The experiments were carried out at the Chemical Dynamics Beamline at the Advanced Light Source, Lawrence Berkeley National Laboratory and supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231, through the Chemical Sciences Division.

1. Sample Loading
<ol>
	<li>Remove the back flange and disassemble the 3/8" stainless nozzle tube from the apparatus (See Figure 1 and Figure 2) and make sure it is clean and the 100 mm orifice is clear (This can be done by looking at a light source through it). For cleaning, fill the tube with ~1 ml ethanol and scrub the inside using cotton tips. Alternatively, place the nozzle in an ultrasonic bath filled with soap and water or ethanol for about 20 min. Then dry with compressed air.</li>
	<li>Using a small, clean spatula, place about 250 mg of sample in the front part of the nozzle, close to the orifice but not blocking it. A good method to avoid the orifice from getting blocked is to place a small aluminum foil ball or glass wool in front of the orifice and then add the sample powder. Use a cotton tip to push the sample into the tube to ensure it is in the front 25 mm of the tube. This front part will comprise the heated zone.</li>
	<li>Reattach the nozzle to the apparatus carefully to avoid moving the sample powder inside. Then attach the birdcage adapter (See Figure 2), heater block and thermocouple (See Figure 3).</li>
	<li>Before closing the vacuum chamber, measure the distance from the flange surface to the tip of the nozzle to be 22.5 inches; this will allow 0.5 inch between the nozzle and the skimmer.</li>
	<li>When the vacuum chamber is closed, test the heater cartridge and thermocouple connections to make sure they are well connected to the feed-through connectors.</li>
	<li>Make sure the carrier gas inlet valve is closed.</li>
	<li>Close the venting valve (if it was used).</li>
	<li>Slowly begin pumping the chamber using the roughing pumps (4 valves), and when the pressure in the chamber is &lt;1 torr, start the turbomolecular pumps (5 pumps).</li>
	<li>When the pressure in the chamber is &lt;10-6 torr, apply the voltages to the ion optics of the time of flight mass spectrometer, and the micro-channel plate detector (the voltage on the latter should be turned on gradually) (See Figure 1 for various voltages).</li>
	<li>Open the VUV shutter to allow the photon beam in the chamber.</li>
	<li>Open the carrier gas inlet valve and set the backing pressure regulator to 460 (this is a vacuum regulator, measuring in a negative scale from 0 to -760 torr, hence when set to 460 it will regulate the pressure in the line to 300 torr).</li>
	<li>Under these conditions the pressure in the source and mass spectrometer chambers should be ~1 x 10-6 torr and ~1 x 10-6 torr, respectively.</li>
</ol>
2. Acquisition of a Mass Spectrum
<ol>
	<li>Start the FAST card (model number P7889, 100 ps/bin) software on the computer and let it run in the background.</li>
	<li>Open the Labview data acquisition program: "General Interface.vi"* (Figure 4)</li>
</ol>
(*This software and the other Labview codes were developed at the beamline and are available to share for no cost from the corresponding author)
<ol start="3">
	<li>Using the ALS Control tab in the Labview software, set the photon energy to the desired wavelength.</li>
	<li>On the scaler tab, set the number of time units to be binned together (typically 32), the range (number of bins) and sweeps (the number of mass spectra added on top of each other to form the final mass spectrum), then click accept, so that these values will be stored and used.</li>
	<li>Next, click get data to begin the data acquisition. When the acquisition is over, the mass spectrum will appear on the screen.</li>
	<li>Save the mass spectrum by clicking the save button. (the X-axis of the obtained spectrum corresponds to the ion flight time in 100 ps units)</li>
</ol>
3. Acquisition of a Photoionization Efficiency Curve (PIE)
<ol>
	<li>Using the ALS Scan tab (Figure 5) in the Labview software, it is possible to acquire data while tuning one of the beamline motors. In this case, select the motor "Mono T3 energy" to tune over different photon energies (The undulator inside the synchrotron will move automatically to match the desired wavelength). Set the photon energy to the desired value (in eV).</li>
	<li>Enter the Start and Stop energies (in eV) as well as the Step size.</li>
	<li>Do not enter the number of sweeps - this will be updated automatically by the value you entered in step 2.4.</li>
	<li>Click Read current from K486 to read the photocurrent measured by the photodiode.</li>
	<li>Next, click Start to begin the scan. You will be prompted to choose a filename where the data will be stored at the end of the run.</li>
	<li>The first column in the data file contain the bin number (Bin#) and need to be converted to mass units13. Typical values are: Mass = 0.6 + 1xE-3 (Bin#) + 5xE-7 (Bin#)^2 (A more precise mass calibration can be done using a known mixture of gases or even room air i.e. mostly O2,N2 and H2O mixture and fitting their arrival time to a second order polynomial)</li>
	<li>Save the data file with the first column converted to mass.</li>
	<li>To plot a PIE curve, one easy way is to use a second Labview program called "ALS energy scan.vi" which is designed to analyze the scan data and produce PIEs.</li>
</ol>
4. Plotting a Photoionization Efficiency Curve (PIE)
<ol>
	<li>As noted above, the analysis can be done using the "ALS energy scan.vi" program (see Figure 6), however we will also describe here the steps needed to analyze the data without it.</li>
	<li>When starting the program you will be prompted to select the file containing the data. This is the file you saved in step 3.7 and contain masses in the first column and ion counts at different photon energies in the next columns. Note that the first and second rows in the file indicate the photon energy and photocurrent of the data in that column, respectively.</li>
	<li>In the top panel there is a 2D plot of the data; moving the red horizontal marker selects a mass spectra at a specific photon energy to be displayed in the lower panel.</li>
	<li>The next step is to integrate the ion counts of a specific mass at each photon energy while subtracting the background signal. In the lower panel the two vertical red markers should be set around the mass peak to be integrated while the two blue markers around a nearby region with no data which can serve as background value. The software will present the integrated data minus the background in the panel on the right.</li>
	<li>To present a true PIE curve one must correct the ion counts to the varying photon flux at every step. This is done automatically by the software. If you choose to skip this correction, click to turn off the current correction button to the right of the top panel. If you choose to do this step manually, the quantum efficiency of the photodiode per photon energy has to be considered as well (obtained from the photodiode manufacturer and available via the corresponding author), see equation 1. Otherwise, this is all done automatically by the software.</li>
</ol>
<img alt="Equation 1" fo:src="/files/ftp_upload/50164/50164eq1highres.jpg" src="/files/ftp_upload/50164/50164eq1.jpg" />
<ol start="6">
	<li>Click save spectrum in the lower right corner to save the corrected PIE curve.</li>
</ol>

