阅读说明：本技术 样品生长装置、样品生长方法及分子束外延系统 (Sample growth device, sample growth method and molecular beam epitaxy system ) 是由 杨钢 薛聪 王庶民 董建荣 于 2021-09-09 设计创作，主要内容包括：本发明公开了一种样品生长装置、样品生长方法及分子束外延系统。所述样品生长装置包括真空腔室以及位于真空腔室内的旋转部分和倾斜调节部分,旋转部分包括旋转台、旋转机构和承载于旋转机构上的基片,旋转机构设置于旋转台上且驱动基片绕旋转台周向公转；倾斜调节部分包括倾斜调节机构及与倾斜调节机构相连的分子束源炉,倾斜调节机构在基片公转的过程中调整分子束源炉的倾斜角度,使分子束源炉入射的分子束全覆盖住不同公转位置处的基片。本发明的结构简单紧凑,成本较低,且装卸方便,定位精度高,生产多片样品可通过单个分子束源炉调整角度,进行喷射位置的改变,很好地保证喷射的均匀性。(The invention discloses a sample growth device, a sample growth method and a molecular beam epitaxy system. The sample growth device comprises a vacuum chamber, a rotating part and an inclination adjusting part, wherein the rotating part and the inclination adjusting part are positioned in the vacuum chamber; the inclination adjusting part comprises an inclination adjusting mechanism and a molecular beam source furnace connected with the inclination adjusting mechanism, and the inclination adjusting mechanism adjusts the inclination angle of the molecular beam source furnace in the revolution process of the substrate so that the molecular beams incident from the molecular beam source furnace completely cover the substrate at different revolution positions. The invention has simple and compact structure, lower cost, convenient assembly and disassembly and high positioning precision, can change the spraying position by adjusting the angle of a single molecular beam source furnace for producing a plurality of samples, and well ensures the uniformity of spraying.)

1. A sample growth apparatus, the apparatus comprising:

a vacuum chamber, and a rotation part and a tilt adjusting part located within the vacuum chamber;

the rotating part comprises a rotating table, a rotating mechanism and a substrate carried on the rotating mechanism, the rotating mechanism is arranged on the rotating table and drives the substrate to revolve around the rotating table in the circumferential direction, and the rotating table can rotate;

the inclination adjusting part comprises an inclination adjusting mechanism and a molecular beam source furnace connected with the inclination adjusting mechanism, and the inclination adjusting mechanism adjusts the inclination angle of the molecular beam source furnace in the revolution process of the substrate, so that the molecular beams incident from the molecular beam source furnace can completely cover the substrate at different revolution positions.

2. The sample growth apparatus of claim 1, wherein: the rotary mechanism comprises a first driving motor, a connecting rod, a sample support and a heating part, the first driving motor is connected with the sample support through the connecting rod, the substrate is borne on the sample support, the heating part is arranged on the sample support and heats the substrate on the sample support, and the first driving motor drives the sample support through the connecting rod to drive the substrate to revolve around the central shaft of the rotary table.

3. The sample growth apparatus of claim 1, wherein: the inclination adjusting mechanism comprises an inclination adjusting platform, an elastic compression piece and an adjusting component, the inclination adjusting platform comprises an upper pressing plate, the molecular beam source furnace is fixed on the upper pressing plate, the elastic compression piece is connected with the middle part of the upper pressing plate, the adjusting component is connected with one end of the upper pressing plate, the adjusting component compresses or stretches the elastic compression piece to drive the upper pressing plate to incline, and drives the molecular beam source furnace to incline while inclining, so that the incident angle and the range of the molecular beam source furnace are changed.

4. The sample growth apparatus of claim 3, wherein: the inclined angle of the upper pressing plate is equal to that of the molecular beam source furnace.

5. The sample growth apparatus of claim 3, wherein: the inclination adjusting platform further comprises a base located below the upper pressing plate, the adjusting assembly comprises a second driving motor, a moving shaft and a moving groove, one end of the moving shaft penetrates through the upper pressing plate to be connected with the second driving motor, the other end of the moving shaft extends into the moving groove, the moving groove is formed in the base, the moving shaft is driven by the second driving motor to move along the moving groove, and the upper pressing plate is driven to incline when moving.

