconductor structure, after which the nanoparticle together with the cantilever are placed into the scanning electron microscope chamber, where nanoparticle transfer from the substrate to the point of the cantilever needle tip is performed using the located on the three-coordinate micromanipulator in the scanning electron microscope chamber metal tip. In the second embodiment, the semiconductor nanoparticle is formed directly on the cantilever needle tip by irradiating the unfunctionalized semiconductor cantilever tip for atomic force microscopy brought into contact with the thin metal layer surface, by the laser pulses with duration of not more than the microsecond.

EFFECT: technical solution enables high spatial resolution and sub-wavelength resolution.

6 cl, 8 dwg

Description

The invention relates to measuring technique and can be used in scanning probe microscopy to obtain patterns of the distribution of the near field of nanoscale samples in a wide spectral range.

A known probe for scanning probe microscopy (SPM) (US Patent No. 7528947 B2, IPC No. G01Q 70/16, priority date 07/10/2003, publication date 05/05/2009), which is a cantilever with a needle, a functionalized layer of material containing nanoparticles forming active medium for electromagnetic radiation. The disadvantage of the technical solution is a narrow spectral range in which the functional layer is an active medium for electromagnetic radiation, which is determined either by a narrow luminescence band of quantum dots or molecules, or by the plasmon resonance width of metal nanoparticles, as well as the relatively low level of the optical signal received from the functionalized probe.

A known probe for SPM (US Patent No. 7621964 B2, IPC No. G01Q 60/22, priority date September 5, 2006, publication date 11/24/2009) is a cantilever into which a light emitting diode is integrated using local doping with a focused ion beam. The photoluminescence of the probe was excited by applying the electric potential difference to the regions of the pn junction. The disadvantage of the technical solution is the fact that, despite the fact that the radiation spectrum of the pn junction was relatively broadband, it was nevertheless limited by the band gap of the semiconductor materials used (the proposed version showed radiation in the range 500-700 nm). In addition, the technology of forming the probe requires the use of a focused ion beam, with each probe being characterized by an individual shape and luminescence spectrum. Finally, for the proposed probe arrangement, there is a spatial separation of the geometric position of the probe tip, which studies the topography of the sample surface, and the effective position of the radiation source, which complicates the interpretation of the results.

A known probe of an atomic force microscope with a nanocomposite emitting element doped with quantum dots of a core-shell structure selected as a prototype (RF Patent No. 2541422 C1, IPC No. G01Q 60/24, priority date 08.19.2013, publication date 10.02.2015), representing a probe of an atomic force microscope with a nanocomposite emitting element doped with quantum dots of the core-shell structure, including a cantilever connected to a probe needle with a nanometer radius of curvature of the vertex, which is connected to a sphere made made of glass with nanometer pores filled with quantum dots of the core-shell structure. The sphere is attached to the probe by rigidly fitting the tip of the probe needle with a nanometer radius of curvature into one of the pores of the glass sphere with nanometer pores, the remaining pores with filled quantum dots of the core-shell structure are covered with a protective polymer layer transparent to the wavelength of an external electromagnetic source of excitation of quantum dots core-shell structures and wavelengths with a Stokes shift generated by quantum dots of the core-shell structure. The main disadvantage of the technical solution is the low spatial resolution in the topography signal and the optical signal obtained by using the probe in scanning probe microscopes, associated with the large diameter of the glass sphere used. In addition, the probe is characterized by a narrow emission spectrum determined by the luminescence band of the used quantum dots.

A known method of creating a probe for SPM (Hoshino, K., Gopal, A., Glaz, M.S., Vanden Bout, D.A., & Zhang, X. Nanoscale fluorescence imaging with quantum dot near-field electroluminescence. Applied Physics Letters, 101 (4), 043118 (2012).), In which a layer of colloidal CdSe / ZnSe quantum dots transferred from the initial substrate is placed on top of a silicon probe for atomic force microscopy. Quantum dots are coated on top with a conductive material, which ensures the formation of an electrical contact to the layer, a second contact is formed during the deposition of Pt under the action of a focused ion beam. Chemical etching is used to form the tip on top of the probe. The excitation of the fluorescence layer of quantum dots is carried out by applying the difference of electric potentials. The formed probe is attached to a quartz tuning fork. The disadvantage of this method is the fact that the electroluminescence spectrum was relatively narrow, and the spectral position of the radiation maximum was determined by the choice of the size of the used quantum dots. In addition, the radiation source formed by this method is not point-like; its size is poorly controlled when the probe is pressed against the substrate with the initial layer of quantum dots.

