Showing papers in "Journal of Vacuum Science & Technology B in 2016"

Faraday cage angled-etching of nanostructures in bulk dielectrics

Abstract: For many emerging optoelectronic materials, heteroepitaxial growth techniques do not offer the same high material quality afforded by bulk, single-crystal growth. However, the need for optical, electrical, or mechanical isolation at the nanoscale level often necessitates the use of a dissimilar substrate, upon which the active device layer stands. Faraday cage angled-etching (FCAE) obviates the need for these planar, thin-film technologies by enabling in situ device release and isolation through an angled-etching process. By placing a Faraday cage around the sample during inductively coupled plasma reactive ion etching, the etching plasma develops an equipotential at the cage surface, directing ions normal to its face. In this article, the effects that Faraday cage angle, mesh size, and sample placement have on etch angle, uniformity, and mask selectivity are investigated within a siliconetching platform. Simulation results qualitatively confirm experiments and help to clarify the physical mechanisms at work. These results will help guide FCAE process design across a wide range of material platforms.

Direct transfer of corrugated graphene sheets as stretchable electrodes

Abstract: The authors present the fabrication and characterization of corrugated graphene sheets on polydimethylsiloxane (PDMS) substrates for flexible and stretchable electrodes. The graphene sheets were grown on imprinted Cu foil via atmospheric pressure chemical vapor deposition. The grown graphene sheets with both corrugated and flat surfaces were then transferred from the Cu foil to PDMS substrates using a novel, direct transfer method, where PDMS was directly casted and cured on the graphene sheets followed by removal of Cu via wet etching. This process largely eliminated the formation of cracks in the graphene caused by traditional transfer processes. The corrugated graphene sheets were characterized using Raman spectroscopy and conductivity measurements under the application of lateral strain parallel and perpendicular to the graphene corrugation on the PDMS substrates, demonstrating a smaller shift of the two dimensional Raman peak for the corrugated graphene electrodes as compared to the flat graphene. It was shown that the maximum achievable strain prior to a change in electrode resistance increased from 8% for the flat graphene sheet to 15% for the corrugated graphene electrode. Preliminary results also showed that the corrugated graphene sheet maintained its material integrity and electrical conductivity under multiple cycles of high strains.

Displacement Talbot lithography nanopatterned microsieve array for directional neuronal network formation in brain-on-chip

Abstract: Commercial microelectrode arrays (MEAs) for in vitro neuroelectrophysiology studies rely on conventional two dimensional (2D) neuronal cultures that are seeded on the planar surface of such MEAs and thus form a random neuronal network. The cells attaching on these types of surfaces grow in 2D and lose their native morphology, which may also influence their neuroelectrical behavior. Besides, a random neuronal network formed on this planar surface in vitro also lacks comparison to the in vivo state of brain tissue. In order to improve the present MEA platform with the above mentioned concerns, in this paper, the authors introduce a three dimensional platform for neuronal cell culturing, where a linear nanoscaffold is patterned on a microsieve array by displacement Talbot lithography (DTL) and reactive ion etching. Good pattern uniformity is achieved by the DTL method on the topographically prepatterned nonflat surface of the microsieve array. Primary cortical cells cultured on the nanopatterned microsieve array show an organized network due to the contact guidance provided by the nanoscaffold, presenting 47% of the total outgrowths aligning with the nanogrooves in the observed view of field. Hence, the authors state that this nanopatterned microsieve array can be further integrated into microsieve-based microelectrode arrays to realize an advanced Brain-on-Chip model that allows us to investigate the neurophysiology of cultured neuronal networks with specifically organized architectures.

Effect of porosity and pore size on dielectric constant of organosilicate based low-k films : an analytical approach

Abstract: An analytical approach allowing to analyze effect of porosity, pore size, and interconnectivity on dielectric constant of organosilicate based low-k materials is developed. Within the framework of this approach, a good agreement between the calculated and experimentally measured dielectric constants for several porogen (template) based organosilicate glasses low-k films is demonstrated. It is shown that the best agreement between the calculated and measured k-values corresponds to low-k structure with CH3 groups localized on pore wall surface. The results also demonstrate a good agreement with recently published results of similar analysis based on numerical approach.