6. The sample growth apparatus of claim 5, wherein: the inclination adjusting mechanism further comprises an inclination positioning component, and the inclination positioning component is arranged at the other end of the upper pressing plate and used for positioning the inclination of the upper pressing plate.

7. The sample growth apparatus according to claim 6, wherein the inclined positioning assembly comprises a support rod and a positioning groove, one end of the support rod is fixed to the upper platen, the other end of the support rod is a spherical head, the positioning groove is an arc-shaped groove formed on the base, and the spherical head is located in the arc-shaped groove and tangent to the arc-shaped groove.

8. The sample growth apparatus according to claim 5, wherein the tilt adjustment mechanism further comprises a pre-tightening force providing member, one pre-tightening force providing member is disposed on each of two sides of the elastic compression member, and the pre-tightening force providing members are disposed between the upper platen and the base.

9. The sample growth apparatus of claim 7, wherein the tilt angle of the molecular beam source furnace is calculated by the formula:

；

wherein, a is the inclination angle of the molecular beam source furnace, n is the rotation speed of the second driving motor, p is the pitch of the moving shaft, D is the distance between the central axis of the moving shaft and the central axis of the support torque rod, t is the rotation time of the second driving motor, and n & ltt & gt is the number of rotations of the second driving motor.

10. A method of growing a sample, comprising: growing a thin film on a substrate using the sample growth apparatus of any one of claims 1-9, thereby obtaining a sample.

11. A molecular beam epitaxy system characterised by comprising a sample growth apparatus according to any one of claims 1 to 9.

Technical Field

The invention belongs to a molecular beam epitaxy technology, and particularly relates to a sample growth device and a sample growth method based on the molecular beam epitaxy technology.

Background

Molecular Beam Epitaxy (MBE) is a technique for growing high quality crystalline thin films on crystalline substrates. The principle is that in a super-high vacuum chamber, a molecular beam source furnace of required components is heated to generate steam, the steam is collimated by a small hole to form a molecular beam or an atomic beam, the molecular beam or the atomic beam is sprayed onto a single crystal substrate at a proper temperature according to a certain beam intensity proportion, and the molecular beam is controlled to scan the substrate and interact with the surface, so that molecules or atoms are arranged in a crystal and grow layer by layer to form the required material.

Molecular beam epitaxy has been widely used in the semiconductor device industry where substrates for epitaxial growth have dimensions of 2 inches, 4 inches, 6 inches, etc. In order to improve the growth efficiency of samples, the molecular beam epitaxy equipment on the market currently mainly comprises a plurality of masers, i.e. a plurality of masers can be produced at one time (for example, 4 masers can simultaneously produce 4 samples at a time). Meanwhile, a large sample holder is often required for producing a plurality of samples, and a plurality of substrates are placed on the sample holder side by side, so that the size of the sample holder is increased undoubtedly, the design size of a sample growth chamber is correspondingly enlarged, and the design cost and difficulty are increased; because the incident angle of the molecular beam source furnace is not adjustable, and a plurality of molecular beam source furnaces are also needed for spraying when a plurality of molecular beam source furnaces are produced simultaneously, the uniformity of a sample is difficult to ensure, and the layout difficulty and the cost are increased.

How to solve the difficult problems such as high design cost and uniformity of multi-disc sample production, provide a multi-disc sample growth device that cost performance is high, be the problem that needs to solve at present urgently.

Disclosure of Invention

The invention mainly aims to provide a sample growth device, a sample growth method and a molecular beam epitaxy system, thereby overcoming the defects of the prior art.

In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:

a sample growth apparatus, comprising:

a vacuum chamber, and a rotation part and a tilt adjusting part located within the vacuum chamber;

the rotating part comprises a rotating table, a rotating mechanism and a substrate carried on the rotating mechanism, the rotating mechanism is arranged on the rotating table and drives the substrate to revolve around the rotating table in the circumferential direction, and the rotating table can rotate;

the inclination adjusting part comprises an inclination adjusting mechanism and a molecular beam source furnace connected with the inclination adjusting mechanism, and the inclination adjusting mechanism adjusts the inclination angle of the molecular beam source furnace in the revolution process of the substrate, so that the molecular beams incident from the molecular beam source furnace can completely cover the substrate at different revolution positions.

