Secondary Mass Spectrometry Research Articles

Enhancing Cu interconnect reflow in back-end-of-line metal wiring with ultrathin Co liners

Abstract This research investigates the gap-fill characteristics of Cu in back-end-of-line (BEOL) interconnects, focusing on Co liner deposition using chemical vapor deposition (CVD) and cyclic-CVD (C-CVD). Providing superior gap-fill characteristics for BEOL interconnect applications is important. Three methods—CVD, C-CVD, and a combination of the two—were compared in terms of their effects on Cu reflow and electrical performance. CVD exhibited the lowest resistivity (44 μΩ cm at 10 nm thickness) and the fewest carbon impurities, confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Atomic force microscopy (AFM) revealed that CVD produced the smoothest surface (Rq ~0.5 nm), enabling better adhesion and uniform Cu reflow. At 300°C, Co liners deposited by CVD achieved void-free Cu–Mn filling in 20 nm trenches, which showed CVD to outperform other methods. These findings highlight CVD as the most effective technique for precise Co liner deposition, ensuring reliable Cu interconnects in advanced semiconductor nodes.


Bortezomib-releasing silica-collagen xerogels for local treatment of osteolytic bone- and minimal residual disease in multiple myeloma

BackgroundAccumulation of malignant plasma cells in the bone marrow causes lytic bone lesions in 80% of multiple myeloma patients. Frequently fracturing, they are challenging to treat surgically. Myeloma cells surviving treatment in the presumably protective environment of bone lesions impede their healing by continued impact on bone turnover and can explain regular progression of patients without detectable minimal residual disease (MRD). Locally applicable biomaterials could stabilize and foster healing of bone defects, simultaneously delivering anti-cancer compounds at systemically intolerable concentrations, overcoming drug resistance.MethodsWe developed silica-collagen xerogels (sicXer) and bortezomib-releasing silica-collagen xerogels (boXer) for local treatment of osteolytic bone disease and MRD. In vitro and in vivo (tissue sections) release of bortezomib was assessed by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Material impact on bone formation was assessed in vitro regarding osteoclast/osteoblast numbers and activity. In vivo, drilling defects in a rat- and the 5T33-myeloma mouse model were treated by both materials and assessed by immunohistochemistry, UPLC-MS/MS, µCT, and ToF-SIMS. The material’s anti-myeloma activity was assessed using ten human myeloma cell lines (HMCLs) and eight primary myeloma cell samples including four patients refractory to systemic bortezomib treatment.ResultssicXer and boXer show primary stability comparable to trabecular bone. Granule size and preparation method tailor degradation as indicated by release of the xerogel components (silica and collagen) and bortezomib into culture medium. In vitro, both materials reduce osteoclast activity and do not negatively interfere with osteoblast differentiation and function. The presumed resulting net bone formation with maintained basic remodeling properties was validated in vivo in a rat bone defect model, showing significantly enhanced bone formation for boXer compared to non-treated defects. Both materials induce myeloma cell apoptosis in all HMCLs and primary myeloma cell samples. In the 5T33-myeloma mouse model, both materials stabilized drilling defects and locally controlled malignant plasma cell growth.ConclusionsThe combination of stabilization of fracture-prone lesions, stimulation of bone healing, and anti-tumor effect suggest clinical testing of sicXer and boXer as part of a combined systemic/local treatment strategy in multiple myeloma and non-malignant diseases.

Towards Pharmaceutical Particle Imaging in Ultrathick Organic Films: 3D Visualization and Image Distortions Using Gas Cluster Bombardment Secondary Ion Mass Spectrometry

ABSTRACTPolystyrene spheres ranging in diameter from 2, 5, 10, to 20 μm were embedded in five different types of thick organic films (> 50 μm) to serve as model systems to evaluate the use of time‐of‐flight secondary ion mass spectrometry for the localization and particle sizing of pharmaceuticals in orodispersible drug delivery films. It was found that certain films, such as gelatin and ethyl cellulose, are prone to developing micron‐scale topography which can affect the linearity of the sputter yield, which can ultimately affect the maximum analyzable depth. Surprisingly, the sputter yield of the film was more of a determining factor for affecting the measurement of spheres. It was possible to more accurately extract the true dimensions of the buried spheres in faster sputtering films, while slower sputtering films were associated with matrix effects and sputtering artifacts that degraded the quality of the reconstructed image. Signal attenuation was also found to be problematic and quite significant for certain film chemistries, which placed a limit on the size of the particles that could be visualized. Overall, visualization of particles embedded in thick organic films is possible, but the extraction of quantitative data such as size and the amount of material is difficult given the influence of sample dependent sputtering artifacts.