Novel electron monochromator for high resolution imaging and spectroscopy

Abstract: A mirror electron monochromator has been developed for reducing the energy spread of commonly used high brightness electron sources from the characteristic range of 0.3–1 eV to values below 100 meV. The monochromator utilizes mirror optics and thereby exploits the symmetry inherent in reversing the electron trajectory to monochromatize the primary beam with a knife edge instead of a conventional slit. The performance of the key electron-optical components of the monochromator has been simulated. These components include the combination of an electron mirror with a magnetic prism array. In initial testing, the monochromator has demonstrated the ability to reduce the energy spread of a 5 keV electron beam that was generated by a Schottky electron emitter from its initial value of 0.65–0.75 eV to 180 meV with an exit beam current exceeding 1 nA and to 100 meV with an exit beam current of 50 pA. Here, the attainable energy resolution was found to be limited by the noise on the power supply. The monochromator ...

Parallel imaging MS/MS TOF-SIMS instrument

Abstract: The authors have developed a parallel imaging MS/MS capability for the PHI nanoTOF II time-of-flight secondary ion mass spectrometry (TOF-SIMS) instrument. The unique design allows a 1 Da wide precursor mass window to be extracted from a stream of mass separated secondary ions while all other secondary ions are detected in the normal manner at the standard TOF-SIMS detector. The selected precursor ions are deflected into an activation cell where they are fragmented using high energy collision induced dissociation and mass analyzed in a separate linear TOF mass spectrometer. This TOF-TOF approach allows MS/MS to be accomplished at a high speed maintaining the primary ion beam repetition rates used in TOF-SIMS. The new MS/MS capability enables molecular identification to be extended to higher mass ions where the mass accuracy of TOF-SIMS is not sufficient to unambiguously identify molecular structure. The ability to acquire TOF-SIMS and MS/MS data simultaneously from the identical analytical volume is a pow...

Electrostatic-focusing image sensor with volcano-structured Spindt-type field emitter array

Abstract: The authors have developed a highly sensitive, compact image sensor comprising a field emitter array (FEA) and a high-gain avalanche rushing amorphous photoconductor (HARP) target with the ultimate aim of developing an ultrahigh sensitivity, compact, high-definition television camera. Double-gated field emitters have the advantage of a compact electron beam focusing system; however, image intensities reproduced by a sensor with the double-gated, Spindt-type field emitter array with the focusing electrode stacked 1.5 μm above the gate electrode were nonuniform owing to low electron beam current. The minimum required electron beam current extracted from the double-gated field emitter array is considered for possible use with the sensor. Furthermore, a suitable field emitter array pitch to balance the electron beam current and the electrostatic-focusing lens strength was simulated. For the sensor's design guidelines, a field emitter array pitch of approximately 3 μm would be reasonable in the case of employing the volcano-structured, double-gated, Spindt-type field emitter array with the focusing electrode placed 0.2 μm below the gate electrode hole. Based on simulation results, an image sensor with the volcano-structured, Spindt-type, 3.1-μm-pitch FEA with the focusing electrode placed 0.2 μm below the gate electrode hole was fabricated. It was confirmed that the minimum electron beam current extracted from the volcano-structured FEA was approximately 2 μA/pix, and the sensor could obtain images with improved image intensity uniformity by utilizing the electrostatic-focusing effect. These results indicate that the volcano-structured, double-gated, Spindt-type FEA is potentially suitable for high-definition television FEA-HARP image sensors.

Thickness characterization of atomically thin WSe2 on epitaxial graphene by low-energy electron reflectivity oscillations

Abstract: In this work, low-energy electron microscopy is employed to probe structural as well as electronic information in few-layer WSe2 on epitaxial graphene on SiC. The emergence of unoccupied states in the WSe2–graphene heterostructures is studied using spectroscopic low-energy electron reflectivity. Reflectivity minima corresponding to specific WSe2 states that are localized between the monolayers of each vertical heterostructure are shown to reveal the number of layers for each point on the surface. A theory for the origin of these states is developed and utilized to explain the experimentally observed featured in the WSe2 electron reflectivity. This method allows for unambiguous counting of WSe2 layers, and furthermore may be applied to other two-dimensional transition metal dichalcogenide materials.

