ASTM F1438-93(2020)
(Test Method)Standard Test Method for Determination of Surface Roughness by Scanning Tunneling Microscopy for Gas Distribution System Components (Withdrawn 2023)
Standard Test Method for Determination of Surface Roughness by Scanning Tunneling Microscopy for Gas Distribution System Components (Withdrawn 2023)
SIGNIFICANCE AND USE
5.1 The use of STM images and data is for purposes of textural quality assessment and calculation of figures of merit, and for high purity gas system clean room components.
5.2 This test method defines a standard data presentation format and suggests figures of merit that utilize STM's ability to analyze three-dimensional surface features.
SCOPE
1.1 The purpose of this test method is to define a method for analyzing the surface texture of the above-mentioned components using a scanning tunneling microscope (STM). STM is a noncontact method of surface profiling that can measure three-dimensional surface features in the nanometer size range, which can then be used to represent the surface texture or to provide figures of merit. Application of this test method, where surface texture is used as a selection criterion, is expected to yield comparable data among different components tested.
1.2 Limitations:
1.2.1 This test method is limited to characterization of stainless steel surfaces that are smoother than Ra = 0.25 μm, as determined by a contact-stylus profilometer and defined by ANSI B46.1. The magnifications and height scales used in this test method were chosen with this smoothness in mind.
1.2.2 Intentional etching or conductive coating of the surface are considered modifications of the gas-wetted surface and are not covered by this test method.
1.2.3 This test method does not cover steels that have an oxide layer too thick to permit tunneling under the test conditions outlined in 11.3.
1.3 This technique is written with the assumption that the STM operator understands the use of the instrument, its governing principles, and any artifacts that can arise. Discussion of these points is beyond the scope of this test method.
1.4 The values stated in SI units are to be regarded as the standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
WITHDRAWN RATIONALE
The purpose of this test method is to define a method for analyzing the surface texture of the above-mentioned components using a scanning tunneling microscope (STM). STM is a noncontact method of surface profiling that can measure three-dimensional surface features in the nanometer size range, which can then be used to represent the surface texture or to provide figures of merit. Application of this test method, where surface texture is used as a selection criterion, is expected to yield comparable data among different components tested.
Formerly under the jurisdiction of Committee F01 on Electronics, this test method was withdrawn in November 2023. This standard is being withdrawn without replacement because Committee F01 was disbanded.
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F1438 − 93 (Reapproved 2020)
Standard Test Method for
Determination of Surface Roughness by Scanning
Tunneling Microscopy for Gas Distribution System
Components
This standard is issued under the fixed designation F1438; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Semiconductor clean rooms are serviced by high-purity gas distribution systems. This test method
presentsaprocedurethatmaybeappliedfortheevaluationofoneormorecomponentsconsideredfor
use in such systems.
1. Scope 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 Thepurposeofthistestmethodistodefineamethodfor
responsibility of the user of this standard to establish appro-
analyzing the surface texture of the above-mentioned compo-
priate safety, health, and environmental practices and deter-
nents using a scanning tunneling microscope (STM). STM is a
mine the applicability of regulatory limitations prior to use.
noncontact method of surface profiling that can measure
1.6 This international standard was developed in accor-
three-dimensionalsurfacefeaturesinthenanometersizerange,
dance with internationally recognized principles on standard-
which can then be used to represent the surface texture or to
ization established in the Decision on Principles for the
providefiguresofmerit.Applicationofthistestmethod,where
Development of International Standards, Guides and Recom-
surface texture is used as a selection criterion, is expected to
mendations issued by the World Trade Organization Technical
yield comparable data among different components tested.
Barriers to Trade (TBT) Committee.
1.2 Limitations:
1.2.1 This test method is limited to characterization of 2. Referenced Documents
stainless steel surfaces that are smoother than R =0.25 µm, as
a
2.1 ASTM Standards:
determined by a contact-stylus profilometer and defined by
E691Practice for Conducting an Interlaboratory Study to
ANSI B46.1.The magnifications and height scales used in this
Determine the Precision of a Test Method
test method were chosen with this smoothness in mind.
