Name: quantitative hardness measurement by instrumented afm-indentation
Uploaded: 2016-11-22T14:00:00
Description: Watch this Scientific Journal Video about Quantitative Hardness Measurement by Instrumented AFM-indentation at JoVE.com

A.C. is grateful to KoreaTech for financial support.

1. Instrumental Set-up and Calibration

<ol>
	<li>Instrumental set-up
	<ol>
		<li>Use a stiff diamond-coated cantilever of the type DT-NCLR or CDT-NCLR with a first free resonance frequency f0,1 &#8805; 180 kHz, a quality factor Q &#8805; 300, and a bending stiffness k &#8805; 40 N/m.</li>
		<li>Mount the selected cantilever onto a clamping holder provided by the AFM manufacturer. Take special care to place the cantilever such that its long axis is p...

<ol>
	<li>Tabor, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The hardness of metals. , (1951).</li><li>Fischer-Cripps, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Nanoindentation. , (2004).</li><li>Michalke, T. A., Houston, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dislocation+Nucleation+at+Nano-Scale+Mechanical+Contacts.">Dislocation Nucleation at Nano-Scale Mechanical Contacts.</a> Acta Mater. 46 (2), 391-396 (1998).</li><li>Kiely, J. D., Houston, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanomechanical+Properties+of+Au(111)+(001),+and+(110)+Surfaces.">Nanomechanical Properties of Au(111) (001), and (110) Surfaces.</a> Phys. Rev. B. 57 (19), 12588 (1998).</li><li>Kiely, J. D., Jarausch, K. F., Houston, J. E., Russell, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Initial+Stages+of+Yield+in+Nanoindentation.">Initial Stages of Yield in Nanoindentation.</a> J. Mater. Res. 14 (19), 2219-2227 (1999).</li><li>Egberts, P., Bennewitz, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atomic+Scale+Nanoindentation:+Detection+and+Indentification+of+Single+Glide+Events+in+Three+Dimensions+by+Force+Microscopy.">Atomic Scale Nanoindentation: Detection and Indentification of Single Glide Events in Three Dimensions by Force Microscopy.</a> Nanotechnology. 22 (42), 425703-1-425703-9 (2011).</li><li>Filleter, T., Bennewitz, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanometer+Scale+Plasticity+of+Cu(100).">Nanometer Scale Plasticity of Cu(100).</a> Nanotechnology. 18 (4), 044004-1-044004-4 (2007).</li><li>Asenjo, A., Jaafar, M., Carrasco, E., Rojo, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dislocation+mechanisms+in+the+first+stage+of+plasticity+of+nanoindented+Au(111)+surfaces.">Dislocation mechanisms in the first stage of plasticity of nanoindented Au(111) surfaces.</a> Phys. Rev. B. 73 (7), 075431 (2006).</li><li>Paul, W., Oliver, D., Miyahara, Y., Gruetter, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Minimum+threshold+for+incipient+plasticity+in+the+atomic-scale+nanoindentation+of+Au(111).">Minimum threshold for incipient plasticity in the atomic-scale nanoindentation of Au(111).</a> Phys. Rev. Lett. 110 (13), 135506 (2013).</li><li>Kracke, B., Damaschke, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+nanohardness+and+nanoelasticity+of+thin+gold+films+with+scanning+force+microscope.">Measurement of nanohardness and nanoelasticity of thin gold films with scanning force microscope.</a> Appl. Phys. Lett. 77 (3), 361-363 (2000).</li><li>Sansoz, F., Gang, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+force-mapping+method+for+quantitative+hardness+measurements+by+atomic+force+microscopy+with+diamond-tipped+sapphire+cantilevers.">A force-mapping method for quantitative hardness measurements by atomic force microscopy with diamond-tipped sapphire cantilevers.</a> Ultramicroscopy. 111, 11-19 (2010).</li><li>Silva, E. C. C. M., Van Vliet, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Robust+approach+to+maximize+the+range+and+accuracy+of+force+application+in+atomic+force+microscopes+with+non-linear+position-sensitive+detectors.">Robust approach to maximize the range and accuracy of force application in atomic force microscopes with non-linear position-sensitive detectors.</a> Nanotechnolgy. 17 (21), 5525-5529 (2006).</li><li>Caron, A., Bennewitz, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lower+Nanometer-Scale+Size+Limit+for+the+Deformation+of+a+Metallic+Glass+by+Shear+Transformations+Revealed+by+Quantitative+AFM+Indentation.">Lower Nanometer-Scale Size Limit for the Deformation of a Metallic Glass by Shear Transformations Revealed by Quantitative AFM Indentation.</a> Beilstein J. Nanotechnol. 6, 1721-1732 (2015).</li><li>Andriotis, O. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanomechanical+assesment+of+human+and+murine+collagen+fibrils+via+atomic+force+microscopy+cantilever-based+nanoindentation.">Nanomechanical assesment of human and murine collagen fibrils via atomic force microscopy cantilever-based nanoindentation.</a> J. Mech. Behavior Biomed. Mater. 39, 9-26 (2014).</li><li>Bischel, M. S., Vanlandingham, M. R., Eduljee, R. F., Gillespie, J. W., Schultz, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+use+of+nanoscale+indentation+with+the+AFM+in+the+identification+of+phases+in+blends+of+linear+low+density+polyethylene+and+high+density+polyethylene.">On the use of nanoscale indentation with the AFM in the identification of phases in blends of linear low density polyethylene and high density polyethylene.</a> J. Mater. Sci. 35 (1), 221-228 (2000).</li><li>Zhang, L., Wang, W., Zheng, L., Wang, X., Yan, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+characterization+of+mechanical+property+of+annealed+monolayer+colloidal+crystal.">Quantitative characterization of mechanical property of annealed monolayer colloidal crystal.</a> Langmuir. 32 (2), 451-459 (2016).</li><li>Ne&#269;as, D., Klapetek, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gwyddion:+An+open-source+software+for+SPM+data+analysis.">Gwyddion: An open-source software for SPM data analysis.</a> Cent. Eur. J. Phys. 10 (1), 181-188 (2012).</li><li>Hahn, B. H., Valentine, D. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Essential Matlab for Engineers and Scientists. , (2013).</li><li>Nonnenmacher, M., Greschner, J., Wolter, O., Kassing, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scanning+Force+Microscopy+with+Micromachined+Silicon+Sensors.">Scanning Force Microscopy with Micromachined Silicon Sensors.</a> J. Vac. Sci. Technol. B. 9 (2), 1358-1362 (1991).</li><li>Cannara, R. J., Brukman, M. J., Carpick, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cantilever+tilt+compensation+for+variable-load+atomic+force+microscopy.">Cantilever tilt compensation for variable-load atomic force microscopy.</a> Rev. Sci. Instrum. 76 (5), 053706 (2005).</li><li>Johnson, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Contact Mechanics. , (1985).</li><li>Mohr, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Young's+Modulus,+Fracture+Strength,+and+Poisson's+Ratio+of+Nanocrystalline+Diamond+Films.">Young's Modulus, Fracture Strength, and Poisson's Ratio of Nanocrystalline Diamond Films.</a> J. Appl. Phys. 116 (12), 124308-1-124308-10 (2014).</li><li>Arnault, J. C., Mosser, A., Zamfirescu, M., Pelletier, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastic+recovery+measurements+performed+by+atomic+force+microscopy+and+standard+nanoindentation+on+a+Co(10.1)+monocrystal.">Elastic recovery measurements performed by atomic force microscopy and standard nanoindentation on a Co(10.1) monocrystal.</a> J. Mater. Res. 17 (6), 1258-1265 (2002).</li><li>Cao, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoindentation+measurements+of+the+mechanical+properties+of+polycrystalline+Au+and+Ag+thin+films+on+silicon+substrates:+Effect+of+grain+size+and+film+thickness.">Nanoindentation measurements of the mechanical properties of polycrystalline Au and Ag thin films on silicon substrates: Effect of grain size and film thickness.</a> Mater. Sci. Eng. A. 457 (1-2), 232-240 (2006).</li><li>Lilleodden, E. T., Nix, W. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microstructural+length-scale+effects+in+the+nanoindentation+behavior+of+thin+gold+films.">Microstructural length-scale effects in the nanoindentation behavior of thin gold films.</a> Acta Mater. 54 (6), 1583-1593 (2006).</li><li>Corcoran, S. G., Colton, R. J., Lilleodden, E. T., Gerberich, W. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anomalous+plastic+deformation+at+surfaces:+Nanoindentation+of+gold+single+crystals.">Anomalous plastic deformation at surfaces: Nanoindentation of gold single crystals.</a> Phys. Rev. B. 55 (24), R16057 (1997).</li><li>Van Vliet, K. 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A method has been presented for performing a series of indentations on an Au(111) thin-film surface with a diamond-coated AFM tip. Non-contact AFM imaging and AFM indentation were performed with the same force sensor. The requirements for non-contact imaging are a high first free resonance frequency f0,1 &#8805; 180 kHz and a high quality factor Q &#8805; 300. In AFM indentation, the vertical force to be applied is in the range of several micro-newtons, and a cantilever with a high bending st...