Semitransparent ZnO-based UV-active solar cells: Analysis of electrical loss mechanisms

Abstract: Three different ZnO-based diodes are compared that can be employed as semitransparent ultraviolet (UV)-active solar cells: a Schottky diode using platinum oxide as front contact, a p+n diode with magnetron-sputtered nickel oxide and a pn diode with a pulsed laser deposited NiO front contact. The UV conversion efficiencies are 4.1% for the Schottky diodes and 3.1% for the NiO-based cells. In the NiO-based structures, a strong deformation of the current–voltage characteristics under white light illumination (one sun) is observed, leading to reduced open-circuit voltages. Measurements of the external quantum efficiency with and without simultaneous white-light illumination reveal that also the collected photocurrent in these devices types is significantly reduced under strong illumination. It is shown that the magnitude of both the injected current and the recombination current of photogenerated carriers is increased in this state. A model is proposed that explains both effects within the framework of an opt...

Development of transparent microwell arrays for optical monitoring and dissection of microbial communities

Abstract: Microbial communities are incredibly complex systems that dramatically and ubiquitously influence our lives. They help to shape our climate and environment, impact agriculture, drive business, and have a tremendous bearing on healthcare and physical security. Spatial confinement, as well as local variations in physical and chemical properties, affects development and interactions within microbial communities that occupy critical niches in the environment. Recent work has demonstrated the use of silicon based microwell arrays, combined with parylene lift-off techniques, to perform both deterministic and stochastic assembly of microbial communities en masse, enabling the high-throughput screening of microbial communities for their response to growth in confined environments under different conditions. The implementation of a transparent microwell array platform can expand and improve the imaging modalities that can be used to characterize these assembled communities. Here, the fabrication and characterization of a next generation transparent microwell array is described. The transparent arrays, comprised of SU-8 patterned on a glass coverslip, retain the ability to use parylene lift-off by integrating a low temperature atomic layer deposition of silicon dioxide into the fabrication process. This silicon dioxide layer prevents adhesion of the parylene material to the patterned SU-8, facilitating dry lift-off, and maintaining the ability to easily assemble microbial communities within the microwells. These transparent microwell arrays can screen numerous community compositions using continuous, high resolution, imaging. The utility of the design was successfully demonstrated through the stochastic seeding and imaging of green fluorescent protein expressing Escherichia coli using both fluorescence and brightfield microscopies.

Bioinspired broadband midwavelength infrared antireflection coatings on silicon

Abstract: Silicon has been extensively used in manufacturing refractive infrared optics due to its high refractive index and excellent transmission over a very broad range of infrared wavebands. However, the high refractive index of silicon leads to large reflection loss which greatly limits the performance of the final optoelectronic devices. Here, the authors report a simple and scalable templating nanofabrication technology for making subwavelength-structured, broadband antireflection coatings on crystalline silicon wafers, targeting the midwavelength infrared (MWIR) waveband (3–8 μm), which has important implications for various civilian and military purposes. Periodic arrays of silicon nanopillars with tapered shapes, which mimic the microstructured cornea of nocturnal moths, can be patterned on both surfaces of silicon wafers using self-assembled monolayer silica colloidal crystals as structural templates. The resultant moth-eye gratings can greatly enhance optical transmission for the entire MWIR region. Finite-difference time-domain simulations have also been performed and the theoretical predictions agree reasonably well with the experimental optical measurements.

Amorphous Si/SiO2 distributed Bragg reflectors with transfer printed single-crystalline Si nanomembranes

Abstract: A distributed Bragg reflector (DBR) consisting of a single-crystal Si nanomembrane (NM) layer formed by the transfer printing technique on top of an evaporated amorphous Si (a-Si)/SiO2 DBR structure was demonstrated. The reflectivity of different DBR structures/pairs is measured and verified it by the simulation. An improved surface roughness of the top layer by employing a Si NM suggests that the smoother single crystalline surface not only minimizes light scattering loss but also can be an epitaxial template layer for subsequent Si growth without contributing any strain. The results indicate a simple pathway toward achieving high performance Si/SiO2 DBRs employing Si NM as a top layer. This method could also lead to the fabrication of large-area, high performance NM based DBRs at low cost with high throughput.