<ol>
	<li>Golan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ionization+of+dimethyluracil+dimers+leads+to+facile+proton+transfer+in+the+absence+of+hydrogen+bonds.">Ionization of dimethyluracil dimers leads to facile proton transfer in the absence of hydrogen bonds.</a> Nat. Chem. 4, 323-329 (2012).</li><li>Belau, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vacuum-Ultraviolet+Photoionization+Studies+of+the+Microhydration+of+DNA+Bases+(Guanine,+Cytosine,+Adenine,+and+Thymine).">Vacuum-Ultraviolet Photoionization Studies of the Microhydration of DNA Bases (Guanine, Cytosine, Adenine, and Thymine).</a> The Journal of Physical Chemistry A. 111, 7562-7568 (2007).</li><li>Golan, A., Ahmed, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ionization+of+Water+Clusters+Mediated+by+Exciton+Energy+Transfer+from+Argon+Clusters.">Ionization of Water Clusters Mediated by Exciton Energy Transfer from Argon Clusters.</a> The Journal of Physical Chemistry Letters. 3, 458-462 (2012).</li><li>Nicolas, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vacuum+Ultraviolet+Photoionization+of+C3.">Vacuum Ultraviolet Photoionization of C3.</a> Journal of the American Chemical Society. 128, 220-226 (2005).</li><li>Kamarchik, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectroscopic+signatures+of+proton+transfer+dynamics+in+the+water+dimer+cation.">Spectroscopic signatures of proton transfer dynamics in the water dimer cation.</a> Journal of Chemical Physics. 132, (2010).</li><li>Khistyaev, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+microhydration+on+ionization+energies+of+thymine.">The effect of microhydration on ionization energies of thymine.</a> Faraday Discussions. 150, 313-330 (2011).</li><li>Bravaya, K. 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The monomers and dimers are generated in a supersonic jet expansion which gives rise to a molecular beam. A small sample of the DNA base is placed in a thermal vaporization source and heated to generate sufficient vapor pressure. Argon gas carries the vapors through a 100 &mu;m orifice and passes a 2 mm skimmer to produce a cold molecular beam14. Alternatively, an effusive beam source can be used, where the sample is placed in a heated oven attached to the repeller plate (ion optics) of the mass spectrometer.<...

