Name: quantification of hydrogen concentrations in surface and interface layers and bulk materials through depth profiling with nuclear reaction analysis
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We greatly appreciate M. Matsumoto for implementing the software that enables the automated measurement of NRA H depth profiles by remotely controlling the MALT accelerator parameters from the data acquisition PC. We thank K. Namba for skillfully performing Pd(110) sample preparations and NRA and TDS measurements at the BL-1E UHV system, and C. Nakano for technical assistance in the accelerator operation. The SiO2/Si(100) specimen is gratefully received as a courtesy of Z. Liu of NEC Corporation, Japan. This work is partially supported by Grants-in-Aid for Scientific Research (Grant numbers 24246013 and 26108705) of the Japan Society for the Promotion of Science (JSPS), as well as through a Grant-in-Aid for Scientific Research in Innovative Areas &#39;Material Design through Computics: Complex Correlation and Non-Equilibrium Dynamics&#39; from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

1. Planning of Experiments
<ol>
	<li>Identify the MALT accelerator beam line of interest depending on the measurement task (BL-1E for surface hydrogen, BL-2C for bulk or interfacial hydrogen). Contact the assisting scientist (currently M.W. or K.F.) to discuss details of the NRA measurements and their necessary preparations.</li>
	<li>Download a beam time application form and observe the submission deadline on the MALT website31. 
	Note: The MALT facility invites new project proposals each March and Sep...

<ol>
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Figure 4 demonstrates the efficient distinction and quantitation of surface-adsorbed from bulk-absorbed hydrogen through 15N NRA at the example of a Pd(110) single crystal in the BL-1E UHV system. The high reproducibility of the surface H peak in the three profiles attests to the reliability of the in-situ UHV sample preparation and to the non-destructive nature of the NRA measurement. The quantitative agreement of the determined H coverage with the expected atomic saturation density ...

The ubiquity of hydrogen as an impurity or as a constituent of a vast variety of materials and the wealth of hydrogen-induced interaction phenomena make revealing the hydrogen distribution in the near-surface region and at buried interfaces of solids an important task in many areas of engineering and fundamental material science. Prominent contexts include studies of hydrogen absorption in storage and purification materials for hydrogen energy applications, fuel cell, photo-, and hydrogenation catalysis, hydrogen retention and embrittlement in nuclear and fusion reactor engineering, hydrogen-induced surfactant effects in epitaxial growth fabrication and hydrogen-related electrical reliability issues in semiconductor device technology.
Despite its omnipresence and simple atomic structure, the quantitative detection of hydrogen poses analytical challenges. As hydrogen contains only a single electron, otherwise versatile elemental analysis by electron spectroscopy is rendered ineffective. Common hydrogen detection methods through mass analytical, optical, or nuclear resonance techniques such as metallurgical fusion, thermal desorption, infrared absorption or NMR spectroscopy are principally insensitive to the depth location of hydrogen. This precludes, e.g., discriminating between surface-adsorbed and bulk-absorbed hydrogen which differ substantially in their physical and chemical material interactions, and their distinction therefore becomes increasingly important for the analysis of nanostructured materials that comprise small volumes and large surface areas. Hydrogen profiling by secondary ion mass spectroscopy, although providing depth-resolved quantitative H concentrations, is equally destructive to the analyzed target as metallurgical fusion, and sputtering effects may render the depth information obtained near the surface unreliable.
Nuclear reaction analysis with the narrow energy resonance (Eres) of the 1H(15N,&#945;&#947;)12C reaction at 6.385 MeV1-3, on the other hand, combines the advantages of non-destructive hydrogen quantitation with high depth resolution in the order of a few nanometers near the surface. The method determines surface H coverages with a sensitivity in the order of 1013 cm-2 (~1% of a typical atomic monolayer density). Hydrogen concentrations in the interior of materials can be assessed with a detection limit of several 1018 cm-3 (~100 at. ppm) and a probing depth range of about 2 &#956;m. The near-surface depth resolution is routinely 2-5 nm in surface-normal incidence of the 15N ion beam onto the analyzed target. In surface-grazing incidence geometries, the resolution can be enhanced further to values below 1 nm. See Ref. 3 for a detailed account.
