JPH05110011A - Manufacture of electrode substrate - Google Patents

Abstract

PURPOSE:To contrive simplification of an electrode substrate manufacturing process, and to obtain the manufacturing method with which the condition as the expected recording medium can be satisfied when the electrode substrate, constituting a recording medium with which the record reproduction and the like of information is conducted using a tunnel current, is manufactured. CONSTITUTION:The title electrode substrate has rugged surface of 1nm or less, and it has a smooth surface of 1mum square or larger. This is an electrode substrate manufacturing method in which an amorphous metal layer 102 is characteristically provided on the substrate 101 having the main surface formed by cleaved crystal or fused glass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode substrate, and more particularly to a method for manufacturing an electrode substrate used for a recording medium of an information processing device utilizing the principle of a scanning tunneling microscope (hereinafter abbreviated as STM).

[0002]

2. Description of the Related Art In recent years, the use of memory materials has become the core of the electronics industry for computers and related equipment, video discs, digital audio discs, etc., and the development of such materials is extremely active. The performance required for memory materials varies depending on the application, but in general, high density and large recording capacity, fast recording / playback response speed, low power consumption, high productivity, low cost, etc. Can be raised.

Until now, semiconductor memories and magnetic memories made of magnetic materials or semiconductors have been mainly used, but with the recent development of laser technology, optical memories using organic thin films such as organic dyes and photopolymers have become inexpensive. High-density recording media have appeared.

On the other hand, recently, a scanning tunneling microscope (hereinafter abbreviated as STM) has been developed which enables direct observation of the electronic structure of surface atoms of a conductor [G. Binnig et al. P
hys. Rev. Lett, 49, 57 (198
2)], high-resolution measurement of real space images can be performed regardless of whether it is a single crystal or an amorphous material. Moreover, it has the advantage that it can be observed with low power without damaging the sample with an electric current. Since it operates and can be used for various materials, a wide range of applications are expected.

Such an STM utilizes the fact that a tunnel current flows when a voltage is applied between a metal probe (probe electrode) and a conductive substance to bring them close to a distance of about 1 nm. This current is very sensitive to changes in the distance between the two. By scanning the probe so that the tunnel current is kept constant, it is possible to read various kinds of information regarding the whole electron cloud in the real space. At this time, the resolution in the in-plane direction is about 0.1 nm.

Therefore, if the principle of STM is applied,
It is possible to sufficiently perform high-density recording / reproducing on the atomic order (sub-nanometer). For example, JP-A-61
In the recording / reproducing apparatus disclosed in -80536, atomic particles adsorbed on the surface of a medium are removed by an electron beam or the like, writing is performed, and this data is reproduced by STM.

A method has been proposed in which recording / reproducing is performed by STM using a thin film layer of a material having a memory effect for voltage / current switching characteristics, such as a π-electron organic compound or a chalcogen compound, as a recording layer. [JP-A-63-
161552, JP-A-63-161553]. According to this method, the recording bit size is 10n.
If m is set, a large capacity recording / reproducing of 10 ¹² bit / cm ² is possible.

FIG. 3 shows a configuration example of an information processing apparatus to which the STM is applied. The following is a description with reference to the drawings.

Reference numeral 101 is a substrate, 102 is a metal electrode layer, 1
Reference numeral 03 is a recording layer. 201 is an XY stage, 202 is a probe electrode, 203 is a support for the probe electrode, 204
Is a Z-axis linear actuator that drives the probe electrode in the Z direction, and 205 and 206 are X and Y stages, respectively.
A linear actuator driven in the Y direction, and 207 is a pulse voltage circuit.

Reference numeral 301 denotes the probe electrode 202 to the recording layer 1
This is an amplifier for detecting a tunnel current flowing to the electrode layer 102 via 03. Reference numeral 302 is a logarithmic compressor for converting a change in tunnel current into a value proportional to the gap distance between the probe electrode 202 and the recording layer 103, and 303 is a low-pass filter for extracting surface unevenness components of the recording layer 103. .. 304 is a reference voltage V _REF and a low pass filter 303
Is an error amplifier for detecting an error from the output of the Z-axis linear actuator 204, and 305 is a driver for driving the Z-axis linear actuator 204. A drive circuit 306 controls the position of the XY stage 201. A high-pass filter 307 separates the data components.