<table border="1">
 <tr>
 <td>Name of Reagent/Material</td>
 <td>Company</td>
 <td>Catalog Number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Uracil</td>
 <td>Sigma</td>
 <td>U0750</td>
 <td></td>
 </tr>
 <tr>
 <td>1,3-Dimethyluracil</td>
 <td>Aldrich</td>
 <td>349801</td>
 <td></td>
 </tr>
 </table>

molecular beam mass spectrometry with tunable vacuum ultraviolet (vuv) synchrotron radiation

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy and dynamics1-4. Fundamental studies of photoionization processes of biomolecules provide information about the electronic structure of these systems. Furthermore determinations of ionization energies and other properties of biomolecules in the gas phase are not trivial, and these experiments provide a platform to generate these data. We have developed a thermal vaporization technique coupled with supersonic molecular beams that provides a gentle way to transport these species into the gas phase. Judicious combination of source gas and temperature allows for formation of dimers and higher clusters of the DNA bases. The focus of this particular work is on the effects of non-covalent interactions, i.e., hydrogen bonding, stacking, and electrostatic interactions, on the ionization energies and proton transfer of individual biomolecules, their complexes and upon micro-hydration by water1, 5-9.
We have performed experimental and theoretical characterization of the photoionization dynamics of gas-phase uracil and 1,3-dimethyluracil dimers using molecular beams coupled with synchrotron radiation at the Chemical Dynamics Beamline10 located at the Advanced Light Source and the experimental details are visualized here. This allowed us to observe the proton transfer in 1,3-dimethyluracil dimers, a system with pi stacking geometry and with no hydrogen bonds1. Molecular beams provide a very convenient and efficient way to isolate the sample of interest from environmental perturbations which in return allows accurate comparison with electronic structure calculations11, 12. By tuning the photon energy from the synchrotron, a photoionization efficiency (PIE) curve can be plotted which informs us about the cationic electronic states. These values can then be compared to theoretical models and calculations and in turn, explain in detail the electronic structure and dynamics of the investigated species 1, 3.

Figure 7 shows a typical mass spectrum of the supersonic expansion of 1,3-dimethyluracil vapors (A) and the PIE curves of the three main features (the monomer at m/z 140, protonated monomer at m/z 141, and the 1,3-dimethyluracil dimer at m/z 280) as extracted from a VUV scan between 8 eV and 10 eV (B). The gray shadow is the standard deviation from three consecutive scans.
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_uplo...

Watch this Scientific Journal Video about Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation at JoVE.com

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

A molecular beam coupled to tunable vacuum ultraviolet photoionization mass spectrometer at a synchrotron provides a convenient tool to explore the electronic structure of isolated gas phase molecules and clusters. Proton transfer mechanisms in DNA base dimers were elucidated with this technique.

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy ...

molecular-beam-mass-spectrometry-with-tunable-vacuum-ultraviolet-vuv

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12.9K Views.  Lawrence Berkeley National Laboratory. A molecular beam coupled to tunable vacuum ultraviolet photoionization mass spectrometer at a synchrotron provides a convenient tool to explore the electronic structure of isolated gas phase molecules and clusters. Proton transfer mechanisms in DNA base dimers were elucidated with this technique.