2.2 ANSI Standard:
1.2.2 Intentional etching or conductive coating of the sur-
ANSI B.46.1-85,“Surface Texture (Surface Roughness,
faceareconsideredmodificationsofthegas-wettedsurfaceand 3
Waviness, and Lay),” ANSI/ASME, 1985
are not covered by this test method.
1.2.3 This test method does not cover steels that have an
3. Terminology
oxide layer too thick to permit tunneling under the test
3.1 Definitions of Terms Specific to This Standard:
conditions outlined in 11.3.
3.1.1 artifact—anycontributiontoanimagefromotherthan
1.3 This technique is written with the assumption that the
true surface morphology. This could include such examples as
STM operator understands the use of the instrument, its vibration, electronic noise, thermal drift, or tip imperfections.
governing principles, and any artifacts that can arise. Discus-
3.1.2 center line (graphical center line)—lineparalleltothe
sion of these points is beyond the scope of this test method.
directionofprofilemeasurement,suchthatthesumoftheareas
1.4 The values stated in SI units are to be regarded as the contained between it and the profile contained on either side
are equal (see Calculation Section).
standard.
1 2
This test method is under the jurisdiction of ASTM Committee F01 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Electronicsand is the direct responsibility of Subcommittee F01.10 on Contamina- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
tion Control. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 15, 2020. Published May 2020. Originally the ASTM website.
approvedin1993.Lastpreviouseditionapprovedin2012asF1438–93(2012).DOI: Available fromAmerican National Standards Institute, 13th Floor, 11 W. 42nd
10.1520/F1438-93R20. St., New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1438 − 93 (2020)
3.1.3 cutoff length (l )—for profiles in this context, the 3.1.22 tip crash—touchingoftiptosurface,duringrastering
c
sampling length, that is, the length of a single scan, in orattemptstoinitiatetunneling,usuallyresultingindamageto
nanometers (see Calculation Section). one or both.
3.1.4 current— in this context, the tunneling current (ex-
3.1.23 top view—image represented as a surface viewed
pressed in nanoamperes) that flows in either direction between
from overhead.
the tip and surface, under the conditions specified.
3.1.24 tunneling—in this context, the flow of current
3.1.5 feature height—datum (height in the z-direction) of
betweenthetipandsurface(see current);morediscussioncan
any point in the scan area, relative to the lowest point in the
be found in additional references.
scan area, as derived from tunneling current during tip raster-
3.1.25 valley— lowest point between two crossing points of
ing.
a profile and its center line.
3.1.6 filter—process of modification of surface data for
3.1.26 voltage—bias voltage, expressed in volts (V) or
purposes of numerical analysis or data presentation. Examples
millivolts (mV), applied between the tip and the surface.
include high or low pass filters and plane-fitting.
3.2 Abbreviations and Symbols:
3.1.7 gold ruled grating—gold surface having uniformly
3.2.1 HOPG—highly ordered pyrolytic graphite; used for
spaced grooves of known depth and separation; used for
atomic scale x-y calibration of the scanning tunneling micros-
micrometer scale x-y calibration.
copy.
3.1.8 illuminated surface—three-dimensional image repre-
3.2.2 STM—scanning tunneling microscopy (or micro-
sentation that simulates a reflective surface illuminated
scope).
obliquely or from overhead.
−9
3.2.3 nA—nanoamperes (1×10 amperes).
3.1.9 image—surface topography represented by plotting
3.2.4 Pt/Ir—platinum and iridium alloy wire used to make
feature height as a function of tip position. The feature height
tunneling tips.
data is derived from the amount of tunneling current flowing
3.2.5 R —see mean roughness.
a
between the tip and surface during rastering.
3.2.6 R —maximum height difference between the high-
max
3.1.10 line plot—three-dimensional image given as side-by-
est and the lowest points on the profile over the length of the
side surface profiles.
profile (see Calculation Section).