Secondary Ion Mass Spectrometry Approach for Measuring the Diffusion Range in Optical Fibers with Nanostructured Cores.

A new class of optical fibers with cores composed of various glass nanorods requires a method to determine the internal structure. In particular, the identification of various ion distributions at the fiber cross-sectionwith nanometer accuracy is required. For this purpose, the classical depth profiling mode of the secondary ion mass spectrometry technique is applied. Multiple sampling with various rotation angles allows to retrieve the 1D profile of distribution for particular ions and determine their diffusion ranges. As a proof-of-concept, a nanostructured fiber composed of germanium-doped silica and ytterbium-doped silica rods is measured and the accuracy of the measurement is 3 nm. We show that the average diffusion length of germanium and ytterbium is about 41.5 and 116.6 nm, respectively. It is only 23% and as much as 153% of the initial rod diameter for Ge and Yb ions, respectively. The real diffusion range of particular ions has a significant impact on the refractive and gain media distribution in the fiber and influences the optical properties of the fiber. Therefore, information on diffusion is necessary to design nanostructured optical fibers correctly.

Subcellular ToF-SIMS Imaging of the Snow Alga Sanguina nivaloides by Combining High Mass and High Lateral Resolution Acquisitions.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging has demonstrated great potential for metabolic imaging; however, achieving sufficiently high lateral and mass resolution to reach the organelle scale remains challenging. To address this, we have developed an approach that combines imaging acquisitions close to the highest lateral resolution (<150 nm) and mass resolution (9,000) reachable by ToF-SIMS. The data were then merged and processed using multivariate analysis (MVA), providing the identification and annotation of 85% of the main contributors to the multivariate analysis components at high lateral resolution. Insights into the electron microscopy sample preparation were provided, especially as we revealed that at least three different osmium-containing complexes can be found depending on the specific chemical environment of organelles. In cells of the snow alga Sanguina nivaloides, living in a natural environment limited in nutrients such as phosphorus (P), we mapped elements and molecules within their subcellular context, allowing for the molecular fingerprinting of organelles at a resolution of ∼150 nm, as confirmed by correlative electron microscopy. It was thus possible to highlight that S. nivaloides likely absorbed selectively some inorganic P forms provided by P-rich dust deposited on the snow surface. S. nivaloides cells could maintain phosphorylations in the stroma of the chloroplast, consistently with the preservation of photosynthetic activity. The presented method can thus overcome the current limitations of ToF-SIMS for subcellular imaging and contributes to the understanding of key questions, such as P homeostasis and other cell physiological processes.

Mapping active pharmaceutical ingredients Distributions in tablets using Time-of-Flight secondary ion mass spectrometry with multivariate curve resolution

This study introduces an advanced approach to identifying signals associated with indapamide, amlodipine, and perindopril in solid dosage form using time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with multivariate curve resolution (MCR). The primary objective was to obtain and characterize these signals through MCR factors, which then led to identifying unique signals specific to each active pharmaceutical ingredient (API). These unique signals were crucial for constructing detailed 2D and 3D images of the API distribution within the tablet. The results demonstrated that indapamide and amlodipine exhibited multiple unique peaks, while perindopril had only one. Additionally, the study revealed non-homogeneous distribution patterns of APIs and excipients, such as SiO2 and Mg stearate. This work highlights the significance of applying advanced analytical techniques such as ToF-SIMS and MCR in the pharmaceutical field to ensure consistent therapeutic efficacy through a better understanding of API distribution.