Video: Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. During insertion or removal of alkali metal ions, the redox states of transition metals in the compounds change and structural transformations such as phase transitions and/or lattice parameter increases or decreases occur. These behaviors in turn determine important characteristics of the batteries such as the potential profiles, rate capabilities, and cycle lives. The extremely bright and tunable x-rays produced by synchrotron radiation allow rapid acquisition of high-resolution data that provide information about these processes. Transformations in the bulk materials, such as phase transitions, can be directly observed using X-ray diffraction (XRD), while X-ray absorption spectroscopy (XAS) gives information about the local electronic and geometric structures (e.g.&#160;changes in redox states and bond lengths). In situ experiments carried out on operating cells are particularly useful because they allow direct correlation between the electrochemical and structural properties of the materials. These experiments are time-consuming and can be challenging to design due to the reactivity and air-sensitivity of the alkali metal anodes used in the half-cell configurations, and/or the possibility of signal interference from other cell components and hardware. For these reasons, it is appropriate to carry out ex situ experiments (e.g.&#160;on electrodes harvested from partially charged or cycled cells) in some cases. Here, we present detailed protocols for the preparation of both ex situ and in situ samples for experiments involving synchrotron radiation and demonstrate how these experiments are done.

We describe the use of synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques to probe details of intercalation/deintercalation processes in electrode materials for Li-ion and Na-ion batteries. Both in situ and ex situ experiments are used to understand structural behavior relevant to the operation of devices

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Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

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This paper details the fabrication process of a gate-tunable graphene device, decorated with Coulomb impurities for scanning tunneling microscopy studies. Mapping the spatially dependent electronic structure of graphene in the presence of charged impurities unveils the unique behavior of its relativistic charge carriers in response to a local Coulomb potential.

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Failure Analysis of Batteries Using Synchrotron-based Hard X-ray Microtomography

Imaging morphological changes that occur during the lifetime of rechargeable batteries is necessary to understand how these devices fail. Since the advent of lithium-ion batteries, researchers have known that the lithium metal anode has the highest theoretical energy density of any anode material. However, rechargeable batteries containing a lithium metal anode are not widely used in consumer products because the growth of lithium dendrites from the anode upon charging of the battery causes premature cell failure by short circuit. Lithium dendrites can also form in commercial lithium-ion batteries with graphite anodes if they are improperly charged. We demonstrate that lithium dendrite growth can be studied using synchrotron-based hard X-ray microtomography. This non-destructive imaging technique allows researchers to study the growth of lithium dendrites, in addition to other morphological changes inside batteries, and subsequently develop methods to extend battery life.

Synchrotron-based hard X-ray microtomography is used to image the electrochemical growth of dendrites from a lithium metal electrode through a solid polymer electrolyte membrane.

Imaging morphological changes that occur during the lifetime of rechargeable batteries is necessary to understand how these devices fail. Since the advent ...

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can potentially contribute to the exposure of biota and humans. The diffusive gradients in thin films technique is introduced here for in-situ measurements of Pu bioavailability and speciation. A diffusion cell constructed for laboratory experiments with Pu and the newly developed protocol make it possible to simulate the environmental behavior of Pu in model solutions of various chemical compositions. Adjustment of the oxidation states to Pu(IV) and Pu(V) described in this protocol is essential in order to investigate the complex redox chemistry of plutonium in the environment. The calibration of this technique and the results obtained in the laboratory experiments enable to develop a specific DGT device for in-situ Pu measurements in freshwaters. Accelerator-based mass-spectrometry measurements of Pu accumulated by DGTs in a karst spring allowed determining the bioavailability of Pu in a mineral freshwater environment. Application of this protocol for Pu measurements using DGT devices has a large potential to improve our understanding of the speciation and the biological transfer of Pu in aquatic ecosystems.