These capabilities have proven 1H(15N,&#945;&#947;)12C NRA as a powerful technique to elucidate the static and dynamic behavior of hydrogen at surfaces and interfaces in a large variety of processes and materials3. Established by Lanford4 in 1976, 15N NRA was first used predominantly to quantitatively determine volume H concentrations in bulk materials and thin films. Among other purposes, the absolute hydrogen concentrations obtained through 15N NRA have been used to calibrate other, not directly quantitative, hydrogen detection techniques5,6. Also 15N NRA hydrogen profiling in targets with well-defined interfaces in layered thin film structures has been described7-10. More recently, much progress has been achieved in studying hydrogen in the near-surface region of chemically clean and structurally well-defined targets by combining 15N NRA with surface analytical ultra-high vacuum (UHV) instrumentation to prepare atomically controlled surfaces in situ for the H analysis3.
By quantifying the hydrogen coverage on single crystal surfaces, NRA has contributed significantly to the current microscopic understanding of hydrogen adsorption phases on many materials. 1H(15N,&#945;&#947;)12C NRA is furthermore the only experimental technique to directly measure the zero-point vibrational energy of surface-adsorbed H atoms11, i.e., it can reveal the quantum-mechanical vibrational motion of adsorbed H atoms in the direction of the incident ion beam. Through the capability of nanometer-scale discrimination between surface-adsorbed and bulk-absorbed H, 15N NRA can provide valuable insight into the hydrogen ingress through material surfaces, such as relevant to mineral hydration dating12 or for observing hydride nucleation underneath surfaces of H-absorbing metals13-15. High-resolution 15N NRA applications have demonstrated the potential to detect sub-monolayer thickness variations of adlayers16 and to distinguish surface-adsorbed from volume-absorbed hydrogen in Pd nanocrystals17. The combination with thermal desorption spectroscopy (TDS) allows for unambiguous identifications of H2 thermal desorption features and for the depth-resolved assessment of the thermal stability of adsorbed and absorbed hydrogen states against desorption and diffusion13,15,18. Due to its non-destructive nature and high depth resolution 1H(15N,&#945;&#947;)12C NRA is also the ideal method to detect hydrogen buried at intact interfaces, which allows for studying hydrogen trapping at metal/metal19-22 and metal/semiconductor interfaces16,23-25 and for tracking hydrogen diffusion in stacked thin film systems9. By directly visualizing hydrogen redistribution phenomena between interfaces of SiO2/Si-based metal-oxide-semiconductor (MOS) structures that relate to electrical device degradation, NRA has made particularly valuable contributions to device reliability research26.
The hydrogen detection principle in NRA is to irradiate the analyzed target with a 15N ion beam of at least Eres=6.385 MeV to induce the resonant 1H(15N,&#945;&#947;)12C nuclear reaction between 15N and 1H in the material. This reaction releases characteristic &#947;-rays of 4.43 MeV that are measured with a scintillation detector nearby the sample. The &#947;-yield is proportional to the H concentration in a certain depth of the target. Normalizing this signal by the number of incident 15N ions converts it into absolute H density after the &#947;-detection system has been calibrated with a standard target of known H concentration. 15N ions incident at Eres can react with hydrogen on the target surface. The concentration of buried hydrogen is measured with 15N ions incident at energies (Ei) above Eres. Inside the target material, the 15N ions suffer energy loss due to electronic stopping. This effect provides the high depth resolution, because the 1H(15N,&#945;&#947;)12C nuclear reaction resonance has a very narrow width (Lorentzian width parameter &#915; = 1.8 keV) and the stopping power of materials for 6.4 MeV 15N ranges between 1-4 keV/nm, so that the passage of the 15N ion through only a few atomic layers is sufficient to shift its energy outside the resonance window. Thus, the resonant reaction detects buried H at Ei &#62; Eres in a probing depth d=(Ei-Eres)/S, where S is the electronic stopping power of the analyzed material3.