Optical and electrical transport properties of α-Ga2O3 thin films with electrical compensation of Sn impurities

Polycrystalline α-Ga2O3 thin films containing secondary phase SnO were grown on BaF2 substrates by magnetron sputtering. The impurity tin concentration, electron concentration, and room temperature mobility of the α-Ga2O3 films are 4.5 × 1020 cm−3, 1.5 × 1015 cm−3, and 26.9 cm2 V−1 s−1, respectively, determined by secondary ion mass spectrometry and Hall effect experiments. The mobility vs temperature dependence confirms that the electrons are mainly subject to polar optical phonon scattering and ionized impurity scattering in the temperature range of 160–400 K. Two ionization energies, 29 and 71 meV, were determined for different temperature ranges by logarithmic resistivity vs the reciprocal of temperature, where the former is the shallow donor SnGa formed by the incorporation of tin into gallium sites. The latter is the shallow acceptor VSn–H associated with secondary phase SnO, and it is the electrical compensation of this shallow acceptor that results in the very low carrier concentration of α-Ga2O3 films. The photoluminescence spectrum exhibits 280 and 320 nm UV radiation, where 280 nm is due to the radiation recombination of electrons trapped by the deep donor state (EC−1.1 eV) with holes trapped by the VSn–H complex. In addition, there are several narrow radiation peaks in the visible region, and the energy levels involved in the radiation transitions are determined one by one after excluding the effects of interference and diffraction.

Diffusion of oxygen in amorphous HfO2

We carefully prepared 100-nm-thick amorphous hafnia (a-HfO2) thin films of a homogeneous structure, and measured the diffusion profile of oxygen using secondary-ion mass spectrometry with a stable isotope (18O) as a tracer. The diffusion coefficient of oxygen, D, in a-HfO2 was 3.5 × 10−24 to 7.8 × 10−20 m2 s−1 at annealing temperatures from 300 to 500 °C, which are smaller than all previously reported values. The Arrhenius plots of D showed a curvature, from which we determined the activation energy for oxygen diffusion to be 1.42 and 2.24 eV for fast and slow diffusivity, respectively. Our results suggest the atomic movement of oxygen in a-HfO2 is very sensitive to the local structure.

Single quartz δ18O: A new frontier in detrital provenance analysis (Bengal Fan, IODP Expedition 354)

Quartz is the most abundant mineral in sediments and sedimentary rocks but efforts to reliably identify its provenance have been only partially fruitful so far. Even advanced methods such as cathodo-luminescence, Raman spectroscopy, synchrotron X-ray absorption spectroscopy, and laser ablation spectrometry have led to limited success. This article demonstrates how the δ18O of detrital quartz provides useful additional insight. The oxygen-isotope signature primarily depends on source rocks and their formation conditions, being highly different for different crustal sources and highest for carbonate rocks.This study illustrates a new protocol to analyze δ18O signatures of single quartz grains and shows how provenance from magmatic, metamorphic, or sedimentary domains can be discriminated. In each sand sample from rivers draining exclusively a single Himalayan tectonic domain (e.g., Trans-Himalaya, Greater Himalaya, Lesser Himalaya, and Tethys Himalaya), ~200 quartz grains were analyzed by ion microprobe LG-SIMS (Large Geometry Secondary Ion Mass Spectrometry) to characterize their oxygen-isotope variability. In each turbidite sample collected from the Bengal Fan during IODP Expedition 354, ~150 quartz grains were analyzed next to quantify the relative contribution of each Himalayan domain. This allowed us to complement data obtained with other bulk-sediment to single-mineral approaches, thus enhancing provenance resolution and highlight the erosional evolution of the Himalayan-Tibetan orogen through time.

Alkaloids are associated with increased microbial diversity and metabolic function in poison frogs.

Shifts in host-associated microbiomes can impact both host and microbes.1,2,3,4,5,6 It is of interest to understand how perturbations, like the introduction of exogenous chemicals,7,8,9,10,11,12,13 impact microbiomes. In poison frogs (family Dendrobatidae), the skin microbiome is exposed to alkaloids that the frogs sequester for defense.14,15,16,17,18,19 These alkaloids are antimicrobial20,21,22; however, their effect on the frogs' skin microbiome is unknown. To test this, we characterized microbial communities from field-collected dendrobatid frogs. Then, we conducted a laboratory experiment to monitor the effect of the alkaloid decahydroquinoline (DHQ) on the microbiome of two frog species with contrasting alkaloid loads in nature. In both datasets, we found that alkaloid-exposed microbiomes were more phylogenetically diverse, with an increase in diversity among rare taxa. To better understand the isolate-specific response to alkaloids, we cultured microbial isolates from poison frog skin and found that many isolates exhibited enhanced growth or were not impacted by the addition of DHQ. To further explore the microbial response to alkaloids, we sequenced the metagenomes from high- and low-alkaloid frogs and observed a greater diversity of genes associated with nitrogen and carbon metabolism in high-alkaloid frogs. From these data, we hypothesized that some strains may metabolize the alkaloids. We used stable isotope tracing coupled to nanoSIMS (nanoscale secondary ion mass spectrometry), which supported the idea that some of these isolates are able to metabolize DHQ. Together, these data suggest that poison frog alkaloids open new niches for skin-associated microbes with specific adaptations, such as alkaloid metabolism, that enable survival in this environment.