Electrostatic modeling of an in-plane gated field emission cathode

Abstract: In this study, the authors develop an electrostatic model for an in-plane gated field emission cathode. This structure is based on two electrodes lying on the same plane. One electrode (bias electrode) allows biasing the field emitter element, a whisker in present study. The other electrode (gate electrode) is being used to electrostatically control the system. Our model points out the main geometrical parameters to be bias electrode characteristic size and whisker height, as confirmed by simulations. This model gives access to the extraction field experienced by the whisker emitter on its apex, in turn giving access to emission current dependencies on the various parameters of the model. The proximity of the gate as compared to the emitter apex enables low bias voltage to modulate the current with high susceptibility.

Investigation of dilute-nitride alloys of GaAsNx (0.01 < x < 0.04) grown by MBE on GaAs (001) substrates for photovoltaic solar cell devices

Abstract: Dilute-nitride GaAsNx epilayers were grown on GaAs (001) substrates at temperatures of ∼450 °C using a radio-frequency plasma-assisted molecular/chemical beam exitaxy system. The concentration of nitrogen incorporated into the films was varied in the range between 0.01 and 0.04. High-resolution electron microscopy was used to determine the cross-sectional morphology of the epilayers, and Z-contrast imaging showed that the incorporated nitrogen was primarily interstitial. {110}-oriented microcracks, which resulted in strain relaxation, were observed in the sample with the highest N concentration ([N] ∼ 3.7%). Additionally, Z-contrast imaging indicated the formation of a thin, high-N quantum-well-like layer associated with initial ignition of the N-plasma. Significant N contamination of the GaAs barrier layers was observed in all samples, and could severely affect the carrier extraction and transport properties in future targeted devices. Dilute-nitride quantum-well-based photovoltaic solar cells were fabri...

Secondary ion and neutral mass spectrometry with swift heavy ions: Organic molecules

Abstract: The authors report on experiments regarding the electronic and nuclear sputtering of organic films. The newly built swift heavy ion induced particle emission and surface modifications setup [Meinerzhagen et al., Rev. Sci. Instrum. 87, 013903 (2016)] at the M1 Branch at the universal linear accelerator (UNILAC) beam line at GSI in Darmstadt, Germany, has been used for research on organic molecules in the electronic sputtering regime. This setup has the unique capability not only to investigate electronically sputtered ions by projectiles with kinetic energies up to several giga-electron-volt but also to detect their neutral counterparts as well by laser postionization. For this purpose, the experiment is equipped with a laser system delivering 157 nm pulses with photon energies of 7.9 eV to be utilized in single photon ionization. In addition to the investigation of sputtered ions and neutrals in the electronic sputtering regime, a comparison of typical fragments between fundamentally different sputtering ...

Nanoscale Schottky barrier mapping of thermally evaporated and sputter deposited W/Si(001) diodes using ballistic electron emission microscopy

Abstract: Ballistic electron emission microscopy has been utilized to demonstrate differences in the interface electrostatics of tungsten-Si(001) Schottky diodes fabricated using two different deposition techniques: thermal evaporation using electron-beam heating and magnetron sputtering. A difference of 70 meV in the Schottky barrier heights is measured between the two techniques for both p- and n-type silicon even though the sum of n- and p-type Schottky barrier heights agrees with the band gap of silicon. Spatially resolved nanoscale maps of the Schottky barrier heights are uniform for the sputter film and are highly disordered for the e-beam film. Histograms of the barrier heights show a symmetric Gaussian like profile for the sputter film and a skewed lognormal distribution for e-beam film. A Monte-Carlo model is developed to simulate these histograms which give strong indication that localized elastic scattering is causing this skewing as forces the hot electrons to need a greater total energy to surmount the barrier. These differences are attributed to silicide formation from the unintentional substrate heating during the e-beam deposition, which is confirmed with transmission electron microscopy.