By measuring the &#947;-yield while scanning the incident 15N ion energy in small increments, one obtains a nuclear reaction excitation curve that contains the density-depth distribution of hydrogen in the target. In this excitation curve (&#947;-yield vs. 15N energy), the actual H depth distribution is convolved with the NRA instrumental function that adds a predominantly Gaussian broadening and is the main limitation for the depth resolution3. At the surface (i.e., at Ei = Eres) the Gaussian width is dominated by a Doppler Effect due to zero-point vibration of the H atoms against the target surface.11,27,28 The yield curve of buried hydrogen detected at Ei &#62; Eres is affected by an additional Gaussian broadening component due to random 15N ion energy straggling inside the target. The straggling width increases in proportion to the square root of the ion trajectory length in the material 29,30 and becomes the dominant resolution limiting factor above probing depths of 10-20 nm.
To demonstrate a few very typical hydrogen profiling applications with 15N NRA, we here exemplarily describe (1) the quantitative evaluation of the surface H coverage and of the bulk-absorbed hydrogen concentration in a H2 exposed palladium (Pd) single crystal, and (2) the evaluation of the depth location and hydrogen layer densities at buried interfaces of SiO2/Si(100) stacks. The NRA measurements are performed at the MALT 5 MV van-de-Graaf tandem accelerator31 of the University of Tokyo, which delivers a highly stable and well-monochromatized (&#916;Ei &#8805; 2 keV) 15N ion beam of 6-13 MeV. The authors have developed a computer control system for the accelerator to enable automated energy scanning and data acquisition for hydrogen profiling. Reflecting the two different NRA measurement tasks presented by the above H profiling applications, the MALT facility provides two ion beam lines with specialized experimental stations: (1) a UHV surface analytical system with a single bismuth germanate (BGO, Bi4Ge3O12) &#947;-scintillation detector dedicated to the NRA quantitation of hydrogen surface coverages, to zero-point vibration spectroscopy, and to H depth profiling at atomically controlled single crystal targets in a unique combination with TDS; and (2) a high vacuum chamber equipped with two BGO detectors positioned very close to the target for increased &#947;-detection efficiency, providing for a lower H detection limit and faster data acquisition. This setup has no sample preparation facilities but allows for rapid sample exchange (~30 min) and thus for a higher throughput of targets for which a well-controlled surface layer is not an essential part of the analytical task, such as H profiling at buried interfaces or the quantitation of bulk H concentrations. At both beam lines, the BGO detectors are placed conveniently outside of the vacuum systems because the &#947;-rays penetrate the thin chamber walls with negligible attenuation.
<img alt="Figure 1" src="/files/ftp_upload/53452/53452fig1.jpg" /> 
Figure 1. NRA setup in the BL-1E UHV system. (A) Schematic top view into the BL-1E UHV system equipped with sputter ion gun, low energy electron diffraction (LEED), and Auger electron spectroscopy (AES) for the in-situ preparation of atomically ordered and chemically clean single crystal surface targets and combined NRA and TDS measurements with a quadrupole mass spectrometer (QMS) mounted on a linear translation stage. (B) Pd single crystal specimen attached on the sample holder of the cryogenic manipulator. <a href="https://www.jove.com/files/ftp_upload/53452/53452fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 1 (A) illustrates the UHV system at beam line (BL)-1E, which is fully equipped for the in-situ preparation of atomically ordered single crystal surfaces and has a base pressure &#60;10-8 Pa to maintain surface cleanliness. To provide sample access for the surface-analytical tools, the 4&#34; BGO scintillator is placed on the 15N ion beam axis ~30 mm behind the target. The sample is mounted on a 4-axis manipulation stage for precise (x, y, z, &#920;) positioning and can be cooled with liquid nitrogen to ~80 K or with compressed He to ~20 K. Figure 1 (B) shows a Pd single crystal target mounted by spot-welded Ta support wires to a He compression cryostat. Quartz sheet spacers insulate the sample holder plate electrically from the cryostat body. This enables the incident 15N ion beam current measurement necessary for quantitative NRA and allows for electron bombardment heating from the tungsten filament on the backside of the sample holder. A type K thermocouple is spot-welded to the edge of the Pd specimen. A quartz plate attached on the manipulator axis above the sample is used to monitor the ion beam profile and for sample-beam alignment. Figure 2 (A) shows the setup at BL-2C with two 4&#34; BGO detectors arranged at 90&#176; with respect to the 15N beam with their front face no further than 19.5 mm apart from the beam axis. The sample holder (Figure 2 (B)) provides a simple clamping mechanism for quick sample exchange and allows for rotation of the sample around the vertical axis to adjust the 15N incidence angle.