FIG. 4 shows a cross section of a conventional recording medium and the tip of the probe electrode 202.

Reference numeral 401 is a data bit recorded in the recording layer 103, and 402 is a crystal grain formed when the electrode layer 102 is formed on the substrate 101. The size of the crystal grain 402 is about 30 to 50 nm when a normal vacuum deposition method, a sputtering method, or the like is used as a method for manufacturing the electrode layer 102.

The gap between the probe electrode 202 and the recording layer 103 can be kept constant by the circuit configuration shown in FIG. That is, after detecting the tunnel current flowing between the probe electrode 202 and the recording layer 103 and passing through the logarithmic compressor 302 and the low-pass filter 303, this value is compared with a reference voltage so that this comparison value approaches zero. On the probe electrode 2
The gap between the probe electrode 202 and the recording layer 103 can be made constant by controlling the Z-axis linear actuator 204 that supports 02.

Further, by driving the XY stage 201, the probe electrode 202 traces the surface of the recording medium, and by separating the high frequency components of the signal at point (a), the data in the recording layer 103 can be detected.

FIG. 5 shows the signal intensity spectrum with respect to the frequency of the signal at point (a) at this time.

A signal having a frequency component of f ₀ or less is transmitted to the substrate 101.
This is due to the gradual ups and downs of the medium due to warpage and distortion of the medium. The signal centered on f ₁ is due to the unevenness of the surface of the recording layer 103, and is mainly due to the crystal grains 402 generated when the electrode material is formed. f ₂ is a carrier wave component of recording data, and 403 is a data signal band. f ₃ is the recording layer 1
This is a signal component generated from the 03 atom and molecular arrangement.

[0017]

When the recording medium shown in the prior art is used, there are the following problems.

In order to perform high-density recording by utilizing the high resolution characteristic of STM, the data signal band 403 is set to f ₁ and f _3.
Must be placed between. In this case, the high-pass filter 307 having the cutoff frequency f _c is used to separate the data components.
To use.

However, the foot of the signal component of f ₁ overlaps the data signal band 403. This is because the signal component of f ₁ is caused by the crystal grains 402 of the electrode layer 102, and the data recording size and the bit interval are close to 1 to 10 nm with respect to 30 to 50 nm of the crystal grains 402. by. Therefore, the S / N ratio of data reproduction may decrease.

In order to enable a high S / N ratio and high-speed reproduction, it is important to keep the spread of the signal component of f ₁ small. For this purpose, an electrode substrate having a smooth surface with surface irregularities of 1 nm or less and a size of 1 μm □ or more is desired.

As one means for obtaining such an electrode substrate, the surface unevenness is 1 nm or less and the size is 1 μm □.
An electrode layer is formed on the first substrate having a smooth surface as described above by a vapor deposition method or the like, then a second substrate is prepared, an adhesive is applied to the second substrate, and then electrodes are formed. There is a method of forming a desired electrode substrate by bringing it into close contact with a first substrate, transferring the electrodes formed on the first substrate to the second substrate, and copying the first smooth surface. But
In such a method, the process for obtaining an electrode substrate having a smooth surface is complicated, and there are restrictions such as selecting an electrode material having weak adhesion to the first substrate for transferring the electrode layer, which is industrially limited. A more efficient and simple manufacturing method has been desired.

That is, the object of the present invention is to
An object of the present invention is to provide a simpler method for manufacturing an electrode substrate by eliminating the complexity of the manufacturing process as described above.

[0023]

The structure of the present invention for achieving the above object is as follows.

That is, the surface unevenness is 1 nm or less,
On a base material having a smooth surface with a size of 1 μm □ or more,
It is a method for manufacturing an electrode substrate, which is characterized by forming an amorphous metal layer.

As the base material, it is preferable to use a crystal substrate whose main surface is cleaved or a glass substrate whose main surface is formed by melting.
When forming the above-mentioned amorphous metal layer, a manufacturing method in which the amorphous metal layer is formed by directly adhering to the base material from the gas phase is preferable.

According to such a manufacturing method, an electrode substrate having a smooth surface can be manufactured efficiently and simply as compared with the conventional method.