For the last 150 years, hardness values have been used to characterize the mechanical behavior of materials and to predict their performance under various loading conditions. The hardness of a material describes the resistance of its surface to the penetration of a harder indenter. For metallic materials, the hardness relates to resistance to plastic flow.
Although the implementation of hardness testing has proven to be relatively easy, the yielded results have long been rather empirical, making them unable to describe the intrinsic properties of the investigated material. The empirical nature of hardness testing results has been a consequence of the use of various indenter geometries, each of which has a different established hardness scale. However, all empirical hardness scales, such as the Brinell hardness (HB) test for spherical indenters and the Vickers (HV) and Knoop (HK) hardness tests for different types of four-sided pyramids, have one thing in common: the hardness number is determined from the ratio of the applied load to the developed area of the remaining indent. In an attempt to relate the hardness of metals to their fundamental mechanical properties, the hardness measured with a spherical indenter has been defined as the ratio of the applied load to the projected area of the remaining indent. This hardness value, also known as the Meyer's hardness (H), is equal to the mean contact pressure and directly relates to the yield strength of non-work-hardening metals1. 
Hardness testing has long been limited to the macro-scale, in which case the sizes of indents have been measured by optical means. The development of instrumented indentation, where force-displacement curves are recorded, has been recognized as a valuable alternative for determining the hardness of a material, although the size of the remaining indent may be too small to be accurately imaged. In this case, the projected area of the indent is calculated from the tip displacement according to a so-called indenter-area function2. Due to this development, the analysis of the curvature of force-displacement curves and of the occurrence of distinct plasticity events in the shape of pop-ins is now widely used to study the mechanisms of plastic deformation at the micrometer scale, such as by means of nanoindentation3.
It is well accepted that the carriers of plastic deformation in metals, i.e., dislocations, operate at the nanometer scale. To understand their modes of operation at the atomic level, new experimental techniques with atomic resolution are needed. Initial investigations of atomistic plasticity events at the interfaces between nanometer-sized single asperities and single crystalline Au surfaces of different orientations have been carried out by interfacial force microscopy (IFM)4, 5. Atomic force microscopy (AFM) indentation has been applied to observe the nucleation and gliding of single dislocations in KBr(100) single crystals6, Cu(100)7, and Au(111)8, 9. There, atomistic plasticity events were observed in the shape of pop-ins, with lengths in the range of 1 &#197;. AFM indentation has also been used to measure the nano-hardness and -elasticity of gold nano-island grown on mica10. In this work, the nano-hardness was found to be smaller than the bulk value and was observed to depend linearly on the indentation area. Also, a detailed measurement protocol has been proposed to determine the hardness of hard surfaces, such as fused quartz and silicon, by AFM indentation with a diamond-tipped sapphire cantilever11. In particular, this method takes into account the non-linearity of the photo-sensitive deflection detectors for large cantilever deflection12. More recently, AFM indentation and non-contact AFM imaging have been combined to quantitatively determine the hardness and the fundamental mechanisms of plastic deformation of a Pt(111) single crystalline surface and Pt-based metallic glass13. For Pt(111), plastic deformation mechanisms at the nanometer scale were found to be consistent with the discrete mechanisms established for larger scales. Further, the nanometer-scale plastic deformation of the metallic glass was found to be not discrete, but rather continuous and highly localized around the indenting tip. These results revealed a lower size limit for metallic glasses, below which shear transformation mechanisms are not activated by indentation. AFM indentation has also been used to determine the hardness values of biological samples (such as collagen fibrils)14, polymers15, and colloidal crystals16.
In the present work, a careful experimental procedure is described that includes the force sensor selection, its calibration, the calibration of the cantilever deflection detection system, and the minimization of instrumental drift for accurate and reproducible force-distance measurements. Also, a method for the data analysis is presented that allows the extraction of force-penetration curves from recorded force-distance curves. Further representative results are shown and discussed in the light of recent findings in the field of plastic deformation of small volumes.
For this experiment, an atomic force microscope (AFM) was used. The cornerstone of an AFM is its micro-fabricated force sensor (usually a cantilever beam), with a sharp tip at the end whose radius is in the range of several nanometers. In the particular configuration of the instrument used for this experiment, the cantilever is mounted onto a piezo-electric z-scanner, while the sample to be investigated is mounted onto a piezo-electric x/y-scanner. During AFM imaging, the force sensor tip is scanned over a sample to register interaction forces with the sample surface that result in a deflection of the cantilever according to Hooke's law. The static or dynamic deflection of the cantilever can be measured with an optical beam deflection detector, consisting of a laser diode, a set of mirrors, and a photodiode that converts the cantilever deflection into a voltage. During imaging, the signal at the photodiode is controlled by a feedback loop so as to keep the interaction forces at the sample surface; this results in adjustments of the z-scanner position, which are recorded and displayed as a topography image.
Prerequisites for the experiment described below are that the piezo-electric scanners of the atomic force microscope are well-calibrated and that the instrument stays in the laboratory at a constant temperature and humidity level. The reader should be aware that, depending on the atomic force microscope model, some of the experimental procedure steps may have to be modified. In particular, all measurements are performed after setting the scanners' ranges to "small"; this function allows for the reduction of the x/y-scanner range to 5 x 5 &#181;m&#178; and the z-scanner range to 4 &#181;m, which ensures a resolution at small scales. This function is not available on all commercial AFM and is not mentioned in the remainder of the text.
For data analysis, the use of the free SPM data analysis software Gwyddion17 and the Matlab software package18 are recommended.
This protocol gives a description of the experimental procedure to be followed in order to perform instrumented hardness measurements by AFM. Since the handling of different commercial AFMs may differ from one model to the other, the reader should refer to the manual provided by the AFM manufacturer for detailed setting procedures and software information. In the following text, in order to reproduce the described experiment, it is assumed that the reader is familiar with the handling of the particular AFM used here.