3.1.11 mean roughness (R )—average deviation from the
a
3.2.7 root mean square (RMS)—see algebraic definition in
mean of all profile heights (see algebraic definition in the
Calculation Section.
Calculation Section).
3.2.8 R —the 10-point mean roughness; that is, the average
z
3.1.12 peak—highestpointbetweentwocrossingpointsofa
differenceinheightbetweenthefivehighestpeaksandthefive
profile and its center line.
lowest valleys over the length of the profile (see Calculation
3.1.13 profile—the cross-sectional data that has been high
Section).
pass filtered with a two-pole filter having a gain of 75% at the
3.2.9 x-direction—see scan.
cutoff length l (in nanometers).
c
3.2.10 y-direction—the direction, in the sample plane, over
3.1.14 raster—repetitive scanning in the x-direction while
which successive scans are taken, orthogonal to the scan
moving stepwise in the y-direction; also the area defined by
direction.
such action.
3.2.11 z-direction—the direction perpendicular to the
3.1.15 scan—a single, continuous movement in one direc-
sample plane. Also referred to as the feature height direction.
tion (defined as the x-direction) of the tip relative to sample
3.2.12 Z—same as feature height (see Calculation Section).
i
surface.
3.2.13 Z —maximum height difference over entire sur-
max
3.1.16 scan area—area covered by successive, side by side
face (see Calculation Section).
scans.
3.2.14 Z —root-mean-square of all surface heights (see
rms
3.1.17 scan length—distance from start to end of a single
Calculation Section).
scan, without moving in the y-direction (see cutoff length).
4. Summary of Test Method
3.1.18 scan rate—the speed at which the tip moves relative
to the surface.
4.1 In this test method a sharp, conductive tip is scanned
over very closely but not in contact with a conductive surface;
3.1.19 shaded height plot—image representing feature
thatis,theyareseparatedbyagapofseveralangstroms.Abias
height as dark or light shades (any color) over a two-
voltage present between them causes a flow of electrons
dimensional area. Higher features are shaded lighter and lower
through,ratherthanover,theenergybarrierrepresentedbythis
features are shaded darker.
tip-surface gap. This flow is referred to as the tunneling
3.1.20 thermal drift—movement of the surface with respect
to the tip due to a lack of thermal equilibrium.
3.1.21 tilted surface—three-dimensional image showing
Binning, G., et al., “Surface Studies by Scanning Tunneling Microscopy,”
surface tilted away from viewer, as opposed to a topview. Physical Review Letters, Vol 49, No. 1, July 1982, pp. 57–61.
F1438 − 93 (2020)
current. The manner in which the current fluctuates during the 7.2 Inert atmospheres, temperature controls, acoustic
scanning process is used to indicate the surface’s topography. isolation, and vibration isolation are to be provided as neces-
Thoughthetiporsamplecanbescanned,themethoddescribed sary to obtain artifact-free images.
here considers only the tip to be in motion. A more extensive
8. Sampling
discussion of the operating principles can be found in other
literature.
8.1 Many components are too large or irregularly shaped to
permit STM analysis without cutting a sample from the
4.2 In this test method, stainless steel tubing is used as an
component. Low speed cutting, preferably without lubricants,
example of a component surface.An area of the surface is first
using a diamond blade saw is recommended over high speed
scanned at a width of 500 nA, then 2000 nA. Even though
abrasive cutting or hacksaws.
larger areas can be scanned by most instruments, these mag-
nifications are chosen to show surface texture in a size range
8.2 This sampling must not modify the surface topography,
beyond that measured by contact stylus type surface profiling
such as effects due to stress, heat, corrosion, or combination
instruments, but not at an atomic scale. The surface scans are
thereof, from its condition as found in the component.
then compared for damage, artifacts, etc. Numerical analysis
8.3 Cleaning the surface using an inert fluid to remove
canthenproceedusingthesedataforroughnessorsurfacearea
cutting contamination is permitted.
or both, following the model of other standards such asANSI
B46.1.
