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- Nadhom, Hama, 1986-
(author)
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Area Selective Chemical Vapor Deposition of Metallic Films using Plasma Electrons as Reducing Agents
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Metallic films are used to improve optical, chemical, mechanical, magnetic, and electrical properties and are therefore of high importance in many applications, from electronics and catalysis, environmental protection and health, to wearable and flexible electronic materials. Many of these applications, however, require that the metal films are deposited uniformly on topographically complex surfaces and structures. Some form of chemical vapor deposition (CVD) where the deposition is governed by the surface chemistry is needed for uniform film deposition on topographically complex surfaces. Furthermore, area selective deposition (ASD) has gained large considerations lately, where films deposited only on specified areas of the substrate, and not on others, simplifies the processing significantly and opens the way for less complex fabrication of, for instance, nanoscaled electronics. ASD occurs when the surface chemical reactions are disabled on selected areas of the substrate. Since the metal centers in CVD precursor molecules typically have a positive valence, a reductive surface chemistry is required to form a metallic film. This is usually done by using a second precursor, i.e., a molecular reducing agent. The negative standard reduction potential of the first-row transition metals (Ti, V, Cr, Mn, Fe, Co, and Ni) means that CVD of these metals requires either very high temperatures or very powerful molecular reducing agents. This thesis describes a new low temperature CVD method for depositing metallic films where instead free electrons in a plasma discharge are utilized to reduce the metal centers of chemisorbed precursor molecules. By applying a positive bias voltage to the substrate holder, the plasma electrons are attracted to the substrate for electron-precursor interactions. This was demonstrated by successfully depositing iron, cobalt, and nickel films from their corresponding metallocene precursors. The electrical resistivity of the substrate and the polarity of the substrate bias were shown to play an important role in depositing metallic films with this CVD approach. The experimental results show that films deposited, with +40 V bias voltage, on silver substrates contain substantially higher metal concentration compare to films deposited on silicon substrates. Deposition on electrically insulating silicon dioxide substrates however yielded no detectable amount of metal atoms on the substrate surface. This indicates that electron current through the substrate is essential to grow metal films in this CVD process. The effect of the electrical resistivity of the substrate was studied for ASD. The new CVD method is shown to be inherently area selective from the surface electrical resistivity by depositing iron from ferrocene on silicon dioxide substrate partially coated with silver. No, or very small, detectable amount of metal atoms could be found on areas with high resistivity, whereas several hundred nm thick iron films are deposited on areas with low resistivity. The only heating of the substrate emanates from the electric current from the plasma through the substrate holder, resulting in a slight heating to 35–50 °C, depending on the substrate bias voltage. This was regarded as the deposition temperature. Such low deposition temperature was exploited to achieve ASD by a masking approach with different temperature sensitive materials such as polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polystyrene (PS), Parafilm, Kapton tape, Scotch tape, and office paper. These materials were used to mask area of the substrate in the new CVD method as demonstrated by depositing iron from ferrocene on partially masked silver substrates. All initial experiments rendered only a phenomenological understanding of the new CVD process. Therefore, a quartz crystal microbalance (QCM) system was modified, by the addition of a positive bias voltage, and used to further understand the chemical and physical processes controlling the deposition process. The results show that differences in film deposition with different deposition parameters, such as plasma power and bias voltage, can be observed using the new QCM approach where the QCM crystal indeed works as a substrate in our new CVD process. In summary, a new CVD concept has been developed for metallic thin films. This method uses the free plasma electrons as reducing agents and can also be utilized for ASD of metal thin films. This
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- Shu, Rui, 1990-, et al.
(author)
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Influence of Metal Substitution and Ion Energy on Microstructure Evolution of High-Entropy Nitride (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr) Films
- 2021
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In: ACS APPLIED ELECTRONIC MATERIALS. - : American Chemical Society (ACS). - 2637-6113. ; 3:6, s. 2748-2756
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Journal article (peer-reviewed)abstract
- Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr, 0.12 <= x <= 0.30) films were deposited on Si(100) substrates at 400 degrees C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from similar to 10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 <= x <= 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1-x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached similar to 3.1 GPa in Hf- and Cr-containing films deposited at -130 V. The hardness reached a maximum value of 28.0 +/- 1.0 GPa at a negative bias >= 100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1-x films can thus guide the design of protective high-entropy nitride films.
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- Borgmästars, Emmy, et al.