Also known is a device and method for manufacturing a probe for SPM (US Patent No. 6396050 B1, IPC No. G01Q 60/18, priority date 02/05/1999, publication date 05/28/2002), in which a pointed metal probe is coated with a multilayer structure including conductive layers metal and layers of organic compounds serving as electronic and hole type conductors. Luminescence excited by the application of a potential difference between the probe core and the outer metal coating is removed from the waveguide formed by the conducting layers to the tip of the probe due to the presence of an opening in the outer metal layer. The disadvantage of this method is the fact that luminescence of this type is characterized by a relatively narrow spectral band, and the wavelength is determined by the chemical composition of the organic layers, which forces the composition to be changed for experiments in different spectral ranges.

A known method of manufacturing probes for SPM (US Patent No. 201110303021 A1, IPC No. G01Q 70/12, priority date 08/01/2007, publication date 08/18/2011), selected as the prototype method, which consists in the fact that the tip of the cantilever needle Atomic force microscopy fixes the structure of a thin filament, after which the probe with the filament is placed in the chamber of a scanning electron microscope, and material is deposited at the end of the filament by irradiating the tip with a stream of charged particles accelerated by a voltage of 5 to 50 kV. As a result, a particle is formed on the tip from the deposited material, having the shape of a spheroid. The disadvantage of the prototype method is the need to use an additional technological stage - deposition induced by an electron beam, as well as restrictions on the material and composition of the resulting nanoparticles imposed by this growth method.

The problem of expanding the spectral range of the radiation of the optically active region of the probe for scanning probe microscopy while maintaining high spatial resolution while visualizing topography and subwave spatial resolution in studying the optical properties of the samples, as well as the task of simplifying and cheapening the method of manufacturing probes for scanning probe microscopy with optically active region.

The essence of the invention lies in the fact that the probe for scanning probe microscopy, containing a cantilever for atomic force microscopy and a needle, is functionalized using a semiconductor nanoparticle with a metal coating (preferably a silicon nanoparticle with a gold coating) and a diameter of 50-300 nm, placed on the tip of the needle a probe. In this case, a metal-coated semiconductor nanoparticle is an optically active region with a wide luminescence spectrum excited by laser irradiation of a particle.

A method of manufacturing a probe for scanning probe microscopy consists in forming on the tip of a cantilever needle for atomic force microscopy a nanoparticle with a shape close to a spheroid for this a nanoparticle of a semiconductor material is preliminarily made by laser ablation from a layered metal-semiconductor structure deposited on a transparent substrate, after which the nanoparticle together with the cantilever is placed in the camera of a scanning electron microscope, where the nanoparticles are transferred from the substrate to the cantilever needle tip with a metal tip located on a three-coordinate micromanipulator in a scanning electron microscope chamber. In this case, laser pulses are used for laser ablation with a duration of less than a microsecond, and the layered metal-semiconductor structure consists of amorphous silicon and gold.

The second variant of the method for manufacturing a probe for scanning probe microscopy is the formation of a cantilever tip for atomic force microscopy of a nanoparticle with a shape close to a spheroid, a semiconductor nanoparticle is formed directly on the tip of a cantilever needle by irradiating the tip of a non-functionalized semiconductor cantilever for atomic force microscopy, brought into contact with the surface of a thin metal layer, by laser pulses lasting less than a microsecond.

The basis of the present invention is the fixation of a single nanoparticle created by laser ablation from a layered metal-semiconductor structure at the top of the cantilever tip for atomic force microscopy. The composition of the nanoparticle, including a semiconductor material (preferably silicon) and a metal coating (preferably gold), provides photoluminescence of the nanoparticle in a wide spectral wavelength range when irradiated with powerful focused pulsed laser radiation of no more than microsecond duration (preferably, pulses of no more than several hundred femtoseconds ) Both components of the nanoparticle — the semiconductor core and the metal coating — play an important role in ensuring the radiative characteristics of the nanoparticle. The semiconductor core of the nanoparticle provides effective luminescence due to the presence of the band gap in the material. The preferred material for the semiconductor core of the nanoparticle is silicon. This material is indirect gap, which allows one to obtain luminescence in the energy range from direct to indirect transitions (from 3.5 to 1.1 eV). Also, an additional broadening of the luminescence spectrum occurs due to quantum-size effects arising in nanoscale (less than 5 nm) silicon crystallites. In turn, the metal coating plays the role of an effective absorber of exciting laser radiation, provides injection of hot charge carriers into the semiconductor, and also provides an additional relaxation channel for hot charge carriers with the emission of photons through interaction with plasmons. Gold is the preferred material because of the relatively low losses and high refractoriness, which allows the use of more intense excitation. The excitation of luminescence is preferably carried out by laser pulses with a duration of not more than a few hundred femtoseconds, which avoids overheating and subsequent melting of the nanoparticles. The cantilever tip with a nanometer radius provides a high spatial resolution when visualizing the sample topography, while the metal-coated semiconductor nanoparticle located directly on the tip of the cantilever needle is close to a point source of optical radiation (the nanoparticle diameter is in the range of 50-300 nm) , which determines the subwavelength resolution in the study of the optical properties of the sample. In this case, the photoluminescence of the nanoparticle included in the probe for scanning probe microscopy occurs in the ultra-wide spectral range (at least 400-900 nm), which distinguishes this invention from the prototype device. An additional advantage of the present invention is that the radiation source is in close proximity to the tip of the cantilever needle, which makes it easy to compare the resulting optical signal with the topography of the sample being measured in parallel with the optical signal.