<img alt="Figure 2" src="/files/ftp_upload/53452/53452fig2.jpg" /> 
Figure 2. NRA setup at BL-2C. (A) Schematic top view into the high vacuum chamber at BL-2C equipped with two BGO &#947;-detectors close to the target position. (B) Sample holder with a large chip target of SiO2/Si(100) clamped on. Fogging up this sample type with water vapor after the NRA analysis visualizes the spots that were irradiated by the 15N ion beam. <a href="https://www.jove.com/files/ftp_upload/53452/53452fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table>
	<tbody>
		<tr>
			<td>Pd single crystal&#160;</td>
			<td>SPL (Surface Preparation Laboratory), http://www.spl.eu/products.html, or any other suitable supplier</td>
			<td>Order made to specification</td>
			<td>Disk, 9 mm diam., (110) oriented, aligned to &#60; 0.5 degree or less, one side polished to &#60; 0.3 mm roughness, self-prepared specimen&#160;</td>
		</tr>
		<tr>
			<td>H2 gas</td>
			<td>Joutou Gas Corporation, Ltd., Japan, http://www.jyotougas.co.jp/item/gas.html</td>
			<td></td>
			<td>(99.9995%), or any other suitable supplier</td>
		</tr>
		<tr>
			<td>O2 gas</td>
			<td>Joutou Gas Corporation, Ltd., Japan, http://www.jyotougas.co.jp/item/gas.html</td>
			<td></td>
			<td>(99.99%), or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Ar gas</td>
			<td>Joutou Gas Corporation, Ltd., Japan, http://www.jyotougas.co.jp/item/gas.html</td>
			<td></td>
			<td>(99.99995%), or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Tantalum / Wire</td>
			<td>The Nilaco Corporation, http://nilaco.jp/en/order.php</td>
			<td>TA-411325</td>
			<td>(99.95%), 0.3 mm diam., or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Alumel / Wire&#160;</td>
			<td>The Nilaco Corporation, http://nilaco.jp/en/order.php</td>
			<td>851266</td>
			<td>0.2 mm diam., or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Chromel / Wire (Chromel)</td>
			<td>The Nilaco Corporation, http://nilaco.jp/en/order.php</td>
			<td>861266</td>
			<td>0.2 mm diam., or any other suitable supplier</td>
		</tr>
	</tbody>
</table>

quantification of hydrogen concentrations in surface and interface layers and bulk materials through depth profiling with nuclear reaction analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

Figure 4 shows near-surface NRA H profiles of H2-exposed Pd(110) measured in the BL-1E UHV system at a sample temperature of 90 K under a H2 background pressure of 1.33&#215;10-6 Pa. The 15N ion incidence energy has been converted into probing depth using the stopping power of Pd (S = 3.90 keV/nm). The open symbol profile was obtained after pre-exposing the Pd(110) sample to 2,000 L H2 at 145 K to induce abso...

