WO2008046398A2

WO2008046398A2 - Method for producing self-assembled monolayers on solid body surfaces

Info

Publication number: WO2008046398A2
Application number: PCT/DE2007/001833
Authority: WO
Inventors: Bernd Holzapfel
Original assignee: Philipps-Universität Marburg
Priority date: 2006-10-16
Filing date: 2007-10-16
Publication date: 2008-04-24
Also published as: WO2008046398A3; DE102006049432A1

Abstract

The present invention relates to a method for producing self-assembled monolayers (SAMs) on solid body surfaces, wherein impurities of the surfaces are minimized by the use of solvents and/or oxygen. The substances to be assembled are evaporated and vapour deposited in the oxygen-free gas stream onto the solid body surface to be coated at pressures ranging between 10<SUP>-6</SUP> and 10<SUP>-8</SUP> mbar. Conventional methods in which SAMs are deposited from a solution require deposition times ranging from some hours to several days. The inventive method, however, allows the deposition of monolayers within 30 to 60 minutes.

Description

Patent application

Process for the preparation of self-aggregating monolayers on solid surfaces

The present invention describes a process for the preparation of self-aggregating monolayers (SAMs) in a high vacuum in the gas phase with oxygen exclusion in the protective gas stream. The surface to be vaporized is cleaned and heated in a high vacuum to a temperature ≥ 100 O. The substance to be aggregated is heated until it evaporates and this vapor is vaporized onto the surface via an introduction system together with an oxygen-free inert gas. Monolayers form within 30 to 60 minutes.

Description and introduction of the general field of the invention

The present invention relates to the fields of physical solid state chemistry, surface chemistry and materials science.

State of the art

Self-assembling monolayers, also known as self-assembling monolayers or SAMs for short, are used in electronic switches, microelectronic and nanoelectronic components, optical and electro-optical devices, gates, storage media and sensors, since they offer a variety of surface modification possibilities. The interest in these monolayers is due to applications in terms of settable wettability, biocompatibility and corrosion resistance of surfaces.

SAMs are highly ordered molecular assemblies that form spontaneously by chemisorption of functionalized molecules on a variety of solid-state surface substrates. The molecules that make up the self-aggregating monolayer organize laterally; This is usually done by van der Waals interactions between long aliphatic chains.

The use of SAMs, for example, is of interest for many electronic, optical and electro-optical devices, as SAMs allow the targeted modification of surface areas, such as the modification of surface hydrophobicity, packing of the layers and electrical insulation. Since SAMs have excellent barrier properties, their use as a protective layer on metallic surfaces is considered because they are thin, highly crystalline Form barrier films. Gold is widely used as a surface material and is used extensively in the electronics industry, for example, for the manufacture of integrated circuits. As a relatively inert metal, it is also used as a protective layer in certain chemical environments; for example, as liner material for the ink chambers in printheads of ink jet printers. However, gold dissolves under suitable chemical or electrochemical conditions, therefore the ability of SAMs to form a very thin protective layer for such metallic surfaces under such chemical conditions is considered a very attractive utility of self-aggregating monolayers.

However, SAMs also have some disadvantages that still limit their commercial applicability in industrial processes. In the vast majority of the previously known methods, the deposition of the SAMs from suitable solvents. As a rule, the surface of a solid to be coated contains discontinuities which result from the production process determined by the desired application, so that the deposition of a monolayer in the form of a flat layer on the solid surface is difficult to control. Furthermore, impurities of the solvent lead to impurities in the self-aggregating monolayer and the deposition proceeds very slowly. Typical deposition times range from a few hours to several days.

The prior art knows a variety of methods for the production of

SAMs out of solutions. For example, US 2006/008678 A1 describes the preparation of SAMs comprising dendrimers, the dendrimers being precipitated from a solution. or the substrate to be coated is exposed to a dendrimer in compressed or supercritical CO2. The use of compressed CO2 as a solvent medium for a substance to be deposited as SAM is also disclosed in US 2002/0197879 A1 and US 2002/0164419 A1. No. 5,514,501 A1 describes a process for the photostructuring of thiolate SAMs in which two SAM layers of thiolates are deposited successively on a noble metal substrate, the thiolates being in solution before deposition. US Pat. No. 6,821,485 B2 discloses a device for guiding a microfluidic flow within canals and a method for the production thereof, wherein the channels are coated with a SAM and the SAM is precipitated from solution. US Pat. No. 6,485,984 B2 discloses a method for producing biochips which contain calixarene SAMs on a gold carrier, wherein the SAMs are precipitated from solution.