9. Calibration
9.1 Calibration frequency may vary with different instru-
5. Significance and Use
ment manufacturers. It should be performed, at least initially,
5.1 The use of STM images and data is for purposes of then yearly, and after any repair or addition to the instrument’s
textural quality assessment and calculation of figures of merit,
hardware and software.
and for high purity gas system clean room components.
9.2 Following the manufacturer’s recommendations, the
5.2 This test method defines a standard data presentation STMwillbecalibratedusingtheHOPG,goldruledgrating,or
some other suitable dimensional standard, depending upon the
format and suggests figures of merit that utilize STM’s ability
to analyze three-dimensional surface features. size range to be used and the accuracy of the standard.
10. Conditioning
6. Interferences
10.1 Aconductive path for the sample shall be provided for
6.1 Some(stainlesssteel)componentsurfaceshaveanoxide
voltage biasing of the sample with respect to the tip.
layer that prevents tunneling from occurring under any condi-
10.2 Mount the sample so the tip will scan an arbitrarily
tions without affecting tip or surface morphology. This results
in ambiguous surface data. Such surfaces require the use of chosen representative area.
other techniques for topographic measurement.
10.3 Bring the sample and microscope to thermal equilib-
rium.
6.2 This test method assumes that the images obtained are
unperturbed by very thin, non-solid layers (for example,
11. Procedure
hydrocarbons, moisture) on the surface.
11.1 As stated in 1.2.3, this test method does not cover
6.3 Operationwiththesurfaceinair,vacuum,orunderinert
steels that have an oxide layer too thick to permit tunneling
liquids is permissible. (The liquids must be suitably inert and
under the test conditions outlined in this test method.
fluid, so as to not modify the apparent surface topography or
11.2 Make sure that a minimum of 200 data points is
introduce artifacts into the image.)Water is not recommended.
collected in the x-direction, and at least 200 scans per raster is
6.4 The tip shall be made from platinum/iridium or tung-
in the y-direction (200×200=40000 data points).
sten.
11.3 Initiate tunneling between a Pt/Ir tip and the sample in
NOTE 1—Caution: The tip must not have previously touched any
accordance with the manufacturer’s instructions under condi-
surface (see 11.7).
tionstoprovideartifactfreeimages.Suggestedstartingvalues:
voltage bias of 1800 mV, and current levels monitored at 0.1
7. Apparatus
nA (Standard Test Conditions—Room temperature and ambi-
ent pressure (101.3 kPa, 25° 6 2°C)).
7.1 Scanning Tunneling Microscope ,capableofthefollow-
ing may be used:
11.4 Scan an area 500-nm across at a rate of approximately
7.1.1 Scanning lengths up to at least 50 µm,
2 s/µm (or slow enough to prevent the tip from touching the
7.1.2 Substaining 6 3 V between the tip and sample,
surface during rastering), collecting at least 200 data points
with each x-direction scan.
7.1.3 Monitoring tunneling current as low as 0.05 nA,
7.1.4 Traversing feature height variations as great as 2 µm
11.5 Collect area scans so that comparisons can be made
without touching the tip to the surface, and
between the first two successive rasters. Ensure that the area
7.1.5 Providing the surface topography as a shaded height has not drifted more than 10% of the scan width in any
plot or line plot. direction. If it has, discontinue scanning for sufficient time to
F1438 − 93 (2020)
allow thermal equilibrium to be obtained. Determine this by 11.12 If there is any u
...
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: F1438 − 93 (Reapproved 2020)
Standard Test Method for
Determination of Surface Roughness by Scanning
Tunneling Microscopy for Gas Distribution System
Components
This standard is issued under the fixed designation F1438; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Semiconductor clean rooms are serviced by high-purity gas distribution systems. This test method
presents a procedure that may be applied for the evaluation of one or more components considered for
use in such systems.