Watch this Scientific Journal Video about Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis at JoVE.co

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

The overall goal of nuclear reaction analysis with the resonant 15 nH nuclear reaction is to measure the density of absorbed hydrogen atoms on solid surfaces, and to determine the concentration versus depth distribution of absorbed hydrogen in the volume of materials. Clarifying the hydrogen content on surfaces, in the near surface region, and at shallow interfaces of solids is a key question in many fields of fundamental material science and engineering. The main advantage of nuclear reaction analysis is that it reveals the concentration and depth location of hydrogen quantitatively, nondestructively, and with nanometer depth resolution.Hydrogen profiling with NRA supports research of hydrogen storage and purification materials. Fuel cell and hydrogenation catalysts, hydrogen retention and embrittlement, device fabrication and hydrogen-related reliability concerns in semi-conducted technology. In this video, we demonstrate a unique combination of NRA with surface science instrumentation for the quantification of a hydrogen-layered densities on atomically-controlled target surfaces and at shallow interfaces.These nuclear reaction analysis experiments take place at the University of Tokyo's MALT accelerator facility. Measurements of surface hydrogen are done on beam line 1E in this ultra-high vacuum chamber. This chamber has been loaded with a palladium 110 single crystal sample and is held at less than 10 nanopascals at room temperature.This top view schematic of the sample chamber gives an overview of the equipment layout. The nitrogen ion beam line including a deflector and a Faraday cup comes in at the left. In addition, there is an ion gun for sputtering as well as an input for hydrogen.The chamber is equipped to perform low energy electron diffraction and Auger electron spectroscopy for INC2 preparation of targets. The final two instruments are quadrupole mass spectrometer shown at the bottom of the schematic and a scintillation detection system at the right. The sample is held by a sample holder on an XYZ stage near the center of the chamber and can be viewed through a viewport.This picture provides an example of the sample holder with a sample that is currently in the chamber. Tantalum wires support a single crystal specimen. The holder also facilitates electrical and thermal measurements.Begin with cleaning the target surface in the chamber through sputtering and annealing. Operate the XYZ stage to position the sample in the center of the chamber. In addition, rotate the sample to properly align it.The sample should face the gas doser between the ion gun and the viewport. To fine adjust the angle, turn on the ion gun power supply. Adjust emission control to 20 milliamps.Observe the sample through the viewport while fine adjusting its angle. The goal is to have the mirror image of the ion gun filament visible on the sample surface. Once fine adjustment is complete, change the ion gun power supply setting for the beam energy to 800 electron volts.Next, at the bottom of the chamber, close the NEG pump gate valve. Use a variable leak valve to introduce 9 millipascal argon gas into the chamber. For sputter ion current reading, consult the digital tester connected between the sample and ground.Confirm that the current is around two microamps for the 10-minute duration of the sputter. Stop the sputtering by closing the variable leak valve and turning off the ion gun power supply. Continue preparations by bringing liquid nitrogen to the manipulator and adding about 100 milliliters to the cryostat.Stay at the manipulator to make electrical connections for annealing. Connect the filament heater lids to the heater power supply. Also, connect the thermocouple feedthrough to a digital tester to monitor the temperature.Ground the filament by connecting it to the chamber body. Finally, connect the sample contact to the bias voltage power supply. At this point, set up the high voltage power supply.Apply a sample bias of one kilovolt. Proceed to anneal the sample at 1, 000 Kelvin and oxidize it at 750 Kelvin. After annealing and oxidation, prepare to do low energy electron diffraction on the sample.Observe the diffraction pattern and look for a clear structure with bright spots and low background noise as in this example. Be prepared to repeat the sputtering, annealing, oxidation, and reduction steps as necessary. The next step is to align the nitrogen ion beam to the single crystal target for nuclear reaction analysis.Center the sample in the XY plane and adjust the Z position to the height of the mass spectrometer front aperture. Rotate the sample back to face the beam line. Next, lower the sample holder to put the beam profile monitor into position for nuclear reaction analysis.Set a camera on the window flange to transmit beam profile images to the control room. Return to the manipulator and remove all electrical contacts to the sample. After this, attach the sample current line.Now, prepare for introducing the ion beam. Set the electrostatic deflector voltage on the beam line to 8, 500 volts. Enter the control room to continue.There, switch the current integrator from standby mode to operate. This schematic represents a portion of the accelerator beam line before the ion beam is stirred to the different experiment beam lines. The experiment beam lines are also represented.There are four components that are important for this protocol. BM03 is a 90-degree sector magnet. It selects the ion beam energy