Marangoni-Induced Honeycomb Structures in Spin-Coated Polymer Nanocomposite Films.

This study investigates Marangoni effect-induced structural changes in spin-coated polymer nanocomposite (PNC) films composed of poly(methyl methacrylate)-grafted silica nanoparticles (NPs) and poly(styrene-ran-acrylonitrile). Films cast from methyl isobutyl ketone (MIBK) solvent exhibit distinct hexagonal honeycomb cells with thickness gradients driven by surface tension variations. Atomic force microscopy reveals protruded ridges and junctions at cell intersections, where NP concentration is the highest. Upon annealing at 155 °C, NPs segregate to the surface due to their lower surface energy, and the initially protruding features flatten and eventually form depressed channels while maintaining higher NP density than surrounding areas. Time-of-flight secondary ion mass spectrometry corroborated these findings, highlighting enhanced surface segregation of NPs in MIBK films. These defects can be eliminated using methyl isoamyl ketone (MIAK) as a solvent that produces homogeneous films of uniform thickness. This study highlights the impact of the Marangoni effect on the microstructure and surface properties of PNC films, providing insights for enhancing film quality and performance.

The impact of helium on plasma-driven hydrogen permeation and implications for direct internal recycling in the fusion fuel cycle

Abstract Metal foil pumps (MFPs) are the leading technology for direct internal recycling (DIR) of hydrogen isotopes from the plasma exhaust in future fusion plants. MFPs rely on the concept of superpermeation, where superthermal H atoms directly absorb into the metal foil, rapidly diffuse, and desorb downstream. To date, studies of superpermeation have predominantly employed either pure hydrogen or in some cases trace levels of impurities. The plasma exhaust is expected to contain just ~1% helium, but in DIR the source gas would be enriched in helium as hydrogen isotopes are extracted. In this work, we explore the impact of helium on hydrogen superpermeation at low temperature (75-200 ºC) using Pd-based foils. To first order, the flux scaled linearly with the hydrogen mole fraction. Stable permeation was observed until the helium fraction reached ~80%, where the flux began to decline slowly with time. In addition, short term (1-5 minute) exposure to pure helium plasma significantly attenuated subsequent hydrogen plasma permeation, and the degree was more dramatic at elevated temperature. This attenuation was correlated with He retention in the foils, which was detected by time-of-flight secondary ion mass spectrometry at low levels (&lt; 0.1 at. %) and limited to the near surface (&lt; 10 nm). Similar trends were observed among all alloys (Pd, PdAg, PdCu), and the foils were restored to full performance with an Ar+ sputter clean. The potential for helium plasma exposure to impact MFP performance under these conditions has not been previously reported, and these findings have significant implications to the design and implementation of practical DIR systems.

Interface Degradation of LaCl3-Based Solid Electrolytes Coupled with Ultrahigh-Nickel Cathodes.

Despite competitive compatibility with high-nickel cathodes, chloride solid electrolytes (SEs) still experience inevitable side reactions at the cathode/SE interface, causing capacity decay in all-solid-state lithium batteries (ASSLBs) during cycling. Herein, a three-electrode ASSLB testing device is developed to comprehensively reveal the interface failure mechanisms of the ultrahigh-nickel LiNi0.92Co0.05Mn0.03O2 (NCM92) cathode paired with LaCl3-based chloride SE Li0.447La0.475Zr0.059Ta0.179Cl3 (LLZTC). Distribution of relaxation time (DRT) analysis clearly shows the ASSLB degradation accompanied by a significant NCM92/LLZTC interface impedance increase, which becomes more pronounced at the higher cutoff charging voltage of 4.8 V vs Li+/Li. Furthermore, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and focused ion beam scanning electron microscopy (FIB-SEM) analysis also confirm the deterioration arising from active lattice oxygen and loss of physical contact at the NCM92/LLZTC interface. These findings reveal both electrochemical degradation and physical contact failure at the cathode/SE interface as key causes of the ASSLBs' capacity decay.