Furthermore, the prior art knows processes for the production of SAMs, in which the SAMs are first applied from a solution to a stamp and then applied by means of stamping technique on the substrate to be coated - a solid surface. Thus, US Pat. No. 6,180,288 B1 describes a method for producing a sensor device which contains a SAM, wherein the SAM is applied from solution by means of stamping technology. No. 6,866,791 B1 describes a process for coating nickel oxide, in which first a stamp is coated with the dissolved SAM substance and the stamp is then stamped on nickel oxide. No. 6,380,101 B1 discloses how SAMs from alkanephosphonic acids can be applied to indium zinc oxide or indium tin oxide substrates by means of microcontact printing. In addition, methods are known in which SAMs are deposited from the vapor phase on a substrate. Thus, US 2006/0062921 A1 describes a method for producing a gradient on a surface by means of vapor diffusion, in which a surface is held under a set of one or more conditions, wherein the set of conditions is selected from pressure, pH, temperature and combinations thereof. Subsequently, a stamp comprising a fugitive stencil material is positioned adjacent to that surface and then varying the one or more conditions to thereby deposit variable concentrations of the stencil material at various points on the surface. DE 10 2004 009 600 A1. Describes the deposition of a substrate on a gate electrode, wherein the material for the gate electrode is present in solution. Then the gate electrode becomes _. with an organic compound having a phosphonic acid group, brought into contact to deposit a SAM on the gate electrode. The SAM can be applied by vapor deposition. US 2004/0223256 A1 discloses a coating method for applying corrosion protection to magnetic read-write heads, in which the monolayer surface passes through. a vacuum coating process can be applied; however, this process does not include a permanent inert gas flow. US 2004/0025733 A1 describes a method for surface modification of optical elements by applying a SAM in order to adjust the hydrophilicity or hydrophobicity of the element, wherein the modifying agent from which the SAM is formed is released into a vacuum chamber and the surface to be coated also located in this vacuum chamber. However, no inert gas is used in this process. In the known processes which deposit SAMs from the gas phase, the deposition does not take place in a permanent stream of inert gas; therefore, impurities of the SAMs to be formed by oxygen can not be excluded.

By contrast, the present invention is based on the deposition of a SAM on a solid surface in the permanent, oxygen-free gas stream at pressures between 10 ^"6 and 10 ^{" 8} mbar and provides within a few minutes SAMs ₁ which are substantially free of contaminants. The adhesion of the SAMs on the solid surfaces is achieved by adhesion. The process according to the invention therefore offers the following advantages over known processes: time savings in the production, saving of chemicals (solvents) and devices (stamps) as well as higher purity of the products.

task

The object of the present invention is to provide a process for the production of self-aggregating monolayers (SAMs) on solid surfaces, in which contamination of the surfaces by solvents and / or oxygen is minimized.

Solution of the task

This object is achieved by the substance to be aggregated or the substances to be aggregated is heated to evaporation and this steam in a permanent, oxygen-free gas stream at a temperature of ≥ 100 O and a pressure of 10 ^'6 to 10 ^{' 8} mbar within from 30 to 60 minutes on the coated solid surface is evaporated.

In the process according to the invention, the adhesion of the self-aggregating monolayers to the solid surface occurs by adhesion. The deposition of the SAM molecules takes place in the permanent gas stream.

Surfaces that can be coated by the method of the present invention include, but are not limited to, metals, metal oxides, conductive polymers, electroactive materials, and semiconductors. For example, but not limited to, metals and metal oxides are selected from titanium, titanium dioxide, tin, tin oxide, silicon, silica, iron, iron ¹¹¹ oxide, silver, gold, copper, platinum, palladium, nickel, aluminum, steel, indium. indium tin oxide, fluoride doped tin oxide, ruthenium oxide, germanium cadmium selenide, cadmium selenide, cadmium sulfide, titanium alloys. Furthermore, the surface may be a single substrate, for example, a semiconductor material such as silicon, silicon germanium, silicon carbide, a disk substrate for magnetic recording media, or a composite substrate in which one or more films of one or more further materials were deposited on the single substrate. The film materials may be, for example, a metal such as gold or silver or an insulator such as silicon oxide, silicon nitride, silicon oxynitride, a dielectric material, a polysilicon or a metal silicide, a glass or an indium tin oxide.