In a preferred embodiment, the rotating mechanism includes a first driving motor, a connecting rod, a sample holder and a heating portion, the first driving motor is connected to the sample holder through the connecting rod, the substrate is supported on the sample holder, the heating portion is disposed on the sample holder and heats the substrate on the sample holder, and the first driving motor drives the sample holder to drive the substrate to revolve around a central axis of the rotating table through the connecting rod.

In a preferred embodiment, the inclination adjusting mechanism comprises an inclination adjusting platform, an elastic compression part and an adjusting component, the inclination adjusting platform comprises an upper pressing plate, the molecular beam source furnace is fixed on the upper pressing plate, the elastic compression part is connected with the middle part of the upper pressing plate, the adjusting component is connected with one end of the upper pressing plate, the adjusting component compresses or stretches the elastic compression part to drive the upper pressing plate to incline, the molecular beam source furnace is driven to incline while the upper pressing plate is inclined, and the incident angle and the range of the molecular beam source furnace are changed.

In a preferred embodiment, the inclination angle of the upper platen is equal to the inclination angle of the molecular beam source furnace.

In a preferred embodiment, the tilt adjusting platform further comprises a base located below the upper pressure plate, the adjusting assembly comprises a second driving motor, a moving shaft and a moving groove, one end of the moving shaft penetrates through the upper pressure plate to be connected with the second driving motor, the other end of the moving shaft extends into the moving groove, the moving groove is formed in the base, the moving shaft is driven by the second driving motor to move along the moving groove, and the moving shaft drives the upper pressure plate to tilt while moving.

In a preferred embodiment, the moving shaft and the moving groove are connected through a screw thread.

In a preferred embodiment, the tilt adjusting mechanism further comprises a tilt positioning assembly, and the tilt positioning assembly is arranged at the other end of the upper pressure plate and used for positioning the tilt of the upper pressure plate.

In a preferred embodiment, the inclined positioning assembly comprises a supporting rectangular rod and a positioning groove, one end of the supporting rectangular rod is fixed with the upper pressure plate, the other end of the supporting rectangular rod is a spherical top head, the positioning groove is an arc-shaped groove formed in the base, and the spherical top head is located in the arc-shaped groove and tangent to the arc-shaped groove.

In a preferred embodiment, the tilt adjusting mechanism further comprises a pretightening force providing member, two sides of the elastic compression member are respectively provided with the pretightening force providing member, and the pretightening force providing member is located between the upper pressure plate and the base.

In a preferred embodiment, the formula for calculating the tilt angle of the molecular beam source furnace is as follows:

；

wherein, a is the inclination angle of the molecular beam source furnace, n is the rotation speed of the second driving motor, p is the pitch of the moving shaft, D is the distance between the central axis of the moving shaft and the central axis of the support torque rod, t is the rotation time of the second driving motor, and n & ltt & gt is the number of rotations of the second driving motor.

A method of sample growth, comprising: and growing a thin film on the substrate by using the sample growing device, thereby obtaining a sample. Further, the sample growth method is to grow a thin film on the substrate by using a molecular beam epitaxy method.

A molecular beam epitaxy system comprising said sample growth apparatus. Further, the molecular beam epitaxy system may further include other conventional auxiliary mechanisms, such as a control device, a vacuum device, and the like, without being limited thereto.

Compared with the prior art, the invention has the beneficial effects that: the sample growth device provided by the invention can be used for carrying out multi-substrate molecular beam epitaxial growth by driving the substrate to revolve and adjusting the inclination angle of the molecular beam source furnace in a matching way, so that the substrate can be positioned at different revolution positions, and the molecular beam incident from a single molecular beam source furnace can completely cover the revolution position of the substrate in the substrate revolution process by adjusting the inclination angle of the molecular beam source furnace. Compared with the traditional multi-piece sample growing device, the sample growing device has the advantages of simple and compact structure, lower cost, convenience in loading and unloading and high positioning precision, can adjust the angle of a single molecular beam source furnace to produce a plurality of samples, change the spraying position and well ensure the spraying uniformity.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a sample growth apparatus in an initial state according to one embodiment of the present invention;

FIG. 2 is a schematic view of a rotating part according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a beam source furnace in an inclined state according to an embodiment of the present invention.