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">AFM XE-100</td>
			<td style="width:71px;">Park Instruments</td>
			<td style="width:119px;">discontinued</td>
			<td style="width:167px;">Atomic force microscope</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">CDT-NCLR</td>
			<td style="width:71px;">NanoSensors</td>
			<td style="width:119px;">CDT-NCLR</td>
			<td>Conductive diamond coated non-contact lever</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">100 nm thick Au(111) thin film on Mica</td>
			<td style="width:71px;">Phasis</td>
			<td align="right">20020011</td>
			<td>atomically smooth gold thin film</td>
		</tr>
	</tbody>
</table>

quantitative hardness measurement by instrumented afm-indentation

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness measurements on an Au(111) surface with atomistic resolution of single plasticity events. A careful experimental procedure is described that includes the force sensor selection, its calibration, the calibration of the cantilever deflection detection system, and the minimization of instrumental drift for accurate and reproducible force-distance measurements. Also, a method for the data analysis is presented that allows the extraction of force-penetration curves from recorded force-distance curves. A typical curve displays a clear elastic deformation regime up to the first plasticity event, or pop-in, with a length in the range of one to two Burger's vectors. Later plasticity events exhibit the same magnitude. The work of plasticity is further extracted from the measurements. Finally, the hardness is determined in combination with the indentation curve using non-contact atomic force microscopy images of the remaining indents.