Uranium ion yields from monodisperse uranium oxide particles

Abstract: Secondary ion mass spectrometry(SIMS) plays an important role in nuclear forensics through its ability to identify isotopic ratios of particles accurately and precisely from samples obtained by inspectors [Boulyga et al., J. Anal. At. Spectrom. 30, 1469 (2015)]. As the particle mass can be on the order of subpicograms, it is important to maximize the sample utilization efficiency of U+ to make high-quality isotopic measurements. The influence of primary ion beam species and polarity on U+ sample utilization efficiency has been previously investigated by Ranebo et al. [J. Anal. At. Spectrom. 24, 277 (2009)]. However, the effect of sample substrate on uranium ion production efficiency and sputtering profile has not been investigated. This work will explore those influences on sample utilization efficiency by analyzing monodisperse uranium oxide microspheres deposited onto graphite and silicon planchets. The particles were mapped using an automated scanning electron microscope, and their coordinates were converted to the SIMS coordinate system using fiducial marks. Results indicate higher U+ sample utilization efficiencies when sputtering with O− and O2− on graphite planchets compared with O2+, whereas O2− gave higher U+ sample utilization efficiencies with silicon wafers compared to O− and O2+. Additionally, during sputtering of uranium particles on silicon wafers with O− and O2−, a sudden drop in U+ signal intensity was observed, which was not present during sputtering with O2+ or any primary ion species for particles on graphite. This drop in U+ signal intensity occurred simultaneously with an increase in UO+ and UO2+ signals, indicating a change in the local matrix around the uranium particle that is unique to silicon compared to graphite.

Novel low-temperature fabrication process for integrated high-aspect ratio zinc oxide nanowire sensors

Abstract: The authors present a new low-temperature nanowire fabrication process that allows high-aspect ratio nanowires to be readily integrated with microelectronic devices for sensor applications. This process relies on a new method of forming a close-packed array of self-assembled high-aspect-ratio nanopores in an anodized aluminum oxide (AAO) template in a thin (2.5 μm) aluminum film deposited on a silicon substrate. This technique is in sharp contrast to the traditional free-standing thick film methods, and the use of an integrated thin aluminum film greatly enhances the utility of such methods. The authors have demonstrated the method by integrating ZnO nanowires onto the metal gate of a metal-oxide-semiconductor (MOS) transistor to form an integrated chemical field-effect transistor (ChemFET) sensor structure. The novel thin film AAO process uses a novel multistage aluminum anodization, alumina barrier layer removal, ZnO atomic layer deposition (ALD), and pH controlled wet release etching. This new process ...

Performance enhancement of MgZnO ultraviolet photodetectors using ultrathin Al2O3 inserted layer

Abstract: In this study, the magnesium zinc oxide (MgZnO) films and ultrathin alumina (Al2O3) inserted layers were subsequently deposited on sapphire substrates using a plasma-enhanced atomic layer deposition system, and applied in metal-semiconductor-metal ultraviolet (UV) photodetectors (MSM-UPDs). The dark current of the MgZnO MSM-UPDs was decreased from 1 to 0.34 nA with an increase in Al2O3 layer thickness from 0 to 5 nm. The ultrathin Al2O3 inserted layer effectively passivated the dangling bonds on the MgZnO surface and blocked leakage current. At a bias voltage of 5 V, the maximum UV-visible rejection ratio of the MgZnO MSM-UPDs was 1.78 × 103 with 5-nm-thick Al2O3 inserted layer. Furthermore, the noise equivalent power and detectivity of MgZnO MSM-UPDs with 5-nm-thick Al2O3 inserted layer were improved from 1.26 × 10−14 W and 2.50 × 1013 cm Hz1/2 W−1 to 0.93 × 10−14 W and 3.40 × 1013 cm Hz1/2 W−1 in comparison with MgZnO MSM-UPDs without Al2O3 inserted layer. The high performances of MgZnO MSM-UPDs were achieved by using ultrathin Al2O3 inserted layer.

Electromigration behavior of Cu metallization interfacing with Ta versus TaN at high temperatures

Abstract: High-temperature stability of Cu-based interconnects is of technological importance for electronic circuits based on wide band gap semiconductors. In this study, different metal stack combinations ...