Description of reference numerals: 1. the vacuum chamber comprises a vacuum chamber, 2, a rotating part, 21, a rotating platform, 22, a rotating mechanism, 221, a first driving motor, 222, a connecting rod, 223, a sample holder, 224, a heating part, 3, an inclination adjusting part, 31, a baffle plate, 32, an inclination adjusting mechanism, 321, an elastic compression piece, 322, an upper pressure plate, 323, a base, 33, a molecular beam source furnace, 34, a second driving motor, 35, a moving shaft, 36, a moving groove, 37, an inclination positioning component, 371, a support moment rod, 372, a positioning groove, 38, a pre-tightening force providing piece, 4, a substrate, 5, a fixed cushion block, 6 and a spring support rod.

Detailed Description

The present invention will be more fully understood from the following detailed description, which should be read in conjunction with the accompanying drawings. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed embodiment.

Referring to fig. 1, a sample growth apparatus according to an embodiment of the present invention includes a vacuum chamber 1, and a rotation part 2 and an inclination adjustment part 3 located in the vacuum chamber 1, wherein the vacuum chamber 1 mainly provides a clean vacuum environment for sample (e.g., substrate 4) growth, ensuring that a proper molecular mean free path is provided, so as to effectively control the molecular beam to be directed to the sample surface for epitaxial growth without colliding with impurity molecules.

The rotating part 2 is used for carrying a substrate 4 to be epitaxially grown and driving the substrate 4 to revolve. In this embodiment, as shown in fig. 2, the rotating part 2 includes a rotating table 21, a rotating mechanism 22 and the substrate 4, the rotating table 21 is rotatable, the substrate 4 is carried on the rotating mechanism 22, and the rotating mechanism 22 is disposed on the rotating table 21 and drives the substrate 4 to revolve around the central axis of the rotating table 21. In this embodiment, the rotation mechanism 22 specifically includes a first driving motor 221, a connecting rod 222, a sample holder 223, and a heating unit 224, wherein the first driving motor 221 is preferably mounted on the central axis of the rotation stage 21, and may be mounted on another position of the rotation stage 21. The first driving motor 221 is connected with the sample holder 223 through the connecting rod 222, the central axis of the sample holder 223 is parallel to the central axis of the rotating table 21, the sample holder 223 and the central axis of the rotating table 21 are adjusted and placed at a certain distance (the distance can be adjusted as required), the substrate 4 is supported on the sample holder 223, and the first driving motor 221 drives the sample holder 223 through the connecting rod 222 to drive the substrate 4 to revolve around the central axis of the rotating table 21. Preferably, the heating part 224 is disposed on the sample holder 223 and is configured to heat the sample holder 223, so that the molecular beam emitted from the molecular beam source furnace 33 is deposited on the substrate 4 at a certain temperature, and the substrate 4 reacts with the molecular beam to perform molecular beam epitaxial growth to form an epitaxial layer.

The tilt adjusting part 3 is used for adjusting the tilt angle of the molecular beam source furnace 33, so that the molecular beam incident from the molecular beam source furnace 33 completely covers the substrates 4 at different revolving positions during the revolution of the substrates 4 driven by the rotating part 2. In this embodiment, the tilt adjusting portion 3 specifically includes a baffle 31, a tilt adjusting mechanism 32, and a molecular beam source furnace 33 connected to the tilt adjusting mechanism 32, and the tilt adjusting mechanism 32 specifically includes a tilt adjusting platform, an elastic compression member 321, and an adjusting assembly, where the tilt adjusting platform includes an upper press plate 322 and a base 323 that are oppositely disposed from top to bottom, the upper press plate 322 is horizontally disposed, the elastic compression member 321 is disposed in the middle of the upper press plate 322 and located between the upper press plate 322 and the base 323, and a central axis of the elastic compression member 321 preferably coincides with a central axis of the upper press plate 322, and in implementation, the elastic compression member 321 may be a flexible corrugated tube. The molecular beam source furnace 33 and the baffle 31 are fixed on the upper press plate 322, the lower end of the molecular beam source furnace 33 is fixed on the upper press plate 322 through a fixed cushion block 5, the molecular beam source furnace 33 is vertical to the upper press plate 322, preferably, the molecular beam source furnace 33 is heated, so that molecules in the molecular beam source furnace 33 are sprayed on the surface of the substrate 4 with certain beam intensity, and epitaxial growth is carried out. A shutter 31 is positioned in front of the molecular beam source furnace 33 for controlling the switching on and off of the molecular beam source furnace 33, thereby changing the composition and doping of the epitaxial layer formed on the substrate 4. Specifically, the shutter 31 blocks the exit of the molecular beam from the molecular beam source furnace 33, and when the molecular beam is ejected by heating the molecular beam source furnace 33, the shutter 31 is opened, and the molecular beam is emitted.