The present invention will be described in detail below. First, a smooth substrate 101 is prepared. This substrate has a surface roughness of 1n
It is necessary to have a smooth surface of m or less and 1 μm □ or more. Here, in the measurement of the surface unevenness, the tip of the microprobe is brought close to the sample substrate surface, and the atomic force acting between the tip atom of the microprobe and the atom on the sample substrate surface is measured to observe the sample surface shape. AFM (Atomic-Force)
-Microcopy).

When such an AFM is used, the conductivity of the sample,
It is possible to measure the surface shape of a sample with atomic resolution regardless of the insulating property. The present inventors evaluated the surface of various materials using AFM, and found that the following materials were suitable as the smooth substrate in the present invention. ． Cleavage surface of crystal: A very smooth surface can be easily obtained as the cleavage surface of the crystal.
Examples thereof include gO, TiC, Si, and HOPG (highly oriented graphite). ． Molten glass surface ... For example, float glass, #
7059 fusion, fused quartz, etc. are mentioned.

When the surface shape of the above material was measured by AFM, the surface unevenness was 1 in all areas of 10 μm square.
It was less than or equal to nm. In particular, the mica cleavage surface is suitable for the smooth substrate used in the present invention because it has few steps on the lattice plane that occur during cleavage.

Next, as shown in FIG. 1, the electrode layer 102 is formed on the smooth substrate 101. Electrode layer 10 according to the present invention
A material having conductivity and being amorphous is desired as 2. The metal that can be the amorphous metal layer is A
u-Si, Au-Ge, Au-Sn, Au-Pb, Au
-Si-Ge, Au-Pb-Si, Ag-Pb, Ag-
Cu, Ag-Pb-Si, Cu-Zr, Pd-Si, P
d-Cu-Si, Pt-Sb, Pt-Ge, Pt-T
a, Rh-Nb, Rh-Ta, Re-Si, Ir-N
There are many materials such as b, Ir-Ta, Ir-Ta-B, and transition metal alloys. A large number of these amorphous metals can be considered depending on the combination of constituent elements and compositions, and the degree of freedom can be expanded depending on the forming method.

Well-known methods for forming an amorphous metal layer are a method of directly depositing an amorphous metal on a substrate from a vapor phase such as vapor deposition or sputtering, and a method of rapidly cooling a liquid. However, the liquid quenching method is difficult to form directly on a smooth substrate, and vapor deposition, ion plating, cluster ion beam, sputtering, and other methods that directly form an amorphous metal on the substrate from the vapor phase are suitable. ing.

The above-mentioned forming method is conventionally known as a thin film forming technique, and when forming an amorphous metal layer, this technique can be sufficiently formed, but preferably an amorphous metal is formed. At this time, it is desirable to sufficiently cool the smooth substrate 101. This is because the composition range of the constituent elements forming the amorphous metal layer film can be expanded by cooling. In addition, the formed electrode layer 1
It can be confirmed by X-ray diffraction that 02 is amorphous.

Since the electrode layer 102 made of the amorphous metal layer thus obtained has no crystal grains, the substrate 1
A smooth electrode substrate having a smooth surface with surface irregularities of 1 nm or less and 1 μm □ or more is obtained, which well reflects the smoothness of No. 01.

Next, as shown in FIG. 1, the recording layer 103 is formed on the electrode layer 102 of the smooth electrode substrate. As the recording layer 103, a material having a memory switching phenomenon (electric memory effect) in current-voltage characteristics, for example, a molecule having both a group having a π electron level and a group having only a σ electron level is formed on an electrode. It is possible to use a laminated organic monomolecular film or a cumulative film thereof. The electric memory effect is brought to a state (ON state, OFF state in FIG. 6) which shows two or more different conductivity in the state where the thin film such as the organic monomolecular film and its accumulated film is arranged between the pair of electrodes. By applying a voltage exceeding a threshold value that allows transition, it is possible to reversibly transition (switch) to a low resistance state (ON state) and a high resistance state (OFF state). Further, each state can be retained (memory) without applying a voltage.

