Evolution of hyperbranched polyglycerols as single-dopant carriers
Introduction
Traditional semiconductor devices such as metal-oxide-semiconductor field effect transistors (MOSFET) are created by introducing dopants into semiconductors [[1], [2], [3]]. Following the Moore’s law, modern MOSFET transistors have been scaled down to have a few discrete dopants in the device channel [4,5]. The random distribution of dopants results in a significant fluctuation in threshold voltages among MOSFET transistors [6,7], which in turn degrades the reliability of the integrated circuitry [8]. Deterministic doping at atomic level will help relieve this issue [9]. In 2006, Japanese scientists first demonstrated the deterministic doping arrays at atomic level by single ion implantation [5]. Later on a group led by M. Simmons in Australia demonstrated the control of single phosphorus dopant on silicon surfaces by scanning tunneling microscopy [10,11]. Transistors based on single phosphorus atoms were also demonstrated. In 1998, Kane first proposed a quantum computer architecture based on single phosphorus atom in silicon, which requires a precise control of single P atoms [12]. With the recent progress in single dopant manipulation, it looks quite promising to realize the Kane architecture for quantum computing [[13], [14], [15]]. Moreover, the dopant regulation will be useful for improving electronic properties of silicon-based biosensors, for example NO detection [16,17], bacteria detection [18,19], and plant cellular signal detection [20,21].
However, from the engineering point of view, the existing ion implantation and STM manipulation are time-consuming serial processes. It requires a parallel process to mass produce single dopants at arbitrary locations for commercialization. To data, linear polymer grafting with thermal decomposition can achieve the discrete atomic doping [22,23]. But, the self-limitation of linear polymer cannot occupied the specific doping region, owing to the cross-linking of linear polymers onto planar surface [24,25]. By employing the self-assembled monolayer doping technique (so-called molecular doping) [26,27], we previously proposed to use macromolecules as dopant carriers to control the dopant atom locations via self-assembly of the macromolecule carriers onto chemically pre-patterned silicon surfaces, as shown in Fig. 1 [28,29]. When the macromolecules and the patterns are comparable in size, a space-limiting process may occur, i.e. only one macromolecule will be immobilized on each pattern. Before the wide application of dopant polymer carriers in molecular monolayer doping and single electron transistors preparation, the effect of dopant carriers on electronic properties and grafting method should be well investigated. A large array of single dopants will be created if each macromolecule carries only one dopant atom and this dopant atom can be incorporated into silicon with a high success rate. In this work, we successfully synthesized hyperbranched polyglycerols (hbPGs) molecules which was carefully characterized by several techniques. The results indicate that each hbPGs molecule carries only one phosphorus atom. The phosphorus atoms carried by the molecules were then driven into the silicon substrate by rapid thermal annealing with a success rate of every two hbPGs molecules contributing one phosphorus dopant to the Si substrate. To improve the doping efficiency of hbPGs, different pre-dealing process, only Ar annealing and Ar annealing with peroxidation under oxygen ambient, were performed to remove the carbon contamination. Low Hall measurement and relative characterization demonstrated that the pre-oxidation can significantly improve the activation rate of doped phosphorus element.
Section snippets
Synthesis and characterizations of hbPGs molecules
hbPGs molecules were synthesized to carry phosphorus atoms by anionic ring-opening multibranching polymerization (ROMP) [[30], [31], [32]], in which diphenylphosphinyl hydroquinone (PPQ, A molecule in Fig. 1) is the aromatic initiating core [33] (SI Fig. S1). To obtain high molecular weight hbPGs, the molar ratio of monomers to cores was set at ∼100. The polymerization process was performed in anhydrous 1, 4-dioxane [34], and the crude product was purified by a dialysis bag (molecular weight
Conclusion
In summary, we reported the synthesis of hbPGs molecules as phosphorus dopant carriers. The molecules are characterized by NMR, ICP and SEC/MALLS techniques. The results indicate that each hbPGs molecule carries only one phosphorus atom. After the hbPGs molecules were immobilized on the surfaces, rapid thermal annealing was applied to drive the phosphorus dopants into the silicon substrate. Through the pre-oxidation process, the minimal carbon contamination was obtained and the electrical
CRediT authorship contribution statement
Haigang Wu: Conceptualization, Investigation, Validation, Methodology, Data curation, Writing - original draft, Supervision, Project administration, Visualization, Funding acquisition. Qunzhi Chen: Methodology, Formal analysis, Investigation, Writing - review & editing. Nan Huang: Data curation, Investigation, Formal analysis. Xueyan Lian: Investigation, Visualization. Ke Li: Investigation, Validation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The work is supported the Talent-Postdoctoral Program from Henan Province Funding (ZYQR201810168), Young teacher’s Founding of Henan University and Henan province development breakthrough program (202102310110).
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Thermal decomposition mechanism investigation of hyperbranched polyglycerols by TGA-FTIR-GC/MS techniques and ReaxFF reactive molecular dynamics simulations
2023, Biomass and BioenergyCitation Excerpt :As shown in Fig. 2B-C, we can observe only terminal unit, dendritic unit, and linear units (1, 3-unit, L13, and 1, 4-unit, L14). According to previous report [45], branch degree (DB) of prepared hbPGs be calculated using abundance of repeating units (Tables 1 and 2) and DB was approximately 0.54, which was consistent with our previous report [46]. Finally, we also examined the molecular weight of hbPGs using gel permeation chromatography (GPC) technique (SI Fig.S1), and GPC result showed that the molecular weight of hbPGs (Mn) was approximated 101,000 g/mol with low polydispersity index (PDI) value (∼1.4).
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These authors are equal to this work.