during depth profiling.FC04 is a Faraday cup that can be inserted into the beam to read the ion beam current and prevent the beam from reaching the sample. MQ04 is a magnetic quadrupole lens used to focus the beam onto the sample. And BM04 is a bending magnet that directs the beam into the beam lines.Take steps to adjust the ion beam energy and direct the beam onto the target in the vacuum chamber. Set the MQ04 magnetic quadrupole lens, XCC and the YCC lens parameters to approximately focus the beam. Open the gate valves between the accelerator and the beam line and then open the Faraday cup, FC04.Use the monitor to observe the ion beam profile on the quart's plate in the target chamber. With this feedback, fine-tune the bending magnet, BM04 and the magnetic quadrupole lens settings. The goal is to obtain a well-focused ion beam in the center of the profile monitor plate.Close the Faraday cup and record the parameters before returning to the beam line. Back on beam line 1E, use the filament heater to flash heat the palladium sample to 600 Kelvin then set the filament heater to about 3.6 amps to maintain the sample temperature at 145 Kelvin. Isolate the chamber from the accelerator and NEG pump before exposing the sample to 2, 000 langmuirs of hydrogen at 145 Kelvin.Turn off the filament heater and when the temperature reaches 80 Kelvin, adjust the hydrogen background pressure to be one micropascal. Back in the control room, arrange for the nitrogen ion beam to have the desired starting energy. For this experiment, ensure that Faraday cup 04 registers a beam current of 10 to 20 nanoamps.Next, enter the parameters for the energy scan and the acquisition time into the control software before starting automated data acquisition. These are typical parameter values for BM03 to control the energy scan. Values are given for selecting the initial energy, the final energy, and the change in energy with each step.The acquisition time is 50 seconds. Measurements of bulk and interface hydrogen are done on beam line 2C. This manipulator has been removed from the beam line and is ready with a new sample in the sample holder.For these measurements, the sample is a thin film of silicon dioxide on a silicon 100 surface. With the sample aligned parallel to the transfer tube access, tighten the clamp screws to secure it in place. Retract the sample into the transfer tube and secure it with a locking screw.Move the manipulator to its position on the beam line and reinstall it on the gate valve. When the system is ready, lower the sample into position for the NRA measurement. As in this schematic, align the sample surface normal to the incident beam.Use a beam line camera and monitor for this purpose. At the manipulator head, connect the sample current line to the control room current integrator. Move to the control room to continue.Coursely align the beam by setting the bending magnet and the magnetic quadrupole lens parameters. Observe the beam profile on the profile monitor while further optimizing the parameters for beam transmission and keeping the profile on target. Next, set the BM03 parameter to determine the starting beam energy for the scan.At the computer, enter the desired parameters for the energy scan and start the automated scan of energy to acquire a depth profile. This near surface depth profile is from single crystal palladium that has had its 110 surface exposed to hydrogen gas. The experiment was performed in beam line 1E with a hydrogen background pressure of 1.3 micropascals.The bottom horizontal axis gives the nitrogen ion beam energy. The top axis provides a measure of the depth based on the stopping power of palladium. The open symbols correspond to an experiment with palladium that was pre-exposed in 100 seconds to 2, 000 langmuirs of hydrogen gas at 145 Kelvin.The data were taken at 90 Kelvin. The profile can be decomposed into a peak at depth zero in black and a plateau in blue. The area of the peak provides information on hydrogen surface density.In this case, the coverage is 1 1/2 hydrogens per surface palladium atom. The plateau reveals that hydrogen has been absorbed to a depth of at least 20 nanometers. The gray and black symbols are for experiments with no pre-dosage of hydrogen.These data were taken at 170 Kelvin. These plots represent data from a series of experiments with silicon dioxide on silicon performed in beam line 2C. As before, the ion energy is shown on the bottom axis.The depth along the top. The positions of the interface between the materials is indicated by a vertical dashed line. All profiles show two peaks indicating a non-uniform distribution of hydrogen including hydrogen just a few nanometers in front of the silicon oxide silicon interface.The experiments in this video demonstrate that the NRA technique can distinguish surface-absorbed and volume or interface-absorbed hydrogen in solid targets. NRA furthermore quantifies the hydrogen content at their respective depth locations without destroying the sample material. Please be aware that especially the temperature and pressure during hydrogen exposure, very critically influence the depth distribution of palladium-absorbed hydrogen.If these experimental parameters are changed, hydrogen profile is different from those shown in this video will likely result. After watching this video, you should have a good impression of how nuclear reaction analysis measurement is performed at MALT facility to quantitatively determine hydrogen densities on surfaces and in the interior of solid materials through nanoscale depth profile.

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