The surfaces on which a self-aggregating monolayer is to be applied are preferably cleaned beforehand. Those skilled in the methods for cleaning surfaces on which SAMs are to be applied, known. He can use them without departing from the scope of the claims. These cleaning methods include rinsing the surface with an organic solvent such as ethanol, acetone, isopropanol, further purification by oxidation with Caro's acid H ₂ SO ₅ or by UV light and cleaning in an ultrasonic bath followed by drying.

The oxygen-free gas for generating the permanent gas stream is selected from the group helium, neon, argon, krypton, xenon, nitrogen, carbon monoxide, carbon dioxide. High purity gas is used, i. the degree of purity is at least 3.5 according to dot notation.

The substance to be aggregated on the solid surface is selected from Biphenyls, for example nitrobiphenylthiol, hydroxybiphenyl,

Alkylchlorosilanes, for example monochlorosilanes, perfluorooctadecyltrichlorosilanes, tridecafluoro-x-tetrahydrooctyltrichlorosilanes or, generally, alkylhalosilanes, non-chlorine-containing dimethylaminosilanes

- Alkenes, for example 1-octadecene

Fullerenes and disilabutanes for the deposition of high-temperature-resistant SiC monolayers,

- Alkyl siloxanes, alkyl silanes, alkyl thiols

Alternatively, a precursor material can also be used. A precursor here is to be understood as meaning a precursor substance whose molecules contain the material-constituting chemical constituents of the layer, i. The self-aggregating monolayer to be formed already contains all or part of its molecular structure. Precursor materials which can be used according to the invention consist of molecules having a functional group which reacts with a surface of silicon if silicon is chosen as the solid surface to be coated. These include, for example, all organic chlorosilanes, including perfluoroalkylchlorosilanes and dimethyldichlorosilanes.

Alternatively, a mixture to aggregating substances or their precursors can be evaporated, if the vapor pressures of substances to be aggregated or precursors differ by a maximum of 2 ⁴ IO ^"4 mbar. Self-aggregating monolayers which are produced on solid surfaces by means of the method according to the invention can be used, for example, in the production of electronic, optical and electro-optical components, for example in sensor technology or in microswitches for airbag deployment. The person skilled in the art knows how to use mask-lithographic methods for nano-structuring of semiconductors on solid surfaces with SAMs. Furthermore, the SAMs produced by the method according to the invention can be chemically changed by means of electron beams. SAMs are also suitable as corrosion protection and as adhesion promoters in composite materials.

The inventive method is also suitable for the production of medical stents, wherein the metallic solid state materials of the stents for the purpose of better tissue compatibility with SAMs are coated from a physiologically acceptable material. Semipermeable membranes and substrates for biological cell cultures can also be produced by SAMs according to the method of the invention.

embodiments

1. Hydroxybiphenyl Monofag on Siliconhydrideoberflächen by deposition from the gas phase

Caro's acid is freshly made from 30% hydrogen peroxide and concentrated sulfuric acid (1: 3 v / v). Silicon wafers (3 cm * 1 cm * 0.5 mm) are placed in the freshly prepared Caro's acid for 30 minutes, then rinsed with water with a maximum conductivity of 0.05 μS and then with methanol pa and dried in a stream of nitrogen. Thereafter, the wafers are placed in 48% hydrofluoric acid for 5 minutes to 10 minutes, rinsed with anhydrous toluene and first pre-dried in a stream of nitrogen. Thereafter, the wafer (FIG. 1) are in an argon-purged vaporization converted in vacuo at 9 * 10 ^"7 mbar within 30 min dried. 97% sodium 4-hydroxybiphenyl is sublimed twice at 80 O and then (in the piston 1) at 80 O and a pressure of 10 ^"5 mbar under argon atmosphere (3) evaporated. The piston is heated for this purpose by means of the thermostat (6). Subsequently, the valve A (2) is opened and the silicon wafer (4) at 10 ^"5 mbar and 80 O within 30 min to 60 min with hydro xybiphenyl vaporized. After completion of vapor deposition, the argon supply is terminated by valve A (2) is closed The heater (thermostat, 6) is switched off, after another 5 min, the argon supply is stopped by closing valve A (2), the vaporised wafers are allowed to cool for 1 h within the evaporator, then valve B (5) is closed and the Evaporating system ventilated by opening valve A (2) with argon. The coated with a Hydroxybiphenyl monolayer silicon wafers are then rinsed with ethyl acetate pa, cleaned for 5 ± 2 min in an ultrasonic bath, dried in a nitrogen stream and stored under argon atmosphere. Argon used has a purity of 4.8 after dot notation; the purity of the nitrogen used is 4.6 after dot notation. The vaporization system is shown schematically in FIG. The XPS diagram (X-ray photoelectron spectroscopy) of the hydroxybiphenyl-SAM (HBP-SAM) formed is shown in FIG. 2. An aluminum anode served as a source for the X-radiation; The energy of K _α -ünie is 1486.6 eV with a half-width of about 1 eV.