Visualizing the Li distribution in an all-solid-state battery composite electrode using combined plasma focused-ion beam microscopy and secondary-ion mass spectroscopy

Using a Li metal anode, the all-solid-state battery (ASSB) promises a step change in specific energy over Li-ion batteries and the potential for increased battery safety. ASSBs rely critically on the efficient movement of Li charge carriers through a Li-conducting solid electrolyte (SE) separator and throughout a composite cathode (CC) comprising active particles, particulate SE, polymeric binder, and carbon. Unfortunately, there is no readily accessible laboratory method to visualise Li distributions at both particle and electrode scales to help understand and optimise Li electrode dynamics in ASSBs. We report a method to map all electrode elements in a 3D volume, including Li, within a typical ASSB composite cathode. The method combines a xenon plasma focused-ion beam (PFIB) for 3D milling, energy dispersive X-ray spectroscopy (EDS) to map non-Li elements, and secondary ion mass spectrometry (SIMS) to map Li. We manipulate 3D EDS and SIMS datasets into a common format and then recombine them in 3D to differentiate the different materials at high resolution. This new approach can be applied to understand and optimise the role of microstructure in controlling ASSB performance.

Hydrophilic Modification of Macroscopically Hydrophobic Mineral Talc and Its Specific Application in Flotation.

Sodium diethyldithiocarbamate (DDTC), a common collector used to enhance the hydrophobicity of minerals in froth flotation, nevertheless weakens the hydrophobicity of the talc surface. To rationalize this anomaly, the interactions of a hydrophobic alkyl group and hydrophilic mineralophilic group (-NCS2-) of heteropolar surfactant DDTC, and a water molecule with the talc (001) surface, were investigated. Herein, DFT simulations found that the talc (001) surface features natural hydrophobicity determined by the competition between adhesion (surface water) and cohesion (water-water interactions). The interaction of the hydrophobic alkyl group of DDTC with the talc surface is more favorable compared to that of the -NCS2- group and H2O, favoring the hydrophilic modification of the talc surface. Additionally, adsorption isotherms, time-of-flight secondary ion mass spectrometry (ToF-SIMS), microflotation tests, and contact angle measurements also indicate that the differences in adsorption orientation of the heteropolar surfactant DDTC on the talc surface enhance the hydrophilicity of the talc surface, leading to a decreased recovery of the talc. This study provides crucial surface chemistry evidence for the selective adsorption of heteropolar surfactants and contributes to the understanding of the mechanism for the efficient flotation separation of molybdenite from talc.

Mechanism of Cu Ion Targeting Combined with an Organic Depressant To Enhance the Flotation Depression of Pyrite.

In this study, pyrite was used as the research object, and the behavior and mechanism of a copper-ion-enhanced organic depressant in depressing pyrite flotation were studied. Microflotation experiments showed that, after the addition of CuSO4 and N,N-dimethyldithiocarbamate (N,N-DDS), the floating collection efficiency of pyrite declined from 82.37 to 21.03% at pH 8.5. Infrared spectroscopy studies indicated that the addition of CuSO4 caused a significant enhancement in the characteristic N,N-DDS peaks on the pyrite surface. X-ray photoelectron spectroscopy (XPS) revealed that, following the addition of CuSO4 and N,N-DDS, the relative atomic concentration of N 1s considerably enhanced on the surface of pyrite, with N 1s derived from N,N-DDS. Time-of-flight secondary ion mass spectrometry showed that, before and after the addition of CuSO4, the normalized peak values of CSN- on the pyrite superficial layer were 0.0116 and 0.0032, respectively. All of the above-mentioned results indicate that the Cu ion promotes the adsorption of N,N-DDS on pyrite and facilitates the formation of complex ((CH3)2NCSS)2Cu. The N and S atoms in -NCS and metal ions formed chemical bonds, which were the primary mechanism of the interaction between N,N-DDS and pyrite. This process reduces the floatability of pyrite and achieves the selective depression of pyrite.