(author)
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Circulating tissue polypeptide-specific antigen in pre-diagnostic pancreatic cancer samples
- 2021
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In: Cancers. - : MDPI. - 2072-6694. ; 13:21
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Journal article (peer-reviewed)abstract
- Early detection of pancreatic ductal adenocarcinoma (PDAC) is challenging, and late diagnosis partly explains the low 5-year survival. Novel and sensitive biomarkers are needed to enable early PDAC detection and improve patient outcomes. Tissue polypeptide specific antigen (TPS) has been studied as a biomarker in PDAC diagnostics, and it has previously been shown to reflect clinical status better than the ‘golden standard’ biomarker carbohydrate antigen 19-9 (CA 19-9) that is most widely used in the clinical setting. In this cross-sectional case-control study using pre-diagnostic plasma samples, we aim to evaluate the potential of TPS as a biomarker for early PDAC detection. Furthermore, in a subset of individuals with multiple samples available at different time points before diagnosis, a longitudinal analysis was used. We assessed plasma TPS levels using enzyme-linked immunosorbent assay (ELISA) in 267 pre-diagnostic PDAC plasma samples taken up to 18.8 years before clinical PDAC diagnosis and in 320 matched healthy controls. TPS levels were also assessed in 25 samples at PDAC diagnosis. Circulating TPS levels were low both in pre-diagnostic samples of future PDAC patients and in healthy controls, whereas TPS levels at PDAC diagnosis were significantly increased (odds ratio 1.03; 95% confidence interval: 1.01–1.05) in a logistic regression model adjusted for age. In conclusion, TPS levels increase late in PDAC progression and hold no potential as a biomarker for early detection.
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- Borgmästars, Emmy, et al.
(author)
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Metabolomics for early pancreatic cancer detection in plasma samples from a Swedish prospective population-based biobank
- 2024
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In: Journal of Gastrointestinal Oncology. - : AME Publishing Company. - 2078-6891 .- 2219-679X. ; 15:2, s. 755-767
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Journal article (peer-reviewed)abstract
- Background: Pancreatic ductal adenocarcinoma (pancreatic cancer) is often detected at late stages resulting in poor overall survival. To improve survival, more patients need to be diagnosed early when curative surgery is feasible. We aimed to identify circulating metabolites that could be used as early pancreatic cancer biomarkers.Methods: We performed metabolomics by liquid and gas chromatography-mass spectrometry in plasma samples from 82 future pancreatic cancer patients and 82 matched healthy controls within the Northern Sweden Health and Disease Study (NSHDS). Logistic regression was used to assess univariate associations between metabolites and pancreatic cancer risk. Least absolute shrinkage and selection operator (LASSO) logistic regression was used to design a metabolite-based risk score. We used receiver operating characteristic (ROC) analyses to assess the discriminative performance of the metabolite-based risk score.Results: Among twelve risk-associated metabolites with a nominal P value <0.05, we defined a risk score of three metabolites [indoleacetate, 3-hydroxydecanoate (10:0-OH), and retention index (RI): 2,745.4] using LASSO. A logistic regression model containing these three metabolites, age, sex, body mass index (BMI), smoking status, sample date, fasting status, and carbohydrate antigen 19-9 (CA 19-9) yielded an internal area under curve (AUC) of 0.784 [95% confidence interval (CI): 0.714–0.854] compared to 0.681 (95% CI: 0.597–0.764) for a model without these metabolites (P value =0.007). Seventeen metabolites were significantly associated with pancreatic cancer survival [false discovery rate (FDR) <0.1].Conclusions: Indoleacetate, 3-hydroxydecanoate (10:0-OH), and RI: 2,745.4 were identified as the top candidate biomarkers for early detection. However, continued efforts are warranted to determine the usefulness of these metabolites as early pancreatic cancer biomarkers.
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| 7. |
- Borgmästars, Emmy, et al.