In general, most of the organic materials exhibit an insulating property or a semi-insulating property, so that there are a great variety of organic materials having a group having a π electron level applicable to the recording layer. Examples of the structure of a dye having a π electron system suitable for the recording layer include a dye having a porphyrin skeleton such as phthalocyanine and tetraphenylporphyrin, an azulene dye having a squarylium group and a croconic methine group as a binding chain, quinoline, and benzothiazole. , Benzoxazole, and other two nitrogen-containing heterocycles bound by a squarylium group and a croconic methine group, or a cyanine-similar dye, or a condensed polycyclic aromatic compound such as a cyanine dye, anthracene, and pyrene, and an aromatic ring and a heterocycle A chain compound obtained by polymerizing a compound and a polymer of a diacetylene group, further, a derivative of tetracyanoquinodimethane or tetrathiafulvalene and its analog and its charge transfer complex, and further ferrocene,
Examples thereof include metal complex compounds such as trisbipyridine ruthenium complex.

Examples of suitable polymer materials for the recording layer include biopolymers such as addition polymers such as polyacrylic acid derivatives, condensation polymers such as polyimide, ring-opening polymers such as nylon. ..

Regarding the formation of the recording layer 103, a vapor deposition method, a cluster ion beam method or the like can be applied concretely, but Langmuir is known among the known prior arts because of its controllability, ease and reproducibility. Blodgett method (LB)
The method is very suitable.

According to this LB method, a monomolecular film of an organic compound having a hydrophobic site and a hydrophilic site in one molecule or a cumulative film thereof can be easily formed on a substrate, and a molecular order thickness is obtained. It is possible to stably supply a uniform and uniform organic ultrathin film having a large area.

In the LB method, in a molecule having a structure having a hydrophilic site and a hydrophobic site in the molecule, when the balance between them (the amphipathic balance) is appropriately maintained,
This is a method for forming a monomolecular film or a cumulative film thereof by utilizing the fact that the molecule becomes a monomolecular layer with the hydrophilic group facing downward on the water surface.

Examples of the group constituting the hydrophobic moiety include various widely-known hydrophobic groups such as saturated and unsaturated hydrocarbon groups, condensed polycyclic aromatic groups and chain polycyclic phenyl groups. Each of these alone or in combination of a plurality thereof constitutes a hydrophobic site.

On the other hand, the most typical constituents of the hydrophilic moiety are, for example, a carboxyl group, an ester group, an acid amide group, an imide group, a hydroxyl group, and further an amino group (1,2,3 and quaternary group). ) And other hydrophilic groups.

Organic molecules having both these hydrophobic groups and hydrophilic groups in a well-balanced manner can form a monomolecular film on the water surface, and are extremely suitable materials for the present invention. ..

The electric memory effect of the compounds having these π-electron levels has been observed at a film thickness of several tens of nm or less, but from the viewpoint of film forming property and uniformity, the film thickness should be 5 to 300 Å. Is preferred.

FIG. 2 shows the frequency spectrum of the signal at point (a) when the recording medium using the smoothing electrode substrate according to the present invention is used in the information processing apparatus of FIG. The signal of the frequency component of f ₀ or less is due to the gradual undulation of the medium due to the warp or distortion of the substrate 101. f ₂ is a carrier wave component of recording data, and 403 is a data signal band. f ₃ is a signal component generated from the atomic and molecular arrangement of the recording layer 103.

The signal centered on f ₁ is a slight irregularity of the surface of the base material transferred to the surface of the electrode layer 102, and this irregularity is made equal to or smaller than the recording signal of data. The change in the unevenness is 1 nm or less in the recording / reproduction applying the STM. Further, in the recording medium using the electrode substrate of the present invention, the size of the smooth surface of the recording layer 103 is 1 μm □ or more. As a result, the following operational effects are obtained. ． The signal component f ₁ and the data signal band 403 due to the unevenness of the surface of the recording layer 103 do not overlap with each other, and the S / N is not reduced due to the spread of the spectrum of f ₁ . That is, the data error rate can be reduced. ． Since there is no unevenness on the surface of the recording layer 103, the recording layer 103
The Z-axis displacement of the probe electrode 202 is small when XY scanning is performed while keeping the gap between the surface of the probe electrode 202 and the probe electrode 202 constant. Therefore, the XY stage 201 can be driven at an extremely high speed. ． Since there is no unevenness on the surface of the recording layer 103, the tip of the probe electrode 202, that is, the position of the tip atom through which the tunnel current flows is stably selected. In addition, as seen on the surface of the recording layer 103 having irregularities, the probe electrode 202
The so-called ghost phenomenon that tunnel current flows between the plurality of atoms and the recording layer 103 disappears.