The technique of diffusive gradients in thin films (DGT) is proposed for speciation studies of plutonium. This protocol describes diffusion experiments probing the behavior of Pu(IV) and Pu(V) in presence of organic matter. DGTs deployed in a karstic spring allow assessment of the bioavailability of Pu.

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Using Synchrotron Radiation Microtomography to Investigate Multi-scale Three-dimensional Microelectronic Packages

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data acquisition times with high spatial resolution. In the electronics industry there is serious interest in performing failure analysis on 3D microelectronic packages, many which contain multiple levels of high-density interconnections. Often in tomography there is a trade-off between image resolution and the volume of a sample that can be imaged. This inverse relationship limits the usefulness of conventional computed tomography (CT) systems since a microelectronic package is often large in cross sectional area 100-3,600 mm2, but has important features on the micron scale. The micro-tomography beamline at the Advanced Light Source (ALS), in Berkeley, CA USA, has a setup which is adaptable and can be tailored to a sample&#39;s properties, i.e., density, thickness, etc., with a maximum allowable cross-section of 36 x 36 mm. This setup also has the option of being either monochromatic in the energy range ~7-43 keV or operating with maximum flux in white light mode using a polychromatic beam. Presented here are details of the experimental steps taken to image an entire 16 x 16 mm system within a package, in order to obtain 3D images of the system with a spatial resolution of 8.7 &#181;m all within a scan time of less than 3 min. Also shown are results from packages scanned in different orientations and a sectioned package for higher resolution imaging. In contrast a conventional CT system would take hours to record data with potentially poorer resolution. Indeed, the ratio of field-of-view to throughput time is much higher when using the synchrotron radiation tomography setup. The description below of the experimental setup can be implemented and adapted for use with many other multi-materials.

For this study synchrotron radiation micro-tomography, a non-destructive three-dimensional imaging technique, is employed to investigate an entire microelectronic package with a cross-sectional area of 16 x 16 mm. Due to the synchrotron&#39;s high flux and brightness the sample was imaged in just 3 min&#160;with an 8.7 &#181;m spatial resolution.

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Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt interfaces required for high-quality high-electron-mobility transistors (HEMTs). A procedure is presented for the growth of N-polar InAlN HEMTs, including wafer preparation and growth of buffer layers, the InAlN barrier layer, AlN and GaN interlayers and the GaN channel. Critical issues at each step of the process are identified, such as avoiding Ga accumulation in the GaN buffer, the role of temperature on InAlN compositional homogeneity, and the use of Ga flux during the AlN interlayer and the interrupt prior to GaN channel growth. Compositionally homogeneous N-polar InAlN thin films are demonstrated with surface root-mean-squared roughness as low as 0.19 nm and InAlN-based HEMT structures are reported having mobility as high as 1,750 cm2/V&#8729;sec for devices with a sheet charge density of 1.7 x 1013 cm-2.

Molecular beam epitaxy is used to grow N-polar InAlN-barrier high-electron-mobility transistors (HEMTs). Control of the wafer preparation, layer growth conditions and epitaxial structure results in smooth, compositionally homogeneous InAlN layers and HEMTs with mobility as high as 1,750 cm2/V&#8729;sec.

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Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

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A method for producing simple and efficient thermally-activated delayed fluorescence organic light-emitting diodes (OLEDs) based on guest-host or exciplex donor-acceptor emitters is presented. With a step-by-step procedure, readers will be able to repeat and produce OLED devices based on simple organic emitters. A patterning procedure allowing the creation of personalized indium tin oxide (ITO) shape is shown. This is followed by the evaporation of all layers, encapsulation and characterization of each individual device. The end goal is to present a procedure that will give the opportunity to repeat the information presented in cited publication but also using different compounds and structures in order to prepare efficient OLEDs.

A protocol for the production of simple structured organic light-emitting diodes (OLEDs) is presented.

A method for producing simple and efficient thermally-activated delayed fluorescence organic light-emitting diodes (OLEDs) based on guest-host or exciplex ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...

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.