(author)
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Metabolomics for early pancreatic cancer detection in plasma samples from a Swedish prospective population-based biobank
- 2024
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In: Journal of Gastrointestinal Oncology. - : AME Publishing Company. - 2078-6891 .- 2219-679X. ; 15:2, s. 755-767
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Journal article (peer-reviewed)abstract
- Background: Pancreatic ductal adenocarcinoma (pancreatic cancer) is often detected at late stages resulting in poor overall survival. To improve survival, more patients need to be diagnosed early when curative surgery is feasible. We aimed to identify circulating metabolites that could be used as early pancreatic cancer biomarkers.Methods: We performed metabolomics by liquid and gas chromatography-mass spectrometry in plasma samples from 82 future pancreatic cancer patients and 82 matched healthy controls within the Northern Sweden Health and Disease Study (NSHDS). Logistic regression was used to assess univariate associations between metabolites and pancreatic cancer risk. Least absolute shrinkage and selection operator (LASSO) logistic regression was used to design a metabolite-based risk score. We used receiver operating characteristic (ROC) analyses to assess the discriminative performance of the metabolite-based risk score.Results: Among twelve risk-associated metabolites with a nominal P value <0.05, we defined a risk score of three metabolites [indoleacetate, 3-hydroxydecanoate (10:0-OH), and retention index (RI): 2,745.4] using LASSO. A logistic regression model containing these three metabolites, age, sex, body mass index (BMI), smoking status, sample date, fasting status, and carbohydrate antigen 19-9 (CA 19-9) yielded an internal area under curve (AUC) of 0.784 [95% confidence interval (CI): 0.714–0.854] compared to 0.681 (95% CI: 0.597–0.764) for a model without these metabolites (P value =0.007). Seventeen metabolites were significantly associated with pancreatic cancer survival [false discovery rate (FDR) <0.1].Conclusions: Indoleacetate, 3-hydroxydecanoate (10:0-OH), and RI: 2,745.4 were identified as the top candidate biomarkers for early detection. However, continued efforts are warranted to determine the usefulness of these metabolites as early pancreatic cancer biomarkers.
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| 9. |
- Chang, Jui-Che, et al.
(author)
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HiPIMS-grown AlN buffer for threading dislocation reduction in DC-magnetron sputtered GaN epifilm on sapphire substrate
- 2023
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In: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 217
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Journal article (peer-reviewed)abstract
- Gallium nitride (GaN) epitaxial films on sapphire (Al2O3) substrates have been grown using reactive magnetron sputter epitaxy with a liquid Ga target. Threading dislocations density (TDD) of sputtered GaN films was reduced by using an inserted high-quality aluminum nitride (AlN) buffer layer grown by reactive high power impulse magnetron sputtering (R-HiPIMS) in a gas mixture of Ar and N2. After optimizing the Ar/N2 pressure ratio and deposition power, a high-quality AlN film exhibiting a narrow full-width at half-maximum (FWHM) value of the double-crystal x-ray rocking curve (DCXRC) of the AlN(0002) peak of 0.086° was obtained by R-HiPIMS. The mechanism giving rise the observed quality improvement is attributed to the enhancement of kinetic energy of the adatoms in the deposition process when operated in a transition mode. With the inserted HiPIMS-AlN as a buffer layer for direct current magnetron sputtering (DCMS) GaN growth, the FWHM values of GaN(0002) and (10 1‾ 1) XRC decrease from 0.321° to 0.087° and from 0.596° to 0.562°, compared to the direct growth of GaN on sapphire, respectively. An order of magnitude reduction from 2.7 × 109 cm−2 to 2.0 × 108 cm−2 of screw-type TDD calculated from the FWHM of the XRC data using the inserted HiPIMS-AlN buffer layer demonstrates the improvement of crystal quality of GaN. The result of TDD reduction using the HiPIMS-AlN buffer was also verified by weak beam dark-field (WBDF) cross-sectional transmission electron microscopy (TEM).
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| 10. |
- Crespi, Ângela Elisa, et al.
(author)
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Low resistivity amorphous carbon-based thin films employed as anti-reflective coatings on copper
- 2020
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 712
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Journal article (peer-reviewed)abstract
- Amorphous carbon-based coatings deposited on copper substrates by magnetron sputtering at different target-to-substrate distances were investigated. Films deposited at short distances as 2 cm presented the best results in terms of morphology, density, and resistivity. Ultraviolet near-infrared range spectrometry measurements determined total reflectance and ellipsometry, extinction coefficient, refraction index, and pseudo bandgap. Amorphous carbon films of 150 nm deposited at 2 cm reduced the total reflectance by up to 60 ± 5% in the near-infra-red range when compared to pure copper films. The addition of Fe* boosts the absorption of the coating reducing the total reflectance by up to 70 ± 5% in near-infrared. (Fe*: deposited from stainless-steel target used in direct-current magnetron sputtering). Also, Fe* reduces the electrical resistivity by a factor of 100 compared to that of pure amorphous carbon films. The reduction in total reflectance induced by the presence of the amorphous carbon-based films on copper depends, as expected, on light penetration depth and the absorption coefficient.
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