A method of manufacturing a probe for scanning probe microscopy is based on the formation of metal-coated semiconductor nanoparticles. The advantage of the proposed method over the prototype method is to reduce the time and cost of manufacturing the probe by using a cheap and easy to implement laser ablation method. An additional advantage of the first implementation of the method, which implies the preliminary fabrication of nanoparticles by laser ablation of thin layers of a semiconductor and a metal, is the possibility of preliminary characterization of the optical properties of nanoparticles on a substrate and subsequent transfer of nanoparticles with optimal radiation characteristics to the tip of the cantilever needle. An advantage of the second variant of the method, which implies the formation of a nanoparticle by laser ablation directly on the tip of a cantilever needle brought into contact with a thin layer of gold, is a further reduction in the cost of the manufacturing method by eliminating the step of transferring the nanoparticle to the tip, which requires operation in a vacuum chamber of a scanning electron microscope.

The invention is illustrated by drawings, where:

in FIG. 1 shows the construction of a probe for scanning probe microscopy.

in FIG. Figures 2 and 3 show the steps of creating a probe for scanning probe microscopy based on a cantilever with a semiconductor nanoparticle with a metal coating on the tip, characterized by a broadband photoluminescence spectrum.

in FIG. 4 shows a micrograph of a probe for scanning probe microscopy with a silicon nanoparticle with a metal coating on its tip, obtained by scanning electron microscopy;

in FIG. Figure 5 shows the photoluminescence spectrum of a single silicon nanosphere with a diameter of 200 nm with a gold coating upon excitation by femtosecond laser pulses;

in FIG. 6 shows an optical image of a luminescent silicon nanoparticle with a metal coating, obtained using optical microscopy;

in FIG. 7 shows an image of a sample representing a silicon nanodisk dimer obtained by scanning electron microscopy;

in FIG. Figure 8 shows the image of the distribution of the near-field signal of a sample in the form of a silicon dimer at wavelengths of 650, 700, 750, and 800 nm, obtained using a probe probe for scanning microscopy with a silicon nanoparticle with a metal coating on its tip.

The probe for scanning probe microscopy (Fig. 1) is a cantilever for atomic force microscopy 1 with a needle 2, on the tip of which a metal-coated semiconductor nanoparticle 3 is fixed.

A method of manufacturing a probe for scanning probe microscopy is illustrated in FIG. 2 and FIG. 3. In the first embodiment of the method (Fig. 2), a layered structure 5 of thin layers of semiconductor 6 and metal 7 is applied onto an optically transparent carrier substrate 4 (preferred quartz or glass materials). Amorphous silicon and gold are the preferred materials of the layered structure. Next, the carrier substrate 4 with a layered structure 5 is irradiated using focused pulsed laser radiation 8 (the preferred wavelength is 1050 nm, the pulse duration is 150 femtoseconds, the pulse repetition rate is 1 kHz, the energy density in the pulses is from 100 to 500 mJ / cm ² ). As a result of ablation by a focused laser beam, semiconductor nanospheres with a metal coating 3 are separated from the layered structure 5, which are deposited on an auxiliary substrate 9. Then, an auxiliary substrate 9 with a semiconductor nanoparticle with a metal coating 3 and cantilever for atomic force microscopy 1 are placed in a vacuum chamber of a scanning electron microscope 12. In it, a metal-coated semiconductor nanoparticle 3 is transferred from the auxiliary substrate 9 to the tip of the cantilever needle 2 with with a metal tip 10 fixed on a three-coordinate micromanipulator 11.

In the second embodiment of the method (Fig. 3), a metal-coated semiconductor nanoparticle 3 is formed directly on the tip of the semiconductor cantilever 2 by irradiation with powerful focused pulsed laser radiation. To do this, a thin layer of metal (preferably gold) is deposited by thermal spraying onto the carrier substrate 16. Then, the tip of the cantilever needle 2 for atomic force microscopy 1 is brought into contact with the thin metal layer 15 on the carrier substrate 16. The tip of the cantilever needle 2 irradiated with powerful laser pulses with a duration of no more than a microsecond 13, focused by the lens 14. The ablation process leads to the formation of cantilever 2 on the tip of the needle 2 nanoparticles 3 of cantilever materials and a thin metal layer.