The adjusting component is connected with one end (such as the left end) of the upper pressing plate 322, and the adjusting component drives one end of the upper pressing plate 322 to incline downwards or upwards by compressing or stretching the elastic compressing piece 321, and synchronously drives the molecular beam source furnace 33 to incline while inclining, so as to change the incidence angle and range of the molecular beam source furnace 33. In this embodiment, the adjusting assembly further includes a second driving motor 34, a moving shaft 35 and a moving slot 36, wherein one end of the moving shaft 35 passes through the upper pressing plate 322 and is connected to the second driving motor 34, and the other end of the moving shaft extends into the moving slot 36, and in practice, the moving shaft 35 may be a threaded shaft. The moving groove 36 is formed on the base 323, and the moving shaft 35 and the moving groove 36 may be screwed during implementation. The moving shaft 35 is rotated by the second driving motor 34, moves up and down along the moving groove 36 while rotating, and moves while tilting the upper platen 322. Specifically, when the moving shaft 35 moves downward along the moving groove 36, the upper press plate 322 is driven to compress the flexible corrugated pipe, so as to drive the corresponding end of the upper press plate 322 to incline downward, and the molecular beam source furnace 33 on the upper press plate is driven to incline leftward while the upper press plate 322 inclines; on the contrary, the corresponding end of the upper press plate 322 is driven to incline upwards, and the molecular beam source furnace 33 on the upper press plate is driven to incline rightwards while the upper press plate 322 is inclined.

The inclination angle of the upper platen 322 is equal to the inclination angle of the molecular beam source furnace 33, wherein the inclination angle of the upper platen 322 can be specifically calculated by the following formula:

；

where a is an inclination angle of the molecular beam source oven 33, n is a rotation speed of the second driving motor 34, p is a pitch of the moving shaft 35, the pitch is a distance that a thread of the moving shaft 35 rotates for one turn, D is a distance between a central axis of the moving shaft 35 and a central axis of the torque rod 371, t is a time for the second driving motor 34 to rotate, and n £ t is a number of turns of the second driving motor 34 to rotate.

Preferably, the tilt adjusting section 3 further includes a tilt positioning assembly 37, and the tilt positioning assembly 37 is disposed at the other end (e.g., right end) of the upper press plate 322 for positioning the tilt of the upper press plate 322. Specifically, in this embodiment, the inclined positioning assembly 37 includes a support rectangular rod 371 and a positioning groove 372, wherein one end of the support rectangular rod 371 is fixed to the upper press plate 322, specifically, one end of the support rectangular rod 371 is provided with a thread, that is, one end of the support rectangular rod 371 is fixedly connected to the upper press plate 322 through the thread, so as to ensure that the upper press plate 322 is stressed in a balanced manner when inclined; the other end of the support rectangular rod 371 is a spherical top, the positioning groove 372 is an arc-shaped groove formed on the base 323, and the spherical top of the support rectangular rod 371 is positioned in the arc-shaped groove and tangent to the arc-shaped groove and used for sliding positioning of the inclination of the upper pressure plate 322. Specifically, when the left end of the upper platen 322 is tilted downward, the spherical heads of the support rectangular rods 371 arc-slide to the upper right along the arc-shaped grooves, whereas the spherical heads of the support rectangular rods 371 arc-slide to the upper left along the arc-shaped grooves.