1. Scope 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 The purpose of this test method is to define a method for
responsibility of the user of this standard to establish appro-
analyzing the surface texture of the above-mentioned compo-
priate safety, health, and environmental practices and deter-
nents using a scanning tunneling microscope (STM). STM is a
mine the applicability of regulatory limitations prior to use.
noncontact method of surface profiling that can measure
1.6 This international standard was developed in accor-
three-dimensional surface features in the nanometer size range,
dance with internationally recognized principles on standard-
which can then be used to represent the surface texture or to
ization established in the Decision on Principles for the
provide figures of merit. Application of this test method, where
Development of International Standards, Guides and Recom-
surface texture is used as a selection criterion, is expected to
mendations issued by the World Trade Organization Technical
yield comparable data among different components tested.
Barriers to Trade (TBT) Committee.
1.2 Limitations:
1.2.1 This test method is limited to characterization of 2. Referenced Documents
stainless steel surfaces that are smoother than R = 0.25 µm, as
a
2.1 ASTM Standards:
determined by a contact-stylus profilometer and defined by
E691 Practice for Conducting an Interlaboratory Study to
ANSI B46.1. The magnifications and height scales used in this 2
Determine the Precision of a Test Method
test method were chosen with this smoothness in mind.
2.2 ANSI Standard:
1.2.2 Intentional etching or conductive coating of the sur-
ANSI B.46.1-85, “Surface Texture (Surface Roughness,
face are considered modifications of the gas-wetted surface and
Waviness, and Lay),” ANSI/ASME, 1985
are not covered by this test method.
1.2.3 This test method does not cover steels that have an 3. Terminology
oxide layer too thick to permit tunneling under the test
3.1 Definitions of Terms Specific to This Standard:
conditions outlined in 11.3.
3.1.1 artifact—any contribution to an image from other than
1.3 This technique is written with the assumption that the true surface morphology. This could include such examples as
STM operator understands the use of the instrument, its
vibration, electronic noise, thermal drift, or tip imperfections.
governing principles, and any artifacts that can arise. Discus-
3.1.2 center line (graphical center line)—line parallel to the
sion of these points is beyond the scope of this test method.
direction of profile measurement, such that the sum of the areas
contained between it and the profile contained on either side
1.4 The values stated in SI units are to be regarded as the
standard. are equal (see Calculation Section).
1 2
This test method is under the jurisdiction of ASTM Committee F01 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Electronicsand is the direct responsibility of Subcommittee F01.10 on Contamina- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
tion Control. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 15, 2020. Published May 2020. Originally the ASTM website.
approved in 1993. Last previous edition approved in 2012 as F1438–93(2012). DOI: Available from American National Standards Institute, 13th Floor, 11 W. 42nd
10.1520/F1438-93R20. St., New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1438 − 93 (2020)
3.1.3 cutoff length (l )—for profiles in this context, the 3.1.22 tip crash—touching of tip to surface, during rastering
c
sampling length, that is, the length of a single scan, in or attempts to initiate tunneling, usually resulting in damage to
nanometers (see Calculation Section). one or both.
3.1.4 current— in this context, the tunneling current (ex-
3.1.23 top view—image represented as a surface viewed
pressed in nanoamperes) that flows in either direction between
from overhead.
the tip and surface, under the conditions specified.
3.1.24 tunneling—in this context, the flow of current
3.1.5 feature height—datum (height in the z-direction) of
between the tip and surface (see current); more discussion can
any point in the scan area, relative to the lowest point in the
be found in additional references.
scan area, as derived from tunneling current during tip raster-
3.1.25 valley— lowest point between two crossing points of
ing.
a profile and its center line.
3.1.6 filter—process of modification of surface data for
3.1.26 voltage—bias voltage, expressed in volts (V) or
purposes of numerical analysis or data presentation. Examples
millivolts (mV), applied between the tip and the surface.
include high or low pass filters and plane-fitting.
3.2 Abbreviations and Symbols:
3.1.7 gold ruled grating—gold surface having uniformly
3.2.1 HOPG—highly ordered pyrolytic graphite; used for
spaced grooves of known depth and separation; used for
atomic scale x-y calibration of the scanning tunneling micros-
micrometer scale x-y calibration.
copy.