In this work, the bending stiffness of the cantilever k was calculated according to the geometrical beam theory19. For the particular diamond-coated cantilever used in this work, we found k = 55.69 N/m. Note that we neglected the diamond coating; the thickness of the diamond coating is one to two orders of magnitude smaller than the cantilever thickness and thus does not significantly increase its bending stiffness (although its Young&#39;s modulus is signific...

Watch this Scientific Journal Video about Quantitative Hardness Measurement by Instrumented AFM-indentation at JoVE.com

Quantitative Hardness Measurement by Instrumented AFM-indentation

This experimental protocol describes how atomic force microscopy can be used to measure hardness at the true nanometer scale and to detect single atomistic plasticity events.

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness ...

The overall goal of this AFM based experiment is to quantitatively determine the nano hardness of gold thin film. This method can help on the key question in the nano mechanics of materials field regarding the strengths of materials at the nanometer scale and help to determine the mechanisms responsible for plasting deformation The advantage of this technique, how it's high special and forced resolutions. To begin, mount a stiff diamond coated cantilever with the first free resonance frequency of at least 180kHz, a quality factor of at least 300 and a bending stiffness of at least 40 N/m onto a clamping holder of the AFM.Mount the cantilever holder onto the AFM head align the laser beam and perform a frequency sweep to determine the first free bending residence of the cantilever. Then, in the set up menu of the AFM software, select the default value of the photodiode sensitivity for the particular cantilever type. Place a smooth and non-compliant surface such as nano crystal and diamond or sapphire into the sample holder.Next, draw the cantilever towards the reference sample surface, using the step motor of the AFM. Keep the cantilever in focus during course approach and stop the course approach before the sample surface is in perfect focus in order to avoid contacting the surface. Next, click the approach button to bring the cantilever tip into contact with the reference sample at a load of 10 nano newtons.In the force spectroscopy menu, set the relative retraction and extension of the z scanner to 50 N/m and the z scanner retraction and extension to 0.3 micrometers per second. Click on the acquire button in the forced spectroscopy menu to record a forced distance curve on the non compliant surface. In the calibration menu of the software, fit the repulsive part of the forced distance curve with the linear function, then substitute the determined value with the default value by clicking the execute calibration button.Mount the sample onto a magnetic sample holder and place the holder onto a scanner. Prior to measuring the sample, set the oscillation frequency slightly off resonance at 200.26 khz and the oscillation amplitude to 23.35 nm. Then, enter an oscillation set point of 5 nanometers.Next, draw the cantilever towards the sample surface using the step motor of the AFM. Keep the cantilever in focus during course approach and stop the course approach before the sample surface is in perfect focus in order to avoid contacting the surface. Now, click on the approach button to automatically approach the foresensor.Once the oscillation amplitude has reached its set point the tip is ready to scan the typography of the sample surface. Record a series of typography images on areas ranging from 5 micrometers by 5 micrometers to one micrometer by one micrometer. As needed, adjust the slope of the typography signal by tilting the xy scanner.Make sure that successive images of the same area do not exhibit any sign of drift and that the z scanner position remains almost constant. While attempting this procedure it is important to remember to minimize the instrumental drift. To do so, successive imaging of an area to be indented can be performed prior to the measurements.Once the system has stabilized in the smooth one micrometer square area has been found, click on the retract button to back the fore sensor a few micrometers from the sample surface. Then, select the fore spectroscopy mode, set the fore set point to 10 nanometers and move the fore sensor to the middle of the pre-selected one micrometer square area. Monitor the position of the z scanner until it remains constant.Select a two by two grid of points whose center corresponds to the center of the pre-selected area and set the distance between the two next neighboring points at 500 nanometers. Also, set the relative scanner distance to go from 0 to 150 nanometers at a speed of 300 nanometers per second and then to retract over the same distance and at the same velocity. Apply a tilt correction as described elsewhere by moving the lateral scanner by z times tangent pi during a vertical scanner extension of length z where pi is the tilt angle.At this point, press the start button to begin the acquisition of the AFM indentation data. Once the AFM indentation measurements have been completed, retract the fore sensor a few micrometers away from the sample surface. Then, perform a scan over the same 1 micrometer square surface area so as to locate the exact position of the indents.Perform additional scans over a 500 by 500 nanometers square surface area to image the remaining indents with greater detail. Shown here are non contact AFM typography images of a gold thin film surface. The thin film surface was found to consist of grains in the micrometer range.Each grain exhibits an atomically flat gold 111 surface consisting of large terraces and mono atomic steps. This gold 111 surface was indented four times by an AFM tip with a maximal vertical force of 7.2 micronewtons. The typographical difference between the two surfaces shows that the indents were the only major change to the surface.The projected area of each indent can be measured by masking the area with negative typography values relative to the unmarred surface. From this information, the hardness of the material can be calculated though it is likely to be underestimated because of elastic recovery. After watching this video, you should have a good understanding of how to determine the hardness of a metallic material at the true nanometer scale in under two hours.While attempting this procedure, it is important to remember to minimize the instrumental drift. To do so, successive imaging of an area to be indented can be performed prior to the measurements. After its development, this technique paved the way for researchers in the field of surface science to explore the atomistic mechanisms of plastic deformation in solid materials.