Core–shell carrier and exciton transfer in GaAs/GaNAs coaxial nanowires

Abstract: Comprehensive studies of GaAs/GaNAs coaxial nanowires grown on Si substrates are carried out by temperature-dependent photoluminescence (PL) and PL excitation, to evaluate effects of the shell formation on carrier recombination. The PL emission from the GaAs core is found to transform into a series of sharp PL lines upon radial growth of the GaNAs shell, pointing toward the formation of localization potentials in the core. This hampers carrier transfer at low temperatures from the core in spite of its wider bandgap. Carrier injection from the core to the optically active shell is found to become thermally activated at T > 60 K, which implies that the localization potentials are rather shallow.

Auger electron spectroscopy study of semiconductor surfaces: Effect of cleaning in inert atmosphere

Abstract: In this paper, the authors demonstrate that Auger electron spectroscopy (AES) is an effective characterization tool in the analysis of the cleaning of semiconductor surfaces under different atmospheres. AES has several advantages for this purpose: it is nondestructive, surface specific {the analysis depth is only 4–50 A [Childs et al., Handbook of Auger Electron Spectroscopy (Physical Electronics, Eden Prairie, MN, 1995)]}, and very sensitive to common contaminants such as carbon and oxygen. Furthermore, the authors have proven that AES allows us to describe the effectiveness of surface cleaning in a quantitative manner by comparing the peak-to-peak height of the oxygen signal for different samples. In this work, the surface cleaning of five semiconductors, namely, Si, Ge, GaAs, In0.5Ga0.5As, and In0.5Al0.5As, was investigated. The same standard HF cleaning procedure was applied in two different atmospheres, air or nitrogen. The latter was used to prevent reoxidation after cleaning. The authors found that...

Toward synthesis of oxide films on graphene with sputtering based processes

Abstract: The impact of energetic particles associated with a sputter deposition process may introduce damage to single layer graphene films, making it challenging to apply this method when processing graphene. The challenge is even greater when oxygen is incorporated into the sputtering process as graphene can be readily oxidized. This work demonstrates a method of synthesizing ZnSn oxide on graphene without introducing an appreciable amount of defects into the underlying graphene. Moreover, the method is general and applicable to other oxides. The formation of ZnSn oxide is realized by sputter deposition of ZnSn followed by a postoxidation step. In order to prevent the underlying graphene from damage during the initial sputter deposition process, the substrate temperature is kept close to room temperature, and the processing pressure is kept high enough to effectively suppress energetic bombardment. Further, in the subsequent postannealing step, it is important not to exceed temperatures resulting in oxidation of the graphene. The authors conclude that postoxidation of ZnSn is satisfactorily performed at 300 °C in pure oxygen at reduced pressure. This process results in an oxidized ZnSn film while retaining the initial quality of the graphene film.

High-temperature Ta diffusion in the grain boundary of thin Cu films

Abstract: In order to ascertain the applicability of the technologically well-established Cu metallization in high-temperature circuits, the authors have investigated layered metal stacks having one Ta/Cu interface at temperatures from 400 to 700 °C. The authors have found that Ta releases from the Ta layer and moves through the Cu film to the opposite interface via the grain boundaries. In the simplest bilayer stack with Cu on top of Ta, the up-diffused Ta on the surface spreads out over the Cu grains so as to cover the Cu grains completely at 650 °C. The activation energy for the grain boundary diffusion is found to be 1.0 ± 0.3 eV. The Ta diffusion in the grain boundaries leads to stabilization of the Cu grain size at 360 nm and an increase in sheet resistance of the metal stack. The latter is in fact observed for all metal stacks having Cu in contact with Ta on one side and TaN or nothing at all on the other. The implication is that the Cu metallization with one Ta/Cu interface has to be stabilized by a preanne...

Selective release of InP heterostructures from InP substrates

Abstract: The authors report here a method of protecting the sidewall for the selective release of InGaAsP quantum-well (QW) heterostructure from InP substrates. An intact sidewall secured by SiO2 was demonstrated during the sacrificial layer selective etching, resulting in the suspended InGaAsP QW membranes which were later transferred to the Si substrate with polydimethylsiloxane stamp. The quality of the transferred InGaAsP QW membranes has been validated through photoluminescence and EL measurements. This approach could extend to arbitrary targeting substrate in numerous photonics and electronics applications.