3.1.8 illuminated surface—three-dimensional image repre-
3.2.2 STM—scanning tunneling microscopy (or micro-
sentation that simulates a reflective surface illuminated
scope).
obliquely or from overhead.
−9
3.2.3 nA—nanoamperes (1 × 10 amperes).
3.1.9 image—surface topography represented by plotting
3.2.4 Pt/Ir—platinum and iridium alloy wire used to make
feature height as a function of tip position. The feature height
tunneling tips.
data is derived from the amount of tunneling current flowing
3.2.5 R —see mean roughness.
a
between the tip and surface during rastering.
3.2.6 R —maximum height difference between the high-
max
3.1.10 line plot—three-dimensional image given as side-by-
est and the lowest points on the profile over the length of the
side surface profiles.
profile (see Calculation Section).
3.1.11 mean roughness (R )—average deviation from the
a
3.2.7 root mean square (RMS)—see algebraic definition in
mean of all profile heights (see algebraic definition in the
Calculation Section.
Calculation Section).
3.2.8 R —the 10-point mean roughness; that is, the average
z
3.1.12 peak—highest point between two crossing points of a
difference in height between the five highest peaks and the five
profile and its center line.
lowest valleys over the length of the profile (see Calculation
3.1.13 profile—the cross-sectional data that has been high
Section).
pass filtered with a two-pole filter having a gain of 75 % at the
3.2.9 x-direction—see scan.
cutoff length l (in nanometers).
c
3.2.10 y-direction—the direction, in the sample plane, over
3.1.14 raster—repetitive scanning in the x-direction while
which successive scans are taken, orthogonal to the scan
moving stepwise in the y-direction; also the area defined by
direction.
such action.
3.2.11 z-direction—the direction perpendicular to the
3.1.15 scan—a single, continuous movement in one direc-
sample plane. Also referred to as the feature height direction.
tion (defined as the x-direction) of the tip relative to sample
3.2.12 Z —same as feature height (see Calculation Section).
i
surface.
3.2.13 Z —maximum height difference over entire sur-
max
3.1.16 scan area—area covered by successive, side by side
face (see Calculation Section).
scans.
3.2.14 Z —root-mean-square of all surface heights (see
rms
3.1.17 scan length—distance from start to end of a single
Calculation Section).
scan, without moving in the y-direction (see cutoff length).
4. Summary of Test Method
3.1.18 scan rate—the speed at which the tip moves relative
to the surface.
4.1 In this test method a sharp, conductive tip is scanned
over very closely but not in contact with a conductive surface;
3.1.19 shaded height plot—image representing feature
that is, they are separated by a gap of several angstroms. A bias
height as dark or light shades (any color) over a two-
voltage present between them causes a flow of electrons
dimensional area. Higher features are shaded lighter and lower
through, rather than over, the energy barrier represented by this
features are shaded darker.
tip-surface gap. This flow is referred to as the tunneling
3.1.20 thermal drift—movement of the surface with respect
to the tip due to a lack of thermal equilibrium.
3.1.21 tilted surface—three-dimensional image showing 4
Binning, G., et al., “Surface Studies by Scanning Tunneling Microscopy,”
surface tilted away from viewer, as opposed to a topview. Physical Review Letters, Vol 49, No. 1, July 1982, pp. 57–61.
F1438 − 93 (2020)
current. The manner in which the current fluctuates during the 7.2 Inert atmospheres, temperature controls, acoustic
scanning process is used to indicate the surface’s topography. isolation, and vibration isolation are to be provided as neces-
Though the tip or sample can be scanned, the method described sary to obtain artifact-free images.
here considers only the tip to be in motion. A more extensive
8. Sampling
discussion of the operating principles can be found in other
literature.