An example of a specific implementation of the method.

When using the first variant of the method for creating a probe for scanning probe microscopy, the first stage, a layer of amorphous hydrogenated silicon 6 with a thickness of 60 nm was deposited on the surface of a glass substrate 4 of K-8 grade by means of gas-phase deposition of plasma activated plasma. Then, a layer of gold 7 with a thickness of 15 nm was deposited by thermal deposition. Then, using the focused radiation of an 8 pulsed femtosecond laser with a wavelength of 1053 nm, the layered structure 5 (silicon - gold) was ablated, as a result of which hybrid metal-coated semiconductor nanoparticles 3 (a-Si: H / Au) were formed. At the next stage, using a micromanipulator 10 located in the SEM chamber, a separate nanoparticle with a diameter of about 180 nm was transferred to the needle tip of a silicon cantilever (SEM image of the tip of a cantilever needle with a particle is shown in Fig. 4). Further, the cantilever tip with a nanoparticle fixed on it was irradiated with a focused beam of a femtosecond laser with a wavelength of 1053 nm, which ensured the luminescence of the nanoparticle in a wide spectral range (400-900 nm, Figs. 5, 6).

When using the second variant of the method for creating a probe for scanning probe microscopy of the first stage, a 15-nm-thick layer of gold 15 was deposited by means of thermal deposition on the surface of a glass substrate 16 of K-8 grade. Next, the tip of the silicon cantilever 1 was brought into contact with a thin layer of gold using standard feedback techniques for cantilever oscillation parameters. Then, the tip of needle 2 of the silicon cantilever was irradiated with a focused beam of a femtosecond laser 13 with a wavelength of 1053 nm, which led to the ablation of a thin layer of gold and silicon at the tip of the needle of the cantilever and the formation of cooling materials of silicon nanoparticles with a metal coating 3 on the tip of the needle of the cantilever.

In the process of studying the optical properties of the samples, the created probe was brought into contact with the surface of the sample, which is a dimer of silicon disks (Fig. 7) using standard feedback techniques for cantilever oscillation parameters. The luminescence signal was collected using a micro lens and analyzed using a confocal spectrometer. Mapping of the luminescence spectra for various relative positions of the probe and the sample was carried out by moving the sample holder with piezoscanners (Fig. 8).

Thus, the advantages of the inventive probe for scanning probe microscopy, which provides high spatial resolution for visualizing the topography of the sample and subwavelength resolution for studying the optical properties of the sample in a wide spectral range due to the use of the optically active region located near the tip of the cantilever and characterized by an ultra-wide (not less than 400 -900 nm) photoluminescence spectrum when excited by laser pulses with a duration of no more than a microsecond.

Claims (6)

1. A probe for scanning probe microscopy containing a cantilever for atomic force microscopy with an optically active region located on the tip of a cantilever needle, characterized in that the active region is a hybrid nanoparticle of a semiconductor material with a metal coating with a diameter of 50-300 nm. 2. The probe according to claim 1, characterized in that the cantilever material is silicon or silicon nitride. 3. The probe according to paragraphs. 1, 2, characterized in that the nanoparticle consists of silicon with a gold coating. 4. A method of manufacturing a probe for scanning probe microscopy, which consists in forming on the tip of a cantilever needle for atomic force microscopy a nanoparticle with a shape close to a spheroid, characterized in that the nanoparticle is made of semiconductor material beforehand by ablation with laser pulses of a duration of no more than a microsecond of a layered a metal-semiconductor structure deposited on a transparent substrate, after which the nanoparticle together with the cantilever is placed in the scanning electron chamber microscope, where the transfer is carried out on the nanoparticles with the substrate needlepoint cantilever metal tip disposed on three-coordinate micromanipulator in the chamber of a scanning electron microscope. 5. The method according to p. 5, characterized in that femtosecond laser pulses are used for laser ablation, and the layered metal-semiconductor structure consists of amorphous silicon and gold. 6. A method of manufacturing a probe for scanning probe microscopy, which consists in forming on the tip of a cantilever needle for atomic force microscopy a nanoparticle with a shape close to a spheroid, characterized in that the semiconductor nanoparticle is formed directly on the tip of the cantilever needle by irradiating the tip of an unfunctionalized semiconductor cantilever for atomic Force microscopy brought into contact with the surface of a thin metal layer by laser pulses of a duration not exceeding microseconds s.

Images