[0046]

EXAMPLES Examples of the present invention will be specifically described below.

Example 1 As shown in FIG. 1, a mica plate is cleaved in the atmosphere to form a smooth substrate 101. Then, a Pt-Ta alloy (Pt 50%, Ta 50
%) To form the electrode layer 102. The electrode layer 10
2, the substrate temperature was kept at room temperature, Ar pressure was 2 mTorr,
Deposition rate 300Å / min, ultimate pressure 5 × 10 ^-7 Tor
r and film thickness 2000Å.

X of the electrode layer 102 thus obtained
When line diffraction measurement was performed, no peak other than the peak of the mica plate was observed and it was an amorphous layer. Further, when the surface was observed by STM, the surface irregularities were 1 nm or less in 10 μm □.

Next, a four-layer polyimide LB film was formed on this smooth electrode substrate to form a recording layer 103. Hereinafter, a method of forming the recording layer 103 using the polyimide LB film will be described.

A polyamic acid represented by the chemical formula 1 is mixed with an N, N'-dimethylacetamide-benzene mixed solvent (1: 1 V /
V) (monomer equivalent concentration 1 × 10 ⁻³ M),
A separately prepared 1 × 10 ⁻³ M solution of N, N-dimethyloctadecylamine in the same solvent was mixed at a ratio of 1: 2 (V / V) to prepare a polyamic acid octadecylamine salt solution represented by the chemical formula (2).

[0051]

[Chemical 1]

[0052]

[Chemical 2] The solution was spread on a water phase made of pure water having a water temperature of 20 ° C. to form a monomolecular film on the water surface. After evaporation of the solvent, the surface pressure was increased to 25 mN / m. While keeping the surface pressure constant, speed 5 across the water surface of the smooth electrode substrate.
After gently immersing at 5 mm / min, then 5 mm / mi
It was gently pulled up with n to produce a two-layer Y-type monomolecular cumulative film. This operation was repeated to form a monolayer cumulative film of four layers of octadecylamine polyamic acid salt.

Next, the substrate is depressurized (up to 1 mmHg).
Under heating at 300 ° C. for 10 minutes, the octadecylamine polyamic acid salt is imidized (Formula 3),

[0054]

[Chemical 3] A 4-layer polyimide monomolecular cumulative film was obtained.

Next, the surface shape of the recording medium manufactured by the above-described method was examined by the information processing apparatus shown in FIG. 3, and the surface of the recording medium reflected the smooth surface of the electrode. The surface roughness was 1 nm or less.

Next, recording / reproducing experiments were conducted. A probe electrode 202 made of platinum / rhodium was used as the probe electrode 202. This probe electrode 202 is controlled by a piezoelectric element so as to keep the current constant by controlling the distance (Z) from the surface of the recording layer 103.
Is finely controlled. Further, the linear actuators 204, 205, 206 keep the distance Z constant,
It is designed to allow fine movement control in the in-plane (X, Y) directions.

Further, the probe electrode 202 can directly perform recording / reproducing / erasing. Further, the recording medium is placed on the high precision XY stage 201 and can be moved to an arbitrary position.

The recording medium having the recording layer 103 in which the above-mentioned four polyimide layers are accumulated was placed on the XY stage 201. Next, the probe electrode 202 and the electrode layer 1 of the recording medium
A voltage of +1.5 V was applied between the probe electrodes 202 and 02, and the distance (Z) between the probe electrode 202 and the surface of the recording layer 103 was adjusted while monitoring the current. At this time, the probe current Ip for controlling the distance Z between the probe electrode 202 and the surface of the recording layer 103 was set to be 10 ⁻¹⁰ A ≧ Ip ≧ 10 ⁻¹¹ A.

Next, the probe electrode 202 is attached to the recording layer 103.
Information was recorded at a pitch of 100 Å while scanning above. To record such information, the probe electrode 202 is
Side, the electrode layer 102 to the-side, the rectangular pulse voltage (first pulse voltage) _exceeding the threshold voltage V _th ON at which the electric memory material (4 layers of polyimide LB film) changes to a low resistance state (ON state). Was added. After that, the probe electrode 202 was returned to the recording start point, and the recording layer 103 was scanned again.
At this time, adjustment was made so that Z = constant when reading the recording. As a result, it was shown that the probe current of about 10 nA flows in the data bit 401 and is in the ON state.