8.1 Many components are too large or irregularly shaped to
permit STM analysis without cutting a sample from the
4.2 In this test method, stainless steel tubing is used as an
component. Low speed cutting, preferably without lubricants,
example of a component surface. An area of the surface is first
using a diamond blade saw is recommended over high speed
scanned at a width of 500 nA, then 2000 nA. Even though
abrasive cutting or hacksaws.
larger areas can be scanned by most instruments, these mag-
nifications are chosen to show surface texture in a size range
8.2 This sampling must not modify the surface topography,
beyond that measured by contact stylus type surface profiling
such as effects due to stress, heat, corrosion, or combination
instruments, but not at an atomic scale. The surface scans are
thereof, from its condition as found in the component.
then compared for damage, artifacts, etc. Numerical analysis
8.3 Cleaning the surface using an inert fluid to remove
can then proceed using these data for roughness or surface area
cutting contamination is permitted.
or both, following the model of other standards such as ANSI
B46.1.
9. Calibration
9.1 Calibration frequency may vary with different instru-
5. Significance and Use
ment manufacturers. It should be performed, at least initially,
5.1 The use of STM images and data is for purposes of
then yearly, and after any repair or addition to the instrument’s
textural quality assessment and calculation of figures of merit, hardware and software.
and for high purity gas system clean room components.
9.2 Following the manufacturer’s recommendations, the
STM will be calibrated using the HOPG, gold ruled grating, or
5.2 This test method defines a standard data presentation
format and suggests figures of merit that utilize STM’s ability some other suitable dimensional standard, depending upon the
size range to be used and the accuracy of the standard.
to analyze three-dimensional surface features.
10. Conditioning
6. Interferences
10.1 A conductive path for the sample shall be provided for
6.1 Some (stainless steel) component surfaces have an oxide
voltage biasing of the sample with respect to the tip.
layer that prevents tunneling from occurring under any condi-
tions without affecting tip or surface morphology. This results 10.2 Mount the sample so the tip will scan an arbitrarily
chosen representative area.
in ambiguous surface data. Such surfaces require the use of
other techniques for topographic measurement.
10.3 Bring the sample and microscope to thermal equilib-
rium.
6.2 This test method assumes that the images obtained are
unperturbed by very thin, non-solid layers (for example,
11. Procedure
hydrocarbons, moisture) on the surface.
11.1 As stated in 1.2.3, this test method does not cover
6.3 Operation with the surface in air, vacuum, or under inert
steels that have an oxide layer too thick to permit tunneling
liquids is permissible. (The liquids must be suitably inert and
under the test conditions outlined in this test method.
fluid, so as to not modify the apparent surface topography or
11.2 Make sure that a minimum of 200 data points is
introduce artifacts into the image.) Water is not recommended.
collected in the x-direction, and at least 200 scans per raster is
6.4 The tip shall be made from platinum/iridium or tung-
in the y-direction (200 × 200 = 40 000 data points).
sten.
11.3 Initiate tunneling between a Pt/Ir tip and the sample in
NOTE 1—Caution: The tip must not have previously touched any
accordance with the manufacturer’s instructions under condi-
surface (see 11.7).
tions to provide artifact free images. Suggested starting values:
voltage bias of 1800 mV, and current levels monitored at 0.1
7. Apparatus
nA (Standard Test Conditions—Room temperature and ambi-
7.1 Scanning Tunneling Microscope , capable of the follow- ent pressure (101.3 kPa, 25° 6 2°C)).
ing may be used:
11.4 Scan an area 500-nm across at a rate of approximately
7.1.1 Scanning lengths up to at least 50 µm,
2 s/µm (or slow enough to prevent the tip from touching the
7.1.2 Substaining 6 3 V between the tip and sample, surface during rastering), collecting at least 200 data points
with each x-direction scan.
7.1.3 Monitoring tunneling current as low as 0.05 nA,
7.1.4 Traversing feature height variations as great as 2 µm
11.5 Collect area scans so that comparisons can be made
without touching the tip to the surface, and
between the first two successive rasters. Ensure that the area
7.1.5 Providing the surface topography as a shaded height has not drifted more than 10 % of the scan width in any
plot or line plot. direction. If it has, discontinue scanning for sufficient time to
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