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Optical Trap Loading of Dielectric Microparticles In Air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

Standardized Method for Measuring Collection Efficiency from Wipe-sampling of Trace Explosives

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Optimized sampling protocols and the development of new wipe materials can be facilitated by standardized measurements of collection efficiency from wipe-sampling. Our approach for sampling trace explosives uses an automated device to control speed, force, and distance during wipe-sampling followed by extraction of collected explosives.

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common ...

Micro/Nano-scale Strain Distribution Measurement from Sampling Moir&#233; Fringes

This work describes the measurement procedure and principles of a sampling moir&#233; technique for full-field micro/nano-scale deformation measurements. The developed technique can be performed in two ways: using the reconstructed multiplication moir&#233; method or the spatial phase-shifting sampling moir&#233; method. When the specimen grid pitch is around 2 pixels, 2-pixel sampling moir&#233; fringes are generated to reconstruct a multiplication moir&#233; pattern for a deformation measurement. Both the displacement and strain sensitivities are twice as high as in the traditional scanning moir&#233; method in the same wide field of view. When the specimen grid pitch is around or greater than 3 pixels, multi-pixel sampling moir&#233; fringes are generated, and a spatial phase-shifting technique is combined for a full-field deformation measurement. The strain measurement accuracy is significantly improved, and automatic batch measurement is easily achievable. Both methods can measure the two-dimensional (2D) strain distributions from a single-shot grid image without rotating the specimen or scanning lines, as in traditional moir&#233; techniques. As examples, the 2D displacement and strain distributions, including the shear strains of two carbon fiber-reinforced plastic specimens, were measured in three-point bending tests. The proposed technique is expected to play an important role in the non-destructive quantitative evaluations of mechanical properties, crack occurrences, and residual stresses of a variety of materials.

A sampling moir&#233; technique featuring 2-pixel and multi-pixel sampling methods for high-accuracy strain distribution measurements at the micro/nano-scale is presented here.

This work describes the measurement procedure and principles of a sampling moir&#233; technique for full-field micro/nano-scale deformation measurements. ...

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. This paper proposes a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation. The polydimethylsiloxane (PDMS) chip was fabricated using the multi-layer soft lithography method. Hexadecane containing surfactant was used as the continuous phase, and PEGDA with the ultraviolet (UV) photo-initiator was the dispersed phase. Surfactants allowed the local surface tension to drop and formed a more cusped tip which promoted breaking into tiny micro-droplets. As the pressure of dispersed phase was constant, the size of droplets became smaller with increasing continuous phase pressure before dispersed phase flow was broken off. As a result, droplets with size variation from 1 &#181;m to 80 &#181;m in diameter could be selectively achieved by changing the pressure ratio in two inlet channels, and the average coefficient of variation was estimated to be below 7%. Furthermore, droplets could turn into micro-beads by UV exposure for photo-polymerization. Conjugating biomolecules on such micro-beads surface have many potential applications in the fields of biology and chemistry.