Preferably, the tilt adjusting portion 3 further comprises a preload providing member 38, and in this embodiment, a preload providing member 38 is disposed on each of two sides of the elastic compressing member 321, and the preload providing member 38 is located between the upper pressing plate 322 and the base 323. In practice, the pre-tightening force providing element 38 may be implemented by a spring, the spring is fixed on the spring support rod 6, the upper pressing plate 322 and the base 323 are respectively provided with a spring support rod 6, the upper end and the lower end of the spring are respectively fixed with a spring support rod 6, and the pre-tightening force providing element 38 provides the installation pre-tightening force of the upper pressing plate 322 and the coupling force during the tilting movement thereof.

In addition, the rotating part 2 and the tilt adjusting part 3 are independent and matched with each other, preferably, the sample holder 223 of the rotating part 2 and the molecular beam source furnace 33 are parallel to each other, and the central axis of the sample holder 223 is coaxial with the central axis of the molecular beam source furnace 33, so that the layout space occupied by the two parts is minimum, and the tilt adjusting coverage of the tilt adjusting part 3 is large.

The specific working principle of the sample growth device in this embodiment is as follows: in the initial state, the position of the whole device is as shown in fig. 1, specifically, the upper press plate 322 is in the horizontal state, the flexible corrugated pipe is in the initial uncompressed or uncompressed state, the molecular beam source furnace 33 is vertically arranged and perpendicular to the upper press plate 322, and the spherical top of the support rectangular rod 371 is vertically positioned in the middle of the arc-shaped groove of the base 323 and tangent to the arc-shaped groove. In the working state, the first driving motor 221 of the rotating part 2 drives the sample holder 223 to drive the substrate 4 to revolve around the central axis of the rotating table 21 through the connecting rod 222, in the process of revolution, as shown in fig. 3, the second driving motor 34 of the inclination adjusting part 3 rotates to drive the threaded shaft to rotate, the threaded shaft is driven to rotate downwards along the moving groove 36 while rotating, the left end of the upper pressing plate 322 is driven to compress the middle flexible corrugated pipe while moving downwards, when the support rectangular rod 371 at the right end of the upper pressing plate 322 rotates downwards along the threads of the threaded shaft, the spherical top head freely slides upwards in the arc-shaped groove due to the inclination of the left end of the upper pressing plate 322, so as to drive the right end of the upper pressing plate 322 to incline upwards, and ensure the whole inclining process of the upper pressing plate 322. The angles of the molecular beam source furnace 33 and the baffle 31 fixed on the upper press plate 322 are also inclined, when the substrate 4 on the sample support 223 revolves around the central axis of the rotating table 21, the direct incidence angle of the molecular beam source furnace 33 is changed by adjusting the inclination angle of the upper press plate 322, so that the molecular beam sprayed by a single molecular beam source furnace 33 can completely cover the surface of the substrate 4, further the epitaxial growth of a plurality of samples is carried out, and the growth uniformity is ensured. In the case of performing epitaxial growth of a plurality of samples, a plurality of substrates 4 may be placed on the sample holder 223, and the plurality of substrates 4 may be uniformly epitaxially grown by rotation of the rotation mechanism 22 and tilt adjustment of the tilt adjustment section 3.

In the present embodiment, by driving the substrate 4 to revolve and adjusting the inclination angle of the molecular beam source furnace 33 in coordination, the substrate 4 can be made to perform multi-substrate molecular beam epitaxial growth by adjusting the inclination angle of the molecular beam source furnace 33 at different revolving positions, and making the molecular beam incident from a single molecular beam source furnace 33 fully cover the revolving position of the substrate 4 during the revolution of the substrate 4. Compared with the traditional multi-piece sample growing device, the sample growing device has the advantages of simple and compact structure, lower cost, convenience in loading and unloading and high positioning precision, can adjust the angle of the single molecular beam source furnace 33 to produce a plurality of samples, change the spraying position and well ensure the spraying uniformity. By using the sample growth device, high-quality crystal thin films can be grown and formed on substrates such as sapphire substrates, SiC substrates, GaN single crystal substrates and the like.

The aspects, embodiments, features and examples of the present invention should be considered as illustrative in all respects and not intended to be limiting of the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

The use of headings and chapters in this disclosure is not meant to limit the disclosure; each section may apply to any aspect, embodiment, or feature of the disclosure.

Unless specifically stated otherwise, use of the terms "comprising", "including", "having" or "having" is generally to be understood as open-ended and not limiting.

While the invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions and/or additions may be made and substantial equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated any use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.