Efficient and ultrafast optical modulation of on-chip thermionic emission using resonant cavity coupled electron emitters

Abstract: Here, the authors explore microscale optical cavities coupled to thermionic emitters as a means to enable a class of efficient and ultrafast optically modulated, on-chip, thermionic electron emitters. They term this class of devices optical cavity thermionic emitters (OCTET). The devices consist of a microfabricated optical cavity, such as Fabry–Perot or ring resonator, and a heterostructured thermionic emitter with a small bandgap or metallic thermionic emitter (e.g., LaB6) deposited on a wider bandgap electrical and thermal conductor (e.g., doped Si). By tuning the resonant wavelength of the optical cavity, the authors can ensure photons are efficiently and selectively absorbed by the small bandgap/metallic emitter, enabling design of gigahertz–terahertz regime on-chip electron emission sources. The work here focuses on elucidating the properties of single cavity-single emitter OCTETs, but may be applied to more complex cavity-tip structures. First, the authors establish fundamental design rules based s...

Tailored SU-8 micropillars superhydrophobic surfaces enhance conformational changes in breast cancer biomarkers

Abstract: Here we report the fabrication of lotus-leaves-like tailored SU8 micropillars and their application in the context of a multi-technique characterization protocol for the investigation of the structural properties of the two estrogen receptors (ERα66/ERα46). ER (α) expression is undoubtedly the most important biomarker in breast cancer, because it provides the index for sensitivity to endocrine treatment. Beside the well-characterized ERα66 isoform, a shorter one (ERα46) was reported to be expressed in breast cancer cell line. The superhydrophobic supports were developed by using a double step approach including an optical lithography process and a plasma reactive ion roughening one. Upon drying on the micropillars, the bio-samples resulted in stretched fibers of different diameters which were then characterized by synchrotron X-ray diffraction (XRD), Raman and FTIR spectroscopy. The evidence of both different spectroscopic vibrational responses and XRD signatures in the two estrogen receptors suggests the presence of conformational changes between the two biomarkers. The SU8 micropillar platform therefore represents a valid tool to enhance the discrimination sensitivity of structural features of this class of biocompunds by exploiting a multi-technique in-situ characterization approach.

Massive Ta diffusion observed in Cu thin films but not in Ag counterparts

Abstract: This letter presents an extensive investigation by means of microscopic and chemical analyses finding Ta diffusion in Cu films but not in Ag films. This difference in Ta diffusion persists in all samples containing either Cu/Ta or Ag/Ta interfaces, wherein both a driving force for diffusion and point defects for mediation of atomic movement are present. By referring to atomistic simulation results in the literature, it is plausible that the subtle difference between the Cu/Ta and Ag/Ta interfaces plays a crucial role in differentiating them in making Ta available for diffusion. The energetically favored binding between Cu and Ta assists in liberating Ta atoms from being strongly bound by surrounding Ta atoms, as the bond strength of Cu-Ta is about one third that of Ta-Ta. Hence, the formation of the much weaker Cu–Ta bonds acts as an important intermediate step. Such a mechanism does not exist for the Ag/Ta interface.

Design and implementation of a custom built variable temperature stage for a secondary ion mass spectrometer

Abstract: The authors have built, designed, and implemented a variable temperature stage for a Cameca IMS 7f-GEO with an achievable temperature range of −150 to 300 °C and designed a new sample holder for rapid thermal stabilization. This paper focuses on the design and implementation aspects of the variable temperature stage in detail. The authors demonstrate applications where temperature control is useful for analyses that are not possible at room temperature.

Additive chemistry and distributions in photoresist thin films

Abstract: The lithographic performance of thin photoresist films is a function of the distribution of formulation components, such as photoacid generator (PAG) molecules, and how these components undergo chemical modification and migrate within the film during the lithography processing steps. Argon gas cluster ion beam – secondary ion mass spectrometry depth profiles were used to monitor the PAG and quencher base distributions before and after exposure and postexposure bake processing steps for different photoresist formulations. PAG and quencher base distributions were correlated to depth of focus lithographic performance results.