Generation of Size-controlled Poly ethylene Glycol Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Here, we present a protocol to illustrate the fabrication processes and verifying experiments of a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation.

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. ...

Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves several steps, include drawing samples, cooling, cutting, transport to the laboratory, and analysis. The whole analysis process requires more than 30 minutes, which hinders on-line process control. Laser-induced breakdown spectroscopy is an excellent on-line analysis method that can satisfy the requirements of vacuum induction melting because it is fast and noncontact and does not require sample preparation. The experimental facility uses a lamp-pumped Q-switched laser to ablate melted liquid steel with an output energy of 80 mJ, a frequency of 5 Hz, a FWHM pulse width of 20 ns, and a working wavelength of 1,064 nm. A multi-channel linear charge coupled device (CCD) spectrometer is used to measure the emission spectrum in real time, with a spectral range from 190 to 600 nm and a resolution of 0.06 nm at a wavelength of 200 nm. The protocol includes several steps: standard alloy sample preparation and an ingredient test, smelting of standard samples and determination of the laser breakdown spectrum, and construction of the elements concentration quantitative analysis curve of each element. To realize the concentration analysis of unknown samples, the spectrum of a sample also needs to be measured and disposed with the same process. The composition of all main elements in the melted alloy can be quantitatively analyzed with an internal standard method. The calibration curve shows that the limit of detection of most metal elements ranges from 20-250 ppm. The concentration of elements, such as Ti, Mo, Nb, V, and Cu, can be lower than 100 ppm, and the concentrations of Cr, Al, Co, Fe, Mn, C, and Si range from 100-200 ppm. The R2 of some calibration curves can exceed 0.94.

During vacuum induction melting, laser-induced breakdown spectroscopy is used to perform real-time quantitative analysis of the main-ingredient elements of a molten alloy.

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves ...

A Random-displacement Measurement by Combining a Magnetic Scale and Two Fiber Bragg Gratings

Long-distance displacement measurements using optical fibers have always been a challenge in both basic research and industrial production. We developed and characterized a temperature-independent fiber Bragg grating (FBG)-based random-displacement sensor that adopts a magnetic scale as a novel transferring mechanism. By detecting shifts of two FBG center wavelengths, a full-range measurement can be obtained with a magnetic scale. For identification of the clockwise and counterclockwise rotation direction of the motor (in fact, the direction of movement of the object to be tested), there is a sinusoidal relationship between the displacement and the center wavelength shift of the FBG; as the anticlockwise rotation alternates, the center wavelength shift of the second FBG detector shows a leading phase difference of around 90&#176; (+90&#176;). As the clockwise rotation alternates, the center wavelength shift of the second FBG displays a lagging phase difference of around 90&#176; (-90&#176;). At the same time, the two FBG-based sensors are temperature independent. If there is some need for a remote monitor without any electromagnetic interference, this striking approach makes them a useful tool for determining the random displacement. This methodology is appropriate for industrial production. As the structure of the whole system is relatively simple, this displacement sensor can be used in commercial production. In addition to it being a displacement sensor, it can be used to measure other parameters, such as velocity and acceleration.

A protocol to create a full-range linear displacement sensor, combining two packaged fiber Bragg grating detectors with a magnetic scale, is presented.

Long-distance displacement measurements using optical fibers have always been a challenge in both basic research and industrial production. We developed ...

Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and multi-intermediates. Thermogravimetry-mass spectrum (TG-MS) is seen as a powerful tool to study reaction features. However, reaction details and reaction mechanics have not been effectively obtained directly from the ion current of TG-MS. Here, we provide a method of an equivalent characteristic spectrum analysis (ECSA) for analyzing the mass spectrum and giving the mass flow rate of reaction gases as precise as possible. The ECSA can effectively separate overlapping ion peaks and then eliminate the mass discrimination and temperature-dependent effect. Two example experiments are presented: (1) the decomposition of CaCO3 with evolved gas of CO2 and the decomposition of hydromagnesite with evolved gas of CO2 and H2O, to evaluate the ECSA on single-component system measurement and (2) the thermal pyrolysis of Zhundong coal with evolved gases of inorganic gases CO, H2, and CO2, and organic gases C2H4, C2H6, C3H8, C6H14, etc., to evaluate the ECSA on multi-component system measurement. Based on the successful calibration of the characteristic spectrum and relative sensitivity of specific gas and the ECSA on mass spectrum, we demonstrate that the ECSA accurately gives the mass flow rates of each evolved gas, including organic or inorganic gases, for not only single but multi-component reactions, which cannot be implemented by the traditional measurements.

Precise determination of the evolved gases&#39; flow rate is key to study the details of reactions. We provide a novel quantitative analysis method of equivalent characteristic spectrum analysis for thermogravimetry-mass spectrum analysis by establishing the calibration system of the characteristic spectrum and relative sensitivity, for obtaining the flow rate.

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and ...

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, where the yarns in each layer are oriented parallel to each other and held in place using binder resins and thin polymer films. The armor is constructed by stacking the unidirectional layers in different orientations. To date, only very preliminary work has been performed to characterize the ageing of the binder resins used in unidirectional laminates and the effects on their performance. For example, during the development of the conditioning protocol used in the National Institute of Justice Standard-0101.06, UD laminates showed visual signs of delamination and reductions in V50, which is the velocity at which half of the projectiles are expected to perforate the armor, after ageing. A better understanding of the material property changes in UD laminates is necessary to comprehend the long-term performance of armors constructed from these materials. There are no current standards recommended for mechanically interrogating unidirectional (UD) laminate materials. This study explores methods and best practices for accurately testing the mechanical properties of these materials and proposes a new test methodology for these materials. Best practices for ageing these materials are also described.

The goal of the study was to develop protocols to prepare consistent specimens for accurate mechanical testing of high-strength aramid or ultra-high-molar-mass polyethylene-based flexible unidirectional composite laminate materials and to describe protocols for performing artificial ageing on these materials.

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, ...

Method Development for Contactless Resonant Cavity Dielectric Spectroscopic Studies of Cellulosic Paper

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of data that can be obtained from an individual sample and renders it difficult to produce statistically relevant data for unique and rare materials. Resonant cavity dielectric spectroscopy is a non-destructive, contactless technique which can simultaneously interrogate both sides of a sheeted material and provide measurements which are suitable for statistical interpretations. This offers analysts the ability to quickly discriminate between sheeted materials based on composition and storage history. In this methodology article, we demonstrate how contactless resonant cavity dielectric spectroscopy may be used to differentiate between paper analytes of varying fiber species compositions, to determine the relative age of the paper, and to detect and quantify the amount of post-consumer waste (PCW) recycled fiber content in manufactured office paper.

A protocol for the non-destructive analysis of the fiber content and relative age of paper.

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of ...

Calibration Procedures for Orthogonal Superposition Rheology

Orthogonal superposition (OSP) rheology is an advanced rheological technique that involves superimposing a small-amplitude oscillatory shear deformation orthogonal to a primary shear flow. This technique allows the measurement of structural dynamics of complex fluids under non-linear flow conditions, which is important for the understanding and prediction of the performance of a wide range of complex fluids. The OSP rheological technique has a long history of development since the 1960s, mainly through the custom-built devices that highlighted the power of this technique. The OSP technique is now commercially available to the rheology community. Given the complicated design of the OSP geometry and the non-ideal flow field, users should understand the magnitude and sources of measurement error. This study presents calibration procedures using Newtonian fluids that includes recommendations for best practices to reduce measurement errors. Specifically, detailed information on the end-effect factor determination method, sample filling procedure, and identification of the appropriate measurement range (e.g., shear rate, frequency, etc.) are provided.

We present a detailed calibration protocol for a commercial orthogonal superposition rheology technique using Newtonian fluids including end-effect correction factor determination methods and recommendations for best practices to reduce experimental error.

Orthogonal superposition (OSP) rheology is an advanced rheological technique that involves superimposing a small-amplitude oscillatory shear deformation ...