2. Preparation of gold wafers with nitrobiphenylthiol from solution

Gold wafers (3 cm ^* 1 cm * 0.5 mm) are subjected to ozonolysis with UV light for two hours and then rinsed with DMF pa. Then they are cleaned for 5 minutes in an ultrasonic bath, rinsed with DMF pa and then with ethanol pa and finally dried in a stream of nitrogen, purity 4.6 according to dot notation. The wafers are added to a 50 ml Schlenk flask (2 wafers per flask) and a solution of nitrobiphenylthiol (NBPT) in DMF pa, c (NBPT) = 10 mmol / L added. The flask is sealed, degassed in vacuo and stored for three days under a nitrogen atmosphere and light. Thereafter, the wafers are removed and rinsed with DMF. The wafers are then treated in a DMF-filled beaker for 5 minutes in an ultrasonic bath. The wafers will now multiply with DMF pa and then Rinsed several times with ethanol pa, preferably 5 rinses are carried out with DMF or ethanol. Thereafter, the wafers are treated in an ethanol pa filled beaker for 5 minutes in an ultrasonic bath, rinsed with ethanol pa, dried in a stream of nitrogen and stored until further use under a nitrogen atmosphere.

Figure 3 shows the XPS plot of the NBPT SAMs so obtained on gold wafer (NBPT / Au _s ). Anode material and energy of Kα radiation were as described in Example 1. An AFM (Force Field Microscopy) image was taken using silicon nitride vane valve (tip radius 10 nm, spring constant 0.2 N / m). The scan area of the AFM / LFM head was 80 μm * 80 μm in the x, y plane. It was scanned in contact mode with a force of 12 nN. The height difference (in the z-direction) of the deposited NBPT molecules was at most 10 nm.

3. Preparation of gold wafers with nitrobiphenylthiol from the gas phase

The gold wafers are prepared as described in Example 2.

Thereafter, the wafer be in a purged with argon vaporization exceeded resulting in vacuo at 9 * ^{10 -7} mbar within 30 min.

In piston (1) is summed twice at 80 O nitrobiphenylthiol at 80 ^<C and a pressure of 10 ^"5 mbar under an argon atmosphere (3) is evaporated. Subsequently, the valve is opened A (2) and the gold wafers at 10 ^'5 mbar and 80 ⁰ C steamed with NBPT within 30 min to 60 min. After completion of the evaporation, the argon supply is stopped by valve A (2) is closed. The heating (thermostat, 6) is switched off. After a further 5 minutes, the argon supply is terminated by closing valve A (2). The vapor-deposited wafers cool for 1 h within the vaporization unit. Then valve B (5) is closed and the steaming system is vented by opening valve A (2) with argon.

The gold wafers coated with a nitrobiphenylthiol monolayer are then rinsed with ethyl acetate pa, cleaned for 5 ± 2 minutes in an ultrasonic bath, dried in a stream of nitrogen and stored under an argon atmosphere. Argon used has a purity of 4.8 after dot notation; the purity of the nitrogen used is 4.6 after dot notation. Figure 3 shows the XPS plot of the NBPT SAMs so obtained on gold wafers (NBPT / Au _G ). Anode material and energy of Kα radiation were as described in Example 1. An AFM (Force Field Microscopy) image was taken using silicon nitride vane valve (tip radius 10 nm, spring constant 0.2 N / m). The scan area of the AFM / LFM head was 80 μm * 80 μm in the x, y plane. It was scanned in contact mode with a force of 12 nN. The height difference (in the z-direction) of the deposited NBPT molecules was at most 10 nm. LIST OF REFERENCE NUMBERS

1st piston

2. Valve A 3. Oxygen-free gas

4. Wafer

5. Valve B

6. Thermostat

7. Vacuum gauges 8. Back-up pumps

9. Main vacuum pump

10. cold trap

Figure legends

Fiα. 1

Fig. 1 shows schematically a vapor deposition system.