The probe voltage is a threshold voltage V _th OFF at which the electric memory material changes from the ON state to the OFF state.
It was also confirmed that all recording states were erased and transitioned to the OFF state as a result of tracing the recording position again by setting the voltage to 10 V (second pulse voltage) exceeding the value. Further, when the error rate of the read data was examined at a constant read speed, it was 10 ⁻⁴ in the conventional example, but 10 in the present example.
It became possible to make it extremely small as ^-7 .

Example 2 A fused quartz plate was used as a smooth substrate 101.
And Pt-Ta on the smooth substrate 101 by the sputtering method.
An alloy (Pt 50%, Ta 50%) is formed into a film, and the electrode layer 10 is formed.
Form 2. The electrode layer 102 has a substrate temperature kept at room temperature, an Ar pressure of 2 mTorr, and a film forming rate of 300 Å / mi.
n, ultimate pressure 5 × 10 ⁻⁷ Torr, and film thickness 2000 Å.

X of the electrode layer 102 thus obtained
A line diffraction measurement was performed, but no crystallinity peak was observed. Also, when the surface was observed by STM, it was 10
In μm □, the surface irregularities were 1 nm or less. Further, when a recording layer was formed in the same manner as in Example 1 and recording / reproduction / erasing experiments were performed, the same results as in Example 1 were obtained.

(Example 3) A fused quartz plate was used as a smooth substrate 101.
Then, an Au—Y alloy (Au 80%, Y 20%) is deposited on the smooth substrate 101 by the sputtering method to form the electrode layer 102. The electrode layer 102 has a substrate temperature cooled by liquid nitrogen, an Ar pressure of 2 mTorr, and a film forming rate of 300Å /
min, ultimate pressure 5 × 10 ⁻⁷ Torr, film thickness 2000Å
It went on condition of.

X of the electrode layer 102 thus obtained
A line diffraction measurement was performed, but no crystallinity peak was observed. Also, when the surface was observed by STM, it was 10
In μm □, the surface irregularities were 1 nm or less. Further, when a recording layer was formed in the same manner as in Example 1 and recording / reproduction / erasing experiments were performed, the same results as in Example 1 were obtained.

[0065]

As described above, according to the manufacturing method of the present invention, it is possible to easily obtain a smooth electrode substrate in one step without complicated steps, and there is no step of separating electrode layers. As a result, it is not necessary to consider the adhesiveness, and as a result, the degree of freedom in material selection is expanded, and it is possible to supply an electrode substrate used for an information processing device or the like to which STM is applied extremely industrially.

[Brief description of drawings]

FIG. 1 shows a schematic sectional view of an electrode substrate obtained by the present invention.

FIG. 2 shows a frequency spectrum diagram of a recording medium using an electrode substrate obtained by the present invention.

FIG. 3 shows a block diagram of an information processing apparatus to which STM is applied.

FIG. 4 shows a schematic cross-sectional view of a conventional electrode substrate.

FIG. 5 shows a diagram of a frequency spectrum of a reproduction signal of a recording medium using an electrode substrate obtained by a conventional example.

FIG. 6 shows a current-voltage characteristic graph when recording is performed on a recording medium.

[Explanation of symbols]

 101 substrate 102 electrode layer 103 recording layer 201 XY stage 202 probe electrode 203 support 204 Z-axis linear actuator 205 X-axis linear actuator 206 Y-axis linear actuator 207 pulse voltage circuit 301 amplifier 302 logarithmic compressor 303 low-pass filter 304 error amplifier 305 Driver 306 Drive circuit 307 High-pass filter 401 Data bit 402 Crystal grain 403 Data signal band

Claims (3)

[Claims] 1. A method of manufacturing an electrode substrate, comprising forming an amorphous metal layer on a base material having a smooth surface having surface irregularities of 1 nm or less and a size of 1 μm □ or more. 2. The method of manufacturing an electrode substrate according to claim 1, wherein a substrate made of glass whose main surface is cleaved or glass formed by melting is used as a base material. 3. The method for producing an electrode substrate according to claim 1, wherein the amorphous metal layer is formed by directly adhering to the base material from a vapor phase when forming the amorphous metal layer.