Investigation of sub-nm binary oxidic surface modifications on mixed ionic electronic conductors with ToF-SIMS: Oxidic overlayer stability and ionic interdiffusion behavior

Modifications of mixed ionic electronic conductor (MIEC) surfaces are a promising approach to improve oxygen exchange reaction (OER) kinetics and can have a tremendous impact on surface charges and secondary ion yields. Utilizing time-of-flight secondary ion mass spectrometry (ToF-SIMS), we examined degradation, segregation, and cation interdiffusion behaviors on La0.6Sr0.4CoO3-δ (LSC) and Pr0.2Ce0.8O2-δ (PCO) thin films modified with ∼0.5 nm CaO, TiO2, and SnO2 overlayers after annealing at 700 °C and 800 °C, respectively. Surface profiles (AFM; ToF-SIMS) and depth profiles (ToF-SIMS) revealed structural and chemical transformations, including particle formation and surface roughening. The overlayer stability varied significantly for different overlayers on the same material and for the same overlayer on LSC and PCO. All oxidic overlayers were more stable on PCO than LSC. Depth profiling indicated that 40Ca+ ions penetrated the entire LSC and PCO layers (30 nm). 48Ti+ aligns more accurately with a typical analytical solution to Fick’s diffusion equation for finite systems, showing higher diffusion coefficients in LSC than PCO. 120Sn+ exhibited minimal penetration, indicating high stability on the surface and less intermixing with either MIEC. These results hint at the need to differentiate between the stability of the binary oxides on the surface and the bulk diffusivity.

Automated Single Cell Phenotyping of Time-of-Flight Secondary Ion Mass Spectrometry Tissue Images.

Existing analytical techniques are being improved or applied in new ways to profile the tissue microenvironment (TME) to better understand the role of cells in disease research. Fully understanding the complex interactions between cells of many different types and functions is often slowed by the intense data analysis required. Multiplexed Ion Beam Imaging (MIBI) has been developed to simultaneously characterize 50+ cell types and their functions within the TME with a subcellular spatial resolution, but this results in complex data sets that are challenging to qualitatively analyze. Deep Learning (DL) techniques were used to build the MIBIsight workflow, which can process images containing thousands of cells into easily digestible reports and plots to enable researchers to easily summarize data sets in a study and make informed conclusions. Here we present the three types of DL models that have been trained with annotated MIBI images that have been pathologist validated as well as the associated workflow for the evolution of raw mass spectral data into actionable reports and plots.

On the Surface Hardening of Zinc Sulfide Windows by Gallium Sulfide.

This study examines the effect of gallium doping on the phase transformation, transmission, and hardness of commercial multispectral-grade ZnS specimens exposed to Ga2S3 vapor. Using secondary ion mass spectrometry, we show that Ga diffusion extends into the subsurface down to several tens of microns. X-ray diffraction patterns reveal minimal to no precipitation of wurtzite, resulting in limited infrared transmission loss after treatment. We report a monotonic increase in Vickers surface microhardness with increasing Ga concentration, reaching values more than double those of untreated windows. Future work will focus on optimizing this process and evaluating its effectiveness in enhancing the durability of ZnS windows under harsh environmental conditions.

Growth and characterization of n-type Ga2O3 films on sapphire substrates by APMOVPE

In this study, n-type Ga2O3 thin films were grown on c-plane sapphire substrates by atmospheric pressure metalorganic vapor phase epitaxy using tetraethoxysilane (TEOS) as the silicon (Si) precursor. X-ray diffraction measurements confirmed that the deposited films were polycrystalline, predominantly consisting of the stable β-phase and the metastable κ-phase. Surface and optical characterizations indicated that lower growth temperature and appropriate Si doping reduce the grain size of three-dimensional Ga2O3 islands, thereby enhancing optical transmittance by mitigating surface scattering. Hall effect measurements demonstrated a maximum electron carrier concentration of approximately 1 × 1017 /cm3 at room temperature, while secondary ion mass spectrometry (SIMS) revealed that Si atomic concentrations were exceeding 1 × 1020 /cm3 in all n-type samples indicating low doping efficiency of Si. Carbon (C) impurities were also measured by SIMS with concentrations as the same order or higher than that of Si, implying they may be one of the reasons for the degraded electrical conductivity and originated from incomplete decomposition of the precursors during low temperature growth. From these results, it is crucial to reduce C impurities and enhance surface flatness to improve electrical and optical properties.