In the flask (1), the substance to be aggregated is evaporated; the heating takes place via the thermostat (6). Via valve A (2), the vaporized substance can be directed into the vessel with the wafers (4) to be vaporized. In the vessel with the wafers to be vaporized (4) further oxygen-free gas (3) is introduced.

The pressure of 10.sup.- ⁶ mbar to 10.sup.- ⁸ mbar which is necessary for carrying out the process according to the invention is produced by fore-vacuum pumps (8) and main vacuum pump (9) with cold trap (10); the evacuation of the steaming system takes place via valve B (5). Fig. 2

X-ray photoemission diagram (XPS diagram) of hydroxybiphenyl SAMs on silicon wafers, cf. Embodiment 1.

An aluminum anode served as a source of X-radiation. The energy of the K _α line is 1486.6 eV with a half width of about 1 eV.

Fig. 3

X-ray photoemission diagram (XPS diagram) of nitrobiphenylthiol SAMs

(NBPT-SAMs) on Goldwafem. An aluminum anode served as a source of X-radiation. The energy of the K _α line is 1486.6 eV with a half width of about 1 eV. The upper curve shows an NBPT-SAM, which was deposited from the gas phase by means of the method according to the invention (NBPT / AU _G ), cf. Exemplary embodiment 3. The lower curve shows an NBPT-SAM which has been deposited from solution (NBPT / Aus), cf. Embodiment 2.

Claims

claims

1. A process for the preparation of self-aggregating monolayers (SAMs) on solid surfaces, characterized in that the substance to be aggregated or the substances to be aggregated heated until evaporation and this steam in a permanent, oxygen-free gas stream at a temperature of> 100 O and a pressure of 10 ^"6 to 10 ^{" 8} mbar is deposited within 30 to 60 minutes on the surface of the solid to be coated.

2. The method according to claim 1, characterized in that the solid-state surface is selected from the group of metals, metal oxides, conductive polymers, electroactive materials and semiconductors.

3. The method according to claim 2, characterized in that the solid-state peroberfläche is a metal or metal oxide selected from titanium, titanium dioxide, tin, tin oxide, silicon, silicon dioxide, iron, iron oxide ^111, silver, gold, copper, platinum, palladium , Nickel, aluminum, steel, indium, indium-tin oxide, fluoride-doped tin oxide, ruthenium oxide, germanium cadmium selenide, cadmium selenide, cadmium sulfide, titanium alloys.

4. The method according to any one of claims 1 to 3, characterized in that the substance to be aggregated is selected from biphenylene, alkylchlorosilanes or generally alkylhalosilanes, non-chloro-containing dimethylaminosilanes, alkenes, fullerenes, disilabutene, alkylsiloxanes, alkylsilanes and alkylthiols.

5. The method according to any one of claims 1 to 4, characterized in that instead of the aggregating substance, a precursor material is used.

6. The method according to claim 5, characterized in that the precursor material is an organic chlorosilane.

7. The method according to any one of claims 1 to 5, characterized in that a mixture of substances to be aggregated or their precursors is vapor-deposited, wherein the vapor pressures of substances to be aggregated or precursors differ by a maximum of 2 * 10 ^ mbar.

8. The method according to any one of claims 1 to 7, characterized in that the oxygen-free gas for generating the permanent gas stream is selected from the group helium, neon, argon, krypton, xenon, nitrogen, carbon monoxide, carbon dioxide.

9. Self-aggregating monolayers (SAMs) on solid surfaces, obtainable by the method according to one of claims 1 to 8.

10. Use of SAMs on solid surfaces according to claim 9 for the production of electronic, optical or electro-optical components.

11. Use of SAMs on solid surfaces according to claim 9 in mask-lithographic processes for the nanostructuring of semiconductors.

12. Use of SAMs on solid surfaces according to claim 9 as corrosion protection.

13. Use of SAMs on solid surfaces according to claim 9 as adhesion promoters in composite materials.

14. Use of SAMs on solid surfaces according to claim 9 for the production of medical stents.

15. Use of SAMs on solid surfaces according to claim 9 for the preparation of semipermeable membranes.

16. Use of SAMs on solid surfaces according to claim 9 for the production of substrates for biological cell cultures.